Risk factors associated with subclinical mastitis in dairy cows on Swiss organic and conventional production system farms

Epidemiological studies comparing risk factors for subclinical mastitis (SM) in organic (OP) and conventional dairy production systems (CP) are lacking. In 60 OP and 60 CP farms, 970 cows were used to study risk factors for SM at 31 days postpartum. Cows showing a positive (≥ 1+) California Mastitis Test (CMT) in at least one quarter, but without clinical symptoms, were classified SM-positive. For OP cows increased (P < 0.05) odds ratios (OR) for SM were found for other than Simmental and Simmental × Red Holstein breeds, for increasing number (> 27) of cattle on the farm, for the use of mineral feed supplements, for irregular milking intervals (< 12 and > 12 h/day), and for milk urea concentrations of 210.1-270 mg/dl, whereas decreased OR for SM were recorded for cows kept in barns on beddings other than on rubber mats or concrete, for farms with rinsing water temperatures of milking systems between 54.75 and 60°C, for milk lactose > 50.5 g/l, and for blood albumin levels of ł 38.5 g/l. For cows on CP farms, increased (P < 0.05) OR for SM were found for other than Simmental ´ Red Holstein and Simmental breeds, for a bedding area width of > 117 cm, and for antibiotic mastitis treatment since the last dry period, whereas reduced (P < 0.05) OR for SM were found for farms with a moderate (in contrast to good) hygiene status and for routine application of antibiotics during the dry period. Observed differences between OP and CP were assumed to be partially related to system-specific management, such as antibiotic dry cow therapy, nutrition and milking routine.