PREDICTION OF PROTEIN-DEGRADATION OF FORAGES FROM SOLUBILITY FRACTIONS

Two experiments were conducted to determine the relationship between e nzymatic digestion of forage protein and fractionation based on solubi lity. The first experiment used 42 forages, each replicated three time s, including different species, stages of maturity, and methods of con servation. Crude protein was fractionated into six parts for each fora ge by sequential extraction in TCA, bicarbonate-phosphate buffer, acet one, detergent at pH 7, and detergent with acid. Multiple regression a nalysis, with all the solubility fractions as independent variables, r esulted in prediction of CP degradation by ruminal enzyme extract at 2 and 24 h; R(2) were .88 and .81, respectively. Greater solubility in the buffer and the detergent at pH 7 was associated with higher protei n degradation; solubility in acetone, detergent with acid, and insolub ility were associated with lower degradation. In the second experiment , eight forages each replicated twice were digested with ruminal enzym e for 0, 2, 6, and 24 h and then were extracted as described. Solubili ty in TCA and acetone increased during degradation, but solubility in buffer, detergent with acid, and insolubility decreased. For both expe riments, buffer-soluble CP was the only uniform fraction across forage s; other fractions contained proteins that degraded at diverse rates. Solubility of CP is related to degradation properties, but further res earch is needed to improve the accuracy of predictions based on solubi lity.