COMPARISON OF A PROSTAGLANDIN-F2-ALPHA-BASED REPRODUCTIVE PROGRAM WITH AN ESTRUS DETECTION-BASED REPRODUCTIVE PROGRAM ON A LARGE COMMERCIAL DAIRY-HERD

The purpose of this study was to describe biological outcomes of two reproductive management strategies in commercial dairy cows: estrus detection with and without the use of prostaglandin-F2-alpha. At regular preinsemination examinations, cows were allocated randomly to two cohorts: 1) prostaglandin cohort -- cows with palpable corpora lutea were injected with 25 mg dinoprost tromethamine and were bred by appointment 72 and 96 hours later, followed one week later by standard estrus detection practices (twice daily observation and tail chalking, with breeding approximately 12 to 24 hours later); and 2) estrus detection cohor -- cows identified as exhibiting estrus (observed estrus) were bred through the above standard procedures, without exposure to prostaglandin therapy. Age, milk production, weight, milk progesterone levels and reproductive data were collected for all cows. Although certain between-cohort effects were statistically significant, no differences could be found between the cohorts regarding standard measures of reproductive performance (average days in milk at conception (P = 0.79), services per conception (P = 0.48), proportion of animals failing to conceive to artificial insemination (P = 0.53), and survival analysis on time to conception (P = 0.30). With evidence for biological equivalence between the two reproductive strategies, nonbiological standards such as economics or ease of execution would be appropriate in choosing between the two strategies.