Editor’s Note: This is an excerpt from Understanding Equine First Aid by Michael A. Ball, DVM. 

Normal gestation in a mare lasts anywhere from 320 to 360 days. The average is about 341 days. A foal born at less than 320 days will display immature characteristics such as silky hair coat, overly pliable ears, weak or lax flexor tendons, and small size. Another term used to describe foals which may be of normal gestational age but are in fact immature, is dysmature. This is why records of a mare’s previous pregnancies are so important.

Foals can be born prematurely for a variety of reasons. The most common reasons for a premature delivery are infection of the placenta (placentitis) or long-standing placental insufficiency. Other causes include severe stress on the mare from illness such as pneumonia, diarrhea, or colic. Placentitis can be identified by noticing a vaginal discharge from the mare. This indicates infection of the placenta and your veterinarian should evaluate the mare immediately to begin treatment.

Premature foals are much more likely to survive than foals that are “aborted” by their very sick mothers or foals taken by Caesarean section. The foals born spontaneously often are more immature due to chronic stress. The prognosis for premature foals varies depending on the cause and the ease of the delivery