# Carbohydrate Metabolism in the Intercaruncular Endometrium Is Affected by Form of Supplemental Selenium at Maternal Recognition of Pregnancy in Beef Heifers

## TL;DR

This study shows that the form of selenium supplement affects carbohydrate metabolism and pregnancy-related gene activity in beef heifers.

## Contribution

The study reveals that a mixed form of selenium influences endometrial gene expression and serum metabolism during pregnancy recognition.

## Key findings

- Mixed selenium supplementation increased Dio2 selenoprotein transcript abundance in the endometrium.
- Selenium form affected serum glucose and cholesterol levels during pregnancy establishment.
- RNA-Seq showed selenium-induced changes in transcripts regulating carbohydrate metabolism.

## Abstract

Selenium (Se)-deficient soils result in forages that are deficient in this trace mineral. These forages do not meet the nutritional requirement for Se in grazing beef cattle. To overcome this, producers provide Se as a supplement, typically using an inorganic form (ISe), although organic forms of Se (OSe) are available when cattle graze on forage. This Se is incorporated into a class of proteins (selenoproteins) that function as potent antioxidants, protecting cellular membranes from the toxic effects of exposure to free radicals. We previously reported that heifers supplemented with a 1:1 ratio of organic and inorganic forms of Se (MIX), versus the industry standard of ISe alone, develop longer conceptuses during maternal recognition of pregnancy. This study was designed to investigate the relationship between the form of supplemental Se, the expression of selenoproteins in the intercaruncular (ICAR) endometrium, serum concentrations of glucose, triglycerides, and cholesterol, and the global ICAR transcriptome in heifers during this pivotal period in the establishment of a pregnancy.

Selenium (Se)-deficient soils result in Se-deficient forages that do not meet the nutritional requirement for this trace mineral in grazing cattle. Supplementation of Se conventionally occurs through a basal vitamin/mineral mix containing Se in an inorganic form (ISe), although organic Se (OSe) is available when cattle graze on forage. We previously reported that the provision of supplemental Se as a 1:1 mixture of ISe:OSe (MIX), in contrast to the industry standard of ISe alone, increases early luteal phase concentrations of systemic progesterone (P4) and increases the length of the conceptus at day 17 of pregnancy. The objectives herein were to determine the effect of the form of supplemental Se on (1) the abundance of mRNA transcripts encoding the family of selenoproteins in the ICAR endometrium; (2) systemic concentrations of glucose, triglycerides, and cholesterol; and (3) the global transcriptome of the ICAR endometrium. Commercial Angus-cross heifers (N = 20) were subjected to a 45-day period of Se depletion, followed by a 45-day period (Se repletion) where they were supplemented with ISe alone. They were then randomly assigned to receive a vitamin/mineral mix containing 35 ppm Se as either ISe (n = 10) or a 1:1 ratio of ISe and OSe (MIX, n = 10) for at least 90 days prior to synchronization of estrous. Following synchronization of estrous and artificial insemination, heifers were killed on day 17 of presumed pregnancy (maternal recognition of pregnancy, MRP) with their reproductive tracts and conceptuses recovered. When pregnancy was confirmed (n = 6 per treatment), ICAR biopsies were sampled from the uterine horn ipsilateral to the functional corpus luteum (CL) for targeted qPCR and RNA-Seq analyses. Targeted qPCR analysis revealed an effect of treatment (p < 0.05) on the abundance of one selenoprotein transcript (Dio2) during MRP. The quantification of serum parameters (d 0, 7, and 17) revealed treatment effects (p < 0.05) on systemic concentrations of glucose and cholesterol, but not triglycerides. RNASeq analysis revealed significant Se-induced changes in transcripts regulating carbohydrate metabolism. Overall, coinciding with the increase in conceptus length, the form of Se affected serum parameters during the establishment of pregnancy and intercaruncular transcriptomics during MRP.