Monitoring the resistance of Rhipicephalus microplus to amitraz, flumethrin, coumaphos, and ivermectin on cattle farms in Mexico.

The prevalence, resistance ratios and factor associated with Rhipicephalu microplus populations resistant to amitraz, flumethrin, coumaphos, and ivermectina (IVM) in Mexico were studied. Field tick populations were collected from 54 farms in 15 different states of Mexico. The dose-response bioassays were carried out using the larval immersion test (amitraz and IVM) and the modified larval packet test (flumethrin and coumaphos) against R. microplus. Mortality data were subjected to probit analysis to calculate lethal concentrations at 50%. A logistic regression model was used to evaluate the relation between resistance and possible associated factors. The phenotype was defined as high resistant (HR), low resistant (LR) or susceptible (S). The overall prevalence of cattle farms with R. microplus resistant to coumaphos, amitraz, flumethrin and IVM were 25.9, 46.2, 31.5 and 68.5%, respectively. For coumaphos, 74.1, 22.2, and 3.7% were classified as S, LR, and HR, respectively, whereas, for amitraz, 53.7, 24.1, and 22.2% of phenotypes were S, LR, and HR, respectively, for flumethrin 68.5, 14.8, and 16.7% were S, LR and HR respectively, and for IVM, 31.5, 46.3, and 22.2% were S, LR, and HR, respectively. We identified that cattle farms without acaricide rotation program (OR: 7.66, CL95%: 1.70-34.47, P: 0.008) had a higher probability of developing R. microplus resistant to amitraz. We concluded that amitraz and IVM resistance in R. microplus is frequent, but mainly at a low level in cattle farms of Mexico. Cattle farms without acaricide rotation program had higher probability of developing R. microplus resistant to amitraz.

Field Evaluation of the Effectiveness of an Oral Toltrazuril and Iron Combination (Baycox® Iron) in Maintaining Weaning Weight by Preventing Coccidiosis and Anaemia in Neonatal Piglets.

Effectiveness of an oral combination of toltrazuril and iron dextran (Baycox(®) Iron) to maintain weaning weight by preventing coccidiosis caused by Isospora suis and iron-deficiency anaemia in neonatal piglets was investigated on three commercial pig farms with a history of coccidiosis: two in Mexico and one in Brazil. On day (SD) 2 of life, piglets were randomised within litter by bodyweight to treatment or control group. On SD 3 piglets allocated to the control group (CG) each received 1 mL Baycox(®), containing 50 mg/mL toltrazuril orally and commercially available iron (200 mg/piglet) by intramuscular injection. Piglets allocated to the treatment group (TG) each received 1 mL toltrazuril and iron combination orally (Baycox(®) Iron) containing 50 mg/mL toltrazuril and 228 mg iron as iron dextran. All piglets had access to creep feed. 6493 piglets completed the study. Bodyweight at weaning on SD 21 of piglets treated with the oral toltrazuril and iron combination was confirmed to be non-inferior to the control treatment with <1 % difference between group mean body weights. Faecal samples from at least 10 % of litters on SD 14 demonstrated control of coccidiosis. Haemoglobin levels on SD 21 were lower in the oral toltrazuril and iron combination treated piglets compared to control levels but above minimum haemoglobin levels to maintain health. There was no difference in mortality between the two groups. This large scale field evaluation clearly demonstrated the effectiveness of a combination of oral toltrazuril and iron (Baycox(®) Iron) in maintaining body weight at weaning compared to conventional treatment. The combination was effective in preventing coccidiosis and anaemia and thus provides a valuable alternative that reduces stressful events in neonatal piglets. There were no product related adverse events.