An experiment was undertaken to examine the effect of using sorghum as a substitute for maize on digestibility and nitrogen retention in the growing pig. Two levels of sorghum, 200 and 400 g/kg, substituting for maize on a weight basis, were used. The chemical composition of control and test diets was similar. In the metabolism trial, digestibility coefficients for dry matter, crude fibre, nitrogen and gross energy were significantly lower for the animals given the higher level of sorghum. In the feeding trial, no significant differences were recorded between the three groups in relation to food conversion ratio, daily live-weight gain, killing-out proportion and carcass quality. It is concluded that yellow sorghum may replace up to 400 g of maize per kg in diets for growing pigs without having detrimental effects on animal performance.

Piglets were weaned at 21 days of age, and given diets containing 13·5 or 17·0g crude protein per MJ digestible energy and either 14·7 or 16·8 MJ digestible energy per kg in a 2 × 2 factorial experiment until 56 days of age. There was no effect on performance or food intake when the diets were offered ad libitum, but energy intake was increased with the higher concentration of dietary energy. The higher levels of both protein and energy improved performance in a metabolism experiment with food intake restricted to 0·80 of ad libitum intake, and the higher protein level increased nitrogen retention (g/day per kg live weight) and plasma urea nitrogen. These results suggest that the level of food intake can affect the response to changes in dietary energy and protein concentrations, and indicate that conclusions from metabolism experiments using restricted feeding may be inappropriate under other conditions.