Apparent prevalence of and risk factors for infection with Ostertagia ostertagi, Fasciola hepatica and Dictyocaulus viviparus in Swiss dairy herds

Highlights

• First bulk tank milk serosurvey on Ostertagia ostertagi, Fasciola hepatica, and Dictyocaulus viviparus in Swiss dairy cattle.

• Herd seroprevalence for O. ostertagi was 95.5% (95% C.I.: 94.0–96.6) with a mean ODR of 0.83.

• Herd seroprevalence for F. hepatica was 41.3% (95% C.I.: 38.3–44.4), for D. viviparus 2.9% (95% C.I.: 1.6–4.7).

• Geographic clusters of, and risk factors for, higher antibody levels were identified.

Abstract

Infections with helminth parasites can negatively affect performance of dairy cows. Knowledge on infection intensity, spatial distributions and risk factors are key to develop targeted treatment strategies. Canada and most EU countries have conducted large investigations, but respective data for Switzerland were missing. We now performed a bulk tank milk serosurvey for Ostertagia ostertagi, Fasciola hepatica, and Dictyocaulus viviparus on a total of 1036 voluntarily participating dairy herds that were sampled at confinement periods, i.e. in winter 2014/15 or 2015/16, respectively. All samples were analyzed with commercial ELISAs for antibodies (AB) against O. ostertagi and F. hepatica, and those of the first sampling period additionally with an in-house ELISA for AB against D. viviparus. Testing for the latter parasite was not done in the second year of the study, as the sampling period might have missed infections due to the short lived nature of specific antibodies. The possible influence of geographic, climatic, and farm management variables on AB levels were assessed for each parasite using scanning cluster and multiple regression analysis.

Overall seroprevalence for O. ostertagi was 95.5% (95% C.I.: 94.0–96.6), with a mean optical density ratio (ODR) of 0.83, for F. hepatica 41.3% (95% C.I.: 38.3–44.4), and for D. viviparus 2.9% (95% C.I.: 1.6–4.7). There were no significant differences between the two sampling periods. For all parasites, significant geographic clusters of higher AB levels could be established. Furthermore, AB levels against all three parasites were positively correlated with each other, indicating either cross-reactions or co-infections. For O. ostertagi, herd size and percentage of pasture in the ration were positively correlated with AB levels. For F. hepatica, altitude above sea level (a.s.l.) positively, and milk production per cow and year was negatively correlated with AB levels.

This work provides baseline data for further studies performing in-depth risk factor analysis and investigating management as well as targeted treatment options to control the parasites.

Introduction

In Switzerland, as generally in Western Europe, dairy production is an important part of agriculture representing about 20% of the total revenue of Swiss agriculture (Leuenberger, 2016). In the last years, however, the number of dairy herds and dairy cows declined because producers had to face a drop in the milk price (Leuenberger, 2016). In this tough economic environment, producers aim at optimizing their systems. Thus, subclinical infections with parasites that have negative effects on productivity, such as Ostertagia ostertagi (reviewed in Charlier et al., 2009), Fasciola hepatica (Schweizer et al., 2005, Charlier et al., 2012), and Dictyocaulus viviparus (Dank et al., 2015, Charlier et al., 2016) gain more attention from both producers and veterinarians. The availability of anthelmintic drugs with zero day withdrawal for milk makes deworming of dairy cows attractive. However, there is a risk of anthelmintic resistance development, if drug pressure increases, as shown by emerging resistant gastrointestinal (GI)-nematodes in cattle (Demeler et al., 2009, Sutherland and Leathwick, 2011, Geurden et al., 2015), and, as a consequence of repeated treatments due to poor immunological response of cattle against liver fluke, triclabendazole-resistant F. hepatica (Brennan et al., 2007). Anthelmintic drugs therefore should only be used upon indication.

The availability of ELISAs that measure antibodies in bulk tank milk (BTM) against O. ostertagi, F. hepatica, and D. viviparus allow timely and cost reduced diagnostics on herd level and large seroepidemiological surveys. Such surveys have been conducted in e.g. Canada and many European countries in the last decade (among others: Forbes et al., 2008, Bennema et al., 2010, Höglund et al., 2010, Vanderstichel et al., 2012). They have evidenced marked differences in respective seroprevalences between different countries (Forbes et al., 2008, Bennema et al., 2010). Information about spatial distribution of the parasites and risk factors for infection helps in designing targeted treatment protocols, ideally reducing the number of anthelmintic treatments. For Switzerland, such studies have been lacking so far. The aims of the present study therefore were to (1) determine apparent seroprevalences for O. ostertagi, F. hepatica, and D. viviparus in Swiss dairy herds, and (2) to identify risk factors for infection as well as geographic clusters of high prevalence for each of the three parasites.