Udder health on dairy farms. 1. Results of a longitudinal study on 300 Dutch farms

Udder health was studied in 300 dairy herds grouped in three categories acc ording to the bulk milk somatic cell count. In all herds, lactating cows we re housed in a free-stall barn during the winter. All herds participated in a three or four-weekly milk recording system, had annual production quota between 300,000 and 900,000 kg, and were stocked with cows of the Holstein- Friesian or Dutch Friesian breeds. The incidence of clinical mastitis was not different among herds with a low (less than or equal to 150,000), middle (151,000 to 250,000), or high (251 ,000 to 400,000 cells/ml) bulk milk somatic cell count. Clinical mastitis c aused by Gram-negative pathogens occurred more often in herds with a low bu lk milk somatic cell count. Clinical mastitis caused by Staphylococcus aure us, Streptococcus dysgalactiae, or Streptococcus agalactiae occurred more o ften in herds with a high bulk milk somatic cell count between the categori es could be explained by the management practices studied. The incidence of clinical E. coli mastitis was mostly related to housing, hygiene, and milk ing machine. The incidence of clinical Staphylococcus aureus mastitis milki ng machine. The incidence of clinical Staphylococcus aureus mastitis was as sociated with factors that were related to the bulk milk somatic cell count and to factors of which it was not clear whether they were a cause of effe ct of the high incidence of Staphylococcus aureus mastitis. The incidence o f clinical Streptococcus dysgalactiae mastitis was related to nutrition, mi lking technique, and milking machine. The incidence of clinical Streptococc us uberis mastitis was associated with housing, nutrition, and milking mach ine. Two groups of farmers and herds could be differentiated. The first gro up was identified as 'Clean and Accurate', and the second group as 'Quick a nd Dirty'. The relationship between these two groups and bulk milk somatic cell count category was high. However, the relationship between the two gro ups and the incidence of clinical mastitis was weak.