Effect of dietary energy, protein, and lysine content on performance and yields of two strains of male broiler chicks

In a factorial arrangement of treatments Arbor Acres and Ross male broiler chicks were given four diets with 3,200 kcal ME/kg and four diets with 2,880 kcal ME/kg two CP levels per energy level (23.1 and 33.6% in the high-energy diet and 21.0 and 29.7% in the low-energy diet) and two Lys levels per CP level per energy level (1.20 and 1.36% per CP level in the high-energy diets and 1.08 and 1.22% per CP level in the low-energy diets). The diets were given to 8 wk of age. Weight gain of Arbor Acres chicks was significantly higher (P < .05) than that of Ross chicks at 6 and 7 wk of age, but feed to gain ratios were also significantly higher (P < .05) at 6, 7, and 8 wk of age. Weight gain and feed to gain ratios were significantly better (P < .05) on the high-energy diets than on the low-energy diets at 6, 7, and 8 wk of age. With equal Lys content, the normal-CP diets gave significantly higher gains (P < .05) than the high-CP diets at 6, 7, and 8 wk of age. With equal CP content, the high-Lys diets gave significantly more gain (P < .05) than the normal-Lys diets at 6, 7, and 8 wk of age. Oven-ready and breast meat yields of Ross chicks were significantly higher (P < .001) compared with those of Arbor Acres chicks at 6, 7, and 8 wk of age and yields of edible organs, skin and fat, and remaining carcass were significantly lower (P < .05). Percentage yields of thighs, drumsticks, wings, and neck of both strains were not different at the three slaughtering ages. Significantly higher (P < .05) oven-ready yield was obtained with the high-energy, normal-CP, and high-Lys diets. Higher breast meat yield was obtained with the normal-CP and high-Lys diets (P < .05). Higher drumstick yield was obtained with the low-energy and high-CP diets (P < .05). The low-energy diets but also the high-CP diets resulted in the lowest skin and fat yield (P < .05). Most yield values were affected by age. By increasing age from 6 to 8 wk, yield of oven-ready, breast meat, thighs, skin and fat, and remaining carcass increased, but yield of edible organs, wings, and neck decreased (P < .001).