Comparative productivity of growing cattle treated with two injections of doramectin (200 mcg/kg) or one injection of ivermectin (630 mcg/kg) for parasite control.

A study was conducted in Brazil, from May to October 1999, to compare the anti-parasitic efficacy and productivity effects of 2 subcutaneous injections of doramectin (200 mcg/kg) administered 56 days apart with that of a single injection of ivermectin (630 mcg/kg) in growing cattle. Ninety-six crossbred male cattle were randomly allocated to 3 groups of 32 animals, based on bodyweight. All animals grazed the same pasture during the study. Treatments consisted of either 2 injections of doramectin (days 0 and 56), one injection of ivermectin (day 0), or no treatment (controls). Cattle weight, nematode egg counts, coprocultures, tick counts, tropical warble nodule counts, and presence of screw worms were determined on days 0, 28, 56, 84, 112 and 140. Mean fecal egg counts from cattle in both medicated groups were significantly reduced compared to those of controls. Coprocultures showed a predominance of Cooperia spp. and Haemonchus spp. On days 84 and 112, fecal egg counts of doramectin-treated cattle were significantly (p<0.05) lower than those for ivermectin-treated cattle. Tick counts were also reduced in the doramectinand ivermectin-treatment groups compared to those for controls. On day 84, ticks counts of doramectin-treated cattle were significantly lower than those of ivermectin-treated cattle. At the end of the 140-day study, doramectin-treated cattle had a mean weight gain of 11.3 kg and 14.1 kg higher than that of ivermectin-treated cattle (p<0.05) and controls (p<0.05), respectively. It is concluded that, growing cattle treated with two injections of doramectin (200 mcg/ kg) administered 56 days apart had better productivity and parasite control over a 140-day period, than cattle treated with a single injection of ivermectin (630 mcg/kg).