Season-long effectiveness of stocker-calf treatment at turnout with eprinomectin extended-release injection or a combination of injectable doramectin and oral albendazole

On May 22, 2013, 128 stocker calves enrolled in an internal parasite control study were treated according to structured allocations and placed directly onto treatment-specific, randomly allocated, similar pastures (4 animals/2 acres (0.8 hectare) pasture). Treatment groups were saline injection (8 pastures); 0.09 mg/lb (0.2 mg/kg) BW doramectin injection concomitantly with 4.54 mg/lb (10 mg/kg) BW albendazole oral suspension (12 pastures); and 0.45 mg/lb (1 mg/kg) BW eprinomectin extended-release injection (12 pastures). Over the 119-day grazing period, average daily gains ñ SE were 1.21ñ0.07, 1.46ñ0.04, and 1.52ñ0.04 lb (0.55ñ0.03, 0.66ñ0.02, and 0.69ñ0.02 kg)/day for the saline, combination, and extended-release groups, respectively; calves in the combination and extended-release groups outgained the control group (P<0.05). In comparison to the saline-treated group, there were statistically significant (P<0.05) reductions of strongyle fecal egg counts at 14, 30, and 58 days post-treatment (combination group) and at 14 and 30 days post-treatment (extended-release group). No significant differences in adult Haemonchus placei, Ostertagia ostertagi, Cooperia punctata, and Oesophagostomum radiatum populations between treatment groups were seen at necropsy. The combination treatment group had fewer O. ostertagi early fourth-stage larvae than did controls (P<0.05). Based on results of this study, a single treatment of heavily infected and challenged stocker calves in the spring in Arkansas with either extended-release eprinomectin or doramectin+albendazole was not sufficient for adequate parasitic nematode control.