BVDV free? Let’s keep you that way
- Dr Enoch Bergman, Swans Veterinary Services
- Mar 31
- 7 min read
Updated: 3 days ago
Dr Enoch Bergman, Swans Veterinary Services
We are entering into the third year of ASHEEP & BEEF’s Meat & Livestock Australia Producer Demonstration Site (PDS) project focusing on demonstrating the value of implementing “Annual Heifer Pre-Mating Screening for Exposure to BVDV (Bovine Pestivirus)”. Within the project, Swans Veterinary Services will collect blood samples from 5% or a minimum of 6 of your replacement heifers, preferably a couple of months prior to joining. Producers in the Esperance port zone are welcome to get involved. Read on to understand both the why and the how.
BVDV is the most economically significant infectious disease of cattle within the Esperance district in my opinion. If you don’t know your BVDV status, now is the time to find out. With assistance from MLA in funding this Producer Demonstration Site project, from IDEXX to subsidise the cost of testing, and with some free vaccine for participants from Zoetis, now is the perfect time to investigate BVDV within your herd.
The results from the PDS have been surprising so far! It appears that there is far less BVDV in the district than there had been historically. The results have shown that BVDV is controllable, that we can eradicate it at the individual herd level, and, if we work together, that we could eradicate or at least minimise it within the district, allowing us all to enjoy the benefits of BVDV freedom.
Almost 20 years ago, Swans Veterinary Services ran a project across Esperance in conjunction with the Department of Ag and Pfizer Animal Health (now DPIRD and Zoetis). On close to 150 properties across Esperance we collected samples from a small number of heifers or young cows and had the samples tested for exposure to BVDV, Lepto, Neospora, and Vibrio. From that survey work, 75% of the properties had evidence of exposure to BVDV at that time! Since then we have been working with individual producers to help them control BVDV, now thanks to this project, we can start helping you!
Over the last two years, as part of the PDS, we have been conducting free blood testing of replacement heifers for properties across Esperance and we are continuing to offer that free testing this year in what may be the final year of the project. Contact Sarah Brown or Swans Veterinary Services to take part.
By simply blood testing a small proportion of your replacement heifers, we can accurately identify groups of heifers that have been exposed to a PI (or wherein a PI still remains) vs. groups without any immunity to BVDV (conclusive proof that none of the replacement heifers are a PI). If a group of heifers has a PI within its numbers, it can be a serious risk to other management groups on your property and conversely if they have no immunity, should other management groups on your property still harbour a PI, they could be at risk. By screening your replacement heifers prior to joining, as is the thrust of this project, you can invest in the best strategy to progress towards BVDV freedom. By screening them annually, you will be in control of your properties BVD status and will be able to maintain BVDV freedom. Get involved!
Remarkably, of the properties surveyed in the first two years, the heifers tested on 63% of the properties yielded no antibodies to BVDV at all! This means that the heifers on well over half of the properties in Esperance had never met an animal persistently infected(PI) with BVDV and in most cases, those properties are likely to be BVDV free. Further, of the 62 properties screened, only 11 had evidence that one or more of the heifers could be a PI animal! The graph below shows the distribution of the percentage of heifers found to be immune to BVDV at screening within individual groups of heifers.
So what are the benefits of eradicating BVDV?
Exposure to an animal persistently infected with BVDV leads to transient infection with BVDV. Animals transiently infected with BVDV will suffer mild to severe immune suppression and potentially, reproductive losses, before recovering and developing immunity. The timing of exposure changes the outcome, from infertility, embryonic loss, abortion, congenital defects, or the production of another PI calf.
Analysing the raw data from the PDS’s survey work, pregnancy rates were lower than expected on properties which had heifers with evidence of past exposure to BVDV (Immunity, Seropositivity, Positive Blood Tests), and within the exposed properties, those which did not remove PI’s (ear notch) their heifers had the lowest pregnancy rates of all. Within the management groups without immunity to BVDV, properties which chose to vaccinate their heifers with Pestigard had better pregnancy rates than those which did not vaccinate.
Mother natures has made the last two years difficult for joining heifers, so pregnancy rates were lower across all groups. The differences in pregnancy rates between groups were expressed as variance from “par” working on a 60% pregnancy rate per joining opportunity. As an example, heifers joined for six weeks are expected to achieve 60% plus 60% of the remaining 40% (24%) for a total expected (par) pregnancy rate of 84%. In this way, properties with 9 week vs. 3 week joinings could be compared. The raw numbers and a graph are expressed below, combining data from both year 1 and 2.
