Organization of mammary blood vessels as affected by mammary parenchymal region and estradiol administration in Holstein heifer calves

Abstract

Mammary blood flow is central to mammary growth, development, and productivity, but the 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 mammary parenchymal tissue. Holstein heifer calves (n = 12) received daily injections on the days immediately preceding euthanasia at 82 d of age. Treatments were control (CON), short-term estradiol (STE), and long-term estradiol (LTE). The CON calves received corn oil injections, the STE calves received 9 injections of corn oil followed by 3 injections of estradiol, and the LTE 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. Results showed that LTE calves had a greater tissue area occupied by epithelium than CON and STE calves, and the epithelial area in CON and STE calves was similar. Edge parenchyma had a greater percentage of proliferating epithelial cells than center parenchyma across all treatment groups. In the edge region, LTE calves had the greatest percentage of proliferating epithelial cells, coinciding with greater epithelial area. The number of blood vessels per unit of tissue area was greater in center than in edge parenchyma; the corresponding vessel surface area per unit of tissue area followed the same pattern. Mammary blood vessel measures were not markedly influenced by estradiol treatment. These results highlight the marked difference in the number and organization of blood vessels in different mammary parenchyma regions but indicate that the effects of estradiol on stimulating mammary epithelial proliferation does not directly translate to increasing numbers of blood vessels.

Estradiol administration in Holstein heifer calves differentially affects the fatty acid composition of subcutaneous adipose and the mammary fat pad tissues

“…The extended duration of estradiol administration resulted in a reduced abundance of C18:2 t10 c12 in the SCA relative to MFP tissues of LONG calves ( P < 0.05); this effect was absent for CON and SHORT calves ( P > 0.05). This result is associated with the fact that LONG calves had significantly more mammary epithelial growth than that of CON and SHORT calves (Hardy et al ., 2021). Further, C18:1 t10 was significantly differentially affected ( P = 0.01) and C18:1 t11 demonstrated a numerical difference ( P = 0.08) by the interaction of estradiol treatment and adipose depot.…”

“…The relative abundance of the different fatty acids (percentage, %) were designated as the dependent variables in separate models and analyzed using PROC MIXED in SAS 9.4 (SAS Institute Inc., Cary NC). A model structure like that described by Hardy et al (2021) was used to analyze the resulting percentages, which included the fixed effects of estradiol treatment (n = 3), adipose tissue depot (n = 2), and their interaction. Calf BW block, and the interactive effect of BW block with estradiol treatment were specified as random effects.…”

“…A model structure like that described by Hardy et al . (2021) was used to analyze the resulting percentages, which included the fixed effects of estradiol treatment ( n = 3), adipose tissue depot ( n = 2), and their interaction. Calf BW block, and the interactive effect of BW block with estradiol treatment were specified as random effects.…”

“…The tissues examined were collected from an experiment previously detailed by Hardy et al . (2021), of which experimental procedures were approved by The Ohio State Institutional Animal Care and Use Committee (Protocol 2019A-00000018). Briefly, 12 prepubertal Holstein heifer calves were purchased from a single commercial dairy at 7 d of age and reared on a common ration for the duration of the trial, which lasted for approximately 11 weeks.…”

“…All treatment injections were administered subcutaneously on alternating sides of the neck. Because estradiol is lipid soluble, it was first dissolved in an absolute ethanol and benzyl benzoate mixture and then combined with corn oil, yielding a final injectable solution of 10% absolute ethanol, 20% benzyl benzoate, and 70% corn oil by volume as previously detailed (Hardy et al ., 2021). 17β estradiol (Sigma-Aldrich Co., St. Louis, MO; cat no.…”