- Dec 16, 2016
The end of one year and the beginning of another is an exciting time for many breeders, as it likely marks the last trimester of their mares’ pregnancies. Due to the rapid changes that occur in the last few months of gestation, it is imperative that owners monitor mares closely. Udder development, abdominal distension, and presence of vaginal secretions are some of the most important changes to monitor.
Average gestational length is around 11 months and a week, or 335 to 342 days. However, sometimes the duration is shorter or longer (330 to 360 days or more) with no detrimental effects on the fetus or mare.
Remove mares from endophyte-contaminated tall fescue pastures no later than 10 months of gestation to prevent abnormal prolonged pregnancy, decreased milk production, and even abortion, and work with your veterinarian to determine whether a mare needs to be medicated with a prolactin stimulation product to negate the endophyte’s effects.
Lack of udder development four to six weeks before foaling in a mare that is not grazing tall fescue or is not on pergolide medication for equine Cushing’s disease should not be a cause for alarm. Normal udder development starts in the month prior to delivery. Typically, the udder becomes engorged within the last few days before foaling (parturition). Waxy accumulation at the nipples from early colostrum (the mare’s antibody-rich first milk) production occurs one to four days before foaling but sometimes earlier. Occasionally, milk leaks from teats for several days to weeks before foaling, resulting in colostrum loss. If this occurs, work with your veterinarian to find an alternative source of colostrum for the neonate before foaling.
Take premature lactation (a clinical sign of placentitis) seriously and have your veterinarian examine the mare’s uteroplacental thickness (abnormal thickness can indicate issues such as placentitis). At the same time he or she should perform a vaginal exam and make sure no vaginal discharge is visible until a few days before delivery. Although abdominal distention is normal and more noticeable in the last trimester, have sudden and excessive distention evaluated to rule out hydrops conditions (excess placental fluids) or excessive edema (fluid swelling) that can weaken the ventral abdominal musculature.
By the tenth month of gestation, the fetus will no longer be able to turn around. At this time mares can be examined using rectal ultrasound to determine fetal presentation. Although we can’t predict complications such as dystocia (a difficult birth), we can determine if the foal’s head is facing the cervix properly (anterior presentation). If the veterinarian can’t visualize the foal’s eyeball through the rectal wall on an ultrasound exam, this could indicate a possible breech (posterior presentation). Additionally, the veterinarian can evaluate uteroplacental thickness, examine the vulva for signs of discharge, and open the vulva if the mare had ever undergone a Caslick’s operation (sutures to prevent reproductive tract contamination). The veterinarian should also boost the mare’s immune system by administering her 10-month vaccinations; this will help her produce antibodies that will ultimately pass through the colostrum to the newborn in the first few hours after birth. The vaccines given will depend on the mare’s geographic location and her risk of disease exposure. Owners should move mares to a foaling facility, if necessary, at this time.
During the final two weeks before her due date, the veterinarian should examine the mare frequently for physical changes such as vulvar laxity and edema, mucoid (resembling mucus) vulvar discharge, broad ligament (which suspends the uterus in the abdomen) relaxation, and udder size and secretion. Predicting the exact time of parturition is challenging, particularly in first-time foaling mares. The vet can, however, measure calcium and magnesium levels in udder secretions, which will increase in the last two to four days before parturition, to predict the time of foaling.
The actual foaling process is short and explosive, with delivery usually occurring in 20 to 30 minutes. If labor progression is slow, or if delivery lasts longer, the veterinarian should assess the mare immediately and correct any foal positioning abnormalities if necessary.
ABOUT THE AUTHOR
Juan C. Samper, DVM, MSc, PhD, Dipl. ACT, practices in British Columbia specializing in reproduction.