Evaluation of anti-Ostertagia ostertagi antibodies in individual milk samples as decision parameter for selective anthelmintic treatment in dairy cows.

The aim of this study was to explore whether anti-Ostertagia ostertagi antibody levels measured by ELISA in individual milk samples hold promise as a decision parameter for either herd-level decisions or selective anthelmintic treatments by investigating (1) the relationship between individual and bulk-tank milk ELISA results; (2) the relationships of individual milk ELISA results with non-parasitic cow factors and (3) the relationship between individual milk ELISA results and the milk production response after anthelmintic treatment. Twelve farms were randomly allocated to a whole-herd treatment with eprinomectin or a placebo in October 2004 and individual milk samples and a bulk-tank milk sample were collected 1 month before and 1 month after treatment. Linear mixed models were used to investigate the associations of ELISA results with (a) breed, actual milk production, lactation stage, somatic cell count, age and sampling month and (b) the milk production response after anthelmintic treatment. There was a reasonable correlation between the mean individual and bulk-tank milk ELISA results (r=0.72). Individual cow ELISA results increased with higher lactation number and were lower in November than September. The associations with the other non-parasitic factors were weak and not significant. Milk yield responses to anthelmintic treatment were greater when treatment was given in early lactation and increased with the pre-treatment ELISA result and cow age. However, these latter two interaction terms were not significant when they were put in the model together. We conclude that (1) O. ostertagi ELISA results from individual milk samples may provide more information on the herd's parasitic status than a single bulk-tank milk result; (2) lactation number should be taken into account when interpreting ELISA results from individual milk samples and (3) the value of the O. ostertagi antibody level in individual cow milk samples to predict individual production responses after anthelmintic treatment remains equivocal.

Charlier J ，Vercruysse J ，Smith J ，Vanderstichel R ，Stryhn H ，Claerebout E ，Dohoo I ... -  《-》

Predicting milk-production responses after an autumn treatment of pastured dairy herds with eprinomectin.

The objectives of this study were (1) to determine the effect of a treatment with eprinomectin in autumn of pastured dairy herds on the anti-Ostertagia ostertagi bulk-tank milk antibody level, (2) to determine the overall effect of this treatment on three milk-production parameters (milk yield, protein % and fat %) and (3) to investigate the value of the pre-treatment Ostertagia-specific bulk-tank milk antibody level to predict the production response after anthelmintic treatment. One hundred and nineteen herds in Flanders (Belgium) were randomly assigned to a treatment with eprinomectin or a placebo in October 2004. Bulk-tank milk samples were collected monthly from August 2004 until April 2005, and the antibody levels against O. ostertagi were determined as optical density ratios (ODRs) with an ELISA. The treatment effect over the 4 months following treatment on three production parameters (milk yield, milk-protein %, milk-fat %) was estimated by mixed models with herd as a random effect. The treatment effect on milk yield was also investigated within six categories of the pre-treatment ODR. The ODR values were lower in the eprinomectin group than in the control group at each time point after treatment. The overall effect on milk yield was estimated at 1.2 kg/cow/day, whereas no effect on the milk-protein % and milk-fat % was observed. Herds in the highest pre-treatment ODR category (>0.84) had a positive milk-yield response of 4.0 kg/cow/day (95%-confidence interval: 1.0; 7.0), while the 95%-confidence intervals of the milk-yield responses in the other categories all included zero. This study demonstrates that treatment with eprinomectin of pastured dairy cows in autumn will lower the Ostertagia-specific bulk-tank milk antibody level during the stabling period and can result in a consistent increase in milk yield. The results indicate that an O. ostertagi bulk-tank milk ELISA can be used to identify the herds where the greatest milk-yield response after an anthelmintic treatment is expected.

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

A longitudinal study of gastrointestinal parasites in Canadian dairy farms. The value of an indirect Ostertagia ostertagi ELISA as a monitoring tool.

