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EquineRepro@yahoogroups.com FAQ's about the pregnant mare

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Q1: My mare is about 120 days pregnant and I saw her in heat today. Should I get her checked to see if she is still in foal?
A: While it would certainly be worth getting your mare checked for pregnancy again if you have concerns, in all probability what you are seeing is a not infrequently seen response to increasing hormone levels in some pregnant mares. Estrogen levels start to increase significantly by about 70 days of pregnancy and this can result in some mares displaying estrus ("heat"). Some of these mares may even go so far as to allow the stallion to breed her, which is not a desirable occurrence during pregnancy!
Q2: My pregnant mare has started behaving like a stallion, is this indicative of a problem or that she is carrying a colt?
A: Neither! At certain stages of pregnancy hormone levels in the mare will fluctuate as a result of the mare herself increasing secretion, or the fetal-placental unit (FPU) secreting increased amounts of some hormones (which then of course increase circulating levels in the mare). One of the hormones that is secreted by the FPU - of both male and female fetuses - is testosterone. If the level gets high enough, it can produce stallion-like behaviour in the mare, which will decline further on in pregnancy as the testosterone secretion reduces.
Q3: My mare is 7 months pregnant [var: some other duration before 300 days] and her udder has developed and I saw milk dripping from her teats today. Is this a cause for concern?
A: Yes!!! You should have your vet out to evaluate the mare immediately!!! Inappropriate lactation any time before about 300 days of pregnancy is usually an indication of impending abortion. That abortion may be due to a variety of causes, some of which you can do nothing about at this stage (twinning for example), but others may respond favourably to suitable treatment - one such problem could be placentitis. An experienced reproductive veterinarian will perform a rectal palpation (to determine if there is fetal movement or not - if the foal is already dead, then attempting to retain a pregnancy is not desirable), and an ultrasound. The ultrasound will be used to evaluate CTUP, which stands for "combined thickness of the uterus and placenta". At various durational points of pregnancy this thickness should be no more than a certain thickness. If the CTUP is thicker than it should be, that indicates that there is inflammation of the placenta (which is what placentitis is). Treatment for placentitis generally includes progestin therapy, anti-prostaglandin release therapy, and a broad-spectrum antibiotic therapy. Use of Clenbuterol (VentipulminTM is now regarded as not being beneficial as long-term treatment will not suppress uterine contractions).
Q4: When is it necessary to have the mare pregnancy checked for twins?
A: Mares should be checked by ultrasound before the conceptus "fixes" - at about 16 days post-ovulation - typically at 15 days. the earlier that twins are detected and one is pinched off, the more successful the outcome. There is also the need to check the mare again no later than day 28 post-ovulation though, as if there was a second "asynchronous ovulation" (one that occurs on a different day from the primary ovulation), there is the possibility that the second pregnancy may not be detectable on day 15, as pregnancies have occurred with a second ovulation taking place as much as 6 days after the breeding and primary ovulation!
Q5: Are there situations where it is better to leave a twin?
A: In most cases, NO! If one is checking the mare after fixation has taken place and find twins sitting next to each other and touching, then one may contemplate leaving them until day 28 post-ovulation at the latest to see if one will naturally resolve. A high proportion of pregnancies start as twins (as much as 30% on older Thoroughbred mares!), but many are naturally resolved. If on the day 28 check the twins are still found to be present with no indication of one resolving, it is probably pest to give prostaglandin and start the breeding all over again when the mare comes back into estrus.
Q6: What happens if I don't check the mare and she has twins? Isn't it good to have two foals rather than one?
A: In the vast majority of cases, the mare will abort during mid- to late-term pregnancy. The equine uterus is not designed by nature to provide sufficient nutrition for two foals, and what usually happens is that one of the foals - or both - will die in utero as a result of starvation. Sometimes one (or both) foals may make it to term, but often the foals are stunted, and commonly one or both will die shortly after birth. Other not uncommon sequela include dystocia and loss of the mare and/or damage to the mare's reproductive tract during delivery rendering her infertile or a problem breeder in the future.
Q7: Is it really such a big issue for a mare to be found to be carrying twins? My neighbour has a mare that has three sets of twins with no problem!
A: Yes it is a big issue. Your neighbour should buy lottery tickets, they have tremendous luck!!!
Q8: Are there blood [var: urine/saliva] tests for pregnancy? [var: Twins? Fertility?]
A: There are several blood tests available to determine pregnancy status of the mare. They test for specific hormone presence in the blood, and those hormones may only be present at certain stages of pregnancy, so correct timing of the testing is essential. Additionally, there may be instances of false positives or negatives, so no blood test is going to be as conclusively reliable as a well-performed rectal ultrasound examination by a competent technician. There are essentially three tests offered:
  • The Early Pregnancy (or Conception) Factor test (EPF or ECF). This was introduced in 2004 and was heralded as being capable of indicating pregnancy status as early as 6 days post ovulation, which had tremendous positive implications for persons doing embryo transfer. Unfortunately, it rapidly became apparent that the reliability was not what it was thought to be, and it has now been withdrawn by reputable marketing companies.
  • The "Pregnamare" stall-side test kit, which test for "Equine Chorionic Gonadotropin (eCG)". This hormone becomes apparent at around 35 days of pregnancy, and the test is not recommended to be performed before about 40-45 days of pregnancy. Similarly, the hormone will cease to be apparent anywhere from about 90 days on, so testing should be performed before about 70 days. An additional problem exists in that if the mare loses the pregnancy after the secretion of eCG is commenced, the blood test will still show the mare as being pregnant despite the fact that she is not.
  • Estrone sulfate and/or total estrogens can be tested for with reliable results for pregnancy indication after about 100 days of pregnancy through to term. There is a stall-side assay available in North America and the southern hemisphere called the "FoalProof" test kit (follow that link to their site).
Urine or saliva is not generally used as a testing source, although assaying of estrogens from the urine has been indicated as being reliable, although it will require a laboratory test, not the FoalProof test kit. There are no tests other than ultrasound that can indicate twinning. Testing for fertility covers such a huge field that one cannot give a generalized answer that will cover all aspects.
Q9: My mare is overdue, what should I do?
A: The first thing to be aware of is that there is no such thing as a "due date" in the pregnant mare!!! The average pregnancy duration is around 340 days, but the "normal" range is anywhere between 320 and 370 days! The next aspect to consider is if the mare has been exposed to an endophyte fungus (via fescue grass for example). If gestation duration is prolonged and she has been exposed to an endophyte, then it is important to have the mare evaluated by a veterinarian with a view to initiating treatment if felt appropriate (such treatment may include use of Domperidone). A valuable resource for persons concerned about pregnancy duration is the article entitled Is my mare overdue?
Q10: My mare aborted this morning, should I sent the aborted fetus for necropsy?
A: Probably, yes. There are many causes for abortions, and some of them may be repeatable and yet can be avoided in the future with suitable management, so it can be very valuable to realise there is a requirement for that management. You should also send off the placenta, as much can be told from that as well. Contact your veterinarian and they will probably be able to tell you what to do and where to send it.
Q11: When should I vaccinate my pregnant mare, and for what?
A: Pregnant mares should be immunized against the abortion strain of Rhinopneumonitis (EHV-1, strain 1) at a minimum of 5, 7 and 9 months of pregnancy. If they are in high risk situations (still competing, live in a boarding barn etc.) then immunizing at 3 months may also be warranted, and if she is not looking as though she is going to foal by 11 months, then reimmunizing then is good too. It is important to use the correct vaccine for the abortion strain of "Rhino" - the regular "spring shot" vaccination will not protect against the abortion strain.

