Use of electrophoresis to quantify ruminal degradability of protein from concentrate feeds

Abstract

Proteins in soyabean meal, spray-dried and ring-dried blood meals, maize grain, and maize dried distillers grains were extracted before and after ruminal fermentation in vitro. Extracts were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and stain intensity of the bands was quantified by densitometry. Undegradability values (proportion of total protein) for soyabean meal, spray-dried blood meal, ring-dried blood meal, maize grain, and distillers grains were 0.40, 0.99, 0.97, 0.56, and 0.82, respectively, after 2 h of fermentation in vitro and 0.09, 0.79, 0.82, 0.49, and 0.59, respectively, after 20 h of fermentation. Soyabean meal and spray-dried blood meal contained slowly degradable, soluble proteins. Individual proteins within feedstuffs showed different degrees of degradation. The basic subunit of glycinin was degraded much slower than were other proteins in soyabean meal. Zein proteins in maize grain and distillers grains were much less degradable than were the glutelin proteins. Electrophoresis has potential as a method for measuring degradability of both particle and fluid associated proteins and to account for bacterial protein contamination.