Pregnancy rates and non-return rates following artificial and natural breeding in dairy herds

Information routinely supplied during the conduct of a dairy herd health program was analysed to evaluate the performance of artificial breeding in Victoria. A comparison was made between 60 to 90-day non-return rates (supplied by artificial breeding centres) and pregnancy rates (determined by manual pregnancy diagnosis) for first artificial inseminations in 108 herd years in which both items were available in the 1973 and 1974 breeding seasons. The values were 69.3% and 58.2% respectively (P less than 0.001). Non-return rates and conception rates were found to decline as herd size increased. Pregnancy rates to first artificial and natural services did not differ significantly from each other but pregnancy rates were significantly more variable to natural than artificial service (P less than 0.001). The mean pregnancy rate to artificial insemination for all herd years studied was 57.5% and the pregnancy rate to natural service was 58.0%.