A model for the effects of energy nutrition on the pregnant ewe

Abstract

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. 357

The effect of body condition and nutrition during late pregnancy on the performance of grazing ewes during lactation

“…The individual rations were calculated using the model of Geisler and Neal (1979). The grass pellets provided during pregnancy were from a single batch and had a gross energy concentration of 18-43 MJ/kg DM, with a mean metabolizability of 0-455 measured in vivo using 2-year-old ewes during their 17th week of pregnancy.…”

A teleonomic model describing performance (body, milk and intake) during growth and over repeated reproductive cycles throughout the lifespan of dairy cattle. 2. Voluntary intake and energy partitioning

“…The modulation of Q Y by priority S is consistent with the more pronounced effect of underfeeding on milk production in early lactation (Broster, 1972) and the favoured diversion of energy surplus into milk, when this option is available, rather than into body reserves (Friggens et al, 2004). As in the model of energy requirements of the pregnant ewe developed by Geisler and Neal (1979), the supply of energy to ensure an optimal foetal growth is seen as a 'protected' function. This formalism implicitly assumes that the flow P* corresponds to an optimal foetal growth.…”