Ten colostrum-deprived calves were assigned to 1 of 2 treatment groups (5 calves/group), and fed colostrum that had either low (naturally infected cows) or high (immunized cows) antibody titers to bovine coronavirus (BCV). All calves were inoculated orally and intranasally with virulent BCV when they were 24 to 48 hours old and challenge exposed 21 days later. Blood, feces, nasal secretions, tears, saliva, and bronchoalveolar lavage (BAL) fluids were collected weekly from each calf for 5 weeks after inoculation. The titers to whole BCV or the relative amounts of isotype-specific antibodies to BCV structural proteins were evaluated in these samples by ELISA or immunoblotting, respectively. Both pools of colostrum contained primarily IgG1, IgG2, and IgA antibodies to the E2 and E3 BCV proteins. Calves fed the high-titer colostrum had correspondingly higher amounts of passive IgG1 and IgA antibodies to whole BCV and to the E2 and E3 BCV proteins in serum, feces, and BAL fluid at postinoculation week 1 than those calves fed low-titer colostrum. Active IgG1, IgA and IgM antibody responses in serum and active IgA and IgM antibody responses in most mucosal secretions to whole BCV and to the E2 and E3 proteins were lower or delayed in calves fed high-titer colostrum, compared with responses in calves fed low-titer colostrum. In contrast, increased responses to the BCV N protein were observed in all samples (except in serum and BAL fluid) in the calves fed high-titer colostrum, compared with calves fed low-titer colostrum. Upon challenge exposure, responses to E2 and E3 BCV proteins in serum and BAL fluid were lower in the group fed high-titer colostrum, compared with those in the group fed low-titer colostrum. Our findings indicate that the level of passive immunity in calves at the time of BCV inoculation can influence the development of active antibody responses in serum, feces, and mucosal secretions to whole BCV and to some BCV proteins individually.

Immunoglobulin values were determined in fetal and kitten sera. In the fetal and precolostral kitten sera, only IgG was detected, except in 1 case in which IgM was detected. The IgG, IgA, and IgM were transferred to the kittens through colostrum ingestion with some selectivity. Concentration of the transferred IgG, IgA, and IgM decreased significantly with half-lives of 4.15 +/- 1.29 days, 2.03 +/- 0.33 days, and 2.2 +/- 1.2 days, respectively. As a result of this decrease and increase of de novo immunoglobulin synthesis, IgG, IgA, and IgM were at their lowest values when kittens were 20 to 25 days, 14 to 20 days, and 8 to 10 days old, respectively. After their nadir was reached, IgG values increased gradually, IgA slowly, and IgM rapidly, as a result of de novo immunoglobulin synthesis. When the kittens were 90 days old, their immunoglobulin values were 80% (IgG), 7% (IgA), and 100% (IgM), compared with those of adult cats. These findings suggest that kittens that receive inadequate colostrum from their mothers will be particularly susceptible to infection after they are 5 weeks old.

Blood, feces, nasal secretions, and tears werecollected weekly from 5 randomly selected 1- to 8-week-old calves in a large commercial dairy herd. Clinical signs and bovine coronavirus (BCV) shedding from the respiratory and enteric tracts of calves were monitored through the 8-week period by direct immunofluorescence of nasal epithelial cells, protein A-gold immunoelectron microscopy on feces, and ELISA on nasal secretions and feces. All samples were analyzed for antibody isotypes to BCV structural proteins by immunoblotting. All calves had BCV respiratory tract infections and 4 of 5 calves shed virus in feces. Several calves had multiple or prolonged periods of BCV respiratory tract or enteric tract shedding or both. All calves (except 1) had passive IgG1 antibodies to some BCV proteins (mainly the E2 and E3 proteins) in their serum when they were 1 week old. The presence of these passive serum antibodies (mainly to the E2 and E3 BCV proteins) was associated with decreased or delayed systemic and mucosal antibody responses in calves, in particular IgA responses in nasal secretions and tears to the E2 and E3 BCV proteins, but not to the N protein. Moderate amounts of maternal BCV E2- and E3-specific antibodies in serum did not prevent BCV enteric tract or respiratory tract infections in calves, but may have delayed the development of active antibody responses to these BCV proteins. However, calves with BCV respiratory tract or enteric tract infections had no detectable passive antibodies to any BCV proteins in nasal secretions or feces.