Effect of genotype on the morphological characteristics, chemical composition and feeding value of nine barley straws, and responses to soya-bean meal supplementation

Abstract

Three experiments were conducted to investigate the effect of genotype on the morphological characteristics, chemical composition and feeding value of nine chopped barley straws, and responses of the feeding value to a supplement of soya-bean meal (SBM). In experiment 1, the straws were offered ad libitum to 12 wethers and measurements were made of straw intake and dry (DMD) and organic (OMD) matter digestibility using a balanced lattice design with three periods. Experiment 2 used the same experimental design but the straws were offered ad libitum with 200 g SBM. Experiment 3 measured the dry matter losses (DML) of ground straws from nylon bags placed in the rumen of three wethers. The extent (b) and rate (c) of DML were estimated using the equation DML = a + b(l – ect).

There were significant differences in the stem height (P < 0·001), leaf proportion (P < 0·001), and protein (P < 0·001) and modified acid detergent fibre (P < 0·01) concentrations between the straws. Significant (P < 0·05) effects of genotype on intake were seen but the variation in intake between them decreased when the protein supplement was added. Effects of genotype on DMD (P < 0·05) and OMD (P < 0·05) were seen in unsupplemented straws and differences of OMD (P < 0·05) were still apparent when SBM was given with straw. Although there were significant (P < 0·05) differences in DML after 48 h incubation, the constants b and c were similar (P > 0·05) across the genotypes. Protein concentration in the straw, although closely correlated with intake, appears to have less value as a predictor of feeding value than previously thought.