Normal reproductive parameters in large "California-style" dairies

Reproductive parameters are important in evaluating modern dairy management performance. Successful dairying results from constant attention to daily events, requiring more sensitive and immediate measurements of performance. Definitions of formulas, numerators, denominators, and population included or excluded are essential for proper interpretation and comparison of results. Veterinarians understanding these statistics and indexes, and using stratification of data to investigate production losses, will serve their clients well. My advice is to approach a herd with a perceived reproductive problem by evaluating these parameters; they are the means of determining if a problem exists and, if so, where it is. Find out how the various parameters are calculated so your interpretation will be correct. Herds with average days in milk of less than 165, culling rates below 25 per cent, and a milking rate of 85 per cent or more do not have long-term reproductive problems. If management techniques fail to achieve these levels, first look at those areas involving people. Conception rates measure all the components that, when multiplied, equal fertility: insemination technique, semen quality, heat detection accuracy, and the cow factors involved. Poor conception rates require investigation into these areas individually. Heat detection intensity leading to prolonged days in milk at first service is another common finding. Comparison of inseminators and sires may identify a problem area. Cow factors require more intense investigation to determine their cause. Use the information outlined in the periparturient period to assist you. In most cases, a combination of failures in many of the independent factors creates the problems in reproduction that we encounter. A large data base including all the information discussed and additional information is necessary to define, correct, and monitor reproductive management performance. Since performance ultimately is determined by the quality of the labor force, ongoing monitoring for accountability and education is necessary for success.