The new publication can be referred to as the National Academy of Science, Energy, and Medicine (NASEM) revised eighth edition, Dairy NRC (National Research Council) 2021, and/or Dairy v.8. Whichever name you use, it is a must read and review by dairy farmers, nutritionists, consultants, and veterinarians.
The huge effort required a committee of 12 selected and voluntary dairy scientists led by Bill Weiss, The Ohio State University, and Rich Erdman, University of Maryland, as co-chairs. Fifteen companies and organizations provided funds supporting the development of latest research-based chapters, references, and recommendations used around the world to efficiently feed dairy cows, calves, heifers, and dry cows.
The four-day conference featured committee members discussing their research findings and recommendations in each chapter. Several chapters are discussed below, listing the topic, presenter, bullet summary points, and my (Hutjens) comments. A feeding column in the October issue will summarize the remaining chapters.
Feed intake
Led by Mike Allen, Michigan State University:
- Four mechanisms control dry matter intake, including animal factors and fill factors.
- The dry matter predictions for high producing cows were lowered by four pounds with increased dry matter intakes for lower producing cows compared to NRC 2001.
- The number of days with lower dry matter intake after calving was shortened to 31 days, allowing early lactation cows to achieve higher dry matter intake earlier in lactation.
- Refinement on the amount of dry matter needed to change body condition scores were made in the model.
- Fill factors that limit dry matter intake included forage neutral detergent fiber (NDF), digestible neutral detergent fiber (NDF), and fragility (forage particle length during digestion).
- Ratio of acid detergent fiber (ADF) to NDF or lignin levels in forages can be used to adjust dry matter intake.
- The level of protein and fat were not used to predict dry matter intake.
Hutjens’ comments: These changes reflect field observations when balancing rations. Compared to the NRC 2001 model program, nutrient requirements could be met with less total dry matter intake. Dry matter costs money, reflecting lower feed costs with lower dry matter intakes. Healthy, early lactation cows with higher dry matter intake reduces the risk of ketosis and weight losses. Dry matter intake is a key factor to support milk yield, immunity, and fertility. Forage quality impacts dry matter intake, lowering rumen fill and increasing rate of passage.
Feeding of fat
Led by Lou Armentano, University of Wisconsin:
- Rations can be evaluated based on the fatty acid composition of fat sources (an improvement over ether extract).
- Lipids were grouped in 11 categories based on their source and characteristics with an assigned digestibility that can be changed in the model.
- Basal fats (such as corn oil in corn silage or corn grain) were assigned 73% digestibility.
- Digestibility of commercial fat digestibility can also be changed based on research results.
- No depression in dry matter intake is related to the level of total fat in the ration.
- Fats do not generate methane compared to carbohydrates, providing more calories in a model program when substituted as an energy source.
Hutjens’ comments: Moving to evaluating fats based on fatty acid composition is a plus as it allows the model to estimate the levels of polyunsaturated (PUFA) and saturated fatty acids, which can impact rumen fermentation and milkfat test. Adjusted energy digestibility by different classes or commercial sources allow for accurate energy formulation using the model program. Lower dry matter intake in early lactation due to feeding fat was a concern when added fats provides needed energy.
Carbohydrate considerations
Led by Mary Beth Hall, USDA ARS Dairy Forage Research Center, Madison, Wis.:
- Neutral detergent soluble carbohydrates (NDSC) is part of a new fraction called residual organic matter (ROM). ROM plus starch replaces nonfiber carbohydrate (NFC). NDSC consists of starch (analyzed in labs); water soluble carbohydrates (WSC), including sugar, oligosaccharides, and fructans; and neutral detergent soluble fiber or NDSF (pectin and beta-glucans).
- The ROM calculation used in the model has the following equation: ROM = dry matter – ash – crude protein – NDF – fatty acids – starch – WSC – NDSF – organic acids – glycerol.
- No adjustments were included related to processing (such as particle size or steam flaking).
- The use of 48-hour NDF is recommended as the standard time measurement for tests.
