Arginine Beneficial to Breeding Efficiency in Mares

Uterine fluid accumulation in mares is thought to decrease fertility and is often cited as a factor in early embryonic loss. Arginine, which is an essential amino acid in horses, is metabolized into several substrates including nitric oxide, a substance known to have vasodilatory properties and positive implications on reproductive processes. Scientists at the University of Florida hypothesized that mares supplemented daily with arginine would have increased uterine blood flow, which would hasten clearance of uterine fluid following parturition and possibly improve fertility.

Researchers placed 16 pregnant light-horse mares into a supplemented or nonsupplemented group 21 days prior to their estimated foaling date. Both groups were given a basal diet of unlimited coastal bermudagrass hay and a grain mix concentrate formulated for gestating and lactating mares, but supplemented mares also received 100 grams/day of arginine mixed into a concentrate meal. Transrectal ultrasound examination was performed on mares daily beginning the day after birth, and intrauterine fluid accumulation was estimated. Uterine artery flow was also measured.

Researchers found that mares supplemented with arginine had a significant reduction in the amount of intrauterine fluid present and increased blood flow to the previously pregnant horn. Arginine may therefore enhance fertility of mares with chronic intrauterine fluid accumulation. These researchers also investigated whether arginine supplementation of mares increased colostral immunoglobulin transfer to their foals. Arginine supplementation of mares did not enhance passive transfer of immunity to foals.

This study was presented at the 2011 Equine Science Society Symposium in Murfreesboro, Tenn. The proceedings from this symposium are available from the Journal of Equine Veterinary Science.