Introduction and elimination of Bovine Viral Diarrhoea Virus in a commercial beef herd: a case study

Abstract

Routine Bovine Viral Diarrhoea Virus (BVDV) monitoring of a commercial beef herd in southern New South Wales over a 10-year period provided an opportunity to assess the impact of the introduction of BVDV on that herd. BVDV antibody testing provided strong evidence that the herd was initially free of BVDV (2009-2011). Testing from 2012 suggested BVDV had been introduced into the herd and this was confirmed in 2015 with the identification of persistently infected (PI) animals. Having become established in the herd, the owners then set out to eliminate BVDV from the herd. Antigen testing aimed at identifying PI animals revealed BVDV was already absent from the herd. Subsequent antibody testing confirmed that the herd was now free from BVDV. Despite the incursion of BVDV in this herd, there was little measurable impact on reproductive performance (pregnancy rates), although suspected increased calf losses from birth to calf marking were reported. This is the first time such self-clearance has been documented as part of a longitudinal study under Australian conditions.

Modeling the Effect of Bovine Viral Diarrhea Virus in Australian Beef Herds

“…Apart from undetected losses, difficulty in communicating the negative impacts of BVDV to stakeholders is partly due to the wide variation in outcomes that could occur during an outbreak of BVDV. Poor conception and reduced pregnancy risks are often identified during BVDV outbreaks ( 70 ); however, this study, consistent with Allworth et al ( 65 ), found that the pregnancy risk in a herd of 400 animals was largely unaffected by BVDV. The joining practices used in this model and described by Allworth et al ( 65 ) are similar to industry-recommended joining practices for seasonal calving beef herds in NSW (McConchie 2007, MLA 2019).…”

“…Poor conception and reduced pregnancy risks are often identified during BVDV outbreaks ( 70 ); however, this study, consistent with Allworth et al ( 65 ), found that the pregnancy risk in a herd of 400 animals was largely unaffected by BVDV. The joining practices used in this model and described by Allworth et al ( 65 ) are similar to industry-recommended joining practices for seasonal calving beef herds in NSW (McConchie 2007, MLA 2019). These short duration joining periods are designed to limit infertility and might also reduce the apparent reproductive effects of BVDV infection.…”

“…It was not possible to ascertain the infection status of these animals retrospectively, and it is possible that introduction of multiple infected animals may have contributed to a longer time to elimination. In addition to elimination time, data from the model for the 400-breeder herd showed that the 2-and 4-year seroprevalence in the 73-day period prior to joining were comparable to the values reported by Allworth et al ( 65 ). The model also demonstrated that the highest daily prevalence of viremia following subsequent BVDV introductions became lower as herd seroprevalence increases; a relationship which is well recognized in the literature ( 11 ).…”

“…The mean herd viremic prevalence (1%), median age of PI animal death (6.7 months) and the median herd seroprevalence two years after a single BVDV introduction (40%) were all analogous to the corresponding median/mean values obtained in the literature. The mean prevalence of PI animals (0.7%), the median pregnancy risk (88%) for a naïve herd and the calf mortality rate in an infected herd (5%) was also within the range of the external reference values (0.2-0.8%; 85-89% and 5-7%, respectively) (64,65). The median value for abortion rate, calf mortality rate and the percentage of light sale steers following a single BVDV introduction did not match the external data; however, the 95% range of these parameters did include their corresponding reference value.…”

“…While the median duration of BVDV outbreak in the simulated 400-breeder herd (4 years) was shorter than that reported for a similar sized Australian outbreak, the 95% range included the published values for elimination time [6-8 years; Allworth et al (65)]. In the case study, Allworth et al (65) speculates that BVDV was introduced into the NSW farm via breeding stock.…”