Electrophoretic Examination of Alfalfa Silage Proteins

¹ Department of Dairy Science, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691

Effects of silage additives on proteolysis of ensiled alfalfa were studied using PAGE. First-cutting alfalfa was wilted (40% DM), chopped, and ensiled into 60 x 10-cm polyvinyl chloride silos. Treatments were control or treatment with glucose (50 g/kg DM), ammonium hydroxide (25 g/kg DM), or formic acid-formaldehyde (2:1 mixture of 90% HCOOH:37% HCOH applied at 1.83% of the DM). Samples were collected on d 0, 1, 2, 4, 7, 21, and 50 of fermentation. Samples were analyzed for N, NPN, ammonia N, pH, lactic acid, acetic acid, and soluble sugar. Also, buffer-soluble protein was characterized using PAGE. During fermentation of control silage, pH and concentrations of soluble sugar declined, and concentrations of lactic and acetic acids and NPN increased, indicating a normal fermentation. Similar shifts in concentrations of compounds occurred in treated silage but to a different extent. Proteins from alfalfa herbage and silage were characterized into molecular weight ranges based on relative mobility, and their disappearance with time of fermentation was estimated. Buffer-extractable proteins decreased rapidly with time of fermentation and essentially disappeared by d 7. Proteolysis was inhibited by formic acid-formaldehyde and ammonium hydroxide treatments but not by glucose. Formic acid-formaldehyde decreased the amount of extractable proteins by decreasing their solubility in the extraction buffer. Apparent degradation and extractability of proteins by buffer were affected by silage treatments; however, because buffer-extractable proteins represented only 36 to 40% of total plant proteins, results must be interpreted cautiously until better extraction procedures are developed.

Key Words: alfalfa silage • proteolysis • protein

Submitted on April 9, 1990
Accepted on August 27, 1990