During the certification of the bulls at an artificial breeding centre for freedom from pestivirus infection, a single viraemic bull was identified, and further testing confirmed that it was persistently infected. 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, motility and morphological criteria. Approximately 600 doses of semen had been distributed for sire evaluation purposes to 97 dairy farms. An examination 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 two were persistently infected, but that the others were healthy and uninfected. It was concluded that the semen from this bull was a potential source of pestivirus infection for 'clean' herds.

When 73 heifers (60 of which were seronegative to pestivirus) were inseminated with pestivirus-contaminated semen from a transiently infected bull, the conception rate to a single insemination was found to be normal (65 per cent). Only three animals became systemically infected, as determined by viraemia and seroconversion. Pestivirus was isolated from the reproductive tracts of two of these heifers when they were slaughtered 42 or 43 days after insemination. Although the initial incidence of infection was low, a cycle of secondary transmission occurred approximately 29 days after insemination, with a further eight heifers (all seronegative) becoming infected from one group of 11 seronegative and four seropositive animals.

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When 73 heifers (60 of which were seronegative to pestivirus) were inseminated with pestivirus-contaminated semen from a transiently bull, the conception rate to a single insemination was found to be normal (65 percent). Only three animals became systemically infected, as determined by viraemia and seroconversion. Full article published in Veterinary Record (1997) 140, 124-127

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