ENERGY-METABOLISM AND PROTEIN BALANCE IN GROWING RATS HOUSED IN 18-DEGREES-C OR 28-DEGREES-C ENVIRONMENTS AND FED DIFFERENT LEVELS OF DIETARY-PROTEIN

A study was performed to investigate the effect of environmental tempe rature and increasing levels of protein in the diet on visceral organ size, digestibility, protein balance and energy metabolism in rats. Th irty-six male Wistar rats, initial body weight 77-80 g, were used in a factorial design consisting of three levels of dietary protein and tw o environmental temperatures of either 18 or 28 degrees C. Three fish meal-based diets were prepared to contain 91, 171 and 262 g protein (N x 6.25/kg diet). Gas-exchange measurements were made and urine and fe ces were quantitatively collected. The weights of the visceral organs from rats housed at 18 degrees C were greater (P < 0.05) than those of rats housed at 28 degrees C. The digestibilities of dry matter and pr otein were not affected by environmental temperature, whereas fat and energy digestibilities were higher (P < 0.05) at 18 degrees C than at 28 degrees C. As the level of protein was increased, the digestibiliti es of protein, energy and Pat increased (P < 0.05). Protein intake and protein retention were higher at 18 degrees C (P < 0.05) than at 28 d egrees C and increased (P < 0.05) as dietary protein concentration inc reased. Apparent biological value was lower (P < 0.05) at 18 degrees C than at 28 degrees C and decreased (P < 0.05) as dietary protein leve l increased. Heat production as a percentage of metabolizabIe energy w as higher (P < 0.05) for the low protein diet than for the medium and high protein diets. The efficiency of energy utilization was depressed (P < 0.05) for the high protein diet when rats were kept at 28 degree s C. The results suggest that thermogenesis was induced when low prote in was fed, The increase in thermogenesis may have been important in r egulating energy balance and maintaining a constant body temperature i n a cold environment.