The impact of pestivirus on an artificial breeding program for cattle

Abstract

After the introduction of pestivirus into a herd undergoing an embryo transfer and artificial insemination program, substantial post-weaning calf losses occurred. The predominant clinical feature was severe respiratory disease, in contrast to the commonly recognised mucosal disease. Thirty-one of 76 calves were affected, with a case fatality rate of 58%. All calves which were persistently infected with pestivirus died during the study period. There was a significant association in the surviving calves between the occurrence of recent pestivirus infection and respiratory disease. The losses on this property clearly indicate the need to routinely screen animals in an artificial breeding program for freedom from pestivirus infection.

Bovine viral diarrhoea virus in beef heifers in commercial herds in Australia: mob‐level seroprevalences and incidences of seroconversion, and vaccine efficacy

“…The acceptable pregnancy rate of 89% in placebo‐treated heifers in mob Ab, despite the high incidence of seroconversion and high prevalence of infected calves, may have been because BVDV entered the mob during the mating period after most pregnancies were sufficiently advanced to avoid embryonic and fetal mortality but not to avoid development of persistent infections in fetuses. An alternative explanation is that the particular BVDV strain that was introduced to this mob was virulent for causing persistent infections in fetuses but relatively avirulent for causing embryonic and fetal mortality, consistent with the findings of a previous Australian study . However this explanation seems unlikely as, pregnancy rates were lower in the placebo‐treated heifers that seroconverted between second vaccination and pregnancy diagnosis compared to those that were initially strongly seropositive (results not shown).…”

“…An alternative explanation is that the particular BVDV strain that was introduced to this mob was virulent for causing persistent infections in fetuses but relatively avirulent for causing embryonic and fetal mortality, consistent with the findings of a previous Australian study. 23 However this explanation seems unlikely as, pregnancy rates were lower in the placebo-treated heifers that seroconverted between second vaccination and pregnancy diagnosis compared to those that were initially strongly seropositive (results not shown). There appears to be limited genetic variability among Australian isolates, 24 but there is ample evidence that some Australian stains of BVDV can reduce reproductive performance.…”

Bovine viral diarrhoea virus (‘pestivirus’) in Australia: to control or not to control?

“…In 1971, antibodies against BVDV were reported in up to 12% of individual Australian sheep and up to 17% of sheep flocks . Over successive years, the virus has been implicated in congenital, clinical and reproductive disease of both sheep and cattle …”

“…Direct losses attributable to BVDV from ill‐thrifty PI animals (at risk of mucosal disease) or from reproductive disease are widely reported internationally. Other costs, such as decreased production, poor growth and increased incidence of other diseases, may have an additional associated cost …”

“…Seroconversion occurs between 14 and 28 days post infection, with antibodies present in detectable levels for at least 3 years . Although the exact mechanism is unclear, acute BVDV infection has been demonstrated to have an immunosuppressive effect, resulting in increased susceptibility to secondary infections and an increase in the severity of clinical disease …”