The bovine viral diarrhoea or BVD eradication programme was introduced in a voluntary capacity in January 2012, followed by a compulsory phase of the programme, which started on 1 January 2013. The initial aim of the programme was to eradicate BVD from Irish farms through a combination of three years of compulsory calf testing (for farmers who did not partake in the voluntary phase) followed by three years of herd monitoring.

After a highly successful voluntary phase, in which over 450,000 calves were tested, and impressive results in reducing the prevalence on farms, as detailed in Table 1, the programme is facing some challenges in getting all persistently infected (PI) animals removed. We spoke with Animal Health Ireland (AHI) to get its views on the future of the programme and ask if plans are still on track to eradicate the disease.

The reduction of over 30% in the number of PI calves from 13,955 in 2013 to 9,604 in 2014 shows impressive improvement. However, it is worrying to note that 1,194 PI calves born in 2013 have been retained in 789 herds, with a further 2,064 PI calves born in 2014 also retained. If the retention of PI calves is not addressed, will the programme be able to stay on track to move to a herd monitoring phase?

The retention of PI calves is a cause of significant concern to the cross-industry BVD Implementation Group (BVDIG) that oversees the programme. In the absence of the current programme, the results suggest that about 28,000 unidentified PI calves would have been born in 2013 and 2014, and would have been able to move freely between herds. Against this baseline, it is clear that significant progress has indeed been made, with the majority of PI calves identified having been removed and those which remain on farm being subject to movement restriction.

Despite this good progress, the retention of PI calves by a minority of herd owners presents a clear threat to the rate of progress. The BVDIG has consistently communicated the reasons why PI animals should not be retained.

The rate of removal of PI calves has been better in 2014 than in 2013, and it is a key goal of all members of the BVDIG to improve this further in 2015 to ensure continued progress.

According to your website, the percentage of PI calves was 0.67% in 2013 and this fell to 0.46% in 2014. Was AHI expecting these figures, and where does AHI see the percentage of BVD animals in 2015 and 2016?

This represents a reduction of about one-third in the number of PI calves born, and marks significant progress. However, it is probable that even greater progress could have been made if certain additional actions had been consistently implemented. These include the prompt removal of all PI calves and testing of dams, the performance of wider herd investigations, where indicated, and the putting in place of appropriate biosecurity measures to prevent accidental introduction of infection. Most of the PI calves that will be born in 2015 are already in utero (cows already pregnant), so there is little opportunity at this stage to influence these figures for the current year (with the exception of autumn-calving herds). The primary focus should already be on taking all possible steps to minimize the number of PI calves born in 2016 by implementing the measures mentioned above. Given that these factors are largely beyond the control of AHI, it is difficult to predict the prevalence figure that can be achieved in 2015. However, the herds that entered the programme in 2014 had an overall prevalence in 2014 of 0.26%. While these herds are not necessarily representative of the national herd, they do give a pointer for the prevalence in 2015 for those herds that are entering their third year of testing. The technical working group (TWG) of AHI is undertaking a detailed modelling exercise which will provide estimates for 2016 and beyond, taking into account factors including the retention of PI calves.

Also, according to your website, the percentage of infected herds fell from 11.3% in 2013 to 7.5% in 2014. Is this within targets set for the first two years of compulsory tagging?

The reduction by one-third in the number of herds with positive calves between 2013 and 2014 is in line with the reduction in prevalence at the animal level and we would expect to see the herd-level prevalence continue to fall in line with the results from individual animal testing.

In your opinion, will it be possible to eradicate BVD from the country while PIs are retained in herds?

By definition, BVD will not have been eradicated while some herds are holding on to PI animals. From a practical perspective, the retention of PI calves will slow the rate of progress of the programme and result in a delay in eradication being achieved.

Why do you think some farmers have held on to PIs? Has AHI any strategy to encourage more farmers to dispose of their PIs?

Though not the case in every county, most PI animals retained are in beef herds. Reasons for retention may vary. In beef herds, where the calf represents the only income from the heifer or cow, farmers may seek to obtain some financial return by attempting to fatten the animals. This may be tempting, particularly where the calf appears healthy at birth, but both international and national experience indicates that this is the wrong decision not only for the individual farmer but also for the national goal of eradication.

AHI, in conjunction with CVERA, has undertaken research that provides clear evidence of the importance of removal of PI calves. Each herd owner with a positive calf is also written to and advised to cull it. During 2014, the Department of Agriculture introduced revised financial incentives for the removal of PIs and also made their removal a condition of payments under the Beef Genomic Scheme. Both of these measures are credited with contributing to the increased rate of removal of PIs in 2014. The Department is expected to shortly announce the measures and supports that it will introduce in 2015 to support the programme and it is hoped that these will provide further encouragement for the removal of PIs.

