131 Selenium-form effects on hepatic function and selenoprotein mRNAs in the early pregnant heifer
Authors: Jackson Jordan , Stamper Elizabeth , Crites Benjamin , Son Kwangwon , Carr Sarah , Bridges Phillip 
Published: March 2024

Abstract
Selenium (Se) is an integral component of selenoproteins, with effective scavenging of harmful reactive oxygen species (ROS) by selenoproteins necessary to protect cells from oxidative stress. Due to the presence of Se-deficient soils in large portions of the US, including the southeast cow-calf producing states, grazed forages are insufficient in this trace mineral and dietary supplementation is recommended. We have investigated the effects of providing Se in an inorganic form (ISe, the industry standard) versus a 1:1 mixture (MIX) of ISe to organic Se (OSe), and have observed significant effects on luteal function, endometrial function and conceptus development. Herein, our objective was to determine the effect of form of Se on 1) clinical markers of total antioxidant capacity and liver function, and 2) the expression of mRNAs encoding selenoproteins in the liver. Following consecutive 45-d periods of Se-depletion then repletion, Angus-cross heifers were assigned to 90 d of treatment with a vitamin-mineral mix containing 35-ppm Se as ISe or MIX. Heifers were then inseminated at estrus (d 0) with serum collected at d 0, 7 and 17 to quantify albumin, beta-hydroxybutyrate (BHBA) and aspartate aminotransferase (AST). Liver samples were collected at euthanasia on d 17 (n = 6 pregnant heifers per treatment) for the quantification of the relative abundance of 25 selenoprotein mRNAs using qPCR. There was no effect of treatment on circulating albumin (P &gt; 0.05). Hepatocyte-secreted albumin is the most prominent antioxidant in the circulation, with this result suggesting that albumin-driven redox capacity is not sensitive to the form of Se supplied to achieve a Se-adequate status. Systemic concentrations of BHBA and AST were increased (P &lt; 0.05) in MIX- versus ISe-treated heifers at d 7 and 17 of pregnancy. Circulating BHBA is considered a primary indicator of liver function and the hepatic response to increased metabolic demands, whereas increased AST is conventionally considered a marker for liver damage. These results suggest increased demands on the liver in MIX versus ISe-treated heifers, however not at the level indicative of dysfunction or disease. Additionally, the serum concentration of urea nitrogen was quantified and determined to be reduced (P &lt; 0.05) at estrus in MIX- versus ISe-treated heifers, indicative of form-induced changes in hepatic nitrogen metabolism. Targeted qPCR analysis to determine the effect of treatment on the abundance of encoding selenoproteins by mRNA, including the iodothyronine deiodinases, glutathione peroxidases and thioredoxin reductases, was largely unaffected by treatment, with only the abundance of mRNA encoding Selenoprotein V tending to differ (P = 0.07) with treatment. Overall, this study revealed form of Se-effects on markers of hepatic health and function, as well as blood urea nitrogen, but did not reveal form of Se-effects on the expression of hepatic selenoproteins mRNAs.