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Optimising Genetic Potential for Wool Production and Quality Through AFBM Journal volume 2 – number 1 © Copyright AFBMNetwork Optimising genetic potential for wool production and quality through maternal nutrition Sue Hatcher and PR Johnson NSW Department of Primary Industries, Orange Agricultural Institute Forest Rd, Orange NSW 2800 Australia [email protected] Contents Introduction Genetic potential – can we maximise it? The follicle group – initiation and maturation • Primary follicles • Secondary follicles • S/P ratio Maternal effects and the follicle population • Breed differences • Timing of the nutritional stress Follicles and the fleece characteristics Matching the breed cycle to feed availability on the farm Implications for commercial wool producers Lifetime Wool – optimising wool production and quality Conclusion References Appendix Abstract. This paper reviews the development of the wool follicle population with a view to the management of breeding ewes so as to optimise the genetic potential of the progeny for wool production and quality throughout their lifetime. It highlights the importance of the pre-weaning environment (i.e. maternal nutrition through pregnancy and lactation) on the initiation and maturation of the secondary follicle population and identifies the last third of pregnancy as the most critical period. The implications of this for the commercial wool producer are discussed in terms of matching the breeding cycle of the ewes to available pasture and provision of supplementary feed. Finally, it introduces a national project 'Lifetime Wool' funded by Australian Wool Innovation which aims to develop profitable ewe management guidelines for wool growers across Australia to adopt in order to optimise the genetic potential of their flock for wool production and quality. Keywords: genetic potential, follicle development, breeding ewe, nutrition, lifetime wool Introduction more intensive management of the breeding With the development and increasing use of flock in order to optimise the wool production electronic identification systems for sheep of the breeding ewe herself as well as that of and the continuing progress in the her progeny. accompanying hardware and software Genetics play a key role in determining the systems to support electronic data capture potential lifetime wool production and wool and use on-farm, the opportunity exists for quality of an individual sheep. However the the sheep industry to move more towards environment also plays a significant role. precision wool growing. Using individual Environmental factors can be divided into animal identification and on-farm fibre pre-weaning and post-weaning influences. measurement to assist with clip preparation The nutritional intake of the ewe during and selecting replacement ewes for the pregnancy and lactation is the governing breeding flock has been shown to be an factor of the pre-weaning environment. The effective means of increasing profit in many ewes’ nutrient intake must be sufficient to wool enterprises (Atkins et al. 2004). The satisfy her own bodily needs for maintenance authors further concluded that the real and wool growth as well as supply adequate benefit of individual animal measurement will nutrients to her foetus for growth and come from additional uses of the information development until weaning. such as implementation of specific grazing Post-weaning influences largely reflect the groups, allocating ewes to particular sires and impact of changing seasonal conditions and strategic use of sheep coats. They believed hence feed availability on the functioning of that options such as these would lead to the existing follicle population. In times of additional economic benefits from an abundance such as the spring flush of individual animal identification and pasture growth a greater amount of nutrients measurement system (Atkins et al. 2004). are available to the follicles in the skin One possible additional use of individual resulting in an increase in both wool growth animal identification which could play a key and average fibre diameter. However as the role in improving the profitability of a Merino nutrients available to the foetus pre-weaning, breeding enterprise in particular is through during pregnancy and lactation, can have a http;\\www.afbmnetwork.orange.usyd.edu.au\afbmjournal\ page 51 AFBM Journal volume 2 – number 1 © Copyright AFBMNetwork significant impact on the development the wool by reducing the number of follicles follicle population there is an opportunity developed. Lambs whose mothers are being through improved management of the poorly fed, progeny of young ewes and twin breeding ewe flock, to maximise the wool lambs develop fewer follicles and this reduces production and wool quality potential of their adult wool-producing capacity (Marston future generations of Merino sheep. 