The effect of four schemes of parasite control on production in Merino wether weaners in two environments

The effect on wool production and liveweight changes of four parasite control programs, differing only in the number and timing of anthelmintic treatments, was compared in two experiments. In one program (Salvage), only individual clinically affected sheep were treated, to avert death. In a summer rainfall environment, increases in wool production of 18.4, 25.0 and 34.2% above the Salvage control scheme were recorded, respectively, for Curative (4 thiabendazole, 1 rafoxanide), Preventive (5 thiabendazole, 5 rafoxanide) and Suppressive (11 thiabendazole, 5 rafoxanide) programs of control. In the area of dominantly winter rainfall, the increases in wool production over the Salvage scheme were 17.9, 26.4 and 45.9 % for the Curative, Preventive and Suppressive programs, involving 3, 3 and 11 treatments with thiabendazole, respectively. The three treatments in the Curative program were given 3, 0 and 1 month later than in the Preventive program. Liveweight gains followed a similar pattern to wool production, but with some compensatory gain in the spring at the lower levels of control in the summer rainfall environment. The final gains were 17.4, 20.7, 23.7 and 24.7 kg in the first experiment, and 12.3, 18.3, 19.5 and 22.6 in the second experiment, for the four schemes of parasite control. The high level of production resulting from the Suppressive program was attributed to the reduction of the contamination/reinfection cycle to a low level. The experimental design involved thorough replication and required that different treatment groups be grazed separately so as to facilitate the measurement of true production differences.