Form of Supplemental Selenium in Vitamin-Mineral Premixes Differentially Affects Early Luteal and Gestational Concentrations of Progesterone, and Postpartum Concentrations of Prolactin in Beef Cows

Abstract

Soils with marginal to deficient levels of selenium (Se) are widespread in the northwest, northeast, and southeast US. Supplementation to the diet of forage-grazing beef cattle with a vitamin-mineral mix containing additional Se is recommended in these geographic regions. We have reported that the form of supplemental Se provided to Angus-cross beef cows can affect circulating levels of progesterone (P4) on day 6 of the estrous cycle, a time when increased P4 is known to promote fertility. The objectives of this study were to (1) confirm and expand upon our initial report that the form of Se provided to cows affects early luteal-phase concentrations of systemic P4, (2) determine the effects of the form of Se on concentrations of P4 during gestation, and (3) determine the effects of the form of Se on concentrations of prolactin (PRL) during lactation. Throughout this study, Angus-cross beef cows had ad libitum access to a vitamin-mineral mix containing 35 ppm of Se in either an inorganic form (ISe) or a 1:1 mix of inorganic and organic forms (MIX). We observed a MIX-induced increase (p = 0.006) in systemic concentrations of P4 on day 7 but not on days 4 or 10 of the estrous cycle, consistent with our earlier report. We observed a MIX-induced increase (p = 0.02) in the systemic concentration of P4 at months 1, 3, 5, and 7 of gestation, and a MIX-induced decrease (p < 0.05) in systemic concentrations of PRL at months 5 and 6 of lactation. In summary, the form of Se provided to cows can be manipulated to affect the early luteal phase and gestational concentrations of P4, and postpartum concentrations of PRL.

Form of Supplemental Selenium Affects the Expression of mRNA Transcripts Encoding Selenoproteins, and Proteins Regulating Cholesterol Uptake, in the Corpus Luteum of Grazing Beef Cows

“…The concentration of P4 was quantified in serum collected on Days 5, 6 and 7 of the estrous cycle. Although in the present study there was no observed effect of form of Se on systemic P4 (Table 2, Year 3), the difference of ~1 ng/mL between the treatment groups on Day 7 is consistent with previous studies from our lab [33,34] that used a larger number of animals (Table 2, Year 1 and Year 2). Additionally, there was no difference (p > 0.05) in the weight or the diameter of the CL, consistent with our previously reported results [33].…”

“…Further, we analyzed serum concentrations of P4 collected from cows on Days 5 to 7 of the early luteal phase to model the previously defined MIX-induced increase in P4. Our previous studies reported a 1.7 ng/mL increase in Day 6 (year one) concentrations of P4 [33], and a 1.0 ng/mL increase in Day 7 (year 2) P4 [34]. In the present study, we mimicked this difference with a 1.1 ng/mL increase in P4 on day 7 of the estrous cycle in the MIX treatment group.…”

“…In this study, we sought to investigate the mechanism responsible for increases in early luteal phase concentrations of peripheral P4 after supplementation with MIX versus the industry standard ISe [33,34]. The specified objectives were to investigate the effect of supplementation with ISe or MIX-form Se on (1) the relative abundance of mRNA transcripts that encode selenoproteins and targeted steroidogenic enzymes in the CL, and (2) the ability of dissociated luteal cells to synthesize P4 in response to key agonists in vitro.…”

“…Research has indicated differences in the assimilation of Se, dependent on the form being fed, with lower blood and milk concentrations of Se in cows supplemented with an inorganic (ISe) versus organic (OSe) form [25][26][27][28][29][30][31][32]. Previously, our lab demonstrated that a 1:1 blend of ISe and OSe (MIX) provided to cows to achieve a Se-adequate status resulted in a 1.0 to 1.7 ng/mL increase in early (Days 6 and 7) luteal phase concentrations of P4 when compared to cows supplemented with ISe and/or OSe alone [33,34]. This elevated P4 occurs without any effect on diameter of the CL [33].…”

“…With no knowledge of how different forms of supplemental Se affect the expression of transcripts encoding selenoproteins in the CL, nor of the mechanism by which supplementation with MIX increases early luteal phase [33,34] or gestational [34] concentrations of systemic P4, the primary objectives of this study were to determine the effect of form of Se on (1) the relative abundance of mRNA transcripts that encode selenoproteins and targeted steroidogenic enzymes in the CL, and (2) the ability of dissociated luteal cells to synthesize P4 and respond to key agonists in vitro. To achieve this goal, we assigned cows to form of Se-treatment regimens (ISe versus MIX) that achieved a Se-adequate status in all cows, then collected CL from these cows on Day 7 of the estrous cycle for molecular and in vitro analyses.…”