Foot-and-mouth disease vaccination: a multifactorial study of the influence of antigen dose and potentially competitive immunogens on the response of cattle of different ages

Groups of 68 and 66 cattle aged 12 and 24 months respectively were each subdivided into 16 groups and inoculated with foot-and-mouth disease vaccines containing O1Campos, A24Cruzeiro and C3Pando virus strains. The 140S antigen mass of the O1and A24valencies was varied while that of C3was held constant. Multifactorial comparisons between the 21 day serum neutralising antibody titres showed that over most of the range there was a linear log dose response relationship. Doubling the antigen dose increased the serum antibody litres against both A24Cruzeiro and O1Campos by approximately 0·15 log10. The A24antigen was about 30 times more immunogenic than the O1with C3intermediate between the two. At high antigen doses the responses flattened but the level at which this occurred depended on the immunogen administered. No difference could be demonstrated between the responses of 12- and 24-month-old cattle and there was no evidence of competitive inhibition or enhancement between the virus strains included in the vaccines.