Q: I’m interested in breeding a large (ideally full-sized) pony for my children. The mare that I have is a park hack, around 15.1hh. If I put her to a pony stallion will she likely have a pony foal? Or is it better to start with a pony mare?
Becks, Manawatu
Vet Dave replies:
You will typically get the midpoint between stallion and mare size when breeding with the usual variations of normal biological systems. It actually doesn’t matter who is the larger or smaller of the parents.
Horses are relatively unique as mammals, in that their simple placental unit restricts the size of the foal, so that it is born to the size of the mare’s uterus and in proportion to her pelvis size as well.
Thus there are very rarely issues like there are in cattle, where you can get a mismatch in size between the mother and baby, and problems with a baby that is too large trying to get out of a pelvis that is too small.
As a result of this placental unit, a foal from a small mare will be born smaller than that from a larger mare – irrespective of the stallion size.
However, this is only the size at birth – not the final adult heigh. Once the foal is on the ground, then genetics of the mare and stallion come into play, with the final adult height being the product of both parents.
So, for argument’s sake, a larger mare to a smaller stallion will have a larger foal at birth who will then grow a smaller amount. A similar pairing of the opposite sexing (small mare, larger stallion) will have a small foal at birth that will grow a larger amount to be roughly the same adult size.
In your case, as long as you choose a pony stallion of a sensible size, then you stand an excellent chance of producing a pony from a 15.1 hand mare.
