Abstract
The aim of this study was to reveal an interactive curve-linear relationship between altered carbohydrate macromolecular structure traits of hulless barley cultivars and nutrient utilization, biodegradation, as well as bioavailability. The cultivars had different carbohydrate macromolecular traits, including amylose (A), amylopectin (AP), and β-glucan contents, as well as their ratios (A:AP). The parameters assessed included: (1) chemical and nutrient profiles; (2) protein and carbohydrate sub-fractions partitioned by the Cornell Net Carbohydrate and Protein System (CNCPS); (3) total digestible nutrients (TDN) and energy values; and (4) in situ rumen degradation kinetics of nutrients and truly absorbed nutrient supply. The hulless barley samples were analyzed for starch (ST), crude protein (CP), total soluble crude protein (SCP), etc. The in situ incubation technique was performed to evaluate the degradation kinetics of the nutrients, as well as the effective degradability (ED) and bypass nutrient (B). Results showed that the carbohydrates (g/kg DM) had a cubic relationship (p < 0.05), with the A:AP ratio and β-glucan level; while the starch level presented a quadratic relationship (p < 0.05), with the A:AP ratio and cubic relationship (p < 0.05), with β-glucan level. The CP and SCP contents had a cubic relationship (p < 0.05) with the A:AP ratio and β-glucan level. The altered carbohydrate macromolecular traits were observed to have strongly curve-linear correlations with protein and carbohydrate fractions partitioned by CNCPS. For the in situ protein degradation kinetics, there was a quadratic effect of A:AP ratio on the rumen undegraded protein (RUP, g/kg DM) and a linear effect of β-glucan on the bypass protein (BCP, g/kg DM). The A:AP ratio and β-glucan levels had quadratic effects (p < 0.05) on BCP and EDCP. For ST degradation kinetics, the ST degradation rate (K(d)), BST and EDST showed cubic effects (p < 0.05) with A:AP ratio. The β-glucan level showed a cubic effect on EDST (g/kg DM) and a quadratic effect on BST (g/kg ST or g/kg DM) and EDST (g/kg DM). In conclusion, alteration of carbohydrate macromolecular traits in hulless barley significantly impacted nutrient utilization, metabolic characteristics, biodegradation, and bioavailability. Altered carbohydrate macromolecular traits curve-linearly affected the nutrient profiles, protein and carbohydrate fractions, total digestible nutrient, energy values, and in situ degradation kinetics.