AHEAD IN ANIMAL HEALTH
Results of 15 years milk quality assurance for paratuberculosis in Dutch dairy herds Maarten F. Weber1,2, Marian Aalberts1, Thomas Dijkstra1 and Ynte H. Schukken1,2,3 1 Royal GD, Deventer, the Netherlands, m.weber@gdanimalhealth.com 2 Dept. of Population Health Sciences, Faculty of Veterinary Medicine, Utrecht University, the Netherlands 3 Quantitative Veterinary Epidemiology, Dept. of Animal Sciences, Wageningen University, the Netherlands
Introduction In 2006, a Milk Quality Assurance Programme (MQAP) for paratuberculosis in Dutch dairy herds was initiated to control Mycobacterium avium subsp. paratuberculosis (Map) in participating herds and reduce the concentration of Map in milk delivered to the milk processing industry. The aim of this study was to evaluate results achieved in a 15-year period (2006-2020) in 718 dairy herds that entered the MQAP in 2006 and 2007.
The MQAP A herd status is assigned based on the results of herd examinations. Each herd examination consists of testing individual milk samples of all lactating cattle by ELISA or serum samples of all cattle ≥ 3 years of age for antibodies against Map, followed by optional confirmatory faecal PCR assay. The initial assessment of participating herds consists of a single herd examination (Fig. 1). Test-negative herds enter a surveillance procedure and are assigned status A. The surveillance of status A herds consists of biennial herd examinations. Test-positive herds enter a control procedure and are assigned status B (if all testpositive cattle have been removed from the herd) or status C (otherwise) followed by annual herd examinations. If a herd examination in a status B herd yields negative results only, the herd progresses to status A.
Initial assessment ELISA once Suveillance
Control
Status A ELISA once / 2 yr
Status B or C ELISA once / yr
Fig. 1 Layout of the milk quality assurance programme
Results 2,5% 1,00%
Apparent prevalence
Apparent prevalence
2,0%
1,5%
1,0%
0,5%
0,50%
0,00%
0,0% 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
0
1
2
Fig. 2 A pparent prevalence at a cut-off S/P ratio of 1.00 in all age groups (511,287 samples from 717 herds)
Proportion of dairy herds
Survival (t)
Cattle born < 5 years before initial assessment of the herd Cattle born < 5 years after initial assessment of the herd
0,85 Cattle born 5 - 10 years after initial assessment of the herd
4
6
7
8
9
10
11
12
13
14
Status C
8
Age (year) Fig. 4 F itted survival curves showing the proportion of cattle that remained ELISA negative until a specific age in a subset of 136 Dutch dairy herds that were assigned status B or C at the initial assessment with at least 2% of the ELISA results in Year 0 having an S/P ≥ 1.0 (data of 47,492 cattle from 136 herds).
10
Status B
80%
60%
40%
Status A
20%
0%
0,8
2
6
100%
0,95
0
5
Fig. 3 A pparent prevalence at a cut-off S/P ratio of 1.00 in heifers tested for the first time at 2 years of age (116,141 samples from 713 herds)
Cattle born ≥ 10 years after initial assessment of the herd
0,9
4
Year after initial assessment
Year after initial assessment
1
3
Discussion and conclusion The observed decreasing apparent prevalence (Figs. 2 and 3), increased age at onset of ELISA-positivity in cattle born after the initial assessment (Fig. 4) and increased proportion of herds with status A (Fig. 5) are indicative of a reduced transmission of Map after long-lasting participation in the MQAP. The results of this study indicate that the MQAP positively contributes to the control of Map in the Dutch dairy herds.
0
2
4
6
8
10
12
14
Time after first herd examination (year) Fig. 5 A ssignment of 718 Dutch dairy herds to status A, B or C over time after the initial assessment.
m.weber@gdanimalhealth.com www.gdanimalhealth.com
GD2614/06-22