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Studies of factors affecting sheep deaths during lot-feeding and sea transport

Norris, Richard Thomas (1991) Studies of factors affecting sheep deaths during lot-feeding and sea transport. PhD thesis, Murdoch University.

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The export of live sheep from Australia is an important industry. However, deaths during sea transport are not only costly but also raise concerns about animal welfare. This thesis records studies conducted as a part of a large multi-disciplinary investigation in Western Australia to reduce mortality and improve the welfare of export sheep.

Records of deaths aboard ships were analysed to determine death rates and predisposing factors. The annual death rate was approximately 2%, with almost 80% of deaths occurring before arrival at the first port. Several factors were associated with mortality. Sheep exported in the second half of the year had twice the risk of death compared with those exported in the first half. Death rates were higher in adult wethers than in younger wethers. Death rates were lower on a relatively small ship on voyages of up to 14 days than on larger ships on longer voyages. Sheep exported to Singapore had lower death rates than those bound for the Middle East, in the first eight days at sea.

Farm groups of adult wethers were selected for study on arrival at commercial feedlots. The sheep were examined during lot-feeding and accompanied to the Middle East. There were few deaths during lot-feeding and few sheep rejected before embarkation; most deaths occurred during sea transport. Death rates varied widely between farm groups of sheep, with half of all deaths aboard ship in only 13% of 189 farm groups.

Information on the history of the sheep before arrival at the feedlot was tested for association with total death rates and cause-specific death rates on seven voyages. However, there was no consistent association between any of the factors and mortality. It was established that wethers classified as "fat" on arrival at the feedlot had twice the risk of death from inanition aboard ship. Collectively, it was considered that sheep with the highest risk of death aboard ship were adult wethers in "fat" condition that were exported in the second half of the year.

Bars covered with dye and attached to feed troughs were used to identify sheep that ate pelleted feed. Sheep which did not eat pelleted feed (non-feeders) during lot-feeding had a high risk of death from inanition and from salmonellosis aboard ship.

Consequently, management strategies and therapeutic treatments for feedlot non-feeders were evaluated in experiments. Some sheep persistently failed to eat despite provision of extra feed troughs or ad libitum feeding. Separating feedlot non-feeders from feeders had no effect on death rates aboard ship. However, prophylactic and therapeutic treatments given at the start and finish of lot-feeding reduced the number of feedlot non-feeders by 21% and shipboard deaths by 43% in a voyage to the Middle East. The treatments included an anthelmintic, magnesium sulphate, and vitamins B1, B12 and E.

It was concluded that there remains further scope to reduce mortality of sheep during lot-feeding and sea transport, and that this can be achieved by better adoption of preventive measures.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary Studies
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Richards, R.B. and Swan, Ralph
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