Ácido guanidinoacético e metionina na alimentação de novilhos em confinamento

Abstract

The finishing phase of confined cattle is a critical period for producers, where every detail can make a difference. The search for technologies, such as the use of feed additives, to improve the performance of confined animals is constantly evolving. Guanidinoacetic acid (GAA) is a precursor of creatine, naturally produced in animals, and its supplementation has proven effective for lean mass gain in poultry and swine; however, studies are still investigating its efficacy in ruminants. The use of GAA in combination with essential amino acids, such as methionine, may improve ruminant performance due to greater nitrogen retention in the rumen. Therefore, the objective of this study was to evaluate GAA and methionine as additives in the diet of 40 Angus steers, approximately 20±2 months old and with an average initial weight of 431.9±8.89 kg, during feedlot finishing. Performance, carcass and meat characteristics, blood, and ruminal parameters were evaluated. The animals were divided into four treatments with ten replications each. The treatments were: GAA – diet with 6 grams of guanidinoacetic acid per animal/day; GAA + MET – diet with 6 grams of guanidinoacetic acid combined with 5 grams of methionine per animal/day; MET – diet with the addition of 5 grams of methionine per animal/day; and TEST – control treatment with no additives. No significant differences (P>0.05) were found for final weight (533 ±8.9 kg), dry matter intake (12.02±0.44 kg/day), average daily gain (1.32±0.06 kg/day), or feed conversion (9.27±0.54 kg of DM/day). There were no significant differences in hot (52.72%) and cold (52.10%) carcass yield, carcass conformation (11.04 points), or longissimus muscle area, which averaged 64.70±2.78 cm². Marbling had an average score of 4.83 points. Total VFA (volatile fatty acids) concentration was higher in the additive treatments compared to the control, with 60.74 mmol/L for MET+GAA, 53.83 mmol/L for GAA, and 50.81 mmol/L for MET, while the TEST treatment was 42.13 mmol/L. However, the acetate-to-propionate ratio (3.33) and ruminal pH (6.97) showed no differences (P>0.05) between treatments. In plasma metabolite analysis, blood creatinine averaged 11.73 mg/L, blood urea averaged 256.33 mg/L, and estimated urinary urea excretion was 169.56 g/day. GAA may alter the total VFA concentration in ruminal fluid, but due to the high energy level in the diet, animals receiving the additives showed no differences in performance or carcass traits compared to the control group.