FOALING SEASON TOPICS

Jennifer G. Adams, DVM, ACVIM

Vaccinations - be sure to have your mare vaccinated for Rhinopneumonitis (EHV 1; use a killed vaccine) at 5, 7, and 9 months of pregnancy to help prevent abortion due to this herpes virus. Also, a booster of the usual vaccinations (tetanus, west nile encephalitis, eastern and western equine encephalitis, influenza, rhino (EHV 1/4) at 4-6 weeks prior to foaling is important to ensure that good antibody levels will be included in the mare's colostrum. This is the best way to prevent tetanus in both mare and foal. A tetanus antitoxin is not necessary after foaling if the mare is vaccinated prior and the foal receives good quality colostrum. The mare should also be dewormed at or close to foaling to decrease exposure of the neonate to GI parasites. The vaccination schedule for weanlings has recently been revised because of new information regarding the foal's response to vaccination while maternal antibody is still present. Basically, it is recommended that some vaccines be given later than the previous recommendations, especially the influenza vaccine, and that 3 boosters are necessary initially rather than two.

Prediction of foaling - The equine fetus can be palpated or ultrasounded rectally during the first few months of pregnancy. During this time, ultrasound measurements of the fetus or specific body parts may be utilized to try and estimate the age of the fetus. However, after 4-5 months, it is no longer possible to palpate the entire uterus rectally as it is located beyond the rim of the pelvis down in the more ventral area of the abdomen. Ultrasound via the abdominal wall may be used if a good image can be obtained and measurements of body parts can be taken. However, these are just estimates. It is very difficult to predict an accurate foaling date based on these types of examinations. Therefore, knowledge of an accurate breeding date is one of the best ways to help prepare for baby's arrival. Mares that have had multiple foals will often follow a similar pattern as far as gestation length. Udder formation will begin in the last month in most mares; however, some do seem to wait until the last minute. In the last week or so, the secretion from the udder changes from a watery substance to a thick sticky form that is the antibody-rich colostrum. The muscles and ligaments around the pelvis and vulva will also relax in the last week. The colostrum can be tested for electrolyte and/or calcium content; however, this change does not occur until the last few days before parturition. All this information can be used to try and determine when the baby will arrive; however, it is rare to predict very accurately without an accurate breeding date.

Attendance at foaling is always a good idea if possible so that dystocias and weak foals can be identified early. However, moms and babies need some time to bond so as little intervention as possible is best if things are proceeding normally. In other words, try not to "hover" too much, especially with maiden mares.

There are devices available that can be used to alert the owner when foaling is actually occurring. One is a transmitter that is sutured across the vulva. It will send a signal to a receiver when the connection is broken by stretching of the area during parturition; the receiver sends another signal to a pager carried by the owner or caretaker. A baby monitor system used by human parents may also be useful if your barn is within range of these products. One can listen without actually having to be present. Video cameras can be installed over foaling stalls with remote monitors located in the house or other areas to allow owners to view the action from the comfort of their homes without disturbing the mare at all. However, there is also the low-tech version of physically checking every hour or so in the last week.

Edema or fluid buildup in the skin of the ventral abdomen and udder is normal in most mares during late gestation. It is caused by sluggish circulation similar to that seen in some pregnant women. It should not be more than a few inches thick. More than this may indicate there is a problem with the uterus. Exercise is a good way to minimize edema - daily turnout is best.

Premature lactation is the loss of milk from the udder during gestation. Milk can be seen dripping or sometimes even streaming from the teats at times. This is not the same as the "waxing" of the teats that is seen just before parturition. The "wax" is a thick substance that just seems to hang at the teat orifice. This usually develops in the last few days before birth. Premature lactation causes loss of colostrum and therefore antibodies, which can leave the foal susceptible to infection. Although it may be that changing hormone levels may cause premature lactation when it occurs just before foaling, this has not been specifically determined. Premature lactation is not an indication that the foal is ready for birth; in fact, just the opposite is often true. Although it may result in loss of antibody for the foals, loss of milk/colostrum just before foaling is not a reason to induce parturition. The pregnancy should be allowed to continue and plans should be made to provide an alternate source of antibody for the foal. When it occurs earlier in gestation, premature lactation can be associated with abnormalities of the placenta. If this occurs long before the foal is due, the placenta should be examined using ultrasound by a veterinarian. Medication may be necessary to treat placentitis if it is present, and to help the mare maintain the pregnancy at this time. The antibody level (IgG) of foals from mares with premature lactation should be measured after 12 but before 24 hours from the time of birth so that if an antibody supplement is necessary, it can be given in a timely fashion.

