Evaluation of the Impact of the Ivermectin Sustained Release (SR) Bolus on Weight Gain and Parasite Control In Dairy Heifers During Their First Grazing Season

Abstract

Thirty-six Holstein heifers, 5-6 months of age were selected and ranked by weight to form 18 replicates of 2 aminals each with an average weight of 318 pounds at turn out. The six heaviest replicates were assigned to a paddock block, the next to the second block and the lightest six replicates to the third block. Within replicates animals were randomly assigned to treatment with the ivermectin sustained-release bolus or assigned as unmedicated controls. Two adjacent paddocks formed a block. Each paddock within a block was assigned to a treatment group. During the entire 175 days of the grazing trial, weight gains were recorded and levels of parasitism were determined by EP5G fecal counts and fecal cultures.

Results and recommendations for bovine practitioners will be discussed in this presentation.