Tests of two theories of food intake using growing pigs - 1. The effect ofambient temperature on the intake of foods of differing bulk content

An experiment was carried out on pigs to provide a test of two current conc eptual frameworks available for the understanding and prediction of food in take. Framework 1 assumes that food intake will be that which allows potent ial (genetic) performance to be achieved. If this is not achieved then it i s because intake is being constrained. Framework 2 sees food intake as bein g a consequence of a process of optimization such that biological efficienc y (the ratio of net energy ingested to oxygen consumed) is maximized. Both frameworks predict that a reduction in temperature will increase the intake of a high quality food. For a food of low quality framework 2 predicts tha t intake will also be increased when temperature is decreased while framewo rk 1 predicts that it will not. This difference between the predictions of the two frameworks allows them to be tested by means of an experiment in wh ich foods of different quality were given to animals at different environme ntal temperatures. Forty pigs were randomly allocated to a control (C) food based on micronize d wheat with 13.1 MJ digestible energy (DE) and 232 g crude protein (CP) pe r kg fresh food, or one of two high bulk foods. The high bulk foods contain ed either 650 g/kg of unmolassed sugar-beet pulp (SBP) or 650 g/kg of wheat bran (WB). Half the pigs were maintained at a thermoneutral temperature of 22 degreesC for a period of 14 days followed by a temperature of 22 degree sC for 14 days. Food intake was recorded daily and live weight twice weekly . There was a highly significant food x temperature interaction (P < 0.001) f or food intake. A reduction in temperature resulted in an increase in food intake on C and WB but had no effect on the intake of SBP. There was a high ly significant effect of both temperature and food on intake (P < 0.001). A reduction in temperature resulted in a significant increase in food intake , intake on WB was higher than that of either C or SBP. There was no overal l effect of temperature on live-weight gain although a reduction in tempera ture resulted in a non-significant increase in the gain of C and reduction in the gain of WB and SBP. There was a highly significant effect of food (P < 0.001) on live-weight gain, as gain on C was higher than that on either WB or SBP. The results of the experiment were in agreement with the predictions set fo rward by the first framework that growing pigs are eating to achieve maximu m performance subject to constraints.