Changes in total and individual proteins during drying, ensiling, and ruminal fermentation of forages

Effects of wilting, drying, and ensiling on concentrations of proteins in alfalfa, crown vetch, perennial ryegrass, orchardgrass, and tall fescue were studied using SDS-PAGE. Seven to nine proteins were identified in the samples. Wilting forages for 24 h on a laboratory bench had little effect on the relative amounts of proteins. Drying forage (on a laboratory bench) for 5 d resulted in a 25 to 30% loss in electrophoretically identified proteins. A 45-kDa protein was more susceptible to hydrolysis during drying than were most other proteins. After ensiling, < 10% of the proteins in fresh alfalfa and fescue remained, but crown vetch silage contained 46% of its original proteins. A 54-kDa protein was extremely susceptible to hydrolysis during ensiling, but a 30-kDa protein was relatively resistant. Fresh forage and hay samples were incubated in vitro for 5 h to determine degradation of proteins. In general, the 54-kDa protein was most susceptible, and the 30-kDa protein was least susceptible, to ruminal hydrolysis. Certain proteins in hay were more degradable than those in fresh forage. Among fresh forages, alfalfa and fescue contained the lowest concentrations of undegradable proteins. Differences among forage species were considerably less for hay samples.