Probiotics are dietary supplements containing potentially beneficial bacteria or yeasts. According to the currently adopted definition by FAO/WHO, probiotics are: ‘Live microorganisms which when administered in adequate amounts confer a health benefit on the host’.

Lactic acid bacteria (LAB) are the most common type of microbes used. LAB have been used in the food industry for many years, because they are able to convert sugars (including lactose) and other carbohydrates into lactic acid. This not only provides the characteristic sour taste of fermented dairy foods such as yogurt, but also by lowering the pH may create fewer opportunities for spoilage organisms to grow, hence creating possible health benefits on preventing gastrointestinal infections. Strains of the genera Lactobacillus and Bifidobacterium, are the most widely used probiotic bacteria.

Probiotic bacterial cultures are intended to assist the body's naturally occurring gut flora, an ecology of microbes, to re-establish themselves. They are sometimes recommended by doctors, and, more frequently, by nutritionists, after a course of antibiotics, or as part of the treatment for gut related candidiasis. Claims are made that probiotics strengthen the immune system to combat allergies, excessive alcohol intake, stress, exposure to toxic substances, and other diseases.[2][4] In these cases, the bacteria that work well with our bodies (see symbiosis) may decrease in number, an event which allows harmful competitors to thrive, to the detriment of our health.

Maintenance of a healthy gut flora is, however, dependent on many factors, especially the quality of food intake. Including a significant proportion of prebiotic foods in the diet has been demonstrated[citation needed] to support a healthy gut flora and may be another means of achieving the desirable health benefits promised by probiotics.

History of probiotics
Probiotics, which means "for life", have been used for centuries as natural components in health-promoting foods. The original observation of the positive role played by certain bacteria was first introduced by Russian scientist and Nobel laureate Eli Metchnikoff, who in the beginning of the 20th century suggested that it would be possible to modify the gut flora and to replace harmful microbes by useful microbes.[5] Metchnikoff, at that time a professor at the Pasteur Institute in Paris, produced the notion that the ageing process results from the activity of putrefactive (proteolytic) microbes producing toxic substances in the large bowel. Proteolytic bacteria such as clostridia, which are part of the normal gut flora, produce toxic substances including phenols, indols and ammonia from the digestion of proteins. According to Metchnikoff these compounds were responsible for what he called “intestinal auto-intoxication”, which caused the physical changes associated with old age. It was at that time known that milk fermented with lactic-acid bacteria inhibits the growth of proteolytic bacteria because of the low pH produced by the fermentation of lactose. Metchnikoff had also observed that certain rural populations in Europe, for example in Bulgaria and the Russian Steppes who lived largely on milk fermented by lactic-acid bacteria were exceptionally long lived. Based on these facts, Metchnikoff proposed that consumption of fermented milk would “seed” the intestine with harmless lactic-acid bacteria and decrease the intestinal pH and that this would suppress the growth of proteolytic bacteria. Metchnikoff himself introduced in his diet sour milk fermented with the bacteria he called “Bulgarian Bacillus” and found his health benefited. Friends in Paris soon followed his example and physicians began prescribing the sour milk diet for their patients.

Henry Tissier, also from the Pasteur Institute, was the first to isolate a Bifidobacterium. He isolated the bacterium from a breast-fed infant and named it Bacillus bifidus communis.[7] This bacterium was later renamed Bifidobacterium bifidum. Tissier showed that bifidobacteria are predominant in the gut flora of breast-fed babies, and he recommended administration of bifidobacteria to infants suffering from diarrhea. The mechanism claimed was that bifidobacteria would displace the proteolytic bacteria that cause the disease.
German professor Alfred Nissle, in 1917 isolated a strain of Escherichia coli from the feces of a First World War soldier who did not develop enterocolitis during a severe outbreak of shigellosis.[8] In those days, antibiotics were not yet discovered, and Nissle used the strain with considerable success in acute cases of infectious intestinal diseases (salmonellosis and shigellosis). Escherichia coli Nissle 1917 is still in use and is one of the few examples of a non-LAB probiotic.

In 1920 Rettger demonstrated that Metchnikoff’s “Bulgarian Bacillus”, later called Lactobacillus bulgaricus, could not live in the human intestine, and the fermented food phenomena petered out. Metchnikoff’s theory was disputable (at this stage), and people doubted his theory of longevity.

After Metchnikoff’s death in 1916, the centre of activity moved to the US. It was reasoned that bacteria originating from the gut were more likely to produce the desired effect in the gut, and in 1935 certain strains of Lactobacillus acidophilus were found to be very active when implanted in the human digestive tract.[10] Trials were carried out using this organism, and encouraging results were obtained especially in the relief of chronic constipation.

