The effect of mixed grazing of sheep and cattle on worm burdens in lambs.

Lambs from ewes grazed without cattle at 4.9, 7.4 and 9.9 ewes and lambs per hectare and from ewes run with steers at an equivalent median stocking rate at four ratios in which sheep comprised 30%, 40%, 50% and 70% of the animal equivalents were killed and examined for worms. When sheep grazed alone, there was no significant increase in the number of worm species normally found in sheep, namely Ostertagia circumcincta and Nematodirus spathiger, with an increase in stocking rate. When sheep grazed with cattle, there was a decrease in the number of worm species normally found in sheep but an increase in the number of those normally found in cattle, namely Cooperia oncophora and Trichostrongylus axei, as the proportion of cattle in the ratio increased. The total worm burdens were low due to the management of the flock and parasites were not shown to have affected productivity. The results are discussed and the practical aspects of the findings are presented.