Eleven-year analysis of changes in the incidence and recurrence of cystic ovarian disease in a herd of dairy cattle in California

Daniel T. Scholl From the Departments of Epidemiology and Preventive Medicine (Scholl, Farver) and Reproduction (BonDurant), School of Veterinary Medicine, University of California, Davis, CA 95616.

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Robert H. BonDurant From the Departments of Epidemiology and Preventive Medicine (Scholl, Farver) and Reproduction (BonDurant), School of Veterinary Medicine, University of California, Davis, CA 95616.

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Thomas B. Farver From the Departments of Epidemiology and Preventive Medicine (Scholl, Farver) and Reproduction (BonDurant), School of Veterinary Medicine, University of California, Davis, CA 95616.

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SUMMARY

Individual card records of all cows that began 1 or more lactations between the inclusive dates of Jan 1, 1976 and Dec 31, 1986 were obtained from a California dairy herd. Calving date, lactation number, physical examination date, conception date, and clinical findings pertinent to cystic ovarian disease (cod) were extracted from the records. Lactation-specific data were organized into cohorts by quarter and year in which lactation began, and the following estimates were calculated for each of the 44 cohorts: separate actuarial cumulative incidences for cows in their first lactation, cows in the second or later lactation, and all cows combined; separate proportions of the incident cases that were in their second or greater lactation and that had recurred from any previous lactation; proportions of the incident cases that had recurrence of cod 1 or more times, and recurrence 2 or more times during the lactation; and the mean number of days in lactation at diagnosis of the incident case. Time-series analysis and multiple-regression modeling procedures were used to characterize changes in the overall incidence rate over the study period and to describe the contribution of additional measures to the dynamics of the incidence rates. The quarterly actuarial cumulative incidences of cod increased concurrently with the increased incidence among cows in the second or later lactation. Neither the proportion of incident cases that were diseased during a previous lactation nor the proportion of cases that were in the second or later lactation contributed to the observed changes in the overall incidence rate. The proportions of incident cases that recurred 1 or more times during the lactation did not increase, but the proportions that had 2 or more recurrences increased equivocally.

SUMMARY

Individual card records of all cows that began 1 or more lactations between the inclusive dates of Jan 1, 1976 and Dec 31, 1986 were obtained from a California dairy herd. Calving date, lactation number, physical examination date, conception date, and clinical findings pertinent to cystic ovarian disease (cod) were extracted from the records. Lactation-specific data were organized into cohorts by quarter and year in which lactation began, and the following estimates were calculated for each of the 44 cohorts: separate actuarial cumulative incidences for cows in their first lactation, cows in the second or later lactation, and all cows combined; separate proportions of the incident cases that were in their second or greater lactation and that had recurred from any previous lactation; proportions of the incident cases that had recurrence of cod 1 or more times, and recurrence 2 or more times during the lactation; and the mean number of days in lactation at diagnosis of the incident case. Time-series analysis and multiple-regression modeling procedures were used to characterize changes in the overall incidence rate over the study period and to describe the contribution of additional measures to the dynamics of the incidence rates. The quarterly actuarial cumulative incidences of cod increased concurrently with the increased incidence among cows in the second or later lactation. Neither the proportion of incident cases that were diseased during a previous lactation nor the proportion of cases that were in the second or later lactation contributed to the observed changes in the overall incidence rate. The proportions of incident cases that recurred 1 or more times during the lactation did not increase, but the proportions that had 2 or more recurrences increased equivocally.

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