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A systems biology approach applied to guanidine acetic acid nutrition in the growing and finishing stages of Nellore bulls


The Rearing is a period of greater animal growth, however, it is the longest phase in the beef cattle production cycle. This is because this rearing phase is carried out in pasture systems, in which the seasonality in the supply and quality of forages interferes with the growth of the animal. On the other hand, as the animal approaches maturity, there is a slowdown in growth rate and changes in gain composition, requiring more energy to meet performance demands. Several feeding strategies in rearing, mainly with protein and energy-based supplements and in different offers, are currently used to improve growth, reduce the production cycle and bring earlier animals to slaughter to enhance the quality of the meat. In addition, feed additives such as guanidine acetic acid are used in medicine for treatments to prevent muscle atrophy and as hypertrophy stimulants in individuals who perform physical activity. Also, this compound has been used in poultry and swine production, and recently in cattle, only in feedlot finishing to improve performance. This proposal aims to evaluate the biological and metabolic mechanisms and the animal response to nutrition with guanidine acetic acid during the growth and finishing stages in Nellore bulls through a systems biology approach. Forty-eight newly weaned Nellore calves weighing approximately 210 kg and eight months of age will be housed in 12 paddocks with Brachiaria spp. Before starting the experimental period, calves will be weighed, blocked, and randomly assigned to four treatments. A single protein supplement (29% CP) and a single finishing diet will be used in the growing phase. On the supplement and termination diet, three doses of guanidine acetic acid will be included for each phase as follows: AGA3 (Supplement: 0.3%/kg DM; termination diet: 0.03%/kg DM), AGA6 (Supplement: 0.6%/kg DM; finishing diet: 0.06%/kg DM), AGA9 (Supplement: 0.9%/kg DM; finishing diet: 0.09%/kg DM) and CON (Supplement and finishing diet without guanidine acetic acid). During the rearing phase, the animals will be weighed every 28 days, and at the finishing phase, the weights will be recorded at the beginning, middle, and end of the feedlot. From the recorded weights, calculations of daily weight gain and feed efficiency will be performed, and for the finishing phase, the carcass weight gain yield will be estimated. Ultrasound measurements such as loin eye area and subcutaneous fat thickness will be obtained in the Longissimus thoracis muscle between the 12th and 13th ribs and fat thickness in the rump steak in the biceps femoris muscle. Additionally, at the end of the rearing phase and during slaughter, liver, plasma, and Longissimus thoracis muscle samples on the right side will be collected for gene expression, proteomics, and metabolomics analysis. At slaughter, the carcass weight will be recorded for carcass yield calculations, and later the cold carcass weight for cooling losses. The pH and temperature of the carcasses will be recorded after the animal is skinned and 24 hours post-mortem. Meat samples will be collected for analysis of the chemical composition, color, shear force, cooking losses, and sarcomere length. The expected results in this research will be earlier animals for slaughter, improving the qualitative characteristics of the meat, as well as a faster return on investment associated with a short production cycle. (AU)

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