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  Discussion on Placenta Previa
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Posted on Saturday, Apr 3, 1999 - 12:09 pm:

Hello Kate, we had a rather thorough discussion of this condition last year and this is one of the posts:

We have several issues to deal with here. There is no firm answer to the question "should I induce or not", but let's explore the pros and cons.

First, for those wondering what placenta previa is all about. In a normal birth, the placenta ruptures at the cervix, while remaining attached everywhere else, and the allantoic (thin and white) membrane, with the foal inside, presents just outside the vulva. The placenta remains attached to the uterine wall and continues to supply the foal with oxygen during the birth. Birth in the horse is a rapid process requiring less than 30 minutes and the placenta is released shortly after the birth.

In premature separation of the placenta (p. previa) the unruptured placenta (thick and dark red) presents at the vulva first. This is a sign the placenta has detached from the uterine prematurely. Since this is the foals only source of oxygen he will suffocate shortly after the placenta has detached.

Now the question Judy and P. F. have is "since my mare has had this problem once, is it better to induce labor or not"? The advantages to this technique is that if problems develop, help is right there. But the procedure also increases the chances of complications. The most common problem is immaturity of the foal's respiratory system quickly followed by dystocia which risks both the mare and foal. If we had good statistical data it would be a simple calculation to determine which held the greater risk, at least from a monetary stand point. But no such data exists. Of course if some problem in the mare has been identified that you know will cause problems at birth the choice is easy, you induce. Mares with a history of neonatal isoerythrolysis, severe past vaginal trauma may fall into this class. Repeated episodes of premature separation would fall into this class, but I am not sure after one episode it is indicated. So often we do not know why this mare had this problem at this time and so do not know if she will so it again.

There are some things that can be done to help decrease problems associated with induced abortion. The most important is to ensure the fetus is mature enough to make it on his own. Fortunately this is not hard. There is a strong correlation between changes in the electrolyte concentrations in the mammary secretions and the foals maturity. Particularly the concentration of calcium and the ratio of sodium and potassium. Calcium concentrations are easily monitored with Softcheck Test Strips (Environmental Test Systems, Elkhart, IN). Dilute the milk sample with double distilled water with one part milk to 6 parts water. Dip the strip into the solution and when the hardness rises above 250 ppm parturition can be induced

Ideally you would want the mare at a facility where a Caesarean could be performed, but at the least oxygen, resuccitation equipment, obstetrical supplies and equipment, anesthetic induction drugs and a surgical pack should be available.

There are several techniques used to induce mares. Low dose oxytocin (<20 IU) given IV either slowly or as a bolus. Usually mares will begin parturition within 15 minutes with foaling completed within an hour.

The other technique uses the prostaglandins, prostalene (4mg. SC) or fenprostalene (two 0.5mg. doses SC at 2 hour intervals). Mares will usually foal within 4 hours. As long as the mammary secretions indicate the foal is ready the prostaglandin method may have a lower incidence of complications.

The complications associated with induction have been: prematurity, failure of passive transfer, myometrial spasm, premature separation of the placenta, malpresentation of the foal, and retained placenta.

There are other posts with more information and experiences but can only be accessed through the Repro Problem Menu in the Member's Site.
The Advisor Vet, RN Oglesby DVM

Posted on Sunday, Apr 25, 1999 - 8:04 am:

Dr. Oglesby's reply mentioned Ca+ levels in the udder secretions. We have been using this as a predictor for foaling. However, my professor has misplaced the articles about the original research. I'm hoping that someone can provide the references. Thanks.

Posted on Monday, Apr 26, 1999 - 6:44 am:

Hello Sara,
Thank you for the emailed kudos Sarah. This is one of several by the fellow who did most of the original work, JC Ousey:


Preliminary studies of mammary secretions in the mare to assess foetal readiness for birth.
Equine Vet J 1984 Jul;16(4):259-63
Ousey JC, Dudan F, Rossdale PD

The status of the mare and foetus in relation to readiness for birth was assessed by measurement of the electrolytes sodium, potassium and calcium in mammary secretions pre-partum. Sixteen Thoroughbred mares were allowed to foal spontaneously and the ionic status of their mammary secretions was measured over three to five weeks pre-partum. From these measurements, a scoring system was developed where an ionic score of 35 points or more suggested that the mare was within 24 h of foaling. On the basis of this ionic score, 10 pony mares were induced with either oxytocin or fluprostenol and assessment of foal maturity was made by physical, behavioural and physiological criteria. Eight pony mares, induced when the ionic score was 35 points or more, delivered full term foals; two mares were induced when their scores were 30 and 20 points and delivered a full term and slightly immature foal respectively. These results suggest that foetal maturity may be related to electrolyte concentrations in mammary secretions and that an ionic score of 35 points or more may indicate that induction would be successful in terms of maturity of the newborn foal.
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