A healthy and well-functioning digestive system is important for the horse's overall health and well-being. Abrupt dietary changes have an effect on the functioning and balance of the digestive system 1,2. The disruption of this balance can lead to health problems that affect the general health and well-being of the horse 3.
The horse's digestive system consists of the esophagus, stomach, small intestine, large intestine, appendix and rectum. A well-functioning digestive system is important for the digestion and absorption of nutrients from the ration. In addition, it is also important for the overall health and well-being of the horse. Created with BioRender.com
The digestive system of the horse can be divided into two parts. In the first part of the digestive system, digestion of nutrients mainly takes place by means of enzymes 4. The second part consists of the small intestine, large intestine and appendix. By means of micro-organisms in the intestines, fiber from the ration is digested into the volatile fatty acids butyrate, acetate and propionic acid 5. Volatile fatty acids provide 60 to 70% of the energy required for metabolic processes in the body 6. As a result, the energy supply of the horse mainly depends on the fermentation of fibers in the intestines 7.
The intestines contain different types of micro-organisms that perform different functions, such as bacteria, fungi, archaea, protozoa and bacteriophages 8. The composition of the intestinal flora has an effect on the digestion of volatile fatty acids and the health of the horse 2 In addition, the composition of the intestinal flora also has an effect on the horse's immune system and dysbiosis can lead to a reduced immune system. The composition is mainly influenced by nutrition. The fermentation of fibers from roughage and the production of volatile fatty acids stimulates micro-organisms that have a positive effect on intestinal function and intestinal health 9,10.
| "The composition of the intestinal flora is mainly influenced by diet."
Due to abrupt changes in the ration or if the feed contains a high amount of sugar and starch, the balance in the intestines can be disturbed 11. The digestive system of the horse is not able to digest high amounts of starch. When the amount of starch in the ration exceeds the requirement, part of the starch passes the enzymatic digestion and ends up in the intestines, causing fermentation of the undigested starch 12. This has an effect on the activity and effectiveness of the fiber digestion 13 Changes in the activity and composition of the microorganisms in the gut are measured by pH, lactic acid and volatile fatty acids in manure 1. Studies show that the fermentation of starch in the gut results in the production of lactic acid leading to a drop in pH value to 11.12. In addition, an acidic environment, due to starch fermentation, has also been shown to be associated with the growth of lactic acid-producing bacteria in the gut, such as the bacterial species Streptococcus 11,14. Research shows that disturbances in the balance of the intestinal flora, leading to low pH and the production of lactic acid, result in an increased risk of colic and laminitis in horses 15,16.
In addition, changes in the intestinal flora also have an effect on the horse's behavior 17,18. Research shows that changes in the gut flora resulting from a diet high in starch results in an increase in reactive behavior 19. In contrast to horses whose rations contain a high amount of fiber and the gut flora has a different composition, these horses show calmer behavior 19.
In short, a well-functioning intestinal flora is essential. That is why it is important to provide the horse with a balanced ration. In addition, supplements can be used to support the intestines and a healthy intestinal flora.
