How to Tell how Far Along a Mare is when It is Pregnant
Only your vet can tell for sure how far along a mare is when it is pregnant. This is a valuable bit of information and can be very valuable because it can give you an idea of when to expect your mare will foal. Your vet can palpate (feel) or for a little more money your vet can tell how far along your pregnant mare is, and how large and healthy the foal is, through ultrasound.
One other way to tell how far along a mare is when it is pregnant is to calculate the number of days since the horse was bred- or from when you suspect she may have been bred- the average gestation period for a horse is 340 days.