Associations between worm egg count and production in Dorper sheep

By Joshua Paul Alexander Sweeny Supervisor: Kevin Bell

A thesis submitted to fulfil the requirements for the Honours degree in Bachelor of Animal Science and the Animal Science Research Project ANS450 at Murdoch University, 2008.

October 2008

- 1 - Declaration

I declare this thesis is my own account of my research and contains as its main content, work which has not been previously submitted for any degree and is not currently being submitted for any other degree or qualification.

I certify that any help received in preparing this thesis, and all sources used, have been acknowledged in this thesis.

......

Signature Joshua Paul Alexander Sweeny

- 2 - Acknowledgements

I thank the following people for their help during the project, Dr. Robert Dobson, Peter McGilchrist and Dr. Graham Gardner for assistance both with statistics and methods used for data analysis, Murdoch University staff, in particular Dr Caroline Jacobson for laboratory assistance. I also thank Dr. Brown Besier and Dr. Johan Greeff for their guidance in problem solving associated with the project. The Gardner family at Kojonup, in particular Tamesha and Andrew were also most helpful, in giving me an opportunity to conduct this project on Dorper sheep. I would also like to express my sincere thanks to my supervisor Professor Kevin Bell for his support and input into the project throughout the year. Finally I thank those who assisted in measuring the production attributes of two Dorper sheep flocks and successfully collecting individual faecal samples from all sheep. These included Tom Sweeny, Pauline Sweeny and Tamara Backes.

Abstract

With changes to the Australian sheep industry, breeds that have a meat emphasis are becoming increasingly adopted by farmers. One such breed is the Dorper sheep, which was used in this study to investigate the relationship between worm egg count and production attributes. Gastrointestinal worm burden was measured by worm egg counts (WECs) and production attributes that were examined included liveweight, body condition score (BCS), c-site fat depth and eye muscle depth. Two flocks of Dorper lambs (two-hundred and eighty nine Dorper ewe lambs, and two-hundred and thirty four entire Dorper ram lambs), were weaned onto two separate paddocks for grazing and natural worm challenge on a Kojonup property. At post weaning (approximately 10 months of age), each flock had their production attributes measured, along with individual WECs. Each flock was drenched at weaning and not drenched again until after individual WECs were measured.

The measured flock WEC frequency distribution reinforced the concept that high flock WECs are influenced by a small percentage of the sheep within the flock and that Dorper sheep are similar to other breeds with respect to parasite population dynamics.

- 3 - The relationships found between WEC and production attributes of both liveweight and eye muscle depth were positive, contradicting the hypothesis of that a negative relationship exists between WEC and production in the Dorper. Although this relationship between WEC and liveweight was weak and unexpected, the relationship was still significant (P<0.05). With an increasing WEC, BCS fell by 56.6% and 37.7% of average ram BCSs in twin and single born rams respectively (P<0.05), while an 18.6% decrease of average ewe BCS was observed in twin born ewes (P<0.05). The drop in body condition score and c-site fat depth may have contributed to overall leaner and lighter carcases (particularly in the ram flock). Given that the liveweights were actually higher in these same animals, this suggests a reduced dressing percentage due to increased non- carcase components, possibly gastrointestinal tissue mass.

With increasing WEC the association of liveweight increase and BCS decline indicated that sheep with a higher worm burden may have heavier intestines, when compared to sheep with a low worm challenge. By using liveweight change to assess GIN impact on productivity, production losses linked to gastrointestinal parasite infection may be underestimated. Instead of using liveweight change in assessing the effect of a worm challenge, measurements of the carcass yield may be a more reliable measure in revealing the real economic impact of gastrointestinal worms on sheep meat production systems.

List of Abbreviations

ASBV – Australian Sheep Breeding Value BCS – Body Condition Score EPG – Eggs per Gram GIN – Gastrointestinal Nematode PPRI – Periparturient Relaxation of Immunity SAMM – South African Meat Merino UFD – Ultrasonic Fat Depth WEC – Worm Egg Count

- 4 - List of Figures

Figure 1.1: National cost of disease to the sheep industry, combined control costs (expenses) and production losses (reduced income) (adapted Sackett et al. 2006) ...... 13 Figure 1.2: Life cycles of the most common sheep nematodes (adapted from Woodgate 2002 and Hobbs et al. 2007)...... 14 Figure 1.3: Schematic representation of the effect of GIN on protein metabolism in sheep (ME preferentially utilised by the alimentary tract for its maintenance and local immune response evoked by the GINs, which occurs at the expense of peripheral tissues) (adapted from Coop and Sykes 2002)...... 16 Figure 1.4: Pattern of faecal worm egg counts (WECs) in eggs per gram (EPG) for ewes, lambing between February and March (indicated by dark block). Redrawn from the first recording of rising faecal egg counts during lactation in sheep. (adapted from Taylor 1935)...... 17 Figure 1.5: The heritability of faecal WECs of sheep increases with age (adapted from Bisset and Morris 1996) ...... 21 Figure 1.6: Sources of variation in WEC of Haemonchus contortus and Trichostrongylus colubriformis across research flocks (adapted from Eady et al. 1996) ...... 22 Figure 1.7: ASBV examples from Merino Superior Sires; selecting different sires for desired production traits (WEC highlighted in red box) (adapted from Australian Merino Sire Evaluation Association. 2007) ...... 23 Figure 1.8: Changes in Australian temperature from 1910 – 2006 (adapted from PMSEIC 2007) ...... 24 Figure 3.4 Hand position during BCS (adapted from Suiter 1994) ...... 34 Figure 4.1 The frequency distribution of strongyle WEC of individuals from the ram flock...... 36 Figure 4.1.1 The frequency distribution of logstrongyle+25 WEC of individuals from the ram flock...... 36 Figure 4.1.2 The frequency distribution of strongyle WEC of individuals from the ewe flock...... 37 Figure 4.1.3 The frequency distribution of logstrongyle+25 WEC of individuals from the ewe flock ...... 37

- 5 - Figure 4.1.4 The effect of different birth types within sexes on logstrongyle WEC (logstrongyle+25 WEC)...... 38 Figure 4.1.5 The effect of different birth types within sexes on lognematodirus WEC (lognematodirus+25 WEC)...... 38 Figure 4.1.6 The effect of different birth types within sexes on logtotal WEC (logtotal+25 WEC)...... 39 Figure 4.2 The effect of different age points and birth types within sexes on liveweight (E=ewe, R=ram, PW=post weaning, W=weaning, Y=yearling)...... 40 Figure 4.2.1: The effect of logstrongyle+25 WEC (eggs per gram) on ram liveweights in kg and antilogstrongyle+25 WEC...... 41 Figure 4.2.2: The effect of logstrongyle+25 WEC (eggs per gram) on ewe liveweights in kg and antilogstrongyle+25 WEC...... 42 Figure 4.2.3: The effect of lognematodirus+25 WEC (eggs per gram) on ram liveweights in kg and antilognematodirus +25 WEC...... 43 Figure 4.2.4: The effect of lognematodirus+25 WEC (eggs per gram) on ewe liveweights in kg and antilognematodirus +25 WEC...... 43 Figure 4.2.5: The effect of logtotal+25 WEC (eggs per gram) on ram liveweights in kg and antilogtotal+25 WEC...... 44 Figure 4.2.6: The effect of logtotal+25 WEC (eggs per gram) on ewe liveweights in kg and antilogtotal+25 WEC...... 45 Figure 4.3 The effect of different birth types within sexes on body condition score (E=ewe, R=ram, PW=post weaning, W=weaning)...... 46 Figure 4.3.1: The effect of logstrongyle+25 WEC (eggs per gram) on ram body condition scores and antilogsgtrongyle+25 WEC...... 47 Figure 4.3.2: The effect of logstrongyle+25 WEC (eggs per gram) on ewe body condition scores and antilogsgtrongyle+25 WEC...... 48 Figure 4.3.3: The effect of lognematodirus+25 WEC (eggs per gram) on ram body condition scores and antilognematodirus+25 WEC...... 49 Figure 4.3.4: The effect of lognematodirus+25 WEC (eggs per gram) on ewe body condition scores and antilognematodirus+25 WEC...... 50 Figure 4.3.5: The effect of logtotal+25 WEC (eggs per gram) on ram body condition scores and antilogtotal+25 WEC...... 50 Figure 4.3.6: The effect of logtotal+25 WEC (eggs per gram) on ewe body condition scores and antilogtotal+25 WEC...... 51

- 6 - Figure 4.4 The effect of different birth types within sexes on c-site fat depth (mm) (E=ewe, R=ram)...... 52 Figure 4.4.1: The effect of logstrongyle+25 WEC (eggs per gram) on ram c-site fat depth and antilogstrongyle+25 WEC...... 53 Figure 4.4.2: The effect of logstrongyle+25 WEC (eggs per gram) on ewe c-site fat depth and antilogstrongyle+25 WEC...... 54 Figure 4.4.3: The effect of logtotal+25 WEC (eggs per gram) on ram c-site fat depth and antilogtotal+25 WEC...... 55 Figure 4.4.4: The effect of logtotal+25 WEC (eggs per gram) on ewe c-site fat depth and antilogtotal+25 WEC...... 56 Figure 4.5 The effect of different birth types within sexes on eye muscle depth (mm) (E=ewe, R=ram, PW=post weaning, W=weaning, Y=yearling)...... 57 Figure 4.5.1: The effect of logstrongyle+25 WEC (eggs per gram) on ram eye muscle depth and antilogstrongyle+25 WEC...... 57 Figure 4.5.2: The effect of logstrongyle+25 WEC (eggs per gram) on ewe eye muscle depth and antilogstrongyle+25 WEC...... 58 Figure 4.5.3 The effect of logtotal+25 WEC (eggs per gram) on ram eye muscle depth and antilogtotal+25 WEC...... 59 Figure 4.5.6: The effect of logtotal+25WEC (eggs per gram) on ewe eye muscle depth and antilogtotal+25 WEC...... 60

List of Tables

Table 1.1 Annual major costs of major sheep diseases to Australian sheep producers (adapted from Sackett et al. 2006)...... 13 Table 3.2: The nutritional components of sheep supplementary feed...... 32 Table 3.2.1: Estimated available Feed on offer (FOO, in kg/hectare of dry matter) in the ram and ewe paddocks...... 33 Table 3.4 Body condition score guidelines for measuring the muscle and fat tissue covering the bones of the animal. (Suiter 1994) ...... 34 Table 4.0 Percentage of strongyle larval species in ram and ewe flocks after faecal larvae cultures, with mean WEC from each flock...... 35

- 7 - Table 4.2 F-values and degrees of freedom for the effects of log strongyle, nematodirus and total worm egg count (WEC) and animal factors (birth type, sexes and age), on liveweight...... 40 Table 4.3 F-values and degrees of freedom for the effects of log strongyle, nematodirus and total worm egg count (WEC) and animal factors (birth type and sexes), on BCS...... 46 Table 4.4 F-values and degrees of freedom for the effects of log strongyle, nematodirus and total worm egg count (WEC) and animal factors (birth type and sexes), on c-site fat depth...... 52 Table 4.5 F-values and degrees of freedom for the effects of log strongyle, nematodirus and total worm egg count (WEC) and animal factors (birth type and sexes), on eye muscle depth...... 56

- 8 - Table of Contents

Declaration...... 2 Acknowledgements ...... 3 Abstract ...... 3 List of Abbreviations ...... 4 List of Figures ...... 5 List of Tables ...... 7 Table of Contents ...... 9

Chapter One: Literature Review ...... 12

1. Introduction ...... 12 2. The Significance of Parasites to the Australian Sheep Industry .. 12 2.1 The Economic Effects of Nematode Helminth Infestation ...... 12 2.2 Major Nematodes of Sheep ...... 13 2.3 Nematode Pathophysiology ...... 14 3. Measurement of Sheep Performance ...... 18 3.1 Body Condition Score (BCS) Measurement ...... 18 3.2 Backfat Analysis ...... 18 4. Measurement of Nematode Challenge ...... 19 4.1 Faecal Worm Egg Count (WEC) ...... 19 4.2 Larval Differentiation ...... 19 5. Importance of Breeding Sheep for Parasite Resistance ...... 20 5.1 Resistance and Resilience ...... 20 5.2 Resistance; an Acquired Immunity ...... 21 6. Genetic Variation to Nematode Challenge in Merino Sheep ...... 21 6.1 Australian Sheep Breeding Values (ASBVs) ...... 22 7. New Trends in Sheep Breeds of Australia ...... 23 7.1 Environmental Impact ...... 24 7.2 Market Impact ...... 25 8. The Dorper Sheep ...... 25 8.1 History ...... 25 8.2 Desirable Production Traits ...... 26

- 9 - 8.2.1 Reproductive Performance ...... 26 8.2.2 Body Weight and Growth Performance ...... 27 8.3 Internal Parasite Resistance of the Dorper ...... 27 9. Hypothesis and Conclusion ...... 27

Chapter Two: Scientific Paper – Worm Egg Count and

Production loss in the Dorper sheep ...... 29

2. Introduction ...... 29 2.1 Justification for a Focus on Gastrointestinal Parasitism ...... 29 2.2 The Dorper Hair Sheep ...... 30 2.2 Gastrointestinal Parasitism in the Dorper ...... 30 3. Material and Methods ...... 31 3.1 Animals and Experimental Design ...... 31 3.2 Diet and Composition ...... 32 3.4 Production Attribute Measurements ...... 33 3.5 Parasitological Measurements and Drench History ...... 34 3.6 Statistical Analysis ...... 35 4. Results ...... 35 4.0 Larval Differentiation ...... 35 4.1 Strongyle, Nematodirus, and Total Worm Egg Counts ...... 35 4.2 Liveweight ...... 39 4.2.1 Age, Sex and Birth Type Effects ...... 39 4.2.2 Strongyle Worm Egg Count Effects ...... 40 4.2.3 Nematodirus Worm Egg Count Effects ...... 42 4.2.4 Total Worm Egg Count Effects ...... 44 4.3 Body Condition Score ...... 45 4.3.1 Sex and Birth Type Effects ...... 45 4.3.2 Strongyle Worm Egg Count Effects ...... 46 4.3.3 Nematodirus Worm Egg Count Effects ...... 48 4.3.4 Total Worm Egg Count Effects ...... 50 4.4 C-site Fat Depth ...... 51 4.4.1 Sex and Birth Type Effects ...... 51 4.4.2 Strongyle Worm Egg Count Effects ...... 52

