The influence of formic acid and formaldehyde additives and type of harvesting machine on the utilization of nitrogen in lucerne silages: 2. Changes in amino-acid composition during ensiling and their influence on nutritive value

Abstract

SummaryLucerne was made into ten silages using either a flail or a precision-chop harvester with application of formaldehyde or a range of rates of formic acid during harvesting. Amino-acid analyses were done on the silages and on samples taken from the herbage at ensiling.In excess of 70% of aspartic acid, serine, glutamic acid, tyrosine, threonine, lysine, histidine and arginine were destroyed in untreated silages when a flail harvester was used and in excess of 50% when a precision-chop harvester was used. Glycine, leucine, iso-leucine, valine and methionine showed little change, with net losses or increases of up to 10%, whilst proline, cystine + cysteine and phenylalanine were intermediate between these two categories. Net synthesis of alanine and α and γ amino-butyric acids occurred in the untreated silages. Increasing rates of formic acid addition, and the use of the precision-chop harvester, reduced the loss of the amino acids which were extensively degraded in the untreated silages and minimized the increases in alanine and α and γ amino-butyric acids. Formaldehyde treatment also reduced amino-acid degradation, apart from apparently high losses of lysine, histidine and tyrosine. It was concluded, however, that these losses arose through problems of estimation in formaldehyde-treated silages following HCl hydrolysis.It is suggested that the most probable precursors for alanine and α and γ aminobutyric acids were respectively aspartic acid, threonine and glutamic acid. Voluntary intake and the utilization of silage nitrogen by young sheep were related to the net changes in amino acids involved in decarboxylation reactions, the best measures of this being the interconversions involving the formation of alanine and α and γ aminobutyric acids. Deamination reactions appeared to be of much less importance in limiting silage nutritive value than those involving decarboxylation.