Title page for ETD etd-05192003-133446


Type of Document Master's Thesis
Author Forrest, James Walter
Author's Email Address jforrest@vt.edu
URN etd-05192003-133446
Title Effects of varying energy intakes on mammary growth and development in prepubertal heifers
Degree Master of Science
Department Dairy Science
Advisory Committee
Advisor Name Title
Akers, Robert Michael Committee Chair
Howard, Rick Dale Committee Member
Pearson, Ronald E. Committee Member
Keywords
  • estrogen receptor
  • heifers
  • mammary
  • extracellular matrix
  • nutrition
Date of Defense 2003-05-16
Availability unrestricted
Abstract
Rapid rearing of dairy heifers during late prepuberty has been linked to impairments in mammary development and reductions in milk yield. Our objective was to determine how varying energy intakes between 2 and 14 wk of age affect mammary parenchymal development. At 2 wk of age, Holstein calves were assigned to 1 of 4 treatments (HH, HL, LH, and LL) with 2 levels of energy intake (High or Low) and 2 periods of growth (2 to 8 and 8 to 14 wk of age). At 14 wk, parenchyma at the stromal interface, mid-gland, and above the cistern were collected, fixed, and embedded in paraffin. Digital images of stained sections were used to determine tissue composition (% epithelium, lumen, and stroma). Immunochemistry revealed estrogen receptor (ER) and Ki67 (nuclear proliferation antigen) positive cells, type IV collagen, fibronectin (FN), and laminin. Images representing 4 increasing grades were used to quantify ECM protein deposition. Lumenal and stromal areas were 3.5 ± 1.4% higher (p<0.01) and 4.0 ± 1.7% lower (p<0.01), respectively, in HH and HL heifers. Ki67 labeling in terminal ductular units and subtending ducts was 2.1 ± 0.8% (p<0.01) and 1.4 ± 0.7% (p<0.05) lower for the same feeding level combination. FN deposition was also increased (p<0.05) in HH and HL heifers. High rates of gain between 2 and 14 wk of age resulted in greater lumenal area and reduced cell proliferation in mammary parenchyma at 14 wk of age. Changes in FN deposition could have mediated growth differences.
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