USE OF FENBENDAZOL TO REDUCE CONTAMINATIO N CAUSED BY A SUBCLINICAL GASTROINTESTINAL PARASITOSIS IN CALVES

The experiment was carried out in Valdivia, Chile, from October 1992 t o March 1993. The effect of 5 mg/ kg Fenbendazol, administered orally, was analyzed in 20 Holstein Friesian calves which had adquired a norm al parasitosis after a month of grazing. Calves had an initial average weight of 133 kg. Parasite eggs in the faeces of each individual were counted in nineteen opportunities. The body weight of the calves was recorded at the beginning and on day 35, 77 and 141 of the experiment. Infestation of the pasture was determined once a month. When the egg output of the treated group (10 calves) surpassed 200 epg (on days 3, 77 and 141) the animals were treated with Fenbendazol. The other calve s remained as control without antihelmintic treatment. During the firs t 45 days, both groups were managed on a clean pasture and afterwards on a pasture with a moderate parasitic infestation. When the lot of ca lves was managed on a clean pasture, the treated group presented eithe r no egg output or a very low one, while the control group reached a m ean egg output of 1.175 epg. At the same time, both groups presented a daily weight gain of over 800 g/day. When the calves were managed on a moderate infested pasture, the treated group surpassed the 200 epg i n two opportunities, remaining negative during 21 days after each trea tment; the control group had a constant egg outpout of almost 200 epg. The treated group had a weight gain of 754 g/day and the control grou p 514 g/day. The Fenbendazol treatment contributed to reducing pasture contamination as well as to reducing the decline in weight gain in un treated calves during the spring and summer period.