EFFICACY OF INJECTABLE DORAMECTIN IN THE PROTECTION OF CASTRATED CATTLE AGAINST FIELD INFESTATIONS OF COCHLIOMYIA-HOMINIVORAX

Three studies were conducted in Latin America-one in Venezuela, one in Argentina and one in Brazil-using a common protocol to investigate th e efficacy of a single subcutaneous injection of doramectin in the pre vention and control of Cochliomyia hominiuorax infestations in castrat ed cattle, In each study, two groups of 20-28 animals each were alloca ted to a treated (T1) or to a control (T2) group on the basis of body weights. Animals of T1 received doramectin at 200 mu g kg(-1) (1 ml pe r 50 kg) and animals of T2 received saline solution at 1 ml per 50 kg of live weight. After treatment all cattle were castrated surgically, Animals were examined on treatment day and at 2, 4, 6 and 12 days post -treatment, At each observation day, the presence of C, hominivorax in festations was recorded. Doramectin was 100% effective in the preventi on and control of screwworm strikes in castrated cattle exposed to con tinuous field infestations of C, hominivorax in tropical and subtropic al areas of Latin America. Over the 12 day duration of the studies, 85 %, 60% and 65% of animals in the control groups had infested wounds in Venezuela, Argentina and Brazil, respectively. Affected animals requi red repeated therapeutic treatment, whereas none of the doramectin-tre ated cattle were infested (P < 0.0001), A high proportion of the castr ation wounds in doramectin-treated cattle had the presence of characte ristic C, hominivorax eggs but none developed into larvae, There were no clinical signs of adverse reactions to treatment in any of the thre e studies.