Criteria for case farms were: (1) a markedly reduced
milk yield (>15% over a period of at least 3 month), (2)
increased losses due to fatalities or euthanasia (>5% during
the last 12 month), (3) a markedly increased replacement
rate (>35% of the herd during the last year or an increase
of > 10% compared to the year before), (4) an increased
percentage of recumbent animals (>10% during the last
12 month) and (5) the subjective impression of the farmer
or veterinarian of chronic herd health problems.