Persistent activity of doramectin and ivermectin in the prevention of cutaneous myiasis in cattle experimentally infested with Cochliomyia hominivorax.

A study was conducted to evaluate the activity of a single administration of doramectin or ivermectin against severe, induced infestations of Cochliomyia hominivorax. Twenty-four Holstein bull calves were allocated to four groups of six animals each and treated either with saline, doramectin 1%, or either one of two formulations of ivermectin 1% at a dose rate of 200 microg/kg. On Day 12 after treatment, each calf was anesthetized and two wounds were created on the left side of the shoulder and rump of each calf and 2 h later, each wound was implanted with 100 newly hatched larvae of C. hominivorax. On Day 15 after treatment, the procedure was repeated on the right side of each calf. Wounds were examined daily for 5 days and evidence of live larvae was recorded. Doramectin provided reduction in myiasis of 90.9 and 83.3% at 12 and 15 days after treatment, respectively, compared to the saline control treatment (P < 0.0001). In contrast, there were no significant differences in the number of calves with myiasis between those treated with either of the ivermectin formulations and the saline control.

Ovicidal action of oxfendazole on sheep nematodes.

Groups of five sheep naturally infested with gastrointestinal nematodes were dosed with oxfendazole at the rates of 2.5, 3.5, or 4.5 mg per kg and a similar group of five kept as controls. Frequent observations were made on worm egg output and the hatchability of the eggs passed. The first ovicidal activity was apparent five hours after treatment. Within eight hours 99.7 per cent or more of the eggs voided were sterile and by 30 hours there was a 99.9 per cent reduction in the numbers of larvae hatching compared with the controls. Within three days of dosing the faeces of the treated sheep were negative for worm eggs.