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 designed to demonstrate the value of “Utilising Heifer Pre-Mating Serology to Manage BVDV”.
The goal of the PDS is to demonstrate the value of understanding the immune status of a group of heifers prior to mating allowing involved producers to invest in the most cost effective intervention. Simply put, owners with a high proportion of immune heifers are encouraged to ear notch each heifer in order to identify and eliminate Persistently Infected (PI) heifers and those with a low proportion of immunity to BVDV are encouraged to vaccinate them instead.
The concept of the intervention is to assist producers to work towards herd level eradication and to allow them to simultaneously surveil for reintroduction.
32 individual producers surveyed their heifers in 2023, and 30 in 2024. Blood was collected from the tail vein of either 5% of the total number of heifers from each management group, or from a minimum of six animals. The blood samples were then screened for evidence of exposure to BVDV. As BVDV is almost exclusively transmitted by PI animals, evidence of exposure to BVDV indirectly indicates exposure to a PI. A group of animals with “high seroprevalence” would indicate that most of them have been exposed to BVD and have measurable immunity to the virus. “Low seroprevalence” would indicate that only a small proportion or none of the heifers have been exposed to the virus.
When serological results were reported back to individual producers, management advice was provided in line with recommendations from the Australian Cattle Veterinarian (ACV) Beef BVDV Management Guide.
The ACV BVDV Beef Guide suggests vaccinating groups of heifers with 0 to 50% seropositive animals within the sample population, to pursue further diagnostics between 50 and 80%, and to ear notch all of the heifers should the proportion of seropositive animals exceed 80%.
Remarkably, of the 62 individual groups of heifers surveyed over the first two years of the PDS, no results have led to advice to pursue further serological diagnostics, instead clearly directing the producer to either vaccinate or ear notch all of their replacement heifers.
In the final year, we hope to resurvey participating produces as well as enrol new producers. The goal is to encourage them to consider implementing the advice found within the ACV BVDV Guidelines. This advice will be tailored based on the serological results from their replacement heifers, helping both individual producers and potentially the entire district move closer to achieving BVDV freedom.
Pregnancy and calving data are also being collected and the results are quite interesting. It would appear that harbouring BVDV and potentially by choosing not to implement control measures could be associated with poorer production outcomes.
Pregnancy rates within individual heifer mating groups were compared taking into consideration their length of joining. It was assumed that 60% conception rate per 21 days was the maximum achievable pregnancy rate. In this sense, for a three week joining, 60% is “par”, 84% for a six week joining. Integration of fixed time artificial insemination (FTAI) was viewed as a single mating opportunity of one week’s duration. In this sense, “par” for cows enrolled in a FTAI program without bull back up would be 60%, and if backed up for one cycle, would be 84%. Essentially for each week of the first three weeks of joining to natural cover, 20% could be expected to fall pregnant, thereafter we would expect 8% per week for the following three weeks, and 3% per week for the third cycle. If AI’d, the first week would be apportioned 60%, the following three weeks 8% per week, then 3% thereafter. As an example, see Table A.
The pregnancy rate amongst the properties with high premating seroprevalence to BVDV were on average 12.1% lower than “par” at pregnancy testing. Further, within that group, those which chose to ear notch their heifers with the goal of removing any PI’s were on average 10% lower than “par” at pregnancy testing.Those who chose not to ear notch their heifers to remove PI’s were 18% lower than “par” at pregnancy testing.
The pregnancy rate amongst the properties with low premating seroprevalence to BVDV were 6.3% lower than “par” at pregnancy testing. Further within that group, those which chose to vaccinate were 2.6% lower than “par” vs. those which chose not to vaccinate who were on average 10.7% lower than “par”. (See Table B)
Calving data is still being collected.
Regardless, please get involved this year in this project! Your replacement heifers need to be in stable contact with each other for a minimum time of 2 months and must be at least 8 months old. By screening a small proportion (5% or a minimum of 6) we can direct you to the most cost effective intervention.
It is remarkable how low the apparent incidence of BVDV is within the Esperance district when compared to prior survey work done nationally and completed in the early 2000’s within our shire. The cost of blood testing is covered by the project and as a thank you for your involvement Zoetis is providing a free 100 ml packet of Pestigard. For more information contact Sarah or Enoch.
Contact:
Enoch Bergman, Swans Veterinary Services, (08) 9071 5777
Sarah Brown, ASHEEP & BEEF