The term “probiotics” was first introduced in 1953 by Kollath (see Hamilton-Miller et al 2003). Contrasting antibiotics, probiotics were defined as microbially derived factors that stimulate the growth of other microorganisms. In 1989 Roy Fuller suggested a definition of probiotics which has been widely used: “A live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance”. Fuller’s definition emphasizes the requirement of viability for probiotics and introduces the aspect of a beneficial effect on the host.

In the 1960s the dairy industry began to promote fermented milk products containing Lactobacillus acidophilus.[citation needed] In subsequent decades other Lactobacillus species have been introduced including Lactobacillus rhamnosus, Lactobacillus casei, and Lactobacillus johnsonii, because they are intestinal species with beneficial properties.

Adverse Effects
There is no published evidence that probiotic supplements are able to completely replace the body’s natural flora when these have been killed off; indeed bacterial levels in faeces disappear within days when supplementation ceases.[13] While the oral use of probiotics is considered safe and even recommended by World Health Organization under specific guidelines. in some specific situations (such as critically ill patients) they could be potentially harmful. In one therapeutic clinical trial, a probiotic cocktail increased the death rate of patients with acute pancreatitis. Probiotics have been shown to be beneficial for other types of patients.

Potential benefits
Experiments into the benefits of probiotic therapies suggest a range of potentially beneficial medicinal uses for probiotics. For many of the potential benefits, research is limited and only preliminary results are available. It should be noted that the effects described are not general effects of probiotics. All effects can only be attributed to the strain(s) tested, not to the species, nor to the whole group of LAB (or other probiotics).

Managing Lactose Intolerance

As lactic acid bacteria actively convert lactose into lactic acid, ingestion of certain active strains may help lactose intolerant individuals tolerate more lactose than what they would have otherwise. In practice probiotics are not specifically targeted for this purpose, as most are relatively low in lactase activity as compared to the normal yogurt bacteria.

Prevention of Colon Cancer
In laboratory investigations, some strains of LAB have demonstrated anti-mutagenic effects thought to be due to their ability to bind with heterocyclic amines, which are carcinogenic substances formed in cooked meat. Animal studies have demonstrated that some LAB can protect against colon cancer in rodents, though human data is limited and conflicting. Most human trials have found that the strains tested may exert anti-carcinogenic effects by decreasing the activity of an enzyme called β-glucuronidase(which can generate carcinogens in the digestive system). Lower rates of colon cancer among higher consumers of fermented dairy products have been observed in some population studies.

Cholesterol Lowering
Animal studies have demonstrated the efficacy of a range of LAB to be able to lower serum cholesterol levels, presumably by breaking down bile in the gut, thus inhibiting its reabsorption (which enters the blood as cholesterol). Some, but not all human trials have shown that dairy foods fermented with specific LAB can produce modest reductions in total and LDL cholesterol levels in those with normal levels to begin with, however trials in hyperlipidemic subjects are needed.

Lowering Blood Pressure
Several small clinical trials have shown that consumption of milk fermented with various strains of LAB can result in modest reductions in blood pressure. It is thought that this is due to the ACE inhibitor-like peptides produced during fermentation.

Improving Immune Function and Preventing Infections
LAB are thought to have several presumably beneficial effects on immune function. They may protect against pathogens by means of competitive inhibition (i.e., by competing for growth) and there is evidence to suggest that they may improve immune function by increasing the number of IgA-producing plasma cells, increasing or improving phagocytosis as well as increasing the proportion of T lymphocytes and Natural Killer cells.Clinical trials have demonstrated that probiotics may decrease the incidence of respiratory tract infections and dental caries in children. LAB foods and supplements have been shown to be effective in the treatment and prevention of acute diarrhea, and in decreasing the severity and duration of rotavirus infections in children and travelers' diarrhea in adults.

Helicobacter pylori
LAB are also thought to aid in the treatment of Helicobacter pylori infections (which cause peptic ulcers) in adults when used in combination with standard medical treatments.

Antibiotic-associated diarrhea
A meta-analysis suggested probiotics may reduce antibiotic-associated diarrhea. A subsequent randomized controlled trial also found benefit in elderly patients.

Reducing Inflammation
LAB foods and supplements have been found to modulate inflammatory and hypersensitivity responses, an observation thought to be at least in part due to the regulation of cytokine function.Clinical studies suggest that they can prevent reoccurrences of inflammatory bowel disease in adults, as well as improve milk allergies and decrease the risk of atopic eczema in children.

Improving Mineral Absorption
It is hypothesized that probiotic lactobacilli may help correct malabsorption of trace minerals, found particularly in those with diets high in phytate content from whole grains, nuts, and legumes.

Prevents Harmful Bacterial Growth Under Stress
In a study done to see the effects of stress on intestinal flora, rats that were fed probiotics had little occurrence of harmful bacteria latched onto their intestines compared to rats that were fed sterile water.

