Internal parasites are one of the major constraints toliveweight gain (LWG) in young grazing ruminants. However, even in parasite-free animals, diets low in crude protein can constrain LWG from values expected on the basis of metabolisable energy intake alone. We investigate the impact of protein supplementation in overcoming reduced growth rates of parasitised animals. This was done via a dynamic model which assumes increased maintenance requirements (immune requirements, increased cell turnover and mucous production) in parasitised animals. A key output from the model is LWG over an extended grazing period. We calibrated and validated the model using published data from an indoor feeding experiment in which trickle-infected lambs were fed for 20 weeks on three diets providing different amounts of metabolisable protein. The mean liveweight and worm burden predicted from the model compared well with experimental data. Such models will prove useful in designing supplementation strategies for grazing lambs where anthelmintic control of parasites is not a management option.
Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 220-225, 2007
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