The national beef cattle production is characterized by almost exclusively on pasture- systems. Usually, the production of meat are conducted under extensive systems and in central Brazil during the dry period there is a drop in both the availability and quality of tropical pastures, favoring weight loss of animals, increasing age at slaughter, leading to production of meat and carcass with low quality. Supplementation during the dry period is intended to reduce the slaughter age and thereby improve the quality of meat and carcass meat producing species. Myosin is the most abundant protein in skeletal muscle and has a crucial role in the process of muscle contraction, each molecule consists of two heavy chains (MyHC) and two identical pairs, not identical myosin light chain (MyLC). The MyHC has different isoforms: type I (slow), IIA, IIb, IIx / IId, and IIm order to identify and differentiate these proteins in animals from which meat is to correlate the evidence or the proportion of each isoform with the qualitative characteristics of the product end. The objective of this project is characterize the isoforms of myosin heavy chain of the Longissimus dorsi and Semitendinosus and evaluate its relationship with meat quality in cattle (steers and heifers) finished in pasture during the dry period with supplementation. The experiment will be conducted at APTA - Polo's Far West Regional. The design is a randomized block design with three replications in a factorial 2 x 2, two categories of beef cattle (steers and heifers) and two muscles (longissimus dorsi and semitendinosus), a total of four treatments. Eighteen beef cattle Guzera (18 steers and 18 heifers) will be used in the finishing phase, with initial average weight is 330 to 370 kg, respectively, with approximately 18 months old. The animals will be supplemented by 0.8% of body weight. Will be evaluated the pH, ribeye area, fat thickness, marbling, color, tenderness and myosin heavy chain evaluated by SDS-PAGE electrophoresis. The data will be subjected to statistical analysis using the program R (R Development Core Team, 2006) to perform the analysis of variance and Tukey test at a significance level of 5%. Will be calculated the correlation between the isoforms of myosin heavy chain (MyHC) and the quality.
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