Review of “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”
by B Medina*, ID Girard, E Jacotot, V Julliand
*Alltech France, Goussainville, France
Why was this study done?
Horses performing a high level of exercise are often fed large amounts of cereal grains to provide adequate energy. At the same time, these horses may be given low levels of forage. This type of dietary management increases a horse’s risk for colic and laminitis because the small intestine’s ability to digest starch may be overwhelmed by the sizeable grain meals. If this happens, undigested starch reaching the cecum may seriously upset the activity of the gut microflora. Minimizing or decreasing this effect would be desirable because it would allow the feeding of high-grain diets without the risk of digestIe and metabolic problems. This study looked at the effect of supplementation with a live yeast culture on microbes and fermentation in the hindgut.
Eight horses were used in the study. Each horse was given forage (wheat straw) and one of four dietary treatments. Treatment one was a high-starch ration containing 45% barley. Treatment two was a high-fiber ration containing 46% dehydrated alfalfa. Treatments three and four were either the highstarch or high-fiber rations supplemented with 10 grams of a Saccharomyces cerevisiae preparation. The diet was split into two equal feedings each day for a 21-day adaptation period. At intervals during the next two weeks, samples of cecal and colonic contents were withdrawn through surgically prepared fistulas several hours after the horses were fed. Lactic acid level, pH, and numbers of yeast cells and various bacteria were determined.
Cecal and colonic concentrations of live yeast cells were higher in horses on the yeast-supplemented diets. Yeast supplementation resulted in higher numbers of cecal lactobacilli for horses on the high-fiber diet. Horses on the high-starch diet had higher numbers of lactic acid-utilizing bacteria, lactobacilli, and streptococci in the cecum, but lower numbers of cellulolytic bacteria. Yeast supplementation decreased concentrations of streptococci and lactobacilli in the colon among horses eating the high-fiber diet. Lactic acid concentration was higher in the colons of horses fed the high starch and high fiber treatments without yeast. When yeast was supplemented, lactic acid in the colon was reduced.
In this study, feeding the high-starch diet resulted in a large amount of undegraded starch reaching the colon. This allowed the rapid increase of starch-utilizing bacteria such as lactobacilli and streptococci, which in turn produced lactic acid at an increased rate (up to four times greater than Then horses were fed the high-fiber diet). In contrast, supplementing the high-starch diet with yeast culture led to more nearly normal pH values in the hindgut.
The authors suggest yeast supplementation could have led to an increase in bacteria that utilize lactic acid in relation to those producing lactic acid. Another possible explanation of the buffering effect is a yeast-produced enhancement of fibrolytic activity in the hindgut. Because these results agree with findings of some previous studies and differ from others, the authors state, “More studies are required to deeply understand the direct effects of live yeast culture preparation on lower gut microflora and metabolic activities in horses.” The same trends were seen in all horses in the study, although figures for microbial and biochemical parameters showed large variations among the subjects. Other factors such as time of feeding and exercise regimen could also influence how a horse might respond to a particular dietary component. In spite of individual differences, the study suggests that supplementation with Saccharomyces cerevisiae can reduce variation in pH and lactic acid concentration in the horse’s hindgut. This stabilizing influence may allow horses to avoid the digestive upsets that are sometimes caused by feeding a high-starch diet.
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