Dr Enoch Bergman, Swans Veterinary Services
The Cattle Subcommittee of ASHEEP & BEEF is continuing to run three Meat & Livestock Australia Producer Demonstration Sites (PDSs) and you can still be involved.
Utilising Heifer Pre-Mating Serology to Manage BVDV is in its second year. Producers are provided free diagnostic testing to measure exposure to Bovine Viral Diarrhea (BVDV) within their heifers. Partly due to the tough season we have all been through, many producers did not retain heifers or were too busy feeding to organise blood testing. However, if you have mated heifers this year and haven’t screened yet you can still be involved. The project will cover blood testing your heifers at any stage up until preg testing, and if you missed out pre-joining, collecting blood samples at preg testing is a perfect opportunity.
Last year we screened 5% or a minimum of six heifers from 32 different properties around Esperance for evidence of exposure to BVDV. Historically, we had shown that 3/4 local farms had evidence of BVDV exposure with this methodology when screened in the early 2000’s. Remarkably, most of the properties (21 of 32) we screened last season showed zero exposure of their heifers to BVDV. That is almost two thirds of the properties surveyed! 22% (7 of the 32) had evidence of minor exposure, proving that a Persistently Infected (PI) animal was not present within the group of replacement heifers but that some of the heifers had been exposed previously (most likely from exposure from a steer or cull heifer prior to replacement selection or whilst still on their dams). Only 13% (4 of the 32) had evidence of strong exposure within the replacement heifer group, increasing our suspicion of finding a PI (Persistently Infected (Carrier) animal) within the group of replacement heifers. Three of those four properties chose to screen all of their heifers for PI’s by ear notch testing each of them, and on those three farms, a PI was found two thirds of the time.
BVDV is spread almost exclusively by these PI animals, which were in turn produced from having been exposed in utero to the virus. An animal whose mother is a PI or whose mother is exposed to BVDV (by contact with a PI) between one to four months of gestation will usually be born a PI. They can then go forth and complete the cycle again.
Meeting a PI for the first time can cause reproductive losses at any stage of pregnancy and can also seriously impair an animal’s immune system worsening other disease syndromes.
Some groups of heifers will contain a PI animal. That PI animal will eventually likely waste away and die, but in the meantime, she will transmit BVDV to every cow, calf, or bull she ever meets – potentially reducing their productivity. Within management groups where PIs exist, their sisters are usually highly immune by the time of joining, having already suffered the effects of exposure. However, she and any calf she produces will remain a threat to the next calf crop and to any other management group they should meet, especially if the management group they meet does not have pre-existing immunity itself. This is where Utilising Heifer Pre-Mating Serology to Manage BVDV comes in… which is the thrust of the PDS. By knowing the status of your heifers each year, you can implement the best strategy to break the PI cycle, whether that be vaccination or PI hunting.
As per the PDS, by screening 5% or a minimum of six heifers from your replacement heifer group each year prior to joining, you can ensure that you do not retain a PI replacement heifer and identify mobs which would benefit from vaccination with Pestigard. A true value proposition:
If they are already immune = there would be no benefit to vaccination, instead ear notch each heifer individually and cull any PI’s.
If they are not immune= good news… no PI… but vaccination would be worth considering!
If each of your heifer groups annually go forward PI free and immune, you will be able to get on top of any BVDV your property may be harbouring. Without PI animals, BVDV simply doesn’t propagate. By vaccinating groups without immunity, you will have insurance against the accidental reintroduction of a PI should you buy in animals or if a neighbour’s animal strays onto your property.
What does all of this mean? Well, surprisingly the PDS is demonstrating that many groups of heifers within the Esperance region have not been reared around PI animals showing that simple biosecurity and/or vaccination programs can help our individual farmers to progress towards, or ensure ongoing BVDV freedom. If everyone became involved, we could potentially eradicate BVDV from the Esperance area! We may already be well over halfway there! Regardless, it is completely achievable to eradicate BVDV from your own production system, monitor, and maintain that freedom. The key is annual heifer premating BVDV blood testing!
If you haven’t already screened your heifers, make sure to get on board at pregnancy testing! The PDS will cover all diagnostic costs and you will also score a free pack of Pestigard from Zoetis.
Thank you to Meat & Livestock Australia, IDEXX laboratories, and Zoetis Animal Health for their support of this project.
Cheers!
Enoch, Katie, ASHEEP & BEEF, and the Swans Veterinary Services Team
Contact Swans Veterinary Services: 08 9071 5777, admin@swansvet.com
