Preparing your mare for breeding season
Is your mare ready?
It’s important to breed your mare when she’s in her best physical condition.
When evaluating your mare’s condition consider:
- Is she having regular heat cycles?
- Does she have a uterine infection?
- Is her body condition ideal?
- Is she up-to-date on vaccines, dewormers and preventative dental work?
Regular heat cycles and supplemental lighting
Increasing your mare’s exposure to daylight 2 to 2.5 months prior to breeding can ensure regular heat cycles and ovulation.
- To breed in February, start supplemental lighting in late November or early December.
- Mares not previously exposed to supplemental lighting may take a longer time to cycle naturally.
- For a March or April foal, lighting can begin as early as January because some mares won’t naturally cycle until early May.
Guidelines to supplemental lighting
- Add supplemental lighting in the evening and in the winter until 11 p.m.
- Provide 16 hours of continuous lighting daily.
- Use a 200-watt incandescent bulb or two 40-watt fluorescent tubes; you should be able to comfortably read a newspaper anywhere in the stall.
- Expose pregnant mares, due early in the season, to lighting as they may stop cycling following their foal heat.
Rule out infections
Many stud farms require a uterine culture (pre-breeding swab) on open mares to rule out infection. Uterine cultures can also benefit the mare owner by identifying undiagnosed infection. Infections can waste several heat cycles.
Occasionally, maiden windsucking mares will have an infection. For more information on windsucking and other unwanted behaviors see unwanted behaviors and vices in horses. A complete veterinary exam of the reproductive tract can check these mares for injuries and structural defects that affect fertility and cycling. Barren mares likely underwent examination at the end of the previous season and are ready for a recheck.
We recommend breeding your mare when she’s in moderate body condition (body condition score of 5 to 6) and adding just a little weight. Mares in moderate to good condition are more likely to cycle and conceive than mares that are too thin or grossly overweight. Managing your mare’s nutrition can help you establish the ideal body condition. Learn more about body condition scoring.
Make sure you have prepared for any breeding emergencies that may occur, especially during natural cover. During breeding, contact your veterinarian right away if the stallion has:
- Blood on the penis.
- Damage to the penis.
- A swollen scrotum.
While you wait, safely:
- Try to locate the bleed source, check both the mare and stallion.
- Take the vital signs you’re comfortable with on both horses.
- If the penis is out, apply cold water using a hose.
Care of the broodmare
Now that your mare is pregnant, the goal is to keep her healthy through pregnancy and then deliver a normal, healthy foal.
- Keep mares in small groups with others at a similar stage of pregnancy.
- Separate long-term resident mares of the farm from outside mares.
- Isolate pregnant mares from horses likely to shed illness (e.g. show horses, weanlings, etc.).
- Isolate pregnant mares from recently bred mares.
- Isolate pregnant mares using separate barns.
- Don’t share water or feed sources.
Pregnancy exams and normal loss rates
Days 14 to 16: first pregnancy exam
- Ultrasound performed.
- Twin pregnancy corrected.
- Rebreeding planned if the mare isn’t pregnant.
- Mares have a 6 percent chance of aborting by day 40.
Days 24 to 25: Pregnancy Exam (occasionally done)
- Embryonic heartbeat found
Days 30 to 35: Second pregnancy exam
- Confirms the mare is still pregnant.
- You can rebreed the mare successfully if abortion occurs before this time.
- You can’t rebreed the mare if abortion occurs following 35 days; she will be infertile for 3 to 4 months due to endometrial cup formation in the uterus.
- Mares have an 8 percent chance of aborting after day 40.
- Older mares (20 years old) have an 21 percent chance of aborting at day 40, and 15 percent after day 40.
Feed your mare to maintain moderate to good body condition throughout pregnancy and lactation. You can expect your mare to gain 9 to 12 percent of her body weight during pregnancy. The mare will gain two-thirds of this weight in the last three months when the majority of fetus growth occurs.
During the first eight months of pregnancy, a mare’s nutritional requirements remain the same as when she conceived. In the last trimester, the mare’s requirements increase faster than her need for energy so you will need to supplement her diet for the following:
- Protein (requirement: 8 percent in early pregnancy, 11 to 12 percent in late pregnancy)
Free access to high quality, immature grass or alfalfa will usually meet the mare’s energy and protein requirements. But neither of these forages will meet her increased need for phosphorus. Grass forages will also be too low in calcium. To correct this, mares should receive a daily salt-calcium-phosphorus mineral mix supplement. You can purchase supplements specific to the type of forage you feed.
Supplement with vitamins and trace minerals for fetal development. Copper, zinc, manganese, and iron are stored in the fetal liver. Research shows mares that did not get a copper supplement in the last trimester had less sound foals than mares that did get copper. Feeding supplemental copper to the nursing foals didn’t correct the problems.
