Old wives’ tale about foal gender debunked

The lunar phase at the time of a mating will not affect the sex of the resulting foal.

A new study confirms what most of us already knew: The phase of the moon at the time a mare is bred has no influence on the gender of the resulting foal.

A mare in a stall with a newborn foal
A study shows that the sex of a foal is not influenced by the lunar cycle when the mare was bred.

Researchers at the Universidad Nacional de Río Cuarto in Argentina reviewed the records of 65,535 gestations, comparing the lunar phase at the time of mating and eventual gender of the foal. The breeding information, provided by the Argentinean Stud Book, included every mating of registered Thoroughbred and Arabian horses from 2003 to 2011.

Click here to learn how the seasons affect “marish” behavior. 

Overall, 51 percent of the offspring were fillies and 49 percent were colts. These percentages remained statistically consistent regardless of lunar phases.

The researchers sum up their work by saying, “We can strongly conclude that managing the breeding dates in relation to lunar cycles in order to manipulate the sex ratio of the offspring is not a viable option in horses.”

Reference: “Lunar cycles at mating do not influence sex ratio at birth in horses,” Chronobiology International, August 2014

This article first appeared in EQUUS issue #446

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