Glossary of Terms for Foal/Fetal Loss Syndrome

Glossary of Terms

Following is a glossary of terms related to the current fetal/foal loss syndrome in horses. This will be a living document--we will add to it as requested or as necessary. If you have any terms you would like to see listed on this document, please contact Ron Mitchell at

Abortion-birth -- premature loss of fetus, which usually occurs between five months and 320 days of gestation.

Acremonium coenophialum -- the scientific name for the endophyte that infests tall fescue.

Agalactia -- little or no milk production.

Ataxia -- incoordination.

Conceptus -- embryo or fetus and the surrounding embryonic membranes.

Corpus luteum (plural: corpora lutea) -- ovarian follicle after discharge of the ovum (egg); it secretes the hormone progesterone.

Domperidone -- a specific dopamine-2 receptor antagonist used prior to parturition in mares grazing on endophyte-infested tall fescue to try and counteract the problems associated with fescue toxicosis.

Dystocia -- difficult birth.

EFL - early fetal loss, which occurs 45-120 days of pregnancy.

Endophyte -- a parasitic plant organism living in the body of its host.

Endometrial Cups -- specialized endocrine glands that form from the embryonic vesicle and attach to the uterus between days 35-40 of gestation. The endometrial cups produce the hormone equine chorionic gonadotropin (eCG), which causes an increase in the production of progesterone by the ovary. The endometrial cups produce eCG until about Day 120 of gestation even if the pregnancy is terminated before that time, making it difficult to get a mare to cycle with a breedable follicle.

Endophyte-Infested Tall Fescue -- a hardy type of pasture grass that often is infested with the fungal endophyte Acremonium coenophialum. In some areas of the country, 90% or more of pastures contain endophyte-infested tall fescue. Tall fescue was introduced into the United States in the 1940s, and shortly after that more than 35 million acres of land in the United States was planted with tall fescue. (For more information see

Epidemiology -- the science that studies the factors determining and influencing the frequency and distribution of diseases, injury, and health-related events and their causes.

Fescue Toxicosis -- In the late 1970s, it was discovered that much of the tall fescue grass in pastures contained a fungal endophyte that can have highly deleterious effects on the animals consuming it. The scientific name for this fungal endophyte is Acremonium coenophialum. (For more on fescue toxicosis see Fescue toxicosis can cause late-term abortions, dystocia (difficult birth), agalactia (little or no milk production), a thickened or tough placenta, and/or extended gestational period.

Fetus -- the unborn offspring in the postembryonic period after major structures have been outlined.

Leukoencephalomalacia (moldy corn poisoning) -- a mycotoxin disease of the CNS (central nervous system) that affects horses, mules, and donkeys caused by the fungus Fusarium moniliforme. It is associated with feeding moldy corn over a period of weeks and can cause death in horses and other livestock. There is no treatment. (For more information see

Luteinization -- conversion of the ovarian follicle to a corpus luteum.

Manual Exam -- veterinary palpation of a mare's reproductive tract not using ultrasound.

Moldy Corn Poisoning -- see Leukoencephalomalacia

Mycotoxin -- toxins (poisons) produced by molds that can be toxic when consumed "in significant amounts" by livestock. These fungal toxins are only produced at certain stages of mold growth, and they are often resistant to chemical or thermal treatments for destroying mold spores. The problem in Kentucky is thought to have stemmed from a particular environmental scenario. The state experienced a warm spring, followed by a frost, then a drought. There is a wide range of mycotoxins that can cause a loss of appetite, intestinal tract lesions, suppression of immune function, lethargy, ataxia (incoordination), leukoencephalomalacia or moldy corn poisoning (for more information see, increased estrogen production (and thus impaired reproduction), and/or decreased blood pressure in the horse.

Mycotoxin Binder -- large molecular weight polymers that are designed to bind to mycotoxins in the animal's digestive tract, keeping those toxins from being absorbed and passing out harmlessly in the feces. The intended effect is to reduce the amount of toxin absorbed from the feed to the point that it does not affect the animal. The main challenge with mycotoxin binders is finding one that binds several toxins effectively while fed at low levels (if fed at high levels, the binder dilutes the nutrient density of the diet).

Palpation -- a veterinary exam of a horse's internal organs (including the reproductive tract) via the rectum.

Parturition -- birth.

Pericarditis -- inflammation of the pericardium or sac surrounding the heart.

Progesterone -- a naturally occurring hormone whose job is to shut down the estrous-stimulating hormones and to set the stage for maintaining a pregnancy.

Prolactin -- hormone secreted by the pituitary gland that simulates and sustains lactation; also called lactogenic hormone.

Red Bag -- early placental separation where placental membranes begin to exit the vulva before the foal at parturition, often resulting in suffocation of the foal and indicating a thickened or compromised placenta.

Regu-mate -- (altrenogest) is a safe way to prevent a mare from coming into heat and/or maintain a pregnancy.

Resorption - when the fetus and its membranes are destroyed and cleaned up by the mare internally, usually at 24-45 days of gestation.

Stillborn -- a foal born dead.

Toxin -- a poison; frequently used to refer specifically to a protein produced by some higher plants, animals, and pathogenic bacteria that is highly toxic for other living organisms.

Ultrasound -- a machine that uses sound waves bounced off of tissues to view internal structures such as a mare's reproductive tract.

Zearalenone -- primarily produced by the mold Fusarium graminearum. If zearalenone is detected, there is evidence of a high probability that other fusarial mycotoxins might be present. Zearalenone has known estrogenic properties (causes estrus). When zearalenone-contaminated feed or grain is eaten by livestock, it can cause a wide variety of reproductive problems.