[Field trials of a number of IBR vaccines in dairy cattle]

Vaccination of ninety-six cows which showed titres of less than or equal to 1:2 on inoculation, using vaccines containing attenuated live IBR virus (Tracherine, Resbo. IBR PI3, Respacine 3) elicited a moderate serological response. Inoculation of these vaccines in 192 cows showing titres of greater than or equal to 1:3 on vaccination did not result in a significant increase in titre. Inactivated IBR vaccines (Iffavax and Ibeair H) induced a satisfactory serological response in 140 cows, regardless of the IBR virus titres of the animals on inoculation. Within five months after vaccination, four animals vaccinated with Ibeair H were found to be only moderately immune against intranasal infection using virulent IBR virus. The present authors prefer the use of vaccines containing attenuated live virus.