To breed or not to breed is a question that every mare owner asks herself in the spring, especially after seeing those adorable foals running around at the neighbor's farm.  After you decide to breed and you've picked out a beautiful stallion, hopefully your mare will get pregnant immediately.  If she doesn't get pregnant or even come into estrous, here are some common reasons. 

Horses don't all come with a good history.  If your mare doesn't come into heat, could it be that she is already pregnant?  Every year we find some mares that aren't supposed to be pregnant, yet are.  How can you tell if your mare is already pregnant?  If one day there is a foal by her side, the answer is obvious.  If she is just big, she could be pregnant or may just have a big hay belly, so palpation by a veterinarian will answer that question. 

Horses all become a year older on January 1, so if the plan is for this foal to race or show, competing against horses of the same age, it is beneficial for the foal to be born early in the year.  Mares may not cooperate with this plan, as the increase in daylight hours is what induces them to start cycling again after their ovaries have shut down for the winter.  There are ways to fool these mares into thinking that spring has arrived.  The easiest way is to leave the lights on at the end of the day, making the entire day 16 hours long.  A 200 watt bulb over the stall is sufficient to do this.  We can also try using hormones to induce cycling, but this is less effective.  A consistent finding is that mares will start to shed out before they start cycling.  If they haven't started to lose their winter coat, they aren't ready.  

The first cycle in the spring is often a transitional one and may be shorter or longer than a normal cycle.  The average cycle length in a mare is 21 days from the first day of estrous to the next first day of estrous.  The mare may not be producing a breedable follicle or egg during this transitional cycle, so just write down when she is in heat and wait until the next cycle to breed her. Good record keeping is essential as it may tell us what your mare is doing and if she is cycling normally.   

If a mare seems to be coming into heat more frequently then normal, this may be a sign of a uterine infection. Putting semen in an infected uterus won't result in a healthy pregnancy as the uterus is inflamed.  Most stallion owners require a negative uterine culture before breeding, but even if it is not required, it is recommended. 

Fat mares have a harder time becoming pregnant.  There may be problems with the thyroid gland, or these mares may have other health issues such as Cushing's syndrome or Metabolic syndrome.  Pain also interferes with pregnancy, whether it is from arthritis or laminitis.  Will your mare be able to carry a pregnancy to full term gaining over 100 pounds?  That is also something to think about. 

Maiden mares tend to be harder to get in foal than mares that have been pregnant before.  Older maiden mares may be the most difficult as scar tissue forms over time.  Just as older women have trouble getting pregnant, so do these mares.  We consider any mare that is 15 years and up an older mare and less fertile.  To determine how receptive the uterus will be, we will take a biopsy (a small piece of tissue) from the uterus. By looking at it under the microscope, we can determine if there is scar tissue, infection or if it is normal.  Along with that, we know the percentage of mares that will get pregnant with the different types of uterine changes.  

There are many procedures we can try to get your mare pregnant.  Being proactive and keeping excellent records are essential.  Working with your veterinarian and using the latest technology will increase the likelihood of a beautiful foal running around at your farm.