Measurement of antibodies to gastrointestinal nematodes and liver fluke in meat juice of beef cattle and associations with carcass parameters.

In an effort to develop non-invasive methods for the diagnosis of Ostertagia ostertagi and Fasciola hepatica infection in beef cattle, this study was undertaken to evaluate antibody-detection ELISAs in meat juice samples and to investigate the associations between test results and carcass parameters. Preliminary tests were carried out to determine optimal working dilutions of meat juice samples. The Pearson correlation coefficients between ELISA results (expressed as ODR) of serum and meat juice samples from 90 to 100 cows were R=0.82 and 0.75 for O. ostertagi and F. hepatica, respectively. Next, an abattoir survey in Belgian Blue suckler cows was performed, analysing meat juice samples from 726 animals in spring and 724 animals in autumn 2008, originating from a total of 480 herds. There was a large variation in the observed O. ostertagi and F. hepatica ODRs and inter-seasonal differences were observed for F. hepatica (spring>autumn), but not for O. ostertagi. The relationships between individual parasite-specific ELISA results and carcass parameters (warm carcass weight, conformation score, fat coverage) were investigated by linear or logistic mixed models with herd as a random effect, while the relationship between herd average ELISA results and herd averaged carcass weight was investigated by linear regression with mean cow age and season as covariates. An increase in individual O. ostertagi ODR over the interquartile range was associated with an increased likelihood by 1.3 of a low conformation score (score E vs. S), but no significant associations were found with other carcass parameters. However, herd mean ELISA results were negatively associated with a decrease in the herd average carcass weight (P=0.001 and P=0.09 for O. ostertagi and F. hepatica, respectively). An increase in the herd mean O. ostertagi or F. hepatica ODR over the interquartile range was associated with a decrease in herd mean carcass weight of 9.1 and 3.4 kg, respectively. The implications of these results and the value of monitoring parasitic infections by analysis of meat juice samples from the abattoir are discussed.

Charlier J ，De Cat A ，Forbes A ，Vercruysse J ... -  《-》

A survey to determine relationships between bulk tank milk antibodies against Ostertagia ostertagi and milk production parameters.

In temperate climate regions, gastrointestinal nematodes are still widespread in adult dairy cows, but until now there exists no reliable diagnostic tool that can identify herds where the infection interferes with productivity. The objective of this study was to investigate the relationships between levels of antibodies against Ostertagia ostertagi in bulk tank milk and milk production. Bulk tank milk samples of 2553 dairy herds were obtained in spring and 2104 of these herds were sampled a second time in autumn. The antibody levels against O. ostertagi were determined with a milk ELISA and test results were expressed as an optical density ratio (ODR). The effect of bulk tank milk ODR on three different production parameters, kg milk, % and kg fat, % and kg protein was assessed by a multivariable linear regression model on the herds for which production data were available (n = 1063 and 867 in spring and autumn, respectively). The mean and standard deviation for ODRautumn (0.972+/-0.238) were higher than for ODRspring (0.825+/-0.201). Significant negative relationships were found between ODR and milk yield. An increase in ODRspring and ODRautumn from the 25th to the 75th percentile of the available ODR data was associated with a drop in the annual milk yield of 1.1 kg/cow/day, respectively 0.9 kg/cow/day. When a herd's ODR increased between spring and autumn with 0.142, it produced on average 0.4 kg/cow/day less in September than in April, in comparison with herds where the ODR did not increase. A significant negative association was found between ODRautumn and % protein averaged over the period of a year. No significant associations were found between ODR and % fat averaged over the year. When protein and fat production of September were expressed in kg an increase in ODRautumn from the 25th to the 75th percentile was associated with a decrease of 0.037 kg protein/cow/day and 0.042 kg fat/cow/day.

Charlier J ，Claerebout E ，Duchateau L ，Vercruysse J ... -  《VETERINARY PARASITOLOGY》

The use of bulk-tank milk ELISAs to assess the spatial distribution of Fasciola hepatica, Ostertagia ostertagi and Dictyocaulus viviparus in dairy cattle in Flanders (Belgium).