The general objective of this study was to evaluate a crude Ostertagia ostertagi antigen enzyme-linked immunosorbent assay (ELISA) for monitoring gastrointestinal parasites in lactating dairy cattle. A longitudinal study of gastrointestinal parasites in lactating dairy cows was carried out in 38 herds in four provinces of Canada (Prince Edward Island, Quebec, Ontario and Saskatchewan) from September 1999 to October 2000. Bulk tank milk, cow milk, serum and fecal samples were collected monthly or quarterly from all these farms. Information on herd management factors was collected by a standard questionnaire and individual cow production data were obtained from an electronic database. The overall mean optical density ratio (ODR) was 0.30 and ranged from -0.05 to 1.55. Although a clear seasonal pattern was not observed, the ODR values tended to decrease during the housing period and start increasing in the spring before the cows went out to pasture. The second and third or greater lactation cows had significantly higher ODR values compared with first lactation animals. The individual cow ODR had a very low correlation with individual squared root fecal egg counts but showed a reasonably high correlation when herd averages values were computed (r=0.73). A moderate correlation (r approximately 0.50) between the bulk tank and herd average ODR was observed. Milk yield was negatively associated with individual cow milk ODR and a quadratic effect on ODR was observed for days in milk. Twenty-eight of the herds participated in a clinical trial of eprinomectin (Ivomec Eprinex) treatment at calving. The cow level ODR values determined late in the previous lactation had a marginally significant effect (P=0.07) on treatment response, suggesting that high OD cows responded better to the anthelmintic treatment. However, because of the small sample size available in this model, more research is needed to better understand this relationship. In conclusion, the indirect ELISA using an O. ostertagi crude antigen appears useful as a technique for monitoring gastrointestinal parasite burdens in adult dairy cows and holds promise as a potential predictor of response to anthelmintic treatment.

Sanchez J ，Dohoo I ，Nødtvedt A ，Keefe G ，Markham F ，Leslie K ，DesCôteaux L ，Campbell J ... -  《VETERINARY PARASITOLOGY》

A longitudinal study of gastrointestinal parasites in English dairy farms. Practices and factors associated with first lactation heifer exposure to Ostertagia ostertagi on pasture.

The gastrointestinal nematode Ostertagia ostertagi is an important cause of lost production, health, and welfare in cattle. Detailed records were obtained over a 5-yr period (2010-2015) by questionnaires and qualitative interviews to investigate the practices adopted by dairy farmers to control cattle helminth infections and the factors associated with heifer exposure to O. ostertagi on pasture. In total, 1,454 heifers' individual milk samples were collected over a 1-yr period (2014-2015) in 43 dairy farms in England and tested for O. ostertagi antibody by ELISA. Multilevel linear regression models were used to investigate the association between individual milk optical density ratio (ODR) against O. ostertagi and heifer management from birth to time of sampling. Farm and heifer median ODR against O. ostertagi were 0.98 (interquartile range = 0.76-1.02) and 0.64 (interquartile range = 0.42-0.84), respectively. The majority of heifers (88%) received an anthelmintic treatment before sampling in this study. After controlling for the effect of anthelmintic treatments, heifer individual milk ODR against O. ostertagi significantly increased with high stocking rate at first grazing and co-grazing with adult cows before calving. Conversely, heifer individual milk ODR against O. ostertagi significantly decreased when heifers had co-grazed with sheep and pasture grass had frequently been mowed. Overall, these results provide evidence to support targeting grazing management toward limiting the use of anthelmintics in dairy young stock to enable sustainable control of cattle helminth infections in England. However, to be accepted and adopted by farmers, these best practices would need to take into account farmers' perspectives and contextual challenges.

Bellet C ，Green MJ ，Bradley AJ ，Kaler J ... -  《-》

A bulk tank milk survey of Ostertagia ostertagi antibodies in dairy herds in Prince Edward Island and their relationship with herd management factors and milk yield.

Sanchez J ，Dohoo I 《CANADIAN VETERINARY JOURNAL-REVUE VETERINAIRE CANADIENNE》