Pestivirus is a viral disease that causes reproductive failure in breeding herds and ill-thrift and mortality in young cattle. In cattle that have not previously been exposed, pestivirus is capable of crossing the cow's placenta and infecting and damaging the developing foetus. Australian-published serological surveys show that 80-90 per cent of herds have evidence of exposure. Ongoing surveillance in the South East LLS in 2014, showed a similar level of exposure. 

Pestivirus is also referred to as BVDV (bovine viral diarrhoea virus) and mucosal disease virus. It is now well recognised as an insidious cause of losses in beef and dairy herds in Australia. An unseen 'profit thief'. In a previously uninfected herd recently infected with BVDV, production losses of between 25 and 40 per cent have been recorded, otherwise known as 'the pestivirus train wreck'. This is due to a sudden increase in the number of dry cows, mid stage abortions and birth of dead, weak or persistently infected (PI) calves. Ongoing losses in herds where pestivirus is endemic have been notoriously difficult to model or estimate. I have seen estimates of ongoing annual production losses of between one and 30 per cent. Generally it is considered to be a disease of minor to moderate impact resulting in a financial impact between one and 10 per cent annually.

The so called 'train wreck' from pestivirus is not common, but has an impact that extends beyond financial loss. It wreaks havoc with management - and thus morale. As well as making a big financial impact it can be quite depressing. 

The individual effect of pestivirus depends on when the cow is exposed to the virus, but the following spectrum of disorders is generally seen. Cows are unexpectedly dry at preg testing despite sound investment in bulls and cow and heifer fertility. Some calves are then aborted, born dead, or die shortly after birth, resulting in reduced numbers at calf marking. As well as this, many of the calves are born later meaning that suddenly there is a huge range in the size of calves and the marketing of them becomes more difficult. Cows then become 'late calvers' and it will take many years to tighten the calving period again and bring them back into calving in the first month of calving.

Some of these calves are then found to be persistently infected (PI) and may be obviously more woody or ill-thrifty compared to others and may be unmarketable. Other PI calves are not obvious and are sent off with the other calves to the calf sales unbeknown to you or the purchaser. The stress of the calf sales, days off water, crowding, dust and commingling mean that the virus can spread rapidly through any previously uninfected mobs. Purchasers of weaners at the calf sales may find that as a result of the underlying suppression of the immune system by pestivirus the purchased weaners can be affected by respiratory disease and suffer significant mortality. These losses can make the purchaser quite upset and harm your reputation.

Ongoing endemic losses would be similar to this but with a smaller number of cattle affected. A survey conducted in 2014 by Charles Sturt University showed that producers have a pretty good idea of what Pestivirus is and how it may impact on their production system. Producers were a lot less clear on the best way for them to manage the disease and the treatment options available to them. This perhaps reflects a lack of consistency in recommendations and the number of options that can be put to producers.

My next article will focus on management options including doing nothing, use of auto-vaccination, regular testing of heifers and different vaccination options. 

The district and local veterinarian can blood test cattle for you so that you can understand your pestivirus status and management options.