VETERINARY HERD HEALTH MANAGEMENT OF DAIRY HERDS .2. EVALUATION OF FERTILITY PARAMETERS - POSSIBILITIES AND LIMITS

Monitoring of fertility in dairy herds requires reliable methods of documentation and analysis. Through quantitative descriptions of events and intervals with relevance for reproduction, calculations of so-called fertility indices is a starting point for the evaluation of the current status and for detection of trends in the evolution of herd fertility. The retrospective indices of calving interval, days open, calving to last service interval, calving to first service interval, calving to first heat interval, first service to conception interval, services per first insemination, services per pregnancy - pregnant cows, non-return-rate, proportion conceiving at first service, proportion of pregnancies per bred cows, minimum interval first service to conception, heat detection rate, percentage of possible estruses detected are discussed. Prospective indices include days past breeding-age, projected minimum calving interval, non visible estrus, projected minimum calving to first service interval, projected minimum deferral days, undeterminated pregnancies. The formulas for computations of the individual indices are presented and possibilities and limitations of their interpretation and use are evaluated critically. Approaches to the estimation of financial losses due to disturbances of herd fertility through calculation of indices are indicated.