Comparison of in vitro and in situ techniques for estimating protein degradability of selected feedstuffs

The objective of this study was to estimate the protein degradability parameters of 6 common ruminant feedstuff using the nylon bags (in situ) and the innovative in vitro method-the Daisy incubator. Significant differences were observed between the in situ and in vitro methods in estimation of the rapidly soluble (a) fraction (P<0.01), except for soybean meal. The estimation method significantly affected the potentially degradable protein (b) fraction of barley grain, corn grain, alfalfa hay, and corn silage (P<0.05). The fractional rate constant (parameter c) for the disappearance of fraction b (/h) was not affected by the degradability determination method. The estimated b fraction, parameter c, potential of degradability (PD) and effective degradability (ED) in the in vitro method were highly correlated with the estimated values by the in situ method (P<0.01). In conclusion, results showed that the in vitro Daisy method can be used for estimating some protein degradability parameters such as parameter c, PD and ED but not for others (a, b and lag time). In addition, the ability of Daisy method to estimate some parameters was better for some feeds (soybean meal, canola meal and corn grain) than for others (barley grain, alfalfa hay and corn silage).