Chlamydieninfektionen bei Milchkühen in Nordrhein-Westfalen, Prävalenz, Risikofaktoren, Kennziffern und Vorhersagewahrscheinlichkeiten (English shop)

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Chlamydial infections in dairy cows in North Rhine-Westphalia: prevalence, risk factors, indicators and predictive probabilities

The primary aim of this study was to determine the prevalence of Chlamydophila spp. in randomly selected dairy farms in North Rhine-Westphalia by means of a highly sensitive genus-specific real-time PCR. For this purpose, ten animals per herd were sampled on farms with fewer than 100 cows and 10% of the herd on farms with more than 100 cows, using vaginal swabs. Because of the intermittent shedding of the pathogen, a herd was classified as positive if at least one animal of that herd yielded a positive result for Chlamydophila spp. In this way, a prevalence of 61% for a current infection with Chlamydophila spp. was determined in the farms examined (herd level), corresponding to 13.5% of the cows examined (individual animal level). As a second aim of this study, risk factors indicating the spread of the pathogen, as well as those parameters for which differences between positively and negatively classified herds and cows were found and which can therefore be regarded as indicators of infections with Chlamydophila spp., were recorded by means of questionnaires. These contained data from milk recording, from herd management programmes, veterinary data and observational data. In farms classified as positive for Chlamydophila spp., a lower milk yield (-513 kg/year), a lower number of lactations (-0.5) and a shorter voluntary waiting period (-9 days) were found. Interactions between these variables, the Chlamydophila status and the lactation number were not present. Risk factors for infections with the pathogen were identified as the purchase of animals, the use of breeding bulls instead of artificial insemination, the lack of a separate calving area, insufficient cleaning of cubicles and walkways, and unclean cows. Swollen joints, claws and/or locomotor disorders were identified as indicators of infections with the pathogen. In addition, abortions, premature calvings and increased calf mortality occurred more frequently in the farms classified as positive. Positive cows and cows testing negative from positive herds likewise showed a lower milk yield (-383 kg and -298 kg, respectively), more frequent abortions, premature calvings, increased calf mortality, retained placenta, unclean vaginal discharge, an increased number of veterinary treatments after calving and infertility treatments; moreover, a lower somatic cell count (-35,000 cells/ml and -23,000 cells/ml, respectively) and a higher insemination index (2.6) compared with the cows from farms classified as negative (2.2) were observed. As a third aim of this study, a checklist was derived with the aid of the significant variables in various logistic regression models; it is available as a result of this study for determining the Chlamydophila status of unknown farms. This study is the first to establish the prevalence of current infections with Chlamydophila spp. in randomly selected farms.