Fasciola hepatica, Ostertagia ostertagi and Dictyocaulus viviparus are helminth parasites with a wide distribution and an important economic impact in cattle in temperate climates. This paper describes the spatial distribution of F. hepatica, O. ostertagi and D. viviparus in dairy herds in Flanders (Belgium). One thousand eight hundred herds were selected at random from the Flemish dairy population (n=7002), stratified on community level to obtain a sample representative for the entire study area. From each herd, a bulk milk sample collected in autumn 2006 was analysed with previously described antibody-ELISAs in order to identify herds where the parasite infection level is likely to cause production loss (F. hepatica and O. ostertagi) (defined as economic infections) or where patent infections have been present over the past grazing season (D. viviparus). The herd prevalence of economic infections with F. hepatica and O. ostertagi was 37.3% (95% Confidence Interval (CI): 35.1-39.7) and 59.1% (95%CI: 56.8-61.4), respectively. The herd prevalence of D. viviparus was 19.6% (95%CI: 17.7-21.6). On 28.9% (CI 26.8-31.3) of the herds, low levels of infection were observed for all three of the helminths. The presence of clustering of (economic) infections was studied using Moran's I, whereas the location and size of the clusters were studied using the spatial scan statistic, the Local Indicator of Spatial Association and Kernel density plotting. A marked clustering in the spatial distribution of F. hepatica and a mild clustering in the spatial distribution of O. ostertagi were observed. D. viviparus infections were spread evenly over Flanders. Knowledge of locations of high risk areas can lead to increased awareness and may be the start of the development of regionally adapted control measures.

Bennema S ，Vercruysse J ，Claerebout E ，Schnieder T ，Strube C ，Ducheyne E ，Hendrickx G ，Charlier J ... -  《-》

Associations between dairy herd management factors and bulk tank milk antibody levels against Ostertagia ostertagi.

A cross-sectional questionnaire survey was performed on dairy herds in Flanders (Belgium) to detect management factors that are associated with an increased gastrointestinal parasite infection level of adult dairy cows. At the end of the grazing season, information concerning general herd factors, pasture management and anthelmintic treatment strategy was obtained from 956 herds. A bulk tank milk sample was obtained from 779 out of the 956 herds and the antibody levels (ODR) against Ostertagia ostertagi were determined. The associations between ODR and herd management factors were studied by two linear regression models. The first model evaluated the effect of general herd factors and the level of the cows' exposure to pasture. Large sized herds had significantly lower ODRs as compared to medium (P=0.001) or small sized herds (P=0.03). Herds with only dairy cows had lower ODRs than herds with both dairy and beef cows (P=0.02). An increased exposure to pasture of the cows was associated with higher ODRs (P<0.001). The second model was built to evaluate the effect of pasture management factors and anthelmintic treatment strategy. Later turn-out on pasture (P<0.001) and mowing (P=0.002) were both significantly associated with lower ODRs. Cows that had a restricted grazing time per day tended to have lower ODR than cows that grazed 24 h per day (P=0.07). An increased exposure to pasture of the heifers was significantly associated with higher ODRs (P=0.001). No associations were found between ODR and calf related management factors, anthelmintic treatment strategy, time of turn-in, rotational grazing type or stocking rate. Later turn-out on pasture, mowing and restricting the grazing time per day are factors that can be applied immediately on dairy farms to reduce economical losses due to gastrointestinal nematodes.

Charlier J ，Claerebout E ，De Mûelenaere E ，Vercruysse J ... -  《VETERINARY PARASITOLOGY》

The effect of an experimentally induced acute mastitis on the test results of an Ostertagia ostertagi milk ELISA.

Antibody levels against Ostertagia ostertagi in the milk are a promising parameter to identify dairy cows or herds with production losses due to gastrointestinal nematodes. However, milk antibody levels can be influenced by udder-related factors. In this study, the effect of an experimentally induced mastitis on the test results (ODR) of a milk O. ostertagi ELISA was investigated. Twenty-five cows that were naturally infected with gastrointestinal nematodes, were inoculated in their left udder quarters with Escherichia coli P4:O32 and quarter milk samples were collected at several intervals from 24 h before until 144 h after experimental infection. The effect of the contribution of milk from one or more infected quarters on the bulk tank milk ODR was estimated, based on a titration experiment. The mean O. ostertagi antibody levels of the infected udder quarters were significantly (P < 0.001) higher than those of the uninfected udder quarters at each sampling time post-infection. The largest difference was observed at 24 h post-infection with a mean difference of 0.251 ODR (95%CI: 0.172; 0.330). There was also a significant increase (P < 0.001) in total IgG levels with the largest difference being observed at 24 h post-infection. Highly significant (P < 0.005) correlation coefficients were observed between O. ostertagi ODR, total IgG ODR, Na+ and Cl- ion concentration and log transformed somatic cell counts at 24 h post-infection. The results demonstrate that an acute mastitis causes a flow of specific and non-specific antibodies from serum to milk with a subsequent increase in the O. ostertagi ODR values. The effect of the contribution of milk from infected quarters on the bulk tank milk O. ostertagi ODR was estimated to be minor if the relative number of infected quarters is small (< 3%).

Charlier J ，Duchateau L ，Vangroenweghe F ，Claerebout E ，Burvenich C ，Vercruysse J ... -  《VETERINARY PARASITOLOGY》