A couple of weeks ago we looked at the way Pestivirus carriers (“PIs”) are created, and the sorts of health issues they can have. But although PIs are often poorly doing animals, they aren’t really the biggest source of Pestivirus production loss. It’s the reproductive effects of Pestivirus which can be much more serious.
Pestivirus is a very common virus in cattle. Across Australia, we know that around 60-80% of cattle herds have the virus “circulating” to some extent. Last year I tested 8 local cattle herds and found that 6/8 (75%) had some level of Pestivirus exposure.
In most animals, Pestivirus infection causes mild illness, and may go unnoticed. In some situations however, it can cause abortions or the birth of deformed calves.
If Pestivirus is so common, why don’t we see more abortions caused by it? The main reason is that once a heifer or cow has been exposed to Pestivirus, they develop immunity and are therefore “protected” from future infection.
With Pestivirus, it’s all about timing. If a female is exposed before she is first joined, she’ll probably develop good immunity, so she won’t be at risk of losing a calf if exposed to Pestivirus again later, during joining or pregnancy.
However, if a heifer or cow is exposed to Pestivirus for the first time while pregnant, abortions can occur. The difference all comes down to whether or not she is already immune to the virus.
Natural exposure is one way for animals to develop immunity. But what about a mob of heifers who have never been naturally exposed to Pestvirus, and are therefore not protected? The solution in this case is vaccination.
Vaccination acts a bit like natural exposure. Vaccinating an animal for Pestivirus doesn’t give the animal the disease, but it does create temporary immunity, just like natural exposure.
You can see that, when it comes to Pestivirus, female cattle fall into one of three categories – immune (protected) due to natural exposure, immune (protected) due to vaccination, or non-immune (susceptible). It’s that last group where reproductive losses can occur.
Astute beef producers will at this point probably be asking: how do I know if my herd is naturally exposed (and therefore immune)? How do I know if I need to vaccinate?
Fortunately, a simple blood test is available which can tell us if an individual animal has been exposed to Pestivirus. A vet can develop a testing approach which will give you a pretty good picture of the herd’s overall immunity. In a mob of weaner heifers, for example, it might be as simple as testing 5% of animals.
Each producer will require a different approach to Pestivirus. Some should be vaccinating now but aren’t aware that they have a non-immune (susceptible) herd. Some won’t need to vaccinate now (because their herd is immune due to natural exposure), but they might benefit from finding and removing PIs.