Effects of previous and current anthelmintic treatments on productivity in Merino hogget sheep

Abstract

The effects of various drenching programs for hogget (2-year-old) sheep, on productivity in subsequent years was studied at the Pastoral Research Institute at Hamilton during 1976-78. In 1976, liveweight gains and fleeceweights in hoggets were significantly (P < 0.01), dependent on drenching programs in their first year after weaning. Sheep which had been drenched at weekly intervals as weaners in 1975 had significantly (P < 0.01) reduced liveweight gains as hoggets during 1976, regardless of whether they were drenched or not in that year. In 1977 and 1978 previous drenching had a significant effect on liveweight gain in hoggets (P < 0.01) but not fleeceweights (P > 0.12). Sheep drenched at weekly intervals as weaners, then left undrenched as hoggets, had the lowest liveweight gains of any group. Liveweight gains and fleeceweights measured at the end of the third year were unaffected by previous drenching history (P > 0.15). Frequent drenching of weaners may not increase their productivity, and productivity losses due to underdrenching weaner sheep may be compensated for in subsequent years.