Effects of dietary protein levels during early gestation on reproductive performance, oxidative stress, and placental nutrient transport in sows

Early gestation (gestation day 0 to gestation day 30) is a critical window for embryo implantation and placental development. This study evaluated the effects of maternal protein during early gestation on reproductive performance, maternal metabolism, and placental function. Forty-five sows were randomly allocated into three iso-caloric diets containing 12% (low protein, LP), 13.5% (medium protein, MP), or 15% (high protein, HP) crude protein during early gestation. Crystalline amino acids were supplemented to maintain constant ratios of standardised ileal digestible (SID) essential amino acids to lysine. The Lys:NE ratios were 2.66, 2.66, and 2.98 g SID Lys/Mcal NE, respectively. Litter size and live birth rate were not significantly affected (p > 0.05). Sows fed the HP diet exhibited increased serum alanine transaminase (ALT) (p < 0.05), elevated malondialdehyde (MDA) concentration (0.05 ≤ p < 0.10), and enhanced catalase (CAT) activity (p < 0.05) at GD 28. The LP group showed higher serum LDL (p < 0.05), HDL, and total cholesterol (0.05 ≤ p < 0.10). No differences were observed in serum glucose, insulin, progesterone (P4), oestradiol (E2) or inflammatory factor levels among groups (p > 0.05). Serum amino acid profiling revealed higher circulating levels of valine, isoleucine, leucine, tryptophan, and phenylalanine in the HP group (p < 0.05). Placental oxidative stress and nutrient transport were not affected (p > 0.05). Overall, dietary protein within 12%–15% during early gestation did not affect reproductive outcomes or placental function, but influenced maternal oxidative status, amino acid profiles, and lipid metabolism on GD 28.