NASEM Addresses Dairy Feed Additives

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In its most recent iteration of dairy nutrition guidelines, the National Academies of Science, Engineering, and Medicine (NASEM) devotes significant attention to feed additives.

“Feed additives are ingredients not required in dairy cattle rations but may aid digestion, metabolism, and production,” stated Rainey Rosemond, Dairy Extension Educator at Penn State University. “However, they are not nutrients.”

Rosemond summarized the updated discussion of prominent dairy feed additives in NASEM’s recently published industry guidebook, “Nutrient Requirements for Dairy Cattle: Eighth Edition”. Snapshots of her summary include:


  • Ionophores – Chemical compounds produced by bacteria that act as an antibiotic, ionophores alter the flow of ions across cell biological membranes. Alterations to rumen bacterial populations can change how feedstuffs are broken down, along with the concentration and types of volatile fatty acids produced for utilization by dairy cattle. Ionophores typically act on gram-positive bacteria only. The two main ionophores currently approved for dairy calves and heifers are monensin and lasalocid, while only monensin is approved for inclusion in diets of lactating or dry adult dairy cattle.


  • Yeast and direct-fed microbials – Direct-fed microbials (DFM) are feed additives that contain live and viable microorganisms at the time of feeding. The microorganisms must be living at the time of feeding for additives to fit the definition of a DFM. Yeast products have demonstrated increases in milk yield and fat yield with varying impacts on milk protein and dry matter intake. DFMs are typically categorized as either lactic-acid-using or lactic-acid-producing bacteria. DFMs and some yeast products have to be carefully stored and incorporated into rations to be effective in practice.


  • Enzymes ­– These feed additives, produced by bacteria or fungi, target the digestion of fiber, amylose, or proteins. Though many different enzymatic feed additives exist, those used in practice frequently target improved fiber digestion. Enzymes as dairy feed additives perform via many different modes of action, including:
  1. Pre-ingestion breaking of chemical bonds
  2. Enzymatic activity within the rumen
  3. Working in concert with native microbial enzymes
  4. Enhancing attachment to feed particles
  5. Improved microbial growth


  • Essential oils and other phytonutrients – These compounds are extracted from plants, and can directly impact microbial populations in the rumen. Essential oils are a well-known category of phytonutrients that are extracted by steam distillation and thought to modify microbial populations within the rumen. Theoretically, essential oils could alter methane production in the rumen and potentially increase feed efficiency. With current knowledge, the future of essential oils in dairy cow diets is largely unknown, but there is potential use for environmental mitigation.


“Feed additives can be included in dairy cattle diets for a variety of reasons and are advertised as a solution to many feed quality issues,” stated Rosemond. “However, feed additives should not be considered a cornerstone to any farm feeding program.”


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