2007 Annual Report 1a.Objectives (from AD-416) The objectives of this research are to identify the basic mechanisms by which induced ovulation of smaller follicles results in decreased pregnancy establishment and embryonic survival in beef cows. Understanding these basic mechanisms will lead to identifying genes related to fertility. 1b.Approach (from AD-416) The primary experiment in this proposal is to use reciprocal embryo transfer of embryos derived from the ovulation of small or large follicles to the uterus of recipient cows that have ovulated large or small follicles to determine whether the primary obstacles to high pregnancy rates exist at the ovulatory follicle, luteal tissue derived from the ovulatory follicle or the uterus. Secondary studies will focus more closely on differences in the microenvironment of small verses large ovulatory follicles, luteal structures from small or large ovulatory follicles and the uterus following ovulation of small or large follicles and methods to reduce the proportion of cows that ovulate small follicles. 3.Progress Report This report documents research conducted under Reimbursable Cooperative Agreement 5434-31000-014-04R between ARS and the University of Missouri. Additional details of research can be found in the report for the parent project 5434-31000-014-00D, Develop Beef Cattle Better Suited for Sustainable Production. Individual embryos have been flushed from embryo donor cows on day 7 following artificial insemination. Embryos were evaluated for morphological development and embryo quality, and all recovered embryos that were judged to be alive were transferred to recipient cows within 5 hours of recovery. We have evaluated pregnancy using ultrasound in approximately one-third of the embryo recipient cows to date. This work is being conducted at Miles City under the supervision of the ADODR.