Biological Trace Element Research

, Volume 140, Issue 2, pp 151–169 | Cite as

Dietary Supplementation of Selenium in Inorganic and Organic Forms Differentially and Commonly Alters Blood and Liver Selenium Concentrations and Liver Gene Expression Profiles of Growing Beef Heifers

  • Shengfa F. Liao
  • Kelly R. Brown
  • Arnold J. Stromberg
  • Walter R. Burris
  • James A. Boling
  • James C. Matthews
Article

Abstract

In geographic regions where selenium (Se) soil concentrations are naturally low, the addition of Se to animal feed is necessary. Even though it is known that Se in grass and forage crops is primarily present in organic forms (especially as L-selenomethionine, L-selenocystine, and L-selenocystathionine), the feeding of Se in the naturally occurring organic selenium (OSe) compounds produces higher blood and tissue Se levels than the inorganic Se (ISe) salts, and that animal metabolism of OSe and ISe is fundamentally different. Se is commonly added in inorganic form as sodium selenite to cattle feeds because it is a less expensive source of supplemental Se then are OSe forms. A trial was conducted with growing cattle to determine if the addition of OSe versus ISe forms of Se in beef cattle feed produces differences in hepatic gene expression, thereby gaining insight into the metabolic consequence of feeding OSe versus ISe. Thirty maturing Angus heifers (261 ± 6 days) were fed a corn silage-based diet with no Se supplementation for 75 days. Heifers (body weight = 393 ± 9 kg) then were randomly assigned (n = 10) and fed Se supplements that contained none (control) or 3 mg Se/day in ISe (sodium selenite) or OSe (Sel-Plex®) form and enough of a common cracked corn/cottonseed hull-based diet (0.48 mg Se/day) to support 0.5 kg/day growth for 105 or 106 days. More Se was found in jugular whole blood and red blood cells and biopsied liver tissue of ISe and OSe treatment animals than control animals, and OSe animals contained more Se in these tissues than did ISe. Microarray and bioinformatic analyses of liver tissue gene expression revealed that the content of at least 80 mRNA were affected by ISe or OSe treatments, including mRNA associated with nutrient metabolism; cellular growth, proliferation, and immune response; cell communication or signaling; and tissue/organ development and function. Overall, three Se supplement-dependent gene groups were identified: ISe-dependent, OSe-dependent, and Se form-independent. More specifically, both forms of supplementation appeared to upregulate mitochondrial gene expression capacity, whereas gene expression of a protein involved in antiviral capacity was downregulated in ISe-supplemented animals, and OSe-supplemented animals had reduced levels of mRNA encoding proteins known to be upregulated during oxidative stress and cancerous states.

Keywords

Bovine Blood Liver Microarray Nutrient–gene interaction Selenium supplementation 

Abbreviations

ANOVA

analysis of variance

CL-43

collectin-43

GCL

glutamate-cysteine ligase

GCLC

glutamate-cysteine ligase catalytic subunit

GCLM

glutamate-cysteine ligase modifier subunit

IGF

insulin-like growth factor

IGFBP

insulin-like growth factor binding protein

ISe

inorganic selenium

KLF

Kruppel-like factor

OSe

organic selenium

PRKCI

protein kinase C iota

Se

selenium

Introduction

A survey of whole blood Se concentrations to determine the geographic distribution of Se deficiency among beef cows and heifers in the United States found that 42% of cattle in the southeastern United States (including Kentucky) were Se deficient (≤0.080 μg/mL) compared to 18% of deficient animals nationally [1]. For beef cattle production in the low-Se regions of Kentucky, additions of Se to feedstock are necessary [2, 3]. To ruminant feed, selenium is still usually added in inorganic chemical forms (ISe), either as sodium selenite or sodium selenate, as these were the first to be approved as animal feed additives [4, 5]. More recently, Se-enriched yeast, in which L-selenomethionine is the predominant form of Se, has become available and has been approved as a feed additive for beef cattle production [6, 7].

According to the National Research Council [3] and Food and Drug Administration [4], Se can be legally supplemented in beef cattle diets to provide 3 mg/head daily or 0.3 mg/kg in complete diets, although the Se requirement of beef cattle can be met by 0.1 mg/kg of diet. The acceptable level of Se in free-choice salt–mineral mixtures is 120 mg/kg [4].