- The table provides guidelines using minimum forage NDF, minimum NDF, and maximum starch relationships. The values in the table can be adjusted as forage NDF (fNDF) levels can range from 17% to 27% depending on several factors:
- - High dry matter intake for cattle (lowers fNDF)
- - Shorter forage particle size (raises fNDF)
- - Limited bunk space (raises fNDF)
- - Adding buffer (lowers fNDF)
- - Faster starch degradation in the rumen (raises fNDF)
- - Grain fed separately or slug feeding (raises fNDF)
• Physically adjusted NDF (paNDF) is based on the percent of particles on the 8 millimeter screen of the Penn State Particle Separator and measured rumination time targeting rumen pH from 6 to 6.2.
Hutjens’ comments: These changes are welcomed to define carbohydrates based on their chemical structure and impact on rumen fermentation. Starch guidelines are listed and are related to the forage program. While grain processing can impact cow performance, a lack of research data does not allow it to be included in the model. An improvement is defining physically effective fiber for field applications. Rumination times can be measured on farms with rumination collars or tags.
Energy supply
Led by Bill Weiss, The Ohio State University:
- Discount factors for multiples of maintenance were too high in NRC 2001, limiting energy content as dry matter increased to support higher milk in high-producing cows. Discount factors will be based on intake as a percent of body weight instead of a multiple of maintenance. As feed intake changes from the base of 3.5% of body weight, starch digestibility (plus or minus 1 unit), and NDF digestibility (plus or minus 1.1 units) are lowered or raised as dry matter intake changes.
- Changes in starch levels will impact NDF (higher starch levels reduce NDF values, for example).
- Higher levels of by-product feeds, such as soy hulls, may lower NDF values when fed at high levels.
- Starch was separated as an energy source. A new term called residual organic matter looks at sugar, organic acids, and soluable fiber. At the same time, nonfiber carboydrates (NFC) were dropped.
- A summative equation to predict energy content was improved by adding starch, residual organic matter, and modifying the calculation for metabolic fecal energy.
- Starch will have a default value of 0.91 for digestibility, but particle size of corn, steam flaked corn, and corn silage values will fine-tune this value even further.
- In vitro NDF digestibility at 48 hours or a lignin-based equation can be used to estimate NDF digestibility (user can decide).
- Methane production was estimated from digestible fiber (producing more methane) and fat (reducing methane production).
- Energy losses due to urinary nitrogen excretion was estimated at 14.3 kilocalories (kcal) per gram of nitrogen excreted.
Hutjens’ comments: Energy supply adjustments reflect available energy sources. Energy discount values based on a percent of body weight is superior to multiples of maintenance that limit energy value of feed ingredients for high-producing cows. Energy supply was improved with discounts based on percent body weight, lower discounts, accurate methane and nitrogen energy losses, and interaction of fat, starch, and NDF levels in rations.
Energy requirements
Led by Mike VandeHaar, Michigan State University:
- Maintenance requirements were raised 25% for lactating and dry cows to account for higher energy needs in diets.
- Body weight gain reflects structural growth (protein) and fat deposition with a 2.9 Mcal per pound of average daily gain (ADG) change.
- Environmental adjustments were dropped for dairy cows and growing heifers.
- The efficiency of using metabolizable energy was increased slightly, resulting in slightly lower lactation of energy requirements.
- Feed efficient cows eat less dry matter (referred to as residual feed intake) while supporting the same level of milk yield.
Hutjens’ comments: Requirements were adjusted, reflecting changes in body composition and interaction of feed nutrients. Dropping heat stress impacts (increase in maintenance and lower dry matter intake) were difficult to model, but it is happening with global warming. Future genetic selection for more efficient cows is possible and should be considered in your sire selection decisions. The new energy approach will more accurately predict energy needs for high-producing cow.
Order a copy
You can order a hard copy book at www.nap.edu/catalog/25806/ for $149.95 per copy plus shipping. The book with over 500 pages has a projected release date of December 2021. It is advised to order it now. The first Dairy NRC was published in 1945; this eighth revision was is an update from the Dairy NRC 2001-seventh edition.
