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Impacts of exogenous estradiol on mammary collagen distribution in Holstein heifers.

C. T. Oduyelu

Abstract:

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Impacts of exogenous estradiol on mammary collagen distribution in Holstein heifers.
C. T. Oduyelu*, C. L. M. Parsons, A. J. Geiger, R. M. Akers, K. M. Daniels. Virginia Tech Blacksburg, VA.

Mammary collagen distribution is dynamic during growth. The objective was to determine effects of exogenous estradiol on mammary collagen distribution in Holstein heifers fed an enhanced (EH) diet. Twelve Holstein heifers (6 � 2d old) were fed milk replacer (28.9% CP, 26.2% fat, DM basis), at 1.08 kg powder DM/d. Starter (26% CP; DM basis) was offered beginning at 4wk of age. Heifers received ear implants containing either estradiol (EH-E2; n = 6; 25.7 mg estradiol) or placebo (EH; n = 6) at weaning (8wk). Heifers were slaughtered at 10wk. Mammary samples were collected from 2 zones within front right mammary glands (EH-E2, n = 6; EH, n = 4), formalin fixed, and paraffin embedded. Zone 1 (Z1) was the parenchymal area immediately above the gland cistern. Zone 3 (Z3) was the interface of mammary parenchyma and mammary fat pad. Five-�m thick sections were stained with Picro-Sirius Red and Picro-Fast Green. Four to 6 total matched images per heifer and zone were obtained under both brightfield and polarized monochrome conditions using 20x objective lens magnification. A mask of epithelial areas was created per brightfield image with Image ProPlus (version 7; Media Cybernetics). Cell Profiler (version 2.1.1; www.cellprofiler.org) used the mask and monochrome images to measure stromal collagen birefringence. Dependent variables for each image were: total stromal area, stromal collagen area, and collagen as a percent of stromal area. Data were analyzed with a statistical model that included fixed effects of treatment, zone, and their interaction; heifer within treatment was the random effect. Total stromal area did not depend on treatment, zone, or the interaction. Stromal collagen area was not impacted by interaction or treatment but did depend on zone (P < 0.01). Stromal collagen area was 25,902 � 1461�m2 in Z1 and 16,159 � 1461�m2 in Z3. Percent of stromal area occupied by collagen was likewise affected by zone (P < 0.01), averaging 11.8 � 0.7% in Z1 and 7.2 � 0.7% in Z3. Overall, collagen deposition in mammary stroma was not impacted by exposure to exogenous estradiol but was dependent on sampling zone, with established areas (Z1) having more collagen than active growth regions (Z3).

Keywords:

Biography: Tope Oduyelu is a senior in the Dairy Science Department at Virginia Tech. She will be presenting original undergraduate research that she performed in Dr. Kristy Daniels' laboratory.