Antibodies to major pasture borne helminth infections in bulk-tank milk samples from organic and nearby conventional dairy herds in south-central Sweden.

The objective of this randomised pairwise survey was to compare the regional distribution of antibody levels against the three most important helminth infections in organic and conventional dairy herds in Sweden. Bulk-tank milk from 105 organic farms and 105 neighbouring conventional dairy farms with access to pasture in south-central Sweden were collected in September 2008. Samples were also collected from 8 organic and 8 conventional herds located in a much more restricted area, on the same as well as 3 additional occasions during the grazing season, to reveal evidence for seasonal patterns against cattle stomach worm (Ostertagia ostertagi). Antibody levels to the stomach worm (O. ostertagi), liver fluke (Fasciola hepatica) and lungworm (Dictyocaulus viviparus) were then determined by detection of specific antibodies using three different enzyme-linked immunosorbent assays (ELISAs). According to the Svanovir Ostertagia ELISA, the mean optical density ratio (ODR) was significantly higher in the milk from organic compared to conventional herds, i.e. 0.82 (95% CL=0.78-0.86) versus 0.66 (0.61-0.71). However, no significant differences were observed in the samples collected at different time points from the same 16 herds (F(3,39)=1.18, P=0.32). Antibodies to D. viviparus infection were diagnosed with an ELISA based on recombinant major sperm protein (MSP), and seropositivity was found in 21 (18%) of the 113 organic herds and 11 (9%) of the 113 conventional herds. The seroprevalence of D. viviparus was somewhat higher in the organic herds (Chi-square=3.65, P=0.056), but with the positive conventional herds were located in the vicinity of infected organic herds. Of the 16 herds that were sampled on repeated occasions, as many as 10 (63%), were seropositive on at least one sampling occasion. Many of these turned positive towards the end of the grazing season. Only one herd was positive in all 4 samples and 3 were positive only at turn-out. Considering F. hepatica there was no difference in seroprevalence between organic and conventional herds according to the Institute Pourquier ELISA. In general, liver fluke infection was low and it was only diagnosed in 8 (7%) organic and 7 (6%) conventional herds.