Date Published: February 7, 2008
Publisher: BioMed Central
Author(s): Kenji Sato, Paul C Bartlett, Lis Alban, Jens F Agger, Hans Houe.
Several management and environmental factors are known as contributory causes of clinical mastitis in dairy herd. The study objectives were to describe the structure of herd-specific mastitis management and environmental factors and to assess the relevance of these herd-specific indicators to mastitis incidence rate.
Disease reports from the Danish Cattle Data Base and a management questionnaire from 2,146 herds in three Danish regions were analyzed to identify and characterize risk factors of clinical mastitis. A total of 94 (18 continuous and 76 discrete) management and production variables were screened in separate bivariate regression models. Variables associated with mastitis incidence rate at a p-value < 0.10 were examined with a factor analysis to assess the construct of data. Separately, a multivariable regression model was used to estimate the association of management variables with herd mastitis rate. Three latent factors (quality of labor, region of Denmark and claw trimming, and quality of outdoor holding area) were identified from 14 variables. Daily milk production per cow, claw disease, quality of labor and region of Denmark were found to be significantly associated with mastitis incidence rate. A common multiple regression analysis with backward and forward selection procedures indicated there were 9 herd-specific risk factors. Though risk factors ascertained by farmer-completed surveys explained a small percentage of the among-herd variability in crude herd-specific mastitis rates, the study suggested that farmer attitudes toward mastitis and lameness treatment were important determinants for mastitis incidence rate. Our factor analysis identified one significant latent factor, which was related to labor quality on the farm.
Mastitis is defined as an inflammation of the parenchyma of mammary gland, regardless of the specific etiologic agent . Clinical mastitis (CM) is known to be caused by several bacterial pathogens such as Streptococcus agalactiae, Staphylococcus aureus, E. coli and mycoplasma, however, the presence of pathogens in the mammary gland is often not sufficient to cause CM. It is generally believed that management and environmental factors are important contributory causes of CM. Factors such as housing , nutrition [3,4], milk production, milking procedures , and dry cow treatment  have been found to be associated with CM incidence.
Mastitis cases were reported to the Danish Cattle Data Base by veterinarians (77%) and by producers (23%), with duplicate reports being eliminated . The grand mean rate of CM was 44.7 cases per 100 cow-years at risk (median = 41.0, Shapiro-Wilk statistic = 0.935). A total of 34 management variables with P-value < 0.25 in the bivariate test of association with CM are shown in [see Additional file 1]. The limitation of field surveillance data regarding mastitis treatments were discussed in a previous publication . It is recognized that farmers and veterinarians used different diagnostic criteria regarding when mastitis clinical signs were sufficiently severe to warrant antibiotic treatment by their veterinarian. The disease reports from the Danish Cattle Data Base are based upon those diagnostic criteria the farmer used to decide whether or not to call the veterinarian, and the diagnostic criteria the veterinarian used regarding which cows required treatment. As such, our case definition includes those cases of mastitis that were sufficiently severe that the farmers and their veterinarians decided to take therapeutic action and these criteria may be very different from herd to herd . Though risk factors ascertained by farmer-completed surveys explained a small percentage of the among-herd variability in crude herd-specific mastitis rates, the study suggested that farmer attitudes toward mastitis and lameness treatment were important determinants for mastitis incidence rate. Our factor analysis identified one significant latent factor, which was related to labor quality on the farm. The General Linear Model indicated that dairy milk production per cow, claw disease, quality of labor and region of Denmark were significantly associated with mastitis incidence rate. Investigators' farm visits to measure factors such as quality of sanitation or milking hygiene could improve the CM risk analysis. Risk factor analysis would also likely be improved by analyzing agent-specific rates of mastitis rather than overall, composite or crude CM rates that undoubtedly include the effects of many independently operating causal pathways. KS carried out data analysis, interpretation, drafting the manuscript, and coordination among authors. PB conceived of the study, contributed data acquisition, conception, verification of analysis, interpretation of data and revising the manuscript. LA participated in the statistical design and analysis, and revising the manuscript. JFA and HH made substantial contribution to conception and revising the manuscript for important intellectual content in detail. Source: http://doi.org/10.1186/1751-0147-50-4