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Associations between worm egg count and production in Dorper sheep

Sweeny, Joshua (2008) Associations between worm egg count and production in Dorper sheep. Honours thesis, Murdoch University.

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With changes to the Australian sheep industry, breeds that have a meat emphasis are becoming increasingly adopted by farmers. One such breed is the Dorper sheep, which was used in this study to investigate the relationship between worm egg count and production attributes. Gastrointestinal worm burden was measured by worm egg counts (WECs) and production attributes that were examined included liveweight, body condition score (BCS), c-site fat depth and eye muscle depth. Two flocks of Dorper lambs (two-hundred and eighty nine Dorper ewe lambs, and two-hundred and thirty four entire Dorper ram lambs), were weaned onto two separate paddocks for grazing and natural worm challenge on a Kojonup property. At post weaning (approximately 10 months of age), each flock had their production attributes measured, along with individual WECs. Each flock was drenched at weaning and not drenched again until after individual WECs were measured. The measured flock WEC frequency distribution reinforced the concept that high flock WECs are influenced by a small percentage of the sheep within the flock and that Dorper sheep are similar to other breeds with respect to parasite population dynamics.

The relationships found between WEC and production attributes of both liveweight and eye muscle depth were positive, contradicting the hypothesis of that a negative relationship exists between WEC and production in the Dorper. Although this relationship between WEC and liveweight was weak and unexpected, the relationship was still significant (P<0.05). With an increasing WEC, BCS fell by 56.6% and 37.7% of average ram BCSs in twin and single born rams respectively (P<0.05), while an 18.6% decrease of average ewe BCS was observed in twin born ewes (P<0.05). The drop in body condition score and c-site fat depth may have contributed to overall leaner and lighter carcases (particularly in the ram flock). Given that the liveweights were actually higher in these same animals, this suggests a reduced dressing percentage due to increased non-carcase components, possibly gastrointestinal tissue mass.

With increasing WEC the association of liveweight increase and BCS decline indicated that sheep with a higher worm burden may have heavier intestines, when compared to sheep with a low worm challenge. By using liveweight change to assess GIN impact on productivity, production losses linked to gastrointestinal parasite infection may be underestimated. Instead of using liveweight change in assessing the effect of a worm challenge, measurements of the carcass yield may be a more reliable measure in revealing the real economic impact of gastrointestinal worms on sheep meat production systems.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Veterinary and Biomedical Sciences
Supervisor(s): Bell, K.
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