|Hall, Mary Beth|
Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2014
Publication Date: 4/1/2014
Publication URL: http://handle.nal.usda.gov/10113/58837
Citation: Hall, M., Eastridge, M.L. 2014. Carbohydrate and fat: considerations for energy and more. Professional Animal Scientist. 30:140-149. Interpretive Summary: With ruminant animals such as dairy cattle, dietary carbohydrates and fats are commonly perceived as a primary source of energy. However, our scientific understanding is evolving to show that their role is highly variable based on many factors. For example, dietary carbohydrates and fats are not uniform in terms of their value as energy sources. Also, energy does not come from fats or carbohydrates in the form of calories, but as absorbable nutrients that the animal may metabolize to yield energy or to use for productive purposes such as making milk. Different types of carbohydrates and fats can have distinctly different interactions with other dietary components, and there are different recommendations for levels that can be fed in different situations. This review article was written to inform animal nutrition researchers and consultants about these recent findings so that they may provide diets to achieve highly productive and efficient animal performance by considering the specific nutrient value, as well as the energy value, of dietary carbohydrates and fats.
Technical Abstract: Historically, carbohydrates and fats were valued on their caloric contributions to diets. Feeding recommendations for these feed fractions now address inclusion levels, as well as consideration of the positive and negative effects of specific types of these nutrients. Feed carbohydrate characterization has expanded beyond fiber and nonfiber carbohydrates (NFC). Fiber now encompasses acid detergent fiber (ADF), neutral detergent fiber (NDF), physically effective fiber, and fiber digestibility to describe the effect on diet composition, rumination, rumen fill, potential fermentability, and nutrient contribution. The NFC is now parsed into sugars and fructans (both in water-soluble carbohydrates), starch, pectins, and others, all of which may differ in their effects on rumen pH or support of microbial growth. Dietary fat has the advantage of providing energy without increasing the risk of ruminal acidosis. However, there are specific considerations for amounts and types fed in high- vs. low-forage diets. Fats can affect ruminal fermentation, having the potential to depress fiber digestion or affect ruminal methane production. Considerable research in recent years has focused on providing specific dietary fatty acids (FA) to alter the metabolic function of specific tissues or to alter the FA content of milk for nutraceutical purposes. Rising grain prices and diversion of fats for biofuel are driving livestock industries to seek alternative nutrient sources. Most of the nutritional research on which current recommendations are based involved the use of traditional diets which tended to be rich in grains. Fat and carbohydrate feeding recommendations may need to change with diets high in low-starch byproducts. We need to learn how diets with substantially more byproduct feedstuffs ferment and pass from the rumen, and how they affect nutrient supply and feed efficiency. We can then better predict digestion and the effects on metabolism and, thus, target supplementation to have the greatest positive effect on food animal production.