Efficacy of single and double doses of pour-on eprinomectin on small ruminant farms - Is it affected by Haemonchus contortus?

Abstract

The objectives of the study were to determine the efficacy of the manufacturer's recommended dose (1 mg/kg body weight) and double dose (2 mg/kg body weight) of pour-on formulation of eprinomectin (EPN) on three sheep and six goat farms and to compare the EPN efficacy between both host species on two mixed farms. The efficacy of EPN against gastrointestinal nematodes (GINs) was evaluated by the faecal egg count reduction test. According to the WAAVP recommendations, the farms were evaluated as "resistant", "inconclusive", or "susceptible". The composition of the GINs was determined on the day of treatment and on the 14th day after treatment by analysing the morphology of the third-stage larvae (L3). After administration of the recommended dose, two sheep and four goat farms were classified as "resistant". The mean efficacy of the recommended dose on sheep and goat farms ranged 73.1-94.0% and 54.0-86.8%, respectively. After administration of a double dose, the EPN efficacy increased by 5-24%. On mixed farm 1, sheep and goats were categorised as "inconclusive" and "resistant" respectively. After administration of a double dose, efficacy increased from 61% to 95% in sheep, but only from 59% to 64% in goats. On mixed farm 2, both hosts were evaluated as "resistant". Haemonchus contortus was the most prevalent species (68%-95%) on farms classified as "resistant" even after the application of a double dose. The presence of H. contortus on these farms was found to be one of the decisive factors influencing EPN efficacy.