In terms of bioavailability and biopotency of dietary organic Se (OSe) versus ISe supplementation, many comparisons have been made in the last two decades using a variety of domestic animal species [8, 9, 10]. The amount of total Se versus OSe forms in animal tissues has been compared. In the breast and leg tissues of chickens, selenomethionine and selenocysteine accounted for about 67% and 20% and 56% and 32%, respectively, of the total Se content [11]. In lambs, selenomethionine and selenocysteine accounted for about 57% and 36% and 45 and 36% of the total Se content in the tenderloin and rib eye muscles, respectively. In contrast, selenomethionine and selenocysteine accounted for about 20% and 60%, 18% and 60%, and 8.8% and 88%, of the total Se tissue content in the heart, liver, and kidney tissue, respectively, of lambs [11]. Despite these basal tissue-specific differences in selenomethionine and selenocysteine content, a follow-up dose–effect trial found that more of the diet-supplemented selenomethionine accumulated in all of these lamb tissues than did equivalent amounts of dosed selenocysteine [11]. One plausible explanation for the greater accumulation of selenomethionine versus selenocysteine is that selenocysteine incorporation into polypeptide chains requires a selenocysteine-specific tRNA, whereas selenomethionine can substitute for methionine during protein synthesis [12].

With regard to the effect of dietary OSe versus ISe on Se bioavailability and biopotency in cattle, the milk of cows fed high selenomethionine-containing yeast contains more Se than cattle fed equal amounts of sodium selenite [13]. In beef cattle, it was found that the bioavailability (defined as blood and tissue Se concentrations) of Se from OSe was higher (approximately 200%) than that from ISe [14, 15, 16, 17], as was biopotency (blood glutathione peroxidase activity) [15, 16, 18].

In terms of production responses of dietary OSe versus ISe, the majority of studies [15, 16, 19] did not detect any difference between ISe and OSe forms in beef production performance measurements, such as average daily gain, average daily feed intake, or gain:feed ratio. However, some improvements have been reported in the average daily gain of OSe-supplemented feedlot steers [20] and calves born from OSe-supplemented cows [18]. Therefore, OSe was recommended to replace ISe for common beef production practices [8].

In contrast to the number of studies assessing the effects of OSe versus ISe supplementation of beef cattle diets on whole-animal parameters, little research has been conducted to delineate the effect of dietary Se supplementation on gene expression, despite the understanding that form of Se supplementation is thought to mediate different metabolic pathways and predominant forms of Se in liver tissue [2, 5, 8, 11, 21]. Comparison of hepatic gene expression profiles of ISe- versus OSe-supplemented cattle may provide understandings that have critical commercial consequences, including development of supplementation regimens that contain the optimal forms of Se supplementation for a given physiological challenge.

We hypothesized that dietary supplementation of OSe or ISe to a practical diet for maturing beef heifers, that had adequate hepatic Se levels, would differentially affect both the amount of Se in blood and liver and gene expression profiles of liver tissue. The specific objectives of this study were to test the effect of ISe (sodium selenite) versus OSe (Sel-Plex®) on (1) Se concentrations in blood fractions and liver tissue and (2) liver mRNA expression profiles of mature Angus heifers gaining about 0.5 kg/day in body weight.

Materials and Methods

Animal Trial Procedure

Research protocols were approved by the University of Kentucky Institutional Animal Care and Use Committee. The animals were raised, and the trial conducted, at the University of Kentucky Agricultural Research and Education Center (Princeton, KY, USA). Thirty heifers (predominantly Angus) of 261 ± 6 days of age were housed in a dry-lot barn and randomly assigned to six feeding pens of five animals per pen. Although maintained in groups (i.e., pens), heifers were fed individually using 30 Calan gate electronic feeders (American Calan, Inc., Northwood, NH, USA), which allowed for individual feed intake and orts to be measured on a daily basis. The basal diet consisted of cracked corn, cottonseed hulls, soybean hulls, and soybean meal (Table 1) and was fed to each animal at 7.8 kg/day to achieve a growth rate of 0.5 kg/day. A basal mineral–vitamin premix manufactured by Kentucky Nutrition Service (Lawrenceburg, KY, USA) was administered daily by manually mixing into each animal’s ration at 85.1 g/day. The compositions of this mineral–vitamin premix, chemically analyzed by Dairy One Cooperative, Inc. (Ithaca, NY, USA), were (mean ± SD, n = 4, as-fed basis) 13.1 ± 0.2% for Ca, 6.46 ± 0.21% for P, 9.31 ± 0.27% for Na, 15.2 ± 0.53% for Cl, 2.32 ± 0.03% for Mg, 1.05 ± 0.04% for K, 0.68 ± 0.01% for S, 0.35 ± 0.01% for Zn, 0.14 ± 0.01% for Cu, 0.32 ± 0.02% for Mn, 25.5 ± 1.15 mg/kg for Co, 7.52 ± 1.16 mg/kg for Mo, and 0.99 ± 0.07 mg/kg for Se. The compositions of mineral I, vitamin A, and vitamin E in the premix (not chemically analyzed) were no less than 65 mg/kg, 550,000 IU/kg, and 550 IU/kg, respectively, according to the commercial claims of the manufacturer. By calculation, the basal diet plus the basal mineral–vitamin premix provided 0.48 mg Se daily per animal.
Table 1

