The birth of a foal is a remarkable event that must unfold in an expedient manner. Expulsion of the fetal membranes or placenta is a seemingly less glamorous event than the arrival of the newborn foal, yet its well-timed release is equally important to the thriving foal. Discharge of the placenta is an extension of labour and fetal membranes retained beyond eight hours of foaling pose a serious concern to the mare’s health.
The incidence of retained placenta in mares is two to 10 per cent. It is more common in draft horse breeds and is more likely to occur following a difficult birth or abortion. These scenarios result in uterine fatigue and inability of the uterus to complete its involution process. Strong uterine contractions are responsible for shrinking the uterine lumen and release of the placenta.
When involution is incomplete bacteria, inflammatory fluids, and toxins accumulate within the uterine cavity. Mares are sensitive to resorption of these toxins into the bloodstream, with laminitis or death a common sequel. It is important to note that retention is a much more serious affliction in mares than cattle.
Generally, discharge of the placenta occurs within an hour of the foal’s birth. Most often diagnosis of a retained placenta is easy, for the placenta is hanging from the vulva three hours beyond foaling. Initially knotting or tying the hanging placenta prevents the mare from stepping on and tearing it causing further complications.
The gentle weight of the hanging placenta and gravity are a mare’s ally. Between three and eight hours post-foaling, small doses of oxytocin can be given intramuscularly to the mare. This hormonal treatment stimulates purposeful rhythmic contractions of the uterine muscle. Signs of mild colic may be observed following injection. If this occurs walking can soothe the mare’s discomfort.
Beyond eight hours of foaling retained fetal membranes in a mare are considered a veterinary emergency requiring timely intervention and attention.
Although it may be tempting to just pull on the hanging placenta and remove it, complications such as uterine involution, uterine prolapse, uterine hemorrhage or incomplete removal of membranes will likely result. Retention of partial membranes can be equally harmful to the mare.
Veterinary practitioners rely on various techniques and clinical judgment to attend to the mare. Followup care may involve broad-spectrum systemic antibiotics, intrauterine antibiotics, anti-inflammatories, a tetanus booster, and uterine lavage.
Examination of the placenta with an experienced eye is suggested following all foalings to ensure its complete removal. Occasionally the placenta may partially fall away leaving a piece of the placenta in the uterus.
In this case, the characteristic hanging placenta does not exist, however symptoms of illness follow three to seven days post-foaling. The mare will become febrile, depressed, and inappetent. Since her milk production often drops the foal will appear hungry and fail to thrive. Prompt veterinary attention is recommended.
A mare’s reproductive health is also contingent upon timely release of the placenta. Mating a mare at foal heat whom has had a retained placenta or foaling difficulties is not advisable. These mares require a period of time to recuperate and recover, readying themselves for successful conception.