THE OUTCOME OF WIDESPREAD USE OF SEMEN FROM A BULL PERSISTENTLY INFECTED WITH PESTIVIRUS

During the certification of the bulls at an artificial breeding centre for freedom from pestivirus infection, a single viraemic bull was ide ntified, and further testing confirmed that it was persistently infect ed. The two-year-old bull was healthy and of similar bodyweight to its peers. Its semen was of normal quality on the basis of density, motil ity and morphological criteria. Approximately 600 doses of semen had b een distributed for sire evaluation purposes to 97 dairy farms. An exa mination of the breeding records indicated a first service conception rate of 38 per cent. All but one of the 162 cows inseminated with the bull's semen were seropositive compared with 95 of 143 cows (66.4 per cent) inseminated with semen from other bulls. Virological studies of the 61 calves sired by the persistently infected bull revealed that tw o were persistently infected, but that the others were healthy and uni nfected. It was concluded that the semen from this bull was a potentia l source of pestivirus infection for 'clean' herds.