Formulation (As-Fed Basis) and Selected Nutrient Composition (Dry Matter Basis) of the Basal Diet Fed to Growing Heifers

Item

Composition

Ingredients (%)

 Cottonseed hulls

41.90

 Soybean hulls

31.40

 Cracked corn

21.45

 Soybean meal

5.25

Nutrient compositiona

 TDN (%)

68.00 ± 2.07

 NEm (Mcal/kg)

1.51 ± 0.09

 NEg (Mcal/kg)

0.91 ± 0.08

 CP (%)

11.95 ± 1.80

 ADF (%)

47.74 ± 5.96

 NDF (%)

62.65 ± 7.99

 Se (mg/kg)

0.05 ± 0.01

aThe values presented are mean ± SD, which were determined from eight replicate samples at Forage Laboratory Services, Dairy One Cooperative Inc. (Ithaca, NY, USA). The analyzed dry matter content (%) was 90.4 ± 0.50. The analyzed compositions (% of dry matter, mean ± SD) of Ca, P, Mg, K, Na, and S were 0.31 ± 0.03, 0.21 ± 0.04, 0.21 ± 0.01, 1.17 ± 0.04, 0.07 ± 0.01, and 0.11 ± 0.01, respectively. The analyzed compositions of Fe, Zn, Cu, Mn, and Mo (mg/kg of dry matter, mean ± SD) were 201.6 ± 44.3, 30.6 ± 2.5, 7.5 ± 1.1, 25.0 ± 3.1, and 0.25 ± 0.07, respectively

After a 75-day adaptation period to the feeding system and diet, shrunk body weights were determined and heifers (393 ± 9 kg) were randomly assigned (n = 10/treatment) to one of three dietary Se supplementation treatments. For the control treatment (control), no exogenous source of Se was supplemented to the basal mineral–vitamin premix. For the ISe and OSe treatments, the basal mineral–vitamin premix was supplemented with sodium selenite (ISe; Prince Se Concentrate; Prince Agri Products, Inc., Quincy, IL, USA) or Se-enriched yeast (OSe; Sel-Plex®; Alltech, Inc., Nicholasville, KY, USA), respectively. The concentrations of Se in the premix (mean ± SD, n = 4, as-fed basis) were 34.9 ± 2.27 mg/kg for ISe treatment and 33.5 ± 4.10 mg/kg for OSe treatment, as determined by chemical analysis (Dairy One Cooperative). The daily supply of Se from either source was calculated to provide 3.0 mg/head.

After 80 days on dietary treatments, the daily supply of the basal diet was adjusted to 8.2 kg/head to compensate for the increased animal maintenance requirement and a continuous growth rate of 0.5 kg/day. However, the daily supply of mineral–vitamin premix and Se was not changed. Water was freely available throughout the trial.

