Lysine Needs of Starting Chicks and Subsequent Effects During the Growing Period

The lysine requirement for broiler chicks has been studied extensively. Many factors, such as protein quality, experimental conditions, dietary nutrients, and genetic strain, affect lysine needs of chicks. Because lysine increases protein synthesis and decreases protein degradation in chicks, its requirement may vary as meat-type broiler genetics are improved. Two experiments were conducted to evaluate lysine needs in the starter period in a slow maturing commercial broiler (Ross × Ross 508) and to monitor subsequent effects of lysine level on quantities of salable meat. Lysine-deficient diets (0.88% total lysine or 80% of 1994 NRC specifications) were created by blending corn, soybean meal, corn gluten meal, wheat middlings, poultry fat, and crystalline amino acids. Dietary treatments represented graduations of lysine from 80 to 130% of NRC recommendations in 10% increments from Days 1 to 18. All broilers received a common diet from Days 19 to 41 and Days 19 to 42 in Experiments 1 and 2, respectively. Quadratic response curves were fitted to growth performance criteria of chicks. Broilers fed lysine levels below NRC specifications as chicks had reduced growth and carcass attributes at Day 41. The lysine level required (95% of the upper asymptote) for chick growth responses was 107% (1.18% total lysine of diet or 1.07% digestible lysine of diet) to 111% (1.22% total lysine of diet or 1.11% digestible lysine of diet) of NRC recommendations.