I bought a weanling last year but didn't get to pick her up until this fall. She was a little thinish when we got her so started feeding to build her up. She is developing a big belly but not anything else. She isn't getting free choice hay so I don't think it is a hay belly. To me it looks like a "baby belly" but I'm seriously hoping not. She was a year in April. Not any vets close enough to do an ultrasound that I trust. Being here with 3 boys she hasn't shown any heat like the other mares have.