Nonstructural Carb Tolerance in Healthy Horses (AAEP 2011)

Nonstructural Carb Tolerance in Healthy Horses (AAEP 2011)

"A moderate intake of NSC (30% of total DE) is perfectly fine for non-obese normal horses," Pagan concluded.

Photo: The Horse Staff

The words "nonstructural carbohydrates" have become almost synonymous with "bad news" in the horse industry, mainly because many owners' goals have been to reduce these sugars and starches (while increasing fat levels) to provide "safer" calories for horses with certain medical conditions. But until recently it was unclear what an NSC diet means for a "normal," nonobese horse.

At the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas, Joe Pagan, PhD, president of Kentucky Equine Research (KER), described his and colleagues' research on the effects of carbohydrate and fat intake on glucose tolerance in the healthy horse.

Pagan pointed out that there is a perception among horse owners that feeding any nonstructural carbohydrate to healthy horses will lead to insulin resistance (the inability of the hormone insulin released from the pancreas to manage glucose levels in the bloodstream) and metabolic disorders, even when horses aren't obese.

Previous studies conducted at KER found that healthy horses fed high-fat diets have a marked delay in clearing glucose, whereas when consuming carbohydrates from sweet feed, glucose returned to normal clearance rates. To test this theory further, his team evaluated four healthy, nonobese Thoroughbred geldings with body condition scores of 5-6 (out of 9), aged around 21.5 years old. The horses were stalled except for six hours of daily turnout with a grazing muzzle.

The investigators fed four treatment diets for a month by adding one of four energy supplements to regular grass hay. They provided hay rations three times daily and supplements twice daily. The treatment groups were:

  • FIBER: 5.6 kg of additional grass hay
  • ALF: 3.1 kg alfalfa and Bermudagrass blended pellet
  • CHO: 2.3 kg whole oats
  • FAT: 1.3 kg alfalfa cubes with 30% digestible energy provided by 500 grams soybean oil, which is an amount higher than the normal recommended dietary fat level of less than 10%.

All but the CHO diet contained less than 10% NSC; the CHO diet was 20.3% NSC-7% of total calories supplied and 31% from NSC, similar to analysis of 140 diets fed to the sport horses at the 2010 World Equestrian Games. In the FAT diet 30% of total calories supplied came from fat and 12% from NSC. The FIBER diet contained less than 10% NSC that contributed 17% of total calories supplied.

On Day 14, investigators performed an oral glucose tolerance test (a 12-hour fast followed by feeding half the daily energy):

  • The CHO diet produced the greatest glycemic response (glucose circulating in the bloodstream in response to carbohydrate ingestion); as expected, the FIBER or FAT diets had no glycemic response.
  • Resting blood glucose increased after two weeks on the high FAT diet.
  • The CHO diet produced a higher insulin response and lower free fatty acids than the other three treatments.

At Day 28, IV (intravenous) glucose tolerance tests demonstrated that glucose cleared more quickly in CHO-fed horses than the other three diets, returning to baseline 90 minutes more quickly than the FAT diet. Plasma insulin levels in horses fed the FIBER diet were lower than the other three treatments. With the high FAT diet, there was a delayed insulin response to reach peak levels. Pagan pointed out, "The negative effects we found for high fat were from extremely high-fat diets. It is uncertain if these effects would occur at lower fat levels like those commonly used in commercial horse feeds."

Pagan summarized, "A high-fat diet impairs glucose clearance, with a lag phase following the acute insulin response. Glucose intolerance could develop by feeding high fat at levels of 30%. In contrast, feeding of moderate amounts (31%) of nonstructural carbohydrates improved glucose tolerance." Pagan also noted that impaired glucose tolerance could be reversed by feeding two ounces of fish oil, whereas corn oil (long touted as a method to add calories to horses' diets) did not achieve this same effect.

"A moderate intake of NSC (30% of total DE) is perfectly fine for non-obese normal horses," Pagan concluded.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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