PSXII-7 Effects of maternal supplementation of Guanidinoacetic acid at late gestation on skeletal muscle growth and metabolism in beef offspring.

Abstract Maternal nutrition during gestation plays a crucial role in fetal programming, influencing offspring growth and metabolism. Guanidinoacetic acid (GAA) serves as a creatine precursor and as arginine spare molecule, potentially enhancing energy metabolism and muscle development. However, its application in cow-calf performance remains largely unexplored. This study aimed to evaluate the effects of maternal GAA supplementation during late gestation on skeletal muscle growth and adipogenesis in beef calves. Twenty-four pregnant Brahman cows (532 ± 15.1 kg), pregnant of a same sire, carrying male (n = 12) or female (n = 12) fetuses were used. The basal diet (DM basis) included 688 g/kg corn silage, 147 g/kg sugarcane bagasse, 47.7 g/kg corn, 89.6 g/kg soybean meal, 6.86 g/kg urea, and 21.2 g/kg mineral mixture. Cows received the experimental diets from days 180 to 270 of gestation, with treatments consisting of either a control diet (no GAA) or a diet supplemented with 0.2% GAA (DM Basis). At 45 days postpartum, Longissimus lumborum muscle samples were collected via biopsy for mRNA expression and protein abundance analysis. All statistical analyses were performed in SAS Studio, in a mixed model including the fixed effects of treatment and offspring sex, and the random effect of gestation group. A treatment × sex interaction was observed (P = 0.02) for both Akt and mTOR activity, with higher p-Akt/Akt in GAA male calves and greater p-mTOR/mTOR in GAA female calves. Additionally, MYOD1 mRNA expression was upregulated in GAA calves (P = 0.01), whereas MYOG remained unchanged (P = 0.14), suggesting an extended myogenic proliferation phase. PAX7 protein levels tended to be higher in GAA calves (P = 0.07), while PAX3 abundance was reduced (P = 0.01), indicating potential shifts in satellite cell dynamics. No differences were detected for the abundance of adipogenic markers DLK1 (P = 0.10), PPARγ (P = 0.10), or PDGFRα (P = 0.29). These findings suggest that maternal GAA supplementation enhances muscle development in offspring, potentially through Akt/mTOR activation and myogenic regulation, without affecting intramuscular adipogenesis.