A computer-based model of the response of the ewe to energy nutrition during pregnancy is described, based on a previous analysis of energy requirements. A ewe of specified weight and body condition 30 days from conception, carrying a known number of lambs, is predicted to grow them to an optimal weight if the nutritional regime allows. Daily energy requirements of the ewe-foetus system are calculated as the sum of requirements for maintenance and for growth and are compared with the daily energy supplied.If the feed provides energy surplus to requirements, the ewe herself gains weight; otherwise, the ewe mobilizes her own reserves, within limits, to protect the foetus. If this does not produce the energy required for optimal growth, foetal growth is reduced.
Published experimental results are compared with predictions of the model when run under similar conditions; in general, predictions of total maternal weight at the end of pregnancy are within 5 % of those observed in the experiments. Model predictions of the effects of some particular nutritional regimes during pregnancy are presented and the sensitivity of the predictions of the model to certain of the assumptions made in its construction are discussed.