Two experiments were conducted to understand the interactions between calf weaning date, level of nutrition and parasite challenge. In the first experiment, spring-born calves were weaned at 6 or 9 months of age (early or late weaning) and subject to natural parasite challenge, or natural plus an additional dose of 7500 infective larvae/day. Late weaned calves (with cows) also had either high or low pasture allowance treatments imposed. When calves were 9 months of age, calf liveweights (kg) were 253, 302 and 277 (SED 3.9) for the early wean/high nutrition, late wean/high nutrition and late wean/low nutrition treatments respectively and high and low nutrition cow liveweights were 494 and 479 kg (SED 4.8) respectively. At 9 months of age, early weaned calves showed higher faecal egg counts (P<0.05). Dosing with additional parasitic larvae had no effect on early weaned calves, but lowered late weaned calf weights. In the second experiment, calves were weaned at 6 months of age or left un-weaned until the age of 9 months when all calves were slaughtered. Un-weaned calves showed lower gastro-intestinal worm counts than early weaned calves. In both experiments, late weaned calves showed substantial liveweight advantage and lower parasite burdens. Reducing the nutrition of late weaned calves and cows reduced the size of this liveweight benefit. Later weaning is a management option for farmers seeking to reduce reliance on anthelmintic drenches without the associated production loss.

CJ, Boom, GW Sheath, and A Vlassoff

Proceedings of the New Zealand Society of Animal Production, Volume 64, Hamilton, 257-261, 2004
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