Date of Award

8-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

Henry G. Kattesh

Committee Members

Peter D. Krawczel, Ky G. Pohler, Justin D. Rhinehart, Brynn H. Voy, Brian K. Whitlock

Abstract

Corticosteroid-binding globulin (CBG) transports glucocorticoids and progesterone, but little is known about CBG in the bovine reproductive tract. Pseudomonas aeruginosa is an environmental bacteria capable of colonizing the vaginal cavity of other species. P. aeruginosa presence within the bovine vaginal cavity is not well characterized, yet evidence suggests that a controlled internal drug release device (CIDR) can alter the bacterial abundance within the cavity. P. aeruginosa produces a protease that cleaves the reactive center loop of CBG allowing for the release of the steroid into its active form. Thus, the objective of this study was to examine effects of progesterone released from a CIDR on circulating and vaginal concentrations of CBG, the proportion of free progesterone and cortisol, and presence of P. aeruginosa following synchronization of ovulation. Prior to CIDR insertion (d -7) and following removal (d 0), blood and vaginal flush samples were collected from each heifer (n=67). Plasma collected at pregnancy diagnosis (d 38) from pregnant heifers (n=24) had greater (P=0.02) concentrations of progesterone than samples collected on d -7, but were similar to those measured on d 0. Similarly, plasma CBG concentrations measured on d -7 and 0 did not differ, but were greatest (P=0.03) on d 38. The free progesterone index (FPI) calculated from progesterone and CBG concentrations measured on the three sampling days were not different (P=0.16). During the CIDR insertion period, P. aeruginosa abundance decreased (P<0.0001), and on d 0, P. aeruginosa abundance was related to both CBG concentration (r=-0.25; P=0.05) and FCI (r=0.37; P=0.004). The third study aimed to determine if CBG mRNA is expressed within the vagina and uterus of abattoir-sourced reproductive tracts (n=3) to determine the source of CBG within the vaginal cavity. In the tissues collected, CBG gene was not expressed within the vaginal epithelium, but was expressed in the uterine endometrium. In summary, CIDR insertion did not affect CBG concentrations, but CBG may regulate the free fraction of progesterone in circulation during early gestation. Additionally, P. aeruginosa within the vaginal cavity of heifers may alter the free proportion of cortisol as seen by a reduction in CBG concentration.

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