Bovine Viral Diarrhoea Virus
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Presentation by Michael Healy, Student Intern from Sydney University at the Milton Pink Eye Workshop held on the 18th June 2009. This Presentation covers: - What is Bovine Viral Diarrhoea (BVDV) or Pertivirus - Case Study on a South Coast Diary Herd - Control Methods
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Bovine Viral Diarrhoea Virus
- 1. BOVINE VIRAL DIARRHOEA VIRUS (BVDV) or ‘Pestivirus’ Michael Healy
- 13. 15% of heifer calves are PIs! 25 heifer calves have been ‘dummy’ calves About 5 premature looking calves with patchy baldness 75 heifer calves have died or been destroyed! Losses
- 15. Calf hutches
- 17. Over $150,000!
- 19. Beef cattle
- 21. - Be very careful! - Yarding animals together at ‘danger time’ - Conception failure Synchronised AI and embryo transfer breeding programs
- 24. 1. Don’t let your cows or heifers get infected with the virus for the first time when they are being joined or during pregnancy. 2. Controlling PI animals is the key to controlling disease! BVDV 2 key points:
- 27. What can you do to protect your herd against BVDV? There are a few options: - Vaccination - Partial vaccination - Autovaccination - Removal of PI animals - Biosecurity measures
Notas del editor
- Good morning everyone, my name’s Michael Healy and I’m a final year veterinary student from Sydney University. For the last 4 weeks, I’ve been on practical placement with the District Vet in Bega, Ian Lugton. As part of my time there, I completed a project investigating how much of an effect pestivirus has had on a local dairy herd. In today’s presentation, I’ll give an overview of Bovine Viral Diarrhoea Virus and the problems it can cause in cattle, I will summarise the impacts the disease has had on a dairy near Bega, explain some of the effects that BVDV can have on beef cattle operations, and provide some recommendations on how to control or prevent this disease.
- So, what is Bovine Viral Diarrhoea Virus? It’s a bit of a mouthful, and is also known as Pestivirus. Firstly, how many people here have heard of Pestivirus? It might surprise you to know that around 90% of cattle herds in Australia have been exposed to this virus at some point in time. So it’s definitely around. It’s a contagious infection of all breeds of cattle. When an animal is infected with the virus, it develops antibodies against the virus and recovers. It may be more susceptible to other infections, like respiratory disease or scours for a month or two, but after this it will never have another problem due to Pestivirus. The immune response is enough to protect that animal from ever becoming infected again. So why is this disease important and why should we worry about it??
- Because when BVDV is around at the wrong place and the wrong time, it can cause significant reproductive losses. Previously unexposed animals are called “naïve” animals. When naïve heifers and cows are exposed to the virus for the first time around the time of insemination or during the first 6 months of pregnancy, BVDV can cause some real problems. This is the ‘danger time’
- The sort of problems that occur depend on the exact point of time that a female is exposed to the virus. Infection at the time of mating or within a week or two either side of mating, can result in poor conception rates and early abortions. As a result, you might notice an increase in the number of animals returning to heat, or an extended calving season.
- This picture is showing the ‘danger time’ for infection with the virus – around the time of mating. Or in the first 6 months of pregnancy.
- If a pregnant cow or heifer is exposed to BVDV for the first time up to 6 months into pregnancy, the virus travel’s through the cow’s blood and across the placenta, infecting the developing foetus. This can cause mid-term abortions or stillbirths. You can see an aborted foetus there. Sometimes, ‘dummy’ calves are born, which just don’t act normally – and this is because they are born with abnormalities of the brain and sometimes eye. Infection of pregnant females can also result in them giving birth to what is known as “a PI calf”. These PI calves are very important and I’ll explain why.
