Post-weaning growth of beef heifers drenched with long- or short-acting anthelmintics.

Abstract

OBJECTIVE: To determine whether (i) the drenching practices of beef producers in the Central Tablelands of NSW utilising short-acting anthelmintics limit the post-weaning growth of heifers and (ii) a single weaning treatment of a long-acting anthelmintic improves post-weaning growth. METHODS: Commencing at weaning, 20/100 heifers in each of five herds were injected four times at 90-day intervals with long-acting moxidectin to suppress gastrointestinal nematodes. In year 1 the balance was drenched using the owner's usual commercial practice with short-acting anthelmintics (5 herds) or left undrenched (1 herd). In year 2 the balance was drenched with long-acting moxidectin within 3 months of weaning (4 herds) or with short-acting drenches only (2 herds). At each visit live weight (LW) was recorded and a subsample tested for worm egg count (WEC) and plasma pepsinogen. RESULTS: In year 1 by 3 and 6 months' post weaning, suppressed heifers were significantly heavier than the undrenched and short-acting groups, and by 12 months were 40 and 28 kg heavier, respectively. In year 2, the LW of the suppressed and long-acting heifers was not different, but by 3 and 6 months both groups were significantly heavier than the short-acting group and by 12 months were 22 kg heavier. CONCLUSION: The post-weaning growth of beef heifers treated with short-acting drenches as adopted by Tablelands beef producers was slower than heifers drenched suppressively or with a single long-acting drench at weaning.