The great majority of normal mares do go in foal in a breeding season. In fact, many well-run stud farms have pregnancy rates over 90% at the 42-day pregnancy test.

Unfortunately, quite a number of these mares will fail to deliver a live healthy foal and this is not only distressing to owners and stud master alike, but it can also be extremely expensive because loss of the foal means loss of service fee as well as loss of twelve months feeding and handling of the mare.

Early loss of foal can go undetected

When a mare returns home, or for that matter remains on the stud farm, with confirmation that she is pregnant, everyone is usually in a happy frame of mind. The mare is often the topic of conversation - you are all familiar with comments on how great she looks and how well she is letting down as her abdomen gradually stretches to accommodate the developing foal.

Of course this is great if in fact there is still a developing foal present in the mare. It must be remembered that mares on lots of rough feed often become bigger in the abdomen, not only to accommodate the foal, but also to accommodate and improve their digestion of the rough feed they are eating. Therefore, the size and look of the mare is not always a reliable guide to her still being in foal.

Reasons for foal loss before foaling

Mares in foal can lose their foals even as late as 100 days after service and show very little evidence that they have slipped. When this occurs, there are often problems of misunderstanding between stud master and mare owner that have to be overcome with information on what is going on from both sides of the story.

Infections leading to the death of the foal, severe feed changes, and poor feeding in early pregnancy all contribute to foal loss before foaling. Let us look at the various types of infection that can cause early loss of foals.

Low-grade infections

Firstly, some mares have been infected before being served or inseminated. These are usually low-grade infections, which may not readily show in the normal breeding cycle. These mares may have had an infection that has not properly cleaned up after foaling and, while not showing signs of discharge or any other symptoms, may actually be served and go in foal.

However, the infection that is still lying quietly in the uterus as pregnancy progresses can then interfere with the normal development of the foal. This results in the foal’s death followed by abortion or loss of the foal. Occasionally this occurs so early, for example before 80 days after service, when little to no sign of the abortion is seen, leading to the wrongful impression that the mare may not have been in foal when she left the stud farm.

The infection may remain dormant for many months and, due to stretching of the uterus, poor feeding or some stress factor, may then proceed to multiply and cause interference to the developing foal. This may then result in premature foals, full term dead foals or full term, live, weak, sickly foals that can rapidly die soon after being born, even though they have the best treatment at foaling.

Post-service tests for problem mares

These mares are often best detected through biopsy performed by your veterinary surgeon at the commencement of the breeding season, especially if the mare has had a history of several abortions, or missed pregnancies the previous couple of breeding seasons.

Using such measures as taking swabs before service, taking of biopsies from poor breeders and very careful investigation into the size and shape of the ovaries and uterus, can often give an indication of whether trouble is brewing or what trouble has been affecting the mare in previous breeding season.

'Sleepy foal'

Specific diseases, such as ‘sleepy foal’ are due to a bacterial infection that the foal contracts while still being carried by the mare. The mare is most probably the carrier of the disease and can have foals in later years with the same disease. The disease may show as a weakly, sick foal that soon dies despite treatment, or an apparently strong, healthy foal may become rapidly sick within hours. Treatment is not always able to save every foal due to the fact the foal was infected “in” the mare and the infection spreads rapidly in the unborn foal, damaging kidney, liver and other organs very severely, so that the foals often die of kidney problems as well as infection.

Viral abortion

Viral abortion is present in Australia, but at present is most uncommon in Queensland. It is responsible for big losses if infected mares are introduced into a pregnant mare band with a high contact rate. Infection takes place by contact with an aborted foal or infected afterbirth. A period of time passes before the next mare aborts and this can range from 3 to 4 weeks to up to several months. Most foals are usually aborted between 8 months and full term. Foals can be born alive but usually die within 1 to 10 days after birth.

All visiting mares that are carrying foals should be kept separate from the home mares until 28 days after a normal foaling. Introduction of an outside pregnant mare into the farm pregnant mares can affect all the mares in the group if abortion occurs, hence the need for quarantine.

Because this disease is principally spread by contact with the aborted foal and membranes, great care must always be used to avoid pregnant mare coming in contact with such material. Mares should be kept in small groups of 4 - 5 mares to reduce the contact risk. At all times, if virus abortion is even suspected, you should seek veterinary advice and examination of the aborted foal and membranes. Thorough sterilisation of the area is very important to prevent spread.