- PI stands for “persistently infected” with the virus. They are also known as carriers of the virus. A PI calf is produced when a naïve pregnant female is infected with BVDV between 30 and 125 days of pregnancy (or about 1-4 months pregnancy). If the foetus doesn’t die and abort, the calf may be a PI. PI animals are carriers of the infection for life. They are sometimes called virus factories
- PIs are the potential source of infection for your stock – these PI animals spread the infection to any cattle that they come into contact with. The virus is spread in their saliva, faeces, urine, semen, in fact it’s in just about everything they produce! The infection is contagious, so 1 hour of contact with a PI animal is often enough to transmit BVDV to a naïve animal. If your stock don’t come near a PI, then you won’t have a problem due to pestivirus. Most PIs can be recognised or suspected of being a PI because they are “poor-doers” – they grow slower than other calves/weaners and are often sick. I’d say that most of you would have had an animal like this on your properties at some stage – it may have been a PI. Unfortunately, it’s not always that easy to pick out a PI and stop it getting near female stock at mating or during pregnancy, because a small proportion of PIs appear completely normal! They can live for several years and breed successfully if allowed to do so.
- This is not a picture of a cow and her calf, but is actually two heifers who were born at the same time. The one in the background is normal and healthy, but the smaller one is a PI, that always did poorly. Most PIs die before they reach 2 years of age.
- OK, moving on to the project I carried out while on placement in Bega. I investigated the economic impact of a BVDV outbreak on a dairy herd near Bega. The herd is a large one, with 950 cows in the milking herd. Calving is year-round. There are 3 separate properties in this operation: one for the milking herd, one where calves and weaners are reared, and one for heifers. Breeding is by AI, with bulls to mop-up the herd, and bulls do not get PACE tested. The herd is not closed, since sometimes pregnant cows are bought-in.
- In the second half of last year, cows in the mature milking herd began aborting. Heifers have been unaffected. The owners could not work out why they were aborting, but diagnostic tests soon revealed that Pestivirus was the cause. There have been 30 mid-term abortions since this time – these cows were culled. Some cows have also aborted early in pregnancy after being preg-tested in calf – these cows have been given a chance to get back in-calf, but the calving-to-calving interval will be much longer than it should have been. Also, during this time, average conception rate by AI had decreased by 10%. These losses are all caused by BVDV! A high proportion of the milking herd must have been ‘naïve’ – that is, they’d never been exposed to the virus. And a large number of them must have been exposed for the first time during the ‘danger times’ - around the time of insemination and during the first 6 months of pregnancy. For those foetuses that were infected but didn’t abort, we would expect to see dummy calves and PI calves being born within a few months…
- And that’s exactly what happened! Since January this year, every newborn calf has had an ear notch taken for a PACE test – and about 15% of all heifer calves born have turned out to be PIs! Another 25 heifer calves have been ‘dummy’ calves that don’t act normally. Another 5 calves have been ‘premy’ with patchy baldness, which is also caused by Pestivirus. The total result of this has been that 75 heifer calves have died or have had to be destroyed! Good genetics in a lot of these heifer calves means their value was $150, sometimes $200!
- Also, calves that are not PIs have been reared alongside PI calves. When they are infected by the PI calves, they develop lifelong immunity, but for a couple of months they are more susceptible to infections. So there has been a very high rate of respiratory infections and scours in the calf-rearing unit. The infections are likely to have slowed the growth rate of the heifer calves, which means they may take longer to reach the target weight for joining. A few calves have died of respiratory infection at about 4 months old.
- Now, all newborn calves are housed in separate hutches, until they are PACE tested – the calves that are confirmed as PIs are destroyed. The non-PIs can then mix together in the calf-rearing unit and do not become susceptible to infection because they are not exposed to PIs.
- There have been economic losses at many levels of this dairy operation due to the Pestivirus outbreak. The cows that aborted and were culled were replaced in the milking herd by surplus in-calf heifers. This means that there was lost income because these surplus heifers would normally be sold to other farmers. Because heifers replaced cows in the milking herd, there are losses due to reduced herd total milk production, since heifers produce about 80% of the milk that mature cows do. Veterinary bills for visits and diagnostic tests were a significant cost. Labour costs in dealing with the disease outbreak are large. The herd managers are also having to knock back some contracts to rear Wagyu and Friesian calves – the lost profit from contracts to rear calves in 2009 is around $30,000! Also, with less surplus heifers around for the next couple of years, the managers will be less able to cull cows from the milking herd due to poor production or for health reasons such as high somatic cell counts – this will cause economic loss too.
