Abstract

Digestion kinetics were measured for mature (green and non-senescent) components of five grass species using in sacco and in vitro incubations to define rates of degradation and nutrient release. The data will be incorporated into a dairy nutrition simulation model to identify limitations in nutrient supply to cows grazing mature pasture in late spring. Perennial ryegrass, tall fescue, Yorkshire fog, phalaris and paspalum were hand separated into leaf, stem and inflorescence for incubations. Percentages of fibre (NDF) in DM fractions ranged from 50-69% (leaf), 63-75% (stem) and 50-68% (inflorescence). Crude protein concentrations in the DM of the respective fractions were 7.5-23.7%, 3.8-8.3% and 7.9-12.3%. Soluble DM (% of the total) determined after mincing accounted for 31-53% of leaf, 26-55% of stem and 20-48% of inflorescence, and fractional (h-1) degradation of the insoluble DM was very slow, ranging from 0.034-0.113 (leaf), 0.025-0.036 (stem) and 0.033-0.072 (inflorescence). After 24 hours of in vitro incubation plant nitrogen content become limiting for fermentation in most instances.

AV, Chaves, GC Waghorn, IM Brookes, and JL Burke

Proceedings of the New Zealand Society of Animal Production, Volume 61, Christchurch, 8-12, 2001