SAC Symposium - Maedi-Visna - where next - Catriona Ritchie: Transcript
You are listening to an SAC podcast from SAC’s Herd Health Symposium held as part of the VET Trust’s CPD event at Stirling. This event was funded by the Scottish Government under its Veterinary and Advisory Programme or VAS.
The control of the sheep disease Maedi Visna has focused on ensuring that terminal sire flocks are free from infection. However the main impact of the disease is currently being seen amongst commercial flocks where productivity is hit by poor milk production and increased wastage in ewes. SAC Veterinary Investigation Officer, Catriona Ritchie, is the veterinary consultant for Maedi-Visna within SAC’s Premium Health Scheme for Sheep.
Ken Rundle: Catriona; exactly what is Maedi-Visna disease?
Catriona Ritchie: Maedi-Visna is caused by a virus and it’s a slow virus infection so it has a very long incubation period. The types of signs that you see are mainly weight loss in adult sheep. You can also get signs of pneumonia, chronic mastitis, occasionally arthritis and you can get hindlimb paralysis with it too.
KR: So it really does turn the flock into an unproductive unit.
CR: That’s right.
KR: And it’s bad for welfare.
CR: Yes, definitely. It can have quite a severe impact on the flock. If the ewes are in poor condition they tend to have lower conception rates, you get more barren ewes, you tend to get smaller/weaker lambs being born, the colostrum quality is usually poorer and the ewes tend to have less milk so as a result the lamb growth rate tends to be very poor.
KR: A very strange name.
CR: It is. It is an Icelandic name. The Maedi stands for the breathlessness that you get with pneumonia and the Visna means wasting and it’s the wasting of the spinal cord and the neurological signs that its referring to.
KR: As I said in the introduction, the main attack on Maedi-Visna was really with pedigree flocks with the top end of the triangle as it were but now we are seeing something different.
CR: That’s right. The MV Accreditation Scheme has been in place for probably about 30 years and it has tended to be the pedigree terminal sire flocks that have joined the Scheme and have done something to try and keep MV out of their flocks. However now we are seeing increasing evidence of infection in the commercial flocks. These are the flocks that we are starting to see the impact on production in. There is also evidence that these flocks are infecting the accredited flocks. We had more breakdowns within the accredited flocks in the last year. Normally we average about 3 a year whereas last year we had 13 breakdowns in an accredited flocks and it has also been shown that there is over a 2-fold increase in the chances of having a breakdown in an accredited flock if you happen to have non-accredited sheep in the same holding.
KR: What do we put this down to?
CR: It is possible that in past that people have managed to get away with having not brilliant biosecurity on their flocks. Now that there is evidence of infection increasing in the commercial flocks it is putting more pressure on the accredited flocks.
KR: The challenge is greater.
CR: The challenge is greater in that it does mean that it is essential to try and do things as you should do according to the rules.
KR: So what can be done now?
CR: Really flocks should try to keep themselves isolated from neighbouring flocks so at least a 2 metre gap between other sheep flocks if possible. If infection is found in a flock then there are steps that we can take to try and eradicate it, especially if it is found at an early stage where we can test and cull to eliminate the infection. However, if the infection goes on for some length of time then it becomes very difficult to eradicate it and it may get to the stage where the only option is to cull and restock.
KR: Are we getting to that stage now?
CR: Some flocks have had to cull and restock so yes it has been seen in some cases. It is years down the line before a flock will get to that stage and before it gets there there will be significant impact on the productivity.
KR: How concerned are you by these latest developments?
CR: It is a great concern, as I say, once the level of infection gets to a certain level in the flock then it is really a one-way street and it is very difficult to try and manage the infection once it gets passed a certain level.
KR: So what needs to be done? What are the key rules?
CR: Really flockowners should consider buying from other accredited flocks if that is an option. If that is not an option then what they could do is to either have sheep tested before they buy them or else put them in quarantine and test them before they introduce them to their flocks. As I say, they should try and avoid contact with neighbouring flocks if at all possible and if infection is found then its better to do something about it early on.