EFFICACY OF DORAMECTIN IN THE PROTECTION OF NEONATAL CALVES AND POSTPARTURIENT COWS AGAINST FIELD STRIKES OF COCHLIOMYIA-HOMINIVORAX

Two studies were conducted in Latin America, one in Venezuela and one in Argentina, using a common protocol to investigate the efficacy of a single s.c. injection of doramectin in the prevention and control of field infestations of Cochliomyia hominivorax in newborn calves and po st-parturient cows. In both experiments, pregnant cows were paired on the basis of their calving time. The first cow that calved was assigne d to a medicated group, and both cow and calf were treated with dorame ctin. The cow received a dose of 200 mu g kg(-1) and the calf 1 ml of a 1% doramectin solution. The second cow and calf were assigned to a s aline-treated group, and the cow received saline at 1 ml per 50 kg and the calf 1 ml. The procedure was repeated until all animals were allo cated to the two treatments. Animals were examined on the treatment da y and at 2, 4, 6 and 12 days post-treatment. At each observation day, the navel of newborn calves and external genitalia of the cows were in spected and the presence of C. horminivorax infestations was recorded. Doramectin was 100% effective in the prevention and control of screww orm strikes in newborn calves and in post-parturient cows exposed to c ontinuous field challenge of C. hominivorax. Over the 12 day duration of the studies, 48% and 57% of the saline-treated calves had screwworm navel strikes in the studies in Venezuela and Argentina, respectively . Infested animals required repeated therapeutic treatment, whereas no ne of the doramectin-treated calves were affected (P<0.005). In Argent ina, 45% of post-parturient cows in the control group developed genita l screwworm strikes whereas none of the doramectin-treated cows were i n fested (P<0.005). None of the cows of either group developed strikes in Venezuela. There were no clinical signs of adverse reactions to tr eatment in either of the studies.