- Pregnancy rates reduced by 23%. Calf loss increased by 9% – A recent study of factors affecting the reproductive performance of beef breeding herds found that where there was evidence of widespread and/or recent pestivirus infection, the percentage of lactating cows that became pregnant within four months of calving reduced by 23%, and calf wastage increased by 9%.
- 70% greater likelihood of developing Bovine Respiratory Disease (BRD)- Due to its suppressive effects on the immune system, cattle that are infected with pestivirus in feedlots have a 70% greater likelihood of developing Bovine Respiratory Disease (BRD) resulting in increased use of antibiotics in feedlots. Despite this, a cost: benefit of rectifying this situation and implementing mitigation strategies has not been determined.
- $114 million per year in 2015 – Meat and Livestock Australia calculated the estimated cost of pestivirus in Australia was $114 million per year in 2015, only second to cattle tick. Australian cattle prices have doubled since that time.
Thomas Elder Markets (TEM), with the support of Zoetis Australia, have been investigating the impact of Bovine Viral Diarrhoea Virus (BVDV), also known as pestivirus, on the Australian cattle sector and this piece is the third instalment in a series of articles on pestivirus that will focus upon:
- What the virus is, how widely it is distributed and how it is spread (Published 14th October)
- The impact of the virus on cattle, types of infected animals, implications for breeding and current control measures (Published 28th October)
- The economic cost of the virus, impacts to the beef, feedlot and dairy sector
- The international response to the virus and the consideration of a control/eradication program for Australia
The cost of Pestivirus
There have been various models of the economic impact of pestivirus in Australia. All of these have been done with limited scope, such as a focus on the reproductive impacts within beef herds or dairy herds. Therefore, they underestimate the full impact of pestivirus on the national cattle herd and the individual farm arising from its impact on reproduction, calf wastage, increased animal health costs and increased antibiotic usage.
Additionally, the disruption of breeding conception/calving patterns has ramifications for productivity in that breeding season and subsequent seasons have not been accounted for in modelling of the cost of the virus.
- Empty cows or late calves have an opportunity cost and late conceptions will result in less time for recovery post calving in relation to the next joining.
- This can result in genetically sound or superior animals being culled because they were impacted by pestivirus rather than because they were genetically inferior.
- In turn, late calves have less time to grow out and will do so out of the optimal feed quality window resulting in lower end weights and higher cost of gain. In many systems, this results in farmers carrying weaners into the following season.
- This series of events results in increased cattle handling and labour inefficiencies compared with a timely, tighter calving.
- The knock-on effect is that heifers that have failed to achieve target mating weights are likely to join late, calve late and have lower lifetime beef production per breeding unit. No models to date have captured this effect in pestivirus economic impact.
Pestivirus on the dairy farm
There is an increased incidence of reporting and analysis of the impact of pestivirus on the dairy sector, perhaps because the impacts of pestivirus are more easily measurable in dairy than in beef production enterprises. An example of this fact is that it costs more to take an individual blood sample from a cross section of a beef herd to determine herd exposure to pestivirus than taking a single sample from the milk vat from a dairy farm.
The reproductive model used on the farm also has an important impact on the persistence of pestivirus within the herd. Herds that undertake year-round calving tend to have more prolonged episodes of exposure to the virus than seasonal or split calving herds, as there is a higher chance of a persistently infected (PI) animal being present in the herd.
It is estimated that approximately 5% of adult dairy cows will become infected with pestivirus each year in seasonal calving herds that do not undertake any virus control measures and around 2-3% of these infections will occur within the high-risk breeding phase, but not all of these cows will become pregnant.
Nevertheless, across dairy herds with no pestivirus control measures, herds that become infected will experience impacts of the virus on reproductive performance, milk production, cow immunity and calf health compared to dairy herds that are not exposed to the virus.
It’s difficult for farmers to quantify the effect of pestivirus in endemically infected herds due to its impact on many different aspects in the production cycle. Immune suppression, which presents as increased disease events and increased severity of disease is not often attributed to pestivirus. In dairy herds, pestivirus induced immune suppression and tissue damage has been associated with calf scours, pinkeye, mastitis, lameness and pneumonia. Combined these represent the most economically significant diseases in the dairy industry, therefore exacerbating these diseases will have a large downside on dairy farms.
In dairies, there have been severe outbreaks of pestivirus, with multiple PI calves being born over a short time horizon. On many occasions this has occurred when susceptible dairy herds have been exposed to the virus at their most vulnerable stage of the breeding cycle. As with beef herds, this often occurs with introductions to the herd in expansion or recovery phases. Pestivirus has also been introduced with heifers bred away on agistment or taken to dairy shows while pregnant.
Where a high proportion of the dairy cows are identified as susceptible to pestivirus, important strategies are to:
- Implement a vaccination program as a primary risk management tool
- Maintain a high-level biosecurity to limit the chance of exposure and importing the virus onto farm
- Testing should be conducted as part of a regular herd monitoring process
Pestivirus in the feedlot
The incidence of pestivirus in the feedlot sector is relatively common with studies showing that within the first six weeks of entry to a feedlot nearly 70% of susceptible cattle become infected with the virus. Of these cattle that do become infected, their risk of developing bovine respiratory disease (BRD) is 70% higher than uninfected cattle. Despite this, a cost:benefit of rectifying this situation and implementing mitigation strategies has not been determined.
By the time cattle are turned off from the feedlot it was estimated that just 6% of the cattle exiting the feedlot remained unexposed to the virus. Given the absence of the reproductive cycle at the feedlot the impact of pestivirus infection can often be overshadowed by other factors impacting the success of the cattle fattening process.
- McGowan, M., et al., Epidemiology and Management of BVDV in Rangeland Beef Breeding Herds in Northern Australia. Viruses, 2020. 12(10).
Earlier article: The Covid of the cattle industry