In the past I once did breed a 31 1/2 inch mare to a 32" stallion,- and had major problems foaling her out..(She had two successful previous births with a smaller stallion, w/no problems)
Had I not been there, this time to assist the foaling,- both mare and foal would have been lost.. Her foal was locked up inside her, and it was not an easy birth.. After many prayers, and quite a struggle, with the poor mare,- we got things back under control..
Since then, I have changed my "breeding stradegy", with the sizes I am breeding,...and so far so good..
:
Now I prefer to breed the "taller end of the A division", or the B-sized mares with a 30" stallion..
My first foal this season came accidently unattended, but with no complications,- as the mare had everything under control by the time I found the foal..alive and nursing, on its own..(baby in avatar)
My second mare is even taller (abt 36") and isnt due until April, so we still have more time to go with her.
I am more comfortable with the "bigger mare, vs. smaller stallion" situtation, as I believe it contributes to the safety of a positive foaling outcome.
: JMO