Efficacy of ivermectin against Parafilaria bovicola and lesion resolution in cattle.

Thirty-two cattle were included in a study to confirm the efficacy of ivermectin administered at 200 micrograms kg-1 against Parafilaria bovicola and to determine the time required for resolution of the lesions caused by the parasite. Four treated and four control animals were slaughtered over 2 days starting 15, 30, 50 or 70 days after treatment. The number, distribution and surface area of carcass lesions, and the weight of tissue trimmed to render the carcasses aesthetically acceptable, were recorded and parasites were recovered from subcutaneous tissues. Significantly (P less than 0.01) fewer worms were recovered from ivermectin-treated cattle slaughtered 50 or 70 days after treatment than from controls. Reductions in the mean number and surface area of lesions, and in the weight of tissue trimmed, were statistically significant (P less than 0.05) for the ivermectin-treated group slaughtered 70 days after treatment and approached significance (P less than 0.1) for the ivermectin group slaughtered 50 days after treatment.