Detection of anthelmintic resistance of gastrointestinal nematodes infecting Senepol, Charbray*Senepol, and Charolais* Senepol heifers in Puerto Rico

Abstract

The effects of four anthelmintics on nematode fecal egg counts in beef heifers was determined. Senepol [n= 22] and crossbred [Charolais*Senepol and Charbray*Senepol; n= 17] heifers were distributed among treatments with: albendazole (Valbazen®), imidazothiazole (Levasole®), doramectin (Dectomax®) and ivermectin (Ivomec®). Egg counts per gram of feces (EPG) were determined before and after administration of the drugs in order to evaluate their efficacy. Participation in the experiment was limited to animals that presented an EPG ≥ 50 and those included were treated only once (day 0) with one of the anthelmintics. The EPG was monitored on days 0, 9, 15, 22, 29, 36, 43, 60 and 90 after treatment. Animals treated with Ivomec® presented an 86% reduction in nematode egg count, while Levasole® and Dectomax® reduced the FEC by 100% and Valbazen® by 98%. In conclusion, no resistance was detected against Levasole®, Dectomax® and Valbazen®, all of which achieved a nematode egg reduction ≥95%. On the other hand, these results suggest nematode resistance to Ivomec®.

Se determinó el efecto de cuatro antihelmínticos sobre el conteo de huevos de nemátodos en muestras fecales de novillas de reemplazo. Novillas (Senepol [n=22] y cruces (Charolais*Senepol y Charbray*Senepol) [n=17]) fueron distribuidas entre los siguientes tratamientos: albendazole (Valbazen®), imidazothioazole (Levasole®), doramectina (Dectomax®) e ivermectina (Ivomec®). Se seleccionó para participación en el experimento animales que presentaron ≥ 50 huevos de nemátodos por gramo de heces y estos se trataron con uno de los antihelmínticos una sola vez (día 0). Se determinó el EPG los días 0, 9, 15, 22, 29, 36, 43, 60 y 90 después del tratamiento. Animales tratados con Ivomec® tuvieron una reducción de EPG de 86% mientras que Levasole® y Dectomax® redujeron el EPG al 100% y Valbazen® al 98%. En conclusión, no se detectó resistencia contra Levasole®, Dectomax® y Valbazen®, ya que los tres redujeron los huevos de nemátodos ≥ 95%. En cambio, los resultados de esta investigación sugieren resistencia de los parásitos a Ivomec®.