Author ORCID Identifier

Date Available


Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation


Agriculture, Food and Environment


Animal and Food Sciences

First Advisor

Dr. Phillip J. Bridges


Selenium (Se) deficient soils and thus forages are widespread throughout the United States, necessitating supplementation of this trace mineral in the diet of grass-fed cattle to negate detrimental effects of a deficiency on immune function, growth, and fertility. Conventionally, Se is supplemented to cattle in a vitamin-mineral mix as an inorganic form (ISe) although the organic forms (OSe) are available when cattle consumer forage, and OSe has been shown to increase the bioavailability of Se in cattle. Previous research has demonstrated supplementation with 1:1 mixture (MIX) of ISe and OSe compared to ISe alone increases systemic concentrations of progesterone (P4) in the early luteal phase of cows at a time in which the concentration of P4 can critically influence the endometrium and developing conceptus. Herein, a series of experiments were conducted to 1) determine the mechanism responsible for the MIX-induced increase in the early luteal phase concentration of systemic P4, 2) identify form of Se effects on systemic blood metabolites during early gestation, and 3) investigate interferon-induced changes in the caruncular (CAR) tissue of the endometrium as a response of different supplemental forms of Se (ISe vs. MIX) which may affect the ensuing process of implantation. The objectives of Experiment 1 were to confirm and expand upon the initial report of the MIX-induced increase in early luteal phase P4, determining systemic changes in P4 throughout gestation, and prolactin (PRL) throughout lactation. We observed a MIX-induced increase in systemic concentrations of P4 on day 7 of the estrous cycle, consistent with our initial report, with circulating P4 then remaining higher throughout gestation. In contrast, prolactin was lower in the MIX supplemented heifers at months 5 and 6 of lactation; supplemental form of Se can be used to manipulate early luteal phase and gestational concentrations of P4, and postpartum concentration of PRL. The objective of Experiment 2 was to investigate the mechanistic changes in the CL contributing to the increase in systemic P4 by analyzing changes in mRNA transcripts in the CL and the responses of steroidogenic luteal cells to select agonists in vitro. Initially, we observed human chorionic gonadotropin (hCG)-induced increases in P4 in culture media of luteal cells obtained from ISe-supplemented cows. Interestingly, qPCR revealed no significant differences in the steroidogenic transcripts in the CL, however the abundance of mRNA encoding 2 key transcripts regulating cholesterol uptake (Ldlr and Hsl) was increased in MIX-supplemented cows, collectively suggesting that the form of Se-induced effects on luteal production of P4 are the result of changes in cholesterol availability, rather than a direct effect on the expression of steroidogenic enzymes within the CL. Following Experiment 2, we investigated changes in systemic blood metabolites during early gestation in response to the form of Se. Therefore, the objective of Experiment 3 was to quantify relative changes in serum metabolic parameters at estrus, during the early luteal phase, and at maternal recognition of pregnancy (MRP). MIX-supplemented heifers compared to ISe had significantly lower concentration of total serum cholesterol and low/very low-density lipoproteins, as well as changes in serum glucose, aspartate aminotransferase (AST), and beta hydroxybutyrate (BHBA). The objective of Experiment 4 was to investigate transcriptomic changes in the CAR regions of the endometrium at MRP. Results revealed significant changes in interferon signaling and endometrial restructuring that would be expected just prior to implantation. Given the advanced conceptus development observed in MIX vs. ISe-supplemented heifers, coincident with the concurrent decrease in the level of expression of several known MRP-associated transcripts, it appears that the MIX supplement is shifting the timing of MRP, resulting in hastened conceptus development. Encompassing all results, manipulating the form of Se in the diet of grazing beef cattle significantly alters systemic levels of P4, blood metabolites, and transcriptomic changes in the CL and endometrium that can advance conceptus development during early gestation. MIX Se is a novel producer-friendly supplement that can ultimately improve whole animal physiology and fertility.

Digital Object Identifier (DOI)

Funding Information

This study was funded by the Agriculture and Food Research Initiative Competitive Grant no. 2018-67015-27613 from the USDA National Institute of Food and Agriculture (NIFA) from 2018-2023.