Parasitism and production in weaner sheep grazing alternately with cattle

Abstract

Three systems for the post-weaning management of Merino wethers were compared over two years. In all systems, the sheep were given two anthelmintic treatments with levamisole per year; at weaning in January, and in July. In the first system (SC) the same paddock was used as a weaning paddock each year in succession. In the second system (SC 6) sheep and cattle grazed the paddock alternately for 6- month periods from January and July; the third system (SC 12) comprised sheep and cattle grazing alternately for 12-month periods from July of each year. Compared with the SC treatment, weaners from the SC 6 treatment had significantly lower faecal egg counts and lower burdens of Haemonchus contortus, Trichostrongylm axei, Trichostrongylus colubriformis and Nematodirus spp. They had significantly higher numbers of Cooperia oncophora and similar numbers of Ostertagia circumcincta. SC 6 sheep made greater liveweight gains, produced heavier fleeces, and suffered lower mortalities than their SC counterparts. Results for the SC 12 system were usually intermediate. In a third year, the SC 12 system was modified to include a monthly treatment with levamisole. The liveweight gains, egg counts and mortalities of the monthly treatment sheep did not differ significantly from those of the SC 6 sheep. Both systems were superior to the SC treatment in controlling nematode infections in weaner sheep. There were no significant effects of any treatment on liveweight gains of cattle, although outbreaks of ostertagiosis occurred in the third year in two of the four replicates of the SC system.