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Two vaccine, two respiratory (infectious bovine rhinotracheitis [IBR]), and two genital (infectious pustular vulvovaginitis [IPV]) strains of infectious bovine rhinotracheitis virus were compared by neutralization kinetics using late 19 S antibody (AB). The two vaccine strains were indistinguishable from one another, but were neutralized far more rapidly than the other four strains when either anti-IBR or anti-IPV 19 S AB was used. The two IPV strains were indistinguishable from one another, but were neutralized significantly more rapidly than the two IBR strains when anti-IBR 19 S AB was used. The 2 IBR strains were neutralized at a similar rate with the latter globulin preparation. Almost identical results were obtained with anti-IPV 19 S AB, except that one IPV strain was neutralized at a rate similar to the IBR strains. However, when early and late rabbit 7 S AB were used, IBR strains could not be distinguished from IPV strains by neutralization kinetics. Preliminary experiments indicated that both early and late 19 S rabbit antibodies neutralized the homologous strain more rapidly than the heterologous strain, but the difference was more noticeable with late 19 S AB. It was also determined that neutralization of IBR-IPV virus by specific early and late 19 S rabbit AB and early 7 S rabbit AB was markedly enhanced by guinea pig complement. Neutralization of this virus by late 7 S AB, however, was only slightly enhanced by complement. These results suggest that vaccine strains of IBR-IPV virus may be distinguished by neutralization kinetics with late 19 S rabbit AB, and that genital and respiratory strains may possibly also be distinguishable with some 19 S AB preparations.

Various parameters of plaque production by the herpesviruses, DN599, FTC1, and V11 viruses in embryonic bovine trachea cells were investigated. Optimum plaque production by these viruses occurred when freshly seeded cells were infected and covered with a protamine-supplemented agar overlay. The rate at which DN599, FTC1, and V11 viruses were neutralized by specific antiserum was exceptionally slow but relatively high antiserum titers were observed. Reciprocal virus neutralization and indirect fluorescent antibody tests suggested that DN599, FTC1, and V11 viruses were antigenically related. Neutralization tests also revealed that the latter 3 viruses were not serologically related to infectious bovine rhinotracheitis virus.