Effects of anthelmintic treatment on weight gain of weaned dairy calves on the Atherton Tablelands

Abstract

The effects of repeated anthelmintic treatment with levamisole on body weight gain of grazing calves on the Atherton Tablelands are reported. On six farms, calves treated up to 10 times at 3-week intervals with 1.9 mg/kg or 7.5 mg/kg levamisole injected subcutaneously gained up to 37 and 59 kg more than untreated calves grazing the same pasture. Significant differences ( P < 0.05) were found in cumulative weight gains of calves given high doses of levamisole from 18 weeks and at low dosage from 24 weeks compared with untreated controls. The helminths mainly responsible for the reduced weight gain were Haemonchus placei, Oesophagostomum vadiatum and Coopevia species (C. pectinata and C. punctata). Seasonal incidence of nematode egg counts showed an increase in the proportion of H. placei eggs following wet and warm conditions, and O. vadiatum eggs following wet and cool conditions. Untreated calves developed natural resistance to helminth infection as measured by reduced faecal nematode egg counts after 6 months of natural challenge. One-quarter recommended dose of levamisole at 3-week intervals resulted in approximately half the weight gain advantage produced by full dose treatment except in the drier areas of the Tableland, where a higher advantage was recorded at this level.