After the plates were washed, 0.2 ml of a 1:3,000 dilution (inPBS-T20 containing 0.01% merthiolate) of mouse monoclonalanti-bovine immunoglobulin Gl conjugated to horseradishperoxidase (K. H. Nielsen, Agriculture Canada, AnimalDisease Research Institute) was added to each well, incubatedat 24°C for 30 min, and washed as described above.