Ruminally unprotected guanidinoacetic acid supply in sheep diets is effective in improving oocyte quality through mitochondrial function and by modulating regulatory gene markers that encode follicular growth, estrogen synthesis, and antiapoptotic ac

Guanidinoacetic acid (GAA), a precursor of creatine, has emerged as one of the most promising supplements for ruminants in recent years. In its rumen-unprotected form, it is effective in different aspects of animal performance, but there are still no definitive studies on its ability to modulate reproductive responses. The objective of this study was to address this gap by investigating the action of GAA on ovarian function in sheep. Twenty-three sheep were allocated into three groups and fed a total mixed ration (TMR) for 23 days. The control group (n = 6) received the basal TMR diet; the GAA1 group (n = 7) received the same diet plus 0.9 g/kg DM of GAA daily; and the GAA2 group (n = 7) received 1.8 g/kg DM. Seven days after the start of supplementation, the sheep had their follicular wave synchronized with three prostaglandin doses administered every seven days. The GAA groups showed increased diet intake and reduced adipose deposits. GAA2 resulted in a higher number of follicles > 3 mm, greater intraovarian blood perfusion, and increased follicular diameter. At oocyte retrieval, the GAA groups showed lower peripheral glutathione peroxidase and, in oocytes, higher DCF and MT test intensities. In ovarian tissue, GAA2 showed higher expression of the AMH and CCND2 genes, while both GAA groups exhibited lower CYP19A1 and AKT1 transcript levels compared to the control. We conclude that the direct use of GAA in the diet of sheep effectively enhances ovarian function and oocyte metabolic modulation.