Field study comparing fecal egg count reduction, weight gain and product safety in stocker cattle treated with either moxidectin or ivermectin with clorsulon

Abstract

This study was conducted to assess effectiveness, safety and benefit of injectable moxidectin compared to an injectable ivermectin-clorsulon combination. A total 2,022 stocker calves maintained on 11 Arkansas and Missouri cattle farms were randomly and evenly allocated on each farm into either the moxidectin (MXD) or ivermectin-clorsulon (IC) group. No negative controls were utilized in the study. All treatments were administered on a unique day 0 for each farm. Herd sizes ranged from 54 to 544. Naturally infected mixed breed bull, steer or heifer calves, weighing from 241 to 810 lb (110 to 368 kg) on day 0, were used in the study. On days 0, 50 (approx) and 100 (approx), each animal was weighed, and fecal samples were obtained from 20% of the animals (same animals on each sample day) for determination of fecal nematode egg counts and coproculture larvae identification. Both products were easily administered and no adverse effects were noted following administration of either drug. Weight gain from day 0 did not vary significantly between treatment groups at either of the post-treatment sampling dates. In addition, sex by treatment interaction was not significant (P<0.05), as analyzed on those farms that had both male and female cattle in the study population. On day 0, no significant differences were found between treatment groups for strongyle eggs per gram of feces (EPG) counts or coproculture larvae percentages. For days 50 and 100, EPG counts for MXD-treated calves were significantly lower than those for IC-treated calves (P<0.05). Day 0 coproculture data indicated that the primary nematode parasites contributing to the fecal egg counts were Cooperia, Haemonchus and Ostertagia. On days 50 and 100, MXD-treated animal coprocultures yielded higher larvae percentages of Cooperia than did the IC-treated animal coprocultures (P<0.05), as well as significantly lower Ostertagia and Haemonchus larvae percentages. Egg count and coproculture results suggest that both parasiticides were most limited in their ability to control Cooperia, but greater post-treatment egg production by Cooperia, Ostertagia and Haemonchus occurred in calves treated with IC compared to those in the MXD group.