WINTER DYSENTERY DIAGNOSED BY FARMERS IN DAIRY HERDS IN CENTRAL SWEDEN - INCIDENCE, CLINICAL SIGNS AND PROTECTIVE IMMUNITY

The occurrence of winter dysentery, diagnosed by farmers and defined a s an outbreak of diarrhoea among at least 30 per cent of adult cattle in a herd, was monitored in 256 dairy herds in an area of central Swed en. The cumulative incidence of winter dysentery between April 1988 an d March 1989 was 28-5 per cent. A typical outbreak lasted for one to t wo weeks and 74 per cent of the outbreaks occurred between November an d January. A decrease in milk yield was reported in 90 per cent of the affected herds and the cows showed respiratory signs in 57 per cent o f them. There was a significant (P<0.05) association between the occur rence of fever and coughing. In 31 per cent of the outbreaks the farme r also noticed diarrhoea among the calves. One-third of the affected h erds had experienced an outbreak within the previous four years and 18 per cent had at least one further outbreak during the following two y ears. There was a significantly (P<0.05) lower disease score in herds that had had an outbreak within the previous four years than in herds which had had a less recent or no previous outbreak, indicating the de velopment of temporary immunity to the causative agent.