The objective of this work was to evaluate the effect of immunocastration and the use of mineral supplementation with grain, on Massai grass pastures (Megathyrsus maximus) during the rainy season, on the performance, blood biochemical profile and carcass and meat characteristic of ½ Nelore X Limousin heifers. Twenty-eight animals were used, with mean age and initial weight of 13 months and 217 kg, respectively. A completely randomized design with four treatments distributed in a 2 x 2 factorial arrangement was used, two sexual conditions (immunocastrated and non-castrated) and two types of supplementation (mineral supplementation with grain and common mineral). The mineral supplement with grain and the common mineral supplement were supplied in quantity 75 g and 25 g/100 kg body weight, respectively. The immunocastration method consisted of two doses (initial and booster) of the anti-GnRH vaccine Bopriva®, 1 ml in each animal belonging to this treatment, administered subcutaneously. At the end of the experiment the animals were taken to the commercial slaughterhouse located in the city of Araguaína-TO. The slaughter took place following the standards of the industry. Heifers were approximately 18 months old and had no definitive tweezers (zero tooth). There was interaction (P<0.10) of the factors studied for the variables of final body weight and total weight gain, in which the immunocast heifers supplemented mineral supplement with grain promoted lower FBW and TWG (324.27 and 106.57, respectively), compared to uncastrated heifers, and equally supplemented (342.86 and 126.86 kg, respectively). The mean daily gain was influenced by the sexual status (P<0.10), in which immunocastration in heifers resulted in lower performance when compared to uncastrated heifers (0.788 vs 0.860 kg/day). Sexual condition and type of supplement did not influence serum levels of glucose, triglyceride, albumin, total protein and creatine. However, there was interaction (P<0.10) between the factors studied for alkaline phosphatase, cholesterol, plasma urea, alanine aminotransferase enzyme and aspartate aminotransferase. The uncastrated heifers that received mineral supplementation with grain showed higher serum levels of urea than the other treatments. There was interaction (P<0.10) between the type of supplement and the sexual condition for ribeye area and hot carcass weight, in which the immunocast heifers treated with common mineral supplement presented higher RA (63.72 cm2) in compared to uncastrated heifers also supplemented with common mineral (55.80 cm2). Immunocast heifers that received mineral supplementation with grain obtained lower HCW (167.07 kg) compared to non-immunocastrated heifers equally supplemented (174.71 kg). The method of immunocastration associated with the mineral supplement with grain provided a mean of 4.67 kgF/cm2 for shear force, being the only treatment to reach classification of soft meat, according to the literature. The uncastrated heifers receiving a mineral supplement with grain had a lower index of yellow of the meat, but all the treatments maintained the coloration of the appropriate meat. The use of immunocastration associated with the mineral supplement with grain provides a lower of hot carcass weight, however, does not affect its yield and allows the production of quality meat.
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