‘Prebiotic’ approach: Stabilising gut microflora in horses

Equine athletes and other high-performance horses can suffer digestive problems following transport or rapid changes in diet or environment. Such trouble typically stems from imbalances in populations of micro organisms in the digestive tract. In food animals, there already is a large body of research supporting the use of feed products to influence gut microflora, but as yet there is relatively little such work in horses. Recent research along these lines suggests that the use of short-chain fructo-oligosaccharides may be useful as a prebiotic' feed ingredient to counter effects of digestive stress in horses.

A prebiotic is a food or feed component which promotes the growth of certain bacteria, particularly non-pathogenic or beneficial organisms, in the digestive tract. Short-chain fructo-oligosaccharides (scFOS) are among the fibre-type fermentable carbohydrate prebiotics most studied in humans as well as in pets and commercial animal species. They naturally occur in plants such as onions and Jerusalem artichokes but can also be processed from sucrose.

Unlike most other fructans, such as those which accumulate in grass during spring and autumn growth, scFOS have a shorter molecular chain structure and lower degree of polymerisation (DP 3-5). The lower degree of polymerisation may enable more rapid fermentation earlier in the digestive tract, which may also help reduce digestive problems later. In any case, a prebiotic such as scFOS can selectively stimulate the growth of beneficial intestinal bacteria to the detriment of potentially pathogenic bacteria like species of clostridia and salmonella. Recent studies using bio-molecular techniques show that dietary scFOS can increase diversity and stability of the digestive microflora.

Effect through lactobacilli, not bifidobacteria

Bifidobacteria comprise the main population to support the prebiotic effect in humans. By contrast, lactobacillus species may provide the main support in horses, in which researchers have not detected bifidobacteria by culture methods or by RNA-targeted probes. The prebiotic effect of fructo-oligosaccharides may occur through an increase of the whole population of Lactobacillus spp or by changes in the proportions of species and strainsthe strain profile'as suggested by studies with molecular tools in dogs and pigs.

Fructo-oligosaccharides particularly stimulate the growth of Lactobacillus reuteri without being fermented for instance by L acidophilus, which may induce lactic acidosis. Like some other lactobacilli, L reuteri can interact with the intestinal immune system and produce bactericide molecules which act against potential pathogens such as E coli. Studies in horses show that supplementation with dietary scFOS (DP 3-5) does not necessarily increase the concentration of lactobacilli but reduces faecal concentrations of E coli (Pellegrini et al, 1999; Berg et al, 2005). Furthermore, beyond their direct stimulation of some bacterial strains, scFOS indirectly stimulate the growth of the whole lactate-utilising bacterial population in the equine gastro-intestinal tract (Respondek et al, 2005).

Both upper and lower gastro-intestinal effects

The early definition of prebiotic focused only on effects in the colon, but recent research in horses suggests that upper parts of the gastro-intestinal tract are inhabited by a significant amount of bacteria having fermentative activities. Thus the prebiotic concept has been updated as "selectively fermented ingredient that allows specific changes in the composition and/or activity in the gastro-intestinal microflora that confers benefits upon host well-being and health" (Gibson et al, 2004).

A number of researchers report that total anaerobic bacteria can amount to 109 cfu/ml of gastric content, which is relatively highapproaching concentrations found in the large intestine. Interestingly, it seems that dietary scFOS could be completely fermented in the horse stomach, where the prebiotic ingredient can change the environment in a beneficial way (Respondek et al, 2005). Researchers found no effect either on microbial populations or biochemical parameters in the small intestine. Other research shows that, with higher gastric pH in horses receiving an alfalfa hay-grain supplement than in horses fed bromegrass hay, there is a lower risk of ulcers from excessively acidic conditions in the stomach (Nadeau et al, 2000).