Irritable Bowel Syndrome and Colitis
B. infantis 35624, sold as Align, was found to improve some symptoms of irritable bowel syndrome in women in a recent study. Another probiotic bacterium, Lactobacillus plantarum 299V, was also found to be effective in reducing IBS symptoms. Additionally, a probiotic formulation, VSL3, was found to be effective in treating ulcerative colitis. Bifidobacterium animalis DN-173 010 may help.
PROBIOTICS EQUINE SPECIFIC - Thesis by Bridgett Hannigan, Warwickshire College of Agriculture Selected Abstracts
Antibiotic Therapy

Broad-spectrum antibiotics and some anti-parasitic chemicals periodically introduced into the system devastate the beneficial microbial population as well as target pathogens. Chlorine in the water, added by authorities to act as a purifying, antibacterial agent, will also have a detrimental effect on the horse's beneficial gut flora.

Frequent occurrence of disease following antibiotic treatment suggests a protective suppressing effect from the normal resident population. The gut flora acts as an important barrier to pathogenic colonization by monopolizing all available nutrients and residential sites. Some are also able to produce their own antibodies against other species. For example, various lactobacillus strains produce lactic and acetic acids and hydrogen peroxide which inhibit the growth of Eshcerichia coli and other gas producing coliforms which cause disease when their numbers become excessive.

Stress is also a major factor in the horse's life, which will disrupt the gut flora. Stress can be generated by any drastic change in the physical or emotional environment, birth, weaning, traveling or even fear.

The optimum pH for the growth of the beneficial bacterial species (pH 6) is different from that of pathogens (pH 8-9). The imposition of stress on the horse can result in an increase in intestinal pH and therefore favors the development of pathogens. When this occurs, the number of Lactobacilli decreases while the number of coliform increase.

The effects of feeding probiotics
Test results
Extensive work by Dr, Michael Glade in America has shown some incredible results:
If probiotics are added to the diets of pregnant mares six weeks prior to their foaling dates and then on into lactation until the foal is eight weeks old, the volume and composition of her milk will alter in: gross energy, sugar concentrates, total lipids as well as increased levels ofamino acids and proteins. This means more nutrients available to the foal.
Consequently, the foals involved in this research grew faster than those nursing mares that had not received the probiotic supplementation. A significant difference was noted from four weeks of age and by the end of the eight-week study period, those foals were 11 cms taller and 21 kgs heavier than their counterparts.

Fecal samples taken from the mares before, during and after probiotic supplementation have shown probiotics will enhance fiber digestion in the hind gut, increasing digestibility of dry matter of 15, crude protein by 11-14% and phosphorus by 22%.
In conclusion Dr. Glade says the greater efficiency of feed conversion by the mare into foal body weight is 24% greater if there is probiotic supplementation.
Higher foal growth rates can be attributed to both increased quantity of nutrients and the nature of the nutrients consumed.

Dr. Glade has also investigated probiotic supplementation in growing horses:
It is important that a protein source be digestible, but equally critical is the horse's ability to retain the nitrogen it provides and incorporates into the body tissues.

Tests have shown that youngsters given probiotics have increased levels of plasma lysine (most likely to be deficient in growing horses), argenine and methionine. This results in stimulation of growth hormone secretion, increased muscle strength and bone development.
Experiments conducted by Dr. Hoe Pagan have led to the conclusion that probiotics increase the fermentation process in the hind gut and enable the horse to digest phosphorus more efficiently.

Dr Pagan's results have shown that with the use of probiotics fiber digestibility is increased by 7.5% and absorption of phosphorus is 22% greater. By including probiotics, the horse utilizes the phosphorus that is already in the diet more efficiently. This is a far cheaper alternative to additional phosphorus supplementation. Information that was not expected from these experiments was that probiotics also increase calcium digestion.

In conclusion, the fact probiotics improve the fermentation process in the hind gut would also indicate that they can be beneficial in stabilizing digestive disturbances. These result from carbohydrate overload when the horse is fed concentrate ration. Such overloads can bring out colic and laminitis.

The institute of Probiotic Studies in studs and racing stables, in the UK, has carried our research.

Probiotics were fed to five hundred racehorses in flat training, twenty eventers and other competitive horses. All stables reported probiotic fed horses appeared less susceptible to digestive upset, did not seem to suffer the detrimental affects of stress and an improvement in their general health and well being.

On studs, the growth rate and general condition of eight thorough bred foals was improved and scouring was also effectively controlled. Probiotic fed mares showed less stress during parturition and were noted to be in consistently better condition than the controls.
Work at Warwick College had shown that the inclusion of probiotics in the diet resulted in quicker weight gain. Probiotics also helped in rapid recovery from weight loss after strenuous activity.

