Methods for increasing the resistance to rumen inactivation of a cultured Grampositive bacteria strain useful for gastrointestinal delivery of bioactivecompounds to ruminants, which includes the steps of growing a culture of the bacteriastrain through at least one passage in a growth medium containing an amount oflysozyme effective to induce the growth of bacterial cell walls resistant toprotozoal predation； and recovering the bacteria strain from the lysozyme-containingmedium. Rumen-bypass feed supplements produced by the inventive method arealso disclosed, as well as methods for supplementing the diet of a ruminantwith the rumen bypass feed supplements and an in vitro method for evaluating theresistance of Gram positive bacteria strains to rumen inactivation in vivo.
