A survey of internal parasites and parasite control on North Island deer farms

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Abstract
Aim. To evaluate internal parasite control practices and their effectiveness, and to investigate relationships between indices of parasitism and production outcomes by analysis of data collected during a deer herd health and production profiling project. Methods. A longitudinal study of 15 red deer farms in the North Island of New Zealand was carried out from March 1992 to April 1994. Anthelmintic usage was recorded. Sentinel weaner, yearling and adult hinds and stags were blood and faecal sampled in early autumn, winter, spring and summer for serum pepsinogen and faecal egg and larval counts. A descriptive analysis of control programmes and egg and larval counts was produced. In addition, further measurements of parasitism and parasite control, including faecal egg count and faecal larval count data, individual pepsinogen concentrations, timing and numbers of anthelmintic treatments, and a farm calf faecal lungworm larvae count index were firstly subjected to univariate statistical association with production outcomes, followed by stepwise multivariable logistic regression analysis. Timing and numbers of anthelmintic treatments, along with other farm, herd or animal management risk factors, were included into path models. Results. A wide range of anthelmintic programmes in all age groups, within farms between years and between farms was recorded. Weaner deer received three to nine treatments in their first year. Many farmers treated older deer in only one of the years of study. Older stags were treated more often than younger stags. Oxfendazole, ivermectin and moxidectin were the most commonly used anthelmintics. Egg and larval counts varied between properties and between years in some seasons but a higher proportion of deer shed larvae than eggs. In winter the number of weaners shedding eggs was the same as in autumn, but fewer shed lungworm larvae. Counts were lower at 12 months of age. Counts in older stags and hinds were highest in early spring, and counts were higher in yearling stags than in adult stags. Geometric mean pepsinogen concentration was lowest in weaners and rose to adult levels by early spring. Statistical analyses showed a lower weaning weight associated with higher faecal larval count index, and a reduced number of anthelmintic treatments prior to weaning. Weaners grew faster in spring after late winter anthelmintic treatment than those without treatment or with later treatments. There were inverse relationships between both farm mean weaner and adult serum pepsinogen and summer growth of weaners, and weaning percentage of adult hinds, respectively. Conclusion. This study has highlighted current parasite control practices, relationships between indices of parasitism and production outcomes, and has identified areas for further research into parasitism in farmed deer.