Availability of Nitrogen in Different Protein Sources, Particularly as regards Fish viscera Silage for in Vitro Digestibility of Starch and Cellulose

Abstract

The availability of nitrogen from different nitrogen sources for rumen microbial growth was evaluated with in vitro technique. Starch was digested to about the same extent when the nitrogen source was urea or L-amino acid mixture. The L-amino acid mixture was assumed to be 100% available, and relative to that the availability of nitrogen in fish viscera silage was 74.3%, in different peptides from fish viscera silage from 74.0 to 92.1%, in extracted soybean meal 52.5% and in herring meal 39.2%. The cellulose digestibility was low with urea as the sole nitrogen source. The digestibility increased slightly with L-amino acid nitrogen. Peptides with mol.wt. < 500 increased the cellulose digestibility markedly and was further increased with increasing chain length of the peptides. The highest cellulose digestibility was observed with peptides > 10000 in mol.wt. and proteins from extracted soybean meal. This indicateds that cellulolytic microbes need a supply of long chain peptides for optimal growth.

Key Words:

• Microbial growth
• peptides
• amino acids
• urea