The effectiveness of doramectin pour-on in the control of gastrointestinalnematode infections in cow-calf herds

Two field studies were conducted in the USA to determine the efficacy of a single strategically-timed dose of doramectin pour-on in the control of gas trointestinal nematodosis in beef cow-calf herds and the resultant effects on calf productivity. One study was carried out between May and October 199 6 in a spring-calving herd at a site located in Idaho (ID) and the other be tween January and July 1997 in a fall-calving herd at a site located in Mis sissippi (MS). In each study, cow-calf pairs were randomly allotted by sex of calf to pastures and one of two treatment groups (doramectin pour-on at the recommended dose rate of 500 mu g/kg body weight or untreated control). There were four pasture replicates per treatment at each site. Each pastur e contained 12 cow-calf pairs at the ID site and 15 cow-calf pairs at the M S site. Treatment was administered to cows and calves on 21 May 1996 (ID) o r 23 January 1997 (MS). Following treatment, cow-calf pairs were assigned t o their designated pastures where they remained until the calves were weane d 140 (ID) or 168 (MS) days later. Cow and calf fecal egg counts and calf b ody weights were recorded on treatment day and then at monthly intervals un til study termination. Doramectin treatment reduced nematode egg output in cows and calves over the entire grazing season compared to untreated contro ls and resulted in calf weight gain improvements of 9.8 kg (p=0.295) at the ID site and 17.4 kg (p=0.0002) at the MS site. (C) 2000 Elsevier Science B .V. All rights reserved.