A net carbohydrate and protein system for evaluating cattle diets: II. Carbohydrate and protein availability

Abstract

The Cornell Net Carbohydrate and Protein System (CNCPS) has a submodel that predicts rates of feedstuff degradation in the rumen, the passage of undegraded feed to the lower gut, and the amount of ME and protein that is available to the animal. In the CNCPS, structural carbohydrate (SC) and nonstructural carbohydrate (NSC) are estimated from sequential NDF analyses of the feed. Data from the literature are used to predict fractional rates of SC and NSC degradation. Crude protein is partitioned into five fractions. Fraction A is NPN, which is trichloroacetic (TCA) acid-soluble N. Unavailable or protein bound to cell wall (Fraction C) is derived from acid detergent insoluble nitrogen (ADIP), and slowly degraded true protein (Fraction B3) is neutral detergent insoluble nitrogen (NDIP) minus Fraction C. Rapidly degraded true protein (Fraction B1) is TCA-precipitable protein from the buffer-soluble protein minus NPN. True protein with an intermediate degradation rate (Fraction B2) is the remaining N. Protein degradation rates are estimated by an in vitro procedure that uses Streptomyces griseus protease, and a curve-peeling technique is used to identify rates for each fraction. The amount of carbohydrate or N that is digested in the rumen is determined by the relative rates of degradation and passage. Ruminal passage rates are a function of DMI, particle size, bulk density, and the type of feed that is consumed (e.g., forage vs cereal grain).

In vitro protein breakdown by enzyme extracts of rumen origin: comparison with methods in situ and proteases of Streptomyces griseus

“…Mathis et al (2001), who also worked with proteases of Streptomyces griseus, obtained 76% of protein breakdown in alfalfa meal at 48 hours of incubation, similar to the 77.6% observed in this study. The rates of proteolysis (k d ) measured in this study with ruminal extracted enzymes were in ranges comparable to the results published by Sniffen et al (1992) andnRC (2001). For example, in soy bean meal we measured 6.6% H -1 with enzymatic extracts; published values of 6 and 8% H -1 and nRC (2001) reported 7.5% H -1 .…”

“…The substrates evaluated in this research were subjected to a chemical fractionation of the nitrogenous fractions according to the methodology developed by Sniffen et al (1992). The nitrogen fractions were grouped as Pool A, being buffer and TCA soluble n (nPn); Pool B 1 , buffer soluble TCA insoluble proteins; Pool B 2 , buffer insoluble but neutral detergent (nD) soluble nitrogen; Pool b 3 , nD insoluble n but soluble in acid detergent (b 3 =nDF-n -ADF-n) and Pool C, unavailable protein as insoluble in acid detergent (ADF-n).…”

Use of principal component analysis to classify forages and predict their calculated energy content

“…A way to rapidly estimate the iNDF is based on the concept that lignin represents the first factor limiting NDF digestibility and it is highly correlated to the iNDF fraction (Weiss, 1998;Ferreira and Mertens, 2005;Vieira et al, 2012). Currently, the Cornell Net Carbohydrate and Protein System (CNCPS) nutritional model uses a lignin content that is 2.4 times lignin content of NDF to calculate the iNDF (Sniffen et al, 1992;Vieira et al, 2012), whereas iNDF is not considered by Dairy NRC (2001). This simple equation was originally based on long-term (60 to 90 days) methane yield on some waste materials, and then tested on several forages by Traxler et al (1998).…”

“…Historically, the energy content of forages was estimated using empirical singlecomponent equations based on specific nutrients such as NDF, ADF or crude fibre (Mertens, 1992;Rotz et al, 1999;Ferreira and Mertens, 2005). A summative approach was adopted by dynamic nutritional models (Sniffen et al, 1992; -E-mail: francesco.masoero@unicatt.it National Research Council (NRC), 2001; Robinson et al, 2004) to estimate the net energy for lactation (NE L ) content of forage on the basis of their total digestible nutrient (TDN) values and considering the level of intake of animals (Weiss et al, 1992;Weiss, 1998). The empirical and summative approaches differ mainly in the number of parameters required to estimate NE L .…”

Substitution of crude cell wall for neutral detergent fibre in the equations of the Cornell Net Carbohydrate and Protein System that predict carbohydrate fractions: application to sunflower (Helianthus annuus L.)

“…The 'Cornell Net Carbohydrate and Protein System' (CNCPS; Fox et al, 1992;Russell et al, 1992;Sniffen et al, 1992) is a mathematical model linking feed analysis and estimates of nutrient requirements for cattle. In order to predict the supply of metabolisable energy and protein, the CNCPS uses equations to estimate digestion and passage of several feed carbohydrate and protein fractions, each of which is assumed to have a constant rate of ruminal -E-mail: rsfukush@usp.br digestion.…”