Potential of solubility, enzymatic methods and NIRS to predict in situ rumen escape protein

The percentage of feed protein escaping rumen degradation was measured by the in situ method ( for 29 compound feeds, untreated and formaldehyde-treated soybean meal and 12 forages: 3 grass silages, 2 maize silages, fresh grass, grass hay, fodder beets, fresh potatoes, ensiled beet pulp, chopped ear corn silage and brewers' grains. The loss of particles through the bag pores was determined as the difference between the washable fraction (W) and the fraction, soluble in borate-phosphate buffer at pH 6.7 (S). W-S was most pronounced for compound feeds (on average 14.4units), for brewers' grains and maize silages. A correction of assuming that W-S degrades like the potentially degradable fraction, appeared however not appropriate. Solubility in borate-phosphate buffer after 1 h, enzymatic degradability by protease from Streptomyces griseus or ficin after 1, 6 and 24 h and NIRS (for compound feeds alone) were examined as routine method to predict With the buffer and with S. griseus the effect of pH (6.7 vs. 8.0) and at pH 8.0 the effect of the amount of substrate (500 mg sample vs. 20 mg nitrogen (N)) was tested. With ficin, 500 mg samples were incubated at pH 6.7. Predictions were better when compound feeds and forages were considered separately. However, the best in vitro method was different for the two feed categories, being solubility in buffer for the compound feeds and enzymatic degradation of a constant amount of protein with S, griseus at pH 8.0 for forages. NIRS showed potential to predict %EPsitu of compound feeds, but needs more reference samples. The Dutch feed tables appeared more accurate than the best in vitro method for compound feeds, but seemed too rough for some forages like fodder beets, maize silage and ear corn silage.