PROTEIN SOLUBILITY AND DEGRADATION INVITRO AS INFLUENCED BY BUFFER AND MATURITY OF ALFALFA

Factors influencing the extraction of proteins and protein degradation of alfalfa (Medicago sativa L.) in vitro were compared with other forages. Kansas State buffer, a phosphate buffer, and McDougall's artificial saliva, a carbonate buffer, (both commonly used as in vitro digestion buffers) extracted more buffer-soluble proteins than did N-2-Hydroxyethylpiperazine-N'-ethanesulfonic acid, 2[N-Morpholino] ethanesulfonic acid, piperazine-N, N'-bis [2-ethane-sulfonic acid], and imidazole-HCl. Protein solubilities and sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated that Kansas State buffer and McDougall's artificial saliva extracted more high molecular weight proteins than did the other buffers. Proteins soluble in Kansas State buffer were extensively degraded by ruminal microorganisms within t2 h in both stem and leaf tissues; several high molecular weight proteins in leaf tissues did, however, survive 12 h in rumen fluid. Alfalfa initially contained more buffer-soluble protein than other forages, but, similar amounts of undegraded protein remained in all forages after 12 h of digestion. Protein profiles (SDS-PAGE) of birdsfoot trefoil (Lotus corniculatus L.) contained two distinct bands of protein that were apparently unaffected by 12 h of incubation, while alfalfa profiles contained several polypeptides that 'escaped' ruminal fermentation. In contrast, proteins in orchardgrass (Dactylis glomerata L.) were rapidly and completely degraded in 12 h with no identifiable surviving proteins. Identification and characterization of proteins capable of surviving ruminal degradation and factors influencing their accumulation in forages may allow for introduction of forages or management practices which could potentially improve the nitrogen status of the ruminant.