How can you tell if your mare is pregnant? Only a vet can tell you for sure if your mare is pregnant. A vet can ultrasound, palpate (feel), or blood test to confirm a mare is or is not pregnant. If you know your mare well and know her heat cycles, one less precise way to tell if a mare is pregnant is to watch and see if she comes back into heat. A pregnant mare will not show to or tease a stallion.
Do not rely on the size of your mare's belly to let you know if your mare is pregnant or not. A round looking belly can also be caused by worms or other health problems. If you want to know whether your mare is pregnant it is well worth a vet visit to confirm she's pregnant and get the mare proper care.