Probiotics and their use in horses

Dr Elspeth Milne BVM&S PhD DipECVCP FRCVS, Royal (Dick) School of Veterinary Studies, Edinburgh.

Many horse owners will have heard of the term “probiotic” and may have used such preparations for their own horses. This short article is intended to explain what probiotics are and what they can be used for.

What is the “gut flora”?

Like most animals, foals are born with a sterile gut but immediately after birth, they start to acquire bugs from the environment, particularly from their mother’s dung. This gradually settles down to a relatively stable mixed population of bacteria, protozoa, yeasts and fungi that live in the large bowel. These organisms are known collectively as the gut flora. To give an indication of the numbers of bacteria present, approximately one third of the dung is composed of dead bacteria from the gut. Their normal flora has several functions:

1. To protect against undesirable bacteria e.g. Salmonellae, by preventing them from growing in the bowel.

2. The bugs are involved in a wide range of activities. Benefits include breakdown of carbohydrates which the horse would otherwise be unable to digest, and production of some vitamins, amino acids and fatty acids.

3. It alters the gut lining so that it is more able to resist disease and carry out digestion.

4. It increases the rate of flow of digesta through the gut.

What are probiotics?

Probiotics are defined as “a live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance”. Possible means of administering live bugs are the use of yoghurt or the caecal contents of a freshly dead horse, given by stomach tube. However, in most circumstances, these methods are either impractical or undesirable and there are now many manufactured probiotic products available. Most are freeze-dried preparations of live bacteria, yeasts and fungi in the form of powders, pellets and pastes. These may contain Lactobacillus species, Streptococcus species, Bifidobacterium bifidum, Enterococcus species, Aspergillus oryzae (a fungus) and Candida pintolopesii or Saccharomyces species (yeast).

When are probiotics useful?

There are many situations where probiotics are either proven or claimed to be of value.

The main uses are:

1. To help prevent an upset of the normal flora as a result of stress (e.g. travel, competition) or a change in diet.

2. To help restore the normal flora when it has been upset by a bacterial or parasitic infection of the gut. Veterinary treatment for the underlying disease is also required.

3. To help restore the normal flora if it has been upset by antibiotic treatment.

4. To improve diarrhoea of unknown origin (“idiopathic diarrhoea”). It should be emphasised that diarrhoea cases should be fully investigated by your veterinary surgeon and diseases which may require specific treatment eliminated as being the cause before classifying the diarrhoea as idiopathic.

Are probiotics useful in the management of chronic grass sickness?

Examination of faeces and intestinal contents from chronic cases suggests that the disease is likely to have a very adverse effect on the gut flora. Thus, probiotics are likely to be at best beneficial, and at worst harmless. They are therefore frequently used in the chronic cases treated at the Royal (Dick) School of Veterinary Studies. Acute cases should be put down as soon as the diagnosis has been made as there is no justification for using probiotics or any other treatment in such cases.