Pestivirus - You won’t know until you test.
Pestivirus (or Bovine Viral Diarrhoea Virus, BVDV) is an incredibly complicated disease, but one which you can be prepared for and protected from, rather than gamble that you’ve got immunity. This was pretty apparent this month when some blood testing showed very different results in two separate herds.
Before I get into what the results showed, let me summarise Pestivirus for you! (I’ll keep it brief, promise).
There is evidence of antibodies to Pestivirus in about 90% of Australian beef herds, so it’s very common. It is spread by Persistently Infected (or PI) animals. Approximately 1 in 200 animals are PIs, and they can be skinny, underdeveloped poor-doers, or they can look completely healthy. In other words, they can be hard to pick. They have a poor immune system and shed Pestivirus in every cell of their body – faeces, ocular and nasal secretions, birthing fluid, urine etc. You can’t “catch” Pestivirus and become a PI - PIs are born.
Once a PI is in the herd, he exposes all of the “normal” (non-PI) animals to Pestivirus when he comes into contact with them for the first time. If this occurs early in life, during a non-stressful period, you probably won’t notice any issues – the exposed animals have a transient dip in their immune systems, get a bit of a “cold” and carry on to have natural antibodies and immunity to Pestivirus for many years.
However, if the PI comes into contact with naïve animals during a stressful period, for example on entry to a feedlot, or transiting via saleyards, that transient dip in their immune systems can lead to outbreaks of disease such as Bovine Respiratory Disease, the scours or pink eye.
Probably most damaging and spectacular is the effects if the PI comes into contact with naïve animals for the first time when they are pregnant. Depending on the stage of pregnancy, there is a range of outcomes including embryonic loss, abortion or creation of PIs.
Source: Zoetis Australia
So as a cattle producer, it’s worth knowing – is my herd in the 90% of farms with antibodies, or the dangerously exposed 10% of farms with no natural antibodies? The way to know is to blood test a sample of your females pre-joining.
That’s exactly what I’ve done on some farms in recent weeks, and the results are interesting.
On Farm 1, a sample of mixed origin animals showed 100% positive for antibodies. This means that there is no need to vaccinate, and we can rest easy knowing their future pregnancies will be protected.
On Farm 2, blood tests showed that the older animals had antibodies, however the younger heifers had no antibodies. This probably means the PI has died at some point, or is no longer on the farm and this has left the younger cohort of animals with no antibodies. This is a reproductive trainwreck waiting to happen, if a PI is inadvertently introduced to the mob, unless antibodies are provided to those younger animals using Pestigard vaccine prior to joining.
The moral of the story is, don’t guess when it comes to Pestivirus. Either blood test a few animals each year and make sure you’ve got natural immunity; or bite the bullet and vaccinate with Pestigard. Remember, if you choose to vaccinate you will need to continue this each year, religiously, as vaccination will stop the creation of PIs – meaning that without vaccination your herd will be immunonaive.
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