Maternal methionine supplementation in low-protein diets during late gestation and lactation increases performance and alters fecal microbiota of sows and their offspring.

Methionine (Met) is known to enhance antioxidant defense and reproductive efficiency in sows, but its role under low-protein feeding conditions is unclear. This study evaluated the effects of Met supplementation on lactation performance, antioxidant status, and gut microbiota of sows and their offspring. Sixty-six multiparous sows with two parity and similar body weight (244.1 ± 1.73 kg) were assigned to a normal protein diet (18% crude protein [CP]) or low-protein diets (15% CP) containing graded standardized ileal digestible (SID) Met levels (0.23%, 0.30%, 0.37%, 0.44%, and 0.51%, respectively) from d 107 of gestation to d 21 of lactation, with 11 replicates in each group and one sow per replicate. The results showed that sows fed low-protein diets supplemented with 0.30% Met achieved milk yields and piglet growth comparable to those of the normal protein group (P > 0.05). In addition, 0.30% Met supplementation reduced serum urea nitrogen content, enhanced the concentrations of milk immunoglobulin M, glutathione, and taurine, and increased the activities of serum total superoxide dismutase in sows and glutathione peroxidase in piglets when compared with the normal protein diet (P < 0.05). Microbiome analysis indicated higher relative abundance of Christensenellaceae _R-7_group in piglets from the 0.30% Met group, and this relative abundance was positively correlated with growth traits. These findings suggest that supplementation with 0.30% Met within the 15% CP diet supports sow performance and piglet development comparable to normal protein feeding, via enhanced antioxidant capacity and favorable modulation of gut microbiota.