Sample Collection

Because of the feed mill capacity, the basal diet was prepared four to five times each month with the same formula and ingredients, and samples of the diet were collected at each preparation. After 105 or 106 days on dietary treatments, samples of blood and liver tissue were collected from each animal. Each animal was temporarily restrained in a squeeze chute and the head restrained by halter immediately before sample collection. For blood samples, the right neck area was clipped, cleansed with 70% ethyl alcohol solution, and dried. Vacutainer tubes with and without lithium heparin were used to collect blood by jugular venipuncture for whole blood, red blood cells, and plasma, respectively. Samples were placed on ice immediately after collection and then transferred to the laboratory. The red blood cells and plasma were separated and recovered after centrifugation at 3,000 × g for 10 min at 4°C. For each animal, whole blood, red blood cell, and plasma samples were aliquoted into 5 mL cryogenic vials and stored frozen (−20°C). Liver tissue was collected by the aspiration biopsy technique modified from Erwin et al. [22]. Briefly, the area from the 10th to the 12th intercostal spaces and 10 to 30 cm from the dorsal median plane on the right side of the animal was clipped free of hair, cleansed with povidone–iodine and two subsequent 70% ethyl alcohol solution washes. The remaining 70% ethyl alcohol solution was dried with medical gauze. Lidocaine (1.6 mL 2% injectible solution per biopsy site; The Butler Company, Dublin, OH, USA) was subcutaneously injected between the 11th and 12th ribs approximately 10 cm from the dorsal medial plane. A topical anesthetic spray (Cetacaine, 300 mg; Cetylite Industries, Pennsauken, NJ, USA) was administered to the skin 20 cm from the dorsal median plane at the 11th intercostal space for 2 s. The remaining spray was dried with gauze and an incision made with a scalpel. A trocar (7 mm diameter) was used to obtain liver tissue. The collected tissue was weighed and separated for RNA extraction (approximately 400 mg wet tissue) and Se analysis (approximately 1 g wet tissue). Samples were placed into aluminum foil packs and snap frozen in liquid nitrogen and transferred to a −80°C freezer for storage.

Animal Performance and Tissue Selenium Analysis

Full and shrunk body weights of individual heifers were taken at the initiation and conclusion of the dietary treatment period (a total of 115 days). During the treatment period, the full body weight of each heifer was measured at the end of each month to monitor animal growth rate. Animals consumed all offered feed. The average daily feed intake and average daily gain of each animal was calculated for the entire dietary treatment period and used to determine the effect of dietary Se supplementation on animal growth performance measurements.

The selected nutrient compositions of the basal diet and the mineral–vitamin premix were analyzed by the Forage Laboratory Services, Dairy One Cooperative Inc. (Ithaca, NY, USA) using commercial standard analytical methods based on Association of Official Analytical Chemists [23] and National Research Council [24, 25]. Blood hematocrit was determined by the method of capillary centrifugation using the AutocritUltra3 centrifuge (Clay Adams, Parsippany, NJ, USA). Total Se concentrations of blood, red blood cells, plasma, and liver tissue were analyzed [26] at the animal nutrition laboratory of Dr. D. C. Mahan, Department of Animal Science, The Ohio State University according to the fluorometric method of Association of Official Analytical Chemists [23] with an ultraviolet detector (Turner filter, fluorometer, model 112; Unipath, Mountain View, CA, USA).

Microarray Analysis of Gene Expression

Six animals were randomly selected from each of three treatment groups for which a complete set of blood, red blood cell, plasma, and liver tissue samples had been taken for Se analysis. For each animal, total RNA was extracted from 300 to 400 mg of frozen liver tissue using TRIzol Reagent (Invitrogen Corporation, Carlsbad, CA, USA) following the manufacturer’s instructions. Briefly, frozen tissue was homogenized in a 15-mL polypropylene centrifuge tube using a Polytron mixer (1 mL TRIzol per 75 mg tissue) and the homogenate transferred to several 1.5-mL microcentrifuge tubes (1 mL/tube). Chloroform (200 µL/tube) was used to separate RNA from proteins and DNA, and then RNA was precipitated with isopropyl alcohol (600 µL/tube) and washed with 1 mL of 75% ethanol. The resulting RNA pellet was air-dried, dissolved in 100-µL RNase-free water, and stored at a −80°C.

The purity and concentration of total RNA samples was analyzed by a NanoDrop ND-1000 Spectrophotometer (NanoDrop Technologies, Wilmington, DE, USA), which revealed that all samples were of high purity with 260/280 absorbance ratios greater than 1.92 and 260/230 absorbance ratios ranging from 1.4 to 1.8. The integrity of total RNA was examined by gel electrophoresis using Agilent 2100 Bioanalyzer System (Agilent Technologies, Santa Clara, CA, USA) at the University of Kentucky Microarray Core Facility. Visualization of gel images and electropherograms showed that all RNA samples had high quality with RNA integrity numbers being greater than 8.2 and 28S/18S rRNA absorbance ratios greater than 1.8.

