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Table 2 Parameters and values used for a high impact and low impact Schmallenberg virus disease scenario

From: Application of integrated production and economic models to estimate the impact of Schmallenberg virus for various beef suckler production systems in France and the United Kingdom

Parameters

Scenario 1 High impact

Scenario 2 Low impact

References

Reasoning

Number of calves stillborn or malformed due to SBV out of 100 calves born

1-10 most likely = 2

0-1 most likely = 1

[15] and expert opinion

Martinelle et al. 2012 [15]: median SBV morbidity rate in calves was 2% ; the minimum reported by Martinelle et al.[15] was taken as the lower range value and the median value plus one standard deviation as the upper range value.

Number of cows with dystocia out of 100 cows giving birth to a stillborn or malformed calf due to SBV

30

[16],[17] and expert opinion

Baseline dystocia rates in UK are 6.9% in heifers and 2% in cows with abnormal presentations being the cause in 19.8% on average. With an increased proportion of malformations, dystocia rate was assumed to be higher.

Number of cows that need caesarean out of 100 cows with dystocia due to SBV

5-7 most likely = 6

[18],[19] and expert opinion

The proportion of caesareans conducted in the case of dystocia was reported to be between 5 and 7%.

Number of cows with clinical episodes due to SBV out of 100 cows in a herd

3-31 most likely = 7.5

0

[15] and expert opinion

Martinelle et al. 2012 [15]: Median SBV morbidity rate in cattle was 7.5%. The minimum reported by Martinelle et al.[15] was taken as the lower range value and the median value plus one standard deviation as the upper range value.

Number of cows that require treatment out of 100 cows with clinical episodes due to SBV

10

Expert opinion

This figure reflects the regular need for treatment of beef sucklers in the UK presented with unspecific diarrhoea, fever, general depression and/or inappetence.

Number of cows with SBV abortions out of 100 cows in a herd

0-2 most likely = 2

0-1 most likely = 1

Expert opinion

The proportion of abortions due to SBV is uncertain (lack of studies). Experts agreed on these approximated figures based on abortion rates seen in other diseases.

Probability of an aborted foetuses, stillborn, malformed and calves culled to be tested for SBV

0.05

Expert opinion

Investigation of abortions is recommended if incidence >3% in a herd per year or if several abortions occur in quick succession (http://www.defra.gov.uk/ahvla-en/files/pub-cattle-abortion.pdf). Due to the absence of "abortion storms" due to SBV and farmers suspecting the disease, it is assumed that only a small proportion submit aborted foetuses, stillborn or malformed calves to be tested for SBV.

Number of cows that die due to calving difficulties out of 100 cows with dystocia

10

[17],[18] and expert opinion

Day and Meijering report mortality rate due to dystocia as 3.5% on average, and 16.7% for a clinical case observation. Given that SBV causes malformations, the mortality rate is assumed to be on higher than the reported average.

Number of aborted cows that will need to be replaced out of 100 cows with abortions

10

Expert opinion

It was assumed that only in a small proportion of cows the reproductive system will be affected such that the cow is not able to breed anymore and will therefore be replaced.