Failure of passive transfer (FPT) means that a normal amount of immunoglobulins (antibody) has not been transferred to the newborn foal. Foals have no immunity to infection at birth. This is normally transferred to the foal just after birth in the form of colostrum, which is the first milk produced in the 24 hours or so after foaling. Colostrum normally contains high levels of antibody. The foal's GI tract is able to absorb these large molecules only during the first 24 hours following birth. In fact, within 12 hours of birth, this function of the small intestine is rapidly decreasing, so the most effective absorption is thought to occur much earlier rather than later. FPT can happen for many reasons - no colostrum is produced by the mare or poor quality colostrum is produced, the foal is not able to nurse or nurses some but not well enough in the first day of life. If it is obvious that FPT is likely (no milk or weak foal), antibody supplements can be given prophylactically to help prevent infection of the newborn. IgG levels in the foal can be measured after 12 hours of life to determine the effectiveness of passive transfer from the mare in the newborn, and identify the need for supplementation or transfusion if necessary. Before 24 hours, oral IgG supplements can be given to a foal with FPT; after this time, IV therapy is required. If oral products are given after 18 hours, the foal should be checked again to be sure adequate levels have been obtained since we know the GIT does not absorb as well the longer it has been.

Fescue pasture is known to cause several problems for pregnant mares and neonates: weak foals at birth, no or minimal milk production, and prolonged gestation which then can cause dystocia since the foal is larger than usual. The grass contains a fungal organism that produces substances that interfere with normal hormone production in the brain. This results in a lack of normal communication between the pituitary gland and the uterus and the mammary gland. The reproductive organs don't "know" that it's time to make milk and getting close to parturition, so these things don't happen correctly. However, removal from fescue for the last 60-90 days of gestation and during the first few months of lactation will prevent these problems. There is also a medication now available that works fairly well to induce milk production in agalactic mares that have been on fescue. It is a hormone called domperidone; this will correct the deficiency produced by the fescue toxins. It is available in a paste that is administered orally in the last 2 weeks of gestation and/or for the 10 days after foaling if necessary. This treatment should not be utilized alone, removal from fescue is still required.

Meconium is the substance found in the neonatal foal's intestinal tract during gestation; this becomes the first feces that are passed in the first few hours of life. Most often, this is a thick, pasty, dark brown to black substance. After passage of meconium, the feces turn to a golden brown color and initially may be a little soft. Once the meconium is passed, defecation by a normal foal is rarely observed. Since neonates are on an all milk diet, they do not defecate very often, so it is normal not to witness defecation in a foal. Discomfort or difficulty with defecation is usually obvious in a foal as they will be restless, swish their tails a lot, and sometimes strain to defecate. Ingestion of colostrum helps ease the passage of meconium. Therefore, foals that do not nurse well are somewhat more likely to have trouble passing their meconium. Administration of an enema may be helpful in foals who strain vigorously to pass their meconium. However, these must be used carefully and with good restraint to avoid damage to the intestinal tract. Repeated enemas are usually not advisable without veterinary supervision as the procedure can cause irritation of the rectum. This irritation results in discomfort for the foal characterized by straining to defecate. It can then be difficult to determine whether continued meconium retention exists. Therefore, more is not better in this case. If it is known that the foal did not nurse well early on, veterinary intervention may be indicated to provide oral or IV hydration and perhaps oral laxatives to help pass meconium in these cases.

Please contact your veterinarian or an Equine Services veterinarian for more information on any of the topics discussed in this article.

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