I’m not talking about their minds; I am referring to the (sometimes) ­unfortunate aspect of the loss of a pregnancy. “­Pregnancy losses” is not only easier on the ear than the word “abortion” – it is also more accurate, because strictly speaking an abortion is only called as such if the pregnancy is lost after six weeks (after all, the foetus’ organs are developed).

Before this stage, when the pregnancy is still in the embryo stage, a loss is referred to as: embryo death or embryo loss. (For interest’s sake: embryo is the name given to a conceptus before all the organs are formed – about six weeks in the horse and cow – after which it is referred to as a foetus).

Interestingly, successful fertilisation takes place in approximately 90-95% of mares – but often the mare’s uterus is unable to maintain the pregnancy.

So, all too often the assumption is made that “she didn’t take”. The possibility ­exists, however, that she did in fact “take”, but either the uterus was ­unable to sustain the pregnancy or there was an incident of ­embryonic death/loss.

About one sixth of pregnancies are lost ­before day 11 of pregnancy, and another sixth are lost between days 11 and 42 (six weeks) – this is before the pregnancy has even reached the foetal stage (when the loss becomes known as an abortion).

The most common causes of ­embryonic death (< six weeks) are endometritis ­(inflammation of the uterus normally due to a bacterial infection – which is common in mares bred during “foal heat”); insufficient progesterone; nutritional deficiencies and, you guessed it, stress. Stallions are also known to inadvertently transmit bacteria (contaminate) during service, which may then lead to a ­uterine infection and a subsequent embryonic death.

Another interesting fact is that resorption of an embryo in the mare almost never occurs (as it does in many other species). She will always expel the embryo, but it is often too small for it to be noticed.

An abortion, by definition, is the loss of a pregnancy after day 40 (approximately six weeks). Abortions, more often than not, go unnoticed, especially the early and mid-­pregnancies – mares don’t go into labour as would possibly be the case with a late, or full term abortion. The list of what could possibly cause an abortion is very long but, arguably, the most common causes of equine abortion in South Africa are the following:

Equine Herpes Virus (type 1) is a virus that can infect the foetus (normally via the mare’s bloodstream), and cause the abortion of that pregnancy at any time of gestation, but ­abortions are far more common in the second half of the pregnancy. The virus not only causes abortions, it often causes nervous symptoms in mares as well.

The expelled foetus is quite often “fresh” – meaning that it was expelled before any ­decomposition took place in the uterus. There are a few methods to prevent EHV 1 (Equine Herpes Virus type 1): Quarantine programmes when introducing new horses to a group of pregnant mares, also separating horses that are showing nervous symptoms or have ­aborted from pregnant mares not showing these ­symptoms.

The more proactive approach would be to vaccinate mares with an EHV vaccine ­during pregnancy (such vaccines are fortunately ­commercially available in South Africa).

Equine biliary is probably the second most common cause of equine abortions in South ­Africa. The parasite (a protozoon called ­Babesia equi) usually affects the foetus directly and can cause abortion at any stage of pregnancy. More often than not, the mare doesn’t show any signs of the disease itself, but the infection is ­sufficient to affect and kill the foetus.

Equine Encephalosis is probably the ­second most common viral cause (behind EHV 1) of equine abortions in South Africa. There is still a lot to learn about this ­specific cause of ­abortions. Unfortunately a ­vaccine is not ­commercially available against this disease. The ­foetus is ­usually somewhat ­autolysed ­(meaning that it ­underwent a ­degree of ­decomposition in the uterus before it was expelled) at the time of expulsion – which helps differentiate ­Encephalosis from EHV as the cause of the abortion.

Twinning is a common cause of ­pregnancy losses. Unlike many other species, as a rule, the equine placenta is not large enough to ­support two foetuses, therefore if a twin ­pregnancy ­persists, or is allowed to ­persist; this often ­results in the death of one or, ­commonly, both foetuses. If the mare does carry both ­foetuses until full term (which only happens about 10% of the time), the foals probably won’t live ­longer than a week or two.

Bacterial infection is also an issue when it comes to causes of abortion. Most bacteria gain access to the uterus past the cervix (i.e. via the vagina).

When trying to establish the cause of a pregnancy loss, it is essential that the ­necessary tests (smears, blood tests) are carried out as soon as possible (preferably the same day) by a veterinarian. Also, and now I’m really ­starting to sound like a stuck record, if there is any doubt please consult with your veterinarian.

(References available from author)