Comparison of deworming strategies for pre-weaned beef calves

While anthelmintic treatment in young calves at first vaccination has not proven repeatedly effective in improving weight gain, there is evidence that treatment 90 day prior to weaning can enhance weight gain. This is difficult in most California cow/calf operations as after initial vaccination, calves are not again handled until preconditioning just prior to weaning. In an attempt to increase weight gain without the need for anthelmintic retreatment prior to preconditioning, 130 cow/calf pairs were stratified and assigned to three treatments of eprinomectin extended release injection (150 d efficacy), doramectin conventional injection, and an untreated control. Dams and calves received the same treatment. All treatments were commingled on irrigated pasture in Northern California. Sampling included weight (d 0, 75, and 145), fecal parasite (d 0, 14, 75, and 145), cow body condition score (d 0, 75, and 145), and cow pregnancy detection (days bred). Calf weight gain was not impacted by anthelmintic treatment (P = 0.44). However, cow weight gain was impacted by treatment (P