The influence of heat production on voluntary food intake in growing pigs given protein-deficient diets

Abstract

AbstractNinety-six entire male Large White XLandrace pigs were assigned at 13 kg to one of six dietary crude protein (P) treatments (230 g/kg (P1), 201 g/kg (P2), 178 g/kg (P3), 151 g/kg (P4), 125 g/kg (P5), 93 g/kg (P6)) and one of four temperatures (T) (no. = 4) (18°C, 22°C, 26°C, 30°C), and were given food ad libitum until slaughter weight of 30 kg. At all temperatures gut fill was a constant proportion of food intake (Fl) (1·56) but this ratio varied with different protein concentrations. Food intake increased with decreasing temperature and with decreasing protein content to a maximum rate on P4 (1·347 kg) whereafter FI declined. There was a linear decrease in average daily gain (ADG) with decreasing protein content while temperature had a significant curvilinear effect on ADG and food conversion ratio (FCR) with maximum ADG (0·680 kg/day) at 26°C. Body protein content decreased as the dietary protein concentration declined below P3 and there was a corresponding increase in lipid content. Temperature had no effect on body protein content but had a significant effect on lipid content. Similar trends occurred in the rate of protein (PR) and lipid (LR) retention with maximum PR (117·1 g/day) attained on PI, P2 and P3. Protein and temperature had a significant effect on total heat loss (THL). Maximum THL occurred in the protein treatment that resulted in pigs consuming maximum FI. The efficiency of protein utilization increased with increasing temperature but the response was dependent on the protein supply. It is concluded that on low protein diets pigs increase their Fl to maintain potential protein growth until a point is reached where the animal can no longer compensate and FI will decline. The extent of the compensation will depend on the amount of heat the animal can lose which in turn is dependent on the environmental temperature.