- 10 - 4.4.3 Nematodirus Worm Egg Count Effects ...... 54 4.4.4 Total Worm Egg Count Effects ...... 54 4.5 Eye Muscle Depth ...... 56 4.5.1 Sex, and Birth Type Effects ...... 56 4.5.2 Strongyle Worm Egg Count Effects ...... 57 4.5.3 Nematodirus Worm Egg Count Effects ...... 58 4.5.4 Total Worm Egg Count Effects ...... 58 5. Discussion ...... 60 5.1 Significance of WECs ...... 60 5.1.1 Development of Immunity and Diagnostic Value of Faecal WECs ...... 60 5.2 Worm Egg Count Frequency Distribution and Larval Differentiation ...... 61 5.2.1 Ewe Flock ...... 61 5.2.2 Ram Flock ...... 61 5.3 Association Between WEC and Liveweight ...... 62 5.3.1 Significance of Inflammatory Response and Plane of Nutrition ...... 62 5.4 Association Between WEC with Backfat Measurements and Eye Muscle Depth ...... 63 5.4.1 Body Condition Score and C-site Fat Depth ...... 63 5.4.3 Eye Muscle Depth ...... 64 5.5 Worm Egg Count and its Significance to Dressing Percentage ...... 65 5.5 Worm Egg Count and its Significance to Australian Sheep Breeding Values ...... 66 6. Conclusion ...... 66 7. Appendix...... 67 7.1 Sire Evaluation of Dorper Flocks ...... 67 7.1.1 Sires of the Ewe Flock ...... 67 7.1.2 Sires of the Ram Flock ...... 67 7.1.2 Sires of Combined Flocks ...... 68 8. References...... 68

- 11 - Chapter One: Literature Review

1. Introduction

Dorper sheep in Australia are gaining increasing acceptance and adoption by farmers, due to the reduced management and husbandry costs when compared to wool breeds. The Dorper sheep evolved in the semi-arid regions of South Africa, where the worm challenge is low. It has been stated that the ‘hardiness’ of the Dorper is linked to both parasite resistance and tolerance in the breed, although there is contrasting research on this topic. Little evidence exists regarding parasite burdens affecting performance levels in Dorper sheep under temperate conditions, as found in south-west Western Australia. This project sets out to investigate the effects of gastrointestinal worms on production attributes of the Dorper breed.

2. The Significance of Parasites to the Australian Sheep Industry

Gastrointestinal nematode (GIN) parasites have long been a significant production problem for the Australian sheep industry (Beck et al. 1985) and an alarming increase in anthelmintic resistance has added further costs for producers to maintain profitable livestock enterprises (Jackson and Coop 2000; Perry et al. 2002). The diseases of most significance to Australian sheep producers include blowfly strike, lice and GINs. Of these, GINs are associated with the greatest loss in production and have the largest control costs (McLeod 1995; Sackett et al. 2006). In the high rainfall areas of southern tablelands of New South Wales, the south western region of Western Australia and the majority of both Victoria and Tasmania, the adverse production effects of GIN parasites are exacerbated. The total costs of GINs to the Australian sheep industry in 1995, was estimated to be $A220 million. This total is made up of, control costs ($A80 million), losses of production ($A100 million) and mortalities ($A40 million) (McLeod 1995). In a more recent publication by Sackett et al. (2006) GINs were estimated to cost the Australian sheep industry $A369 million, made up of losses of production ($A310 million) and control costs ($A59 million) (Table 1.1).

2.1 The Economic Effects of Nematode Helminth Infestation Internal nematode parasites are regarded as a serious threat to production and are managed accordingly by Australian sheep breeders. Gastrointestinal infections

- 12 - require ongoing management to minimise the associated loss in production (Figure 1.1). Gastrointestinal nematodes are the main contributors to the disease related production costs per year, when compared with other major diseases of sheep. With anthelmintic resistance dramatically rising in Australian sheep flocks, chemical control of GINs is becoming more difficult and costly (Gilleard 2006).

Figure 1.1: National cost of disease to the sheep industry, combined control costs (expenses) and production losses (reduced income) (Sackett et al. 2006).

Table 1.1 Annual major costs of major sheep diseases to Australian sheep producers (adapted Sackett et al. 2006).

2.2 Major Nematodes of Sheep

Nematode gastrointestinal worms of the Trichostrongylidae family are the main challenge to sheep health and welfare in Australia. There are three main members of this family, which are clinically and economically the most important parasites. These

- 13 - are: Trichostrongylus spp. (Black Scour worm), Haemonchus contortus (Barber’s Pole worm) and Teladorsagia (Ostertagia) circumcincta (Small Brown Stomach worm) (Eady 1996 et al; Woodgate 2002). Of lesser importance are the nematodes Cooperia spp. and Nematodirus spp, which induce much smaller losses when compared to the three main nematodes (Woodgate 2002). Life cycles of the Trichostrongylidae nematodes are simple compared to that of the trematodes and cestodes (Figure 1.2). Unembryonated eggs are passed in the faeces by infected sheep. In the external environment eggs are embryonated and develop into first, then second larval stages within the faeces. The L2 larvae feed and increase in size before moulting to the L3 larval stage, but retain their L2 stage cuticle as a sheath for protection against environmental extremes. Infective L3 larvae migrate actively from faecal material, provided that moisture is available, onto vegetation and soil (Besier and Gardner 2005). The L3 infective stage is consumed by the definitive sheep host and the larvae mature into adults in the abomasum or small intestine, depending on the species.

Figure 1.2: Life cycles of the most common sheep nematodes (adapted from Woodgate 2002 and Hobbs et al. 2007).

2.3 Nematode Pathophysiology

Infection with GINs relies on ingestion of the infective L3 larvae. Because the majority of these larvae are found near the soil surface (Callinan and Westcott 1986) the quantity of available pasture plays an important role in the number of L3s ingested.

- 14 - Young lambs from 3 up to 9 months old have been reported to possess less resistance to parasite establishment than adults (Smith et al. 1985). This trait results from a greater adaptive immunity acquired by adult sheep.

Haemonchus contortus adults commence their parasitic phase in the abomasum 17 – 21 days after L3 ingestion. They are blood suckers, which cause symptoms of anaemia (Besier and Gardner 2005). Further pathological characteristics include abomasum tissue damage, a rise in pH due to reduced acid secretion, decreased pepsinogen secretion (Sykes and Coop 1977) and increased repair and protective mucous hyperplasia (Jones et al. 1994; Miller 1996). H. contortus is considered pathophsyiologically the most dangerous GIN, due to both the large egg output and its capacity to contaminate pastures rapidly, with resulting high mortality rates in flocks, particularly in lambs (McClure 2000; Woodgate 2002).

Teladorsagia circumcincta and Trichostrongylus spp. are economically the most significant of all the GINs for sheep producers, commonly being responsible for chronic sub-clinical infections. These worm infections result in sub-optimal performances in an infected flock, caused by the reductions in feed intake and nutrient utilisation (Steel et al. 1980; Symons et al. 1981). T. circumcincta is found in the abomasum causing similar damage to that of H. contortus, which includes: abomasum tissue damage, protein leakage, mucosal hyperplasia, increased abomasum pH, reduced parietal cell number and higher levels of inflammatory infiltrates in the abomasum (Scott et al. 2000). Infections of Trichostrongylus colubriformis in the small intestine of sheep are often associated with diarrhoea. These small intestine infections are characterised by epithelial sloughing (McClure et al. 1992), increased peristalsis and hypercontractility of smooth muscle (Tremain and Emery 1994), fluid and electrolyte movement into the small intestine lumen and villous atrophy (Kyriazakis et al. 1996; Miller 1996).

Cooperia spp. and Nematodirus spp. infections can also be found in the small intestine. Although their symptoms are similar to a Trichostrongylus infection, they are of minor consequence without the aid of another major GIN being present (Heckendorn et al. 2007).

- 15 - The depression in feed consumption of parasitised sheep is a major effect of GINs (Bown et al. 1991a). With reduced energy available due to a lowered feed intake, there is less energy for functional maintenance in infected sheep. Reduction in feed intake is approximately proportional to larval intake and is closely consistent across major nematode species (Sykes and Greer 2003). The overall remaining metabolisable energy is diverted towards an immune response against the GINs, as well as the growth and production of the sheep. This results in a loss of energy being available for the production characteristics of wool and meat, when compared to a parasite free sheep (Figure 1.3) (Louie et al. 2007).

Parasite energy demands

Figure 1.3: Schematic representation of the effect of GIN on protein metabolism in sheep (ME preferentially utilised by the alimentary tract for its maintenance and local immune response evoked by the GINs, which occurs at the expense of peripheral tissues) (adapted from Coop and Sykes 2002). *ME : Metabolisable Energy **MP : Metabolisable Protein

There is a negative correlation between liveweight gain and worm burden of young sheep, as demonstrated in Merino lambs from 3 to 9 months old with a T. colubriformis infection (McClure et al. 1999; Louie et al. 2007). Liu et al. (2005) investigated the physiological consequences of GIN parasites on liveweight and

- 16 - growth rate, with infected Merino rams finishing with a liveweight on average 5kg less than non infected rams. Daily nitrogen balances of sheep with an intestinal and/or abomasal infection have been observed 3 – 5 g less than uninfected sheep, contributing to a reduced liveweight (Bown et al. 1991b). In addition, up to 36% of nitrogen was leaked from the gastrointestinal tract due to damage to gastrointestinal wall, combined with epithelial sloughing and increased mucous protein production (Poppi et al. 1996). The nitrogen and available energy remaining in the gastrointestinal tract is directed to protein synthesis for the preferential repair of gastrointestinal tract tissue (Coop and Sykes 2002).

Pathophysiologic signs associated with GIN infection are exacerbated during mid to late pregnancy in sheep. The periparturient relaxation of immunity (PPRI) to GINs leads to increased contamination of pasture and availability of infective larvae for young lambs. This contributes to production losses (Figure 1.4) (McClure 2000; Houdijk 2008). The increased protein demand induced by lactation is associated with the suppression or abolishment of established protective GIN immunity (Donaldson et al. 1997). This PPRI increases pasture contamination and the risk of low lamb liveweights, with increased morbidity and mortality, particular in H. contortus outbreaks (Holmes and Sackett 1990; Donaldson et al. 1997).

Figure 1.4: Pattern of faecal worm egg counts (WECs) in eggs per gram (EPG) for ewes, lambing between February and March (indicated by dark block). Redrawn from the first recording of rising faecal egg counts during lactation in sheep (adapted from Taylor 1935).

- 17 - Understanding pathophysiology and knowing the clinical signs of the three major GINs could be considered important to sheep farmers, as it is unlikely that a GIN infection within a flock is due to only one nematode species. It is most likely that two or more GIN species are present in any infection, demonstrated Kyriazakis et al. (1996). This study showed an abomasal infection with T. circumcincta accompanied by intestinal infection with T. colubriformis, leading to multiplicative effects that increased production losses through reduced growth rates in sheep.

3. Measurement of Sheep Performance

Sheep performance is a measure of overall welfare and reflects the productive characteristics of an individual animal (Lui et al. 2005; Wolf et al. 2008). Such productive performance attributes include feed intake, immune response, liveweight, growth rate, body condition score (BCS) and c-site fat depth measurement (Lui et al. 2005; Wolf et al. 2008).

3.1 Body Condition Score (BCS) Measurement

Other than measuring liveweight and growth rate of a sheep, BCS is a measure for indicating the nutritional well being and performance of sheep. Body condition score is a measurement at the 13th rib of the amount of tissue and fat extending from the rib to the backbone. Sheep which have a BCS score of 2.5 or less possess very low body fat reserves (Curnow 2006). As a result of this, they are more likely to succumb to disease, have reduced fertility rates and produce lighter lamb offspring at weaning (Butler 2007). Rams with a BCS of 3.5 – 4 will have both maximum testicular mass and sperm reserves for mating, as well as greater production, when compared to rams with a BCS of 2.5 (Oldham and Martin 2005).

3.2 Backfat Analysis

The c-site back fat depth (Ultrasonic fat depth) is measured at the C-site (which is the thickness of tissue over the 12th rib 45mm from the midline) and is determined by conducting an ultrasound scan, which measures ultrasonic fat depth (UFD). Ultrasonic fat depth is calculated by the average of three measurements made at this point (Hopkins et al. 2004). Ultrasonic fat depth is a single measurement of fat depth which correlates with the whole body fatness of a sheep. This backfat reading is of

- 18 - particular importance to farmers as the income they receive from abattoir processors is dependant upon both the hot carcase weight and fat depth at the GR site.

4. Measurement of Nematode Challenge

As a result of the internal nature of GINs, obtaining an accurate measure of the number of worms present in a sheep is very difficult to determine. Post mortem inspections allow the abomasal and intestinal contents to be examined to determine the presence and exact numbers of GIN worms in a sheep. Although this is accurate, it is not practical and other means such as faecal worm egg count (WEC), changes in liveweight, BCS and pasture larval counts are used to measure the GIN effect on sheep flocks.

