Methods and kits for measuring protease activity in feed

A method for detecting protease activity in a feed sample, the method comprising:

• (a) mixing the feed sample with a buffer comprising phosphate and about 0.01% to about 10% sodium dodecyl sulfate (SDS) to form a feed extract;
• (b) contacting an aliquot of the feed extract with a protease substrate to form a reaction mixture, wherein the protease substrate comprises a polypeptide attached to a chromophore;
• (c) incubating the reaction mixture under conditions such that proteolytic cleavage of the protease substrate leads to a color change in the reaction mixture;
• and
• (d) monitoring the color change in the reaction mixture, thereby detecting protease activity in the feed sample.