Presence of Ostertagia ostertagi antibodies in bulk tank milk from cattle herds in northern Spain

The objective of this survey was to investigate the Ostertagia ostertagi infection status of cattle dairy herds from northern Spain through measurement of antibody concentration in the bulk tank milk (BTM). In addition, management and performance data were collected to determine possible relationships with BTM O. ostertagi antibody levels. BTM samples were collected in 118 dairy cattle farms from five northern Spain Autonomic Communities in the autumn of 2009 and spring of 2010. The O. ostertagi antibody levels in milk were determined using a commercial ELISA kit (Svanovir®) and farm management information included type and farm size, production level, access to pasture, grazing regime and anthelmintic treatments. The overall mean optical density ratio (ODR) values of the two sampling times ranged from 0.60 (0.08-1.32) in autumn to 0.56 (0.05-1.24) in spring and no seasonal differences were detected. Herds with access to pasture showed significantly higher titers of O. ostertagi antibodies in milk (mean ODR = 0.69-0.63) than in those without access (mean ODR = 0.36-0.33). The association analyses showed significant correlations between the BTM O. ostertagi ODR and location (Navarra showed the highest ODR values), herd size (ODR decreased with increased herd size), milk production level (ODR negatively associated with milk yield), calves access to pasture (higher ODR when calves <12 months had access to pasture), outside access (no access low ODR, access high ODR) and grazing management (ODR increased proportionally to the percentage of time spent grazing each day). This study emphasizes that O. ostertagi-induced production losses should be considered on dairy farms in northern Spain. Additionally, putative risk-factors should be also considered for preventive measures.