The author is a professor emeritus of animal sciences at the University of Illinois, Urbana.
This article continues our discussion on the new Dairy NRC 2021 that’s more formally referred to as NASEM Dairy 2021. My overall impressions are conservative (using only multiple published research data), highlight milk responses, focus more on the academic versus field applications, and emphasize efficiency and environmental impact. The user will need to use the new NASEM model after its release in December to better appreciate the new equations and diet changes.
My congratulations to the entire committee for an excellent model, which I have not used, and research-based, 500-page book.
Protein and amino acids
Led by Mark Hanigan, Helene Lapierre, and Jeff Firkins:
• A new equation to predict milk protein included five amino acids, a term called “other amino acids,” digestible energy, digestible neutral detergent fiber (dNDF), and body weight (an adjustment to the maintenance requirement).
• Each amino acid has the same digestibility of rumen undegradable protein (RUP) and amino acid protein sources. The model provides predicted diet amino acid efficiencies for each amino acid compared to target efficiency. If the diet amino acid efficiency is close to or greater than the target efficiency, this could indicate the need to supplement amino acid as amino acids may be limiting milk production.
• The concept of first limiting amino acids is considered incorrect (several mixtures of amino acids may result in similar milk protein yield).
• The optimal level of rumen degraded protein (RDP) is 10% of the diet dry matter with a maximum of 12%.
• Accuracy of estimating RDP, RUP, and microbial protein in the feed library were updated this time around.
• Endogenous protein is not considered as a net source of amino acids.
Hutjens’ comments: The protein and amino acid model has been adjusted with a focus on milk protein yield. Mathematical modeling and statistics were used to improve model predictions. Field applications will require use of the NASEM 2021 model, which estimates milk protein response from the diet. If your milk market does not pay for milk protein, the milk protein model has less economic value.
Macrominerals
Led by Rich Erdman:
• Recommendations are based on an absorbed mineral basis using an absorption coefficient (AC).
• A minimum dietary cation anion difference (DCAD) recommendation is presented based on requirements for sodium, potassium, chloride, and sulfur. However, optimal DCAD is an economic decision, not a nutritional requirement.
• Calcium: Small increases, but overall dietary requirements will not change. However, AC also dropped. The net result was little change in dietary requirement for calcium.
• Phosphorous: Dietary sources are highly available, decrease in endogenous losses, and tied to milk protein. Dietary requirements will not change.
• Magnesium: AC adjusted the magnesium-to-potassium equation, reduced milk magnesium requirement, and there was an increase in maintenance. Overall dietary requirement will be higher than previous levels.
• Sulfur: No changes.
• Sodium: Maintenance rose 10 to 15 grams per day, with a drop in lactation requirements by 6 to 12 grams. It’s acknowledged that milk has less sodium than previously because it is related to mastitis, and heat stress guidelines were removed. Overall dietary requirement will be higher than previous levels.
• Potassium: No changes.
• Chlorine: Recommendations received a boost in maintenance by 10 to 15 grams, but milk requirement was reduced so no large change in total requirements.
Hutjens’ comments: No major changes were presented. No recommendations under heat stress for DCAD, sodium, or potassium were included. Some nutritionists and dairy farmers may monitor macromineral levels based on the total amount instead of absorbed levels.
Trace minerals and vitamins
Led by Bill Weiss:
• No adjustments with dietary antagonists were made on the availability coefficient.
• Safety factors are important because NASEM requirements are for the average cow, but NASEM does not include safety factors in this update.
• Dry cows consume about half the dry matter intake compared to lactating cows. Dry cows require fewer milligrams per day than lactating cows, but concentrations are greater due to the differences in dry matter intake.
• AC is not included for organic trace minerals because of limited data, and AC can vary because of the product. If the user has reliable AC data for specific products, they can be entered into the software model.
• Cobalt: Raised to 0.2 ppm.
• Copper: Doubled maintenance requirements, increased AC, and approximate diet concentrations to meet average requirements are 17 ppm for dry cows and 9 ppm for lactating cows.
• Chromium: No recommendations; more data needed before including chromium.
• Iodine: Small changes with basal milk iodine are included in recommendations (higher levels appearing in milk).
• Manganese: AC dropped from 0.75% to 0.4%. That means diets with 40 ppm for dry cows and 30 ppm for milk cows should be adequate for manganese.
• Selenium: No change because data does not indicate that it was inadequate and concentrations are regulated by FDA.
• Zinc: Dry cows raised 10% to approximately 28 ppm; lactating cows climbed 15% to about 60 ppm.
• Vitamin A: Not changed, except for cows producing over 75 pounds of milk; add 450 international units (IU) per day per every pound of milk produced for about 75 pounds.
• Vitamin D: Vitamin D2 has half the biological value of vitamin D3. Maintaining plasma concentrations of vitamin D 25-hydroxy at 30 nannograms per milliliter was used to set requirement, which for lactating cows is 40 IU per kg of body weight.
• Vitamin E: 1,000 IU for far-off dry cows and 2,000 IU for close-up dry cows.
Hutjens’ comments: Significant changes were reported. No adjustments for antagonists are included in the model but should be considered by nutritionists. No guidelines for DCAD, chromium, niacin, or biotin were listed as they are not a requirement. However, supplemental amounts for lactating cows can impact milk production and improve health. No mineral ratios were listed. Areas left for dairy farmers, veterinarians, and nutritionists to evaluate include: role of organic trace minerals, chromium guidelines, and rumen protect choline.
