Clue to Foal Sex Determination

Of the gaining mares, 80% gave birth to colts, while only 3% of those losing weight gave birth to colts. The relationship of body condition to gender is not as simple as this research might make it seem, although research in other species suggests there may be a link.

Studies in mice showed a shift in sex ratio when glucose levels were manipulated. Glucose levels in the blood are quickly regulated by insulin, however, so simply boosting a mare’s grain intake just before breeding is unlikely to have any certain impact on the gender of her next foal.