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Mammary blood vessel development in response to estradiol administration in heifer calves.

N. R. Hardy


Mammary blood vessel development in response to estradiol administration in heifer calves.
N. R. Hardy*1, K. M. Enger1, M. L. Eastridge2, L. E. Moraes2, B. D. Enger1. 1The Ohio State University, Department of Animal Sciences, OARDC Wooster, OH, 2The Ohio State University, Department of Animal Sciences Columbus, OH.

Mammary blood flow is central to mammary growth, development, and productivity, but development of the vasculature network is poorly understood. The objective of this study was to determine how the vascular system adapts to mammary growth by inducing different levels of mammary growth and examining 2 regions of the mammary tissue. Holstein heifer calves received 12 daily injections on the days immediately preceding euthanasia at 82 d of age. Treatments were control (n = 4, CON), short-term estradiol (n = 4, SHORT), and long-term estradiol (n = 4, LONG). CON calves received corn oil injections while SHORT calves received 9 injections of corn oil followed by 3 injections of estradiol; LONG calves received 12 estradiol injections. Mammary tissues were collected from the center and edge parenchymal regions of all right rear mammary glands to quantify the tissue area of various tissue structures, the percentage of proliferating epithelial cells, and the number and form of blood vessels. Data were analyzed using PROC MIXED with the fixed effects of calf treatment and parenchymal region, and calf nested within treatment as a random effect. Results showed LONG calves had a greater tissue area occupied by epithelium (34.0% � 1.5, P < 0.05) than CON and SHORT calves (21.4% and 23.0% � 1.5, respectively), while CON and SHORT calves were similar. Edge parenchyma had a greater percentage of proliferating epithelial cells than center parenchyma across all treatment groups. Within the edge region, LONG calves had the greatest percent of proliferating epithelial cells (P < 0.05). Blood vessel number per unit of tissue area was greater in center than edge parenchyma (395 vs 295 � 19 vessels/mm2, P < 0.001, respectively); the corresponding vessel surface area/unit of tissue area followed this same pattern (23,140 vs 18,166 � 1088 μm/mm2, P < 0.001). These vessel measures were not affected by estradiol treatment (P > 0.1). These results show there is a large difference in blood vessel number in the center versus the edge parenchyma and estradiol treatment elicits mammary growth but not necessarily increases in blood vessel formation.

Keywords: angiogenesis, growth, endothelium.

Biography: Nicole Hardy originates from Bucks County, Pennsylvania and received Bachelors of Dairy Science from Virginia Tech in 2018. Currently, Nicole is a masters student at the Ohio State University, OARDC studying the development of the mammary vasculature in calves under the advisement of Dr. Benjamin Enger. After finishing her degree, Nicole looks forward to starting a career in Agricultural Extension or in an industry position.