4.1 Faecal Worm Egg Count (WEC) Faecal worm egg counts provide a convenient estimate of worm burdens in young sheep, especially in lambs and are useful indicators for treatment of sheep (McKenna 1981). Although WECs are a convenient measure of GIN challenge, they are an indirect measurement of a GIN infection, because they measure worm eggs instead of actual worm numbers. When WECs are used in unison with liveweight measurements, assuming nutrition and welfare are maintained, they indicate the extent of a nematode challenge, due to a change in liveweight. There are documented experiments which demonstrate significant differences between treated and untreated sheep exposed to GINs, with high WECs, contributing to a reduced liveweight gain (Datta et al 1999; Knox 1999; Fthenakis et al. 2005). WECs not only provide an indication of a GIN infection, they signify which species are most likely responsible for the GIN challenge. High WEC of 2000 – 10000 EPG are most commonly caused by H. contortus infections as they produce high numbers of eggs. By comparison WECs of Trichostrongylus infections are more intermediate, ranging from 500 – 1000 EPG that still affects sheep production (Clunies and Gordon 1936; Woodgate 2002). Although these are common WEC ranges of GIN species, a larval differentiation is required to accurately determine the species causing infection.

4.2 Larval Differentiation

WECs, when monitored in unison with changes in body weight and BCS, are the best indicators of sheep performance against a GIN infection (Morgan at al. 2005). While

- 19 - WECs provide a crude estimate of what GIN species are present, they are not reliable. Larval differentiation can provide an accurate indication of which GINs are present in a flock. By culturing the larvae to the L3 infective stage, their species can be identified, allowing for strategic chemical treatment depending on particular species. By identifying the species, it allows any change in sheep performance to be linked to a particular GIN species.

5. Importance of Breeding Sheep for Parasite Resistance

There is a growing interest in the genetic selection of sheep resistant to GINs. This provides an alternative to drenching where an association exists with an increasing resistance of GINs to anthelmintic treatments. Selecting for resistant sheep with reduced worm numbers reduces the productivity impact from GIN infections, lowers chemical requirement and reduces pasture contamination (Gray 1997).

5.1 Resistance and Resilience

Breeding livestock which require minimal drug treatment to both maintain acceptable welfare standards and retain productivity is one method to assist in reducing parasite resistance to drug treatments. Furthermore it helps meet increasing consumer demand for reduced drug/chemical usage in livestock, to produce green, environmentally friendly products. When breeding livestock to possess characteristics which require minimal parasite treatment, there are two different types of genetic traits in hosts which are targeted, these being resistance and resilience. Resistance is the ability to suppress the establishment and/or subsequent development of parasite infection, while resilience is the ability to maintain profitable production while subjected to parasite challenge (Bisset and Morris 1996). Selecting for resilience focuses on livestock that are able to withstand the pathogenic effects of parasite infections and maintain productivity while carrying a parasite burden. A resistance breeding plan focuses on livestock that prevent larvae infection, by selecting animals which have reduced parasite numbers. Selecting for resistance in livestock raised on a pasture based grazing system, reduces the level of pasture contamination through a reduction in WEC (Bisset and Morris 1996).

- 20 - 5.2 Resistance; an Acquired Immunity

There is inevitably a wide variation between individuals in any flock, in their ability to resist parasite infection. For an animal which acts as a host of parasites, its health will depend on an ability to develop an immune response in order to prevent establishment and development of the parasite. Parasite resistance is not an innate phenomenon, rather it is an acquired immunity with a genetic basis which controls a mechanism that regulates the infecting parasite. The heritability of parasite resistance increases with age (Figure 1.5), indicating that variation within a livestock flock is associated with innate immune responses which have different genetic links (Stear et al. 1998).

Figure 1.5: The heritability of faecal WECs of sheep increases with age (adapted from Bisset and Morris 1996)

6. Genetic Variation to Nematode Challenge in Merino Sheep

The utilisation of genetic variation that exists between sheep for natural resistance against parasite infection, has been proposed as a means of reducing the reliance on anthelmintics for parasite control in trials by Piper and Barger (1988). Sheep that have poor resistance towards nematode infection and which require frequent drenching are not suitable for the Australian sheep industry. A study conducted by Eady et al. (2003) concluded that the single most effective treatment for reducing WEC was genetic selection (average 69% reduction) followed by protein supplementation (35%) and strategic drenching (28%). Part of this study by Eady et al. (2003) showed that genetic improvement was found to be the most effective

- 21 - method in reducing and maintaining a low WEC. Selection of parasite resistant sheep based on their WEC from the natural genetic variation within a flock is an effective procedure in retaining those sheep, which best manage a worm burden (Stear et al. 1995). Within the Merino breed, genetic variation for production traits between Merino strains and bloodlines has been well documented (Jackson and Roberts 1970; Mortimer and Atkins 1989; Lewer et al. 1992; Eady et al. 1996). In the GIN study by Eady et al. (1996), the major source of genetic variation for WEC was found within bloodlines (Figure 1.6), with individual sires showing a wide range in resistance of their progeny.

Figure 1.6: Sources of variation in WEC of Haemonchus contortus and Trichostrongylus colubriformis across research flocks. (adapted from Eady et al. 1996)

6.1 Australian Sheep Breeding Values (ASBVs)

With greatest genetic variation in individual sires, sire selection is most vital for breeding sheep with an above average nematode resistance (Eady et al. 1996). There are now Australian Sheep Breeding Values (ASBVs) for all registered sheep sires and documentation to reveal their WEC performance. This is exhibited in Figure 1.7, where specific sires are identified which have below average WECs in their progeny, while group leaders are also evident by the shaded background. If breeding for worm resistance is a production goal, these sires can be selected (Figure 1.7) to build resistance against GIN parasites in a flock.

- 22 -

Figure 1.7: ASBV examples from Merino Superior Sires; selecting different sires for desired production traits (WEC highlighted in red box) (adapted from Australian Merino Sire Evaluation Association. 2007)

7. New Trends in Sheep Breeds of Australia

The difference in profitability of sheep breeds remains one of the most controversial discussion issues among farmers and is one motive for Australian sheep breeders changing to exotic breeds. Sheep breeds that display qualities requiring low maintenance inputs and reduced husbandry costs are an attractive alternative to traditional breeds. Reduction in shearing, crutching and flystrike costs are some of the benefits associated with running some of these exotic non-wool sheep breeds in harsh Australian conditions. Examples of such new exotic breeds which have been introduced to the Australian sheep flock include the Damara, Dorper, Awassi and Karakul. The Dorper and Damara are alternative breeds as meat sheep, producing desirable carcase yields and having a greater ability to cope with nutrition stress when compared to the Merino (Scanlon et al. 2008). They are less selective in their grazing patterns (grazing tough vegetable matter) and shed their hair to aid in maintaining a stable core body temperature during hot temperatures (de Waal and Combrinck 2000; Kilminster et al. 2008). There has been criticism associated with the introduction of these exotic breeds to Australia, due to the risk of Merino wool contamination to neighbouring wool producers. This is because there is the possibility of wool being downgraded due to the presence of hairs in the wool, leading to exotic breeds being perceived as ‘pests’.

- 23 - 7.1 Environmental Impact

The Australian Bureau of Meteorology and International Panel of Climate Change have released detailed reports documenting the evidence of climate change in primary climatological data, that of rainfall and temperature (PMSEIC 2007; Pittock 2003). Overall rainfall has decreased over the last 50 years in the southwest of Western Australia especially during winter (AGO 2006, PMSEIC 2007). Combined with the reduced rainfall there has been an overall increase in the annual Australian and global mean temperature (Figure 1.8)

Figure 1.8: Changes in Australian temperature from 1910 – 2006. (adapted from PMSEIC 2007)

Climate change factors such as increased heavy rainfall events, rising sea levels and rising CO2 levels, will have agricultural implications, with increasing erosion, salinity, water logging and crop damage, all probable consequences (PMSEIC 2007). These agricultural implications, along with increasing temperatures and reduced rainfall contribute to increased selection pressures on Australian sheep producers and their livestock. There will be increased heat stress challenges on livestock, decreased feed on offer, decreased supplementary feed levels available, increased intensity of water borne and food borne diseases and increased water demands (PMSEIC 2007). Australian sheep farmers face a fluctuating quality and quantity of feed throughout the year, which has lead them to introduce exotic sheep breeds such as the Damara and Dorper into their production systems. When exposed to a nutritional challenge, similar to that of the dry summer period of Australia, the Dorper sheep lose less weight than that of the Merino and Damara sheep faced with a similar challenge (Scanlon et al. 2008). Another study conducted by Snyman and Herselman (2005) determined Dorper sheep in South Africa out-performed Merinos when grazing veldt grass by having greater liveweights than the Merino sheep. The Damara and Dorper are alternatives to running Australian Merinos in harsh conditions, with the latter

- 24 - breed being out performed in nutritionally challenging conditions by these exotic breeds.

7.2 Market Impact

With increasing consumer emphasis and demand for organic produce, producers may experience a market premium for such products, as in the egg industry with increased price of free-range eggs compared to battery cage eggs. In a study by Burke and Apple (2007), the carcase quality of the Dorper was desirable, placed second in most carcase attributes behind the Suffolk. The Dorper lambs had a higher dressing percentage than wool sheep breeds (McClure et al. 1991), while producing low fat carcases of similar composition and quality to the Suffolk. However the Dorper meats cuts were rated more tender than the Suffolk and had the highest retail product yield (Burke and Apple 2007). For farmers attracted to a low maintenance, low input sheep breed such as the Dorper, would be of value to obtain information on parasite resistance and any association of this with production attributes.

8. The Dorper Sheep

The need for a sheep breed adapted to adverse conditions as in the semi-arid, extensive regions of South Africa, led to the formation of the Dorper breed in the late 1940s (Cloete et al. 2000). For this reason, along with many other performance traits of the Dorper, their numbers in Australia have increased, while the overall Australian sheep numbers have decreased.

8.1 History

After the First World War in the 1930s, declining wool prices and increased interest in mutton drew attention to the development of a desirable mutton sheep which could produce fast growing lambs in low rainfall areas. Although there was also increased interest in South Africa, in crossing Merino and indigenous sheep with British mutton rams, the English market perceived the fat tail sheep strange and according to their system of grading, undesirable (Milne 2000). The Black Head Persian was selected as a mother breed due to its ability to survive in harsh environmental conditions where veldt grass and shrubs were fodder. The Dorset Horn was selected as it demonstrated a longer breeding season in comparison to other British sheep breeds with favourable mutton production (Cloete et al. 2000). R. Edmeades and co-

- 25 - operators decided on the name ‘Dorper” for their new breed in 1947, with half cross Dorset x Persian ewes inspected and F2 and F3 ewes selected from Rye Dorper Stud. The White Dorper was developed not long after with the crossing of Persian and Dorset Horn rams with Merino ewes, where G. Cole-Rous concentrated his selection on the white variation (Nel 1993; Milne 2000).

8.2 Desirable Production Traits

The Dorper is numerically the second largest sheep breed in South Africa with growing numbers in Australia (de Waal and Combrinck 2000). The Dorper sheds its short hair, while maintaining a natural clean underbelly. Being a natural shedding sheep, the Dorper does not require shearing and as a result, Dorper sheep are less susceptible to flystrike due to their short hair, thereby reducing the husbandry pressures associated flystrike control. These are desirable traits for economic and logistical management, due to the difficulty and cost in hiring shearing contractors, along with carcase downgrading due to grass seed penetration of wool fleeces in Merinos. Below are productive traits which outline the Dorper breed’s advantages over other sheep breeds.

8.2.1 Reproductive Performance By reaching sexual maturity at an earlier age, Dorper sheep have a reproductive advantage over other sheep breeds (Greef et al. 1993). Age of first lambing is reported to be earlier in Dorpers, as shown in a study conducted by Schoeman (1990) comparing South African Meat Merino (SAMM) and Dohne Merino to the Dorper. Mean first lambing age was 3 to 4 months earlier in the Dorper compared to the other two breeds. This reproductive advantage is supported by the higher number of ewes lambing per ewe joined (EL/EJ) than other South African breeds, as illustrated by Schoeman (2000). Litter sizes of the Dorper were higher than other South African wool breeds, as Dorpers averaged lambing litter sizes of 1.30 (Schoeman 1990; Schoeman 2000). Survival rates of Dorper lambs were higher than the Dohne Merino and SAMM, reinforcing their reproductive advantage over other competitor meat breeds.

- 26 - 8.2.2 Body Weight and Growth Performance

Production performance in all meat producing sheep breeds is important to achieve maximum liveweight in the least possible time before slaughter. Birth weights of Dorper were heavier than Dohne Merino, Damara, Merino and SAMM (Schoeman 1990; Schoeman 2000). In a recent study by Burke and Apple (2007), weaning weights of the Dorper were higher than that of other breeds except the Suffolk. The higher weaning weights of the Dorper were supported by Schoeman (1990) and Schoeman (2000), where Dorper sheep weights exceeded those of the Dohne, Merino and SAMM breeds. Growth rates of the Dorper Sheep are another desirable productive trait, as the average daily gain of the Dorper was higher than all other meat breeds trialled (Burke and Apple 2007).

8.3 Internal Parasite Resistance of the Dorper

Hair sheep such as the Dorper have been documented to possess more desirable parasite resistance when compared to temperate wool breeds (Wildeus 1997; Burke and Miller 2004; Burke and Miller 2004). However other studies have contradicted these findings, stating the Dorper as being ‘relatively susceptible’ to GIN infection (Baker et al. 2003; Mugambi et al. 2005a). In studies by Mugambi et al. (2005a and 2005b) the response of the Dorper to both an indoor and pasture based H. contortus challenge, in comparison to the Red Maasai, was examined. The Red Maasai outperformed the Dorper in resistance to H. contortus challenge by having lower WEC than the Dorper. Another GIN study by Matika et al. (2003) compared the Dorper with Sabi sheep in semi-arid regions of Zimbabwe, resulting in the Dorper breed losing less liveweight and having a lower WEC than the Sabi sheep.

