Early this spring, two famous primiparous mares will have their foals. The 2009 Horse of the Year, Rachel Alexandra—the first filly in 85 years to win the Preakness that also has wins in several G1 races including the Kentucky Oaks, Haskell Invitational and Woodward Stakes—is in foal to Curlin, two-time (2007/2008) U.S. Horse of the Year. Her expected due date is Feb. 1, 2012.
The 2010 Horse of the Year, Zenyatta—the darling of the Breeder's Cup and winner of 19 of 20 races, including the Ladies' Classic in 2008 and the Classic in 2009—is in foal to Bernardini with an early March 2012 due date.
Likely, these two dams will show their natural maternal instinct to nurse and protect their foals. But these anticipated births may make us consider what normal maternal behavior is in mares and what triggers it. And what can equine practitioners do when confronted with aberrant mare behavior, foal rejection or outright aggression toward offspring?
Normal maternal bonding behavior
Normal maternal behavior is most likely triggered at parturition by a change in estrogen and progesterone concentrations, the production of prolactin and the release of oxytocin. Prolactin may not initiate maternal behavior, but it helps stimulate milk production.
As the foal is born, cervical stimulation promotes the release of oxytocin that not only initiates milk let-down but also a firing of axons in the olfactory bulb that fosters the mare's recognition when she sniffs the foal's breath and odor and licks the foal's head. With the foal in front of her and her smelling it, she will probably allow it to suckle. Foal recognition is also thought to be assisted by the mare sniffing the perianal region where she picks up the scent of her own digested milk once the foal is already nursing.
Not only does the mare elicit foal recognition and attention, but the foal plays a role in fostering maternal bonding behavior by its first movements toward the head of the mare, vocalizing, seeking the udder and suckling and keeping close to the mare.
Varying degrees of mare aberrant behavior exist, from ambivalence to rejection and aggression. Although rare, each can be a management hurdle for breeding farms but can be assisted by veterinary consultation and intervention.
"There are different extremes where mares may or may not accept their foals," says Karen Wolfsdorf, DVM, Dipl. ACT, Hagyard Equine Medical Institute. "You have to have a lot of patience to work with these mares, especially primiparous ones, to accept their foals."
The mare might accept and lick the foal but not allow it to nurse. This may be the result of the foal touching the mare's sensitive inguinal area as it seeks to nurse. "This relatively new finding is that a given mare is not objecting to having her udder or teats touched but that it's the inguinal fold that is sensitive, which the foal often hits with its head as it approaches the udder," says Katherine Houpt, VMD, PhD, Dipl. ACVB.
"If it is inguinal fold touching that bothers the mare, you can work on desensitizing her to that," Houpt says. "The procedure is for a caretaker to touch the area and gauge her response. If the response is negative, you can trot her around on a lead rope and try touching her again. Eventually she should give in to being gently touched in that area and, thereby, accept the foal's approach, even if not perfect. You can desensitize her until she does not object and then allow the foal to attempt to nurse, which, if done successfully, will relieve her objection."
In some cases, the mare may have little to do with the foal, or, alternatively, the mare might attack the foal, attempting to kick, bite or throw it.
"If you have a mare that routinely doesn't bond with any of her foals and just tries to ravish them, the farm manager understands that when she foals, the baby needs to be removed from the mare because from past behavior she has stomped and killed previous ones," Wolfsdorf says. "When the situation becomes that drastic, it is safer for mare, foal and caretakers just to put the foal on a nurse mare as an alternative."
"If she is overtly aggressive—her ears are pinned, she's chasing the foal, biting or kicking at it—it may be safer to get the foal a surrogate mare because she might well injure or kill the foal," says Houpt.
For primiparous mares, fear of the foal may trigger rejection. The fearful mare may move away from the foal each time it approaches or even try to attack it if the foal is too assertive.
"Especially with maiden mares, they seem to not know what's going on with a newborn that's trying to suckle on them every which way and often," says Wolfsdorf. In addition, maiden mares may have an excessively filled udder, their udders may be a little painful or the mares may not produce enough milk, making the foal go at them often, annoying the mares.
Reestablishing the bond vs. using a surrogate
To decide whether to try to reestablish a bond or go with a surrogate mare, you must determine why the mare is rejecting the foal. Some mares are just frightened of their foals. If this is the case, you can try restraining a mare until she learns that the foal is not going to hurt her.
"You can use drugs, either sulpiride (a dopamine D2-antagonist) or acepromazine, which will also help release prolactin," Houpt says. "If the mare learns that once the foal suckles, it feels good and it relieves tension in the udder, she may be more apt to accept it."
"With problem mares, management may be necessary, with the mare being held and the foal positioned to properly suckle the mare," says Wolfsdorf. "With practice, the mare becomes used to the foal, and as the foal continues to suckle, the mare begins to figure it out."
If you find that suckling is painful, Wolfsdorf says you can administer analgesics or anti-inflammatories.
Inducing lactation in surrogates
"Now that we can produce maternal behavior, I would advise a large breeding farm to have a mare that they can induce lactation in and then can stimulate maternal behavior when they need it, rather than having to purchase an expensive nurse mare, whose own foal then is an orphan," says Houpt.
