Getting the Mare Ready

So, once the method and means by which the semen is available is determined, the next step is to worry about the mare. If you are simply breeding a mare that will carry her own foal, the timing is not as critical as embryo transfer donor mares. Mares will not come into heat or go into estrus during the off season, so once breeding season has begun, you will know because your mares will be cycling. When mares are cycling and getting ready to breed, they will be able to tease with a stallion. If a mare is visibly in heat then a veterinarian should check her with an ultrasound. To walk you through this step by step, the veterinarian wears a palpation sleeve, which is clear plastic like saran wrap but does not cling. This sleeve goes all the way up the arm. The veterinarian pumps a handful of lubricant onto the sleeve and insert it into the rectum of the mare. The mares that are being checked are situated in a stocks which is a large structure with poles that are about 8-10 feet high. The poles are welded to create a box-like canopy which has two doors, one on either end. The mare is led through one door and stopped before going through the other door. When both gates are closed, the horse’s head is usually tied (unless the horse will freak out). The back gate is closed and on an average sized mare this will reach mid-flank. There is also a chest rope that goes across the chest of the mare and holds her back so that the veterinarian is able to reach deep enough. Once the horse and the veterinarian is ready, he or she cleans out the rectum and lower colon simply by reaching in and removing any fecal matter. This is done so that when the ultrasound is used, it is able to detect objects through the walls of the intestine. The ultrasound probe is inserted into the rectum and by precise positioning, the veterinarian can view the uterus and ovaries.

When a mare is in heat and getting ready to be bred, she will start off having many small follicles on both of her ovaries. As time goes on and depending on the particular horse, one or two of the follicles will grow while the others shrink. At the time of breeding, there will be one dominant follicle larger than 35mm. The veterinarian is able to find the follicle with the ultrasound and can measure it using tools on the screen. To the untrained eye it will look like a large, black bubble. As discussed earlier, sometimes to have a better likelihood that the mare will get pregnant on the first time, breeders will breed before and after ovulation. To tell if a mare has ovulated, the veterinarian must check the ovary with the dominant follicle many times a day.