Detrimental Effects of Feeding High Sugar / High Starch Feeds

Typically, grain and concentrate type of rations are higher in sugar and starch than forages. When horses are on a ration or diet that has a high sugar and starch content, it can have dramatic effects on the digestive physiology such as:

  • There is less chewing, less saliva produced, more acidic contents in the stomach – possibly more gas or development of gastric ulcers.
  • The ingested feed moves faster through the small intestine – more sugar/starch substrate enters the hindgut upon which abnormal bacteria feed and proliferate.
  • The bacteria that feed on sugar and starch grow rapidly causing normal gut bacteria to die, bringing about inflammatory changes in the gut, and the dying bacteria give off endotoxins that are absorbed into the bloodstream. This can potentially lead to laminitis. These changes can result in abdominal pain, inflammatory disease, and digestive upset. Thus colic is another possible consequence.
  • The sugar and starch is absorbed rapidly from the small intestine, resulting in an elevated blood glucose level and a subsequent increase in insulin in the blood.

Therefore, three serious problems that occur from ingestion of high-sugar/high starch feeds are: laminitis, colic and insulin resistance.

The body normally produces insulin from the pancreas and it is secreted in response to high blood sugar (which occurs after eating and absorbing sugar and starch). Insulin is used to help the cells use the sugar that is circulating in the blood – it helps transport sugar from the blood into the cells where it is used. In a condition called insulin resistance, the affected horse has a high blood sugar level from sugar and starch digestion. A resulting high insulin level occurs and persists because the body’s cells are not responding to the insulin. Therefore, the cells are not able to transport the sugar from the blood into the cells – it could be likened in some respects to Type II diabetes in humans. The insulin is there but there is an abnormal lack of response to it.

The body’s resistance to insulin can also be involved in laminitis in that the resultant high levels of insulin may cause a decreased blood flow to the hoof and/or the high insulin may affect the uptake of blood sugar into the laminae of the foot. The resulting effect of either is a cascading set of events that result in laminitis or a painful breakdown in the bond between the hoof and the underlying bone.

Other medical conditions that are very sensitive to sugar and starch levels in the feed are:

  • Gastric Ulcers
  • Cushings Disease
  • Equine Metabolic Syndrome
  • Osteochondritis dissecans (OCD)
  • “Tying-up” syndromes like Polysaccharide Storage Myopathy and Exertional Rhabdomyolysis


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