When yeast was removed from the ration, horses lost between ten and thirty kilograms within the following six weeks, even though their ration stayed exactly the same in all other respects.

All researchers reported an improvement in the general health and well-being and even an improvement in the temperament of horses supplied with probiotics.

Scientific evidence suggests that probiotic supplementation will:

  • Improve the composition of the mare's milk
  • Increase early milk production
  • Increase the availability of nutrients to foals, thereby enhancing growth
  • Improve fiber digestion by approximately 7.5%
  • Improve crude protein digestion by 11-14%
  • Improve phosphorus digestion by approximately 22%
  • Improve calcium digestion
  • Increase feed conversion efficiency by up to 24%
  • Increase nitrogen retention, thereby improving growth rates
  • Stabilize the digestive system, reducing the risk of colitis and laminitis
  • Stabilize weight and speed up any weight loss recovery after strenuous exercise
  • Maintain health and condition of the animal

Stimulation of Immunity:
Laboratory experiments have shown germ free animals have much weaker immune systems than those with a normal collection of gut flora. This has been shown by phagocytic activity and lowered immunoglobulin levels.

Recent findings that Lactobacilli given orally can stimulate immunity in a nonspecific way, which creates many more areas of potential benefit, derived from probiotics. Not only do they have the ability to affect the balance of gut flora, but they could also influence diseases, which occur in tissues other than the intestinal tract.

The use of probiotics is more for preventative medicine rather than for use in disease therapy. Pathogens that cause disorders are usually well established by the time the symptoms show, and providing an abundance of beneficial microorganisms at this stage is consequently unlikely to be as effective as present antibiotic strategies.

Probiotics in Horses: Research is the Key to Unlocking Their Potential
Probiotic therapy is emerging as a popular and potentially valuable tool in the practice of human and veterinary medicine. Probiotic therapy may be useful in the treatment or prevention of a number of disorders, particularly diarrheic disease. Still, clinical application is difficult due to a lack of research in horses and questionable quality control of commercial products. Dr. Scott Weese of the Department of Clinical Studies at the University of Guelph is burning to build on his current research of probiotics in horses. His work is contributing to clearly determining the appropriate organisms, appropriate doses and conditions that are potentially treatable with probiotics.

The appealing properties of probiotics include the ability to reduce antibiotic use, the apparently very high index of safety, and the public's perception about "natural" or "alternative" therapies. The definition of a probiotic was refined in 1998 to: "living microorganisms, which upon digestion in certain number, exert health benefit beyond inherent basic nutrition". Regardless of the definition, certain criteria have been developed to evaluate the potential of microorganisms to function as probiotics.

Probiotic organisms must:

  • survive the acidic environment of the stomach and resist bile digestion,
  • adhere to the intestinal lining,
  • colonize the intestinal tract,
  • produce an anitmicrobial factor and inhibit enteric pathogens (disease-causing bacteria).

Other properties such as immunomodulation, modulation of metabolic activities and the inactivation of procarcinogens are also desirable. An organism can only be considered a probiotic after these properties have been identified, and a positive health effect has been documented. Many authors say that probiotics should also be safe, result in no undesirable effects on the host (i.e. excessive gas production), be robust enough to grow in commercial conditions and survive processing and storage.

Research has evaluated the effect of dietary yeast culture on training and performance. But if a product does not contain live microorganisms it cannot be, by definition, a probiotic. Dietary yeast cultures are now being used in many commercial feeds as a means of increasing the digestible energy content of feed. However, these products are nutritional supplements rather than probiotics.

Development of probiotic products requires more than just selection of one or more lactic acid bacteria (common ones are strains of Lactobacillus and Bifidobacterium). Probiotics must be identified at the strain level and testing must be performed on individual strains. Even the probiotic qualities of yogurt depend on the numbers of viable bacteria present and the bacterial strains of lactobacilli, as not all strains have a probiotic effect. Research in human medicine has shown the strain Lactobacillus GG to be effective in the treatment and prevention of a number of problems including acute diarrhea in children, travelers' diarrhea in adults, Crohn's disease and reducing the incidence of antibiotic associated diarrhea in infants.

Labels descriptions on commercial products should be scrutinized. Appropriately labeled products should indicate the number of CFU present at the date of expiry. Extrapolating from recommendations in people, an average horse (450 kg) would likely require 10-100 billion CFU/day of an organism able to colonize the intestinal tract.
Based on existing research in other species, it seems likely that probiotics have a role in equine medicine. However, further research is required to identify organisms that possess probiotic properties in the horse's digestive tract, have clinical effect, and can survive processing and storage.

Dr. Weese has been busy evaluating the contents of several commercial products designed for both veterinary and human use. Results are in and a scientific paper is pending publication. Following this, these results will be available online at This research and a review of probiotics written by Dr. Weese will link to his name in the TEAM section.