The present invention relates to a method for identifying a pepsin resistant alpha amylase enzyme for use in a feed supplement comprising: i) providing an alpha amylase enzyme； ii) admixing said alpha amylase with corn based feed and buffer solution comprising a pepsin concentration of 9000 U/ml at pH 3, 40° C., 500 rpm for at least 120 minutes and analysing alpha amylase activity on said alpha amylase compared to a control sample； wherein said control sample differs in that no pepsin is present during incubation； and iii) selecting an alpha amylase enzyme which substantially maintains alpha amylase activity under the assay conditions； feed supplements and feedstuffs comprising a pepsin resistant alpha amylase and the use of pepsin resistant alpha amylases in feed.
