Scottish Bovine Viral Diarrhoea eradication scheme: consultation on phase five responses

Proposal 4 - Amendment to improve effectiveness of the check test

When implemented correctly, BVD check testing is acknowledged as being an extremely sensitive and reliable indicator of BVD exposure in the herd. However, effective check testing relies on the selection of representative cattle for antibody testing.

In the current BVD Order, the standard check test requires sampling of 5 animals per management group. A "management group" is defined as animals that have been housed or grazed together for at least the past two months. Thus larger herds would be expected to have several different "management groups" and therefore would need to check test multiple sets of 5 animals. However, some larger herds are check tested using 5 animals only. This approach runs the risk of missing BVD exposure through being unrepresentative of the herd, and therefore giving a herd a BVD negative status when, in fact, there is a disease risk.

We sought views on amending the current check test. One possibility was to increase the number of samples submitted for a check test to a number equivalent to at least 10% of the number of calves born on that holding in the past 12 months, in addition to meeting the requirement for sampling 5 animals from each management group (10 animals in the case of the dairy check test).

Question 14(a): Do you think that the check test should be amended to make it more effective?

73% of respondents agreed with the proposal to amend the check test to make it more effective, while 17% disagreed and 9% were unsure if the check test should be amended.

Figure 14: Do you agree that the check test should be amended to make it more effective?

89% of respondents provided comments on this proposal. Those that agreed with the proposal thought that an increase to testing a number of eligible animals equivalent to at least 10% of the number of calves born in 12 months would be reasonable and could encourage farmers to be more conscientious about identifying all management groups which have been together for at least 2 months. One respondent pointed out that it could result in a more thorough check test but we need to be aware it could cause a backlash from increased costs due to additional testing. Several respondents also felt that increasing the number of animals to be tested might help in situations where it is difficult for a vet to be sure of the number of management groups on the farm and of how long the eligible cattle have been kept together.

Respondents emphasised that more should be done to educate farmers and vets on the significance of the group size in providing a reliable epidemiological survey. This view was echoed by several respondents who felt the current check test was fit for purpose. They stressed that the critical point is to test each management group; if the disease is present in the herd, sampling 5 animals from each management group will find it.

A number of respondents felt that farmers should only be allowed to tissue tag all calves at birth, removing the option to set a herds status via the check test.

The respondents who were undecided about amending the check test were of the opinion that more scientific evidence was needed to justify this proposal. They felt that more emphasis should be placed on implementing the existing check test correctly in order to determine the herd status accurately. Respondents pointed out the need for training and knowledge exchange to achieve this.

Question 14(b): Do you think that increasing the minimum number of samples taken at a check test would result in a more robust test?

Around two thirds of respondents, (67%), agreed that increasing the minimum number of samples at a check test would make it a more robust test. 17% of respondents disagreed and 13% were unsure.

Figure 15: Do you agree that increasing the number of samples taken at a check test would result in a more robust test?

64% of respondents gave an explanation to their answer for this question.

The majority of those who agreed with the proposal to increase the minimum number of check test samples thought that this approach would be more likely to find antibody positive animals and would reduce the risk of management groups being ignored or missed. However, one respondent pointed out that increasing the minimum number of samples will reduce the test specificity, i.e. will increase the number of false positives, and would therefore give disadvantages as well as benefits. Another respondent commented that any increase in sample size must be balanced against the cost benefit to the scheme and the potential reduction in compliance of the farming community.

Those that disagreed with the proposal or were unsure generally agreed that the current check test works well. As with the previous question, most respondents were keen to point out that it is more important that every management group be tested properly than to increase the statutory minimum number of samples.