References
1. Grimm, P., Philippeau, C., & Julliand, V. (2017). Faecal parameters as biomarkers of the equine hindgut microbial ecosystem under dietary change. Animal, 11(7): 1136-1145. 2. Julliand, V., & Grimm, P. (2016). Horse species symposium: The microbiome of the horse hindgut: History and current knowledge. Journal of Animal Science, 94(6): 2262-2274. 3. Bland, S.D. (2016). Equine colic: a review of the equine hindgut and colic. Veterinary Science Development, 6(1): 48-51. 4. Strauch, S., Wichert, B., Greef, J. M., Hillegeist, D., Zeyner, A., & Liesegang, A. (2017). Evaluation of an in vitro system to simulate equine foregut digestion and the influence of acidity on protein and fructan degradation in the horse's stomach. Journal of Animal Physiology and Animal Nutrition, 101: 51-58. 5. Collinet, A., Grimm, P., Julliand, S., & Julliand, V. (2021). Multidimensional Approach for Investigating the Effects of an Antibiotic–Probiotic Combination on the Equine Hindgut Ecosystem and Microbial Fibrolysis. Frontiers in Microbiology, 12:1-14. 6. Bergman, E.N. (1990). Energy contributions of volatile fatty acids from the gastrointestinal tract in various species. Physiological Reviews, 70(2): 567-590. 7. Dougal, K., de la Fuente, G., Harris, P. A., Girdwood, S. E., Pinloche, E., & Newbold, C. J. (2013). Identification of a Core Bacterial Community within the Large Intestine of the Horse. PLoS ONE, 8(10): 1-12. 8. Julliand, V., & Grimm, P. (2016). Horse species symposium: The microbiome of the horse hindgut: History and current knowledge. Journal of Animal Science, 94(6): 2262-2274. 9. Raspa, F., Vervuert, I., Capucchio, M. T., Colombino, E., Bergero, D., Forte, C., Greppi, M., Cavallarin, L., Giribaldi, M., Antoniazzi, S. , Cavallini, D., Valvassori, E., & Valle, E. (2022). A high-starch vs. high-fibre diet: effects on the gut environment of the different intestinal compartments of the horse digestive tract. BMC Veterinary Research, 18(187): 1-11.
10. Moore-Colyer, M.J.S., Hyslop, J.J., Longland, A.C., & Cuddeford, D. (2000). Intra-caecal fermentation parameters in ponies botanically fed diverse fibre-based diets. Animal Feed Science and Technology, 84(3–4): 183-197. 11. de Fombelle, A., Varloud, M., Goachet, A. G., Jacotot, E., Philippeau, C., Drogoul, C., & Julliand, V. (2003). Characterization of the microbial and biochemical profile of the different segments of the digestive tract in horses given two distinct diets. Animal Science, 77(2): 293-304. 12. Al Jassim, R. A. M., Scott, P. T., Trebbin, A. L., Trott, D., & Pollitt, C. C. (2005). The genetic diversity of lactic acid producing bacteria in the equine gastrointestinal tract. FEMS Microbiology Letters, 248(1): 75-81. 13. Philippeau, C., Sadet-Bourgeteau, S., Varloud, M., & Julliand, V. (2015). Impact of barley form on equine total tract fiber digestibility and colonic microbiota. Animal, 9(12): 1943-1948. 14. Park, T., Cheong, H., Yoon, J., Kim, A., Yun, Y., & Unno, T. (2021). Comparison of the fecal microbiota of horses with intestinal disease and their healthy counterparts. Veterinary Sciences, 8(6): 1-10. 15. Hudson, J. M., Cohen, N. D., Gibbs, P. G., & Thompson, J. A. (2001). Feeding practices associated with colic in horses. Journal of the American Veterinary Medical Association, 219(10): 1419-1425. 16. Cohen, N.D., Gibbs, P.G., & Woods, A.M. (1999). Dietary and other management factors associated with colic in horses. Journal of the American Veterinary Medical Association, 215(1): 53-60. 17. Bulmer, L., McBride, S., Williams, K., & Murray, J. A. (2015). The effects of a high-starch or high-fibre diet on equine reactivity and handling behaviour. Applied Animal Behavior Science, 165: 95-102. 18. Destrez, A., Grimm, P., Cézilly, F., & Julliand, V. (2015). Changes of the hindgut microbiota due to high-starch diet can be associated with behavioral stress response in horses. Physiology and Behaviour, 149: 159-164. 19. Bulmer, L. S., Murray, J. A., Burns, N. M., Garber, A., Wemelsfelder, F., McEwan, N. R., & Hastie, P. M. (2019). High-starch diets alter equine faecal microbiota and increase behavioral reactivity. Scientific Reports, 9(1): 1-11.
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