Effect of an anthelmintic program with morantel tartrate on the performance of beef cattle.

A field trial was conducted to determine (1) the effectiveness of an anthelmintic program using morantel tartrate (MT) to control subclinical gastrointestinal parasitism among cattle on pasture and (2) the effects of the program on the performance of cattle. Two Hereford herds, each on a separate pasture with forage of comparable quality and quantity, were used. A stocking rate of .62 ha/cow-calf was maintained in both pastures. One herd consisted of 124 cows and 122 calves and served as a non-mediated control group. The second herd consisted of 126 cows and 124 calves. Cows and calves from the latter group were treated with a bolus formulation of MT at a dosage of 10 mg/kg body weight at the beginning of the trial and again 55 d later. Calves were treated again 42 d after the second treatment. Cattle were weighed individually each month and rectal fecal samples for nematode egg counts were obtained from 36 cows and 36 calves from each group at that time. These donor cattle were selected at random at the time of the first weighing; fecal samples were then obtained from the same animals throughout the study. Eggs of the Cooperia-Ostertagia-Trichostrongylus complex predominated in all fecal samplings. There was no difference in the number of nematode eggs from the two groups of cows. However, the medicated cows gained significantly more weight than the controls and had an average weight gain advantage of 28.8 kg. The medicated calves had significantly lower average egg counts and made higher weight gains than the unmedicated calves. The medicated calves had an average weight gain advantage over the control group of 11.1 kg.