Series Two: Episode Three - Bovine Viral Diarrhoea (BVD): Transcript
Sam Thom: In this month's Scottish Agricultural College podcast we're learning about a viral disease which can sweep through herd, it can kill multiple animals and cost a farmer thousands of pounds. Now my name is Sam Thom and I've come to the SAC disease surveillance Centre at Bucksburn in Aberdeen and I'm here to meet veterinary investigation officer Catriona Ritchie, who's going to talk me through BVD, or bovine viral diarrhoea, its causes and how to control it. First of all Catriona, thanks very much for joining me on this podcast.
Catriona Ritchie: No bother.
ST: It's caused by a virus isn't it, what impacts does this disease have on the animals themselves.
CR: When an animal’s first exposed to the virus, it can suppress its immune system, which makes it more susceptible to other infections that are present in the herd. So for example, if the herd already has scour, or calf pneumonia problems, it can make them an awful lot worse, and make the fatality rates much higher as a result. The other main danger of the virus infection is that if a cow or heifer is exposed to the virus for the first time in the first third of pregnancy, then it can create what we call persistently infected or PI animals. And these are the ones that are virus factories - they will shed the virus throughout their lives.
ST: So you can have cattle walking about the field and you may not actually know that they are infected.
CR: That's right. PI animals can look completely healthy, however sometimes they can look ill-thrifty, they might be smaller, not doing as well as other animals in the herd.
ST: Okay, let's get down to the nitty-gritty. Give me some examples of instances when you have detected BVD.
CR: Okay, we have been involved in investigating a few severe outbreaks of BVD. In one case there were 19 animals that died when they were a year old from a fatal BVD infection. It's likely these were all PI animals, they hadn't been thriving very well, and they were brought inside for some further feeding to bring them on, and within a month, 19 of them died from fatal BVD virus infection.
In that case it was a close herd and it's probably the case that there was a low level of herd immunity, and it is thought that the source of infection in that herd was some heifers that they had purchased which were in calf. And although these heifers had been tested for BVD and they were approved antibody positive, which indicates that they were immune, then it's likely that they were exposed to BVD during the critical stage of pregnancy, during the first 120 days. And three of their calves were PI calves. And that's likely to have been the source of infection for this herd.
ST: Does infection always have to come from other animals or can it be carried on clothes and wheels vehicles?
CR: It can be carried in clothes and vehicles, so it's not always an animal which spreads infection into a herd. It is usually the purchase of PI animals which are responsible for that. But even animals having nose-to-nose contact over a fence with a neighbouring herd can introduce infection, too.
ST: Now, you said 19 animals died in that outbreak – that’s a sizeable amount of cash for a farmer.
CR: That's right those animals could be worth £1,000 to £1,100 each, so it can count up to large amounts of money. Another heard that we were involved with, they had 28 PI's detected in a herd of about 100 beef cows and in that case the costs were calculated to be around £21,000. But in an average heard infected with BVD the costs have been estimated to be around £46,000 in 100 cow suckler cow herd over a ten-year period. So even if the infection is not as severe as that it can have a significant impact on profit margins.
ST: Can you give me some idea of how prevalent around Scotland this disease is?
CR: Yes, there was a survey which was carried out about four years ago now and at that time it was found that about 38% of beef herds had evidence of active BVD infection and probably about 16% of herds had evidence of having a PI present.
ST: And do we tend to find this in certain parts of the country?
CR: I don't know if it's been looked at on a county by county basis. It tends to be present throughout most of Scotland, though there are some areas which have lower levels of infection than others, and there are some parts of Scotland such as Shetland which have managed to eradicate BVD virus infection.
ST: So how will the farmer know in that case when he has a BVD outbreak?
CR: A farmer might suspect when they have a BVD problem in herd if problems with calf scour and pneumonia are worse than they would expect, and also if herd fertility is not as good as it should be. So if they have higher barren rates in the cows, and a sort of spread out calving pattern, then it could be that BVD virus is behind the problem.
It's relatively easy to determine if there is BVD virus infection within a herd, because, as I say it might not always be obvious that it is the cause behind these problems. So in a beef herd what we would recommend is that you would screen the calves. Usually you would pick out ones between nine and 18 months of age, and you would test five from each separate group for BVD antibody to see if there was evidence of active infection. And in a dairy herd you can carry out testing for antibodies on bulk milk samples or else on animals which are in their first lactation.
ST: Okay, so we’ve talked about the causes and how it manifests itself, but what the farmers want to know, of course, is how do you solve this?
CR: It is better to try and eradicate an infection if it is identified within a herd. So it's better to test a herd to find and remove PI animals. That should be done in conjunction with a vaccination policy, to protect the breeding herd to prevent further PIs from being created. And it’s also essential to have good biosecurity in place, so that would involve isolating and testing anything that has been bought in, unless it comes from an accredited herd or previously been tested.
And also considering neighbouring herds, try and avoid contact between neighbouring cattle, because although you're doing something about BVD your neighbours may not. It's also worth having cleaning and disinfection points in place at the entrance to the farm for any visitors coming in to try and reduce the risk of virus spread in clothing and vehicles.
ST: Okay, in that case Catriona, I’ll just get you to summarise these into three clear points that farmers should bear in mind - these are actions on how to deal with BVD. Just run through them.
CR: Screen the herd to remove PI's; vaccinate your breeding herd; and have in place good biosecurity.
ST: There you go. That’s the guidelines from Catriona Ritchie. Catriona, thank you very much for taking the time to participate in this SAC podcast.
CR: Thank you