Other vaccinations will depend upon what is prevalent in the way of diseases in your area. That can be discussed with your veterinarian. Note that a full panel of immunizations should be given about 30 days prior to the mare foaling in order to get maximum antibody levels in the colostrum.

There has been much alarm spread since the introduction of the West Nile Virus vaccine about it's use in pregnant mares. Research has found that there is no indication of an increase in pregnancy loss or fetal deformity if this vaccine is used in pregnant mares. This is despite a website that purports to prove such a link - even though there is no scientific evidence presented there!
Q12: I have heard about Neonatal isoerythrolysis, but I am not quite sure if I need to be worried about it with my mare. Should I be?
A: Neonatal isoerythrolysis (NI) is a condition where the foal develops antibodies against its own red blood cells, which are then destroyed. If left untreated, the foal will die (and even if treated some will too). It is more commonly seen in second or subsequent foals rather than first foals (although it may still be seen in first-time foaling mares), and is far more common in mule foals than horses. First signs are often seen 48-72 hours after foaling when the foal starts to be lethargic, and possibly yawns more than normal. Blood testing will indicate low red blood cell content. If undetected, the foal will start to exhibit signs of jaundice, with the whites of the yes, the gums and other membranes becoming yellow. If untreated, the foal will die. This is a condition where "an ounce of prevention is worth several tons of cure"!!! Being aware of incompatible blood groups between the sire and dam is a starting point, as certain groups will be more likely to result in this problem. Pregnant mares can be checked during late term for presence of antibodies in their blood, and if detected, the foal should be prevented from nursing at birth and for up to about 72 hours after (obviously colostrum and milk must be bottle fed from another source). This can be achieved by use of a muzzle. Keep milking the dam out to maintain milk production, as after the 72 hours, the muzzle can be removed and the foal permitted to nurse from the dam. If there is any question of NI being a possibility, but antibody levels in the mare were not checked, then after birth (and before nursing), a sample of blood can be taken from the foal and colostrum from the mare, and a "Jaundiced Foal Agglutination Test" performed to determine if there are antibodies in the colostrum. If there are the above nursing prevention protocol is followed, if not then nursing from the mare is fine.