The protective effect of egg yolk and colostrum powders prepared from hens and cows vaccinated with inactivated bovine coronavirus (BCV) antigen was evaluated in a challenge model with a virulent BCV strain. Twenty three calves from BCV-free herds were randomly divided into control and several treatment groups. All calves were orally challenged with 1 x 10(9) TCID50 of the virulent Kakegawa strain of BCV at 24 to 36 h after birth. Calves in treatment groups received either egg yolk powder or cow colostrum containing BCV specific antibodies. Daily treatment with these antibody preparations started 6 h until 7 days post-challenge. Control calves which received no antibody had severe diarrhea and all died within 6 days after infection. In contrast, calves fed milk containing egg yolk or colostrum with neutralization titers of 1:2560 or 1:10,240 respectively all survived and had positive weight gain unlike the other treatment groups. These results indicate that the orally administered egg yolk and colostrum powders protected against BCV-induced diarrhea in neonatal calves and that the egg yolk used provided a higher degree of protection compared to colostrum powder on a titer basis. Treatment with whole egg yolk from immunized hens therefore provides a more efficacious alternative to the existing methods of specific passive protection against BCV.