Short- and long-term association between individual levels of milk antibody against Ostertagia ostertagi and first-lactation heifer's production performances.

It is agreed that exposure of adult dairy cattle to helminths on pasture can negatively affect production performances as milking herd. Young animals, especially replacement heifers, represent the future of a dairy farm and are among the most vulnerable to helminth infections in a dairy herd. For this reason, dairy farmers tend to frequently treat heifers against helminths, although the impact of helminths on heifers' production performances is still poorly understood. Using different epidemiological and serological tools, this study examines the relationship between heifer exposure to helminths on pasture and production performances over time. During a one-year period, 1,454 individual milk samples were collected from first-lactation heifers in England and tested for Ostertagia ostertagi (O. ostertagi) antibodies. After controlling for other confounders, increasing milk antibody levels against O. ostertagi were significantly associated with decreased milk yield at sampling but not at day 305 of heifer lactation. We did not observe any relationship between milk antibody levels against O. ostertagi in heifers and yields in fat and protein. However, heifers with a high level of milk antibodies against O. ostertagi were more likely to produce dead calf at first calving and present a delay in second calving. Moreover, these heifers had significantly higher levels of milk antibodies against Mycobacterium paratuberculosis (M. paratuberculosis) during their first lactation and were more likely to die before the end of the study. We argue that epidemiological approaches can be useful but must be complemented by other methodologies to better understand the impact of helminth infections in dairy heifers. In order to address the complex dynamics of helminth infections in dairy cattle production we require more comprehensive approaches that include triangulation between data sources and interdisciplinary studies.

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

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 ... -  《-》

Ostertagia ostertagi antibodies in bulk tank milk from dairy cattle in Italy: A nation-wide survey.

The objective of this study was to investigate the exposure to Ostertagia ostertagi in dairy cattle herds across Italy through measurement of antibody concentration in the bulk tank milk (BTM) and to evaluate the possible effect of regions, seasons and pasture management practices on the level of exposure to the parasite. The O. ostertagi antibody levels in milk were determined using a commercial ELISA kit (SVANOVIR® O. ostertagi-Ab) and expressed as optical density ratio (ODR). From March 2015 to September 2017, BTM samples were collected in 1209 dairy cattle farms located in 15 regions of Northern, Central and Southern Italy. As reported in previous studies, BTM samples were classified in three different categories according to the level of exposure to O. ostertagi as follows: (i) positive with ODR values >0.60; (ii) negative with ODR values <0.30 and (iii) grey zone with ODR values between 0.30 and 0.60. Finally, differences in ODR values between regions, seasons and herd management practices were studied using the one-way analysis of variance. The overall mean ODR revealed a value of 0.49 in Italy; in particular, dairy cattle farms located in Southern Italy showed the highest O. ostertagi BTM ODR values than the other regions (p < 0.05). The ODR values ranged from 0.45 in autumn to 0.53 in spring and the seasonal difference was significant (p < 0.05). Furthermore, a positive association was found between the ODR values and the access to pasture; herds with access to pasture showed significantly higher titres (p < 0.0001) of O. ostertagi antibodies in milk (mean ODR = 0.63) than in those in total-confinement housing (mean ODR = 0.42). This study, the first of its kind in Italy, will provide a quantitative assessment exposure to O. ostertagi of Italian dairy herds and represents a significant step forward in evidence-based medicine for dairy veterinarians, advisors and farmers.

Bosco A ，Amadesi A ，Morandi N ，Pepe P ，Maurelli MP ，Cringoli G ，Rinaldi L ... -  《-》

Prevalence and seasonality of bulk milk antibodies against Dictyocaulus viviparus and Ostertagia ostertagi in Irish pasture-based dairy herds.

Infections with Dictyocaulus viviparus and Ostertagia ostertagi nematode parasites are of importance to bovine health and production in temperate areas across the world. Losses due to these parasites in dairy herds can be considerable due to decreased milk productivity and fertility. However, information on current epidemiological patterns in Irish dairy herds is limited. Bulk milk samples were collected from a total of 319 dairy farms across the Republic of Ireland. The D. viviparus samples were tested with an ELISA based on recombinant major sperm protein, while the O. ostertagi samples were tested with an ELISA based on crude saline extract, whole worm O. ostertagi antigen. Management data were collected from the farms using a questionnaire. Logistic regression was used to find significant associations between the presence of antibodies against D. viviparus and O. ostertagi and management factors. The overall prevalence of D. viviparus infection was 62.8%, while over 98% of herds had antibodies to O. ostertagi at the specified cut-off. Both D. viviparus and O. ostertagi antibodies were highest in November, which could be explained by the accumulated uptake of larvae through the grazing season. In herds of farmers that dosed their in-calf heifers with anthelmintics were significantly more likely to be positive for antibodies against D. viviparus infection. This study highlights that both D. viviparus and O. ostertagi infections are widespread in dairy herds in Ireland throughout the grazing season.

Bloemhoff Y ，Forbes A ，Good B ，Morgan E ，Mulcahy G ，Strube C ，Sayers R ... -  《-》

A survey of the exposure to Ostertagia ostertagi in dairy cow herds in Europe through the measurement of antibodies in milk samples from the bulk tank.

Measurement of antibodies to Ostertagia ostertagi in bulk tank milk (BTM) has value as a diagnostic indicator for potential production losses and anthelmintic treatment responses in dairy herds. Most of the recent data on O. ostertagi antibodies in milk have been generated in Belgium and Canada; the purpose of this study was to determine the range of O. ostertagi antibody levels in several European countries. BTM samples were collected during the autumn of 2005 and 2006 from a total of 1185 dairy herds from dairy farming regions in Denmark, Germany, Ireland, Italy, the Netherlands, Portugal, Spain and the United Kingdom. Antibody titres to O. ostertagi were determined by indirect ELISA and expressed as optical density ratios (ODR). In addition, relationships between ODR and management practices were investigated. For each country the mean ODR and the 25th-75th percentile values were determined. Mean BTM ODR values in herds with access to yards, paddocks and pastures ranged from 0.3 in Italy to 0.6 in Portugal and the UK/Ireland. The BTM ODR values obtained in this study were generally lower than those described in the literature for Belgium, but comparable with those in Canada. Variations between different European countries appeared to reflect different husbandry practices, particularly those related to access to pasture. The association analyses showed correlations between the BTM O. ostertagi ODR, outside access and grazing management, consistent with the publications from Belgium and Canada. When diagnostic values appropriate for different production situations and environments have been further validated, the test will provide an objective, quantitative assessment of the O. ostertagi status of a dairy herd and the possible impact this may have on performance and potential responses to anthelmintic treatment. This represents a significant step forward in evidence-based medicine for dairy veterinarians, advisors and farmers.

Forbes AB ，J Vercruysse ，Charlier J 《VETERINARY PARASITOLOGY》