The GeneChip Bovine Genome Array (Affymetrix, Inc., Santa Clara, CA, USA) was used to test the effect of Se supplementation on the expression of 24,016 bovine gene transcripts (as probe sets on the GeneChip). Microarray analysis was conducted according to manufacturer’s standard protocol (Affymetrix) by the University of Kentucky Microarray Core Facility. Briefly, all the RNA samples were first reverse-transcribed to cDNA, and then from cDNA (double-stranded) to cRNA (single-stranded) which were labeled with biotin. The biotinylated cRNA were further fragmented and then used as probes to hybridize the gene chips in the GeneChip Hybridization Oven 640, using one chip per RNA sample. After hybridization, the chips were washed and stained on a GeneChip Fluidics Station 450. The reaction image and signals were read with a GeneChip Scanner (GCS 3000, 7G) and data collected using the GeneChip Operating Software (GCOS, version 1.2). The raw expression intensity values from the software (i.e., the *.cel files from the raw methylation measurements) were imported into Partek Genomics Suite software (version 6.4; Partek Inc., St. Louis, MO, USA). For GeneChip background correction, the algorithm of Robust Multichip Averaging adjusted with probe length and GC oligo content was implemented [27, 28]. The background-corrected data were further converted into expression values using quantile normalization for each chip and then Median Polish summarization of multiple probes [29].

All GeneChip transcripts were annotated using NetAffx annotation database for 3’ IVT Expression on Bovine GeneChip Array, provided online by the manufacturer (http://www.affymetrix.com/analysis/index.affx, Affymetrix, Inc.). The dietary treatment-induced effects on the expression of all the transcripts were subjected to statistical analysis (described below). Transcripts showing treatment-induced effects at the statistical significance level of P < 0.01 were selected for Core Analysis using the Ingenuity Pathways Analysis online software (Ingenuity Pathway Analysis; 8.0-2602; http://www.ingenuity.com; Ingenuity Systems, Inc., Redwood City, CA, USA).

Statistical Analysis

Treatment effects on animal performance data (average daily feed intake, average daily gain, and gain:feed ratio) and Se concentrations of whole blood, red blood cells, plasma, and liver tissue were all subjected to ANOVA analysis for a completely randomized experimental design using the General Linear Means procedure of SAS (SAS Inst., Inc., Cary, NC, USA). When a treatment effect was observed (P < 0.01 for ANOVA F test), the least squares means were separated by Fisher’s least square means test, with P < 0.05 considered as statistically different. The unbalanced experimental units (n = 6, 8, or 9) used for statistical analysis resulted from the loss of one animal and one to three samples during the animal trial, sample collection (as in liver biopsy and venous bleeding), and laboratory analysis.

Treatment effects on the relative expression levels of mRNA obtained from the microarray analysis for each gene transcript in liver tissue were also subjected to ANOVA testing using the Partek Genomics Suite software [29] for a completely randomized experimental design. For a higher degree of confidence (i.e., a conservative approach), when the ANOVA test gave a P value less than 0.01, treatment means were compared by two contrasts (ISe versus Control; OSe versus Control), and the contrast P values less than 0.05 were considered significant.

Results and Discussion

Experiment Model and Animal Performance

Formulation of the practical basal diet fed to the experimental heifers and its nutrient compositions (selected) are presented in Table 1. Dietary concentration of intrinsic Se was 0.05 mg/kg. Therefore, the basal diet plus the basal mineral–vitamin premix (described in “Materials and Methods” section) provided 0.48 mg Se daily per animal. Because animals consumed all offered feed, each control animal received 0.48 mg Se daily, whereas each ISe or OSe-supplemented (3.0 mg Se/day) animal received 3.48 mg Se daily. According to the National Research Council [24] standard, the Se requirement of beef cattle can be met by providing 0.1 mg/kg in the complete diet although Se can be legally supplemented to provide 0.3 mg/kg. The Se concentration of control treatment animals in the basal diet mixed with the basal mineral–vitamin premix used in this study would be 0.06 mg/kg, which was not adequate to meet the National Research Council [24] standard. Because this practical diet is common in the southeastern states, the results generated from this study provide relevant Se supplementation information to beef cattle nutritionists and producers.

