Venous all the mares can be bred again on the first of every month, its called Rollover (and all horses age a year, yearly leaderboards reset etc). You can of course breed anytime assuming the mare hasn't had a foal or been used as a surrogate that year, but most people do their breeding on the 1st
I hope he does well in his show I put him in today I really hope he doesn't refuse like with his last few owners but to be honest paying his level 7 rider will drain my money -HEE Click-