A study from Brazil suggests a possible correlation between a mare’s age and the gender of her offspring.
Researchers at the Pontifical Catholic University of Minas Gerais reviewed the breeding records of nearly 60,000 Mangalarga Marchador horses born in Brazil from 1990 to 2011.
In a multi-step statistical analysis, they compared the sex ratio of offspring to the age of both sire and dam as well as to the age gap between the two. They then performed the same analysis on the records of 253 horses of various breeds foaled from 1989 to 2010.
Analysis of the combined data showed that mares older than 15 were more likely to deliver fillies than were younger mares. On the other hand, the age of the sire seemed to have only a minor effect on gender ratios.
This article first appeared in EQUUS issue #458, November 2015.