The effect of anthelmintic treatments on growth of beef cattle in New South Wales

Abstract

The effects of anthelmintic treatments on the growth of young beef cattle on the Tablelands and North Coast regions of New South Wales were assessed by comparing the liveweight gains of treated and untreated cattle grazing the same pasture. Anthelmintic treatments were given every 4 weeks to suppress gastrointestinal nematode infections and at strategic times. These times were at weaning (in autumn), during winter and in the late summer of the following year, and were chosen to coincide mainly with increasing worm burdens. After weaning, the mean cumulative liveweight responses of suppressively treated groups were often significantly greater during winter and early spring. Strategic treatments in winter but not in autumn also gave a significant liveweight response in some trials. Suppressively treated groups showed considerable variation in their growth rates during spring. This most likely reflected year-to-year variations in pasture growth, but the mean cumulative liveweight responses of several treated groups were significantly greater than those of untreated groups. These results suggest that helminth infections affected the growth of young beef cattle in both winter and spring. There was little liveweight response to suppressive treatments in the late summer and autumn of the second year, when the cattle were 16-20 months old. At the end of autumn, these cattle were usually 20-30 kg per head heavier than untreated cattle. Strategic treatments given in late summer to cattle grazing with untreated cattle did not produce any substantial liveweight response.