Problem Mare Not Getting in Foal: The Options, Step by Step

1. Check the breeding itself

Before the mare is called a problem mare, the simple things are ruled out: was she covered or inseminated close enough to ovulation, was the semen good on the day, and has the stallion got other mares in foal this season. A mare bred with frozen semen needs tighter timing than a mare bred with fresh. If two cycles have failed with good timing and proven semen, the cause is with the mare.

2. Ultrasound of the uterus and ovaries

The scan shows whether she ovulates, whether fluid stays in the uterus after covering, and whether there are cysts or other changes in the lining. Fluid that is still there two or three days after covering is the most common finding in a mare that comes back empty. What the scan cannot show is bacteria. See what the vet sees on the scan of an empty mare.

3. Uterine swab and cytology

The swab is the standard test for infection, and cytology shows whether the lining is inflamed. Both are quick and cheap, and a positive result is reliable. A negative result is less so: in a direct comparison, culture from a swab found 34 % of infected mares and culture from a biopsy found 82 % (Nielsen, Theriogenology 2005). A clean swab is a reason to keep looking, not a reason to stop.

4. Low-volume lavage

A small volume of sterile fluid is flushed through the uterus and collected again, so the sample comes from the whole lining and not from the one spot the swab touched. Vets use it when the swab is clean and the mare still looks infected. More on the three sampling methods in swab vs lavage vs biopsy.

5. Endometrial biopsy

A small piece of the lining is taken and examined under the microscope. It is the only test that shows the condition of the tissue itself: inflammation, scarring around the glands, and how likely the mare is to carry a foal to term. Scarring cannot be reversed, so the biopsy also tells the owner when to stop spending money.

6. Activation before culture

This is the option for the mare whose swab, cytology and lavage are all clean. In chronically infected mares, Streptococcus zooepidemicus has been found in foci 300 to 500 micrometers below the surface of the lining, where a swab does not reach (Petersen et al., Clinical Theriogenology 2009). The bacteria are dormant, so they do not grow in culture and do not respond to antibiotics.

bActivate is a growth medium that the vet instills in the uterus in early estrus. It makes dormant bacteria start growing again, and a normal swab taken afterwards can then find them. In the placebo-controlled study, the organism was found in 64 % of mares after activation and in 8 % after saline; all of them had been negative on lavage and cytology beforehand (Petersen et al., Veterinary Microbiology 2015). bActivate is a diagnostic aid, not a treatment. If the culture is positive, the vet treats on the antibiogram. If it is negative, a dormant streptococcal infection is unlikely and the search moves on.

When it does not apply: a mare with a positive swab already has her diagnosis, and a mare whose biopsy shows severe scarring will not be helped by finding an infection.

7. Treating what the tests find

Infection is treated with the antibiotic the laboratory result points to. Fluid is treated with lavage and oxytocin around covering. Mares that react strongly to semen are managed with one well-timed covering per cycle. None of this is a product choice; it is the vet's treatment, chosen from the results above.

8. Anatomy and hormones

A vulva that lets air in is corrected with a Caslick's operation. A cervix that does not open, common in the older maiden mare, is managed around covering. Hormone tests are used when the mare does not cycle normally or loses pregnancies early. See repeated early embryonic loss.

9. When the uterus cannot carry a foal

If the biopsy shows that the lining is too damaged, embryo transfer to a recipient mare is the remaining route, where the studbook allows it.

What the field series showed

At Hagyard Equine Medical Institute, 64 problem mares were activated: 47 % were culture-positive afterwards, 83 % became pregnant after treatment and covering, and 70 % of those with a known outcome foaled. There was no placebo group (Petersen and Bojesen, Clinical Theriogenology 2014). At Kildangan Stud, 16 of 19 problem mares were activation-positive and 16 of the 18 that were covered became pregnant (Petersen et al., Journal of Equine Veterinary Science 2018). These figures describe the whole sequence of diagnosis, treatment and covering, not the effect of one product.

Frequently asked questions

What is the first thing to check in a mare that will not get in foal?
The timing of covering and the quality of the semen. Only when two cycles have failed with good timing and a proven stallion is the mare herself the likely cause.

My mare's swab and cytology are clean. What is left?
A low-volume lavage, a biopsy, and activation before culture. A clean swab finds only about a third of infected mares, so it does not rule infection out.

Which diagnostic tools do vets use for problem mares?
Ultrasound, uterine swab culture, cytology, low-volume lavage, endometrial biopsy and, when those are clean, activation with a growth medium such as bActivate before a new culture.

Is bActivate a treatment?
No. It makes dormant bacteria grow so that a normal swab can find them. The treatment is the vet's, chosen from the culture result.

When is it time to stop trying?
When the biopsy shows severe, permanent scarring of the lining. That is the one finding that treatment does not change.

Sources

• Nielsen JM. Endometritis in the mare: a diagnostic study comparing cultures from swab and biopsy. Theriogenology 2005;64:510-518. doi.org/10.1016/j.theriogenology.2005.05.034
• Petersen MR, Nielsen JM, Lehn-Jensen H, Bojesen AM. Streptococcus equi subspecies zooepidemicus resides deep in the chronically infected endometrium of mares. Clinical Theriogenology 2009;1:393-409. doi.org/10.5281/zenodo.23847129
• Petersen MR et al. Activation of persistent Streptococcus equi subspecies zooepidemicus in mares with subclinical endometritis. Veterinary Microbiology 2015;179:119-125. doi.org/10.1016/j.vetmic.2015.06.006
• Petersen MR, Bojesen AM. Clinical Theriogenology 2014;6(3):313-314 (Hagyard field series, no placebo group). doi.org/10.5281/zenodo.23846748
• Petersen MR, Rosenbrock A, Osborne M, Bojesen AM. Journal of Equine Veterinary Science 2018;66:117 (congress abstract). doi.org/10.1016/j.jevs.2018.05.162

Written by the Bojesen & Petersen Biotech ApS team. Medical oversight: Prof. Anders Miki Bojesen DVM PhD (University of Copenhagen) and Dr. Morten Rønn Petersen DVM PhD Dipl. ACT.