Since the beginning of the compulsory phase of the BVD eradication programme, over 2 million samples have been tested. Of these, 98.05% were negative, 0.77% positive,
0.03% inconclusive and 1.12% empty on initial sampling (as of 16th September 2013). Overall 97.8% of all calves registered in 2013 have been tested.
If testing has identified persistently infected (PI) animals on your farm – it is important they are culled from the herd immediately.
* While ‘apparently healthy’ at birth, PI animals typically do not thrive, with the majority dying from scour or pneumonia within 6 to 18 months and before reaching a saleable weight.
* PI animals shed very high levels of virus and are the main source of infection for other animals, as all bodily fluids contain virus that can be transmitted either directly (e.g. nose to nose) or indirect-ly (e.g. on hands, clothing, boots) within and between herds.
* Transmission of virus in this way can cause significant problems in other calves. Even more important-ly, it may create further PI calves through infection of pregnant heifers and cows which will not be detected until the following calving season.
Approximately 40% of dairy herds and 10% of beef herds currently vaccinate against BVD virus. Once the national programme has been success-fully completed and BVD eradicated there will no longer be a routine need for vaccination. Maintaining the current momentum and compliance levels of the programme will hasten successful eradication of BVD, and equally shorten the period for which provision for vaccination is required.
However, while testing is on-going, adequate biosecurity measures to prevent the accidental introduction (bio-exclusion) and spread (biocontainment) of infection in herds is critical. Currently, the main reason to vaccinate for BVD is to provide a protective immunity in breeding animals to avoid negative impacts on reproduction (e.g. failure to conceive, abortion, birth defects) and most importantly, the creation of PI calves. As the programme progresses, the prevalence of PI animals will decrease, followed by a decrease in the number of animals with natural immunity. This means the likelihood of pregnant cattle being exposed to virus will decrease, but the potential damaging impact of exposure to BVD would increase. In the absence of natural immunity arising from infection, vaccination may be used as an alternative means of inducing immunity during this period. Vaccination acts as a protective measure should a breakdown in biosecurity occur.
However, note that the available BVD vaccines will not provide 100% protection in all circumstances, even when stored and used correctly, particularly where pregnant cattle are exposed to high levels of BVD virus.
Decisions on the use of BVD vaccine, including when to stop a vaccination programme should be taken by each farmer in discussion with their own veterinary practitioner. Key factors for consideration include the likelihood of introduction of infection. Introduced animals are the single biggest risk, particularly in the first year of the programme when the majority of older animals traded will not have been tested within the programme. The risks from other means of spread including direct contact (e.g. at boundaries, shows and sales) and indirect contact (e.g. contaminated environments, equipment, clothing or hands) should also be considered.
The BVD Implementation Group is currently finalising the requirements for herds to enter the monitoring phase after three years of tissue tag testing and the options for monitoring within this phase.
Two of the key criteria to be met for a herd to move into the monitoring phase will be:
1. The BVD test status of all animals in the herd must be known (on the basis of either ‘direct’ or ‘indirect’ results);
2. No transiently or persistently infected animals present in the herd in the 12 months preceding the transition to the monitoring phase.
These criteria will have immediate relevance to the farmers who entered the programme in the voluntary phase in 2012 and who are anticipating finishing tag testing in 2014. In particular, these herd-owners should be aware that any PI animals on their holdings will need to have been disposed of by the end of this year to enable the transition to the monitoring phase in January 2015.
Further information on the BVD programme is available on www.bvdfree.ie.