The effects of natural trichostrongylid larval challenge on 2-year-old Freisian steers

Abstract The effects of ‘high’ and ‘low’ levels of trichostrongylid larval challenge were examined in two groups of 2-year-old Friesian steers. Different autumn/winter levels of larval infestation were established on two similar suites of paddocks by controlling contamination during summer and early autumn. Maximum pasture larval recoveries during autumn were 2110 larvae/kg herbage for the high challenge and 48 larvae/kg for the low challenge suites. The mean liveweight gain (April–June) of the steers exposed to the higher larval challenge was reduced by about 20 kg. Over the same period the mean plasma pepsinogen level for the high challenge group had more than doubled, whereas that for the low challenge group was virtually unchanged. Faecal egg counts were less than 50 eggs per gram of faeces for both groups throughout the trial. Apart from the divergence in liveweight gain of the two groups there was no other evidence of clinical parasitism. Although possible paddock interaction was not measured, the p...