Effects of naturally acquired mixed helminth parasitism in yearling dairy calves

The effects of Strongyle parasitism were studied in yearling calves. One group (4 calves) was a noninfected control, and 2 groups (4 calves each) were infected by exposure on pasture to the same type and degree of parasitism. One of the 2 infected groups were given coumafos at 4-week intervals and the other was not treated. Few significant differences were found between the control and infected groups in hematologic and serum glucose and urea nitrogen values. The control group gained an average of 2.2 kg/week, as compared with 1.0 kg/week, as compared with 1.0 kg/week for the treated group. The parasitized-untreated group lost 0.2 kg/week. Overall, the control group gained 26.8 kg for the 12-week period, which was significantly different (P less than 0.05) from an 11.4-kg gain by the parasitized-treated group and a 2.3 kg loss for the parasitized-untreated group. In the face of constant pasture challenge exposure, most adult worms were eliminated from the drug-treated animals, but the adverse effects of parasitism were not reversed.