Horse Breeding:

Glossary of Terms

When working with your vet to breed your mare, you may hear a few words you’ve never heard before! The learning curve can be steep, so we hope this gets you off to a good start!

Follicle: these are fluid-filled structures on the ovaries that release eggs. We will measure your mare’s follicles at each visit. Most mares will have one follicle that is the largest, and that one will usually be the one to release the egg.

Ovulation: Releasing of the egg from the follicle. Most mares will ovulate a follicle that is around 40mm in size. Each mare is an individual; some will ovulate a 35mm follicle, and some will ovulate a 60+ mm follicle. If we’ve worked with your mare before, or you have detailed records from previous breedings, we will know what size follicle your mare usually ovulates.

CL: this stands for “corpus luteum”- the structure left behind on the ovary after a follicle has ovulated. This structure produces a hormone called progesterone. Progesterone keeps the mare “out” of heat. The CL will go away and stop producing progesterone a few days before the mare comes back into heat. If an embryo is present, the CL will stay put and maintain the pregnancy.

Uterine edema: Edema means “fluid within the tissues.” On a uterine ultrasound, edema looks like a “wagon wheel” or “cut orange” pattern. Uterine edema means the mare is in heat, and that she has an active follicle that could release an egg. We score edema from 0-4. A mare should have an edema score of around 2-3 when she is bred. We place a lot of emphasis on uterine edema, since the presence of edema at the wrong time, or in the wrong amount, can let us know that the mare has an infection, or that her heat cycle isn’t progressing normally.

Uterine fluid: This is another important thing that we see with our ultrasound. Under most circumstances, a mare should not have fluid inside her uterus (the exception is a small amount of fluid, around the time of ovulation). The amount and appearance of uterine fluid can help us determine that there is a problem in the mare, like an infection, urine flowing backward into her uterus, a scarred cervix, or damage to the uterus.

Culture/cytology: this procedure involves taking a sample (using a long cotton-tipped applicator) from inside the mare’s uterus, to look for any evidence of infection. The cytology is evaluating the appearance of the cells under a microscope (like a pap smear), and the culture is an attempt to grow any bacteria from the mare’s uterus on a petri dish in an incubator. If a mare has bacteria in her uterus, she will usually need treatment for the infection before she can carry a foal. The cost of a culture/cytology is 177. If an infection is chronic or severe, we may recommend additional testing to determine the best way to treat the mare.

Uterine biopsy: This procedure involves taking a small tissue sample from inside the uterus. This tissue is examined in a lab, and we will receive results that indicate how likely it is that your mare can successfully carry a foal to term. We don’t recommend a uterine biopsy for all mares, but if your mare is difficult to get pregnant, has lots of uterine fluid, or has recurrent infections, this may be an important step. The cost of a uterine biopsy is about $450.

Endometritis/uterine infection: Due to the anatomy of mares, it is easy for them to get bacteria into their uterus. If an infection is identified, we can treat it with oral, injectable, or intrauterine antibiotics. Treatment for a uterine infection can range from $300- $3,000 with most treatments at about $900-1,000.

Uterine lavage: A lavage is a “washing” procedure where we use fluid (like the kind we would use for an IV) to rinse the inside of the uterus. This procedure is one of the most common that we perform, and is recommended for some uterine infections, or mares who have fluid and inflammation after they have been bred. A uterine lavage costs $75 but there may be additives to the lavage fluid that can increase cost slightly.