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NUTRITION
Figure 1: Schematic of the pathophysiological events triggered by ingestion of excessive NSC (non-structural carbohydrate, which includes starch and fructan) culminating in colic. Durham, 2013 (Equine Applied and Clinical Nutrition)
that overconsumption of oil leads to some reaching the hindgut. Here its fermentation produces bactericidal fatty acids, which have been shown to suppress fiber fermentation. It is easy to misjudge the amount of oil in the diet, as it accumulates from many different sources. My recommendation would be for a ceiling of 20% of the total energy content of the diet being derived from oil. For a horse in moderate to hard work, this means about 600ml of oil in total from all of these different sources. For example, 13lbs of hay provides ~100ml, 13lbs of a 6% oil racing feed would provide ~360ml and 500g of a 20% oil rice bran product would provide ~200ml – a total of 550ml.
Prebiotics and probiotics are extremely popular for maintaining normal digestive processes, and certainly live yeasts have been shown to be beneficial for hindgut health� Prebiotics and probiotics are extremely popular for maintaining normal digestive processes, and certainly live yeasts (Saccharomyces sp) h ave been shown to be beneficial for hindgut health, as have short chain fructo-oligosaccharides (ScFOS) prebiotics. In other species, mannanoligosaccharides (MOS) have been shown to have a beneficial effect on mucosal integrity. Other ingredients such as beta glucan and glutamine may also be useful. However, supplements are not a substitute for good feeding management, which can reduce the odds ratio of colic significantly.
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Tight junctions that become loose Knowledge of the pathophysiological mechanisms behind colic may provide insight into other conditions observed in horses in training. A change to the balance of microflora in the gut and the subsequent fall in hindgut pH can result in cell death of certain bacteria. Dying bacteria release a cocktail of undesirable substances including exotoxins, lipopolysaccharides, and vasoactive amines. These harmful substances can contribute to colic through changes in blood flow, pain, and effects on gut motility. Additionally, they may initiate a cycle of inflammation, which ultimately results in a loosening of the normally tight junctions or spaces that exist between the absorptive cells in the gut. These tight junctions normally present a formidable barrier to undesirable substances, as well as to undigested or partially digested food material. Once leaky, however, they may be absorbed, leading to systemic effects in the body, and they may even trigger an allergic immune response in certain circumstances. Certainly this is interesting in the context of the chronic loose droppings, skin reactions or hives, or filled legs that are intermittently observed in horses in training and that are often attributed loosely to the plane of nutrition being too high. A picture is emerging to show that dietary factors that disrupt the balance and harmony of bacteria within the digestive tract present a particular problem and potentially exacerbate the risk of colic and other conditions related to the digestive tract. As research progresses in humans, horses, and other animals it becomes apparent just how influential the digestive tract is as an organ, with far reaching effects on allergy and immunity, metabolic disease, and lameness associated with laminitis. Our feeding strategy for horses in training must aim to maintain a healthy balance of microflora in the digestive tract and to minimize its disruption, while providing the energy and nutrients required for training and racing. n