2008 Annual Report 1a.Objectives (from AD-416) Develop strategies that promote cell proliferation and replacement in the bovine mammary gland, in order to increase lactational productivity and efficiency. 1b.Approach (from AD-416) We propose to accomplish the research objective by utilizing and extending current knowledge of mammary stem cell biology. Our specific aims are to manipulate mammary stem cell activity to enhance the growth of mammary epithelium and promote the replacement of senescent cells. 3.Progress Report A study was completed to evaluate the efficacy of xanthosine and inosine infusions into the mammary gland of prepubertal Holstein heifers as a method to increase the number of mammary stem cells. Tissues have been collected and analyses are in progress. A second study to evaluate the impact of treatment of mammary glands of prepubertal heifers with xanthosine or inosine on milk production is in progress and will last the duration of the project. These two experiments address Specific Aim #1 of the grant. Monitoring activities associated with this project included annual updates presented to CSREES-NRI NPS at the ADSA/ASAS National Meeting and submission to CSREES-NRI of an annual progress report.