Maternal supplementation with rumen-protected arginine reshapes the ileal microbiome and enhances neonatal lamb...

The nutritional status of ewes during gestation and lactation is a key determinant of lamb growth performance. Supplementation with rumen-protected L-arginine (RP-Arg) during these stages induces maternal metabolic adaptation, thereby maintaining fetal developmental homeostasis. However, the sustained effects of such metabolic regulation on postnatal lamb growth and immune functions are currently unclear. Twenty-seven pregnant Chinese Merino ewes (at 60 days of gestation) were randomly assigned to one of three dietary treatments: (1) grazing only (control, CON), (2) grazing plus 300 g/day of concentrate feed (SF), or (3) SF diet supplemented with 30 g/day of RP-Arg (ARG). When the lambs reached 14 days of age, ileal and liver tissues were collected. The ileal microbiota was characterized using 16S rRNA gene amplicon sequencing, and untargeted metabolomics was used to examine the hepatic metabolism in the lambs.

Compared with the CON group, both SF and ARG group lambs showed significantly improved early growth performance (P < 0.05), and the ARG group exhibited significantly higher average daily gain and total weight gain (net weight gain) than the SF group (P < 0.05). Milk protein content was significantly higher in the SF and ARG groups than in the CON group (P < 0.05). Notably, compared with the SF group, ARG supplementation elevated colostrum lactoferrin and insulin-like growth factor-1 (IGF-1) concentrations by 28.4% and 34.1%, respectively (P < 0.05). Compared with SF group, ARG group showed a higher relative abundance of ileal Bacteroidota (+ 40%, P < 0.05) and Prevotella (+ 96%, least discriminant analysis > 3.2), increased hepatic glutamine, methionine, and malate (variable importance in projection > 1.3, P < 0.05), and upregulated arginine-proline metabolism and ABC transporters, indicating that RP-Arg was associated with a shift in both the ileal microbiota and hepatic metabolite profile, suggestive of a modest gut-liver metabolic interaction to enhance nitrogen and energy flux, resulting in superior lamb growth.

RP-Arg specifically elevates colostrum IGF-1 and lactoferrin levels, enriches ileal Bacteroidota and Prevotella, and reprograms hepatic arginine-proline and ABC transporter metabolism. Overall, these changes were associated with an increased early growth rate of lambs without affecting milk protein production.