Impact of ivermectin-resistant gastrointestinal nematodes in feedlot cattle in Argentina

Abstract

The aim was to evaluate for 75 days the impact on production of the remaining burden of ivermectin (IVM)-resistant parasites in naturally infected feedlot calves. The herds came from tick-infested areas of cattle breeding where the systematic use of IVM to control tick increases the gastrointestinal parasites resistant to this drug. This investigation was carried out in two commercial feedlots in Buenos Aires province. In feedlot A, two groups of 35 animal each received IVM 1% and the other received ricobendazole (RBZ) 10% respectively. The same was done in feedlot B. On day 0, two groups of 35 animals were made in feedlots A and B. Fecal samples were taken on days 0, 22, 54 and 75 pos-treatment (PT), and body weight was registered, from each animal. Fecal samples were processed for individual count of eggs per gram (EPG) and pooled fecal culture was carried out for identiϐication of the parasite genus in each sampling. Fecal egg count reduction test (FECR) was calculated on day 22 PT. The study design used was a totally randomized block, with commercial feedlot and sex as block variables. For data analysis, a mixed model of the SAS statistical program was used. The FECR average on day 22 was 28.4% in the IVM group, and 94,2 % in the RBZ group . From this date on, signiϐicant differences in EPG were kept until day 54. EPG counts were only equal near the end of the trial, on day 75 (p=0.16). In both commercial feedlots, especially in the IVM group, Cooperia spp. was the most prevalent parasite in the fecal cultures. Signiϐicant differences in weight (P<0.01) on post-treatment day 75 was found between the average weight in the RBZ and the IVM group (246 vs. 238 kg respectively), what means a difference of 8.3% in gains. The importance for production in the antiparasite failure treatment in commercial feedlots was demonstrated, and the need of pos-treatment controls to evaluate the efϐicacy of the antiparasitic administered is emphasized.

The effect of anthelmintic resistance on the productivity in feedlot cattle

“…has already been reported (Herlich, 1965;Keith, 1967;Louvandini et al, 2009;Stromberg et al, 2011) as well as the impact of this genus combined with Haemonchus sp. in feedlot calves (Fazzio et al, 2011(Fazzio et al, , 2012. In this trial, the prevailing parasite genus in PT fecal cultures was Cooperia, while Haemonchus was present in smaller amounts.…”

“…In Argentina, more than 1.100.000 animals a year are fattened in feedlots (Rossanigo et al, 2010). Weight loss due to lack of drug efficacy as a result of AR could be substantial in these production systems (Fazzio et al, 2012).…”

Resistance of Haemonchus, Cooperia, Trichostrongylus, and Oesophagostomum to ivermectin in dairy cattle in Paraná

“…Low efficiency at a lowest dosage of ivermectin in this study was reported by Fazzio et al (2012) in Argentina, who observed an RFEC rate of 28.4%, 22 days after the treatment of calves, while Soutello et al (2010) reported that the highest RFEC (72.2%) was observed 3 days after treatment and for 28 days thereafter, which was evaluated after administration of 1% ivermectin. On the Santa Catarina plateau, 18% of the cattle had an efficacy greater than 95% and 5% and less than 14% (SOUZA et al, 2008).…”

Helminthiasis control in calves raised in a hot Semi-arid area

“…El hecho de que las lactonas macrocíclicas eran los AH de preferencia en las granjas estudiadas podría crear una mayor presión para la selección de NG resistentes. Varios reportes ya existen de la resistencia a la ivermectina en regiones tan diversos como el norte de California, Estados Unidos (32) ; Buenos Aires, Argentina (33) ; y en São Paulo y Minas Gerais, Brasil (30,34) . Esto resalta la importancia de evaluar el perfil de susceptibilidad de un AH en cada región o hato para asegurar que va a ejercer un control efectivo de los NG (33) .…”