Artificial Rumen Investigations. I. Variability of Dry Matter and Cellulose Digestibility and Production of Volatile Fatty Acids,

Abstract

In vitro digestion of feedstuffs was carried out with diluted rumen liquor in glass bottles for 48 hr. Substrates used in the study were forages and a few mixed feeds. Most information was gathered on 39 samples of tall fescus (Festuca arundinacea), representing 2 to 4 cuttings (pasture height) per year of 4 genotypes over a 4-yr. period. Within-trial variation of dry matter digestibility for all substrates digested was generally small. Cellulose digestibility showed a slightly higher within-trial variability, but this was no greater than those given in the literature for other in vitro procedures. Variability in digestibility between trials, estimated by including a standard alfalfa in every trial, indicated differences in the digesting capacity of rumen liquor collected from the same steer on different days. Oven-dry samples proved more suitable than fresh-frozen samples of tall fescue, based on between-trial variability. Molar percentages of acetic, propionic, butyric, and valeric acids were comparable with those reported in other studies on in vitro digestion of forages. Inoculum used influenced molar percentages of acids produced from the standard alfalfa. Frozen and oven-dried tall fescue samples produced essentially the same molar percentages and total amounts of volatile fatty acids.