Understanding the Genetics:
* Bay: A bay horse has a black base coat with red (chestnut) points (mane, tail, legs). They carry the dominant black (B) allele and the dominant red (E) allele.
* Grey: A grey horse carries the dominant grey (G) allele, which over time dilutes the base color to a lighter shade, eventually becoming white. Grey horses can have any base coat color underneath, including black, bay, chestnut, etc.
Possible Outcomes:
1. Grey: The most likely outcome is a grey foal. This is because the grey gene is dominant, so even with a bay parent, the grey allele will be expressed.
2. Bay with Grey Dilution: The foal might be born bay but with grey hairs already present. This grey dilution will continue over time, eventually making the horse appear grey.
3. Bay (rare): It's extremely rare, but there's a slight chance the foal could be born bay and remain bay throughout its life. This would happen if the stallion carries a recessive non-grey allele and the mare happens to be carrying two copies of the recessive non-grey allele.
Other Factors to Consider:
* The stallion's base coat: If the grey stallion is a grey over black, the chance of a black foal is higher than if he's a grey over chestnut.
* Other genes: Other genes influencing coat color like roan, sabino, or frame overo can further complicate the outcome.
In Summary:
While a grey foal is the most likely outcome, you can't definitively predict the final color. It will depend on the specific genes inherited from both parents.