MANY commercially available horse feeds contain yeast of some description and, therefore, horses have benefited from yeast in their diets for a number of years.

Research studies have been conducted to determine the efficacy and mechanism of action of certain strains of yeast.

A common finding in these research studies is an improvement in fibre digestion, which indicates that feeding yeast results in a change in microbial activity in the horse's hindgut.

The first study evaluating yeast in equine diets was reported in 1983.

Since then, yeast has become a common additive to horse diets.

Fibre digestion

The horse's hindgut is where fibre digestion takes place. Since its domestication, with the way he is fed and managed sometimes being at odds with the way he was designed, the horse has had various 'issues' with gut health.

Horses are different from most non-ruminant (single-stomached) animals in that they can digest and utilise large amounts of forage.

Horses have a large caecum (26-34 litres) located between the small and large intestine, and a high volume large intestine (81 litres) that provides the capacity and ability to digest fibre in forages.

Similar to ruminants, horses do not produce the enzymes to digest fibre, but provide the environment and harbour the microorganisms that digest fibre. The microorganisms ferment fibre to volatile fatty acids, which the horse uses for energy.

These microorganisms also break down protein (that was not digested in the small intestine) to ammonia and re-assimilate the nitrogen from ammonia and urea (recycled from the blood) into microbial protein.

Some of the microbial protein is digested and utilised by the horse for its own protein needs. This microbial population also supplies the horse with B-vitamins.

Good or bad bugs?

There are various things that will have a detrimental effect on the good bugs in the horse's digestive system some of which are;

• Stress

• Rapid feed changes

• Wormers

• Antibiotics

• High use of starch

• Hormone imbalance

The impact of the above factors can be minimised via management changes but sometimes the good bugs need a little help. As with most types of supplements for horses there is an array of digestive enhancing additives to choose from.

The jury is currently out as to how effective prebiotic and probiotic supplements are in horses. Research that has actually been carried out in horses (as opposed to humans) is scant although anecdotal evidence is abundant.

However, many of the yeast products e.g. Yea-sacc 1026® do have EU registration for use in horses which means that a myriad of research into its efficacy and safety has been carried out. Yea-sacc 1026® is a live yeast.

It promotes the good bugs, increases digestion of fibre and reduces the effects of lactic acid on both the gut lining and the good bugs.

The stabilising effect of Yea-sacc on hind-gut fermentation means that larger amounts of cereal can be fed to provide energy with a lower risk of colitis, acidosis, enterotoxaemia or laminitis.

Yeast for young, growing horses

Several studies have shown improvements in growth of young horses fed yeast culture. One trial reported weanling horses fed yeast culture were five kg heavier and had a 10% faster growth rate than those not fed yeast culture over a six-month period.

In separate studies feeding yeast culture increased fibre digestion and nitrogen retention in yearling Thoroughbred horses and fibre, calcium, and phosphorus digestibility, and nitrogen retention were improved in three-year-old horses fed diets containing yeast culture and 50-70% forages.

Improving fibre and nitrogen digestibility by feeding yeast culture would allow young horses to convert feed more efficiently for growth and attain faster growth rates than those not fed yeast culture.

Performance horses

More surprisingly feeding yeast to horses during exercising and training may help condition the horse. Lower plasma lactic acid concentrations after 35 minutes of exercise were observed in young adult horses fed yeast culture compared to a diet without yeast culture.

They also found lower heart rates during the first five and final 10 minutes of a 35-minute exercise workout for horses fed a diet with yeast compared to a diet without yeast.

Thus, inclusion of yeast in diets of exercising horses seemed to improve their aerobic metabolic capacity.

The reason for this effect is unclear, but may be related to the improved nitrogen retention or fermentation profile of the gut when horses are fed yeast culture.

Brood mares

Pregnant mares fed yeast culture had greater digestibility of dietary dry matter, fibre, protein, calcium, and phosphorus than those not supplemented with yeast culture.

Improved digestion helps mares cope with the reduced feed capacity and increased nutrient demands during the last trimester of gestation. Feeding yeast in early lactation can improve early milk production of mares and increase foal growth.

Mares supplemented with yeast during the first two weeks of lactation produced more milk than their non yeast fed counter parts. Mares supplemented with yeast culture had foals with similar birth weights as those not supplemented with yeast culture however; foals at 56 days of age from mares supplemented with yeast were heavier than foals from mares not supplemented with yeast.

The foals from the yeast-supplemented mares were also taller at the withers than foals from mares not supplemented with yeast.

Conclusions

There are many things we can do to keep our horse's gut healthy. The most effective is to feed as much fibre as possible and, also to ensure that concentrates are fed little and often to avoid overloading the gut with starch.

Yeast can provide a benefit in horse diets by improving feed digestion, nitrogen retention and reducing the risk of dysfunction due to acidosis.

Increased fibre digestion and better feed efficiency are the most common benefits of yeast supplementation along with a general improvement in the gut environment (less loose droppings etc).