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

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