Increased weight gains of Wisconsin dairy heifers following systematic deworming with fenbendazole.

Average daily weight gains (ADG) were compared among 26 dairy heifers on 11 farms. Half of the heifers were treated with fenbendazole (5 mg/kg) at 30- or 60-day intervals. Treatment every 60 days did not effectively control subclinical nematode parasitism, but did increase ADG by 0.05 kg, P less than 0.05. Treatment every days effectively controlled tha parasitisms and significantly improved ADG by 0.09 kg, P less than 0.01. Repeated treatment increased rate of gain on 10 of 11 farms. Cooperia, Ostertagia, and Nematodirus were the predominant genera found parasitizing the heifers. On several farms, the pattern of infection indicated that overwintering larvae were a source of infection.