Incidence of respiratory disorders during housing in non-weaned Charolais calves in cow-calf farms of Pays de la Loire (Western France).

We assessed the incidence rate of respiratory disorders during the 1999-2000 housing period in non-weaned calves reared in a specific cow-calf farming system in western France, examined its variations according to age of the calf, housing facility and meteorological conditions, and described the different time-distribution patterns of incident cases within the barns. Treatments for respiratory disorders were recorded by the farmers on a specific sheet according a written definition provided. A case "occurred" on a given day if the calf concerned was treated for respiratory disorder on this day but not in the previous 14 days. At the barn level, episodes of respiratory disorder were determined based on the time-distribution of incident cases. An episode started on a given day if at least one case occurred on this day in the barn concerned without any cases occurring in the previous 14 days. Data were suitable for analysis for 6813 calves, in 199 barns, located in 137 farms, where no metaphylactic treatment (mass treatment of ill and not-ill calves at the barn level) was implemented. The incidence rate of respiratory disorders was 1.89 cases per 1000 calf-days at-risk. The proportion of reoccurrent cases was 8.6%. During the 1999-2000 housing period, cases occurred more frequently between 1 November and 20 January. The incidence rate of cases peaked between 14 and 20 days of age and was lower after 105 days of age. Large variation in incidence existed among barns. In one-third of the buildings, no case was observed. A higher incidence of cases was observed in loose-housing yards compared to tied-cow stalls. No clear trend between daily meteorological measurements and daily incidence rate of cases was evidenced. A total of 11 barn-level episodes occurred in 9 tied-cow stalls and 229 barn-level episodes occurred in 120 loose-housing yards. Large variations in the characteristics of episodes (duration, incidence of sick calves) and in their time-distribution existed between barns.