- The estimate I arrived at for the economic losses to this dairy herd is over $150,000!!! The outbreak is still not over yet, so this figure will only rise. So the key message here is that when Pestivirus goes bad because naïve females are infected at mating or during pregnancy, then things really can go seriously wrong! It’s an important disease for vets and cattle producers to know about.
- We can’t be sure where the PI that infected all the pregnant cows in this herd came from. I think it’s most likely that when the dairy bought a herd of pregnant cows and introduced them into the herd a few years ago, one or more of the cows gave birth to a PI calf. The PI calf may have been one of the PIs that grows normally, and was mated, and then when it was introduced into the milking herd it began to infect all the naïve cows which were at various stages of their reproductive cycles. Another possibility is that an introduced cow was a PI. Another possibility is that one of the bulls that was being used was an undetected PI. Cows can also get infected if they come into close contact with a PI from a neighbouring property over a fence.
- Beef breeds are also at risk of infection with BVDV.
- Problems that BVDV can cause in a beef herd are similar to those seen in a dairy herd: Aborted foetuses and stillbirths, poor pregnancy rates, an extended calving period, low weaning rates, poor weaner growth rates, stunted calves, dummy calves, and more calves than usual becoming sick.
- BVDV is a particular danger to breeding programs involving oestrus synchronisation. Economic losses are potentially greater with more valuable offspring. Synchronised breeding programs often involve bringing all the animals together and yarding them for insemination at the same time – around the time of insemination is the ‘danger time’ when BVDV can cause conception failure or early abortion – so if there is one PI in the group, the results can be disastrous. There are reports of only 1 or 2 cows out of a group of 50 becoming pregnant after a synchronised AI program, because they all got exposed to Pestivirus around the time of insemination.
- Studies have investigated the economic losses in beef herds that have problems with BVDV. A study by Phil Holmes investigated the impact of introducing a PI bull into a completely naïve herd of heifers. There were various effects: decreased weaning rate and decreased growth of weaners. Abortions, stillbirths, the birth of dummy calves, and the dreaded PI calves. The study found that some of these PIs grew normally and in 3 years infected more females at the time of breeding or pregnancy, causing another round of reproductive losses. The study found that as a result of the outbreak of Pestivirus, the income of the beef property was decreased for 13 years before it returned to normal. The loss of income averaged $42 per female per year for 13 years!
- When BVDV was introduced into a herd of heifers in which only 30% were naïve, the impact was smaller and there were fewer reproductive losses, but there was still a loss of income of $30 per female per year for several years.
- Bovine Viral Diarrhoea Virus can get pretty complicated. But there are just 2 key points to remember about this contagious disease: Don’t let your heifers or cows get infected with the virus for the first time when they are being joined or during pregnancy. And secondly, PI animals are how the virus spreads to other cattle. So controlling PI animals is the key to controlling disease!
- There are diagnostic tests for pestivirus: The PACE test can be used to detect PI animals. Either an ear notch or blood sample is submitted to the laboratory for the PACE test. PIs have a positive result on the PACE test. This test costs $10 per animal tested. It can be done by the owner and then taken to the vet to submit to the lab. The AGID test is a blood test that can determine if an animal has ever been exposed to the virus in its lifetime. It costs about $12. Animals that have been exposed to the virus before, have Pestivirus antibodies in their blood. So if the AGID test finds Pestivirus antibodies in an unjoined heifer’s blood, then that heifer has already been infected at some point in its life, and there is no danger of it having an abortion or producing a PI calf once it is joined. You can test a few animals from group of unjoined heifers or cows, to estimate what proportion of the group have been exposed to the virus before. If a lot of animals in the group have no Pestivirus antibodies in their blood, this means that there is a danger of reproductive losses occurring, if they come into contact with a PI at the ‘danger time’
- There is a vaccine available – called Pestigard, some of you might have seen it being sold. It’s 81% effective at protecting stock against infection. For best protection, 2 shots of the vaccine are given initially, and then 1 booster shot each year after that. The cost is around $6 per shot.
