42 Quantifying mammary growth and proliferative effects of estradiol in Holstein heifer calves

Abstract

Abstract Growth of the bovine mammary gland is influenced by estradiol during a heifer’s life. The objective of this study was to determine the effect of estradiol administration on two different mammary parenchymal tissue regions and quantify the response in cellular proliferation between different estradiol treatments and regions. Treatments were administered daily during the 12 days prior to euthanasia at 82 days of age. Holstein heifer calves (n = 12) were divided amongst 3 treatments, control (n = 4, CON), short term (n = 4, SHORT), and long term (n = 4, LONG). CON calves were administered corn oil injections while SHORT calves received 9 injections of corn oil followed by 3 injections of estradiol; LONG calves received 12 injections of estradiol. BrdU was administered 2 hours prior to harvest to label proliferating mammary epithelial cells. Mammary parenchyma was dissected from the right rear gland and separated into two regions, center and edge parenchyma, for further examination. Tissues were examined using brightfield microscopy and fluorescent immunohistochemistry. LONG calves had a greater percentage (P < 0.05) of epithelial tissue area (34.0% ± 1.51) than CON (21.4% ± 1.5) and SHORT (23.0% ± 1.51) calves, and a lower stromal tissue area percentage (63.6% vs 73.9% and 74.0% ± 2.10, respectively; P < 0.05). There was a treatment by region interaction in the cellular proliferation. LONG calves had a greater percentage of proliferating epithelial cells than CON calves in the center (P < 0.05) and edge (P < 0.05) parenchymal regions, and a greater percentage of proliferating cells in the center parenchyma than SHORT calves (P < 0.05). These results indicate that duration of estradiol administration elicits different effects on mammary growth and that mammary epithelial cell proliferation is specific to mammary gland region.