The effects of citrulline on horse milk components and fecal metabolism were analyzed based on LC-MS and 16s amplicon.

Abstract

BACKGROUND: The lactation period in mares is critical, as it significantly influences foal health and subsequent reproductive outcomes. Developing a precise nutritional strategy for lactating mares is a primary research focus. L-citrulline, a bioactivenon-protein amino acid and precursor to arginine, has been shown to enhance mammary blood flow and reduce oxidative stress, yielding promising results in livestock lactation studies. However, research on its effects in Equus species remains limited. There is a notable gap in data regarding its impact on lactation performance blood biochemistry, and its role in the fecal microbiota and metabolism of mares. This study, therefore, seeks to explore the effects of L-citrulline supplementation on lactation performance, foal growth, fecal microbiota, and metabolomic profiles in grazing lactating mares, aiming to establish a foundation for dietary optimization and he advancement of the horse industry. RESULTS: In this study, 32 lactating mares were selected and assigned to a control group (no amino acid supplementation) and experimental groups I, II, and III (15&#xa0;g/d, 30&#xa0;g/d, and 45&#xa0;g/d of L-citrulline respectively) under identical grazing conditions, with 8 mares per group. The results demonstrated a significant increase in milk production for mares in group II (30&#xa0;g/d) (P&#x2009;<&#x2009;0.01). Additionally, milk fat percentage, foal weight and body size were higher in all experimental groups compared to the control group. Blood levels of lactate dehydrogenase and creatine kinase were extremely significantly lower in the experimental groups than in the control group. To further explore the effects of L-citrulline on fecal microbiota and metabolites,16&#xa0;S rDNA sequencing and LC-MS/MS analysis were performed on the control group and the experimental group receiving 30&#xa0;g/d (which showed the most pronounced lactation response). The microbiota level, analysis revealed Firmicutes as the dominant phylum, with significant differences in the species F082 and the genus Ruminococcaceae_bacterium_AE2021. Tax4Fun functional annotation showed the highest gene function abundance in digestive metabolism, genetic information processing and environmental information processing pathways. LC-MS/MS analysis identified differential metabolites primarily associated with biological systems and metabolism. In conclusion, L-citrulline supplementation in grazing lactating mares increased milk production, improved milk fat quality, and enhanced foal weight and body size. CONCLUSION: L-citrulline supplementation enhances milk production in mares, improves milk fat, quality, reduces lactate dehydrogenase and creatine kinase levels in the blood, and promote the growth and development of lactating foals.