The production system and disease incidence in a national random longitudinal study of Swiss dairy herds.

A prospective longitudinal observational study based on a stratified random sample of 113 Swiss dairy farms was conducted between April 1993 and July 1994 with the following objectives: (i) to provide statistically valid estimates of disease frequency in the Swiss dairy cow population, and (ii) to evaluate the feasibility and quality of an intensive farm-based data recording system. During the 15-month study period, farmers were asked to record every health and management event related to their cattle herd. This information was mailed back to the study centre at fortnightly intervals. Additionally, farms were visited regularly to verify received data and to discuss specific problems. During these farm visits, management data were recorded using questionnaires. A complete data set of individual animal events with a total observation time of about 1740 cow-years and 275 calf-years was collected and disease-incidence measures were calculated. The most frequent events were reproductive disorders and udder diseases, followed by lameness and metabolic disorders. Experience with the data collection technique used in this study suggests that a farm-based system is effective and reliable, as long as good contact with the farmers is maintained, and incentives to stimulate their motivation are provided.