The IBR-IPV virus-serum neutralization test. Sensitivity and significance of the tissue culture tube test.

A modification of the IBR-IPV virus-serum neutralization test (tissue culture tube test) was used in examinations of three groups of cattle: animals at AI centres; selected herds from infected districts; and pregnant cows and heifers from all over the country. In, respectively, 141 samples out of 1335, 215 out of 344, and 46 out of 7928, a virus-neutralizing effect was demonstrated. Within the three groups of samples, respectively, 2.8 %, 29.4 %, and 28.3 % of samples positive by the modified test were negative by the conventional test, even with undiluted serum. The findings gave strong evidence that all positive reactions were results of a preceding infection. All animals with a history of infection responded serologically when examined by the modified test, but still the distribution of the titers recorded in herd examinations indicates the desirability of a further improvement in the sensitivity of the test.