Resistance/tolerance to facial eczema (FE) is a heritable trait in New Zealand dairy cattle, as measured by genetic variation in liver enzyme levels. AgResearch has been collecting data from herds clinically affected by FE, by blood-sampling all cows in these herds, as a low cost method of phenotyping large numbers of animals. Over the past seven autumns, 66 herds and 14,799 cows were sampled. Breeding values for FE resistance were calculated for 238 sires. One complicating factor was the level of FE-protection provided by zinc sulphate administered through the farm water supply. Variable levels of serum zinc in cows were found, due to factors including water intakes and weather conditions. In zinc-treated herds there were three classes of cows: those still affected by FE, and others seemingly FE-tolerant either through genetics or having enough circulating zinc to provide protection. The zinc status of each herd was recorded at the time of blood sampling after a clinical outbreak. Data were analysed within zinc-treated and not zinc-treated herds to provide genetic parameters for each. Heritabilities in herds according to zinc status were very similar, regardless of zinc status.
Proceedings of the New Zealand Society of Animal Production, Volume 71, Invercargill, 117-121, 2011
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