ABSTRACT. To study whether or not passive immunity of neonatal calves against Shiga toxin-producing Escherichia coli (STEC) O26, O111, and O157 was obtained by colostrum administration, serum antibodies in calves after the feeding were determined by enzymelinked immunosorbent assay (ELISA) in comparison with antibodies in colostrum and sera from donor dams. The highest antibody titers to STEC in colostrum from dams were detected soon after parturition. The antibody titers were found to be elevated in sera of n eonatal calves (4-9 hr after birth) orally administered with colostrum with high antibody titers, suggesting that passive immunity of neonatal calves to STEC infection may be obtained by feeding colostrum. These results suggest that colostrum administration to neonatal calves may play an important role in elevating serum antibodies against STEC in neonatal calves. KEY WORDS: calf, colostrum, STEC.J. Vet. Med. Sci. 66(2): 213-215, 2004 Shiga toxin-producing Escherichia coli (STEC) has been recognized as an etiological agent of an infectious disease in animals and humans. STEC infections are major public health threats because of serious and potentially life-threatening illnesses [10]. Shiga toxin-producing Escherichia coli (STEC) serogroup O157:H7 caused serious outbreaks of food poisoning in Japan in 1996 [6,7]. Although food poisoning caused by STEC is a serious problem, the source and route of STEC infection have not yet been fully understood in Japan. STEC has often been isolated from rectal contents of beef and dairy cattle [3,11,14]; cattle is supposed to be one of STEC reservoirs at the present time. It may be important, therefore, to reduce STEC infections in cattle for prevention of food poisoning caused by STEC. The importance of colostrum consumption by calves soon after birth in relation to disease resistance has already been reported [1,4,5]. Our preliminary study on a few calves with STEC infection also indicates that STEC could not be easily isolated from calves with high titers of serum antibodies. However, little is known about bovine passive immunity to STEC infection, although neonatal calves are susceptible to intestinal damages induced by STEC. Therefore, attempts were made to study whether or not passive immunity of neonatal calves to STEC is obtained by colostrum administration to elevate serum antibodies against STEC.Holstein calves were regularly inspected day and night to separate neonatal calves from their dams before suckling between September and October in 2000. Ten calves before suckling were allocated randomly and administered 1 L of colostrum in nipple-bottles 0 (just after birth), 4-9, 16-21, 28-33, 52-57, and 76-81 hr after birth. In all cases, the time of the first colostrum administration was designated as 0 hr. For the initial administration, colostrum was collected from one and two donor cows after parturition. After the initial colostrum administrations, the calves were moved to a hutch. After the second colostrum administration, the colostrum from three and four d...