Researchers: Mare's Condition Appears to Impact Sex of Foal

A recent study of wild horses in New Zealand has found that broodmares that are healthiest at the time of conception are more likely to have colts.

The study, conducted by researchers Elissa Cameron, MSc, PhD, and Wayne Linklater, PhD, found a striking correlation between the change in a mare's condition and the sex of her foal. In mares that were gaining weight at the time of conception, 80% had a colt, while only 3% who were losing weight gave birth to a colt. The reason for this, the researchers hypothesize, is that strong mares will produce strong foals, and a strong colt would be able to spread the mare's bloodlines more than a strong filly.

Cameron said she believes it is the change in the mother's condition that might determine the sex of the foal. She hopes one day this can be applied to the breeding management of domestic horses, but at present, the mechanism that might be causing this relationship isn't understood.

"It appears that glucose may play a role as we manipulated glucose levels in mice and got a shift in sex ratio," Cameron said. "However the relationship is complicated, especially if it is driven by glucose levels since glucose is pretty well regulated by insulin."

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Liz Brown

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