Avaliação de diferentes concentrações de nitrogênio não proteico em suplementos para bovinos de corte

Abstract

The aim of this study was to evaluate the increasing effect of non-protein nitrogen (NPN) in supplements and maturation times on performance, carcass and physicalchemical characteristics of non-castrated beef ½ Angus × ½ Nellore. Thirty-six ½ Angus × ½ Nellore animals were used, with final average body weight of 496.46 (20.28) kg and 20 months of age, in a completely randomized experimental design (CRD), with four treatments, nine replicates and one bovine per experimental unit (EU). The treatments consisted of four diets: t1: diet without supplementation (WS), exclusive the pasture of Brachiaria brizantha cv. Xaraés; t2: diet with 5.0% NPN (low NPN); t3: diet with 13.1% NPN (medium NPN) and t4: diet with 24.0% NPN (high NPN) in the supplement. All animals received mineral supplementation ad libitum. There was no effect (p > 0.05) of the treatments on weight loss of cooled carcass, meat color (L*, a* and b*), fat color (a_F and b_F), color of steaks (L**, a** and b**), hot carcass pH, subcutaneous fat thickness, cold carcass temperature, drip water loss, loss of liquid by thawing and ether extract. Steers fed pasture (WS) presented the lowest values (p < 0.05) of final body weight, hot carcass weight and cooled carcass weight, in addition to meats with darker (L*) and less red (a*) coloration. Cattle fed diets containing low and medium NPN presented the highest averages (p < 0.05) of carcass yields (CY). In a second trial, the same 36 animals were used, which gave rise to 108 Longissimus dorsi muscle meat steaks, in CRD and factorial scheme, with twelve treatments, from eight to nine replicates and one bovine per EU. The treatments consisted of the combination of the four diets described above and three maturation times (MT; 3rd, 9th and 16th day). MT altered (p < 0.05) the luminosity (L**) and red content (a**) of the steaks, because the highest values occurred between 9 and 16 days. Regardless of NPN concentrations, the average shear force of the meat of the animals on the 3rd day was 3.61 kgf/cm3, a value higher than the average value observed in steaks stored on the 16th day (2.48 kgf/cm3). The difference of 1.13 kgf/cm3 between the 3rd and 16th day indicated that maturation promotes meat tenderization. Crusaders ½ Angus × ½ Nellore supplemented with low and medium NPN concentration in diets present better CY, heavier steaks and more pronounced red color intensity than animals receiving WS diets and with high NPN.