Colostrum is a complex mixture of bioactives that promotes neonate growth. Recently, we have found by in vivo study that skimmed, sterilized, and concentrated bovine late colostrum (SCBLC), obtained from a Holstein herd on days 6-7 after parturition, had an ability to maintain intestinal integrity. In the present study we investigated effects of SCBLC on rat intestinal IEC-6 cell proliferation in vitro. A fraction containing αs1-casein was found to have a robust stimulation effect as compared to other protein fractions from SCBLC and even the αs1-casein fraction from milk from other Holstein herds. Furthermore, the SCBLC αs1-casein molecule demonstrated not only slightly slower mobility on both SDS- and native-PAGE than other bovine milk αs1-caseins, but also a peculiar conformation reminiscent of moltenglobule in the circular dichroism spectrum. These findings may be of relevant to the competence of SCBLC to preserve intestinal integrity.