Too high a level of fermentation from long-chain fructans (DP 2-60) in the large intestine incurs the risk of inducing digestives troubles in horses. By contrast, dietary scFOS are safer as they are completely fermented before reaching the colon. Nonetheless, these scFOS still induce significant changes in the colonic microflora and environment (Respondek et al, 2005), as well as in the faeces (Pellegrini et al, 1999; Berg et al, 2005). Effects in the hindgut might be due to the arrival of bacteria stimulated in the upper part of the gastro-intestinal tract (Fuller et al, 1978).

Maintaining microbial balance

Changes in housing, feeding, or exercise management of horses can cause microbial disturbances that are generally the first impacts to trigger digestive problems. For example, the recent addition of hay to the feeding regimen, or a change in the quality of hay, combined with restricted access to pasture, can impact the intestinal microflora. Such changes also have the highest probability of association with colic in horses. Changes in the type of cereals or feeding more than 2.7 kg of oats per meal are also a risk (Hudson et al, 2001). Through their effect on the digestive flora, scFOS can reduce the incidence of digestive problems in horses subjected to such risks.

A field study, carried out at the stables of the French Republican Guard, demonstrated a reduction of the incidence of digestive problems (7% vs 53%) in a group of 15 horses receiving scFOS in comparison to the same size control group similarly housed and exercised for 3 months (see Table Digestive problems').

This result was confirmed by experiments recording modifications of the colonic microflora and their associated fermentative activities during digestive stress. Researchers focused on the type and quantity of concentrate feed associated with the alteration of the hindgut microflora and risk factors for colic (de Fombelle et al, 2001). In such situations, enzymatic capacities of the small intestine to digest starch are overwhelmed and a significant amount of starch reaches the hindgut where it is fermented.

Stable microflora and higher acetate and butyrate levels

In a study carried out with Professor Julliand at the ENESAD in Dijon, France, after being fed a large meal of barley instead of their usual concentrate pellets, non-scFOS-supplemented horses showed a rapid increase in concentrations of lactate-producing bacteria without a sufficient concomitant increase of lactate-using bacteria. This imbalance of microflora led to a significant increase in D-lactate concentration in the colon. The basal concentration of D-lactate increased by a factor of 8 during a period of 5 hours after the meal.

However, there was no observation of disturbances among bacterial populations or of their fermentative activities in horses receiving the scFOS supplementation. Moreover, trends towards higher concentrations of acetate and butyrate were observed with the scFOS supplementation. This effect has two main implications. First, it suggests that scFOS can reinforce the intestinal barrier as butyrate is the main energy source for cells of the large intestine mucosa. Second, a fermentation pattern oriented towards more acetate and butyrate is more similar to fermentation of high-forage diets than fermentation of high-grain diets. Thus, dietary scFOS could help to rebalance the fermentation of a high-grain diet towards what is observed with high-forage diets, which are considered safer diets in preventing digestive problems.

These demonstrated effects of scFOS in horses have confirmed the concept of fermentable prebiotic fibre for horses, which can have beneficial effects upon animal health by increasing stability of intestinal microflora. One commercial supplier active in both human food and animal feed sectors, recommends dietary supplementation with 30 g per day of its scFOS product for horses subjected to transport and environmental changes.

Dietary scFOS supplementation also may prove interesting for breeding horses. Recent work in dogs demonstrated a positive influence of scFOS feeding to bitches during late gestation and lactation (Adogony et al, 2005). The scFOS-supplemented bitches produced more antibodies in their colostrum than control animals. Thus, transfer of IgA to puppies through the colostrum was higher. Puppies, also supplemented, showed better response to early vaccination. It appears that through their interaction with the intestinal mucosa, lactic bacteria such as lactobacillus species, can enhance mucosal immunity and transfer of passive immunity from mother to their puppies.

Applications for prebiotics in equine diets are topics for ongoing research. Much more needs to be known about digestive problems in horsesparticularly equine athletesassociated with transport and changes in diet and environment. These problems usually involve undesirable changes in gut microbial populations, which may be helped by dietary supplementation with specialised fermentable carbohydrate ingredients, such as scFOS.