|If your mare was in fact a wild species, and you included a thorough and informative note explaining such, then there is no reason for it to be removed.
If an image of a horse and it's foal were posted with no other information then this is why your image is no longer on TN.
Please also note that images of obviously wild species have been removed from TN in the past for not having any note whatsoever. The purpose of this site is for us to learn about nature through photography, so if we are not learning anything from your image and it's note then it really shouldn't be here.
I hope this helps.