Selecting for nutritive value in Digitaria milanjiana. 2. Intake and digestibility of divergently selected full-sibs compared with Digitaria decumbens

Abstract

We compare the voluntary intake and digestibility of 6 genotypes selected from 3 F1 families of Digitaria milanjiana for high or low leaf digestibility, and D. decumbens (pangola grass). Swards were harvested on 6 occasions (4 by 4-week regrowths, 1 by 10-week and 1 by 14-week regrowth) and fed to sheep in metabolism cages. Averaged over families and regrowths, high digestibility selections were significantly superior to low digestibility selections in digestibility, voluntary dry matter intake and intake of metabolisable energy. There was a large range in leafiness of the genotypes. Correlations between leafiness and in vivo digestibility, dry matter (DM) intake and intake of metabolisable energy were positive and statistically significant. Comparison of full-sibs at the same percentage stem (80 and 100%) suggested a higher DM intake, digestibility and intake of metabolisable energy of stem from genotypes selected for high leaf digestibility. Averaged over harvests, none of the selected genotypes was significantly superior to pangola grass in digestibility but all were superior in DM intake and 5 in intake of metabolisable energy. The best selected genotype was 35% better than pangola grass in terms of intake of metabolisable energy. Differences in in vitro digestibility of young leaves from vegetative tillers of full sibs, the characteristic on which the genotypes had been selected, were maintained under sward conditions, although differences were reduced.