Stallion owners customarily request that any mare booked for breeding have a culture. This seems to imply that the culture is performed to protect the stallion from contracting venereal disease from the mare. Actually, venereal disease is rare in horses in this part of the country. Of much greater concern is ruling out infection of the mare’s uterus. Breeding a mare with an infection is an exercise in futility for both the stallion and mare owner since she will be infertile. In addition, infections that are allowed to progress unchecked can cause permanent scarring in the uterus and permanent infertility.
Mares do not show signs of ill thrift or illness with uterine infections, nor do they usually have any other outward signs, such as discharge from the vulva. Your veterinarian may or may not feel any abnormalities after palpating the uterus through the rectum. Since there are usually no outward signs, the only way to tell for sure whether or not a mare has a uterine infection is by laboratory testing.
The first laboratory test that most veterinarians will perform is a cytology. This is an inexpensive, painless test that involves swabbing the inside of the uterus and examining the cells after they have been transferred to a slide and stained. The results are available right away, since the test can be performed right in the veterinarian’ s lab. Normal mares will have uterine cells present on a cytologic stain, but no bacteria or fungi, and very few white blood cells. The presence of numerous white blood cells indicates that an abnormal inflammatory response is occurring in the uterus, and that the swab should be cultured for bacteria. If the culture is positive for bacteria, the lab will incubate the organisms with several different antibiotics and determine which one that the will be the most effective. This is called a sensitivity.
It is important to read a culture result in light of the cytology. Some normal, noninfected mares have bacteria in their uterus naturally, and this will show up as a positive culture. These mares should not be treated, since there is nothing wrong with them. A positive culture should be supported by a positive cytology before a mare is diagnosed with a uterine infection.