Equine cecum

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The Equine Digestive Tract

Horses are non-ruminant herbivores. Their digestive tract includes a foregut, consisting of the stomach and small intestine, where food is partially digested enzymatically. The digestive tract also includes a hindgut, consisting of the cecum and colon, where fermentation is utilized to break down food that cannot be digested in the foregut. (Kline)

Primary Microbial Residents of the Equine Cecum

The natural microflora of the equine cecum includes both gram positive and gram negative bacteria as well as several species of protozoa. The cecum contains several lactic acid producing species in the genus Streptococcus, including Streptococcus bovis http://microbewiki.kenyon.edu/index.php/Streptococcus and Streptococcus equinus. S. bovis is actually the most prolific species in the cecum. Other lactic acid producers located in the cecum are members of the genus Lactobacillus http://microbewiki.kenyon.edu/index.php/Lactobacillus. Several species of gram negative Bacteroides http://microbewiki.kenyon.edu/index.php/Bacteroides are also found in the cecum. (Mackie)

Bacterial Metabolism

The microflora located in the cecum provide several necessary functions for the horse. First and foremost, several of the bacterial species are involved in fermenting complex polysaccharides, changing them into a form that is digestible by the horse. Cellulolysis in the cecum is not currently a well understood process; however, experiments by Julliand et al. have discovered the major bacteria responsible for cellulolysis. Using oligonucleotide probes, they discovered three major species of cellulolytic bacteria. The predominant species found was Ruminococcus flavefaciens http://microbewiki.kenyon.edu/index.php/Ruminococcus. Two other species of cellulolytic bacteria were also found to be present in low levels: Fibrobacter succinogens and Ruminococcus albus. While all three of these species of bacteria are also found in the bovine rumen, Julliand et al. discovered that the equine strains differed from bovine strains in the way they utilized carbohydrates and in the end products they produced. (Julliand) The main products of fermentation of complex polysaccharides are volatile fatty acids (VFAs). The VFAs diffuse into the blood and are the main source of energy for the horse. The main VFAs produced are acetate, propionate and butyrate with isobutyrate, isovalerate and valerate produced in smaller amounts. (Mackie) These VFAs also serve to lower the pH of the cecum helping to prevent the growth of unwanted microflora such as salmonella http://microbewiki.kenyon.edu/index.php/Salmonella. High concentrations of VFAs also inhibit the growth of Escherichia coli http://microbewiki.kenyon.edu/index.php/Escherichia_coli, which explains why they are not found in the cecum. (Kern) While the cecum contains several species of bacteria capable of producing lactic acid, the concentration of lactic acid is normally kept relatively low. The lactic acid fermenters use simple sugars to create the lactic acid; however, most simple sugars are digested enzymatically before they reach the cecum. Another major function of the bacteria in the cecum is to break down amino acids. By the time nutrients reach the cecum, approximately fifty percent of ingested protein has been digested enzymatically. The remaining protein is digested by proteolytic bacteria in the hindgut. This serves to provide valuable nutrients for the horse. Some bacteria in the cecum are capable of decarboxylating amino acids, which provide a source of nitrogen for the horse. (Bailey) Certain bacteria are also able to create vitamins, such as vitamin B, for the horse’s use.

References

“Explaining Laminitis and Founder Part Two: What Causes Laminitis?” The Cyberhorse Guide To Horse Health. 2003. CyberHorse. 2003 <http://www.cyberhorse.net.au/cgi-bin/tve/displaynewsitem.pl?20040325laminitispt2.txt>.

Bailey, S. R., M. L. Baillon, A. N. Rycroft, P. A. Harris, and J. Elliot. “Identification of Equine Cecal Bacteria Producing Amines in an In Vitro Model of Carbohydrate Overload.” Applied and Environmental Microbiology. Apr. 2003. p2087-2093.

Elliott, Jonathan and Simon R. Bailey. “Gastrointestinal Factors Are potential Triggers for the Development of Acute Equine Laminitis”. The Journal of Nutrition. July 2006. Volume 136. p. 2103S-2107S.

Hussein, H.S. and L.A. Vogedes. “Review: Forage Nutritional Value for Equine as Affected by Forage Species and Cereal Grain Supplementation”. Professional Animal Scientist. October 2003.

Julliand Veronique, Albane de Vaux, Liliane Millet, and Gerard Fonty. “Identification of Ruminococcus flavefaciens as the Predominant Cellulolytic Bacterial Species of the Equine Cecum.” Applied and Environmental Microbiology. Aug. 1999. p3738-3741.

Kern, D.L., L. L. Slyter, E.C. Leffel, J. M. Weaver and R. R. Oltjen. “Ponies vs. Steers: Microbial and Chemical Characteristics of Intestinal Ingesta.” Journal of Animal Science. 1974. 36:559-564.

Kern, D.L., L. L. Slyter, J. M. Weaver, E. C. Leffel, G. Samuelson. “Pony cecum vs. Steer Rumen: The Effect of Oats and Hay on the Microbial Ecosystem.” Journal of Animal Science.1973. 37:46-469.

Kline, Robert, Porr, Shea and Cardina, John. The Ohio State University Bulletin. Horse Nutrition. Bulletin 762-00. http://ohioline.osu.edu/b762/b762_5.html.

Mackie, Roderick I., and Clive A. Wilkins. “Enumeration of Anaerobic Bacterial Microflora of Equine Gastrointestinal Tract.” Applied and Environmental Microbiology. Sept. 1988. p2155-2160.

Maczulak, Anne E., Karl A. Dawson, and John P. Baker. “Nitrogen Utilization in Bacterial Isolates from the Equine Cecum”. Applied and Environmental Microbiology. Dec. 1985. p. 1439-1443.

Pollitt, C.C., M. Kyaw-Tanner, K.R. French, A.W. Van Eps, J.K. Hendrikz and M. Daradka. "Equine Laminitis". 49th Annual Convention of the American Association of Equine Practitioners. 2003. New Orleans, LA.

Rowe, James B., Michael J. Lees & David W. Pethick. “Prevention of Acidosis and Laminitis Associated with Grain Feeding in Horses”. The Journal of Nutrition. 1994. Volume 124. p. 2742S-2744S.

Edited by [Tim Shaw and Megan Tambaschi], students of Rachel Larsen