Rinderpest immunity in calves

Rinderpest immunity in calves was investigated by a study of neutralizing antibodies.

In young calves aged from 1 day to 2 months, the progeny of rinderpest susceptible dams, the serological response to viable lapinised rinderpest virus, as measured by the serum titres 21 days after inoculation, did not differ from those of adult susceptible cattle.

Maternally- derived rinderpest antibodies were found to be transferred from the Cam to the calf via the colostrum, No antibodies were detected in the sera of calves before suckling. The colostra of immune dams contained rinderpest antibodies to a higher titre than that of the dams' sera; 30-40 hours after the ingestion of such colostra, newborn calves possessed high antibody levels in their sera, levels greater than those of their dams' sera, approaching but less than those of the colostra ingested. Thereafter the antibody levels in the calves' sera declined linearly. The mean half -life of maternally derived rinderpest antibody in calves was 36.7 days and the extinction point 10.9 months (the extinction point was the thane calculated for, the titre to fall to 100.0, 1 month being equal to 30 days).

Two young calves, from susceptible dams, which each . ingested daily for 5 weeks 1 gallon of milk containing rinderpest antibodies failed to show evidence of their absorption from the intestinal tract.

In calves which were the progeny of rinderpest-immune dams the serological response to viable caprinized rinderpest virus depended upon the level of maternally-derived passive immunity at the time of inoculation. All calves aged & months or more at the time of inoculation produced antibodies, whereas no calves aged 3 months or less do so. Some calves aged between 4 and 7 months were, and others were not, actively immunized. Two critical levels of maternally-derived antibodies occurred, one below which all calves produced antibodies and another above which no calf produced antibodies. The response in calves with preinoculation titres between these two levels varied. There was a significant relationship between the level of maternally - derived antibody at the ti :e of inoculation of vaccine and the amount of antibody produced during the following 3 weeks, the greater the preinoculation titre the smaller the amount of antibody produced. Similarly there was also a significant relationship between the preinoculation titre and the 1 year post -inoculation titre. Also, where calves possessed a high level of antibody before inoculation, but were actively immunized, antibody was produced at a slower rate than in those calves possessing little or no maternally- derived antibody.

The development of an active immunity to rinderpest by those calves possessing maternally-derived antibody was not necessarily associated with a clinical reaction. When passively immune calves failed to produce antibodies following caprinized rinderpest virus inoculation, sensitization of the antibody-forming mechanism did not occur as was demonstrated by failure to show an anamnestic response following later exposure to rinderpest antigen.