Effect of a preparation of Saccharomyces cerevisiae on microbial profiles and fermentation patterns in the large intestine of horses fed a high fiber or a high starch diet.

This research investigated how feeding horses a preparation of Saccharomyces cerevisiae, a kind of yeast, affected the microbial and fermentation patterns in their large intestines depending on whether a high fiber or high starch diet was provided. The study found that, when a starch-saturated diet was given, the addition of the yeast preparation seems to limit undesirable changes in the horse’s digestive system.

Research Methodology

• The study involved eight horses, split into pairs. Each pair comprised one horse with a cecum- and right ventral colon-fistulated modification and another with a cecum-fistulated modification. This allowed the researchers to gather samples directly from the horses’ digestive system.
• The horses were fed either a high-starch (HS) or high fibre (HF) diet with or without a 10g supplement of Saccharomyces cerevisiae yeast, following a 4 x 4 Latin square design to ensure all possible diet combinations were trialed.
• The HS diet provided an overload of starch, while maintaining a high fibre intake, representing a typical diet.
• Following a 21-day adaptation period, the contents of the horses’ cecum and colonic sections were extracted four hours after their morning meal to count several types of bacteria.
• Samples were also collected hourly for the first 12 hours after feeding to measure pH, concentrations of various acids and ammonia.

Main Findings

• Feeding the HS diet caused an increase in total anaerobic and lactic acid-utilizing bacteria in the cecum and an increase in lactobacilli and streptococci in the cecal and colonic content. The number of cellulolytic (fiber-digesting) bacteria decreased. These changes were accompanied by decreased pH and alteration in the ratios between different volatile fatty acids, as well as an increase in lactic acid concentration.
• Adding Saccharomyces cerevisiae yeast to the diet increased the count of viable yeast cells, particularly in the cecum.
• Other effects of adding yeast were minor, causing no significant changes in bacterial concentrations. However, it did affect measures of acidity, concentrations of lactic acid and ammonia, and the balance of volatile fatty acids in the cecal and colonic content, especially when given alongside the HS diet. These alterations tended to be more pronounced in the cecum, aligning with the greater abundance of yeast cells there.

Implications of the Research

• When the horses’ small intestines were saturated with starch, adding Saccharomyces cerevisiae yeast to the horses’ diet appeared to help limit deleterious changes in the horses’ gut ecosystem.
• While further research is needed, the results suggest that Saccharomyces cerevisiae may offer a dietary supplement solution for horses fed high-starch diets, potentially preventing undesirable alterations in their digestive system.