EFFECT OF HULL AND PROTEIN CONTENTS OF BARLEY ON PROTEIN AND ENERGY DIGESTIBILITY AND FEEDING VALUE FOR PIGS

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Abstract
Sixteen simulated barleys, containing combinations of 7.27, 11.27, 15.17 and 19.27 crude protein (CP) (air-dry basis) and 0, 10, 20 and 30% hulls, were made from barley (Hordeum vulgare L. 'Bonanza') that was finely ground and air-classified into hulls, starch, protein and fines fractions. These barleys were supplemented with vitamins and minerals and fed in four replicates to 16 pigs, of 20 kg initial weight, in a digestibility trial. Energy digestibility was highly correlated with percent hulls and percent crude fiber (r = − 0.9 for both factors; P < 0.01). Digestible energy prediction values were developed whereby barley with 0% hulls was 84% digestible and had 15.73 kJ DE/g dry matter; barley with 30% hulls was 64% digestible and contained 12.01 kJ DE/g. The gross energy of hulls was 17.5% digestible and contained 2.94 kJ/g. Apparent digestibility of protein decreased (P < 0.05) from 75.0 to 72.0% as hulls increased from 0 to 30% and from 82.2 to 62.5% as dietary CP increased from 21.9 to 8.0% (dry matter basis). Metabolic fecal protein (N × 6.25) increased from 1.49 to 2.79 g/100 g dietary dry matter as hulls increased from 0 to 30%. Apparent digestibility of hull protein, when fed in 16% CP diets, was 44% and the corresponding value for nonhull barley protein was about 75%. A tentative monetary evaluation of barleys varying in CP and hull or crude fiber contents relative to prices of a reference barley and soybean meal was presented. Key words: Barley, hulls, protein, digestibility, feeding value, pigs