Degradability of Soybean Meal Protein Fractions as Determined by Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis

¹ Virginia Agricultural Experiment Station, Virginia Polytechnic Institute and State University, Blackburg 24061

Degradation of soy protein subfractions was determined by suspending dacron bags containing soybean meal into the rumen from 0 to 72 h. Rumen-cannulated lactating Holstein cows consuming a diet of corn silage, alfalfa haylage, soybean meal, and high moisture shelled corn were used. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to monitor the rates of degradation in the rumen of protein subfractions. Fractional changes with time in the rumen were quantified using densitometric analysis of Coomassie blue stained protein bands. The ß-conglycinin was more susceptible to rumen degradation than glycinin subunits. Acidic subunits (B₁) of glycinin were degraded faster (.144 h^–1) than were basic (B₂) subfractions (.104 h^–1). Estimates of B subfractional components and rates of degradation were used to predict degradability of soybean meal protein (73.8%). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and densitometric techniques can be used for measuring subfractional degradability in the rumen.

Key Words: electrophoresis • degradation rate • protein degradability

Submitted on October 10, 1989
Accepted on February 14, 1990