The Cornell Net Carbohydrate and Protein System (CNCPS) continues to evolve with improved understanding of ration formulation and the publication of new research. Version 6.1 allows nutritional professionals to reduce dietary crude protein levels while maintaining or improving production and profitability, according to Michael E. Van Amburgh, Associate Professor, Department of Animal Science, Cornell University.
"Between analytical improvements, error corrections, and new research being implemented within the CNCPS framework, model accuracy has been improved," Dr. Van Amburgh says. "The resulting changes allow nutritionists to reduce dietary crude protein (CP) levels while maintaining or improving production and profitability."
CNCPS v6.1 includes improved passage rates, feed chemistry and error corrections. As a result, it predicts a greater metabolizable protein supple from feed protein.
CNCPS v6.1 also is more accurate and precise in estimating metabolizable energy (ME) and metabolizable protein (MP) allowable for milk with a lower prediction bias.
"Together, these changes allow nutritionists to formulate diets lower in CP while still meeting the MP requirements of the cow and maintaining milk yield and components, provided the cattle, forages and feeds are properly categorized," Dr. Van Amburgh says.
Guidelines for evaluating diets with CNCPS v6.1 include:
1. Inputted dry matter intake should be within the range of CNCPS and the National Research Council (NRC) predictions. If it is not, bodyweight, environment, and feed amounts should be reviewed.
2. Rumen ammonia should be between 100% and 150%. Diets high in hay silage might have rumen ammonia as high as 200% given ingredient availability limitations. Although from an efficiency perspective this is unacceptable, it is realistic depending on total forage availability.
3. Peptide balance can be ignored.
4. Consideration for urea cost can be minimized. A urea cost of less than 0.25 Mcal/d should be targeted.
5. Non-fibrous carbohydrates for lactating dairy cow diets can vary 30% and 42% depending upon the sources. The use of sugar, starch or soluble fiber should be by user preference. Given that cattle require fermentable carbohydrate, sources of fermentable carbohydrate should vary with local availability and pricing.
6. ME and MP allowable milk should be within 1 kg of each other and should match the observed milk before any ration changes are made. For growing cattle, MP allowable gain should be 0 to 250 grams greater then ME allowable gain. For replacement heifers, lactic acid should be kept to less than 3% of dry matter. Data from the 1980s suggests a direct link between lactic acid intake and empty body fat composition in growing cattle.
7. Physically effective neutral detergent fiber (peNDF) should be greater than 22% dry matter for lactating dairy cows and 8%-10% for feedlot cattle.
8. Lysine should be greater than 6.5% MP and methionine greater than 2.2% MP.
9. The lysine-to-methionine ratio for maximum milk protein yield should be between 2.80-2.95:1
10. Total unsaturated fatty acid intake should be monitored. Values greater than 500 g/d can be a risk factor coupled with quantity and quality of forage NDF. Lower quality forages and/or lower quantities of forage NDF fed increase the risk of milk fat depression.
11. CNCPSv6.1 has implemented the Dairy NRC recommendations for minerals and vitamins, as a dietary supply including bioavailability. NRC recommendations should be followed.