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When compared to cows, ewes, and sows, mares experience a short interval between birth and their next heat cycle. After foaling, the uterus undergoes involution, a process that reduces uterine size, repairs uterine tissues, and restores the uterine environment to a nonpregnant state. Supporting uterine involution is critical because the 11-month gestation of the mare often makes it difficult to maintain every-year foaling, which is typically preferred by commercial breeders. In a recent study, researchers set out to determine the effects of feeding docosahexaenoic acid (DHA), an omega-3 fatty acid, on uterine involution in the weeks after foaling.*

Eighteen pregnant mares were used in this study. The mares were assigned to one of two groups, a treatment group in which a microalgae rich in DHA was fed daily at 0.6 g/kg body weight or a control group. The treatment was fed from 90 days prior to the expected foaling date until seven days after first postpartum ovulation. Otherwise, the mares were fed similarly to maintain moderate to moderately fleshy body condition, including access to Bermudagrass pasture and a commercial concentrate at a rate of 1 kg/day (2.2 lb/day) before foaling and 2 kg/day (4.4 lb/day) after foaling.

Reproductive health parameters were ascertained through rectal palpation and ultrasonographic examination, including uterine and endometrium diameters, intrauterine fluid, uterine tone, and uterine echogenicity. Echogenicity measures the ability of a tissue to reflect an ultrasound wave.

Mares fed the DHA-rich supplement had smaller uterine horn diameters after foaling compared to control mares. Interestingly, DHA-fed mares had greater uterine echogenicity scores. Low echogenicity is generally related to increased estradiol, which induces edema and estrus behavior, so researchers expected lower scores as mares readied for rebreeding.

No treatment effects were observed for the other parameters evaluated.

Researchers concluded that “supplementation with DHA during peripartum may benefit uterine involution process and odds of early conception.”

“This research adds to the emerging volume of work that indicates omega-3 fatty acids, particularly DHA, is a useful nutritional supplement for broodmares,” explained Catherine Whitehouse, M.S., a nutritionist with Kentucky Equine Research. Studies in other species show omega-3s have beneficial effects on reproduction by modifying prostaglandin synthesis and metabolism, and by regulating genes integral to uterine function.

“The source of omega-3 fatty acids is important. Choose a high-quality supplement that delivers DHA directly, such as marine-derived EO-3,” Whitehouse advised.

Further reading:

Mare Care: Improve Colostrum Quality

Broodmare Nutrition: Advantages of Feeding Omega-3s

Omegas Benefit Broodmares Year-Round

*Ferreira, J.R.D.M., S.B. Villela, C. Bianconi, M. Ormieres, G.D. de Melo, G. Pugliesi, and A.A.D.O. Gobesso. 2021. Uterine involution of mares supplemented with dietary algae-derived omega-3 fatty acids during the peripartum period. Journal of Equine Veterinary Science 106:103733.

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