Equine Endocrine Testing Case Studies

Case Studies

A 17-year-old mare is pregnant 260 days and has vaginal discharge. Will endocrine assays give me any indication of fetal viability?

Yes, assay Total Estrogens and Progestagens to gain insight regarding fetal well-being. See paper at this website: “Endocrine diagnostics in the broodmare: what you need to know about total estrogens and progestogens” Between 150 – 320 days of pregnancy, Progestagen concentrations above 10 ng/ml can reflect placentitis. Total Estrogens should be above 1000 pg/ml from days 150 to 320 of pregnancy. The closer the value of Estrogen is to 1000 pg/ml the more likely the ability to salvage the pregnancy with appropriate antibiotics and hormonal therapy. This is irrespective of the concentrations of Progestagens. For example if the Total Estrogens are about 300 pg/mL the chances of saving the pregnancy are about 10%. In contrast, if Estrogens are at least 700 pg/mL the odds increase to about 80%. Serial serum samples at weekly intervals to monitor Progestagens and Total Estrogens will continue to provide critical data on fetal well being and may reflect the efficacy of treatments given.

A 12-year-old mare has had a foal for the last 4 consecutive years with no problems. This year she has been bred four cycles and not detected in foal at 15-day ultrasound checks. Her estrous cycle length is normal. What tests should I run?

The most likely cause for this scenario may be low-grade endometritis and early demise of the corpus luteum if the stallion is fertile. Collect serum at day 12 and at the first ultrasound and assay Progesterone. Mares with serum P4 averaging 2.5 ng/mL or less at day 12-post ovulation had a 21% in foal rate while those with concentrations greater than 2.5 ng/mL had a 70% pregnancy rate. Concentrations of P4 at day 15 should average 6 ng/mL. Low P4 concentrations during the first 40 days of gestation are most likely due to low-grade endometritis which, due to the inflammatory process, releases prostagladin F2 from the uterus, which may cause partial lysis of the CL. Usually treatment with appropriate systemic antibiotics solves this problem. Exogenous progestin therapy will not likely solve this problem. Even if no pathogens are present on cervical uterine culture they may be isolated when uterine lavage or clitoral fossa cultures are taken from these mares.

We recently reseeded most of our pastures with a mixture of grass seed containing rye grass. This spring many of my mares have longer hair coats than normal and are not showing estrous behavior as expected and many have poor cervical relaxation when examined in estrus. What could be the cause?

Rapidly growing rye grass can depress Total Thyroxine (TT4) concentrations to as low as 1 to 2 ng/mL (normal 12 to 25 ng/mL). Overall, mares maintained on rye grass pastures usually have mean concentrations lower than the same breed maintained on pastures free of rye grass. Most often this does not cause a problem but may have a negative impact on estrous expression and possibly embryo survival. Supplementation with appropriate doses of thyroxine adequate to elevate serum levels above 12-ng/mL 24 hours post dosing or removing mares from the affected pasture often solves the problem. The same events can be associated with infected fescue pastures as well.

A 14 year old mare presents with poor uterine tone some fluid accumulation and bred 4 cycles not in foal. What tests should I run?

Often poor uterine tone can be associated with PPID. As in dogs, hyperadenocoticism (present in PPID) causes thinning of muscle layers and therefore the pendulous abdomen in dogs and in some horses with the advanced disease. Running a PPID screen may indicate poor Cortisol rhythmicity or a failure of dexamethasone to depress endogenous Cortisol concentrations. If this occurs, the mare will be very likely to respond to appropriate pergolide therapy in about three weeks time. The fluid accumulation may resolve as well.