The first step is to bring the subject mare into lactation. "You give them estrogen and progesterone, followed by sulpiride, which is a tranquilizer, but it also stimulates the release of prolactin from the pituitary, which will stimulate the mammary gland to produce milk," says Houpt. Domperidone can also be used in lieu of sulpiride.
"Inducing lactation in a surrogate mare works especially well with mares that have previously successfully raised a foal," says Houpt. "It has not worked with mares that reject a foal. It works best with those mares that you know are good mothers, even ones that are aggressive to other adult mares. Inducing lactation is best used with a mare that is multiparous but just happens to be available as a surrogate mother because she is barren."
Once lactation is produced, it helps to stimulate her to accept the foal and allow it to nurse. "To do that, you stimulate the cervix, via the vagina, twice for two minutes at 10-minute intervals," Houpt says. "The mare should then accept the foal because what you're doing by cervical stimulation is mimicking vaginal delivery."
The cervical stimulation causes the nerves in the brain to promote oxytocin release into the blood stream to produce milk let-down and at the same time into the olfactory bulb of the brain, thereby allowing the mare to recognize the foal by smell. "This then creates the maternal trigger for the mare to recognize the foal," says Houpt.
A recent article notes stimulation of maternal behavior without vaginal stimulation using a similar protocol except with a single injection of a large dose of prostaglandin F2-alpha, which is presumed to release oxytocin in the brain.1
According the article, "barren mares that have raised several foals tend to have a mammary gland that is more developed and a more predictable maternal behavior."1 Since these mares are not pregnant, they must be given a very sufficient energy-rich ration because they do not have the same propensity to ingest large amounts of food. The study suggests that the mare be given estradiol benzoate (50 mg/500 kg) and altrenogest (22 mg/day orally) and twice-a-day injections of sulpiride (1 mg/ kg intramuscularly every 12 hours).1 Once the mammary gland has increased in size and filled and milk drops are present, the mare should be milked five to seven times a day for three to seven days. At three to four days with the mare producing about 3 to 5 liters per day, she is ready for adoption.
Using a modified method, another author induced lactation in nonpregnant mares by administering 150 mg progesterone and 50 mg estradiol-17-beta (once daily for seven days on days 1 to 7 ), followed by 5 mg prostaglandin F2-alpha given intramuscularly on day 7 along with 500 mg sulpiride given twice daily on days 1 to 10.2 A foal was placed with each mare beginning on day 1. Oxytocin was administered at 5 IU occasionally. Using this protocol, about 80 percent of treated mares lactated.
Reestablishing the bond
If not creating a surrogate, but trying to correct aberrant behavior in more difficult mares, Houpt recommends putting them behind a pole so that they can't move sideways and tying them so that they can't bite the foal. "Also make sure the foal can't get in front or behind the mare or underneath her so that she can't hurt it," says Houpt. "With the mare so restrained, the foal should be able to get to the udder whenever it likes to easily nurse without a concern of injury."
The reason it is so important to coerce the mare to accept it is that the foal normally suckles every 15 minutes. If the foal has its own access as opposed to your trying to periodically bring the foal to the mare, you are much more likely to get acceptance. You are also much more likely to get acceptance if the foal is within eyesight of the mare and can suckle frequently.
If the mare just doesn't want anything to do with the foal, rejects it or doesn't allow it to nurse, it may think it is another mare's, says Wolfsdorf. "Farm managers are very good about working with these mares, either rubbing the placenta or the mare's manure on the foal to give the foal the mare's smell so the mare then realizes that the foal is hers," she says. "Once the foal makes 'milk-poop' it will also help to promote recognition that the foal smells like her, so she will accept it as her own." Sometimes the unintended consequence of haltering young foals is that the halter might smell of previous foals that have worn them. "This might cause the mare to reject the foal as not hers," says Wolfsdorf.
A nurse mare is another alternative. With nurse mares, sometimes you have to work with them to introduce them to a foal, but with most of them, that's their job, and the farms keep them because of their good temperament and behavior around foals.
"If you're lucky enough to have access to nurse mares, especially when a mare might try to ravage her foal or doesn't have enough milk, and you've tried administering drugs to induce lactation, nurse mares are often times the easier solution, depending upon availability, but may be not the cheapest," Wolfsdorf says. "But nurse mares can save a lot of concern and unhappiness of what an aggressive mare might do to her baby."
And if you try to bottle or hand raise a foal, you have be cautious of its temperament as it matures. You also need to be careful to provide the proper amount of milk, sufficient nursing opportunities and adequate nutrients within the milk replacer. "Also, bottle-raised foals do not have the access to horse social interaction, as they would if raised by a nurse mare," says Wolfsdorf.
The more challenging situation is when you don't have a nurse mare available or when the mare demonstrates only a mild degree of rejection.
"You can provide drugs or hormones to assist milk let-down or to promote mammary development (prolactin, oxytocin) or tranquilize the mare to make them a little bit more amiable to letting a foal nurse," says Wolfsdorf. "People may intervene to hold the mare, to help teach her to accept the foal, to help the foal to more easily nurse and to get the pair accustomed to each other until the bond is established."
Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and veterinary medicine with a background in horses, pets and livestock. Kane is based in Seattle.
1. Daels PF. Induction of lactation and adoption of the orphan foal, in Proceedings. Annual AAEP Resort Symposium, 2006.
2. Steiner JV. How to induce lactation in non-pregnant mares, in Proceedings. Annual AAEP Convention, 2006.