Effects of Dietary Lysine and Feed Intake on Energy Utilization and Tissue Synthesis by Broiler Chicks

Abstract

Abstract An experiment was designed to estimate changes in body composition associated with dietary lysine concentration and independent of energy intake. The hypothesis tested was at a given feed intake, the energy stored as protein (REp) would increase, and the energy stored as fat (REf) would decrease, as the dietary lysine concentration approached the requirement of the broiler chick. A comparative slaughter experiment used an initial slaughter group of 40 10-day-old male chicks, and an additional 120 chicks from the same population were used in the 10-day experiment. The dietary treatments comprised a basal diet supplemented with five levels of lysine; each of the five diets was diluted with six levels of cellulose to ensure a range of intakes under ad libitum feeding. Four individually housed chicks were assigned to each of the 30 diets. Excreta were collected daily from each bird, and at the conclusion of the experiment, the birds were killed. Carcasses were assayed for water, nitrogen, ether extract, ash, and gross energy. The gross energy of carcass fat and protein were found to be 36.19 ± .51 and 25.15 ± .30 MJ4/kg, respectively. The true metabolizable energy corrected to zero nitrogen balance (TMEn) values of the undiluted diets were independent of the lysine concentration. The lysine required for maximum weight gain was about 9.6 g/kg of diet, whereas protein accretion continued to increase at greater lysine concentrations; thus, the lysine requirement varied among response criteria. The gain in carcass fat was lowest at the two highest lysine concentrations. Multiple linear regression analysis showed that at a fixed TMEn intake, the gain of energy as protein increased, whereas that of energy as fat tended to decrease as the dietary lysine increased. At a fixed lysine intake, the change in body weight, fat energy, and protein energy all increased with increasing TMEn intake. The data thus support the basic hypothesis. The relationship between energy retained as fat and as protein was linear, but the slopes varied with dietary lysine concentrations.