Effect of anthelmintic treatment on the milk yield of dairy cows in England, Scotland and Wales.

One hundred and twenty dairy herds collaborated in a trial to determine the effect on milk yield of anthelmintic treatment given at calving. Cows and heifers were divided into five groups. Three were each given a different anthelmintic: thiabendazole, fenbendazole or levamisole. One group was given a placebo and the fifth was untreated. Analysis of data from 9000 lactations showed a treatment effect just significant at the 5 per cent level, of 42 kg milk, 1.8 kg fat and 1.4 kg protein. There was no evidence that the three anthelmintics differed in their effect on yield. The effect of treatment was not greater in heifers than in cows, nor was there a difference between spring and autumn calvers. There was no indication that the effect of treatment was markedly greater in some herds than others and it was not related to periparturient faecal egg count.