Published by Kristina McGinnis, DVM
The first step of deciding to breed your mare or buying a brood mare is to determine whether she is able to conceive and if she is able to maintain a pregnancy. A breeding soundness examination is an important step to ensure you have a fertile mare to breed. Your veterinarian can perform this and it will consist of a detailed general and reproductive history, a thorough general physical examination, body condition scoring, and a comprehensive reproductive examination. Good body condition is necessary for fertility and maintaining a pregnancy. Research indicates that mares with a body condition score (BCS) of 6-7 have higher pregnancy rates. This is based on a scale from 1-9 with 1 being emaciated and 9 being severely obese. Additionally, overall good health is necessary as any illness or injury can result in decreased fertility.
The reproductive examination will include evaluation of the external genitalia, a speculum examination of the vestibule, vagina, and cervix, and a transrectal reproductive ultrasound to examine the uterus for fluid, cysts, or any other abnormalities. A uterine cytology, culture, and biopsy will be performed as well to determine if endometritis (inflammation and infection of the uterus) is present and if the endometrium is capable of maintaining a pregnancy. The endometrial biopsy is probably the single most important indicator of a mare’s ability to conceive and maintain a pregnancy. The biopsy results are placed into 3 categories: 1) 80-90% chance of pregnancy 2a) 50-80% chance 2b) 10-50% chance 3) Less than 10% chance.
Once your mare has “passed” the breeding soundness examination, you may start the breeding process. You first have to choose the stallion and decide whether you would like to breed via live cover or artificial insemination. Your veterinarian will need to check your mare with transrectal ultrasound periodically to determine when she is in estrus (heat) and the best time to breed. Depending on the tendency of the mare to develop post-breeding endometritis, she may need non-steroidal anti-inflammatories (NSAIDs) or corticosteroids at the time of breeding.
The vulvar conformation of the mare is very important in maintaining a pregnancy. If 2/3 of the vulvar lips are above the pelvic brim fecal contamination of the vestibule and vagina is more likely, which can result in inflammation and prostaglandin release that is not compatible with pregnancy as well as provide an avenue for ascending infection. Additionally, mares that are windsuckers will also have inflammation of the vagina and vestibule resulting in prostaglandin release. A caslicks procedure can be performed on these mares at the time of breeding or at pregnancy diagnosis. A caslicks is where the edges of the vulvar lips are incised and sutured together to prevent fecal contamination and/or air irritation. The caslicks will need to be removed just prior to foaling.
The mare should be checked for pregnancy around 14 days after ovulation. The uterus should be thoroughly evaluated for the presence of twins. If two pregnancies are present, one will need to be reduced at that time, as the equine uterus does not tolerate twins well. At the time of reduction, it would be wise to administer a NSAID and supplement with altrenogest (ex. Regu-Mate) to provide a healthy uterine environment for the remaining embryo. Normal healthy broodmares do not require altrenogest supplementation; however, if any irregularity is present at the 14-day pregnancy check, such as poor uterine tone, increased uterine fluid, decreased progesterone, odd appearance to the corpus luteum, or any other worrisome finding, altrenogest supplementation until day 120 of gestation may be warranted.
The fetal heartbeat is present by day 25 of gestation. An ultrasound to evaluate the presence of fetal heartbeat should be performed around that time. Fetal sexing can be determined via ultrasound in two windows: day 58-73 or day 110-120 of pregnancy. Further recheck ultrasounds can be performed periodically throughout pregnancy; the frequency depends on the individual mare and veterinarian preference.
Vaccinating broodmares is imperative for disease prevention, passing immunity to the foal, and prevention of abortion. Equine herpes virus one (EHV-1) is a major cause of abortion in mares. The virus is inhaled and without adequate local immune protection it can cause viremia (systemic illness), which results in uterine ischemia (lack of blood flow) and death to the fetus. Pregnant mares should be vaccinated at 5, 7, and 9 months of gestation. It is possible, although rare, for properly vaccinated mares to abort due to EHV-1. Therefore, it is essential to institute management tactics to prevent infection as well. Such methods include separating all pregnant mares from the rest of the herd as well as isolating mares that have aborted and any horses those mares have come in contact with.
It is important to booster all routine vaccines 4-6 weeks prior to the expected foaling date so that adequate antibodies are transferred to the foal in the colostrum. Routine vaccination includes tetanus, rabies, eastern equine encephalitis, western equine encephalitis, Venezuelan equine encephalitis (if it affects that area), and west nile virus. Additionally, if the farm has a known problem with Rotavirus, which causes profuse watery diarrhea in foals, then the mare should be vaccinated at 8, 9, and 10 months of gestation. Other vaccinations, such as influenza, strangles, botulism, and Potomac Horse Fever, can be discussed on an as needed basis with your veterinarian.
Excellent nutrition based on the mare’s metabolic needs for her reproductive stage is a necessity. Mares have to be in good body condition for fertility and they must maintain the body condition throughout pregnancy. Mares have similar metabolic needs through the first 8 months of gestation. Late gestation dramatically increases metabolic needs of the mare due to the fact that 60-65% of fetal growth occurs during this period. Consequently, the mare will need a significant increase in feed during late gestation (9-11 months). Lactation is also a very metabolically demanding time. Mares will produce 3% of their body weight in milk on a daily basis during the first 12 weeks of lactation; this means the mare needs 70% more calories than her maintenance diet. Determining a feeding regiment that is right for your mare(s) can be done with the consultation of your veterinarian and/or an equine nutritionist. Ensuring the mare has an oral exam annually and teeth floated as needed is important to assist in the maintenance of body condition.