- There are a few different ways you can protect your herd against the danger of BVDV: vaccination, partial vaccination, autovaccination, removal of PI animals, and biosecurity. The best approach will vary from farm to farm, so working with your veterinarian to develop the best strategy for your herd is a good idea.
- Vaccination – for farmers with only a small herd of cattle, rather than performing diagnostic testing of the herd, it might be simplest and easiest to vaccinate the herd. This will have to be done annually to maintain protection. If you stop vaccinating, your herd will be vulnerable again. If your herd isn’t big enough to get through a whole bottle of vaccine, you could organise to share the purchase of the vaccine with your neighbours. In the first year of vaccination, heifers, cows and bulls should be vaccinated twice, with the 2 nd vaccination occurring at least 4 weeks before mating begins. A booster is given annually after that.
- Partial vaccination means vaccinating only some groups of animals on your property. This saves money on vaccine doses, but animals that don’t receive a vaccination are given no protection. You would vaccinate those groups which you think are most at risk. The AGID test could be used on a sample of animals from each group, to identify groups that have a high proportion of animals with no Pestivirus antibodies in their blood. No antibodies means no previous exposure to BVDV and therefore these animals are at risk.
- Autovaccination is another option to protect your herd against losses. This means using a PI to deliberately infect your herd. If you have a confirmed PI on your property, you can yard your heifers with the PI several months before they are joined. Most should become infected and then develop lifelong immunity, so that when it comes time to be mated, they are at no risk because they have already been exposed. If done correctly, this approach can protect > 80% of the group.
- Removing all PIs from a closed herd is another option. To PACE test each animal costs $10. Several rounds of testing are needed to be sure there are no PIs. This option gets expensive in big herds.
- Biosecurity is another way to protect your herd – biosecurity means keeping PIs from outside your farm away from your stock. It is probably the most important control option. Vaccination is not 100% effective so even if you vaccinate you still need to keep PIs away from your vaccinated animals. Removing PIs from your herd must also be combined with good biosecurity to protect your stock.
- So what can you do to stop your vulnerable stock coming into contact with a PI from outside the farm? Keep a closed herd if possible. But if you are going to buy cattle and introduce them to your herd, test all introduced cattle with the PACE test to make sure they are not PIs. This includes asking the breeder you buy a bull from whether he has done a PACE test on the bull before he sells it to you. Keep introduced animals quarantined away from the main herd until the PACE test results are available. Don’t mix groups of animals during the ’danger time’ – and remember the danger time is around the time of mating, or during the first 6 months of pregnancy. Don’t buy pregnant females and introduce them to your herd – one could be a Trojan cow, with a PI calf growing inside. Keep breeding females away from boundary fences where they might have access to neighbouring cattle, or use double fencing or electric outriggers on boundary fences. You don’t want your cows getting up close to your neighbour’s PI. Also, be careful of transporting cattle off the farm, for example on agistment, and then bringing them back to your farm. It’s wise to vaccinate 8 weeks before moving them off your farm.
- Bovine Viral Diarrhoea Virus, also known as Pestivirus, is common in Australian cattle herds so may represent a real danger to your herd. It is potentially a very costly disease. Persistently infected animals spread the infection. So long as you don’t let your female stock get exposed to Pestivirus for the first time around mating or during pregnancy, then you won’t have a problem. Biosecurity measures are really important to protect your herd – don’t let PIs near your stock! Finally, vaccination is worth considering and at $6 per dose, it may be a worthwhile investment that saves you a lot of heartache.