Exigência de lisina digestível para frangos de corte de menor potencial genético para crescimento

Abstract

Lysine is an essential amino acid used as a reference in diets based on the ideal protein concept. Determining the actual requirement for lysine is of great importance to formulate efficient feed without amino acids limitation or excesses. Three experiments were conducted in the Poultry Complex of Integrated Production Centre at Federal Rural University of Rio de Janeiro, objecting to estimate the digestible lysine requirements to broilers of low genetic potential for growth through the assessment of performance, carcass characteristics and breast meat quality. The first experiment corresponds to growth phase I (29-49 days), the second growth phase II (50-69 days) and the third final phase (70-84 days), where during each experiment was used different chickens. All experiments were conducted in a completely randomized design, with five treatments, four replications and twenty experimental units. The treatments were set with increasing lysine amounts obtained from the addition of L-Lysine HCl to the basal diet, replacing the ingredient corn starch as follows: 0.871, 1.011, 1.151, 1.291 and 1.431% in the growth phase I; 0.803, 0.943, 1.083, 1.223 and 1.363% in the growth phase II; and 0.766, 0.906, 1.046, 1.186% and 1.326% in the final phase. At the three stages studied, the lysine values nfluenced quadratically feed intake, weight gain and feed conversion. Lysine intake increased with enhanced amounts of lysine, however, it was detected a decrease in its usage efficiency. It was possible to measure the nutritional requirements for feed intake (1.298, 1.109, 1.150%), weight gain (1.183, 1.199, 1.162%) and feed conversion (1.203, 1.162, 1.126%), respectively for the growth phases I, II and final. The absolute weight as well as carcass and cuts yield were influenced by digestible lysine values of rations, where the highest carcass yield for growth phase I (73.62%) was estimated in the value of 1.162%, growth phase II (74.24%) in the value of 1.068%, and final phase (69.34%) in the value of 1.065% for digestible lysine. For chemical composition of breast meat, birds slaughtered at 70 days of age (growth phase II) was observed linear increase in moisture percentage and crude protein, and reduction the ether extract percentage. Nevertheless, it was not observed significant effect of broilers slaughtered at 85 days of age (final phase). For birds slaughtered at 70 and 85 days of age, the weight loss was significant by thawing and cooking the breast meat, increasing as improved lysine values. Therefore, optimizing feed conversion of Redbro Plumé broilers might be recommended, respectively, 1.203, 1.162, and 1.126% of lysine in the diet at phases 29 to 49, 50 to 69, and 70 to 84 days of age, corresponding to a proportion of digestible lysine:crude protein 6.09, 6.34, and 6.36%.