Lysine requirements of fast- and slow-growing broiler chicks.

Experiments were conducted to determine the lysine requirement of fast-growing (Hubbard x Hubbard) and slow-growing (New Hampshire x Columbian) broiler chicks during the period 8 to 21 days posthatching. A lysine-deficient diet (.51% digestible lysine; 23% CP; 3,200 kcal MEn/kg) based upon corn, feather meal, and soybean meal was supplemented with 10 graded increments of L-lysine.HCl to produce three- to fourfold responses in weight gain. Requirements for digestible lysine were determined to be not greater than 1.01% of the diet for maximal weight gain of both strains. Maximal gain:feed ratio was achieved in both strains at a digestible lysine level not greater than 1.21% of the diet. Daily feed consumption of the fast-growing strain was over twice that of the slow-growing strain, and the digestible lysine requirement for maximal feed efficiency was 675 mg/day for fast-growing chicks compared with 318 mg/day for slow-growing chicks. The portion of the weight gain comprised of protein was roughly the same in both strains. It is evident that the slow-growing crossbred broiler strain. Translating the digestible lysine requirement of 1.21% of the diet to practice, wherein a corn and soybean meal diet would be fed, results in a total lysine requirement of 1.41% of the diet (for maximal feed efficiency) during the broiler chick's 2nd and 3rd wk of life.