Does breeding for improved parasite immunity alter liveweight gain in weaner deer?

Context Internal parasites are an ongoing challenge for deer farmers in New Zealand, with limited effective options to treat parasite burdens. The salivary antibody response to carbohydrate larval antigen (CarLA) has been shown to be heritable in rising yearling deer in New Zealand and is negatively correlated with faecal egg count in sheep. Aims This study investigated the post-weaning liveweight change in progeny sired by red and wapiti stags that had either high or low CarLA estimated breeding values (eBVs). Methods A cohort of 134 weaner deer, specifically bred using four sires representing high and low CarLA breeding values from two breeds, were weighed monthly from weaning (3 months of age) through to slaughter (11 months of age). Within the trial, half of the animals were given a suppressive anthelmintic treatment every 2 weeks, whereas the other animals were treated only when the average liveweight change of the group was less than half of the suppressive group. This occurred only at 6 and 12 weeks post-weaning. Key results There were no effects of sire CarLA eBV on liveweight gain of the progeny. Progeny from high CarLA eBV sires had higher absolute CarLA values at 6, 9, 10, and 11 months of age. There were no CarLA differences in the progeny during the winter period when animals were grazed on a brassica crop. Conclusions The use of suppressive anthelmintic treatment increased 6 month of age liveweight and liveweight gain compared with trigger treatment, indicating that parasite burden may have affected growth during the autumn period. Implications Users of CarLA in the deer industry should have no concerns about negative impacts on production using this test to improve protective immunity to internal parasites.