Guanidinoacetic Acid Improves Growth Performance and Gut Health of Broilers Fed Metabolizable Energy-Reduced Diets

This study was conducted to evaluate the effects of guanidinoacetic acid (GAA) supplementation to diets with different energy levels on growth performance, carcass traits, and gut health status in broiler chickens. A total of 9500 1-day-old Ross 308 broilers (equal numbers of males and females) were allocated to 1 of 5 dietary treatments (10 replicate pens per treatment; 190 broilers per pen) for 41 days. Experimental diets included a positive control (PC) with standard metabolizable energy (ME); negative controls with PC -50 kcal/kg ME (NC1) or -75 kcal/kg ME (NC2); and NC1 and NC2 supplemented with 0.06% GAA. Reducing dietary ME by both 50 and 75 kcal/kg significantly increased feed conversion ratio (FCR) during the finisher phase (25-41 days) and across the entire growth period (0-41 days) (p < 0.05). GAA supplementation in the low-energy diets significantly decreased FCR (p < 0.05), but did not differ significantly from the PC group (p > 0.05) during the respective periods. Dietary treatments had no significant effects on carcass yield, cut yields and abdominal fat percentage (p > 0.05). The relative liver weight increased significantly in all treatment groups compared to the positive control group (p < 0.05). Compared with the PC diet, the villus surface area was significantly reduced in both the NC1 and NC2 diets, while only the NC2 diet resulted in a significant decrease in the number of goblet cells (p < 0.05). GAA supplementation to NC2 significantly improved the villus height-to-crypt depth ratio, villus surface area and goblet cell number in the jejunum (p < 0.05). Lactobacillus and coliform counts were not affected by dietary treatments (p > 0.05), whereas total aerobic counts increased significantly (p < 0.05) in the NC2 + GAA group compared with NC1. Reducing dietary energy by 50 kcal/kg led to a significant decrease in short-chain fatty acid levels, whereas GAA supplementation increased those levels in both low-energy diets (p < 0.05). Conversely, branched-chain fatty acid concentrations were not significantly affected by dietary treatments (p > 0.05). The results indicate that dietary energy reduction adversely affected growth performance and gut health, whereas GAA supplementation compensated for these effects. Furthermore, the inclusion of 0.06% GAA can spare up to 75 kcal ME/kg in broiler diets, while maintaining growth performance and, to some extent, improving gut health.