Effects of grazing management practices on parasite load and weight gain of beef cattle.

Stocking rate, method of grazing (rotational vs. continuous) and supplementation are three grazing management variables which strongly affect weight gain of beef cattle. However, reports on the interaction between these variables and parasitism in beef cattle are often conflicting or not conclusive. Although several studies have shown increased parasite loads with increased stocking rates, few studies have included animals treated and untreated with anthelmintics at several stocking rates. Those that did have this treatment combination did not show greater response in weight gain to treatment with anthelmintics at high stocking rates than at low stocking rates. Experiments designed to investigate the effect of rotational and continuous grazing on parasitism have provided variable results. However, as the high stock densities associated with rotational grazing will probably cause animals to graze closer to the ground and to dung pats, and to spread dung more with their hooves, it is not likely that rotational grazing will reduce the need for chemotherapy. Some studies have shown reduced parasite loads with supplementation of untreated animals, but none has apparently investigated whether weight gain response to treatment with anthelmintics is greater for non-supplemented animals than for supplemented animals. Published studies on the interaction between management factors and parasitism in grazing animals reveal many weaknesses. Elimination of these weaknesses and cognisance of recent trends in design and conduct of grazing experiments will substantially improve the quality and value of research in this field.