Guidelines for Feeding Horses Starch
Scientists have identified a threshold for meal size and starch intake below which horses will avoid undergoing extreme responses in glucose and insulin levels. Even when fed highly processed cereals, horses don't experience an unhealthy rise in blood glucose and insulin if their meals are kept small.
In their study, researchers fed horses anywhere from 0.5 to 3.5 kilograms of feed at a meal. This provided starch at rates ranging from 0.3 to 2 grams per kg of horse bodyweight.
While glycemic response did increase with the amount of starch eaten, there was a point below which the response was only moderate. These results enable the study's authors to recommend the amount of starch and the size of meal that's best for horses.
They advise giving horses meals with less than 1.1 grams of starch per kilogram of bodyweight. For feed with a 30 to 40% starch content, that's a limit of 0.3 kg for every 100 kg the horse weighs.
Translated into imperial units, a horse ought to eat less than 1.8 ounces of starch per 100 pounds of bodyweight. Thus a 1,000 pound horse would do best with no more than three pounds of starchy feed (30-40% starch content) in one meal.
Ingrid Vervuert, Katrin Voigt, Teresa Hollands, Derek Cuddeford and Manfred Coenen. 2008. Effect of feeding increasing quantities of starch on glycaemic and insulinaemic responses in healthy horses. The Veterinary Journal.