Marking rates garnered from survey work told a similar story. Marking rates from properties with evidence of exposure were 93.2% vs. 94.2% amongst those without evidence of exposure. Within the properties with evidence of exposure, those which chose to remove PI animals by ear notch testing all of their heifers enjoyed a 96% marking rate vs. 88% from those which did not hunt their PI heifers. Within the unexposed groups vaccination survey results only showed a small difference.
How is BVDV propagated within and between individual production systems and how can we go about controlling it cost effectively?
BVDV is propagated almost exclusively by Persistently Infected (PI) animals. PI’s were infected with the BVDV virus whilst still in utero, and their developing immune system mistakenly believes the virus to be “self”. Because PIs are “immuno-tolerant” to BVDV, they never clear the infection and shed enormous amounts of the virus into the environment for their entire, typically shortened, lives.
If a PI survives to breeding age, if she produces a calf, it will invariably be born a PI. However, most PI’s are actually born when a PI meets a pregnant animal. If the pregnant animal which met the PI is at the right stage of gestation, if the foetus is not aborted, and if the dam herself lacks prior immunity, the calf will go on to be born Persistently Infected itself. The cycle can then be repeated.
Controlling BVDV centres around identifying and removing PI animals, providing immunity to animals without prior exposure to the virus, and simple biosecurity steps.
Paramount to controlling BVDV is screening replacement heifers prior to their first joining to define their specific “BVDV Risk”. Heifers can then be optimally managed to ensure they are mated both immune and PI free.
The Australian Cattle Veterinarians, a special interest group of the Australian Veterinary Association developed a set of guidelines for the management of BVDV within Beef Herds. The charts in this document, and the strategies employed within the PDS are based upon that document.
By blood testing 5% or a minimum of six animals from each management group of replacement heifers (having been in constant contact for at least two months and being at least 8 months of age), producers can accurately predict which management groups contain PI animals (representing a threat to other management groups) and which management groups have poor pre-existing immunity (other management groups represent a threat to them).
If over 80% of the animals screened have evidence of exposure to the virus, the entire management group is more likely to contain one or more PI animals. Vaccination would be of little benefit, however, by ear notching each individual heifer (collecting a small bit of ear tissue like an ear mark), all PI heifers could be identified and culled prior to mating.
If less than 50% of the animals screened have evidence of exposure to the virus, the entire management group is unlikely to contain a PI, and vaccination would instead be a better investment.
If the seroprevalence falls between 50 and 80%, further veterinary investigation is warranted.
Producers who consistently annually screen their heifer prior to mating for exposure to BVDV can then invest in the most effective BVDV intervention strategy. By ear notching the immune groups and vaccinating the groups without immunity, each producer can ensure that each new group of heifers they produce will go into their first mating both immune and PI free.
By implementing screening annually, producers can ensure their entire breeding population becomes immune and PI free. In this way, herd level eradication of BVDV is both feasible and achievable.
Following the guidelines developed by the Australia Cattle Veterinarians, 18% of the properties had evidence of prolonged exposure to a PI, resulting in a recommendation to ear notch each replacement heifer to diagnose any PI heifers. The other 82% of the properties were advised to consider vaccination.
Globally BVDV is considered one of the most economically important diseases of beef and dairy cattle. Simultaneously, the tests developed to control it are remarkably accurate and easy to sample for. Numerous countries overseas have eradicated BVDV successfully, and many more are under way. Controlling it at your own herd level relies upon understanding the “risk” within your breeding population. As PI’s tend to die out over time, replacement heifers represent the perfect management group to target for control of BVDV. If we are able to ensure that no PI is allowed to be retained as a replacement heifer, and further if we shore up immunity to BVDV where beneficial, we can begin to control BVDV, instead of leaving its control to chance. Get involved in the PDS to better understand Bovine Viral Diarrhea and your herd’s BVDV options.
Useful BVDV resources:
Cattle production webinar recording covering progress on BVDV, bull breakdown and weaning PDS projects (Get the latest progress on our 3 cattle focused Meat & Livestock Australia Producer Demonstration Sites on weaning, BVDV & bull breakdown. Talking us through the projects is vet Dr Enoch Bergman with producers Simon Fowler, Ryan Willing, Nick Ruddenklau.)
BVDV blood testing video Dr Enoch Bergman takes us through the process of taking blood tests for BVDV.
BVDV discussion video Dr Enoch Bergman chats BVDV with vet students.
For more information on ASHEEP & BEEF’s BVDV PDS visit the project page on our website.
