Characterization of protein fractions and amino acids in ensiled alfalfa treated with different chemical additives

Formic acid, formaldehyde, tannic acid or mixtures of two were studied on their effects on ensiled alfalfa (Medicago sativa L.) amino acids and N fractions by the Cornell Net Carbohydrate and Protein System (CNCPS). The alfalfa forage was a second cut and was wilted to a mean over-dry dry matter (DM) content of 330 g/kg. All silages were prepared as mini-silos using 100 ml polypropylene centrifuge tubes (50 g) on a small laboratory-scale, with the additives added in 20 ml aliquots/kg herbage fresh weight (FW). After 35 d of ensiling, most of forage true protein was converted to fraction A and all of the added additives reduced fraction A content in the ensiled forages (P<0.05). The content of fraction B1 in all of the additive-treated silages was higher (P<0.05) than that in control silage. Large proportions of true protein in the tannic acid/formaldehyde- and formic acid/formaldehyde-treated silages were fractions B2 and B3, respectively. No difference was observed on fraction C content between the control silage and silages treated with additives except for the formaldehyde or tannic acid-treated silages. Amino acids were well preserved in additive-treated silages compared with the control silage. Concentration of total amino acid was higher in formic acid-treated silages than that in the control and the other additive-treated silages (P<0.05). The pattern of changes in individual amino acid in all of the silages indicated that branched chain amino acids and methionine were relatively well preserved during fermentation but the basic and acidic amino acids were not.