Recent Advance in Division of Carbohydrate and Protein Fractions of Ruminant Feed and Their Metabolism in Digestive Tract

Accurate assessment of feed’s Carbohydrate (CHO) and protein nutritional values and rumen metabolism are significant for dairy production. Cornell Net Carbohydrate and Protein System (CNCPS) as an important method to evaluate feedstuff nutritional values, hasn’t been widely used in China. In order to illustrate updates of CNCPS systems deeply, the following sections were reviewed: (i) CHO and protein fractions were updated, CA was subdivided into CA1, CA2, CA3 and CA4 in CNCPS v6.1, protein was reclassified into PA1, PA2, PB1, PB2 and PC after CNCPS v6.1. Content of CHO and protein fractions vary in different feedstuff and affected by feed processing; (ii) Degradation rates (Kd) values for the new CA expanded scheme were updated to 0, 7, 5, 40-60 % h-1 respectively, Kd for PA and PB1 decreased to 200 % h-1 and 10-40 % h-1; (iii) Equations for passage rate (Kp) initially includes Kpf (Kp of forages) and Kpc (Kp of concentrates), and adjusted by effective NDF (eNDF), while in CNCPS v5.0, Kpl (Kp of liquids) equation was added and eNDF was replaced by physically effective NDF (peNDF). In CNCPS v6.1, FpBW and CpBW were integrated into Kp equations and peNDF was abandoned. (iv) The relationship and difference among Weende system of proximate analysis, Van Soest fiber analysis [35], NRC (2001) [28] and CNCPS were analyzed. The first two systems laid the foundation for NRC (2001) and CNCPS system. The latter two systems are different in CHO and protein division, also NRC (2001) developed separate Kp equations for wet and dry forages but no equation for Kpl. CNCPS developed a Kp equation that work for wet and dry forages, and Kpl equation was established. In conclusion, the division and development of CHO and protein fractions, the update of Kd and Kp equation were reviewed systematically.