Ivermectin pharmaco-parasitological evaluation on different beef cattle anthelmintic resistance scenarios in Italy and Argentina

Beef cattle farming plays a crucial role in the agricultural economies of both Argentina and Italy. Although both countries have grazing systems of meat production, the heterogeneity of these systems leads to different parasitological scenarios regarding epidemiology and anthelmintic resistance. In this context, considering ivermectin (IVM) is the most widely used anthelmintic for treating gastrointestinal nematodes in cattle, the current study evaluated the efficacy and the pharmacokinetic profile after the subcutaneous (SC) administration of ivermectin (IVM) given both to young calves and adult cows in ten commercial cattle farms from Italy (A to E) and Argentina (F to J). While in Italy adult cows and young calves were included in the study, in Argentina only calves aged 8-14 months old were selected to perform the efficacy trial. On each farm fifteen (15) calves/ cows naturally infected with gastrointestinal nematodes were treated with IVM (0.2 mg/kg). The efficacy was determined at 14 days after treatment by the FECRT. Six (6) adult cows and eight (8) young calves treated with IVM were randomly selected to perform the PK study with blood samples being taken from these animals at regular intervals. Drug concentrations were measured by HPLC. Similar IVM PK trends were obtained for both adult and young cattle. The IVM systemic exposure (expressed as AUC) obtained for adult cows (380±158 ng.d/mL) was similar to that observed in young calves group (313±85.5 ng.d/mL). No statistical differences between both categories were observed for the most representative PK parameters (P>0.05). Surprisingly, while in Argentina IVM resistance was present in all the farms (90% CI = 0%-95%), in Italy a susceptible nematode population was presented in three farms (90% CI = 96%-100%) and a low level of IVM resistance in the rest of the farms (90% CI = 92%-98%). Cooperia spp. and Haemonchus spp. were the main genera resistant to IVM. In conclusion, IVM can be effectively used in both young cattle and adult cows. While its efficacy remains notably high in Italy, its use should always be preceded by a diagnostic assessment of the nematode population’s resistance status. Fil: Cantón, Candela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigación Veterinaria de Tandil. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigación Veterinaria de Tandil. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Centro de Investigación Veterinaria de Tandil; Argentina Fil: Bosco, Antonio. Università degli Studi di Napoli Federico II; Italia