Pregnancy checking mares can safeguard investment

Horse breeders need to take steps to ensure the stork will make its seasonal visit to their operations.

Loss of early term pregnancies is a major concern on horse farms, as an open broodmare can mean significant economic loss if the horse is not rebred in time to produce a foal for the next desired foaling season.

“Some research studies have shown early embryonic losses to be as great as 15 percent to 20 percent,” said Dave Freeman, Oklahoma Cooperative Extension Service equine specialist.

It is the recommended practice to check mares for pregnancy 15 to 20 days after breeding. This allows those mares that are open to be managed for breeding through the next heat cycle.

“Mares should be rechecked between 40 and 60 days after breeding,” Freeman said. “Those mares that have lost embryos may need veterinary treatment before undergoing additional breeding.”

There are several methods by which breeding managers can diagnose broodmare pregnancy.

Teasing is accomplished by exposing a mare to a stallion to determine her behavioral acceptance to a stallion’s sexual advances.

“Checking the mare’s behavioral acceptance to a stallion on the days she is expected to show heat if open will give an indication of pregnancy,” Freeman said.

When open, a mare in estrus will cycle approximately every 21 to 22 days, showing heat for three to seven days.

“Teasing is one of the easiest methods, and requires little input above a teasing stallion and minimal facilities,” Freeman said.

The system does require a knowledgeable person who understands the mare’s reproductive cycle and individual behavior patterns.

Although teasing is used as the sole source of pregnancy determination on some horse farms, the accuracy of this system depends on the relationship of mare behavior and reproductive status of the mare.

“There are several behavioral and physiological occurrences that can decrease this relationship, so it is recommended that teasing be used in combination with other methods such as palpation and ultrasonography,” Freeman said.

Palpation requires a person to physically feel the reproductive tract of the mare through the rectal wall. Physical detection of a fetus in the uterus can be performed accurately about 16 to 20 days post conception, depending on the expertise of the examiner.

Perhaps the single most recommended tool for pregnancy diagnosis is ultrasonography, because it provides visual proof of the embryo. Ultrasonography requires the use of an ultrasound machine and a trained operator.

“A scanner is inserted rectally in the mare, which sends sound waves through the uterus,” Freeman said. “The sound waves that are reflected off tissue are converted electrically to give a visual image of tissue in the reproductive tract.”

While the visible image can provide unquestionable evidence of a fetus, the ultrasound machine and technician can be costly. Many commercial farms use veterinarians who own the machine. This way, the horse breeder does not incur the sole expense of machine and operator.

Other options include several blood tests which can be used in pregnancy diagnosis. The blood tests detect the presence of a hormone produced by structures in the uterus that form as support for the developing fetus.

“The drawback is that the hormone, Equine Chorionic Gonadotrophin, is not measurable to a large extent before 40 to 45 days post conception,” Freeman said.

As such, the tests have less value than other methods of pregnancy detection in helping horse breeders to ensure rebreeding of mares and maintaining a yearly foal interval.

Freeman said it is also important for breeding managers to determine the cause of pregnancy loss.

There are many potential causes: age of the mare, misdiagnosis of the initial pregnancy, chromosomal abnormalities, disease, infection and nutritional and environmental stress being a few.

“The important thing is to find the cause and correct the situation, if it is correctable and economically feasible to do so,” Freeman said.