Year of Publication

2013

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture

Department

Animal Science

First Advisor

Dr. James C. Matthews

Abstract

Estradiol (Compudose®, COM) implants are extensively used in beef cattle production systems to alter body composition and feed efficiency. Little information exists about the physiological mechanisms affected by COM treatment in growing, mature, and senescent female cattle. Moreover, no reports describe the level of blood estradiol resulting from COM treatment. The effect of COM on levels of plasma estradiol and blood metabolites and proteins, and relative content of glutamine synthetase (GS) and other amino acid nitrogen-metabolizing enzymes in liver tissue, was studied using three experimental models relevant to cow-calf production regimens: senescent cows (Trial 1), young mature (young) versus senescent (old) cows (Trial 2), and growing heifers (Trial 3). In Trial 1, plasma estradiol concentrations were 222 % more after 14 and 28 d in COM-implanted than sham implanted (Control) cows. COM treatment did not affect measured blood metabolites and enzymes, but increased hepatic GS protein expression by 350% after 14 d and 200% after 28 d of implantation. In contrast, protein expression of alanine transaminase, aspartate transaminase, glutamate dehydrogenase, and two glutamate transporters was not affected by COM. In Trial 2, plasma estradiol concentrations of COM implanted young and old cows were 48% higher than Control groups, whereas blood metabolites were not affected. COM implantation did not affect GS protein expression in young cows, but tended to increase GS expression in the old cows by 283% after 14 d and 41% after 28 d. GS mRNA content was increased about 38% in both young and old COM-treated cows. Hepatic content of beta-catenin and G protein-coupled receptor 30 (GPR30) content was not affected by COM treatment, indicating that estradiol-mediated GS expression was not regulated by beta-catenin- or GPR30-controlled pathways. In Trial 3, plasma estradiol levels in COM-treated heifers were 70% higher in COM heifers, concomitant with increased levels of total bilirubin and creatine kinase, and decreased creatinine. Correlation analysis of plasma estradiol levels and blood constituents only identified a positive correlation between plasma estradiol and potassium. Collectively, these data describe positive estradiol-mediated effects on hepatic metabolism and blood parameters in female cattle.

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