Effect of Letrozole Administration on Reproductive Performance and Plasma Metabolites of Ewes During Estrus Synchronization Treatment

This study investigated the effects of letrozole (LE) on reproductive performance, hormones, and plasma metabolites in Turpan Black ewes. Sixty-six multiparous non-pregnant ewes were randomly assigned to a Control group or an LE group (0.2 mg/kg body weight, added to the basal diet) for 180 days, both receiving estrus synchronization. LE significantly increased the twinning rate (p < 0.05), but no significant differences were observed in estrus rate, conception rate, or lambing rate (p > 0.05). Hormone analysis revealed significant changes in Luteinizing Hormone (LH), Progesterone (P4) (group, time, and interaction effects), Estradiol (E2), Testosterone (T) (time effect), Gonadotropin-Releasing Hormone (GnRH) (group and interaction effects), and Follicle-Stimulating Hormone (FSH) (primarily time effect). Metabolomic analysis identified 3451 differential metabolites. L-saccharopine and 5-hydroxylysine were downregulated (p < 0.01), and estrone was decreased (p < 0.05). Lysylhistidine was upregulated (p < 0.05), while testosterone and LE showed rising trends without statistical significance (p > 0.05). These metabolites were mainly enriched in amino acid metabolism and lipid metabolism pathways related to reproduction. Significant correlations were also detected between several metabolites and reproductive hormones. LE improves the twinning rate in Turpan Black ewes, likely by modulating key reproductive hormones (LH, P4, GnRH, FSH, E2, T) and altering plasma metabolites involved in amino acid and lipid metabolism. These findings provide new insights into the regulatory mechanisms of letrozole on ovine reproduction.