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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.

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, and A. Pienkowska-Schelling. 2018. Disorder of sexual development in a mare with an unusual tentative mosaic karyotype: 63,X/64,Xdel(Y). Sexual Development. doi: 10.1159/000490861

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