9. Hypothesis and Conclusion

The characteristics and heritability of resistance to GIN parasites are well established for Merino sheep in Australia, with breeding programmes in place to select for reduced WEC. In Australia the Dorper sheep breed is gaining increasing acceptance among sheep farmers, due to an expectation that there are lower management inputs such as shearing, crutching and mulesing. The Dorper sheep evolved in semi- arid areas of South Africa where GIN worm challenge was minimal and little emphasis was placed on selection for worm resistance. Anecdotally it has been claimed this ‘hardiness’ has been linked to both parasite resistance and tolerance,

- 27 - although there is contrasting research on this topic. Little research exists regarding parasite burdens affecting performance levels in Dorper sheep under temperate conditions, as found in sheep farms in Australia. As the breed is now widely established in high, as well as low rainfall areas throughout Australia, it would be valuable to investigate the consequences of GIN challenge on the productive performance of the Dorper. The hypothesis that will be tested is that a negative relationship exists between increasing WEC and production attributes in the Dorper sheep, as measured by liveweight, BCS, eye muscle depth and c-site fat depth.

- 28 - Chapter Two: Scientific Paper – Worm Egg Count and Production loss in the Dorper sheep

2. Introduction

2.1 Justification for a Focus on Gastrointestinal Parasitism

Gastrointestinal parasitism is widely regarded as the major disease problem of sheep in Australia (Love and Coles, 2002) and it’s effects can be traced to three species, namely Haemonchus contortus, Teladorsagia circumcincta and Trichostrongylus spp. GINs have been recognised as a significant production problem for the Australian sheep industry for a significant period (Beck et al. 1985) and an alarming increase in anthelmintic resistance has added further costs upon producers, as they struggle to maintain profitable livestock enterprises (Perry et al. 2002; Jackson and Coop 2000). Sackett et al. (2006) estimated the cost of GINs to the Australian sheep industry was $A369 million, which was mainly due to losses of production ($A310 million). At present, the two main strategies utilised to increase the ability of sheep to develop an effective immune response are, selection of animals that genetically present a strong immune reaction against GINs and nutritional supplementation (Greer 2008). If this immunity to parasites were important to enhance productivity, then selection for improved productivity performance would be linked to an increased parasite resistance. In contrast to the above, it has been documented that this has not occurred, as some lines of sheep selected for improved wool growth or liveweight gain, have been shown to possess WECs that are greater than for unselected sheep (McEwan et al. 1992). Gastrointestinal infections in sheep are characterised by sub-optimal productivity performances, due to reductions in both voluntary feed intake and nutrient utilisation. Reduction in feed intake is approximately proportional to larval intake and is relatively consistent across major nematode species (Sykes and Greer 2003). The overall metabolisable energy intake is diverted towards an immune response against GINs, as well as needing to sustain growth and production. As a consequence, there is a loss of energy made available for the production characteristics wool and meat, when compared to a parasite free sheep (Louie et al. 2007). Such infections therefore would be expected to have a negative impact on animal growth and production and an overall negative relationship established (Datta et al. 1998). However in other

- 29 - research, positive relationships have been confirmed between gastrointestinal WECs and liveweight, as observed in the liveweight gain found in New Zealand Romney sheep (Morris et al. 2000; Bisset et al. 2001) and the Santa Ines hair sheep in Brazil (Louvandini et al. 2006).

2.2 The Dorper Hair Sheep

Dorper sheep in Australia are gaining increasing acceptance and adoption by farmers, due to their reduced management and husbandry costs when compared to wool breeds. It has been stated that the ‘hardiness’ of the Dorper is linked to both parasite resistance and tolerance in the breed, although there is contrasting research on this topic. In fact as the Dorper sheep evolved in the semi-arid regions of South Africa, it is possible there exposure to a significant worm challenge is minimal and that they may be susceptible to GIN in the Australian environment. Little evidence exists regarding parasite burdens affecting performance levels in Dorper sheep under temperate conditions, as found in the south west of Western Australia. Sheep farmers in Australia must manage a fluctuating quality and quantity of feed over the four seasons in most years, which has lead them to introduce exotic sheep breeds such as the Damara and Dorper into their production systems. When exposed to a nutritional challenge, similar to that of the dry summer period of Australia, the Dorper sheep lose less weight than that experienced by Merino and Damara sheep, when faced with a similar challenge (Scanlon et al. 2008). Another study conducted by Snyman and Herselman (2005) determined that Dorper sheep in South Africa gained more liveweight then Merinos when grazing veldt grass.

2.2 Gastrointestinal Parasitism in the Dorper

Hair sheep such as the Dorper have been reported to possess greater parasite resistance when compared to temperate wool breeds (Wildeus 1997; Burke and Miller 2004; Burke and Miller 2004). Other studies have contradicted these findings, stating that the Dorper is ‘relatively susceptible’ to GIN infection (Baker et al. 2003; Mugambi et al. 2005a). The response of the Dorper to both an indoor and pasture based H. contortus challenge in studies by Mugambi et al. (2005a and 2005b), compared the breed to the Red Maasai. The Red Maasai outperformed the Dorper in resistance to a H. contortus challenge, by having a lower WEC than the Dorper. A different GIN study by Matika et al. (2003) compared the Dorper with Sabi sheep in

- 30 - the semi-arid regions of Zimbabwe, resulting in the Dorper breed losing less liveweight and having a lower WEC than the Sabi sheep. With such conflicting research existing among different breeds of sheep and the association between liveweight and gastrointestinal parasite infection, it was deemed worthwhile to examine what relationships may exist between GIN infections and production attributes in the exotic Dorper hair sheep. As this conflict applies even within the Dorper breed, in addition to inter breed comparisons, more work is required to establish an association between production and GIN infection in the exotic Dorper hair sheep breed.

Little research exists regarding parasite burdens affecting production in Dorper sheep under temperate conditions, as found in sheep farms in the south west of Western Australia. As the breed is now widely established in high, as well as low rainfall areas throughout Australia, it would be beneficial to investigate the consequences of GIN challenge on the productive performance of the Dorper. This project aims to investigate the effects of a natural pasture challenge with GIN on production attributes for the Dorper breed. This will be evaluated by examining whether the hypothesis of a negative relationship existing between WEC and production attributes is true in Dorper sheep. Production attributes of the Dorper included in this project will be liveweight, BCS, eye muscle depth and c-site fat depth.

3. Material and Methods

3.1 Animals and Experimental Design Data was collected by assisting with farm husbandry practices at the Ida Vale sheep property; which is located approximately 250km south of Perth near the town of Kojonup, with an average rainfall of 500mm per year. All sheep were handled according to the Code of Practice for Sheep in Western Australia, March 2003 (Department of Local Government and Regional Development. 2003). On this property, 289 White Dorper and Dorper ewe lambs were born between the 20th of June and 6th of July 2007 and had their birth type recorded (either as a single, twin or triplet). They were weaned during the period October 11th to November 6th 2007 (at approximately four months of age) and introduced to a 31.5 hectare paddock, separated from the rams. The stocking rate of this flock was 9.2 Dry Sheep

- 31 - Equivalence per hectare. At post weaning (approximately nine months of age), production attributes were measured on March 3rd 2008. The ewes were not measured as yearlings (12 months of age), as the majority of the flock was sold beforehand. A different flock of 234 entire White Dorper and Dorper ram lambs were born between the 3rd of August and 15th of September 2007 and had their birth type recorded (either as a single, twin or triplet). They were weaned between December 1st to December 31st (at approximately four months of age) and introduced to a 28.5 hectare paddock, separated from the ewes. The stocking rate of this flock was 8.2 Dry Sheep Equivalence per hectare. At post weaning (approximately nine months of age), production attributes of the rams were measured on May 3rd. The ram flock was weighed as yearlings on September 13th.

3.2 Diet and Composition Table 3.2: The nutritional components of sheep supplementary feed. Supplement Metabolisable Dry Matter ADF DDM Crude Calcium Phosphorus Energy (%) (%) (%) Protein (%) (%) (%) (MJ/kg) Milne Feed’s 11.0 92.3 22.3 72.1 14.5 0.7 0.3 Easy One Pellet Rolled Oaten 6.9 91.1 42.9 47.5 3 0.27 0.22 Hay Lupins 12.9 91.4 19.1 91.2 32.9 0.2 0.28 MJ; Mega Joules, ME; Metabolisable Energy, ADF; Acid Detergent Fibre, DDM; Digestible Dry Matter *Milne Feed’s Easy One Pellet composition: Lupins, barley, oats, wheat, triticale, cereal byproducts, cereal straw, limesand, urea, dicalcium phosphate, vitamin E, vitamin/trace mineral premix, lasalocid sodium. The rams were supplemented with Milne Feed’s Easy One pellets ad libitum, with water available ad libitum. The ewes were supplemented with oaten hay (large round rolls) and lupins fed daily, commencing at weaning, with water available ad libitum.

- 32 - Table 3.2.1: Estimated available Feed on offer (FOO, in kg/hectare of dry matter) in the ram and ewe paddocks. Age Point Weaning Post Weaning Yearling Ram Paddock

Size 28.5 hectare

December 15th 2007 FOO 800 FOO 1800 May 3rd 2008 September 13th 2008 Ewe Paddock

Size 31.5 Hectares

FOO 1000 February 26th 2008 October 13th 2007

During the 2006 year, weaner lambs were present on each paddock until late December of that year. Each of the two paddocks (Table 3.2.1) had breaks (deferred grazing) for a period between 6 to 8 months, before the two new weaner mobs were introduced onto each paddock in late 2007. The ewes were on a separate paddock at a different time period to that of the rams (Table 3.2.1).

3.4 Production Attribute Measurements Both flocks were weighed at the age points of weaning (approximately 4 months), post weaning (approximately 9 months) and only the rams at yearling stage (approximately 12 months).The c-site fat depth, body condition score and eye muscle depth of individual sheep were measured at post weaning for both flocks (sheep approximately 9 months of age). The c-site fat depth was measured at the C-site (which is 45mm from the midline over the 12th rib) to determine the body fat deposition of the sheep and was determined by conducting an ultrasound scan. The c-site fat depth was calculated from the average of three measurements made at this point (Hopkins et al. 2004). Body condition score was measured according to the practices and assessment developed by Suiter (1994). Eye muscle depth was

- 33 - measured at the GR site (the tissue depth was found to be 110mm from the midline over the 12th rib) also by ultrasound scan. The eye muscle depth was calculated from the average of three measurements made at this point (Safari et al. 2001). Body condition score was measured at the 13th (last) rib, with the thumb used to feel the backbone and finger tips to feel the ends of the short ribs behind the 13th rib (Figure 3.4) (Suiter 1994). Whilst feeling the back bone and short ribs, muscle and fat cover around the back bone were noted, with overall body condition scoring recorded in 0.5 intervals. Table 3.4 Body condition score guidelines for measuring the muscle and fat tissue covering the bones of the animal. (Suiter 1994) Score Backbone Short Ribs Eye Muscle Ends are sharp and Thin, with surface Prominent and easy to press 1 tending to feel sharp between and hollow around Smooth well- Reasonable depth Prominent and rounded ends can 2 with the surface smooth feel between feeling flat smoothly Ends are smooth Can be felt but and well covered, 3 smooth and firm pressure Full and rounded rounded needed to feel under Detectable with Individual short ribs Figure 3.4 Hand position Full with a covering 4 pressure on the can only be felt with layer of fat during BCS. (Suiter 1994) thumb firm pressure Muscle cannot be Felt with firm Cannot be felt even 5 felt due to thick pressing with firm pressure 3.5 Parasitological layer of fat Measurements and Drench History

Mob faecal WECs were monitored at fortnightly intervals until they reached 600EPG, this was a level where production and welfare of the sheep would be considered at risk. Faeces were collected per rectum from individual sheep for modified McMaster worm egg count determination. The individual worm egg counts were performed using methods described in Australian Standard Diagnostic Techniques for Animal Diseases Manual (Lyndal-Murphy, 1993). Strongyle WEC included all strongyle worm species (except Nematodirus) and total WEC was a combination of both Strongyle WEC and Nematodirus WEC. Both the ewes and rams were drenched at weaning with Virbac’s ‘First Mectin’ at 1ml to 4kg. They were not drenched again until mob WECs increased to 600 EPG and above (post weaning stage). At post weaning, the two flocks were also drenched with 12ml of Virbac’s Avermectin.

- 34 - 3.6 Statistical Analysis

Prior to analysis, triplet birth types were removed from the data set due to there being only three representatives across the entire data set. Worm egg count data for strongyle, nematodirus and the sum of the two (total) were assessed for normality of data distribution. This data proved to be heavily skewed (see Figures 4.2 and 4.2.1) and therefore the most appropriate transformation of log10+25 was used on the data set (+25 was used to enable log of zero WEC values) prior to analysis. General linear models (SAS) were used to analyse the log strongyle, nematodirus, and total WEC data, using sex, birth type (BT; 1= single born, 2=twin born) and their interaction as fixed effects. A similar approach was used to analyse liveweight, using sex, birth type, age point as fixed effects, with log strongyle, nematodirus and total WEC included in the model (each used in a separate analysis) as a covariate. Interactions between fixed effects and the covariate were included, and removed in a step-wise fashion if not significant (P>0.05). Lastly, general linear models were used to analyse the BCS, eye muscle depth, and c-site fat depth data collected at post weaning, using sex, and birth type as fixed effects, with log strongyle, nematodirus and total WEC as covariates (each used in a separate analysis). Once again interactions between fixed effects and the covariate were included and removed in a step-wise fashion if not significant (P>0.05).

