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). / 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.
| Identifer | oai:union.ndltd.org:ADTP/245679 |
| Date | January 2006 |
| Creators | Campbell, Angus |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
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