The Effect of Time of Shearing on Wool Production and Management of a Spring-Lambing Merino Flock
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The Effect of Time of Shearing on Wool Production and Management of a Spring-lambing Merino Flock Angus John Dugald Campbell, BVSc(Hons) BAnimSc Submitted in total fulfilment of the requirements of the degree of Doctor of Philosophy November 2006 University of Melbourne School of Veterinary Science © Angus Campbell, 2006 ABSTRACT Choice of shearing time is one of the major management decisions for a wool-producing Merino flock and affects many aspects of wool production and sheep health. Previous studies have investigated the effect of shearing on only a few of these factors at a time, so that there is little objective information at the flock level for making rational decisions on shearing time. This is particularly the case for flocks that lamb in spring, the preferred time in south-eastern Australia. A trial was conducted in a self-replacing, fine wool Merino flock in western Victoria, from January 1999 to May 2004, comparing ewes shorn annually in December, March or May. Within each of these shearing times, progeny were shorn in one of two different patterns, aligning them with their adult shearing group by 15–27 months of age. Time of shearing did not consistently improve the staple strength of wool. December-shorn ewes produced significantly lighter and finer fleeces (average 19.1 µm, 3.0 kg clean weight), whereas fleeces from March-shorn ewes were heavier and coarser (19.4 µm, 3.1 kg). Fleeces from ewes shorn in May were of similar weight to fleeces from March-shorn ewes (3.1 kg), but they were of significantly broader diameter (19.7 µm). In young sheep, beneficial changes in some wool characteristics for each shearing group were offset by undesirable changes in others. Shearing ewes in March or May, and weaners in March, May or June, significantly increased the risk of post-shearing mortality about three- and four-fold, respectively, compared to unshorn sheep. Substantial, highly significant associations in young sheep between post-weaning mortality, bodyweight and growth rate were also quantified using various survival analysis techniques. For example, the lightest 20% of weaners at weaning contributed 31% of all deaths in the year following weaning, and increasing average growth rate over summer and autumn from 250 to 500 g/month reduced the risk of death by 74%. These results could be used to develop supplementary feeding systems that efficiently reduce weaner mortality, which is a significant animal welfare issue in many Australian Merino flocks. Mortality effects were incorporated into estimates of the total value of wool produced by the different shearing times between birth and culling at 6¼ years of age. Using median historical (1991–2006) wool prices, shearing ewes in March and their progeny first in June, or October (weaner)-December (ewe) shearing produced the greatest total value of wool ($111/head). March (weaners)-March (ewes) shearing had a wool value of $107/head and December (weaners)-December (adults) shearing $103/head. May-shorn ewes produced the smallest value of wool, irrespective of whether their progeny were first shorn in May or July ($93–96/head). i No shearing time consistently improved all animal health measures. May-shorn ewes had significantly more fleece rot in late autumn than the other shearing groups (odds ratio 2.5) and were up to 0.4 condition score lighter during winter, although they had a lower cost of dag (average $0.64/head) and significantly less breech strike risk in spring, compared to December-shorn ewes (odds ratio 0.18). December-shorn ewes had the greatest cost of dag ($1.50/head). March-shorn ewes had an intermediate cost of dag ($1.03/head) but significantly less breech strike than May-shorn ewes (odds ratio 0.38). Overall, December and March shearing were shown to be appropriate alternatives for a self-replacing Merino flock in south-eastern Australia, whereas May was an undesirable shearing time. ii DECLARATION This is to certify that: (i) the thesis comprises only my original work (ii) due acknowledgement has been made in the text to all other material used, (iii) the thesis is less than 100,000 words in length, exclusive of tables, maps, bibliographies and appendices Angus JD Campbell iii All we like sheep have gone astray; we have turned every one to his own way; and the Lord hath laid on him the iniquity of us all.—Isaiah 53:6 v ACKNOWLEDGEMENTS I wish to thank the Vizard Foundation and Mr Maurice and Mrs Jill Glover, who generously made their farms, facilities and sheep available for this trial, and the staff of ‘South Roxby’, particularly Mr Peter Lindeman, for the day-to-day management of the sheep. This work received financial support from the Vizard Foundation and the Australian Sheep Industry Cooperative Research Centre (CRC). The CRC also kindly supported me with a top-up scholarship. I am very grateful to my supervisors, Dr John Larsen and Associate Professor Andrew Vizard, for their guidance and assistance throughout the study. Associate Professor Vizard devised and designed the trial and it was overseen by Dr Larsen, along with other members of the Mackinnon Project at the University of Melbourne, from December 1998 to January 2002, when I took over. Mr Garry Anderson happily and ably provided me with guidance for the statistical analyses that I performed, for which I am very thankful. The amassing of such a large amount of data is due in no small part to the dedicated and meticulous work of Ms Dianne Rees. I will be eternally grateful for her technical assistance and cheerful smile, which made 5am starts on shearing days bearable. I would also like to thank the following people, who generously provided me with information or assistance during my work: Mr Rod Agar (Australian Wool Testing Authority Ltd) for helping with processing of the dyebanded wool samples; Dr Renick Peres (Department of Primary Industries, Geelong) for providing the weather data; and Dr Roger Thompson (Pasture and Veterinary Institute, Hamilton) for kindly providing me with the results of his lamb shearing experiments. This work is dedicated to my partner, Sarah, for her abiding love and support, and to my son, Callum, for making anything I do worthwhile. vii TABLE OF CONTENTS Abstract ...................................................................................................................................................ii Declaration..............................................................................................................................................ii Acknowledgements.................................................................................................................................ii Table of Contents....................................................................................................................................ii List of Tables........................................................................................................................................ii List of Figures.......................................................................................................................................ii C h a p t e r 1 General Introduction ....................................................................................................2 1.1 Background...............................................................................................................................2 1.2 Determinants of Wool Enterprise Profitability & Their Relationship to Shearing Time..........2 1.2.1 Stocking Rate....................................................................................................................2 1.2.2 Wool Production per Sheep ..............................................................................................2 1.2.3 Average Price per Kilogram of Wool ...............................................................................2 1.2.4 Enterprise Costs................................................................................................................2 C h a p t e r 2 Literature Review .........................................................................................................2 2.1 The Effect of Shearing Time on Wool Quality.........................................................................2 2.1.1 Staple Strength & Position of Break.................................................................................2 2.1.1.1 Components of Staple Strength & Position of Break...................................................2 2.1.1.1.1 Fibre Diameter Properties...................................................................................2 2.1.1.1.2 Intrinsic Fibre Strength.......................................................................................2 2.1.1.1.3 Fibre Shedding ...................................................................................................2 2.1.1.2 Associations between Staple Strength, Position of Break & Shearing Time ...............2 2.1.1.3 Shearing Time & Recurring Factors Affecting Staple Strength...................................2 2.1.2 Fleece Weight, Yield & Fibre Diameter ...........................................................................2 2.1.3 Staple Length....................................................................................................................2 2.1.4 Vegetable Matter Contamination......................................................................................2 2.1.5 Time of Shearing & Wool Quality—Summary ................................................................2