Have many farmers failed to engage with the programme by testing their calves? What is being done to force them to participate?

Overall, the level of engagement with the programme by farmers has been exemplary. Of the 2.1 million calves registered in 2013, 99.6% have been tested, with most of those untested being dead. Analysis of results for 2014 indicate that a similar level of compliance will again be achieved. Against this background, it is unfortunate that a very small number of farmers have not yet taken part, with no results having been received to date from 99 herds that registered calves in 2013. These are typically small herds, with a total of 551 calves. The Department is currently following up these herds to ensure they understand what is required of them. In the meantime, they remain unable to move animals born after January 2013 until a negative result is recorded for them.

If a herd retains a PI animal, will compulsory tag-testing continue beyond the planned three-year (four years for farmers in the voluntary phase) testing phase?

As already described, herds that retain PI animals run the risk of producing further PI calves in the following calving season. It is therefore essential that all calves born the following year are also tagged and tested to ensure that any PI calves are detected and removed. The BVDIG is still discussing the impact that retention of PI calves will have on monitoring options beyond the first three years of the programme.

What percentage of herds that had PI calves in 2014 did not have any in 2013?

Data to answer this question will be available in the next month.

When does AHI expect to have BVD eradicated?

The AHI Strategic Plan for 2012-14 set the target of eradication by 2020. This target has been carried forward into the strategic plan for 2015-2017, by the end of which period we would hope to be dealing with mopping up a very small number of cases.

There is a perception on some farms that have undertaken three years of testing that there is now no risk of BVD and vaccination is no longer required. However, is it the case as more herds become naive that there could be a greater risk of an outbreak if PI animals come in contact with these herds? What is AHI’s recommendation on vaccinating for BVD?

As the programme progresses, the prevalence of PI animals is decreasing, followed by a decrease in the prevalence of animals with natural immunity following exposure. On the one hand, this means that the likelihood of pregnant cattle being exposed to BVD virus will decrease. But on the other hand, the potential negative impact of such exposure 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, it should be noted 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, are herd-specific and 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. These include Trojan animals (non-PI dams carrying PI calves), and the BVD TWG will shortly issue guidance on minimising the risk of introduction through the purchase of Trojan animals. The risks from other means of spread including direct contact (eg at boundaries, shows and sales) and indirect contact (eg contaminated environments, equipment, clothing or hands) should also be considered.

What was the total number of herds participating in the voluntary phase in 2012 and how many herds successfully completed the voluntary testing phase?

Approximately 7,300 herds took part in the voluntary phase of the programme in 2012 and are now in their fourth year of testing. These herds are eligible to acquire Negative Herd Status (NHS) from 1 January 2015 on, subject to them satisfying the following two conditions. Firstly, that all animals in the herd have a recorded negative status (either directly, as a result of testing or indirectly through their having produced one or more negative calves). Secondly, the absence of any PI animals from the herd in the preceding 12 months (either born in 2014 or retained from previous years). To date, approximately 4,200 herds have qualified for NHS, with most of the remainder (about 2,400) requiring test results for a small number of animals (typically one to three) to also qualify. To maintain NHS, herds must continue to satisfy the qualifying requirements, including the testing of any added animals of unknown status.

For 2015, tag testing of all newborn calves will be the only method used for monitoring NHS herds. This testing is being made available at a reduced cost (currently about a 25% reduction) for those herds that have achieved NHS, compared to those that have not as yet achieved this status.

The decision to confine the monitoring options to tag testing in 2015 was based on the analysis of the results of the programme to date. Two factors in particular have contributed to this decision: firstly, the retention by a minority of herd owners of PI animals, and secondly, the spread of infection through the purchase of pregnant animals which, while not themselves PI, are carrying PI calves (Trojan animals).

Over the course of 2015, the BVD Implementation Group will communicate with herd owners regarding the availability of additional monitoring options for 2016, taking into account further progress in reducing the disease prevalence nationally. This would potentially take the form of blood samples from a limited number of young stock to check for evidence of exposure to BVD virus.

Will new entrants to suckling in 2015 be required to complete a longer testing phase?

A formal decision has not been taken on this yet. The assembly of a herd from multiple sources, potentially including pregnant animals, clearly carries risks in relation to BVD. On the other hand, the ability to purchase animals that already have a negative test result reduces this risk, particularly where animals come from herds that have achieved negative herd status.

As a buyer of cattle, will I have the same confidence that an animal I buy is BVD-free from a herd in the monitoring phase as an animal that has been tested free of BVD virus during the tagging phase?

During 2015, animals bought from a herd with NHS will typically provide the highest level of confidence, based on both animal- and herd-level results. Thereafter, decisions on the timing of introduction of alternate monitoring options will be taken to ensure a continued high level of confidence in relation to purchased animals.