Energy: How to determine energy level from a commercial feed label
by Paul Davis, Ph.D, Nutritionist
While protein is a component of hooves, hide, hair, organs, muscle and several body chemicals, it still seems that as an industry we tend to overemphasize protein and underemphasize energy.
Over my career, spanning hundreds of producer meetings, farm visits and thousands of phone calls, I have contemplated the reasons for our industry’s obsession with protein content of livestock feeds. I have concluded that it must be related to the fact that “energy” is not listed on the feed tag. While crude protein is almost always listed first, a guarantee of energy either as total digestible nutrients (TDN) or net energy is conspicuously absent. To those interested in providing adequate nutrition to beef cattle, this omission should cause great concern.
Beef cattle nutrition and ration balancing deal largely with creating a ration and offering it in such an amount as to meet the animal’s nutritional requirements and in a safe, manageable and economical manner. Many factors affect nutritional requirements such as sex, age, body weight, and stage of production. Energy is always needed in the greatest daily amounts and is one of the nutrients most affected by stage of production. Regardless, often we know the least about the energy content of a ration. Knowing that energy value is synonymous with calories, cattlemen often use fat percentage as an indication of energy. This can be very misleading.
While fat is an energy source and pound for pound provides 2.25 times the calories of carbohydrates, it is not the tell-all with regard to energy content. Fat is also considered in some calculations of TDN and has some bearing in the calculation of net energy for gain (NEg). However, upon further examination of the energy equations, it is the fiber fractions, that have the larger bearing on energy values.
The fiber in a feedstuff is fractionated out into acid detergent fiber (ADF) and neutral detergent fiber (NDF). ADF is comprised of mostly lignin and cellulose and is inversely related to digestibility. NDF is ADF plus hemicellulose and is inversely related to intake. A feedstuff high in ADF is low in digestibility and low in energy. A high NDF feedstuff may limit the voluntary intake by cattle. So fiber and carbohydrate content have a much larger bearing on energy value than fat does. It would be very easy to have feed with an appreciable amount of fat listed on its label that would be low in total energy. Conversely to that, a feed that is low in fat can be very high in energy. Without laboratory analyses, energy is difficult to determine.
When comparing and choosing feeds, don’t get hung up on fat content; rather consider the total ingredient makeup. Choose feeds with high levels of soluble (digestible) fiber. This type of carbohydrate is fermented into energy by microorganisms in the digestive tract of cattle and other ruminant livestock and is abundant in ingredients such as wheat middlings, soybean hulls, corn gluten feed and citrus pulp. Non-structural carbohydrates such as sugars and starches are energetic and may be appropriate in some rations. Content of corn or other grains is indicative of this type of nutrient. Some grain by-products and roughage products can be high in ADF thus reducing the overall energy value of the ration. Likewise, the overuse of fat can be detrimental. The total dietary fat level should not exceed six percent for mature cattle or about 4.5 percent for growing cattle. High fat levels can lead to reduced digestibility of feedstuffs, interfere with vitamin and mineral absorption, cause fluctuations in feed intake and may result in scours.
While it is unfortunate that energy content isn’t more easily discernible from a feed tag, paying attention to ingredient composition and content of nutrients other than fat can provide some insight. Work with a reputable feed company, a trusted nutritionist or extension personnel to help assure the provision of adequate energy to your livestock. In today’s economic environment, it makes little sense to transport, process, mix and feed rations that are inferior in energy.