4. Results

4.0 Larval Differentiation Table 4.0 Percentage of strongyle larval species in ram and ewe flocks after faecal larvae cultures, with mean WEC from each flock. Flock Haemonchu Teladorsagia Trichostrongylus Oesophagostomum s contortus circumcincta (%) spp (%). (%) (%) Rams 0 5 92 3 Ewes 0 5 25 70

4.1 Strongyle, Nematodirus, and Total Worm Egg Counts

The frequency distribution of strongyle WECs in the ram flock was that of a negative binomial distribution skewed to the left (Figure 4.1). After transformation of the ram strongyle WECs by log10+25, the transformed data represented an approximate normal distribution (Figure 4.1.1). The frequency distribution of the ewe flock

- 35 - resembled a negative binomial distribution (Figure 4.1.2). After the transformation by log10+25, the ewe data also represented an approximate normal distribution (Figure 4.1.3), while it is clear that in this flock there was approximately 14% of sheep within the ewe with low WEC values (0-50EPG). 40

35

30

25

20

Frequency 15

10

5

0 50 250 450 650 850 1050 1250 1450 1650 1850 2050 2250 Strongyle WEC (eggs per gram) Figure 4.1 The frequency distribution of strongyle WEC of individuals from the ram flock. 40

35

30

25

20

Frequency 15

10

5

0 1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 3.3 3.5 LogStrongyle+25 WEC (eggs per gram) Figure 4.1.1 The frequency distribution of logstrongyle+25 WEC of individuals from the ram flock.

- 36 -

45

40

35

30

25

20

Frequency 15

10

5

0

50 250 450 650 850 1050 1250 1450 1650 1850 2050 2250

Strongyle WEC (eggs per gram)

Figure 4.1.2 The frequency distribution of strongyle WEC of individuals from the ewe flock. 45

40

35

30

25

20

Frequency 15

10

5

0 1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 3.3 3.5 LogStrongyle+25 WEC (eggs per gram) Figure 4.1.3 The frequency distribution of logstrongyle+25 WEC of individuals from the ewe flock

- 37 - Logstrongyle WECs differed between both flocks (Figure 4.1.4), with twin born sheep of each flock having a higher logstrongyle WEC than the single born sheep. Twin born rams had the highest logstrongyle WECs (2.567 ± 0.036) (Figure 4.1.4). 2.65 2.6

2.55

2.5

2.45

2.4 LogStrongyle WEC

2.35 BT1 BT2 BT1 BT2 R R E E Figure 4.1.4 The effect of different birth types within sexes on logstrongyle WEC (logstrongyle+25 WEC).

In the ewe flock, single born sheep lognematodirus WECs were higher (1.796 ± 0.013) than for the twin born sheep (1.743 ± 0.029) (Figure 4.1.5). There was no significant difference in lognematodirus WECs between single and twin born rams (Figure 4.1.5). 1.85 1.8 1.75 1.7 1.65 1.6 1.55 1.5

1.45 LogNematodirus WEC 1.4 BT1 BT2 BT1 BT2

R R E E Figure 4.1.5 The effect of different birth types within sexes on lognematodirus WEC (lognematodirus+25 WEC).

- 38 - Logtotal WECs didn’t differ significantly between flocks or between twin and single born sheep (Figure 4.1.6). There was large variance between twin born sheep for logtotal WEC of both flocks. 2.64 2.62 2.6 2.58 2.56 2.54 LogTotal WEC 2.52 2.5 BT1 BT2 BT1 BT2

R R E E Figure 4.1.6 The effect of different birth types within sexes on logtotal WEC (logtotal+25 WEC).

4.2 Liveweight

4.2.1 Age, Sex and Birth Type Effects Liveweights differed between age points (P<0.05; Table 4.2, Column A, B and C). The liveweights between weaning and post-weaning age points increased by approximately 12kg in the ewe flock and approximately 11kg in the ram flock (Figure 4.2). However in the interval between post-weaning and yearling age points, during which only ram data was collected, the ram flock lost approximately 1.8kg of liveweight (Figure 4.2). The single born sheep of both flocks were heavier than twin born sheep (Figure 4.2), but this effect was not consistent across all age points (P<0.01; Table 4.2). In the post-weaning ewe flock, the difference between single and twin born sheep was approximately 3.5kg, while the corresponding difference in the ram flock was approximately 4kg (Figure 4.2). In contrast, at the yearling age point the difference between single and twin born rams was approximately 2kg (Figure 4.2).

- 39 - Table 4.2 F-values and degrees of freedom for the effects of log strongyle, nematodirus and total worm egg count (WEC) and animal factors (birth type, sexes and age), on liveweight. Dependent Variable: Liveweight Column A Column B Column C Effect Log StrongyleWEC Log NematodirusWEC Log TotalWEC covariate covariate covariate NDF,DD F-Value NDF,D F-Value NDF,DD F-Value F DF F Sex 1,1255 1.73* 1,1255 511.83** 1,1255 2.25- Age Point 2,1255 2.87* 2,1255 255.82** 2,1255 2.74+ Birth Type 1,1255 15.39** 1,1255 15.36** 1,1255 15.15** LogWEC 1,1255 8.08** 1,1255 3.24+ 1,1255 6.41** Age Point * Birth Type 2,1255 5.59** 2,1255 4.95** 2,1255 5.28** LogWEC * LogWEC 1,1255 7.02** 1,1255 3.97* 1,1255 5.95* LogWEC * Sex 1,1255 6.43** - - 1,1255 5.03* LogWEC * Age Point 2,1255 6.56** - - 2,1255 4.9**

NDF, DDF, numerator and denominator degrees of freedom -, P>0.1; +, P<0.1; *, P<0.05; **, P<0.01

60 50

40

30

20

Liveweight (kg) 10

0 BT1 BT2 BT1 BT2 BT1 BT2 BT1 BT2 BT1 BT2 W W PW PW Y Y W W PW PW R R R R R R E E E E R PW BT2 E W BT1 Figure 4.2 The effect of different age points and birth types within sexes on liveweight (E=ewe, R=ram, PW=post weaning, W=weaning, Y=yearling).

4.2.2 Strongyle Worm Egg Count Effects The logstrongyle WEC had an impact on liveweight (P<0.01; Table 4.2, Column A) only at the post-weaning age point (P<0.01; Table 4.2, Column A), which was the only time that individual sheep had their WEC directly measured. In the post-weaning ram flock, increasing logstrongyle WEC resulted in a liveweight increase of approximately 7.5kg, between the ranges of 0-770 eggs per gram, while reaching a plateau beyond this point (Figure 4.2.1).

- 40 - 70

60

70 50 60

40 50

40

30 R R 30 Liveweight (kg) R PW Rams BT1 PW RamsPW Rams BT2 YearlingW Rams Rams BT1

Liveweight (kg) 20 20 W Rams BT2 Y Rams BT1 PW Rams BT1 PW Rams BT2 Y Rams BT2 10 Y Rams BT1 Y Rams BT2 10 0 1.097 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497

0 LogStrongyle+25 Worm Egg Count (eggs per gram)

1.397 1.897 2.397 2.897 3.397

AntilogStrongyle+25 Worm Egg Count (eggs per gram)

Figure 4.2.1: The effect of logstrongyle+25 WEC (eggs per gram) on ram liveweights in kg and antilogstrongyle+25 WEC.

The post-weaning ewe flock liveweights increased by approximately 4.5kg as logstrongyle WEC increased between 0-770 eggs per gram (Figure 4.2.3), reaching a plateau beyond this point.

- 41 - 70

60

60

50 4.5 50 4

40 40 3.5 3 30 2.5 30 R R 2 Liveweight (kg) 20 R PW Rams BT1 PW Ewes Liveweight (kg) 1.5 PW Rams BT2 W Rams BT1 20 W Rams BT2 PW EweY Rams BT1 BT1 10 1 PW Rams BT 1 PW Rams BT 2 Y Rams BT2 Body Condition Score 0.5 PW Ewe BT2 PW Rams BT1 PW Rams BT2 10 0 0 1.097 1.0971.397 1.3971.697 1.6971.997 1.9972.297 2.2972.597 2.5972.897 2.8973.197 3.1973.497 3.497 LogStrongyle+20LogStrongyle+25 Worm Worm Egg Egg Count Count (eggs (eggs per per gram) gram) 0 1.397 1.897 2.397 2.897 3.397 AntilogStrongyle+25 Worm Egg Count (eggs per gram)

Figure 4.2.2: The effect of logstrongyle+25 WEC (eggs per gram) on ewe liveweights in kg and antilogstrongyle+25 WEC.

4.2.3 Nematodirus Worm Egg Count Effects With increasing lognematodirus WEC between 0-370 eggs per gram, the liveweight of the post weaning rams was effected (P<0.1; Table 4.2, Column B), decreasing by approximately 2kg (Figure 4.2.3).

- 42 - 80

70

60

50 40

30 PW Rams Yearling Rams 20 Liveweight (kg) PW Rams BT1 PW Rams BT2 10 Y Rams BT1 Y Rams BT2 0 1.097 1.397 1.697 1.997 2.297 2.597 2.897

LogNematodiurs+25 Worm Egg Count (eggs per gram)

Figure 4.2.3: The effect of lognematodirus+25 WEC (eggs per gram) on ram liveweights in kg and antilognematodirus +25 WEC.

For the same WEC ranges as observed in the rams, the post-weaning ewe flock liveweights decreased by approximately 3kg with an increase in lognematodirus WEC between 0-370 eggs per gram (Figure 4.2.4). 80 60 70 50 60

4050

40 30 30 PW Rams Yearling Rams 20

Liveweight (kg) 20 Liveweight (kg) PW Rams BT1 Post WeaningPW Rams Ewes BT2

10 PW Ewe BT1 Y Rams BT1 Y Rams BT2 0 PW Ewe BT2 0

1.0971.097 1.3971.397 1.6971.697 1.9971.997 2.2972.297 2.5972.597 2.8972.897

LogNematodiurs+25LogNematodirus+20 Worm Worm Egg Egg Count Count (eggs (eggs per per gram) gram)

Figure 4.2.4: The effect of lognematodirus+25 WEC (eggs per gram) on ewe liveweights in kg and antilognematodirus +25 WEC.

- 43 - 4.2.4 Total Worm Egg Count Effects In the post-weaning ram flock, increasing logtotal WEC resulted in a liveweight effect (P<0.01;Table 4.2, Column C), being made up of an increase of approximately 6.5kg, between 0-770 eggs per gram, however weights reached a plateau beyond this point (Figure 4.2.5). The combined effect of an increased liveweight associated with logstrongyle WEC (Figure 4.2.1, Figure 4.2.2) together with a decreased liveweight associated with lognematodirus WEC (Figure 4.2.3, Figure 4.2.4), did not lead to a perfectly additive effect in either flock liveweights of logtotal WECs (Figure 4.2.5, Figure80 4.2.6).

8070

70 60 60 50 40 40 30 Post Weaning Rams Yearling Rams

Liveweight (kg) 30 20 PW Rams BT1 PW Rams BT2 Liveweight (kg) R R 10 R PW Rams BT1 20 Y Rams BT1 Y Rams BT2 PW Rams BT2 W Rams BT1 0 W Rams BT2 Y Rams BT1 101.097 1.397 1.697 1.997 2.297 2.597 2.897Y Rams BT2 3.197 3.497 LogTotal+25 Worm Egg Count (eggs per gram) 0 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497

AntiLogTotal+25 Worm Egg Count (eggs per gram) Figure 4.2.5: The effect of logtotal+25 WEC (eggs per gram) on ram liveweights in kg and antilogtotal+25 WEC.

With an increasing logtotal WEC, the post-weaning ewe flock liveweights increased by approximately 4kg between 0-770 eggs per gram (Figure 4.2.6) and reached a plateau beyond this point.

- 44 - 80

70 80 60

6070 50 60 50 50 40

4040 30 30

30 20 Post Weaning RamsPost WeaningYearling Ewes Rams Liveweight (kg) Liveweight (kg) 20 Liveweight (kg) R R PW Rams BT1 PW Ewe BT1PW Rams BT2 R PW Rams BT1 2010 10 Y RamsPW BT1 Rams BT2 WY Rams Rams BT2BT1 PW Ewe BT2 W Rams BT2 Y Rams BT1 0 10 0 Y Rams BT2 1.097 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497 1.097 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497 LogTotal+25LogTotal+20 WormWorm Egg Egg Count Count (eggs (eggs per pergram) gram) 0 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497 AntiLogTotal+25 Worm Egg Count (eggs per gram) Figure 4.2.6: The effect of logtotal+25 WEC (eggs per gram) on ewe liveweights in kg and antilogtotal+25 WEC.

4.3 Body Condition Score

4.3.1 Sex and Birth Type Effects

The BCS differed between sexes (P<0.01; Table 4.3, Column A, B and C). Single born ewes were approximately 0.3 BCS units higher than for twin born ewes (Figure 4.3) and similarly single born rams were approximately 0.25 BCS units higher when compared to twin born rams (Figure 4.3).

