Phenolics, fibre and fibre digestibility in the crop residue from bird resistant and non-bird resistant sorghum varieties

The relationship between phenolics and parameters of in‐vitro digestibility of neutral‐detergent fibre (NDF) in leaves and stems from the crop residue of bird resistant (BR) and non‐bird resistant (NBR) sorghum varieties was determined. The phenolics studied were lignin, insoluble proanthocyanidins, soluble red pigments and soluble phenolics as measured by absorbance (280 nm)and precipitation with ytterbium. Parameters of the digestibility of NDF studied were 48‐h digestibility, potentially digestible NDF, rate of digestion and indigestible NDF as determined by non‐linear regression analysis. Leaves from BR varieties were higher in most phenolics than leaves from NBR varieties. Digestibility of NDF at 48 h, potentially digestible NDF and rate of NDF digestion was lower in leaves from BR varieties. The indigestible NDF was higher in BR varieties. Phenolics in leaves were negatively correlated with digestibility of NDF at 48 h, potentially digestible NDF and rate of NDF digestion and positively correlated with indigestible NDF. Phenolics in stems had non‐significant correlations with parameters of the digestibility of NDF except for a positive correlation between lignin and indigestible NDF. These results indicate that breeding for bird resistance in sorghum would lead to lower nutritive value of the crop residue.