1955). This paper will review the impact of ewe The pre-weaning environment is therefore nutrition during pregnancy and lactation on the critical period for realising the genetic the developing foetus focussing on potential of an individual sheep. However as maximising the genetic potential of her the development of the follicle population progeny for lifetime wool production and wool occurs at clearly defined stages during the quality. We will place this information in pre-weaning period, ‘critical’ time frames can context with the current commercial practices be identified during which adequate maternal of managing the breeding ewe flock and nutrition is vital to ensure maximum introduce a national project, Lifetime Wool, development of follicle population and which seeks to maximise the lifetime wool optimisation of genetic potential. production and quality of progeny by The follicle group - initiation and improved management of the breeding ewe. maturation Genetic potential – can we maximise it? The type and arrangement of follicles in the Individual animals inherit their complement skin of all sheep regardless of breed, is of genes from their parents, 50% from each. similar. The follicle population typically Selection of parents, both rams and ewes consists of a basic group of three primary that have been identified as superior for the follicles arranged in rows and a variable traits of interest is the starting point to number of secondary follicles lying on one determine the genetic potential of the next side of the trio of primaries (Carter 1943; generation. The process of meiosis during the Carter 1955; Ryder and Stephenson 1968) formation of gametes in both the sire and (Figure 1, see Appendix). All primary follicles dam and the fusion of these gametes at are associated with a sweat (sudoriferous) conception provides the genetic blueprint for gland, an arrector pili muscle and a the animal’s potential productivity in its sebaceous gland while secondary follicles lifetime. possess a sebaceous gland only (Carter In practice the heritability (h2) or the degree 1955; Ryder and Stephenson 1968). to which variation in a particular trait is under There are two stages to follicle development; genetic control, of most wool production and firstly the follicles are initiated in the skin. quality traits is moderate to high (Safari and This is followed by the second phase, Fogarty 2003). None reach the theoretical maturation, which indicates that the follicles maximum of 1 which would occur if the have formed a fibre and are now ‘mature’. No genetic potential of an animal was realised. gross deviations in the timing of the This confirms that the environment does development of either the primary or provide a strong mediating influence. And as secondary follicle populations have been a result explains why the phenotype of an identified between breeds with almost all animal (i.e. how the genes are expressed) is secondary follicles being initiated prenatally not necessarily the same as the genotype of (Fraser and Short 1960). However, an animal. considerable variation has been found to The maximum number of follicles that a lamb exist both between and within breeds in the will form is determined genetically (Ryder rate of follicle maturation. Within the Merino and Stephenson 1968). Estimates of breed the follicle population of the Peppin heritability for skin traits are low to Merino has been deemed mature at about 6 moderate., Total follicle density h2 ranges months while South Australian Merino strains between 0.18 to 0.46 (Hill et al. 1997); can take up to 15 months for their follicle Mortimer 1987; Purvis and Swan 1997),and populations to mature and form fibres secondary to primary (S/P) follicle ratio (Schinckel 1955a). between 0.21 and 0.52 (Mortimer 1987; Primary follicles Purvis and Swan 1997), depending on the Isolated primary follicles begin forming in strain of Merino studied. most skin regions of the foetus between day Marston (1955) recognised nearly 50 years 50 and day 70 of pregnancy, these are ago that it was rare for pastured sheep to followed by the rapid appearance of their reach their genetic potential for wool associated lateral primary follicles between production. He concluded that it was possible day 75 to 85 (Carter 1943; Carter 1955; for poor nutrition during pregnancy and Fraser and Short 1960; Hutchison and Mellor lactation to impose a permanent limitation on 1983) (Figure 2, see Appendix). In Merino the subsequent capacity of sheep to produce sheep, all primary follicles produce a page 52 http;\\www.afbmnetwork.orange.usyd.edu.au\afbmjournal\ AFBM Journal volume 2 – number 1 © Copyright AFBMNetwork keratinized fibre by 108-110 days of see Appendix). A feature
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