THE INFLUENCE OF HEAT-PRODUCTION ON VOLUNTARY FOOD-INTAKE IN GROWING PIGS GIVEN PROTEIN-DEFICIENT DIETS

Ninety-six entire male Large White X Landrace 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 degrees C, 22 degr ees C, 26 degrees C, 30 degrees C), and were given food ad libitum unt il slaughter weight of 30 kg. At all temperatures gut fill was a const ant proportion of food intake (FI) (1.56) but this ratio varied with d ifferent 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 a verage daily gain (ADG) with decreasing protein content while temperat ure had a significant curvilinear effect on ADG and food conversion ra tio (FCR) with maximum ADG (0.680 kg/day) at 26 degrees C. Body protei n content decreased as the dietary protein concentration declined belo w P3 and there was a corresponding increase in lipid content. Temperat ure had no effect on body protein content but had a significant effect on lipid content. Similar trends occurred in the rate of protein (PX) and lipid (LR) retention with maximum PX (117.1 g/day) attained on P1 , P2 and P3. Protein and temperature had a significant effect on total heat loss (THL). Maximum THL occurred in the protein treatment that r esulted in pigs consuming maximum FI. The efficiency of protein utiliz ation increased with increasing temperature but the response was depen dent on the protein supply. It is concluded that on low protein diets pigs increase their FI to maintain potential protein growth until a po int is reached where the animal can no longer compensate and FI will d ecline. The extent of the compensation will depend on the amount of he at the animal can lose which in turn is dependent on the environmental temperature.