Epizootiology of helminth parasitism in a beef cow/calf herd in Minnesota

To test the effect of a parasite control program for cattle, 2 groups of similar composition were grazed on separate, but equivalent, improved pastures. Cattle in 1 group were treated with fenbendazole at 5.0 mg/kg of body weight at the time they were turned out on pasture in the spring and again at midsummer, when the cattle were moved to a new pasture. The control group was not treated. Parasite egg counts were significantly (P less than 0.04) lower in the treated group. Trichostrongyle-type eggs were the most prevalent throughout the year, except in the month of May, when Strongyloides papillosus eggs were predominant. The number of worms recovered from tracer calves was lower for those on pastures where the treated group grazed than for those on the control group's pasture. The most consistently recovered parasite was Ostertagia ostertagi, and hypobiosis was observed.