- 45 - Table 4.3 F-values and degrees of freedom for the effects of log strongyle, nematodirus and total worm egg count (WEC) and animal factors (birth type and sexes), on BCS. Dependent Variable: Body Condition Score Column A Column B Column C Effect Log StrongyleWEC Log NematodirusWEC BCS Log TotalWEC covariate covariate covariate NDF,DD F-Value NDF,D F-Value NDF,DD F-Value F DF F Sex 1,511 9.19** 1,511 6.12** 1,511 3.2+ BT 1,511 1.31- 1,511 14.41** 1,511 14.12** LogWEC 1,511 4.87* 1,511 12.56** 1,511 4.13** Sex * BT 1,511 5.31* - - - - LogWEC * LogWEC 1,511 7.7** - - 1,511 9.03** LogWEC * Sex 1,511 13.6** 1,511 3.36* 1,511 7.8** LogWEC * BT 1,511 0.77- - - - - LogWEC * LogWEC * Sex 1,511 16.91** - - 1,511 11.75** LogWEC * LogWEC * BT 1,511 0.55- - - - - LogWEC * BT * Sex 1,511 4.91* - - - - LogWEC * LogWEC * BT * Sex 1,511 4.33* - - - -

BT, NDF, DDF, Birth type, numerator and denominator degrees of freedom -, P>0.1; +, P<0.1; *, P<0.05; **, P<0.01

3

2.5 2

1.5

1

0.5 Body ConditionScore Body

0 BT1 BT2 BT1 BT2 E E R R Figure 4.3 The effect of different birth types within sexes on body condition score (E=ewe, R=ram, PW=post weaning, W=weaning).

4.3.2 Strongyle Worm Egg Count Effects The logstrongyle WEC had an impact on BCS that differed between birth types for each flock (P<0.05; Table 4.3, Column A). For ram flock, single born rams had a decrease in their BCS by approximately 1 unit, while twin born rams had a similar decrease of approximately 1.5 BCS units (Figure 4.3.1). The association between BCS and increasing logstrongyle WEC resembled a curved quadratic pattern (P<0.01; Table 4.3, Column A) for both ram flock birth types (Figure 4.3.1).

- 46 - 70

60

50

4.5

40 4

3.5 3 30 2.5 R R

Liveweight (kg) R PW Rams BT1 2 PW Rams BT2 W Rams BT1 20 1.5 W Rams BT2 Y Rams BT1 Y Rams BT2 1 PW Rams BT 1 PW Rams BT 2

Body Condition Score 0.5 PW Rams BT1 PW Rams BT2 10 0

1.097 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497 0 LogStrongyle+25 Worm Egg Count (eggs per gram)

1.397 1.897 2.397 2.897 3.397

AntilogStrongyle+25 Worm Egg Count (eggs per gram)

Figure 4.3.1: The effect of logstrongyle+25 WEC (eggs per gram) on ram body condition scores and antilogsgtrongyle+25 WEC.

In the post weaning ewe flock, increasing logstrongyle WEC across the same eggs per gram range as for the rams, had no effect on the BCS of single born ewes (Figure 4.3.2). The twin born ewes BCSs decreased by approximately 1 unit, between 0-770 eggs per gram. There is a weak curved quadratic association between BCS and logstrongyle WEC as represented in the twin born ewes (Figure 4.3.2).

- 47 - 4.5 70 4 60 3.5 4.5

3 4 50 3.5 2.5 3

40 2 2.5

1.5 2 30 PW Ewes BT 1 1.5 R R 1 Liveweight (kg) R PW Rams BT1 PW Ewes BT2 Body Condition Score 1 PW Rams BT2PW RamsW BTRams 1 BT1 PWPW RamsEwe BT1BT 2 20 0.5 W Rams BT2 Y Rams BT1 Body Condition Score 0.5 Y Rams BT2PW Rams BT1 PWPW RamsEwe BT2 0 0 10 1.0971.097 1.3971.397 1.6971.697 1.9971.997 2.2972.297 2.5972.597 2.8972.897 3.1973.197 3.4973.497

LogStrongyle+25LogStrongyle+25 Worm Worm EggEgg Count Count (eggs (eggs per gram)per gram) 0 1.397 1.897 2.397 2.897 3.397

AntilogStrongyle+25 Worm Egg Count (eggs per gram) Figure 4.3.2: The effect of logstrongyle+25 WEC (eggs per gram) on ewe body condition scores and antilogsgtrongyle+25 WEC.

4.3.3 Nematodirus Worm Egg Count Effects The lognematodirus WEC had a weak impact on the post weaning ram flock BCSs, that differed sexes (P<0.05; Table 4.3, Column B). Single and twin born post weaning rams had a decrease in BCS by approximately 0.5 in association with an increasing lognematodirus WEC between 0-250 eggs per gram (Figure 4.3.3).

- 48 -

4.5

4 80 3.5 70 60 3 50 2.5 40 2 301.5 PW Rams PW Rams YearlingBT 1 Rams

20 Body Condition Score Liveweight (kg) 1 PW Rams BT1 PW Rams PWBT 2 Rams BT2 10 PW Rams BT1 0.5 Y Rams BT1 Y Rams BT2 0 PW Rams BT2 0 1.097 1.397 1.697 1.997 2.297 2.597 2.897 1.097 1.397 1.697 1.997 2.297 2.597

LogNematodiurs+25Log Nematodirus Worm Worm Egg Egg Count Count (eggs (eggsper gram) per gram)

Figure 4.3.3: The effect of lognematodirus+25 WEC (eggs per gram) on ram body condition scores and antilognematodirus+25 WEC.

Post weaning ewes had no change to their overall BCS with an increasing lognematodirus WEC (Figure 4.3.4). Single and twin ewe BCSs had no change, resembling a plateau across 0-250 eggs per gram. 4.5 80 4 70 3.5 60 3 50 2.5 40 2 30 1.5 PW Rams Yearling Rams PW Ewes BT 1 20 Liveweight (kg) 1 PW Rams BT1PW Ewes BT 2PW Rams BT2

Body10 Condition Score PW Ewe BT1 0.5 Y Rams BT1 Y Rams BT2 0 PW Ewe BT2 0 1.097 1.397 1.697 1.997 2.297 2.597 2.897 1.097 1.397 1.697 1.997 2.297 2.597 2.897 LogNematodiurs+25 Worm Egg Count (eggs per gram) LogNematodirus+25 Worm Egg Count (eggs per gram)

- 49 - Figure 4.3.4: The effect of lognematodirus+25 WEC (eggs per gram) on ewe body condition scores and antilognematodirus+25 WEC.

4.3.4 Total Worm Egg Count Effects The logtotal WEC effect on BCS differed between flocks (sexes) (P<0.01; Table 4.3, Column C). In the single born post weaning rams, the decrease in BCS was approximately 1.5 units associated with increasing logtotal WEC. For twin born rams of the flock, this decrease was approximately 1.25 BCS units with increasing logtotal WEC (Figure 4.3.5). The BCS decrease associated with an increasing logtotal WEC resembled a curved quadratic pattern (P<0.01; Table 4.3, Column C). The

80 combination of BCS losses, as contributed by logstrongyle WEC (-1) and lognematodirus WEC (-0.5) in single born post weaning rams, resulted in almost a 8070 perfectly additive response in logtotal WEC BCS loss (-1.5) (Figure 4.3.5). This did 70 not occur in the twin born rams or any of the ewes (Figure 4.3.6). 604.5

60 4 503.5 50 3 40 402.5 30 2 Post Weaning Rams Yearling Rams

Liveweight (kg) 30 201.5 PW Rams BT1PW Rams BT 1 PW RamsPW RamsBT2 BT 2 Liveweight (kg) 1 R R 10 R PW Rams BT1

Body Condition Score 20 Y Rams BT1 Y Rams BT2 0.5 PW Rams BT1 PW Rams BT2 PW Rams BT2 W Rams BT1 0 0 W Rams BT2 Y Rams BT1 Y Rams BT2 101.0971.097 1.3971.397 1.6971.697 1.9971.997 2.2972.297 2.5972.597 2.8972.897 3.1973.197 3.4973.497 LogTotal+25LogTotal+25 Worm Worm Egg Egg CountCount (eggs(eggs per per gram) gram) 0

1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497

AntiLogTotal+25 Worm Egg Count (eggs per gram)

Figure 4.3.5: The effect of logtotal+25 WEC (eggs per gram) on ram body condition scores and antilogtotal+25 WEC.

In the post weaning ewes, increasing logtotal WEC across the same eggs per gram range as for the rams, had no effect on the BCS of single and twin born ewes (Figure 4.3.6). The ewes BCS decreased by approximately 0.25, between 0-1550 eggs per gram range.

- 50 - 80

7080 4.5

70 4 60 3.560

503 50 2.5 40 40 2 30 1.5 Post Weaning Rams Yearling Rams

Liveweight (kg) 30 20 1 Liveweight (kg) PW RamsR BT1 PWR Rams BT2 PW Ewes BT 1 PW Ewes BT 2 Body Condition Score 10 R PW Rams BT1 0.520 Y Rams BT1 Y Rams BT2 PWPW Rams Ewe BT2BT1 WPW Rams Ewe BT2BT1 00 W Rams BT2 Y Rams BT1 101.0971.097 1.3971.397 1.6971.697 1.9971.997 2.2972.297 2.597 Y2.897 Rams BT2 3.1973.197 3.4973.497

LogTotal+25LogTotal+25 WormWorm Egg Egg Count Count (eggs (eggs per gram)per gram) 0 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497

AntiLogTotal+25 Worm Egg Count (eggs per gram)

Figure 4.3.6: The effect of logtotal+25 WEC (eggs per gram) on ewe body condition scores and antilogtotal+25 WEC.

4.4 C-site Fat Depth

4.4.1 Sex and Birth Type Effects C-site fat depth differed significantly between birth types for each flock (P<0.01; Table 4.3) (P<0.01; Table 4.4, Collumn A, B and C). Single born rams had a thicker c-site fat depth than twin born rams by approximately 0.3mm (Figure 4.4), as did the single born ewes, with a c-site fat depth approximately 0.3mm thicker than for twin born ewes (Figure 4.4).

- 51 -

Table 4.4 F-values and degrees of freedom for the effects of log strongyle, nematodirus and total worm egg count (WEC) and animal factors (birth type and sexes), on c-site fat depth. Dependent Variable: C-site Fat Depth Column A Column B Column C Effect Log StrongyleWEC Log NematodirusWEC LogTotalWEC covariate covariate covariate NDF,DD F-Value NDF,D F-Value NDF,DD F-Value F DF F Sex 1,509 9.55** 1,509 28.45** 1,509 8.65** BT 1,509 2.76+ 1,509 6.15** 1,509 2.63+ LogWEC 1,509 5,51* - - 1,509 4.97* Sex * BT 1,509 8.6** - - 1,509 8.14** LogWEC * LogWEC 1,509 4.27* - - 1,509 7.5** LogWEC * Sex 1,509 9.08** - - - 8.33** LogWEC * BT 1,509 1.73- - - - 1.69- LogWEC * LogWEC * Sex 1,509 7.61** - - - 7.07** LogWEC * LogWEC * BT 1,509 1.17- - - - 1.14- LogWEC * BT * Sex 1,509 7.36** - - - 6.93** LogWEC * LogWEC * BT * Sex 1,509 5.9** - - - 5.53*

BT, NDF, DDF, Birth type, numerator and denominator degrees of freedom -, P>0.1; +, P<0.1; *, P<0.05; **, P<0.01 3.5

3

2.5 2

1.5

1 0.5 C-site Fat Depth (mm)Depth Fat C-site

0 BT1 BT2 BT1 BT2

E E R R

Figure 4.4 The effect of different birth types within sexes on c-site fat depth (mm) (E=ewe, R=ram).

4.4.2 Strongyle Worm Egg Count Effects The logstrongyle WEC had an influence on c-site fat depth differing between birth types for each sex (P<0.01; Table 4.4, Column A). With increasing logstrongyle WEC, c-site fat depth decreased by approximately 0.5mm between 0-1550 eggs per gram in single post weaning rams (Figure 4.4.1). In twin born post weaning rams there was a decrease in c-site fat depth by approximately 0.8mm between 100-1700 eggs per gram (Figure 4.4.1). The c-site fat depth measurements in association with

- 52 - 70

60 an increasing logstrongyle WEC in twin born rams were best represented by a quadratic curved line (P<0.05; Table 4.4, Column A) (Figure 4.4.1). 50 6

5 40 4

3 30 R R

Liveweight (kg) R PW Rams BT1 2 PW Rams BT2 W Rams BT1 20 W Rams BT2 Y Rams BT1 PW Rams BT 1 PW Rams BT 2

1 Y Rams BT2 C-site Fat Depth (mm) PW Rams BT1 PW Rams BT2 10 0 1.097 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497

LogStrongyle+25 Worm Egg Count (eggs per gram) 0

1.397 1.897 2.397 2.897 3.397 AntilogStrongyle+25 Worm Egg Count (eggs per gram)

Figure 4.4.1: The effect of logstrongyle+25 WEC (eggs per gram) on ram c-site fat depth and antilogstrongyle+25 WEC.

In the post weaning ewes of single birth type, increasing logstrongyle WEC across 0- 1550 eggs per gram had no effect on their c-site fat depths (Figure 4.4.2). The c-site fat depths of twin born ewes decreased by approximately 0.6mm with an increasing logstrongyle WEC between 0-1550 eggs per gram. The curved quadratic pattern of c- site fat depths as influenced by logstrongyle WEC, was only present in twin born ewes (Figure 4.4.2).

- 53 - 70

40 60 6 35 5 30 50

25 4 40 20 3

15 30 R R PW Rams BT1 2

Liveweight (kg) R PW Rams BT1 10 PW Rams BT2

PW Rams BT2 WPW Rams Ewes BT1 BT1 PW Ewes BT2 Eye Eye Muscle Depth (mm) 20 C-siteFat Depth (mm) W Rams BT2 Y Rams BT1 PW Rams BT1 5 1 Y Rams BT2 PW Ewe BT1 PW EwePW BT2 Rams BT2

0 0 10 1.097 1.097 1.397 1.397 1.6971.697 1.9971.997 2.2972.297 2.5972.597 2.8972.897 3.197 3.197 3.497 3.497

LogStrongyle+25LogStrongyle+25 Worm Worm Egg CountCount (eggs (eggs per per gram) gram) 0 1.397 1.897 2.397 2.897 3.397

AntilogStrongyle+25 Worm Egg Count (eggs per gram) Figure 4.4.2: The effect of logstrongyle+25 WEC (eggs per gram) on ewe c-site fat depth and antilogstrongyle+25 WEC.

