EVALUATION OF THE EFFECT OF IVERMECTIN ADMINISTERED TOPICALLY AT ZEROAND 6 WEEKS AFTER TURNOUT ON GASTROINTESTINAL NEMATODE INFECTION IN FIRST-SEASON GRAZING CATTLE

A field study was conducted between May and October 1995 to examine th e efficacy of 0.5 mg/kg ivermectin pour-on on parasitic gastroenteriti s of set-stocked calves at turnout and 6 weeks later. A treated group of 10 calves was compared with a separately grazed group of 10 non-tre ated calves; 14 calves were used as tracer animals. Initial infection levels appeared to be very low in both groups and faecal egg counts, p asture larval counts, serum pepsinogen levels and optical density (OD) values of an ELISA with a specific recombinant antigen for Cooperia o ncophora remained low for 4 months. Thereafter, a rapid build up of ga strointestinal nematode infections occurred in both groups. (C) 1998 E lsevier Science B.V. All rights reserved.