1. A deterministic model for thermoneutral heat production of growing pigs on barley-based diets has been developed and validated. The model variables are live weight (20 to 100 kg) and metabolizable energy intake (not less than maintenance). The root-mean-square error for 62 data is 049 MJ/day (3-2%). 2. A deterministic model for heat production of growing pigs below their critical temperature has been developed and validated. The model variables are: air temperature, air velocity, floor type, live weight (20 to 100 kg), and group size. The root-mean-square error for 78 data is 0-77 MJ/day (5-6%). 3. The two heat production models are combined to give a model for the lower critical temperature for growing pigs. 4. These models may be used to quantify and compare the effects on energy balance of different combinations of nutrition and environment. They should help to clarify the issues when practical decisions in pig production are made and should also help in the design of nutritional and physiological experiments.

Energy intake was recorded for two batches of 12 individually-penned piglets weaned at 5 kg live weight and fed milk-based diets of 18·7 MJ metabolizable energy (ME) per kg up to 8 kg live weight and 15.4 MJ ME per kg thereafter. The piglets were kept within their thermoneutral zone throughout the experiments. Regression equations describing the relationship between energy intake and days after weaning were developed for each piglet and the means of the regression coefficients and constants were incorporated in an equation for estimating energy intakes for piglets of 5 to 15 kg live weight. The lower and upper critical temperatures were calculated for each piglet on every day of the trial. These values were extrapolated to give temperature recommendations for piglets of 5 to 15 kg live weight kept in groups of 20. The temperatures ranged from 30°C at weaning to 19°C, 23 days after weaning. This represented a reduction in temperature equivalent to 0·5°C per day.

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ABSTRACT1. The model of the energy system of lactating, and pregnant, cows proposed by Bruce, Broadbent and Topps (1984) has been evaluated using data relating to 166 lactations for dairy cows and 48 lactations for beef cows. The cows in both sets of data were subjected to various nutritional and managerial regimes.2. The discrepancies between observed and predicted values of milk (energy) and live weight were small, both as a proportion of the measured values and total energy intake. For Danish Black and White dairy cows the discrepancies for milk were virtually zero on both bases; those for live weight represented 0·020 of the total energy intake, or an over-prediction by 0·054 in late lactation. For Hereford × British Friesian beef cows, suckled by one or two calves, the discrepancies as a proportion of the total energy intake ranged from 0·005 to 0·051 for milk and 0·001 to 0·063 for live-weight change across the nutritional and managerial regimes.3. It was concluded that the model of Bruce et al. (1984), which considers genetic potential for milk production and growth, nutritional (energy), reproductive and environmental status, may be used to predict milk yield and live-weight change simultaneously from food (energy) input.

Two data sets have been used to evaluate NOSCOW, a model of the energy system of cows which allows milk production and live-weight change to be predicted simultaneously from dietary energy intake (Bruce, Broadbent and Topps, 1984).Black and White Danish Dairy Cows (SDM) were used by Østergaard (1979) to study concentrate feeding strategies. There were nine treatments which differed in the level and pattern of concentrates fed over the first 36 weeks of lactation. These treatments caused substantial differences in the levels and patterns of energy intake.