4.4.3 Nematodirus Worm Egg Count Effects The lognematodirus WEC had no effect on c-site fat depth, although there were differences between birth types (P<0.01; Table 4.4. Column B). Post weaning rams of both birth types had a plateau effect in their c-site fat depth, when associated with an increasing lognematodirus WEC between 0-250 eggs per gram. The post weaning ewes also had no change to their c-site fat depth measurements with an increasing lognematodirus WEC.

4.4.4 Total Worm Egg Count Effects The logtotal WEC effect on c-site fat depth differed between birth types within sexes (P<0.01; Table 4.4, Column C). In post weaning rams of single birth type, an increasing logtotal WEC decreased c-site fat depth by approximately 0.5mm between 0-1550 eggs per gram (Figure 4.4.3). In twin born post weaning rams there was a decrease in c-site fat depth by approximately 0.8mm in association with an increasing logtotal WEC (Figure 4.4.3). This c-site fat depth decrease when associated with an increasing logtotal WEC, had a curved quadratic pattern (P<0.01;

- 54 - 80 40 Table 4.4, Column C) as best fit, similar to that of an increasing logstrongyle WEC 35 70 (Figure 4.4.1).

6 30 60

25 5 50 20 4 40 15 3 PW Rams BT1 10 30 2 PW Rams BT2

Liveweight (kg) R R PW Rams BT1 Eye Eye Muscle Depth (mm) 5 R PW RamsPW BT1 Rams Rams BT2 BT1 20C-site Fat Depth (mm) 1 PW Rams BT2 W Rams PWBT1 Rams Rams BT1 BT2 W Rams BT2 Y Rams BT1 0 PW Rams BT2 10 0 Y Rams BT2 1.097 1.097 1.3971.397 1.6971.697 1.9971.997 2.297 2.5972.597 2.8972.897 3.197 3.197 3.497 3.497

LogTotal+25 Worm Egg Count (eggs per gram) 0 LogTotal+25 Worm Egg Count (eggs per gram) 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497

AntiLogTotal+25 Worm Egg Count (eggs per gram) Figure 4.4.3: The effect of logtotal+25 WEC (eggs per gram) on ram c-site fat depth and antilogtotal+25 WEC.

In the post weaning ewes, increasing logtotal WEC from 0-1550 eggs per gram had no effect on the c-site fat depths of single born ewes (Figure 4.4.4). In twin born ewes, the c-site fat depth decreased by approximately 0.5mm with an increasing logtotal WEC between 0-1550 eggs per gram. 6

5

4

3

2

C-site Fat Depth (mm) 1 PW Ewes BT1 PW Ewes BT2

PW Ewe BT1 PW Ewe BT2 0 1.097 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497 LogTotal+25 Worm Egg Count (eggs per gram)

- 55 - Figure 4.4.4: The effect of logtotal+25 WEC (eggs per gram) on ewe c-site fat depth and antilogtotal+25 WEC.

4.5 Eye Muscle Depth

4.5.1 Sex, and Birth Type Effects Eye muscle depth differed sexes (P<0.01; Table 4.5, Column A, B and C). The eye muscle depth of the single born ewes was approximately 2mm thicker than for twin born ewes (Figure 4.5), while there was no significant difference between single significantly between and twin born rams (single born rams were approximately 0.5mm thicker than twin born ones [Figure 4.5]).

Table 4.5 F-values and degrees of freedom for the effects of log strongyle, nematodirus and total worm egg count (WEC) and animal factors (birth type and sexes), on eye muscle depth. Dependent Variable: Eye Muscle Depth Column A Column B Column C Effect Log StrongyleWEC Log NematodirusWEC Log TotalWEC covariate covariate covariate NDF,DD F-Value NDF,D F-Value NDF,DD F-Value F DF F Sex 1,510 44.26** 1,510 54** 1,510 48.07** Birth Type 1,510 8.59** 1,510 7.44** 1,510 8.29** LogWEC 1,510 9.29** - - 1,510 8.65** Sex * Birth Type 1,510 2.87+ 1,510 2.74+ 1,510 2.55+ LogWEC * LogWEC 1,510 7.77** - - 1,510 7.5** LogWEC * Sex - - 1,510 3.36* - -

NDF, DDF, numerator and denominator degrees of freedom -, P>0.1; +, P<0.1; *, P<0.05; **, P<0.01 29 28

27 26

25

24

Eye Muscle Depth(mm) Muscle Eye 23

22

21 BT1 BT2 BT1 BT2 E E R R

- 56 - Figure 4.5 The effect of different birth types within sexes on eye muscle depth (mm) (E=ewe, R=ram, PW=post weaning, W=weaning, Y=yearling).

4.5.2 Strongyle Worm Egg Count Effects 70 The increase of logstrongyle WEC had no significant effect on eye muscle depth between 0-1550 eggs per gram in post weaning rams (Figure 4.5.1). In single and 40 60 twin born rams there was a weak increase in eye muscle depth by approximately 35 2mm between 25-1550 eggs per gram (Figure 4.5.1). 40 30 50 35

25 30 40

20 25

20 15 30 R R PW Rams BT1

Liveweight (kg) R PW Rams BT1 15 10 PW Rams BT2 W Rams BT1 PW Rams BT1PW Rams BT2

20 10 W Rams BT2 Y Rams BT1 PW Rams BT2

Eye Eye Muscle Depth (mm) PW Rams BT1 Y Rams BT2

5 Eye Muscle Depth (mm) PW Rams BT1 5 PW Rams BT2 PW Rams BT2 0 10 0 1.097 1.097 1.397 1.397 1.697 1.697 1.9971.997 2.2972.297 2.5972.597 2.897 2.897 3.197 3.1973.497 3.497 LogStrongyle+25LogStrongyle+25 Worm Worm EggEgg CountCount (eggs (eggs per per gram) gram) 0 1.397 1.897 2.397 2.897 3.397 AntilogStrongyle+25 Worm Egg Count (eggs per gram)

Figure 4.5.1: The effect of logstrongyle+25 WEC (eggs per gram) on ram eye muscle depth and antilogstrongyle+25 WEC.

The post weaning single and twin born ewes had a slight increase in eye muscle depth by approximately 2mm with an increasing logstrongyle WEC between 0-1550 eggs per gram (Figure 4.5.2).

- 57 - 70 40

6040 35

35 30 50 30 25

4025 20 20 15 PW Rams BT1 3015 R R PW Ewes BT 1 10 Liveweight (kg) R PW Rams BT1 PW Rams BT2 10 PW Rams BT2 W Rams PWBT1 Ewes BT 2

Eye Eye Muscle Depth (mm) PW Rams BT1 20Depth Muscle (mm) Eye W Rams BT2 Y Rams BT1 5 PW Ewe BT1 5 Y Rams BT2 PW Rams BT2 PW Ewe BT2 0 0 1.09710 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497 1.097 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497 LogStrongyle+25LogStrongyle+25 Worm Worm Egg Egg Count Count (eggs (eggs per pergram) gram) 0 1.397 1.897 2.397 2.897 3.397

AntilogStrongyle+25 Worm Egg Count (eggs per gram) Figure 4.5.2: The effect of logstrongyle+25 WEC (eggs per gram) on ewe eye muscle depth and antilogstrongyle+25 WEC.

4.5.3 Nematodirus Worm Egg Count Effects The lognematodirus WEC had no impact on eye muscle depth, but there were differences between birth types (P<0.01; Table 4.5, Column B). Post weaning rams of both birth types had no significant change in their eye muscle depth, with increasing lognematodirus WECs between the ranges of 0-200 eggs per gram, maintaining a plateau through these points. The post weaning ewes also had no significant change to their eye muscle depth with an increasing lognematodirus WEC between 0-370 eggs per gram.

4.5.4 Total Worm Egg Count Effects Logtotal WEC impact on eye muscle depth differed between sexes (P<0.01; Table 4.5, Column C). In the post weaning ram flock, single birth sheep had an eye muscle depth increase of approximately 2.25mm between 0-1550 eggs per gram (Figure 4.5.3). In twin born post weaning rams there was also an increase in eye muscle depth of approximately 2mm with an increasing logtotal WEC, across the same eggs per gram range as that for the single born (Figure 4.5.3). The combination of eye

- 58 - muscle increases in association with logstrongyle WEC (+2mm) and lognematodirus 80 40 WEC post weaning rams, resulted in a greater than additive response in logtotal WEC of eye muscle depth thickening (2.25mm increase; Figure 4.5.3). This did not 35 70 occur in the ewes (Figure 4.5.4). 30 60 40

25 35 50 30 20

40 25 15 20 30 PW Rams BT1 10 15 PW Rams BT2

Liveweight (kg) R PWR Rams BT1

Eye Eye Muscle Depth (mm) 10 5 20 R PW RamsRamsPW BT2 BT1 Rams BT1

Eye Eye Muscle Depth (mm) PW Rams BT2 W Rams BT1 5 PW RamsPW BT1 Rams BT2 W Rams BT2 Y Rams BT1 0 PW Rams BT2 10 0 Y Rams BT2 1.097 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497 1.097 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497 0 LogTotal+25LogTotal+25 Worm Worm Egg Egg Count (eggs (eggs per per gram) gram) 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497

AntiLogTotal+25 Worm Egg Count (eggs per gram) Figure 4.5.3 The effect of logtotal+25 WEC (eggs per gram) on ram eye muscle depth and antilogtotal+25 WEC.

In the post weaning ewes of single and twin birth types, there was an increase in 40 muscle depth of approximately 2mm, with increasing logtotal WEC across 0-1550

35 eggs per gram range (Figure 4.5.4). 40 30 35 25 30 20 25

15 20 15 PW Rams BT1 10 PW Ewes BT1 PW Rams BT2 10 PW Ewes BT2 Eye Eye Muscle Depth (mm) 5 PW Rams BT1 5 PW Ewe BT1 PW Ewe BT2PW Rams BT2 Eye Eye Muscle Depth (mm) 0 0 1.097 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497 1.097 1.397 1.697 1.997 2.297 2.597 2.897 3.197 3.497 LogTotal+25 Worm Egg Count (eggs per gram) LogTotal+25 Worm Egg Count (eggs per gram)

- 59 -

Figure 4.5.6: The effect of logtotal+25WEC (eggs per gram) on ewe eye muscle depth and antilogtotal+25 WEC.

5. Discussion

From these results, sex was significant for all production attributes analysed in the general linear regression models. However, as the ewe and ram flocks were located separately in different paddocks, managed during different periods of the year and had different larval exposure, this significance is confounded. Factors such as different larval species and different levels of larvae exposure may have contributed to this significance, although there may have been multiple variables that could have contributed (for example FOO, supplement and stocking rate).

5.1 Significance of WECs

5.1.1 Development of Immunity and Diagnostic Value of Faecal WECs

The acquisition of immunity (an ability to resist and reject establishment of worms) is vital for young sheep (up to 12 months of age). The development of the host’s immune response has been shown to involve three sequential responses, which in order of timing are, decreased establishment rate of incoming larvae and an increase in the arrested development at L3 stage, decreased egg production by established females and rejection of established worms (Dobson et al. 1990a-c). The development of immunity is also affected by the level and time of infection, plane of nutrition and importantly age of the sheep. As the individual WECs were obtained at approximately nine months of age for both flocks, they reflect the status of young sheep (up to 12 months of age). In young sheep, strongyle WEC has been proven to be a useful predictor for both strongyle worm burden (correlation r=0.74) and seasonal level of infection (correlation r=0.99) (Kingsbury 1965; McKenna 1981). This is not the case for Nematodirus WEC, as the correlation between Nematodirus WEC and Nematodirus worm counts is weak (r=0.34). Hence limited reliance is placed on Nematodirus WECs for diagnostic purposes (Kingsbury 1965; McKenna 1981).

- 60 - 5.2 Worm Egg Count Frequency Distribution and Larval Differentiation

5.2.1 Ewe Flock

The ewe flock strongyle WEC frequency distribution resembled a negative binomial distribution, which has been documented as being a more accurate representation of flock WECs than an aggregated normal distribution (Torgerson et al. 2005). The WEC distribution of the ewes had the majority of moderate (600-1800 EPG) to high (over 1800 EPG) WECs in only 28% of the entire ewe flock. Forty one ewes (15% of the flock) had WECs of zero, while the remaining majority had low WECs (0-500 EPG). This suggests that the majority of the flock had developed an immune response to resist infection and reject further GIN establishment (as indicated by low WECs). The flock WEC frequency distribution reinforces the concept that high flock WECs are influenced by a small percentage of the sheep within the flock (Barger 1985) and that Dorper sheep are similar to other breeds with respect to parasite population dynamics. By treating the 20% of sheep with high WECs within a flock, a 50% reduction in mean worm burden would be achieved (Barger 1985). The twin born ewes had an expected higher log transformed strongyle WECs than single born ewes. The ewe flock had a significantly high Nematodirus WEC although as discussed above, its significance towards loss of production was weak to non existent. The larval differentiation of the ewe WEC samples resulted in the majority of larval species present being identified as Oesophagostomum spp. (70%), with Trichostrongylus spp. making up (25%). Oesophagostomum (the nodule worm) is rarely seen in high percentages in sheep, as modern drenches have been effective in controlling this nematode. The adult worms cause damage to the walls of the large intestine (Roy et al. 2003), with the result that often developing larvae in the large intestine are encapsulated, forming nodules along the intestinal wall (Stewart and Gasbarre 1989). Adult worms cause a thickening of the large intestine mucosa, resulting in possible decreased nutrient absorption.

