Differential ruminal degradation of alfalfa proteins

Alfalfa (Medicago sativa L.) has high crude protein that is rapidly and extensively degraded in the rumen. Our objective was to develop a protocol where individual proteins could be characterized for their ruminal degradation. Proteins from individual genotypes of three alfalfa cultivars were characterized using fluorescence 2D difference gel electrophoresis combined with MALDI-TOF mass spectrometry for protein identification. Twenty-six proteins were characterized, representing between 33 and 41% of the total protein among genotypes. Variation for protein degradation was observed among proteins after 45 and 120 min of incubation in the rumen of a Holstein steer (P < 0.001). After 45 min of ruminal incubation, nine proteins averaged 75% or more remaining, 12 had 50% or less remaining, and five were intermediate. After 120 min of ruminal incubation, four proteins averaged greater than 80%, seven between 80 and 50%, and 15 less than 50% remaining. Although all proteins were degraded over time, the rate and ...