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The Mare In Late Pregnancy

For those of you expecting a foal this year, especially those expecting their first foal, you may be starting to get excited and / or anxious shortly as the spring finally reaches us…

Before I alarm you with what may go wrong, please remember that the incidence of birthing problems in mares is very low, around 5% of the general equine population (there are breed variations) and the vast majority hit the ground safely needing no interference at all from us.

A quick word on care for the mare in late pregnancy: Around 60% of the foal’s birthweight is gained during the last 3 months and hence the mare requires protein, energy, calcium and phosphorous in greater quantities than she has done previously. However, as the uterus grows and takes up more room, the appetite often decreases so it is recommended that in the last 90 days approximately 30% of the total daily intake – which is roughly 3.5kg of concentrate for a 550kg mare (alongside an ad-lib forage). This concentrate should be one specifically formulated for breeding stock as they differ greatly in micronutrient and protein levels from a standard i.e. “working” mix.

If your mare is going to a different location for foaling this should be done at least 28 days before the foal is due, this gives sufficient time for the mare to develop antibodies to whatever “bugs” are in her new environment that she can then pass on to the foal.

If the mare is staying at home to foal it is advised that she is moved to her foaling area a good two weeks prior to her theoretical due date in order to get used to the surroundings. A day and night routine should be established and followed without alteration so that she becomes accustomed to the routine and will not be disturbed by these normal occurrences when she is ready to foal. A mare is remarkably capable of postponing active labour when she does not feel safe or secure.

The foaling area is ideally spacious clean and well bedded affording the mare suitableprivacy. If CCTV is not available please consider the practicalities for whoever will be responsible for checking the mare in terms of access and lighting etc.

Complications in a pregnant mare cause considerable distress to owners and present a diagnostic challenge to the veterinary surgeon. Common presenting signs include colic, premature lactation, vulval discharge and ventral abdominal swelling. Disorders directly affecting the mare are easier to identify than those affecting the foetus or placenta.

Colic or abdominal discomfort is relatively common in the heavily pregnant mare and is often, as would be expected, attributed to active foals changing position or kicking. It is very important to distinguish this from more serious causes of colic which include uterinetorsions or ruptures, excessive placental fluid and ruptures of the abdominal wall.

Premature mammary gland development and lactation is seen for several reasons. The mammary gland usually develops over the last month of pregnancy, with the majority of development in the last two weeks. However, this is very variable, especially in maiden mares, which may fail to develop much of an udder until after foaling. Development of the mammary gland weeks or even several months before the due foaling date may indicate abnormality of the foetus or placenta due to placentitis (infection/ inflammation of the placenta), premature placental separation, in utero death of a twin. It is possible to have a prematurely developed udder with no obvious cause and no ill effect. “Running milk” describes premature secretion of milk which can occur up to several weeks prior to foaling. This does not necessarily indicate a problem with the foal but means that valuable colostrum (the first, antibody rich secretion) is lost before foaling, leading to a failure of transfer of immunity to the foal after birth.

Vulval discharge is not common in late pregnancy and must be distinguished from urinary tract problems. The most commonly seen cause is varicose veins in the uterus of an older mare causing a little bleeding, this is not usually serious. Premature placental separation and placentitis can both cause a vulval discharge.

Abdominal swelling or oedema is relatively common. Healthy mares will develop some swelling on the lower belly as part of the normal process.

The main cause of abortion in mares is equine herpes virus which can be vaccinated against (the vaccine is given at months 5,7 and 9 of pregnancy).

Other abnormalities of pregnancy include prolonged gestation – approximately 1% of pregnancies will go on beyond 370 days and in most cases this is “normal” as mares foal “when they are ready”, attempts to induce these foals is ill-advised. Some mares will continue to show behavioural signs of oestrous or being in season during pregnancy for which no treatment is required. Previous lamenesses or injuries often become more apparent in late pregnancy as more weight is carried, foot abscesses are common in broodmares and laminitis can be seen.

Prediction of foaling date

Duration of pregnancy in the mare is said to be between 335 and 342 days. However, there is a naturally wide range of gestational length from 320 to 400 days, as stated above mares will foal when they are ready. This possible variation can mean many interrupted nights sleep checking the mare or watching CCTV (invaluable, if you are in a position to install it, do it!). Because foaling is such an explosive process compared to many other species there is much less time to correct a problem should one occur and supervision ofthe process with timely intervention if needed can make the difference between joy and disaster.

There are several commercial test kits available which are aimed at measuring levels of certain components in the milk and these are now relatively accurate at telling when foaling is imminent. “Waxing up” refers to the typical wax candles on the ends of mares teats due to foal – usually within the next 24hrs. Relaxation of the ligaments either side of the base of the tail is most obvious if you are familiar with how they normally feel so I advise feeling here regularly during late pregnancy.

Again, can I stress that most foalings are quick and trouble free. Be prepared and don’t panic!

Richard Stringer BVSc MRCVS of Stringer Equine Veterinary Practice