One crucial aspect of nutrition is to keep the mare off of tall fescue grass during breeding and throughout gestation. There is a symbiotic relationship between fescue grass and an endophyte fungus, Acremonium coenephialum, which results in a variety of negative effects on gestation and the foal. Mares who consume this grass can have decreased fertility rates and/or early embryonic death. Pregnant mares consuming the grass can also suffer from prolonged gestation, abortion, dystocia, premature separation of the chorion, placentitis (thickening of the placenta), retained placenta, and agalactia (suppressed milk production). Negative effects on the foal include abnormal maturation, weakness, reduced immunity, and starvation from agalactia. If it is not possible to prevent the broodmare from grazing fescue, there are drugs available to counteract the effects, such as domperidone and reserpine.
Routine deworming of the mare is important prior to and during gestation to produce a healthy foal. The best deworming protocol for your horse/herd should be determined with your veterinarian. It is recommended to deworm at least twice a year. Most dewormers are safe to use during pregnancy; however, it is critical to check the label before administering any drug to a broodmare. It is a common practice to give the mare ivermectin on the day of foaling to decrease the transmission of Strongyloides westeri, which can be spread via nursing four days post foaling.
Lastly, it is essential to properly prepare your mare for foaling. Moving the mare to a clean and dry location that can be closely monitored 4-6 weeks prior to the expected foaling date is strongly recommended. This will allow her to acclimate to her environment as well as build up an immune response to that particular environment that she can then pass on to her foal. The mare’s udder and her underside where the foal may try to nurse should be cleansed. If a caslicks was performed, the vulva should be opened to prevent tearing at parturition. Knowing the signs of impending parturition will help to better predict the time of foaling. Physical changes include relaxation and edema of the vulva, mammary gland development, scant vulvar discharge, relaxation of the tailhead, and changes in the udder secretions.
Mammary gland development, also referred to as bagging up, and secretions are the most useful tools to predict impending parturition. The mammary gland begins developing one month prior to foaling and has a drastic increase in size within two weeks of parturition. The udder is typically engorged within days of foaling. Udder secretions may start as early as one month prior to foaling, and they will change from a clear or yellow color to white and milk-like. The appearance of waxy secretions on the teats usually occurs 1-4 days prior to foaling but can occur as early as 2 weeks. The waxy secretions are from early colostrum formation. Colostrum is the first milk the mare produces, and it contains all of the antibodies she will pass to the foal. Therefore, if the mare is leaking a significant volume several days to weeks prior to parturition, it is strongly encouraged to collect and freeze that colostrum so that it can be fed to the foal at birth to ensure adequate passive transfer. Mammary gland secretions can provide valuable information on impending parturition. There are several milk tests available to determine the electrolyte levels, which change related to fetal maturity and viability, and therefore are informative on the proximity of foaling.
When the mare is close to foaling, she should be closely monitored throughout the day and night. Commonly used monitoring systems include camera stalls and foal alert systems. The foal alert system involves suturing a device into the mare’s vulva that will separate and produce an alarm at foaling.
When the mare is suspected of foaling that evening, it is recommended to clean and dry the perineal region as well as to wrap the tail for a cleaner environment. There are three stages of parturition. Stage one is the preparatory phase, which can last 30 minutes to 4 hours. During this phase the mare can exhibit signs similar to colic, including flank watching, restlessness, raising and swishing the tail, and urinating small volumes frequently. This phase is very important for the repositioning of the fetus into the “diving position” pictured below. Stage two begins at the rupture of the chorioallantois allowing the allantoic fluid to escape the uterus, also known as the water breaking. This phase includes the expulsion of the foal. If there is a red bag present at the mare’s vulva it should be ruptured immediately. Instantly rupturing the membrane is essential to foal survival, as this is indicative of premature placental separation and lack of fetal oxygenation. Calling your veterinarian after the membrane is ruptured is strongly encouraged. If no red bag is present, the white amnion should appear at the vulva within 5 minutes of the water breaking. The foal will normally pass within 30 minutes. If the foal has not passed in that time or if there is no significant progress over 5-10 minutes, it is strongly encouraged to call your veterinarian for assistance. After the foal has passed through the mare’s pelvis, stage 3 begins. This stage consists of the expulsion of fetal membranes and uterine involution. There is a “1-2-3” rule to follow at this point. The foal should stand within the hour, nurse within 2 hours, and pass meconium within 3 hours. The mare should also pass the full placenta within 3 hours of foaling. The placenta can be tied to itself so it hangs just above the hocks to avoid being stepped on. If the placenta has not passed within 3 hours please contact your veterinarian immediately.
The umbilicus usually breaks when the foal attempts to stand or when the mare stands. If the umbilicus does not rupture on it’s own, it should never be cut as that can result in a patent urahcus and/or excessive hemorrhage. There is a pre-determined break site that is evident by a pale strictured area. This point should be identified and the forefingers are used to twist above and below taking great care not to pull excessively on the cord. Once the umbilicus has been torn, the stump should be closely evaluated for hemorrhage, urine leakage, or swelling before being dipped in a dilute 0.5% chlorhexadine solution.
Once the mare has passed the placenta it should be thoroughly evaluated to ensure all pieces are intact. It is crucial to the mare’s health that no pieces of placenta are retained within the uterus as this can result in severe systemic illness (metritis). Saving the placenta in a large bag within the refrigerator is recommended so that your veterinarian can evaluate it fully to look for any missing pieces and signs of placentitis. It is strongly recommended to have your veterinarian evaluate both the mare and foal within 12 hours of parturition to ensure they are both in good health and that the foal has adequate passive transfer.
If you have any questions or concerns regarding your mare or foal’s health please feel free to contact Carter Veterinary Services.
Brinsko, Steven P., Terry L. Blanchard, Dickson D. Varner, James Schumacher, Charles C. Love, Katrin Hinrichs, and David Hartman. Manual of Equine Reproduction. 3rd ed. Mosby Elseveir. Print.