Doramectin resistance and diagnostic alternatives for gastrointestinal helminths selective control in sheep

Abstract

The indiscriminate use of antiparasitic agents during preventive management and treatment has led properties into pharmacological resistance, with high losses. This study evaluated diagnostic tests to verify pharmacological resistance, aiming selective treatment in clinically susceptible animals and/or with high parasitic load. 45 crossbred, male and female sheep, adults and young, from a farm in Uberaba, Minas Gerais, were used. All animals were submitted to appropriate zootechnical management followed by Famacha diagnostic tests, hematocrit, and egg count per gram of feces (OPG). Subsequently, all animals were treated with doramectin and the same diagnostic tests were repeated, comparing the same animal before and after treatment, with paired T test. There was no doramectin resistance in adults (P > 0.05); however, resistance was observed in puppies (P < 0.05). These were subsequently treated with levamisole and diagnostic tests were repeated again, observing parasitic load reduction, hematocrit increases and better Famacha indexes (ANOVA P < 0.05). Adults were not treated with levamisole. The linear regression between the Famacha method and hematocrit evaluated the handler's training degree, with greater difficulties in young animals. The continuous animal monitoring by diagnostic methods allowed to identity doramectin resistance and pharmacological treatment to occur selectively, only in animals with clinical signs and/or high parasite load, minimizing cost and drug resistance possibility.