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 (%EPsitu) for 29 compound feeds, untreated and formaldehyde-treated soybean meal and 12 forages: 3 grass silages, 2 m aize silages, fresh grass, grass hay, fodder beets, fresh potatoes, en siled beet pulp, chopped ear corn silage and brewers' grains. The loss of particles through the bag pores was determined as the difference b etween the washable fraction (W) and the fraction, soluble in borate-p hosphate buffer at pH 6.7 (S). W-S was most pronounced for compound fe eds (on average 14.4%-units), for brewers' grains and maize silages. A correction of %EPsitu, assuming that W-S degrades like the potentiall y degradable fraction, appeared however not appropriate. Solubility in borate-phosphate buffer after 1 h, enzymatic degradability by proteas e from Streptomyces griseus or ficin after 1, 6 and 24 h and NIRS (for compound feeds alone) were examined as routine method to predict %EPs itu. 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 v s. 20 mg nitrogen (N)) was tested. With ficin, 500 mg samples were inc ubated at pH 6.7. Predictions were better when compound feeds and fora ges 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 p rotein 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 me thod for compound feeds, but seemed too rough for some forages like fo dder beets, maize silage and ear corn silage.