Give mares natural vitamin E daily, 30 days before foaling, to increase the passive transfer of antibodies from mare to foal.
Once lactation starts, the mare's energy and protein needs increase further. High quality forage with a mineral supplement can meet these needs, but most mares should also receive a grain/protein mix. You can feed these mixes around 0.5 to 1 pound per 100 pounds of body weight daily.
Most mares are re-bred around this time, and fertility is best when the mare maintains condition. After three months of lactation, a mare's milk production declines. You should start slowly decreasing her grain before weaning to help her dry up.
Most mares benefit from exercise during pregnancy. Many owners use their mares for rigorous athletic competition (including racing and jumping) up to five months with no problems. You can continue light trail riding until the start of the last month of pregnancy. You may need to find a saddle that matches her new shape. We recommend you turn out mares for at least six hours per day if you aren’t riding them.
Most dewormers are safe for use in pregnant mares, but always carefully read the label. Pregnant mares generally remain on the same deworming schedule as other mature horses. Many owners commonly give their mares a dose of ivermectin on the day of birth to help prevent transmission of worms to the foal.
We vaccinate broodmares for several reasons:
- To protect the mare from disease.
- To prevent abortion.
- To protect the foal by passive transfer of immunity through colostrum.
Don’t give your mare vaccines in the first 60 days of pregnancy. Ideally mares have completed their primary course of vaccination before pregnancy. Vaccinating mares in the last 3 to 6 weeks of pregnancy ensures maximal protection of the newborn foal.
In Minnesota, vaccinate your broodmare against the following:
- Equine Herpes Virus-1 (EHV-1).
- Eastern and Western Encephalomyelitis (EEE + WEE, sleeping sickness).
- West Nile Virus (WNV) (late summer booster).
Fortunately, the last month of pregnancy usually lines up with the best time to give spring boosters for EEE, WEE and WNV.
Other diseases to vaccinate broodmares against:
- Herpes virus abortion
- Potomac horse fever
Your vet can advise you on which are best for your situation and when they are best administered. Due to the number of diseases involved, your veterinarian may recommend splitting up the pre-foaling vaccines, giving half six weeks and half three weeks before the foal is due.
Consider the following when transporting your broodmare
How far along in pregnancy your mare is.
- Reliability of the vehicle and person trailering your mare.
- How well the mare travels.
- Weather condition.
Guidelines for trailering your broodmare
- Clean and disinfect the trailer between trips.
- Check the trailer for good ventilation.
- Make sure the trailer has good shock absorption.
- Drive smoothly.
- Plan a route and time that avoids heavy traffic.
- Provide absorbent bedding, water, and hay for longer trips.
- Haulers schedule to stop every five to eight hours.
Research shows that transport (9 hours in moderate temperatures) doesn’t increase the miscarriage rate for mares in early pregnancy (16 to 38 days). In late pregnancy, you should complete long-distance transport at least 30 days before the foal is due. Ensure your mare is at her foaling site four to six weeks before her due date. Mares need time to settle and develop immunity to local organisms.
Signs of approaching foaling
The length of a normal pregnancy is usually 335 to 342 days, but occasionally can range from 315 to 400+ days.
About a month before foaling, many mares start to develop swelling low along their abdomen. Additionally, the udder slowly starts to enlarge and will quickly grow two weeks before term. During early development, the udder remains firm.
A few days before foaling, the udder gradually softens and fills with fluid, which slowly changes in appearance from watery, to thick colostrum. Colostrum is generally present 1 to 2 days before birth. The average mare produces about 2 ½ to 5 liters of colostrum.
Softening of the pelvic ligaments progresses and the mare's tail head may appear more elevated. Wicks of dried mammary secretion (waxing) usually appear about one day before birth and in the last few hours some mares will drip milk.
Preparation for foaling
- Provide the mare an area to foal; grassy paddocks or well-bedded stalls work well.
- Strip-out, disinfect, and re-bed foaling stall.
- Use bedding that is safe for the fall; we recommend clean straw because there is less chance the foal will breathe it in.
- Accustom maiden mares to having their udder handled a few weeks before foaling.
- Wash your mare’s vulva area, inner thighs, and udder when foaling is imminent; you could give her a whole-body bath.
- Wrap your mare’s tail when foaling is imminent.
Things to have available during foaling:
- Phone and numbers for your vet and a close experienced neighbor.
- A clock or watch, notepad and pencil so you can keep track of the timing (estimating time accurately during and after a foaling can be tricky).
- Old clean towels for drying off the foal.
- Disinfectant in a small cup to dip the navel (your vet can help with an appropriate solution).
- Bucket, soap, and warm water for clean-up.
- Strong trash bag for the placenta.
- Plastic or rubber gloves to keep your hands clean.
