Comparison of two long acting pre-lambing anthelmintic treatments on the productivity of ewes in low body condition.

AIM: To determine if there was a benefit from treating ewes with a low body condition score (BCS) with long acting anthelmintic products pre-lambing and to compare the effects of two commonly used treatment options. METHODS: The study was conducted on a single commercial hill country sheep and beef property in the central North Island of New Zealand. Mixed age twin-bearing ewes were preselected by the farmer as being in poor condition 4 weeks before the planned start of lambing, and were sequentially drafted into three equal groups identified with coloured ear tags. The negative control group (n=199) received no anthelmintic treatment; the other two groups received either a controlled release capsule (CRC) containing abamectin, albendazole, Se and Co (n=200) or a long-acting injection of moxidectin (n=200). All ewes were body condition scored (1-5 scale) and weighed at pre-lambing, docking (65 days after treatment) and at weaning (127 days after treatment). Faecal nematode egg counts (FEC) were carried out on 10 ewes from each group at these three times. Most lambs were matched to the ewe treatment groups at weaning, and weighed. RESULTS: At weaning the mean body weight of ewes treated with moxidectin was 3.2 (95% CI=2.3-4.3) kg heavier than controls, and of ewes treated with CRC was 3.6 (95% CI=2.5-4.5) kg heavier than control ewes (p<0.001). At the start of the trial only 61/599 (10.2%) ewes had a BCS≥3. At weaning, more ewes treated with CRC (140/194; 72%) or moxidectin (122/187; 65%) had a BCS≥3 than control ewes (55/179 (31%); p<0.001). In lambs that were matched with ewes from the treatment groups, the mean weight at weaning of lambs from ewes treated with moxidectin was 2.6 (95% CI=1.9-3.3) kg heavier, and from ewes treated with CRC was 2.6 (95% CI=1.9-3.4) kg heavier than lambs from control ewes (p<0.001). CONCLUSIONS AND CLINICAL RELEVANCE: Treating twin-bearing ewes with low BCS pre-lambing with long acting anthelmintic treatments (moxidectin long acting injection or CRC) resulted in an increase in mean body weight of the ewes and lambs at weaning. There were no significant differences between the two pre-lambing treatments used. These results were based on a single property and thus cannot be generalised to all properties where management conditions and parasite populations may differ.