Longitudinal metabolic and progesterone dynamics in estrus-synchronized ewes: influence of pregnancy outcome and litter size.

Metabolic status plays a critical role in reproductive efficiency in small ruminants; however, longitudinal information describing metabolic adaptations from estrus synchronization through gestation and the immediate postpartum period remains limited. This study investigated temporal changes in selected serum metabolic and hormonal parameters in estrus-synchronized ewes and compared pregnant (PR) and non-pregnant (NPR) animals, with particular emphasis on the influence of litter size. A total of 235 ewes were synchronized during the breeding season. Of these, 150 animals (75 PR and 75 NPR) were included in the main comparative analysis, while a subset of 45 ewes (30 PR and 15 NPR) was monitored longitudinally across gestation and the early postpartum period. Blood samples were collected during synchronization (D-14 and D0), pregnancy (D35, 60, 120, and 145), and on Day 1 postpartum (1 dpp). Serum glucose, non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB), aspartate aminotransferase (AST), and progesterone concentrations were determined. Glucose concentrations at D-14 were significantly higher in ewes that subsequently established pregnancy (p<0.05). During gestation, NEFA and BHB concentrations increased progressively, with the highest values observed during late pregnancy, particularly in ewes carrying multiple fetuses (p<0.05). Serum AST activity increased moderately toward late gestation and the postpartum period but remained within physiological reference ranges. Progesterone concentrations were markedly higher in PR ewes from D35 onward (p<0.05) and were positively associated with litter size. These findings demonstrate stage-dependent metabolic adaptations and suggest that assessing pre-mating metabolic status and monitoring metabolism during late gestation may provide useful information for reproductive management, particularly in ewes carrying multiple fetuses.