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Energy Supplements in Forage Diets

By: Levi Trubenbach, Ph.D – Livestock Nutrition Center

Stocker operators often feed supplemental energy to calves on forage-based diets to increase gain, stocking rate, or both. Historically, the standard energy supplement has been grain-based, in conjunction with a protein source to optimize ruminal fermentation. However, our team often recommends hand-feeding a blend of mostly byproduct ingredients, including beet pulp, soybean hulls, wheat middlings, etc. While the calculated, or “book,” energy values (TDN = 69-74%) of these byproducts are significantly lower than that of corn (TDN = 89.5%), several experiments have concluded that their actual nutritive value, when supplementing a forage-based diet, is equal to corn.

How is this possible? If energy consumption increases, then performance rates should follow suit, right? While this concept is fundamental in nutrition models, there is a key distinction to be made between calculated and true energy values that occur in reality. Grains are fermented rapidly in the rumen, causing accumulation of organic acids. Acid accumulation can inhibit proliferation of fiber-fermenting microbes; if fiber fermenters are not populating the rumen in sufficient quantities, then potential fiber digestion rates are often not achieved. In other words, changes in the ruminal environment can have significant effects on the digestibility of individual ingredients. In grain-based feedlot diets (from which book energy values are calculated), intense ruminal acid production reduces fiber digestion substantially, suggesting very low nutritive values for many high-fiber ingredients. Moreover, the total energy lost from undigested fiber is minimal in feedlot diets because roughages (and their potential energy from fiber) typically only represent 10% of the diet or less.

Circle back to the point of this article: forage-based diets contain at least 40-50% forage, so total energy losses from poor fiber digestion can represent a larger percentage of the total available. If our diet is 60% hay, a moderate reduction in fiber digestion rate can lead to substantial losses in actual energy intake and animal performance. The point is: calculated energy values (TDN, for example) do not always tell the whole story. Sometimes we need to rely on controlled experiments to help us define nutritive values in the diets we are feeding, rather than relying on published numbers.

Most grain byproducts are high in fermentable fiber, which means they generally support the growth and productivity of fiber-fermenting microbes. This provides complementary energy supplementation to the basal forage diet. Moreover, these byproducts are often cheaper than corn, and all have protein values equal to or better than that of corn. That means we can reduce the total cost of supplementation, while maintaining targeted performance objectives.