Learning about BVD

On my farm practice placement one of the diseases the vets talked about a lot was bovine viral diarrhoea (BVD). Apparently BVH has a huge economic impact on cattle farming: it can cause poor performance in herds for many years without being treated as farmers may come to accept this as normal. Ongoing infection and re-infection happens via an interesting mechanism including intrauterine transfer to calves and Persistent Infected (PI) individuals constantly shedding virus into the herd’s housing.


What does BVD look like?

BVD infection leads to respiratory problems and poor fertility, as well as compromising the immune system and making cattle more vulnerable to secondary diseases like pneumonia and scouring. In pregnant cows it can cause abortion, embryo death or birth defects, particularly neurological problems. Where cows are infected early in pregnancy their calf becomes exposed to BVD antigens before their immune system is developed enough to recognise it. These calves, if they survive, become the sinister PI cattle responsible for infecting herds more broadly.

What’s the deal with PI cows?

BDV can be transmitted directly or via the environment between infected cows, replicating and causing infection once it touches epithelial cells. Normal individuals will produce antibodies and can become immune, although some will have chronic infections in organs the immune system struggles to reach such as reproductive organs. PI cows, however, “see” the virus as self because it was present before their immune system formed properly. They can never produce antibodies and go around shedding viral material at a thousand times the rate of a normal infected cow.

Many PI calves fail to reach adulthood, often dying from mucosal disease or cerebellar hypoplasia, the aforementioned neurological condition they are likely to be born with. But those that do grow up continue to infect the cows they live with for their entire lives. Identifying and culling these individuals is crucially important to controlling BVD in a herd and restoring herd performance.

What can be done?

As well as removing the PI cows from a herd, biosecurity and vaccination are both important tools. Milk, ear tag and blood samples can be used to test for the presence of antibodies or antigen and look at the infection status of the herd whilst measures such as double fencing and only buying in BVD-free animals can help keep the disease out.

A voluntary BVDFree scheme started in July aiming to eradicate the disease from the UK by 2022. Several Scandinavian countries have proved this to be possible already and practices are encouraging their clients to sign up and gain BVDFree status. This can be expensive but does lead to greatly improved performance of the farm and can be a selling point, for example selling stock certified as BVD-free.

BVD was an interesting disease to learn about even if we never actually dealt with it during my placement week. I’ve listed my references below but a lot of this came from the vets at the practice who were fantastic teachers!

NADIS

RVC BVDFree

The Cattle Site

Ususal disclaimer: I’m not a vet, not even a vet student yet, so please don’t use my blog for vet advice! If you notice things I’ve got wrong or not understood properly, please feel free to point them out. Thanks 🙂

 

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Common health problems in dairy cows

I’ve seen several articles recently which compare dairy cows to high performing athletes. Although they don’t inspire the same awe in the public audience or compete at the Olympics, the lactating cow’s metabolism works at an impressively high rate to convert feed into huge volumes of milk. Unfortunately, this incredible production comes at a cost and our dairy cows do suffer from a variety of common health problems, the most frequent of which I’ve been reading up on.

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Pregnancy diagnosis in sheep

When I started talking about going back to university one of my friends from school got in touch and asked if I wanted to do some “work experience” on his dad’s farm. I was very grateful for the suggestion and even more so when we went along to the farm and his family turned out to be lovely, friendly people and willing to take me on during lambing!

I’ve booked my time off work and agreed to stay with my family in the next village. However their lambing won’t start until late March/early April, which seemed a long way off. So when they called me up and said they were doing pregnancy diagnosis on some of the sheep this weekend I jumped at the chance to go and start learning about sheep farming and try and make myself useful.

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