Facteurs structurels de variation des niveaux de comptage cellulaire du lait et de fréquence des mammites cliniques dans 560 élevages bovins répartis dans 21 départements français

Abstract

Structural factors of variation of herd bulk somatic cell count and mastitis frequency levels within 560 bovine dairy farms located in 21 French departments. An epidemiological survey was carried out in 560 bovine dairy herds located in 21 French departments, as a collaborative project between the Unit of Ecopathology of the INRA and Dairy Herd Improvement Associations (Contrôles Laitiers). It was a preliminary work in order to build a national epidemiological network concerning udder health and milk quality. The surveyed herds were divided into two groups, selected randomly in each department. The first group consisted of herds with a bulk somatic cell count lower than 250 00 cells/ml (CE - group), and the second one of herds with a bulk somatic cell count higher than 300 000 cells (CE+ group). The frequency of clinical mastitis was determined in each herd during the survey, and the herds divided in three groups, according to their mastitis frequency. In the MA- group, mastitis frequencies were lower than 15 %, in the MA+ group they were equal or higher than 15 %, and in the MA? group, herd mastitis frequency could not be precisely evaluated. The structural factors of variation of the herd bulk somatic cell count and of the frequency of clinical mastitis were studied using models of multiple logistic regression. The average frequency of clinical mastitis was 24.3 %, the main characteristics of the surveyed sample of herds being close to the average values calculated into the whole population of the French bovine dairy herds. The variables which characterized CE- herds, compared to CE+ herds, were: 1) a lower frequency of clinical mastitis, the Montbéliarde breed, a higher percentage of primiparous cows, a higher milk yield level, more facility for the farmer to detect and treat mastitis. Within the CE- group, the variables which characterised the MA - herds, compared to the MA+ ones, were: 1) a lower milk yield level ; 2) less difficulty for the farmer to treat efficiently mastitis. These results are discussed within the framework of the French breeding conditions, with the aim of providing methodological issues to future epidemiological studies concerning mastitis risk factors and control.