Antibodies against Dictyocaulus viviparus major sperm protein in bulk tank milk: Association with clinical appearance, herd management and milk production.

The objective of this study was to conduct a comprehensive field survey using a Dictyocaulus viviparus major sperm protein ELISA on bulk tank milk samples from Belgian dairy herds to gain insights in: (1) the sensitivity (Se) and specificity (Sp) of the test under field conditions; (2) the value of the test to predict a future clinical lungworm outbreak; (3) its associations with milk production parameters and (4) its associations with herd management factors. A total of 1248 herds were sampled, with samplings occurring in the middle ("August") and towards the end ("October") of the grazing season. A completed questionnaire on potential risk factors and potentially lungworm-induced clinical signs was obtained from 587 farms and milk production records could be obtained from 343 herds. The median (25th-75th percentile) D. viviparus antibody level (ODR) was 0.25 (0.19-0.31) in "August" and 0.24 (0.19-0.32) in "October". At a threshold of 0.41 ODR, the Se and Sp were estimated using mixture models at 50 and 99%, respectively. At the same threshold, the positive and negative predictive value of the ELISA applied in "August" on the occurrence of farmer-reported lungworm symptoms in the period August-November were 65% and 69%, respectively. D. viviparus antibody levels were significantly higher in the north vs. the south of the country, in large herds and in herds that did not mow pastures or that frequently purchased new animals. An increase in the ELISA result of "August" over the interquartile range was associated with a drop in the annual average milk yield, milk protein% and milk fat% of -0.50kgcow-1day-1, 0.02 and 0.02, respectively. The relationships between the ELISA results in "October" and milk production parameters were also negative, but lower and non- or only marginally significant. We conclude that the bulk tank milk ELISA has a low value to predict lungworm disease on an individual farm based on a fixed sampling date in the middle of the grazing season. On the other hand, the test has been potential to detect subclinical production impacts and study risk factors through epidemiological surveys. Copyright Â