Courtesy of the Coolah Veterinary Clinic
September is the month for:
· Bull Testing
· Vibrio Vaccination of Bulls
· Trisolfen Purchases
· Mare Pre-breeding Examinations
BULLS AND PESTIVIRUS
Nowadays at a lot of bull sales the vendors will describe some of the presale protocols they undertake with regards to Pestivirus. This has lead to a lot of confusion from buyers so we shall try to explain what they all mean.
Many bull sales undergo the Zoetis Five Star Program. This means the bulls have been vaccinated against:-
Leptopsporosis and Clostridial Disease (7 in 1 Vaccine)
Vibriosis (Vibrio Vaccine)
Pestivirus or Bovine Viral Diarrohea (Pestigard Vaccine)
And the bulls have been tested for:-
Negative for the Persistently Infected (PI) or Carrier state of Pestivirus
In this discussion we are going to concentrate on the last two procedures regarding Pestivirus.
We shall start with the last procedure first.
Confirming that a bull is NOT a persistently infected animal is very important. Any PI animal basically has bovine AIDS, meaning a non existent immune system. This means that PI animals will generally die out due to some secondary disease and depending on the stresses put on the animal it may occur at various ages. It used to be thought that most PI animals will die out before the age of two. However a significant proportion of PI’s may survive to an older age and be hidden in your mature herd.
The eventual demise of a PI is not the only concern of this status. PI’s are also carriers or shedders of virus meaning they will spread the disease to naive (unexposed animals) which is further complicated if the naive animals are pregnant.
If a PI is exposed to a pregnant naive animal:-
-in the first 30 days of pregnancy it may undergo early embryonic loss
-from day 30-120 the resulting calf born will be a PI
-from day 120 till term an abortion, stillborn, deformed or normal calf may be produced.
A PI bull will shed the virus in its semen which means often they have suboptimal fertility semen and they may lead to PI calves being produced.
In our district a lot of the effects of Pestivirus are self limiting. This means the disease is present in nearly all our herds, leading to regular PI production and subsequent exposure happening within the herd.
If we had a situation where we had a naive herd or a naive management group on your farm and suddenly a PI bull was introduced the Pest virus train wrecks you have herd about may occur. In a number of herds the purchase of bulls are the only introductions that may occur on a farm.
In investigating a lot of reproductive failures we have occasionally incriminated Pestvirus as the cause. Where we have seen Pestivirus involvement, in hindsight, we have shown that often introduced animals may have come onto the farm in a naive state and lead to exposure of pestivirus occurring. This is commonly a problem where people buy in PTIC heifers which happened to be naive.
In summary buying in a bull that has been tested free of the PI status is a good idea. Further to this if your bulls at home now have not been tested it is advisable to test them. Once confirmed free they are free for life meaning they only need to be tested once. We are able to collect an ear notch and test them at the clinic giving you an answer in about twenty minutes.
The use of the of Pestigard vaccine is to ensure that if the bull by chance is naive it will be protected against coming into contact with a PI at it’s new home. This is again an example of movement of cattle to new surroundings where the Pestivirus status may be completely different to what the animal had previously experienced.
Whether you continue vaccinating your bulls on an annual basis after this is a decision for the individual. It does not mean you are committed to annual vaccinating as a lot of people will not continue to vaccinate and this is not a wrong decision.
-buying PI negative tested bulls is a good idea.
-testing any current bulls on farm to ensure they are PI free is another good idea
-testing young introduced stock onto your place ie PTIC heifers to see their exposure level is a good idea
-getting idea of current Pestivirus activity on you farm by bleeding a group of heifers, first calvers and mature cows is a good idea if you are considering vaccinating with Pestigard.
Pestivirus is a very complicated disease with many different and fluctuating management options please free to talk to use regarding options you can implement on your farm.