The calculation of herbage intake of grazing sheep: A detailed comparison between models

This paper presents a review of the calculation of herbage intake by grazing sheep. A number of different simulation models and feeding recommendation sources are compared, both as to form and as to numerical results for a series of examples. In addition to the overall approach, the following aspects of the calculation of intake are considered; the effects of animal and plant characteristics on intake, the differences between lactating or gestating ewes and dry ewes, the treatment of intake from heterogeneous pastures, and herbage intake when milk, or supplements, are also available. The general conclusion is that the models presented are each likely to have only a limited range of applicability. The main use of this review, then, is to provide guidance in developing empirical models of intake for other situations, rather than to suggest a generally valid model.