Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 4/21/2005
Publication Date: 7/24/2005
Citation: Grabber, J. H., Davidson, C.L., Massingill, L.J. 2005. Non-protein nitrogen formation in legume silages as influenced by condensed tannins, polyphenols, and harvesting methods. ADSA, ASAS, CSAS Annual Meeting. July 24-28, 2005. Cincinnati, Ohio. CDROM 2005 Interpretive Summary:
Technical Abstract: The inhibition of non-protein nitrogen (NPN) formation in legume silages by protein-binding tannins and polyphenols may be influenced by the degree of tissue disruption during harvest. In 2002 and 2003, first and second cuttings of alfalfa, birdsfoot trefoil, and red clover were conventionally conditioned, wilted, and chopped or severely macerated and wilted before ensiling in minisilos. Silages were analyzed for dry matter (DM), pH, total nitrogen (N), ammonia, free amino acids, free peptides, and NPN. Silage DM averaged 34.7% and pH averaged 4.5 with no biologically relevant differences noted between forages and harvest methods. The average N content of alfalfa (3.6% of DM) was slightly greater (P < 0.05) than that of other forages (3.3% of DM). Harvesting method did not affect the N content of silages. Non-protein nitrogen in alfalfa silage (free of both tannins and polyphenols) averaged 69% of total N. The formation of NPN was similar or up to 22% lower (P < 0.05) in low to high tannin populations of birdsfoot trefoil and 37% lower (P < 0.05) in polyphenol-containing red clover. The formation of NPN in silage was also less (P < 0.05) with macerated forage (51% of total N) than with conventionally harvested forage (66% of total N). The NPN fraction of alfalfa silage was composed of 9% ammonia, 46% free amino acids, and 45% free peptides. Tannins, polyphenols, and maceration reduced levels of all NPN components, particularly the peptide fraction. The inhibition of NPN formation by maceration was greater in tannin-containing birdsfoot trefoil than in alfalfa or polyphenol-containing red clover. The results of this study indicate that tannins, polyphenols, and maceration inhibit NPN formation in legume silages, particularly if tannin-containing forages are macerated during harvest.