Breeding Terminology

In providing written reports to interested parties, the AAEP encourages all equine practitioners to use the following terms when conducting reproductive examinations: 

Pregnant: Any filly or mare shall be characterized as “pregnant” if and only if a licensed veterinarian has made such a determination. Any such report should include the method of diagnosis (i.e., palpation per rectum, transrectal ultrasound, etc.) and the approximate length of gestation, if known. A statement by the examining veterinarian should include that the pregnancy appears to be within normal limits. 

Aborted: Any filly or mare that is not pregnant at the time of examination by a licensed veterinarian should be reported as “aborted” rather than “not pregnant” if the person rendering the report is actually aware that (a) an aborted fetus was observed or (b) the mare had been previously declared “pregnant” based on an examination by a licensed veterinarian at 42 days or more post-mating. The term “aborted” is used for the present breeding season or until breeding is attempted in the following season. 

Not Pregnant: Any filly or mare that has been examined for pregnancy by a licensed veterinarian and found not to be pregnant at the time of that examination shall be characterized as “not pregnant.” Any such report shall include the method of determination. Pregnancy examinations conducted by transrectal ultrasound prior to 14 days post ovulation may not detect pregnancy. 

Suitable for Mating: This is a subjective term used in sales conditions interpreting the findings of a single reproductive examination by a licensed veterinarian. Examination of the reproductive tract should include the ovaries, uterus, cervix, vagina, vestibule and perineum with palpation per rectum, and where practical, transrectal ultrasonography as well as visual examination of the vagina and cervix. While other tests and criteria can be used to further evaluate the animal’s potential fertility, employment of such techniques shall be at the discretion of the examiner or their client. Horses placed in “suitable for mating” category are based on the findings of a single examination consistent with a phenotypically female horse lacking major reproductive pathology. This categorization does not offer a guarantee of fertility.

Mating: The physical act of a stallion mounting a filly or mare with intromission of the penis. Artificial insemination qualifies as mating for breeds that permit artificial insemination. 

Mated: Any filly or mare that has undergone the physical act of mating or artificial insemination but whose pregnancy status has not been determined. 

Stillborn: Any foal, after at least 320 days of gestation, that is dead at the time of delivery. 

Neonatal Death: Any foal that dies within 14 days of foaling from a medical condition determined to be existing at or dating from birth. 

Foal Died: Any foal that stands and nurses unassisted and subsequently dies from a condition not determined to be existing at or dating from birth. 

Revised by AAEP board of directors in 2025.