Determining Delivery Time

I have two horses I have purchased not knowing they were pregnant. How will I know that they are close to delivery? Will they lose their appetite like my dogs do, or will there be other signs I should look for in the last month of pregnancy?                    via e-mail

There are several ways to help you tell where your mares are in their pregnancies and when parturition is imminent. First, your mares can have an ultrasound examination by a veterinarian to help determine the size/age of the fetus. A table of fetal orbital/eye socket measures for comparison can be found in Veterinary Reproductive Ultrasonography by Wolfgang Keahn.

There are also physiologic measures you can check to monitor gestation. There are commercially available kits that allow you to monitor changes in the calcium and magnesium levels in your mare's milk, which can be used as an indicator of impending parturition. There are also inexpensive ways to monitor you mares' gestation. In the New Bolton Center Behavior Lab, we use this short checklist, twice daily, when evaluating mares with uncertain due dates. We make careful notes and even drawings, especially if multiple people are checking the animal from day to day. Some of these things have been more or less useful than others for our situation, but each mare is different and careful monitoring for changes seems to be the best overall approach.

Body changes--We check for relaxed ligaments, which result in increased softness in the area on either side of the tail head, changes in the look or size of the vulva, and for a sunken or hollow look in front of the hips.

Loose stool--We note any changes in stool consistency. Especially for mares that are on a diet of mostly pasture, we have observed mares passing very soft stools right before and during parturition.

Udder development--We note the shape and size of the udder, which seems to vary greatly by individual and from day to day, but large increases in size or sudden shape changes are easily noticed with frequent observation. We find the mare with the fullest udder is not necessarily the most likely to foal, but the udder and teats often become more conical near foaling, with less definition between the two parts. We also check for edema or swelling along the belly floor in front of the udder. This swelling seems to phase in and out during udder development. The most direct predictor of parturition that we have found is "wax" or drip-like plugs visible on one or both teats. In our experience, foaling has occurred less than 12 hours after first seeing these drips developing on the teat.

Behavior changes--When we believe parturition is imminent, we look for behavioral signs of early labor. These include, but are not limited to, increased movement and locomotion, signs of discomfort such as wringing or smacking the tail, quick position changes including shifting weight frequently during rest, and quick activity changes such as going from grazing to resting to walking in more rapid succession than usual, or out of sync with the rest of the group.

Any of these signs can vary by individual and situation, but daily monitoring throughout late gestation will help you know what is normal for your mares, and keeping notes will help you see small and large changes and help coordinate the effort when working with more than one person.

About the Author

Elkana Grogan

Elkana Grogan is a senior animal science major at the University of Delaware. Since 2001, she has been a horse behavior research trainee with Sue McDonnell, PhD, Certified Applied Animal Behaviorist in the Equine Behavior Lab at the University of Pennsylvania's New Bolton Center.

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