Bioscientifica Proceedings

Summary. Synchronization of ovulation and subsequent timed artificial insemination became a popular practice in modern, large scale, dairy and beef commercial operations. Popularity was because it became a serious option to eliminate a laborious and low efficiency activity in the industry: checking cows for heat. Synchronization protocols involve the sequential administration of reproductive hormones to manipulate the estrous cycle to provide a fertile oocyte for insemination at a predictable moment. In the last 20 years, great effort was put forth in protocol development and adjustment; current rates of synchronous ovulations are 80–90%. Moreover, fertility to current protocols is similar to that obtained in cows inseminated after heat detection. The present wave of protocol development proposes to face the challenge of further improving pregnancy success of current protocols. The guiding principle is that, due to the intense metabolism associated with copious milk production, steroid hormone concentrations are insufficient for adequate reproductive function. Thus, new protocols have incorporated strategies to adjust the endocrine milieu and consequently support specific portions of the synchronization process. This paper discusses the positive fertility impact of protocol design that incorporated the following concepts: controlling P4 concentrations during follicle growth to increase oocyte quality; reducing circulating P4 prior to AI to increase proportion of cows pregnant; providing estrogen priming during proestrus to benefit conception and reduce embryo mortality; and optimizing progesterone priming during early diestrus to enhance conceptus survival. It is expected that adoption of these concepts will lead to a continuous increase in fertility of lactating dairy cows.

© 2014 Society for Reproduction and Fertility