Prediction of protein degradation of forages from solubility fractions.

Two experiments were conducted to determine the relationship between enzymatic digestion of forage protein and fractionation based on solubility. The first experiment used 42 forages, each replicated three times, including different species, stages of maturity, and methods of conservation. Crude protein was fractionated into six parts for each forage by sequential extraction in TCA, bicarbonate-phosphate buffer, acetone, detergent at pH 7, and detergent with acid. Multiple regression analysis, with all the solubility fractions as independent variables, resulted in prediction of CP degradation by ruminal enzyme extract at 2 and 24 h; R2 were .88 and .81, respectively. Greater solubility in the buffer and the detergent at pH 7 was associated with higher protein degradation; solubility in acetone, detergent with acid, and insolubility were associated with lower degradation. In the second experiment, eight forages each replicated twice were digested with ruminal enzyme for 0, 2, 6, and 24 h and then were extracted as described. Solubility in TCA and acetone increased during degradation, but solubility in buffer, detergent with acid, and insolubility decreased. For both experiments, buffer-soluble CP was the only uniform fraction across forages; other fractions contained proteins that degraded at diverse rates. Solubility of CP is related to degradation properties, but further research is needed to improve the accuracy of predictions based on solubility.