EFFECTS OF FEEDING COUMAPHOS TO DAIRY COWS AT VARIOUS STAGES OF LACTATION ON SUBCLINICAL PARASITE INFECTION AND MILK PRODUCTION

Abstract

Twenty-eight Holstein cows were allocated to 14 blocks of two cows each, balanced for previous lactation performance, stage of lactation and parity number. Cows within each block were randomly assigned to a treated or untreated (control) group. Treated cows received coumaphos on day 0 (December) according to manufacturer's recommendations and were re-treated when fecal worm egg counts increased in April, May and August. Control and treated animals were fed similar rations formulated according to production and had access to different but similar pastures during the pasture season (May to October). Milk was weighed daily and sampled weekly for fat and protein determination during the 50-wk trial. Treatment reduced fecal egg counts by 84.8% initially. Average egg count per 5 g feces was reduced to 15.1 in treated cows compared with 37.1 in controls. Tracer calves that grazed on pasture with control cows had an average of 6.3 times more gastrointestinal worms than calves grazing with treated cows. Milk production was not significantly different between groups for the 50 wk of the trial; however, compared with control cows, treated cows produced 2.07 kg d−1 more milk when on pasture and 3.9 kg d−1 more milk when housed indoors after the grazing season. Treatment reduced milk production during the initial housing period. Key words: Subclinical parasitism, dairy cattle (lactating), coumaphos, host-parasite relationships