Checking a Mare for Pregnancy

Earlier in our series, we joined our Broodmare Farm Manager and Rood & Riddle’s Dr. Riddle to learn about palpating barren and maiden mares in preparation for breeding season. The process of determining the best time to breed a broodmare has been completed and now we have the anticipation of checking for pregnant broodmares!

Broodmares, both seasoned and maiden, find our farm in Lexington, KY home at this time of year. When a mare is confirmed to be ovulating, they are scheduled for cover by a stallion. At the stallion facility, there are covering sheds that are made specifically for this process. The mare is taken to the stallion, returns to the farm, and then we wait.

How long do we wait? 15 days post ovulation

Dr. Riddle prepares a mare for an ultrasound exam.

Fifteen days after the mare is covered, Dr. Riddle returns to the farm to check the mare for pregnancy, using an ultrasound machine. Some mares have innocuous cysts that could be mistaken for pregnancy. Our veterinarian references a cyst map to avoid this mistake since the cysts appear similar to a pregnancy on the ultrasound at this early stage. To prepare for the ultrasound, the rectal path is cleared. A small ultrasound wand is held by Dr. Riddle and inserted into the rectum for a view of the uterus through the rectal wall.

After viewing the uterus, the status of the mare is determined as “in foal” or “not in foal”. If a mare is not in foal, when she returns to estrus (in “heat”), Dr. Riddle will collect a culture and perform a cytology exam to check for bacteria and inflammation, potential reasons as to why the mare did not get pregnant.  If the culture and cytology exam show no signs of a problem, the mare can be bred back a few days later on that same heat. If the culture and cytology show that bacteria or inflammation are present, the mare is treated and bred back on her next heat three weeks later. Other reasons for a mare not being in foal include an unhealthy egg or the stallion’s semen did not live long enough to fertilize the egg. The likelihood of a mare being pregnant after each cover is 60 – 70% for well-managed mares.

If a mare is in foal, the first view of new life is a small, dark mass appearing on the ultrasound monitor, measuring just over a centimeter. The foal first can be seen using an ultrasound machine on the 10th day of gestation, but is extremely small making it difficult to see. To get the best information, the first exam is performed on day 15.

The dark, circular spot seen on this ultrasound monitor is a foal at 15 days gestation.

A second exam is performed on day 17 after breeding, regardless of the results of the 15-day exam. On rare occasions, a mare that did not show as in foal on day 15 could, in fact, be pregnant. An underdeveloped vesicle may not be seen on day 15, but could present itself at the second exam. 

Using ultrasound technology to determine if a mare is pregnant or not provides confirmation earlier than any other method. Having good information earlier means those caring for broodmares can make more informed decisions. Ultrasounds are used throughout the 11-month gestation period. A 28-day exam gives a visualization of the heartbeat. There is a check up exam at day 42 and on day 60, the fetal sex is determined.

The late spring and summer are an exciting time on the farm. New life begins to form from small round spots on an ultrasound monitor and foals fill the paddocks, playing and napping in turn, as the cycle continues.