Production-based control of parasitic nematodes of cattle

Nematode parasite control in cattle is the goal of the parasitologist and the cattle producer. However, the language used to express the impact of that control has been a source of confusion between the two groups. Veterinary parasitologists speak in terms of reduction in worms or worm eggs, and cattle producers in terms of weight gain, milk production or calving rate. During the development of doramectin for cattle in temperate climates worldwide, the point came when we began to look for a different set of parameters to guide trial design and to communicate the results. In this paper, a series of published papers resulting from the yearling portion of this development programme are reviewed from the viewpoint of weight gain in relation to forage/feed availability. A pattern emerged that indicated that yearling cattle, when parasite control was effective (as indicated by egg counts) and forage was sufficient (as indicated by weather patterns), gained from 0.75 to 0.95 kg day(-1) in trials from the USA, Europe and Argentina. When parasite control or forage supply or both were insufficient, these rates of weight gain were significantly reduced. If more attention is spent on forage availability and weight-gain parameters when parasite-control programmes are designed, then researchers might communicate more meaningful information to producers on the value of parasite control.