Monday, February 28, 2011

Equine Twins

Unlike many other species, multiple births or twins are not desirable in horses. Because a mare's uterus is not designed to carry twins, when a mare becomes pregnant with twins, she will either undergo early embryonic death of both embryos before 60 days of gestation or carry them to 7-8 months and then abort the fetuses. Rarely does a mare carry and delivery full term twins. If they do give birth to twins, the foals are usually either dead or very weak and die within 3-4 days. Birthing complications and retained placentas are much more common when mares abort or give birth to twins. There are cases of healthy equine twins being born, but these cases are rare.

This is a picture of our equine reproductive ultrasound. We have two of these units at the clinic. We use these both in the clinic and on the farm to examine a mare's reproductive tract.

Before the advent of the ultrasound in equine medicine, the number of mares producing twins was unknown since they will normally loose these pregnancies early in gestation. Now, with an ultrasound, we can diagnose pregnancy in a mare as early as 14 days after ovulation. Because of this, we can diagnose twins very early in the pregnancy. If twins are picked up on an ultrasonic scan, one embryo can be manually crushed or eliminated. This allows the other embryo to grow and develop normally. This procedure must be performed early in the pregnancy.....before 18 days is ideal. And, the procedure should be performed by an experienced veterinarian. Because we deal with many draft mares and draft type crosses, we commonly pick up twins on the ultrasound. We have become very proficient at successfully reducing twin or even triplet pregnancies to a single pregnancy. We usually see 2-3 mare each season with triplets.
Below is a picture of a sonogram on a Belgian mare, performed by Dr. Scott Nebergall, of a mare who actually had quintuplets....yes, that means 5 embryos! This picture only shows three of them (black circles)....I could not get all 5 on the screen at the same time. This is a record for us at the Arthur Veterinary Clinic.


On December 15, 2008, the state of Kentucky confirmed that a quarter horse stallion was positive for Contagious Equine Metritis or CEM. CEM is considered a foreign animal disease in the United States. It was first discovered in Europe in 1977. Because stallions being imported into the United States must be quarantined, tested and treated before being released into the country, CEM has only appeared twice outside the quarantine stations. In 1979, there was an outbreak. And in 2006, three Lipizzaner stallions imported from Eastern Europe tested positive after their arrival but before they had been used for breeding.

What Is Contagious Equine Metritis?
CEM is a sexually transmitted disease among horses caused by a bacteria Taylorella equigenitalis. Clinical signs may include a mucopurulent vaginal discharge, abortion and infertility. Stallions typically show no clinical signs. Stallions and mares can become chronic carriers of CEM and be sources of infection for future outbreaks. The transmission rate is high and occurs by natural mating. However, contaminated instruments and equipment used for artificial insemination can be an indirect source. The bacteria can also be spread via semen collected for artificial insemination. The disease is treatable with disinfectants and antibiotics.

The last report I read states that the USDA has identified 19 positive stallions and five positive mares. An additional 904 horses have been exposed to CEM. An exposed horse is one that was bred to a positive horse either naturally or via artificial insemination. A horse can also be deemed exposed if epidemiologically linked to a positive horse. State and Federal health officials have conducted the investigation by examining the breeding records and movement history of each infected horse to find other exposed animals. At each step, any exposed animals are quarantined, tested and treated. Owners of exposed horses are contacted by State or Federal animal health officials. There is no need to have your horse tested if you have not been contacted.

These 928 horses are located in 48 states. Exposed mares must have three negative cultures taken 3 days apart. Even if the exposed mare tests negative, she then must go through 5 consecutive days of treatment. Exposed stallions must also be cultured. After a negative culture is determined, the stallion must naturally breed two test mares and the mares must be then cultured. The exposed stallion is then treated for five consecutive days. The culturing, treating and test breeding must be done by an accreditated veterinarian and overseen by a USDA/APHIS veterinarian. While the majority of exposed horses will end up being negative, you can see why this investigation will take a long time because of the prolonged testing and treating that is required. Because of the expanse of this investigation, the source of the outbreak has not been identified. However, State and Federal animal health officials continue to pursue all information obtained from this outbreak.

I was involved in the testing of an exposed mare. While the entire procedure went smoothly and the mare was negative, it was expensive and time consuming. However, as costly and involved as the testing efforts of exposed horses are, they are crucial due to the potentially even more costly consequences to the equine industry and government if CEM becomes established throughout the US and Canada.