Production and economic returns from Merino weaner sheep subjected to four frequencies of anthelmintic administration in East Gippsland, Victoria

Abstract

In East Gippsland. Victoria. 4 treatment groups, designated 'weekly' (W), 'high' (H), 'low' (L). and 'salvage' (S), each consisting of 3 subgroups of 10 Merino weaner sheep, were given different numbers of anthelmintic doses during 1978, 1979 and 1980. The doses were respectively 5 1, 5 1, 50 (W); 9,9, 12 (H); 3,4. 6 (L); and 1, 3, 2 (S). Both anthelmintics were administered according to the manufacturers' recommendations. Subgroups were grazed on separate 1 ha plots and rotated between plots within treatments at 2-week intervals in an attempt to eliminate between paddock differences. Sheep were replaced annually. These programs resulted in major differences in wool production and final liveweight between groups. Over the 3 years of the experiment, sheep dosed frequently grew heavier (P< 0.05) and produced more wool than - did sheep in the Land S groups. Mean final liveweights for the W, H, L, and S groups respectively were 53.6, 51.4.47.0, and 46.4 kg (l.s.d. [P= 0.051 = 3.5 kg). Corresponding figures for wool growth were 5.96, 5.62. 5.07, and 5.17 kg (l.s.d. [P = 0.051 = 0.60). Mortality in the W (5.6%) and H (22%) groups was also lower than in the L (18.9%) and S (27.8%) groups. The H group gave the highest economic return of $21.81 per sheep compared with $17.61 (W group), $16.3 1 (L) and $15.06 (S group). This advantage was maintained throughout a wide cost-price range. However. as both the W and H programs selected strongly for strains of nematodes resistant to anthelmintics. anthelmintic therapy alone cannot be relied upon for long-term parasite control.