Foal rejection is a relatively uncommon phenomenon in broodmares. However, it can jeopardize the foal’s health—even his life—due to failure of passive transfer of immunity (as a result of not ingesting enough colostrum, or first milk) or severe injury. Researchers have shown nearly 20% of rejected foals have been injured or killed by their dam.

To identify foal rejection, it is important to understand the normal mare-foal interaction. Mare-foal bonding starts during parturition (birth), as the mare sniffs, licks, and nuzzles the fetal fluids and membranes. Immediately after foaling, the mare directs her attention to the foal, nuzzling, licking, scraping with teeth, allowing and facilitating nursing, and protecting. Bonding behavior includes nose-to-nose nuzzling and nuzzling of the foal’s perineum (around the anus), particularly during nursing.

Stepping away from the foal while it seeks the udder is a normal mare behavior if not accompanied by aggressive kicking or biting. It is also normal for mares to terminate nursing sessions by walking away while the foal is still nursing. Most maternal aggression occurs when the foal is suckling, and excessive suckling and vigorous bumping of the udder can trigger foal rejection behavior. Stimulating the sympathetic nervous system in aggressive mares in this way could inhibit milk production and exacerbate the problem.

Any deviation from normal behavior toward the foal can be a form of foal rejection. These reactions can range from simple avoidance and ambivalence or lack of attention to severe threats toward and savaging of the foal. Most foal rejection cases (90%) occur in the first 24 hours postpartum, though veterinarians have observed foal rejection as late as four months postpartum.

Foal rejection behaviors include ear pinning, squealing (this can also be ­exhibited in normal mare/foal relationships), tail swishing, pushing, threatening to bite, biting, and kicking.

We don’t fully understand the underlying causes of foal rejection. However, factors suspected to increase foal rejection risk include breed/genetics, parity (number of foals a mare has had), foaling conditions, and foal or mare health.

Foal rejection seems to be more common in Arabian mares than other breeds for reasons unknown. Primiparous (maiden) mares are more likely to reject foals because of inexperience and fear.

Foaling conditions suspected to trigger foal rejection include the presence of too many people, obstetrical intervention, and overt handling of the foal in the immediate postpartum period. All these can interfere with normal mare and foal bonding.

While researchers believe hormonal imbalances could cause foal rejection, scientific evidence is lacking. The hormones oxytocin, estrogen, and prolactin are essential for maternal behavior, and researchers on one study saw no difference in progesterone, estradiol (an estrogen type), or prolactin concentrations in foal-rejecting and normal mares. However, the prostaglandin-E2-to-­progesterone ratio was significantly higher in normal mares than in foal-­rejecting mares. Prolactin concentration decreased significantly from Days 1 to 3 in rejecting mares. Low prolactin might lead to higher anxiety and stress response, culminating with abnormal behavior toward the foal. We must interpret these studies with caution, however, as the number of animals involved is often low.

Foal rejection is also associated with painful conditions in the dam. It is common for primiparous mares to avoid their foals due to a painful udder. However, this behavior typically subsides after a few suckling sessions. (Note that any mare can experience vaginal trauma and sore udders after parturition, and many veterinarians administer NSAIDs such as flunixin meglumine or phenylbutazone in foal-rejecting mares.) Other conditions that can cause mare discomfort and resulting foal rejection include the foal bunting the udder and biting the teat, retained placenta, inflammation of the uterine wall, gastrointestinal pain, udder edema, and mastitis. Foals in critical condition that have been isolated from their dams are at higher risk of being rejected.

Early identification and diagnosis of foal rejection is critical for foal health. Caretakers should observe the mare and foal closely, particularly if it’s the mare’s first foal. An early sign is a lack of licking the foal. Eighty-two percent of dams lick their foals after parturition, compared to 38% of rejecting mares. Rejecting mares also tend to chase their foals.

How to manage foal rejection is often a subject of debate and is mostly based on clinical experience. It’s crucial to collect a thorough history of the mare (including foaling condition and behavioral signs) and conduct a physical examination prior to initiating any treatment.

If the foal rejection becomes permanent, practitioners typically prefer to graft the foal to a calm nurse mare rather than hand-raise it.