Pregnant Mare

As a conscientious owner, you probably have many questions about carrying for your expectant mare.  In truth, you may be a little worried. Relax.  With a little TLC, your mare should progress through her pregnancy without mishap.  Proper nutrition, deworming, exercise and vaccinations will help ensure a healthy pregnancy, and you can look forward to the birth of your new foal with greater confidence.

Precarious Beginnings:
The earliest days of an embryo’s existence are perhaps the most precarious.  During the first 30 days, there is a 10-15 % chance that the embryo will be resorbed.  Stress, illness, uterine infection, hormonal abnormalities, the presence of twins and other factors have been implicated in early embryonic loss.  Often, the cause remains undetermined.

Troublesome Twins:
Some reproductive specialists recommend an ultrasound exam at 14-16 days post-ovulation to detect twins.  Early detection of twins provides an opportunity to eliminate one embryo, thus allowing the other to develop normally.

Helping Nature Take Its Course:
Good broodmare management is the best aid for helping the mare make it through the critical first 30-60 days of pregnancy.  The mare should go into the breeding season fit and perhaps gaining weight.  Severely underweight mares will have more trouble conceiving than will mares of appropriate weight.  Avoid stressing the mare as much as possible.  Stress can cause a drop in progesterone, a hormone which helps maintain pregnancy.  Illness and/or fever can cause the mare’s system to produce prostaglandins, which may cause abortion.

Use Good Judgment:

  1. Transport your mare only if necessary.
  2. Use caution when exposing your mare to other horses.
  3. Provide nutritious forage, but don’t overfeed.
  4. Make sure the mare is current on vaccinations and deworming.
  5. Consult a doctor at Village Veterinary Hospital for recommendations regarding specific vaccinations and deworming intervals during pregnancy.

Coasting through Mid Pregnancy
Unless there are special circumstances, during the first 7 months of pregnancy, treat your horse as you would a non-pregnant one.  She will benefit from moderate riding or exercise. She should always have plenty of clean, fresh water and high quality forage.  The mare will also benefit from routine hoof and dental care, standard vaccinations and regular deworming.

Vaccinations should be current since infectious diseases can trigger abortionA four-way inoculation for Eastern and Western encephalomyelitis, influenza and tetanus is recommended at the beginning of pregnancy.  A booster should be given one month prior to foaling to increase the antibody level in the mare’s colostrums (first milk) and help protect the newborn foal from disease.  Also, the mare should be vaccinated for equine rhinopneumonitis (commonly called virus abortion or rhino) at 5, 7 and 9 months gestation.  Consult a dr. at Village Veterinary Hospital regarding other vaccines that may be advisable in your area, such as rabies, rotavirus and botulism.

Most deworming agents available today are relatively safe for pregnant mares.  Consult a dr. at Village Veterinary Hospital to establish an effective and safe deworming schedule for your mare.

Changing Needs:
During the last four months of pregnancy, the foal will grow rapidly.  To accommodate this growth, the mare’s energy needs increase.  Even so, special nutritional supplements are probably unnecessary.  Good-quality hay and forage should remain the bulk of the expectant mare’s diet.  Concentrated feeds, such as grains, may be added to the ration to bolster energy intake without adding excess bulk.

Home Stretch:  
The average length of pregnancy in the mare is 338-343 days.  However, normal gestation can range from 320-380 days.  If your mare’s pregnancy extends much past 340 days or you’re concerned, call a dr. at Village Veterinary Hospital at 505-869-2627 and we will be glad to set up an appointment and make sure that everything is OK.

Impending Birth:
There are obvious as well as subtle signs of impending birth.  The time frame during which they occur varies from mare to mare.  The most obvious and reliable are:

  1. Filling of the udder (two to four weeks pre-foaling)
  2. Distension of the teats (four to six days pre-foaling)
  3. Waxing of the teats (one to four days pre-foaling)
  4. Obvious dripping of milk

More subtle signs include:

  1. Softening and flattening of the muscles in the croup
  2. Relaxation of the vulva
  3. Visible changes in the position of the foal

Please contact our office if you have any further questions about your pregnant mare at