Redução do nível de proteína bruta e inclusão de volumoso em dieta de alto grão na terminação de novilhas nelore

Abstract

The aim of this study was to evaluate the effect of the reduction in crude protein content and the inclusion of roughage in high-grain diets on intake, performance, digestibility, blood parameters, ingestion behavior and carcass and meat traits of feedlot heifers. Thirty-six Nellore heifers aged between 16 and 18 months and initial body weight of 268.1 kg ± 26.9 kg were used, in a 2 x 2 factorial design, two levels of CP 130 and 110 g.kg-1 of DM and the inclusion or not of 100 g.kg-1 of DM grass silage Megathyrsus maximus cv. Mombasa. The feedlot lasted 89 days, 75 days of trail period. The animals were slaughtered in a commercial slaughterhouse located in the city of Araguaina, TO. The diets inclusion of roughage increased (P<0.05) the intake of dry matter and neutral detergent fiber. The reduction in the CP level reduced (P<0.05) the protein intake and increase (P<0.05) neutral detergent fiber intake, however, it allowed the maintenance of dry matter intake (P>0 .05). Final weight (361.9 kg) and average daily gain (1.27 kg.day-1 ) were not changed by treatments (P >0.05). The protein feed efficiency increased (P<0.05) in lower levels of protein, 1.62 vs. 1.88 kg of gain.kg-1 of CP ingested for treatments with 130 and 110 g of CP.kg-1 of DM, respectively. The inclusion of roughage reduced (P<0.05) the dry matter feed efficiency (0.24 vs. 0.18 kg of gain.kg-1 DM ingested), the protein feed efficiency (1.28 vs. 1.58 kg of gain.kg-1 of CP ingested) and the weight gain rate (0.41 vs. 0.36% BW.day-1 ). Reducing protein content of diet reduced plasma urea levels (P>0.05) and forage inclusion reduced glucose and increased triglycerides of plasm (P<0.05). The apparent digestibility coefficient of dry matter, crude protein, ether extract and neutral detergent fiber were reduced (P<0.05) with the reduction of the crude protein level, while the inclusion of roughage reduced the ether extract digestibility coefficient (P<0.05). Longer rumination time was observed for diets roughage, as well as the number of mericic chews (P<0.05). The levels of crudeprotein and the inclusion of roughage in the diets did not influence the carcass characteristics (P>0.05), with an average of 193.98 kg of hot carcass weight; 53.68% of carcass yield and 6.38 mm of subcutaneous fat thickness. For the physical composition of the carcass and its relationships, the treatments did not differ (p>0.05). The was no influence (P>0.05) of the crude protein (P>0.05), withaverages of 7.21 kf.cm2 of shear force and 2.4 marbling points. The inclusion of forage in the diet increased the shear force (7.80 vs. 6.62 kf.cm2 ), the red index of color (12 vs. 9.80) and the chroma (18.35 vs. 16.96), also it reduced the fat hue (49.25 vs. 54.68). There was no influence of roughage use in the chemical meat composition. The reduction in the dietary protein level from 130 g to 110 g CP.kg 1 DM for Nellore heifers feedlot finished on whole grain diets allows the maintenance of dry matter, energy intakes and animal performance, and does not change the carcass and meat traits of heifers finished in feedlot with high grain diet, preserving the weight of hot carcass and subcutaneous fat thickness. The inclusion of 100 g.kg-1 of roughage DM in high-grain diets in feedlot provides longer rumination time and increased dry matter intake, but maintains the weight gain of the animals, which reduces the efficiency of use of dry matter, as well as the weight gain rate and did not change the carcass traits, however it changed the fat color and increased the meat shear force.