Desempenho e características de carcaça de suínos machos castrados da raça duroc em função dos níveis de proteína e aminoácidos

Abstract

The objective of this study was to evaluate the performance and carcass characteristics of barrows in the different phases of rearing: initial (15 to 30 kg), growth I (30 to 50 kg), growth II (50 to 70 kg) and finish (70 to 90 kg). The experiments were conducted at Swine Sector of the Universidade Federal Rural de Pernambuco (UFRPE), using 50 barrows of Duroc breed in the initial, growth I and II phases, and 25 barrows in the finish phase. The animals were distributed in a randomized design with five treatments and five replicates. The treatments consisted of diets containing five different levels of protein and digestible lysine, using the level of digestible lysine recommended by the Brazilian Tables for Poultry and Swine as the midpoint of the treatments. The parameters evaluated were as follows: performance (weight gain, feed intake and feed conversion), digestibility (crude protein and dry matter), blood parameters (urea, total protein and creatinine) in all phases of rearing, also to evaluated carcass characteristics and beef cuts (carcass yield, loin eye area, backfat thicknesss and ham yield), tissue and chemical composition of the section between the ninth and eleventh rib in the growth II and finish phases. The data collected were submitted to analysis of variance and regression as a function of the lysine levels in the diets. In the initial phase, there was an increasing linear effect for lysine consumption for apparent digestibility of dry matter and crude protein, for total protein and ureia, and decreasing effect for feed conversion. In the growth I phase, was observed a quadratic effect for weight gain, feed conversion and creatinine levels as a function of lysine levels, with estimated optimal levels of 0.925, 0.928 and 0.934%, respectively. There was also a growing linear effect for apparent digestibility of crude protein, total protein and urea. There was no effect of treatments on carcass characteristics in vivo. In the growth II phase, was observed a quadratic effect of treatments on feed intake and daily average weight gain, with optimal levels of 0.79 and 0.81% of digestible lysine, respectively. Evaluating the centesimal composition of the section between the ninth and eleventh ribs was observed a linear increase of the protein content according to the increase of lysine levels. The tissue proportion of fat, mean backfat thickness and fat area presented a significant reduction, while the yield of lean meat, amount of lean meat in the carcass and lean meat deposition rate increased linearly. The ingested nitrogen and apparent digestibility coefficient of the crude protein showed a quadratic effect according to the increase of lysine levels in the diet, while the fecal nitrogen concentration showed a linear increase. Serum levels of urea and absolute and relative weight of the kidneys were also increased. In the finish phase, there was a quadratic effect of the treatments on feed consumption with an estimated maximum level of 0.728% of digestible lysine. There was also a quadratic effect for the protein (0.715% lysine) in the centesimal composition of the section between the ninth and eleventh ribs. The levels of digestible lysine influenced in a quadratic manner the loin eye area, meat:fat ratio, lean meat yield, lean meat amount and lean meat deposition, with estimated maximum levels of 0.734%, 0.759%, 0.777%, 0.775% and 0.775% digestible lysine, respectively. The increase in the lysine level of the diets for initial phase provided positive effects at the 1.24% level for the growth I and II, and finish phases the best performance responses were at the levels of 0.93%, 0.81% and 0.77%, respectively.