Gestation time in horses is primarily determined by:
* Genetics: The mare's own genetics play the biggest role in determining her gestation length.
* Individual Variation: Even within the same breed, there can be a range of normal gestation periods.
* Environmental Factors: Factors like nutrition, stress, and health of the mare can influence the gestation length to a small degree.
While it's possible that a very old or very young sire might have some minor influence due to potential sperm health issues, this is not a well-established or significant factor.
In summary, the age of the sire is not a major factor in determining a horse's gestation time. The mare's genetics and overall health are far more influential.