Monitoring the mare prior to foaling
Monitoring your mare can ensure you’re there for foaling. Aside from changes in her udder, appearance of milk, and waxing, you can also test the milk’s calcium content. While not foolproof, this test can give a reasonable estimate of when the mare may foal. Most mares foal late at night, so milk tests taken in the evening give more accurate results.
Foaling monitors are available that will send a signal to a pager or phone. Again, while not foolproof, these do provide a good estimate.
We usually divide foaling into three stages.
Stage 1: Pre-delivery
The mare’s cervix gradually relaxes.
The mare’s uterus starts to contract, pushing the placenta, foal, and fluids against the cervix.
The mare’s cervix dilates.
The mare’s water breaks.
This process lasts 1 to 6 hours and may go unnoticed. Your mare may appear mildly colicky with signs including:
- Looking at her flank.
- Stretching out.
- Urinating and passing manure frequently.
- Lying down repeatedly.
- Dripping milk.
Stage 2: Delivery
The mare lies on her side. She may stand up and lie down several times before you deliver the head. The mare actively strains, usually in series of 3 or 4 followed by a short rest.
Within about 10 minutes of her water breaking, a whitish translucent fluid-filled balloon (the water bag or amnion) should appear.
Delivering the feet
- A foot will appear in the amnion. The soles of the feet should point to the mare's feet (i.e. the foal is the same way up as the mare).
- It is normal for the legs to protrude further as the mare strains and then slide back in when she relaxes. This gradual movement is important for proper dilation of the birth canal.
- Don’t immediately grab the legs and pull when they appear. Pulling can damage the cervix and vagina and affect future fertility.
Delivering the head
- The nose should appear next, lying on top of the legs. Passage of the head often takes a little longer in maiden mares as the vagina stretches over the poll. Allow time for dilation to occur.
Delivering the chest
- The chest is the widest part of the foal. As the chest enters the birth canal, the mare often strains harder.
- The feet should remain one in front of the other rather than even. This minimizes the width of the shoulders, making them much easier for the mare to pass.
- Once the chest is out the rest of the foal usually passes easily, and the mare often stops straining.
- With normal, healthy foals the water bag usually ruptures by the time the chest is passing so the foal can breathe. If it doesn't, tear it open and clear it away from the head.
Leave the mare and foal alone unless the mare is kicking at the foal.
- The mare generally rolls onto her chest and stands within 15 minutes and the umbilical cord breaks one to two inches from the foal’s abdomen.
Stage 3: Passing the placenta
- Passage of the placenta occurs within 1 hour after the foal’s birth.
- The mare may be slightly crampy while passing the placenta.
- Save the placenta so it can be checked for completeness and for any signs of infection.
When to call for help - signs of a problem
The total time, from water break to the end of delivery, usually takes about 20 minutes. Occasionally this time may extend to an hour. Experience is the best guide to potential problems. Any time the mare isn’t making reasonable progress, a problem may be present. It’s always better to call for help rather than to wait and see. Time is of the essence if we are to get a normal foal.
Call your veterinarian immediately if:
- The amnion or a foot has not appeared in about 10 minutes after the water breaks.
- Only one foot appears and isn't followed by the other.
- The feet are upside down.
- The nose appears first.
- One or both feet are over the top of the head.
- A red bag appears.
- The mare made progress but stopped for more than 10 minutes.
- The mare colics after delivery.
While you wait and if it’s safe:
- Wrap the mare's tail.
- Clean the mare's vulva with mild soap and water.
- Open the membranes if the foal is visible or if you see a thick red sac.
- Keep the placenta, the mare should pass it within 3 hours.
Call your veterinarian immediately if the foal,
- Has severe diarrhea.
- Is lethargic or depressed.
- Isn’t sucking.
- Isn’t standing within 3 hours.
- Starts to nurse but seems to forget how.
- Has swollen joints.
- Is born greater than 1 week before its due date.
- Isn’t allowed to nurse by its dam.
While you wait, milk out the mare if it’s safe, and keep premature foals quiet.
Caring for the newborn foal
Signs of a healthy foal include:
- A very active manner.
- Standing and nursing within two hours.
- Passing urine and orange-brown manure (meconium) within six hours.
When the umbilical cord breaks, dip the navel stump in dilute chlorhexadine diacetate to prevent infection. Repeat this every eight hours for 48 hours.
The mare's first milk (colostrum) is very important for the foal. It contains antibodies needed to ward off infection. If the mare leaks her colostrum, or if the foal fails to nurse well in the first 12 hours, it will be at high risk for life-threatening infections. Newborn foals can develop serious illness quickly. Contact your veterinarian right away if the foal:
- Fails to stand and nurse soon after birth.
- Shows signs of depression.
- Doesn’t nurse as much.
- Is dehydrated.
- Persistently strains to urinate or defecate.
Even if the birthing goes well and your foal appears healthy and normal, we strongly recommend a health check and blood test for antibody levels in the first 24 hours.
Reviewed in 2021