Veterinary Science - Theses
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ItemMortalities in sheep transported by sea( 1995)Major animal welfare concerns existed about mortalities which occurred among the two million sheep transported by sea from Victoria, Australia to the Middle East each year during the 1980s. Research was undertaken to better define the extent of the mortalities, to establish the causes of death, and to prioritise and methodically unravel the underlying causes and risk factors involved. An analysis of five years of existing industry data on 100 sheep shipments from Victoria (1984/85-1988/89) showed that mortality rates ranged mostly between 1% and 4%, with an average of around 2 ½%. These analyses also showed that sporadic episodes of sudden, high mortality occurred in association with hot and humid conditions in Middle Eastern waters. Heat stress was the presumptive diagnosis. While the occurrences were rare, they accounted for 9% of all deaths. Observational studies undertaken on 8 research voyages with sheep to the Middle East showed that two other causes of death – an inanition syndrome and salmonellosis – accounted for the majority of all mortalities. Together, these two conditions caused around three quarters of all deaths. The following risk factors associated with these two major diseases were identified: poor feeding behaviour in the assembly feedlot; physiologic stress at the point of arrival of sheep at the feedlot; and the physical location of sheep on board ships, whereby sheep in the upper tier of pens on every deck of a ship suffered substantially higher mortality rates than those in the lower tier. Specific studies on the inanition syndrome showed that affected sheep were persistent poor consumers of the pelleted shipboard ration. A problem of severe weight loss was detected in an additional 5% of sheep, which appeared to be associated with inanition. Sheep with the syndrome still had an appetite for familiar food such as hay. An hypothesis was developed that the syndrome may be caused by the failure of affected sheep to recognise or accept the pelleted ration as food. The epidemiology of salmonellosis outbreaks in the live sheep trade was elucidated. The outbreaks occurred as rise and fall epidemics starting with a large increase in faecal salmonella excretion from sheep immediately after their arrival in the assembly feedlot near the port of embarkation. Epidemics of mortalities from salmonellosis peaked one to two weeks later, then declined before the voyage was completed. Evidence was obtained that salmonella infections persisted in the feedlot environment between consecutive batches of sheep initiating new epidemics in subsequent consignments. The differences in shipboard mortality rates between upper and lower tier pens (the “tier’ effect) was investigated with observational studies and a major field trial. An hypothesis that the effect was caused by higher light intensity in upper tier pens was tested and rejected. A remaining hypothesis is that the sheep’s fear of elevation in upper tier pens may be the cause. Overall, the research has advanced knowledge substantially on animal health in the live sheep trade. The findings will influence the debate on animal welfare in the trade, they will be of practical use to the industry, and they have focussed research direction for the future.
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ItemThe effect of time of shearing on wool production and management of a spring-lambing merino flock( 2006)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.