Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: March 10, 2008
Publication Date: July 1, 2008
Citation: Daniels, K.M., Capuco, A.V., James, R.E., Mcgilliard, M.L., Akers, R.M. 2008. Diet Does Not Affect Putative Mammary Epithelial Stem Cells in Pre-weaned Holstein Heifers. [abstract]. Journal of Dairy Science.
Overfeeding prepubertal heifers can impair mammary epithelial growth and development, processes that depend on stem cells. In this study we evaluated effects of diet composition on putative bovine mammary epithelial stem cell populations using a 5-bromo-2-deoxyrudine (BrdU; a thymidine analog) label retention method. Stem cells retain BrdU over time through selective segregation of labeled template DNA strands during mitosis, whereas label is diluted in non-stem daughter cells. Twenty-four newborn heifers were fed one of four milk replacer (MR) diets (n=6/diet): CON (20% CP, 21% fat MR fed at 441 g DM /d), HPLF (28% CP, 20% fat MR fed at 951 g DM/d), HPHF (27% CP, 28% fat MR fed at 951 g DM/d), and HPHF+ (27% CP, 28% fat MR fed at 1431 g DM/d). Calves were fed twice daily; water and starter (20% CP, 1.43% fat) were offered free choice. At 30 d of age heifers were given (5 mg/kg BW) BrdU once daily for 4 d. Heifers were euthanized 29 d later. Udders were removed and mammary tissue collected from 4 parenchymal regions (2 peripheral and 2 cisternal) within the left front quarter. Histological sections were prepared and processed for dual-label immunofluorescent detection of Ki67, a nuclear proliferation antigen, and BrdU. Digital images were obtained at 40x magnification from 10 regions per slide. Labeled cells were counted manually and total number of epithelial cells determined using image analysis software. Diet had no effect on percentage of labeled mammary epithelial cells, nor was there a diet by region interaction. The percentage of BrdU-labeled epithelial cells was greatest in cisternal regions of the gland (2.39 ± 0.44) and decreased toward the periphery (0.73 ± 0.45). The opposite was true for Ki67-labeled epithelial cells (8.97 ± 0.81 vs. 10.88 ± 0.77%), consistent with decreased proliferation and increased cell cycle arrest in cisternal regions. In peripheral regions, the percentage of BrdU-labeled epithelial cells averaged 0.12 ± 0.1. Data indicate that number of putative mammary epithelial stem cells was not affected by pre-weaning diet.