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Effects of post-weaning growth rate and sexual condition on performance, carcass composition, meat quality and postmortem muscle metabolism of young Nellore cattle slaughtered at the same carcass fatness degree


Surgical castration is a practice used for decades in livestock. However, in recent years this procedure has been questioned for not addressing animal welfare issues. On the other hand, the use of non-castrated animals for meat production has been an increasing practice, as they are more efficient in transforming food into protein (muscle) of high biological value. In contrast, non-castrated animals have a more aggressive temper (making handling difficult) and deposit less fat in the carcass, impairing the quality of the meat. Recently products have been developed that make it possible for the animals to immunologically castrate, in addition to addressing animal welfare issues, they also favor fat deposition, with a positive impact on meat quality. Several studies have evaluated the effects of castration (surgical mainly) on performance and meat quality, but studies related to immunocastration are still scarce and with controversial results. Thus, this work will be carried out with the objective of evaluating the impact of rearing (intensive / extensive) and sexual condition on growth, performance, carcass characteristics, meat quality and postmortem metabolism of Nellore cattle, slaughtered young ( <24 months) and with the same degree of finishing (5-6 mm of subcutaneous fat). Our hypothesis is that animals raised intensively, fed to high-energy diets and slaughtered young ages do not differ in terms of the final meat quality. For this purpose, 72 male Nellore cattle will be used, with an initial average weight of 200 ± 30kg at the beginning of the experiment and an average age of 9 months old. The animals will be selected according to the initial weight and divided into two groups: 1) SUPL - 36 animals will be kept in pasture and will receive a protein-energetic supplement to achieve an average daily gain of approximately 0.7 kg / day; CONT - 36 animals will be kept in the pasture, receiving mineral supplementation, aiming at an average daily gain of 0.3 kg / day. The animals will remain in the pasture for approximately 9 months, and all animals from each treatment will remain in the same paddock. Sixty days before the beginning of the feedlot, 24 animals will be surgically neutered, another 24 will be immunocastrated (2 doses of immunocastration vaccine applied 30 and 60 days before the beginning of the feedlot) and another 24 will not be neutered. Subsequently, the animals will be transferred to the feedlot and fed with high concentrate diets (90%) until they reach 5-6mm of subcutaneous fat thickness, measured by ultrasound, when they will be slaughtered, to evaluate carcass characteristics and meat quality. During the rearing and feedlot phases, weighing, ultrasound and blood samples (testosterone and cortisol assessments) and temperament assessments will be carried out periodically. During the feedlot period, individual daily food intake will be recorded. After slaughter, the weight and yield of commercial cuts, quality characteristics (color, shear strength and cooking losses), sensory analysis, postmortem metabolism and degradation of myofibrillar proteins will be evaluated. Carrying out this work will bring relevant information for the meat chain as a whole and also for the scientific community, since this topic is of high interest and the results have great potential to be published in scientific journals of great impact in the area. (AU)

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