A mare will usually quit having her estrus (heat cycle). There are some mares that will still show signs of estrus during pregnancy. Usually it isn't as strong in outward physical signs as she was before breeding. The best way to confirm pregnancy is done by rectal palpation. A good technician ot Vet can usually palpate and find a pregnancy 30-45 after breeding. Late in gestation (last 2 months) most mares will develop a pregnancy belly, and sometimes (not always) the foal can be felt/ seen moving on the lower rear hals fo the underline.
Signs of parturition (labor): Most mares will develop small beads of wax on the very tip of the teats any where from ours up to 2 weeks prior to labor starting. The color of fluid expressed from the teat will change from clear to> yellowish> to murky yeallow> to white, the closer parturition timeapproches. If the owner/manager will express a FEW drops of fluid into the palm of the hand each day, they can watch this color change in the milk. Some mares will start to drip just before labor (not all do this though). Most mares will go off feed 8-24 hours, they will also become quiet then a little restless, getting up and down as the labor actually starts. They usually will look back at their stomach and then lay down and some will go flat on their side. Heavy breathing and groaning will occur as the foal moves down the birth canal. Once the mare is actively pushing the foal out, it should take not much more than 15 to 20 minutes for the foal to be delivered. In the event that the foal is not presented in this time it is crucial to have someone trained or very experienced to evaluate the foals position to besure it isn't a dystocia delivery which would require intervention.
Once born it is very important that a foal receive 4-8 ounces of colostrum milk to receive it's mothers antibodies before the gut is unable to absorbe any longer.