Abstract During the 2-year period 1966–67 the production responses obtained from drenching young sheep with anthelmintics were examined in four trials at two sites in South Canterbury. Compared with undrenched controls, drenching at monthly intervals from November until August or September increased mean live-weight gain by 5.3 kg (range 5.1–9.2 kg) and mean greasy fleece weight by 0.62 kg (range 0.41–0.84 kg). Five drenches given in November, January, March, May, and July achieved responses averaging 68% of the live-weight gain and 73% of the increased greasy wool production from sheep drenched at monthly intervals. Starting at the end of October with 6-week-old lambs only 9% of the mean drenching response was obtained in the 2-month period before weaning in late December (0.35 kg), compared with 50% in January–February (1.05 kg), 21% in March–April (0.65 kg), and 40% in May–June (1.25 kg). No significant differences in mean live-weight gain (25.1 and 25.5 kg) or wool-weight (4.52 and 4.59 kg) were obtai...
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