Using the NRC-2001 model and the DVE/OEB system to evaluate nutritive values of Harrington (malting-type) and Valier (feed-type) barley for ruminants

The objectives of this study were to compare chemical characterization, rumen digestive behavior of each feed component, and potential nutrient supply to ruminant animals between malting-type barley (cv. Harrington) and feed-type barley (cv. Valier), which were affected by coarse (Roller miller, 0.533 mm gap) and fine (Hammer mill, 2 mm screen) processing. Results showed that Valier barley was lower (P<0.05) in non-structural carbohydrates (NSC: 502 g/kg DM versus 602 g/kg DM), non-protein N (NPN: 354 g/kg DM versus 415 g/kg DM), and acid detergent insoluble crude protein (ADICP: 20 g/kg CP versus 38 g/kg CP), higher in starch (883 g/kg NSC versus 744 g/kg NSC) and lignin (81 g/kg DM versus 45 g/kg DM) than Harrington barley. True protein fractions (PB1, PB2, PB3) partitioned by the Cornell Net Carbohydrate Protein System (CNCPS) system were similar between two barley varieties, but carbohydrate (CHO) fractions were markedly different. Valier barley had lower rapidly degradable CHO (CA: 86 g/kg CHO versus 188 g/kg CHO), higher intermediately degradable CHO (CB1: 652 g/kg CHO versus 548 g/kg CHO) and unavailable CHO (CC: 60 g/kg CHO versus 34 g/kg CHO). The energy value estimated using a summative approach were similar between two varieties with average TDN1× values of 814 g/kg DM and of DE3×, ME3× and NEL3×, 13.72, 11.99 and 7.64 MJ/kg DM, respectively. The in sacco rumen degradation results showed that using the coarse processing, Valier barley was lower (P<0.05) in effective degradability of DM (EDDM: 472 g/kg versus 631 g/kg) and CP (EDCP: 459 g/kg versus 617 g/kg), but not different (P>0.05) in effective degradability of starch (EDST: average 619 g/kg). However, using the fine processing, the significant differences on rumen degradation characteristics completely disappeared between two barley varieties except of degradation rate of CP. Using the DVE/OEB system to predict the potential nutrient supply found that using the coarse processing, Valier barley had significantly lower (P<0.05) in truly absorbed microbial protein (AMCP: 35 g/kg DM versus 53 g/kg DM), but higher (P<0.05) in truly absorbed rumen undegraded feed protein (ARUP: 69 g/kg DM versus 47 g/kg DM) and endogenous protein (ENDP: 25 g/kg DM versus 15 g/kg DM) in the small intestine. However, total truly digested protein value (DVE) in the small intestine between two varieties was not significantly different (average: 83 g/kg DM). Prediction results by the (National Research Council, Washington, DC, National Academy Press, 2001) model showed that using the coarse processing, Valier barley had significantly lower (P<0.05) in AMCP (34 g/kg DM versus 44 g/kg DM), but higher (P<0.05) in ARUP and similar in rumen endogenous protein (ECP: average 11 g/kg DM), which resulting in a higher (P<0.05) total metabolizable protein value (107 g/kg DM versus 95 g/kg DM) in Valier barley. Again when using the fine processing, all the predicted different effects disappeared. In conclusion, Valier barley had different chemical and nutritional characterization compared with Harrington barley. However, the nutritional characterization (in terms of rumen digestive behaviors and potential nutrient supply) was highly associated with the processing methods.