[Risk factors for persistent presence of salmonella antibodies in bulk tank milk]

Given bulk milk serology, salmonellosis is present on a restricted number of Dutch dairy farms. The affected farms are clustered in some regions of the country. This study was designed to find risk factors for having persistent positive bulk milk serology for salmonella within the regions with the highest prevalence. With that knowledge, a reduction of persistent infected farms may be achieved. To this end, we performed a rather small matched case-control study with two groups of 24 farms each. Case herds were characterized by having a positive bulk milk serology for salmonella for all three samplings during one year, whereas control farms were located near the positive farms and were negative in all these three samplings. Several risk factors were found not significant, while the significant risk factors concerned general on farm hygiene practices. Significant risk factors in the multivariate analyses were less hygienic calf facilities (OR = 6.1, p = 0.04), lower cleaning frequency of alleys (OR = 5.7, p = 0.08), and a higher frequency of claw trimmers visiting the farm (OR = 5.9, p = 0.07). We concluded that these risk factors are similar to those found outside the regions with a high number of farms with a positive bulk milk serology for salmonella.