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.
Two animal experiments were initiated. The first experiment was designed to confirm and extend our previous finding that xanthosine infusion into the mammary gland of prepubertal Holstein heifers increased the number of putative stem cells, assessed by retention of BrdU-labeled DNA for an extended period (~40 d). Five Holstein heifer calves (~3 mo of age) were administered xanthosine into two ipsilateral mammary glands for five consecutive days. Another five calves were administered inosine. BrdU was administered after each nucleoside treatment. Heifers were sacrificed 45 d after the last treatment and tissues collected. We are in final stages of assessing the percentage of label retaining epithelial cells (LREC) in each quarter to determine efficacy of each nucleoside. A second experiment was initiated to test the hypothesis that stimulated expansion of the mammary stem cell population via xanthosine treatment of prepubertal heifers will produce a cascade of progenitor and epithelial cell proliferation, promote entry into lactation with an increased number of functional secretory cells, and support increased milk yield. This will be assessed in heifers reared at moderate (650 g/d) and accelerated (1000 g/d) rates of daily gain prior to puberty. At 2 mo of age, 26 Holstein heifers were randomly assigned to one of the two dietary groups fed to achieve the targeted rates of gain. At 3 mo of age, each heifer had two quarters within the udder treated with xanthosine while contra lateral quarters serve as controls. After heifers reach puberty they will be housed and managed in accordance with the BARC herd’s standard rearing and breeding system. Onset of puberty is being monitored by blood progesterone screening of heifers. Targeted rates of gain are being achieved and heifers are beginning to reach puberty. Following parturition, cows will be milked twice daily and milk yield recorded through lactation. One d/wk cows will be milked with a quarter-milker and milk weights recorded. Milk component analysis and somatic cell count will be assessed. We anticipate the first cow entering lactation in early 2010. These two experiments address Specific Aim #1 of the grant.