1998 J Dairy Sci 81:81:2502–2509 2502 OUR INDUSTRY TODAY Received September 2, 1997. Accepted April 27, 1998. Recommendations for Recording and Calculating the Incidence of Selected Clinical Diseases of Dairy Cattle DAVID F. KELTON, KERRY D. LISSEMORE, and ROCHELLE E. MARTIN Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada N1G 2W1 ABSTRACT The report upon which the current discussion is based was prepared in response to the increasing interest of the dairy industry in the recording of clinical disease data. The major objective was to in- troduce guidelines and standards for the recording and presentation of the diseases of dairy cattle. Eight clinically identifiable diseases of economic importance to the dairy industry were considered: milk fever, retained placenta, metritis, ketosis, left displaced abomasum, cystic ovarian disease, lameness, and clin- ical mastitis. Standardized definitions for these dis- eases were established through consultation with in- dustry partners. Two approaches to summarization and reporting were proposed. For retrospective analy- sis, which is used when historical data are summa- rized for genetic evaluation for example, lactational incidence risk (cumulative incidence) has been recommended. For current analysis, which is used for herd health monitoring, a true incidence rate has been recommended. Milk fever and retained placenta were exceptions to the latter because of their short periods of risk. For these two diseases, lactational incidence risks are reported. ( Key words: dairy cattle, disease, clinical, inci- dence) Abbreviation key: COD = cystic ovarian disease, LDA = left displaced abomasum, LIR = lactational incidence risk, MF = milk fever, RP = retained placenta, TP = time period. INTRODUCTION As the dairy industry prepares for increased global competition, interest in the recording of the diseases of cattle that have economic significance is growing. These data are needed 1 ) to describe, compare, and investigate the occurrence of disease on a national and regional basis; 2) to modify efficiently the management practices that promote the health of cattle; 3 ) to investigate further the genetic compo- nent of disease occurrence and resistance; and 4 ) to monitor the health status of the national dairy herd. A major impediment to this initiative is the lack of consistent standards for the definition of diseases and the presentation of these data. Use of disparate dis- ease definitions makes it difficult to pool or compare rates of occurrence from various studies and reports. For example, the significant variability in the defini- tion of cases of clinical mastitis has become evident with the recent interest in the impact of the use of recombinant bST on clinical mastitis (24). To deal with the confusion over the definition of mastitis, the International Dairy Federation ( 1 2 ) has proposed international guidelines for the recording and presen- tation of mastitis data. The major objective of the report presented to the Cattle Breeding Research Council of Canada ( 1 3 ) was to develop recommendations for reporting and calculating the incidence of selected clinical diseases of dairy cattle. For each disease under consideration, both an explicit case definition and detailed guide- lines for calculating, summarizing, and presenting rates of occurrence were developed. MATERIALS AND METHODS A survey of 13 agencies, organizations, and sys- tems involved in the recording of the diseases of dairy cattle was undertaken in spring 1996 (Appendix 1). The purpose of the survey was to determine which diseases of dairy cattle were currently recorded as well as the degree of consistency in the definition and categorization that existed among the various sys- tems in use. All available information regarding dis- ease recording practices and analytic capabilities of the 13 systems was compiled and analyzed. A search of five citation index databases (Agricola, Medline, CAB Abstracts, Life Sciences, Focus On), consisting of articles spanning 1970 to 1996, was undertaken to collect information pertaining to the