5.2.2 Ram Flock

The frequency distribution of strongyle worm egg counts (WEC) in the ram flock represented a normal distribution, which was skewed to the left. The majority of moderate to high WECs in the rams were attributed to only 21% of the entire flock. Most of the ram flock had low to moderate WECs, with 8 rams (3% of the flock)

- 61 - having WECs of equal to or less than 50. Their WEC distribution indicates that many of the flock are still progressing in their development of immunity, such that they will be able to resist and reject further GIN establishment. The ram WEC frequency distribution also supports this theory, that flock WECs are influenced by a small percentage (approximately 20%) of the sheep within the flock (Barger 1985). As expected, twin born rams had a higher logstrongyle WEC than single born rams. From the WECs, the larval differentiation indicated that the majority of larval species present were Trichostrongylus spp. (92%), with Teladorsagia spp. comprising (5%). Trichostrongylus spp. (the black scour worm) infections are located in the small intestine of sheep and are characterised by the loss of endogenous protein (leakage of plasma proteins and increased mucosa production) into the small intestine (Coop and Kyriazakis 1999; Houdijk et al. 2001). This leakage of nitrogen into the ileum has been reported to range between 1.5 grams (Poppi et al. 1981) to 4-5 grams (Coop and Kyriazakis 1999). This nitrogen diversion supports an increased protein metabolism, which is linked to pathophysiological responses in the intestinal tissues during a GIN infection (Poppi et al. 1981).

5.3 Association Between WEC and Liveweight

5.3.1 Significance of Inflammatory Response and Plane of Nutrition The influence of GINs on sheep productivity is generally expressed in terms of liveweight (Sykes and Greer 2003; Greer 2008). At post-weaning, a positive relationship existed between liveweight and WEC (both logstrongyle and logtotal) in the rams. Although this relationship was weak and increases in liveweight were small (ewes; 4.5kg=10% of average ewe liveweight, rams 7.5kg=15% of average ram liveweight), the relationship was still significant. It has been documented that in the Merino breed, that there has been a negative relationship between WEC and liveweight (Datta et al. 1998). In other cases, there has been reported to be a positive relationship between liveweight gain at post weaning in Romney sheep in New Zealand (Morris et al. 2000; Bisset et al. 2001). In a study by Greer (2008), the acquisition and maintenance of immunity to GINs in sheep was considered a nutritionally costly process stimulating a diversion of nutrients from productive tissues to immunological tissues. This diversion from productive tissues as a result of GIN challenge, would result in less productive tissue (muscle) growth and lighter liveweights (linked to a reduced feed intake when

- 62 - infected with a GIN) (Louvandini et al. 2006). However, the diversion of nutrients to immunological tissues also indicates that the gastrointestinal tissue mass of infected sheep may have increased, due to a stimulated inflammatory response and been a possible reason for a liveweight increase. Increases in the size of the gastrointestinal tract due to GIN infections have been documented in guinea pigs (Symons and Jones, 1983) and in pigs (Thomsen et al. 2006). This increase may be due to stimulation of the local immune response, which causes an increased mucous production and infiltration of mucosal mast cells to help with the arrest and expulsion of larvae (Miller 1987). Sheep selected for low WECs compared to unselected sheep, had heavier intestines (both large and small) relative to carcase weight, reported by Lui et al. (2005) in sheep infected with T. colubriformis and T. circumcincta. Another explanation is that the gastrointestinal contents may have an increased ability to retain water and as a result, contributed to heavier intestines (Jacobson, In Press).

5.4 Association Between WEC with Backfat Measurements and Eye Muscle Depth

5.4.1 Body Condition Score and C-site Fat Depth Although BCS was measured in 0.5 intervals (1, 1.5, etc), which contributed to a greater variation in BCSs within each Dorper flock, there was still a significant negative relationship between BCS and WEC (both logstrongyle and logtotal). With an increasing logstrongyle WEC, BCSs in twin born rams decreased (1.5BCS units=56.6% of average ram BCS) and similarly a decrease was also observed in single born rams (1BCS unit=37.7% of average ram BCS). There was a decrease in BCS only in twin born ewe lambs (0.5BCS units=18.6% of average ewe BCS) associated with an increase in logstrongyle WEC. A strong negative relationship existed between BCS and WEC in both sexes (logstrongyle and logtotal), but more so in the ram flock, as both birth types showed this negative relationship. The negative relationship between BCS and WEC indicates there was a GIN cost to the BCS for each Dorper flock. As BCS is a measure of fat and eye muscle tissue across the 13th rib (Suiter 1994), the fall of BCS in both ram birth types, indicates that their eye muscle depths, c-site fat depths or both, would have more than likely shown a decrease with increased WEC. The positive relationship between liveweights and WECs and negative relationship between BCS and WEC observed in the both

- 63 - Dorper flocks of this experiment, has also been documented in Santa Ines hair sheep in Brazil (Louvandini et al. 2006). In post weaning Dorper rams, a negative relationship existed between c-site fat depth and WEC (both logstrongyle and logtotal). Twin born ram c-site fat depths decreased (by 0.8mm=28% of average ram c-site fat depth) and so did that of the single born rams (by 0.5mm=17.5% of average ram c-site fat depth) with an increasing logstrongyle WEC. Similarly there was a negative relationship between c-site fat depth and WEC (both logstrongyle and logtotal) found in twin born ewes (c-site fat depth decreased by 0.5mm=19.6% of average ewe c-site fat depth). The decrease seen in both backfat measurements (BCS and c-site backfat) with high logstrongyle WEC may indicate the utilisation of fat stores for metabolism, due to stress induced by a GIN infection. This theory is proposed, despite the fact that each flock had a high plane of nutrition, which considered in isolation, would have lead to a reduced need for fat to be metabolised. The drop in fat scores should have contributed to overall leaner carcases (Safari et al. 2001) (particularly in the ram flock) and the fat depth decrease indicates that there may have been lighter carcase weights of these animals (although carcase characteristics were not recorded for this experiment). Given that the liveweights were actually higher in these same animals, this suggests a reduced dressing percentage. Although dressing percentages of these Dorper carcases were not recorded, it needs to be emphasised that both leanness and gut fill may also have effects on dressing percentage (Thompson et al. 1987).

5.4.3 Eye Muscle Depth In both birth types of the Dorper ram flock, eye muscle depth increased slightly (by 2mm=7% of average ram eye muscle depth) with an increasing log WEC (both logstrongyle and logtotal. This also occurred in the ewe flock (an increase of 2mm=7.5% of average ewe eye muscle depth), indicating that a weak positive relationship existed between eye muscle depth and WEC (both logstrongyle and logtotal). As body condition scores and c-site fat depths decreased in both Dorper flocks (particularly in the rams), the eye muscle depths increased slightly against expectations. Gastrointestinal infections are characterised by reduced feed intake and decreased feed efficiency (Coop and Kyriazakis 1999), affecting animal production and growth.

- 64 - Nutritional studies incorporating the effect of parasites are commonly carried out under controlled conditions with a specific level of infection in wool sheep breeds, which have a higher nutritional demand (particular sulphur amino acids) than hair sheep breeds (Louvandini et al. 2006). Studies (Coops and Holmes 1996; Haile et al. 2002) have shown protein supplementation in the diet of sheep infected by GINs, helped in developing host resistance to GIN infection. This also has been documented in trials using Santa Ines hair sheep, where improved carcase traits were observed in sheep which were supplementary fed and drenched (Veloso et al. 2004). This may have been the case with the hair breed sheep, Dorper, in this experiment, as eye muscle depths increased with a high plane of nutritional supplementation in both flocks (especially in the ram flock).

5.5 Worm Egg Count and its Significance to Dressing Percentage

As there was a significant negative relationship between WEC and both BCS and c- site fat depth, along with a weak positive relationship between WEC and liveweight, dressing percentages of these sheep may have been affected by WEC. Dressing percentage represents the weight of the dressed carcase as a proportion of the pre- slaughter liveweight, described as the proportion of the animal retained after slaughter as carcase (muscle, fat and bone) (Hui et al. 2001). It is an important measure for producers, as they are paid on the final cold carcase weight of the animal, therefore dressing percentage is the final determining factor of payment. With a weak increase in liveweight in both Dorper flocks, it could be possible that this increase was due to a greater size of the gastrointestinal tract linked because of an evoked inflammatory response in the sheep. If an increased gastrointestinal size in relation to liveweight is proven and such becomes a consistent finding in GIN challenged sheep, then dressing percentages can be influenced by liveweight gut fill by inflammation (size increase) of the intestines, leading to liveweights which do not accurately reflect the true sizes of the sheep carcase. Therefore measurements of liveweight change as an indicator of the influence of gastrointestinal parasitism on sheep productivity, may not completely illustrate the effects of GIN on dressing percentage and carcase weight. Furthermore dressing percentages are also affected by leanness of the carcase, associated with the negative relationship between WEC and both BCS and c-site fat depth. As c-site

- 65 - fat is a measure that is associated with overall sheep fatness, decreases in this fat depth also contribute to a reduced dressing percentage, as there is both less fat and weight on the finished carcase.

5.5 Worm Egg Count and its Significance to Australian Sheep Breeding Values

Australian Sheep Breeding Values allow for selection of specific traits, leading to an improved performance in characteristics such as wool, liveweight and worm egg count. These are known and documented for each sire. Currently ASBVs allow for the selection of liveweight without taking into account WEC. This provides a challenge to those wishing to accurately assess sire breeding using the best values for liveweight and WEC, as there is a strong possibility that selecting for increased liveweight will also lead to selection for animals with higher WECs. This theory is supported by the positive relationship found between liveweight and WEC found in this experiment. Therefore to accurately document ASBVs for the liveweight of individual sires, WEC needs to be included along with liveweight, to reflect any interaction that may exist between liveweight and WEC. This would allow breeders to more accurately select sires which possessed beneficial ASBVs, of both increased liveweight and decreased WEC. Further research is required to determine the accuracy and profitability in selecting sires for liveweight gain and the corresponding interaction that exists with worm burden levels.

6. Conclusion

In conclusion, it was found that relationships existed between WEC and production for ewe and ram Dorper flocks, grazing annual pasture and challenged by a level of gastrointestinal parasites. Some of these relationships were not expected. A negative relationship was found between WEC and both production attributes BCS and c-site fat depth as anticipated. However an unexpected positive relationship existed between WEC and the production attributes, liveweight and eye muscle depth. Both ewe and ram Dorper flocks exhibited these characteristics, although the strength of these relationships was stronger in the ram flock (especially in twin born rams). Log transformed strongyle WECs were at their highest levels in twin born sheep for both rams and ewes as was expected, indicating that selecting sheep for increased

- 66 - numbers of offspring (twins and triplets), may possibly lead to an increased WEC challenge for an evolving flock.

Observed liveweight increases with increasing WEC suggest that sheep with a higher worm burden, may have heavier small and large intestines, when compared to those sheep with a low worm burden. By using liveweight to assess GIN impact on productivity, production losses which are linked to levels of parasitism infection may be underestimated. Instead of using liveweight or liveweight gain in assessing the effect of a worm challenge, measurements of the carcase yield may be a more reliable measure in revealing the real economic impact of gastrointestinal worms on sheep meat production systems.

7. Appendix

7.1 Sire Evaluation of Dorper Flocks

7.1.1 Sires of the Ewe Flock Sire Number N Mean WEC Std. Error of Mean WEC Minimum WEC Maximum WEC 1 19 362.11 92.349 0 1320 2 76 803 58.197 0 3320 3 17 61.18 58.723 0 1000 4 7 457.14 51.534 280 640 5 5 384 90.863 160 600 6 5 184 41.183 80 280 7 7 434.29 90.049 0 760 8 20 388 172.782 0 3560 9 14 397.14 58.323 80 880 10 21 390.48 85.742 40 1480 11 14 94.29 41.638 0 440 12 5 440 115.931 120 840 13 39 339.49 43.957 0 1240 14 5 656 186.161 80 1120 15 10 272 117.878 0 1120 Total 264 463.29 29.333 0 3560

7.1.2 Sires of the Ram Flock Sire Number N Mean WEC Std. Error of Mean WEC Minimum WEC Maximum WEC 1 25 126 32.802 0 400 2 76 208.55 10.938 0 400

- 67 - 3 13 446.15 3.846 400 450 4 10 225 31.842 50 400 7 6 533.33 10.541 500 550 8 19 586.84 6.446 550 650 9 20 802.5 9.917 750 850 10 19 1302.63 71.377 950 1850 16 10 310 29.627 100 400 17 10 700 10.541 650 750 Total 208 443.75 25.672 0 1850

7.1.2 Sires of Combined Flocks Sire Number N Mean WEC Std. Error of Mean WEC Minimum WEC Maximum WEC 1 44 227.95 46.914 0 1320 2 152 505.78 38.156 0 3320 3 30 228 48.329 0 1000 4 17 320.59 39.514 50 640 5 5 384 90.863 160 600 6 5 184 41.183 80 280 7 13 480 49.068 0 760 8 39 484.87 89.018 0 3560 9 34 635.59 42.322 80 880 10 40 823.75 91.741 40 1850 11 14 94.29 41.638 0 440 12 5 440 115.931 120 840 13 39 339.49 43.957 0 1240 14 5 656 186.161 80 1120 15 10 272 117.878 0 1120 16 10 310 29.627 100 400 17 10 700 10.541 650 750 Total 472 454.68 19.914 0 3560

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Dedication

I would like to dedicate my honours thesis work to my loving grandparents Patrick and Dorothy Sweeny. It was my goal to have them read the finished product, although sadly they never saw it.

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