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by Kentucky Equine Research Staff

Conception problems are the bane of a broodmare manager’s existence.

“Broodmares are notoriously difficult to manage and early pregnancy loss occurs relatively commonly,” said Laura Petroski-Rose, B.V.M.S., a veterinarian at Kentucky Equine Research.

“Compared to mares that can’t stay in foal, failure to become pregnant is a different scenario wrought with a separate set of concerns,” she added. Reasons why mares may not become pregnant, ranging from easy fixes to the worst-case scenarios, include:

  1. The mare was not in heat when bred due to a persistent corpus luteum (hormone-producing follicle on the ovary stopping ovulation) or is in a transitional phase of estrus or even in anestrus;

  2. Silent heat, possibly because she did not like the stallion, her environment, or may be protecting her foal. Some mares never show outward signs of estrus;

  3. Negative energy balance due to insufficient intake of feed with concomitant low body condition;

  4. Poor reproductive anatomy, including a tilted vulva, which may cause pooling of urine and “windsucking,” a term used to describe noise brought about by aspiration and expulsion of air into the vagina;

  5. Cysts, growths, or scarring along the reproductive tract that hinders sperm from reaching the egg;

  6. Infections causing endometritis; and

  7. Genetic abnormalities, such as chromosomal anomalies.

Photo credit: Equine Info Exchange Staff Photographer
Photo credit: Equine Info Exchange Staff Photographer

Classic examples of genetic abnormalities causing infertility are:

  • Equine Turner’s syndrome, where a mare is missing one of her two X chromosomes, called a 63XO mutation. Horses should have 64 chromosomes, including two sex chromosomes, either XX in females or XY in males.

  • Sex reversal in which a female-appearing horse actually has XY sex chromosomes rather than XX.

Other genetic abnormalities have also been identified in mares. Recently, veterinarians described* a mare with a mixture or mosaic of two separate abnormalities: she was both a 63XO and a 64XY instead of the expected 64XX.

“While we cannot alter an infertile mare’s genetics, we can optimize mare health and nutrition in fertile mares, even those posing a challenge to successfully breed. In addition to managing intake of nutrients and overseeing body condition, consider nutritional supplements such as omega-3 fatty acids to support reproductive health,” advised Petroski-Rose. “The best source of omega-3 fatty acids is fish oil.”

Studies show that omega-3 fatty acid supplements containing both EPA and DHA, such as EO-3 created by Kentucky Equine Research, can help with improving fertility, enriching colostrum quality, and enhancing passive transfer of antibodies to foals.

*Neuhauser, S., J. Handler, C. Schelling, et al. Disorder of sexual development in a mare with an unusual tentative mosaic karyotype: 63,X/64,Xdel(Y). Sexual Development. In press.

This article is published here courtesy of Kentucky Equine Research. Visit for the latest in equine nutrition and management, and subscribe to Equinews to receive these articles directly.

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