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Unfortunately it is not just limited to diarrhoea; this is just the most visible of its effects! BVD can affect all ages of cattle and approximately 90% of UK herds have been exposed to BVD virus. BVD has wide ranging effects and is most costly to farms due to impaired herd outputs and the requirement for increased inputs. Conservative estimates of costs to a 100 cow beef suckler herd are in the region of £5,500/year  (or around £55/cow). So how does it cause all this?

BVD is so prevalent due to the ease with which it is spread and the way it can hide itself within animals to better enable that spread. It can be spread through all animal excretions (saliva, urine, faeces, milk and semen) and can also pass vertically, i.e. from a dam to its calf while the calf is in the placenta. It can also become aerosolised and spread across boundaries (distance dependant on wind and climatic conditions - most prevalent with nose to nose contact).

So what happens if my animals come into contact with it? To answer this let's look at the different stages an animal could become infected. If it is a non-pregnant animal (females and males) then often it will occur as a mild transient infection that will result in a scour and a raised temperature that will resolve in 10-14 days. During that time however the immune system will be depressed allowing other bacteria and parasites to cause additional diseases where normally they would be contained; if that is seen then secondary infections may occur such as pneumonia, coccidiosis and mastitis etc. The animal will then produce antibodies to the virus within around 3-4 weeks and will become naturally immune to further infection.

Often when the above occurs in a herd or group that has previously not been exposed to the virus, the first thought is that they have pneumonia or worms so they are usually treated for these and nothing more is thought about it.... In this situation the BVD has gone undiagnosed!

If the animals are infected for the first time when they are early in calf (<110 days) then the virus will cause the above signs together with a number of other more insidious problems that often go unnoticed until later.... These can include early embryonic death, abortions, mummification of foetuses, birth defects and the potential for persistently infected (PI) calves being born. This is where much of the "hidden" costs of BVD can arise, often seen only at pregnancy scanning (or calving) as an increased number of non-pregnant cows, which will mean fewer calves and reduced profits! Infection in later pregnancy (>110 days) can result in abortion, premature calving or the birth of healthy calves that have antibodies to BVD, the costs here being the abortions and premature calves that do not survive!

If a persistently infected (PI) calf is born then this calf will be a source of virus, shedding millions of viruses into the environment. They are often the "poor doer" in a group of calves and will always go on to produce PI offspring... if they survive to reproduce. Often they will die before reaching 24 months as the virus mutates within them resulting in mucosal disease and death. They are the greatest source of BVD in an infected herd, the reservoir of infection!

If animals are infected as calves, they will often suffer more from the effects of immunosuppression than will adult animals. As such they will be more prone to pneumonia, other causes of diarrhoea and will generally fail to develop as quickly as they could, these result in increased time from birth to finishing or sale which in turn results in increased feed to costs to maintain them, all of which takes money off the bottom line.

So how can we tackle this insidious problem? The first part is through diagnosis. Once it has been detected and identified as being present the next step is to decide what to do about it.

The best method of control is through eradication. BVD eradication is possible through whole herd blood testing and elimination of PI animals. Once eradication is conducted, strict biosecurity protocols must be put in place to prevent reintroduction of the disease onto the farm. Measures must be put in place and maintained to assure a continuous disease free status.

Alternatively, where strict biosecurity is not possible (due to movements required or neighbouring cattle etc) then vaccination is the next best way to control the disease. Vaccination comprises two initial doses 3-4 weeks apart and prior to first service and then a booster vaccination at intervals not exceeding 12 months. This will prevent further PI calves from being born due to protection of the foetus through vaccination of the dam. It still requires testing and removal of PI animals from the herd to ensure its effectiveness.

Testing and control do cost money, but when you consider what the costs are (conservatively around £55/cow/year) if you do nothing, they are well worth the return on investment. Estimates on return on investment from New Zealand farmers have been as high as 10:1, and in the current financial markets there are very few investments giving those sorts of returns!

If you have any questions or would like to discuss BVD please speak to your local vet or a consultant vet who can help you generate a suitable control programme. Also watch out for more information through regional educational events happening over the winter delivered through veterinary practices across the country.

Using the University of Reading BVD (suckler) 1.3.1-STM model cost calculator

Peter Aitken BVSc MACVS MRCVS

Peter is a farm vet and partner with Westpoint Three Counties, covering Hertfordshire, Buckinghamshire and Bedfordshire, providing a dedicated service to all livestock keepers and with specialist knowledge of beef health and husbandry.