AHEAD IN ANIMAL HEALTH
Risk factor analysis of introduction of BVDV into previously BVDV-free herds in the Netherlands L. van Duijn, A. Veldhuis, M. Mars, P. Wever, G. van Schaik Royal GD, Deventer, The Netherlands
Objective A voluntary BVDV-programme was available in the Netherlands since 1997. In 2016, 37% of dairy herds and 6% of beef farms were BVDVfree. Since the start of the programme the BVDV prevalence is declining but yearly a smal proportion of BVDV-free herds experience an outbreak (approximately 4% in 2016). The objective of the study was to quantify risk factors for introduction of BVDV in previously BVDVfree Dutch cattle herds. Background Study population and BVDV-programme: in 2016 there were approximately 18.000 dairy herds and 18.000 non-dairy herds in the Netherlands. The BVDV-free programme is based on whole herd screening for BVD virus and removal of the persistently infected (PI) animals, all newborn calves are tested for BVD virus for a period of ten months. PI animals need to be removed. The free status is monitored with biannual Figure.
testing of young stock for antibodies or virus testing of the newborn calves. If virus is found in 1 or more animals, or 3 or more animals are antibody positive the herd has a breakdown. Cattle from non-BVDV-free herds that are introduced into the herd need to be tested for virus with an AG-ELISA.
Methods Herds that were BVDV-free between September 2006 and
Results of multivariable logistic regression analysis of risk factors for a breakdown in BVDV-free herds (Note: in the figure purchase means purchase of pregnant cattle) Non-BVDV-free neighbours are a risk factor for a breakdown in a BVDV-free herd
Month−year of breakdown # free neighbours (dairy)
Main Effects
June 2016 were selected. Herds with a breakdown (case herds) were matched with herds without a breakdown (control herds) by month in which the BVDV-free status was obtained. Multivariable logistic regression analyses were conducted on identification and registration data at herd level to describe the relationship between potential risk factors and a breakdown in previously BVDV-free herds.
# non−free neighbours (dairy) # free neighbours (non−dairy) # non−free neighbours (non−dairy) Presence of sheep No
Presence of sheep is not a risk factor for a breakdown in a BVDV-free herd
Yes
Herd size*Purchase (3x3): Small herd, no purchase (REFERENCE)
Interaction Effects
Small herd, purchase from free herds only Small herd, purchase from non−free herds Medium herd, no purchase Medium herd, purchase from free herds onl
Purchase of pregnant cattle and herd size are a risk factor for a breakdown in a BVDV-free herd
Medium herd, purchase from non−free herds Large herd, no purchase Large herd, purchase from free herds only Large herd, purchase from non−free herds 0
.5
1
1. 5
2
2. 5
3
Odds ratio
Conclusion The odds of an introduction of BVDV into a previously BVDV-free herd increased with the number of non-BVDV-free neighbouring herds, herd size and purchase of pregnant cows. The spatial risk factors had the strongest association with the risk of a BVD breakdown (neighbouring dairy herds posed a larger risk than neighbouring non-dairy herds). The presence of sheep on a farm did not increase the risk of a breakdown. These results stress the importance of national control efforts to further reduce the BVDV incidence in the Netherlands.
l.v.duijn@gdanimalhealth.com www.gdanimalhealth.com
GD2017/08-19