Effects of Milk Feeding Period and Anthelmintic Treatment on Fecal Egg Counts and Growth in Pastured Dairy Steers

Abstract

A 2 x 2 factorial trial with 2 phases was conducted to evaluate the effects of weaning age (6 wk vs 12 wk) and anthelmintic treatment (non vs dewormed) on average daily weight gain (ADG) in 36 Holstein and Jersey X Holstein crossbred steers born in fall (Oct - Nov) and winter (Dec — Feb) 2003 — 2004. Steers were blocked into 4 treatment groups by birth weight and breed. Calves of similar age were managed together in pastures regardless of treatment and group-fed 3.8 to 7.6 L of whole milk/d until weaning. Phase 1 extended from birth until July 15, 2004. Phase 2 started on July 15 and ended on Nov 18, 2004. Dewormed calves received 1 mL ivermectin pour-on formulation/ 10 kg body weight (BW) at 12 and 20 wk of age, and again on July 15 and Sept 23. Fecal samples and BW (birth to Nov 18, 2004) were taken from each calf at 4-wk intervals. Fecal egg counts (FEC), BW, and ADG (during Phase 1, Phase 2, and Phases 1 & 2 combined) were compared among deworm, wean age, % Holstein, birth season, and their interactions. Parasite eggs were not detected until April and were lower in dewormed calves after July and Sept treatments. Fall-born calves usually had lower FEC than winter-born calves. Gains during Phase 1 were higher for fall-born calves. In Phase 2, dewormed calves actually had faster ADG than non-dewormed calves. Gain across Phase 1 and Phase 2 were higher in fall-born calves and tended to be higher in calves weaned at 6 wk. Gains and BW generally were higher with increasing % Holstein. Although steers that were not dewormed had higher FEC and differing ADG during parts of the trial, their overall performance was similar to those that received 4 doses of ivermectin.