Recipient Organization
AGRICULTURAL RESEARCH SERVICE
RM 331, BLDG 003, BARC-W
BELTSVILLE,MD 20705-2351
Performing Department
(N/A)
Non Technical Summary
Efficiency of milk production can be enhanced by decreasing the length of nonlactating periods, or increasing the benefit of these periods to a cow's lifetime production. Two such periods are the time from birth to first lactation, and the nonlactating period between successive lactations (dry period). We propose a unique approach to increase efficiency of milk production by increasing the number of mammary stems. Cell growth and replacement are functions of mammary stem cells. We have established procedures to identify mammary stem cells and to augment their number in vivo by simple infusion of xanthosine (ribonucleoside, a metabolic precursor for DNA and RNA), into the mammary gland. We hypothesize that increasing the mammary stem cell population will enhance the production and turnover of mammary secretory cells. This should permit rapid rearing of heifers (young female cows) and a shortened dry period, without the deleterious effects on milk production that
typically occur under these management conditions. We propose three specific aims to determine effects of xanthosine or inosine (another ribonucleoside) when these are administered: (1) to heifers reared at different rates of gain before puberty (2) to heifers during first pregnancy, when most mammary development occurs, and (3) to cows during an abbreviated dry period, when growth and cell replacement must occur. In addition to production parameters, we will evaluate effects of treatment on mammary gene expression, using state-of-the-art molecular approaches. The potential to increase production efficiency by modulating adult stem cell function is exciting, with implications to other production systems and biological processes.
Animal Health Component
20%
Research Effort Categories
Basic
80%
Applied
20%
Developmental
(N/A)
Goals / Objectives
The objectives of this project are as follows: 1) Determine if treatment of mammary glands of prepubertal heifers with xanthosine or inosine will increase the number of mammary stem cells and progenitor cells, causing a permanent increase in future milk yield. 2) Determine if treatment of mammary glands of primigravid heifers with xanthosine or inosine will increase the number of mammary stem cells and progenitor cells, causing a permanent increase in future milk yield. 3) Determine if treatment of mammary glands of multiparous cows during the dry period with inosine or xanthosine will enhance mammary cell turnover and increase milk production in the subsequent lactation. Results of the research will be published in peer-reviewed scientific journals.
Project Methods
Our broad objective is to develop strategies that promote cell proliferation and the replacement of senescent cells in the bovine mammary gland, in order to increase lactation productivity and efficiency. We previously demonstrated a noninvasive and novel method to expand the putative mammary stem cell population by infusion of xanthosine into the bovine mammary gland, a procedure that was the first non-transgenic, in vivo method to expand a somatic stem cell population. We will test the ability of intramammary infusion of xanthosine or inosine to enhance mammary cell proliferation and milk production. Experiments are designed as half-udder studies in which one side of the udder provides control glands and the other side provides treated glands. This design will increase our ability to detect treatment effects with fewer animals. We will evaluate the impact of treatment during the prepubertal period, first gestation and the dry period, on milk yield and composition
(udder-halves). Additionally, mammary tissue obtained from control and treated mammary glands of prepubertal heifers and multiparous cows during the dry period will be evaluated for parameters of cell kinetics and gene expression. Efficacy of the treatment to stimulate expansion of the mammary stem cell population in prepbuertal heifers will be assessed based on quantitative immunohistochemical analysis of the number of cells that retain bromodeoxyuridine for an extended period after initial in vivo labeling (immortal DNA strand). Epithelial cells, isolated by laser microdissection of cryosections, will also be assessed for telomerase activity and extracted RNA subjected to microarray analysis. Furthermore, ability of xanthosine treatment of the mammary glands of prepubertal heifers to increase subsequent milk production will be tested in heifers reared at normal or accelerated rates of gain. Mammary tissues from cows treated with xanthosine or inosine during an abbreviated dry period
will be assessed for parameters of cell kinetics and expression of genes of interest (by quantitative RT-PCR). These tissue analyses will provide a means to evaluate the nature and efficacy of treatments and to assess the relationship between the presence or absence of treatment-induced changes in cell populations and milk production. The latter information will be important for designing future experiments that may be more efficient or effective. Achievement of our specific aims will increase efficiency of lactation in accordance with two definitions of efficiency: 1) By decreasing the length of non-revenue-generating periods, lifetime milk production efficiency will be increased. This has been a goal of heifer rearing programs for many years and is behind the current reevaluation of shortened dry periods. 2) By increasing the number of highly secretory mammary epithelial cells, milk production will be increased disproportionately to nutrient intake, increasing efficiency of
lactation. Achievement of these goals will have significant impact on future research and application by the dairy industry.