What to do with an Overdue Pregnancy?

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IMG_4623I have a 14 yr quarter horse, five previous foals, typical gestation 12 months. Currently bred to a Jack for mule foal. Breeding dates May 15-June 20, 2015. Going by last breeding date, she is 401 days. Positive pregnancy test. Can see foal moving in abdomen and hind end. Producing milk but bags are not full. Milk is thick, sticky, opaque and sweet. Hind end relaxed, vulva slightly swollen. No “v” shape in abdomen, in fact, she’s not excessively large. She has been like this, excluding sweet tasting milk for six weeks. I am in remote Montana and closest vets want me to haul her into their facilities if I want her seen. All three vets called have basically said “wait and see” and that they will not do an internal ultrasound or palpate because it requires sedation and she is too far along for that. I’m about to pull my hair out. – Jennifer


Hi Jennifer,

Mares bred to donkeys (carrying mule fetuses) typically have a pregnancy length of 372 -374 days (so over a month longer than normal mare pregnancy) but mares may go well beyond their ‘expected’ due date with ‘normal’ pregnancies. They will typically foal when the fetus is mature. So a mare that goes over significantly (more than 30 days) over her due date may have some placental dysfunction resulting in slower maturation of the fetus and a delay in foaling. Parturition (foaling) should not be induced unless there is clear evidence of fetal maturation as this may result in a foal being born dysmature which increases it’s risk of postpartum complications (dummy foal, limb abnormalities, etc).

Another possible reason a mare goes overdue is incorrect calculation of when pregnancy was established. If a mare has been turned out with a male and a breeding was witnessed, the pregnancy may be believed to have been established with that mating; however, if she was left out with the male, he may have covered 21 or 42 days later as well, but the second or third breeding may not have been noted, so the assumption is that the pregnancy was established on the first breeding, when in fact it was established 1 or 2 cycles later.

A far less common reason would be some type of brain defect in the fetus where the pituitary gland doesn’t develop normally so that the normal hormonal cascade from the fetus does not occur to initiate parturition. These fetuses tend to grow to enormous sizes without initiating labor.

Monitoring calcium levels in milk can be performed using water hardness strips (those that test only for calcium, not calcium and magnesium) or by using commercial kits made for this purpose. Elevations in calcium, along with inversion of the sodium:potassium ratio indicate fetal readiness for birth. Calcium levels of 10 mmol/L (40 mg/dL; 400 ppm) indicate readiness for birth and typically foaling will follow within 24 – 48 hours of calcium levels reaching these levels.

Consulting with a veterinarian on the normalcy of the pregnancy is recommended if you have any concerns.

Cheryl Lopate, MS, DVM
Diplomate, American College of Theriogenologists
Board certified in Animal Reproduction

Reproductive Revolutions
18858 Case Rd NE  (equine facility)
Aurora, OR 97002
503-982-5718 (fax)

Wilsonville Veterinary Clinic (small animal facility)
9275 SW Barber St
Wilsonville, OR 97070
503-682-3540 (fax)

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4 thoughts on “What to do with an Overdue Pregnancy?”

  1. We have 2 mares who’s last breeding date was 5/15/20. They were both bred to mammoth jacks. Our vet told me that mule colts can take up to 14 months to foal. It was 14 months yesterday and neither of them are showing serious signs of foaling. One will expel milk when I pull on her teats, the other only clear liquid. They were both confirmed to be in foal by our vet by palpating last year. Is it normal for horses to carry mule babies this long? Neither of our mares are overly large for being 14 months in foal. I’m just so confused! We bred for registered Missouri Foxtrotters previously; this is our first experience with breeding for mules.

    Thanks in advance for any insight!

  2. Good morning, curious what the outcome was. I have a 16yr old mare bred to a jack for a mule baby and we are going on day 407, with all above symptoms also. How many days did your mare go and was the mule healthy?
    Thank you Jacy

    • Here was the reply from Jennifer. Keep in mind this was several years ago. Nice that she got back to us!
      Jennifer’s reply:
      Took my mare into vet for ultrasound. Vet induced labor but foal didn’t survive.
      I asked her if she tried again and here was her response:
      Tried one more time for a mule colt but she didn’t take. Tried following year for horse colt and had a nice filly.

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