Dry cows and transition cows
Led by Bill Weiss:
• Dry matter intake: The level of NDF and weeks before calving are used to estimate dry matter intake (DMI), which will range from 1.8% to 2% of body weight. Springing heifers are set at 88% of mature cows. DMI starts dropping two weeks prepartum, gradually down to 1.6% of body weight in the model.
• Birth weight of the unborn calf is estimated based on parity and cow weight. Protein and energy requirements for the unborn calf begin 10 days after conception (minerals and vitamins requirements start at 190 days prior to calving) and increase on a curve relationship until 280 days. No adjustments are included in the model for twins.
• Protein levels: 12% crude protein (7.2% MP) for dry cows, 13% crude protein (8.6% MP) for close-up dry cows, and 14% crude protein (9.2% MP) for springing heifers based on subsequent milk yield.
• No adjustments for colostrum synthesis were added, but users are urged to consider colostrum nutrient needs.
• No adjustments for rumen protect methionine were made unless needed for amino acid requirements by the dairy animal (does impact immunity, fertility, and liver status).
Hutjens’ comments: The improvements in dry matter intake separating cows and heifers are a plus. Protein recommendations are lower than those used in the field. Colostrum nutrient requirements are important when dry matter intake is declining. Close-up diet protein increases are important along with energy changes listed in the book. One approach is reducing NDF and elevating energy such as starch.
Calf nutrition
Led by Jim Drackley:
• Requirements were completely changed based on dairy calf slaughter results (NRC 2001 used veal calf data).
• Energy allowance based on retained energy basis.
• A new equation for protein deposition related to weight gain was presented.
• Subtropical and moderate environmental impacts are considered in requirements (cold and hot environments). Model users should use the subtropical when temperatures are over 35°C or 95°F.
• For calves fed mainly milk replacer, recommended calcium levels were lower, phosphorus was lowered 15%, potassium was raised (similar to whole milk), copper dropped 50%, iron was reduced 15%, and zinc was raised 40%.
• Recommend 1.5% of calf body weight as milk or milk replacer solids (reduces hunger, stress, and addresses welfare issues).
• Requirements for gain are listed in the table.
Hutjens’ comments: Excellent improvements were made reflecting dairy calf data, environmental effects, and nutrient concentrations. High dry matter solids intakes are important for economic growth rates while encouraging starter intake for rumen development.
Growing heifers
Led by Mike VandeHaar:
• Metabolizable energy (ME) requirements based on dairy heifer data (NRC 2001 was beef data based).
• The Holstein breed is the reference breed (no Jersey or other breed guidelines were included, but the model should fit for specific breed body weights).
• No environmental factors were included in the model (heat, cold, wind speed, hair coat, or mud).
• Gut fill is 15% of body weight.
• For calculations, body condition score is assumed to be at 3 (no adjustment related to age).
• Weight gains over 2.3 pounds (1.1 kilograms) per day may have a negative impact in pre-pubic heifers.
Hutjens’ comments: Converting to an ME energy base removed the need for TDN and NE gain values. Use of dairy heifer data is a plus. Environmental impacts on growth were useful teaching demonstrations in the 2001 Dairy NRC.
Water
Led by Paul Kononoff:
• Minerals dissolved in water are not included as a dietary mineral source because these are generally small.
• For calves, a ratio of four parts water per one part of dry matter is needed.
• Mineral tolerances were based on the NRC 2005-second edition booklet for this update.
• Table of water quality concerns are listed in the book.
• Hardness does not impact free-choice water intake.
• Sulfates in water can impact zinc, iron, manganese, and copper absorption (sulfate levels in water less than 500 milligrams per liter for calves; 1,000 mg per liter for older animals). Sulfate sulfur levels are 33% of sulfate levels.
• No recommendations on water space for animals were included.
Hutjens’ comments: Water continues to be an important nutrient that impacts dry matter intake and animal health. Nutrients and quality issues contained in water were addressed by the committee.
Environment impact
Led by Ermias Kebriab:
• About 4% of greenhouse gases (GHG) are attributed to cows.
• In all, 70% of methane is from rumen fermentation, and 30% is from manure sources.
• Excess hydrogen in the rumen leads to methane production.
• On average, 5.7% of gross energy is lost via methane gas losses.
• As milk production per cow climbed, the level of methane per unit of milk has dropped.
• The 2021 model calculates losses in methane and manure excretion of nitrogen and phosphorous.
• Feed additives that can reduce methane production include seaweed, fatty acids, 3-NOP, oregano, tannins, nitrates, monensin, and several essential oils.
Hutjens’ comments: The environmental chapter and model calculations are a welcomed new addition to dairy cattle feeding, as dairy cattle continue to be a focus of greenhouse gases and environmental issues. Producers can make dietary changes to predict and model the impact on methane product (a win-win for dairy farmers and environmentalists).
Order a copy
You can order a hard copy book at www.nap.edu/catalog/25806/ for $149.95 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 is an update from the Dairy NRC 2001-seventh edition.
One correction from the September 25 column on pages 570 and 571: NASEM should be listed as the National Academy of Science, Engineering, and Medicine.
