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Mares Are Not Cows!

March 16, 2017

That ought to get your attention! You’re probably thinking that I’ve lost my mind. Of course mares are not cows, but it seems to me every year during the breeding season mares are commonly treated like they are cows. Now, let me go on and explain why a mare is not a cow.

A common scenario for me this time of year and as spring progresses is the following conversation: “Hey Doc, my mare foaled last night but she hasn’t cleaned yet. What should I do?” My response is to bring her to me, as soon as you can (last night would’ve been better)! You see, while a cow can have retained fetal membranes or “not clean” for several hours and even days, after about three hours, it can become a life-threatening emergency in a mare. This is because the placenta actually belongs to the foal and not the mare. As soon as the mare foals, the placenta starts to decompose. Because of the way the mare’s placenta attaches to the uterus (think Velcro instead of buttons), this causes a unique situation where the bacteria present at decomposition are able to cross from the placenta to the uterus and enter the bloodstream of the mare. Dying bacteria release toxins that can lead to a life-threatening systemic bacterial infection, uterine infection and laminitis.

So you’re probably asking yourself what am I supposed to do, which brings me to the next reason mares are not cows. If a couple of hours after foaling a mare has not passed her placenta, some common veterinary advice is to give her a dose of oxytocin which, depending on who you ask, maybe up to 5 mL. THAT is a COW dose! There are oxytocin receptors on the surface of the uterus. Once those oxytocin receptors are saturated (in other words they have taken up as much of the oxytocin molecule as they can) any additional oxytocin just causes the uterus to quiver or even seize up instead of having organized contractions. That makes it hard for the placenta to detach. Smaller doses of oxytocin at set time intervals are more effective in producing the kind of contractions that help the placenta let loose. So what do you do if your mare foaled in the middle of the night and you don’t know what time it was? If your foal is up and moving, dried off, and nursing, it has been at least two hours. It’s probably safe to give that first small dose of Oxytocin. After that, it’s time to call for help.

So what are some of the reasons for retained placenta? A difficult birth, infection of the placenta, premature birth and induced labor can all potentially lead to retaine  d placenta. If your mare hasn’t passed her placenta after three hours, please contact me or your regular veterinarian. This situation really is an emergency. Mares are most definitely NOT cows!

Written by Dr. Nichole Logan


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