Heifers were fed enough of a common feed to yield a body weight gain of approximately 0.5 kg/day. This approach was taken to avoid confounding of Se supplement effects by potential differences in average daily feed intake because previous work has demonstrated that differential gene expression can occur with differential amounts of consumption of the same diet for slow growing ruminants [30]. Heifer growth performance for the 115-day experimental period is presented in Table 2. There was no difference (P = 0.27) in average daily feed intake among treatment groups, which was 7.86, 7.88, and 7.89 kg/day for the control, ISe, and OSe groups, respectively. The average daily gain (on a shrunk body weight basis) for the control, ISe, and OSe treatment groups was 0.50, 0.56, and 0.57 kg/day, respectively. Thus, the targeted average daily gain of 0.5 kg/day (on a shrunk body weight basis) for the control group was achieved, while the average daily gain of Se supplementation groups were similar to that of the control group on either full (P = 0.23) or shrunk (P = 0.41) body weight basis.
Table 2

Effect of Dietary Selenium (Se) Supplementation on Animal Performance

Itema

Se supplementationb

SEMc

P valued

Control

ISe

OSe

ADFI (kg/day)

7.86

7.88

7.89

0.014

0.27

ADG (kg/day)

 Full BW

0.58

0.67

0.67

0.040

0.23

 Shrunk BW

0.50

0.56

0.57

0.034

0.41

G:F ratio

0.069

0.083

0.083

0.008

0.13

Values presented are the least squares means calculated from the 29 heifers for the entire dietary treatment period (115 days). One heifer in the control group was lost at the early stage of the animal trial

aAverage daily feed intakes (ADFI) were calculated on an as-fed basis, and the gain:feed (G:F) ratios were calculated on the full body weight (BW). Average daily gain (ADG) was calculated on both full and shrunk BW basis

bSe supplement treatments contained none (control) or 3 mg Se/day as inorganic (sodium selenite, ISe) or organic (Sel-Plex®, OSe) and were mixed with enough of a common cracked corn/cottonseed hull-based diet (0.48 mg Se/day) to support 0.5 kg/day growth for 105 or 106 days

cSEM presented are the pooled standard error of the means; n = 9 for the control (no Se supplementation) group; n = 10 for both the ISe and OSe supplementation groups

dP values presented were obtained from the ANOVA F test

Although the dietary ISe or OSe supplementation had a tendency (P = 0.13) of improvement in gain:feed ratio, animal growth performance was not affected by Se supplementation (Table 2). This “non-affect” observed for slow-growing heifers essentially is in agreement with most other studies that compared effects of OSe and ISe supplementation of beef cattle diets in a variety of cattle models. Nicholson et al. [15], Gunter et al. [16], Richards and Loveday [31], and Davis et al. [19] did not detect any difference between ISe and OSe forms in beef production performance, such as in average daily gain, average daily feed intake, or gain:feed. Nevertheless, some improvements have been reported in average daily gain of OSe-supplemented feedlot steers [20] and calves born from OSe-supplemented cows [18]. Given these improvements in average daily gain, plus the tendency of improvement in gain:feed ratio detected in this study, whether the form of dietary supplementation of Se affects animal growth performance is unclear.

Tissue Selenium Concentration

Several different methods are used to measure bioavailability of Se from Se-containing compounds. One method is to measure the retention (i.e., concentration) of Se in tissues of animals fed different sources or amounts of Se compounds [2, 14]. To compare the bioavailability of Se supplemented in ISe (sodium selenite) versus OSe (Sel-Plex®) forms fed to growing heifers, Se concentrations of major blood fractions and liver tissue were determined. Although dietary Se supplementation did not affect (P = 0.17) blood hematocrit (43.8, 41.1, and 42.4% for control, ISe, and OSe treatment groups, respectively), the Se content of other major blood fractions were increased by dietary Se supplementation (Table 3). In whole blood, Se concentrations for ISe and OSe heifers were 18% and 59% greater (P < 0.05), respectively, than for control animals. In red blood cells, Se concentrations were increased by 31% and 62% (P < 0.05) by ISe and OSe supplementation, respectively. However, plasma Se concentration was not affected (P ≥ 0.29) by form of Se supplementation. Between OSe and ISe treatments, whole blood Se concentrations were 35% higher (P < 0.0001) for OSe than ISe animals, whereas red blood cell Se concentration was 24% higher (P < 0.0001). There was no difference (P ≥ 0.29) in plasma Se concentrations between ISe and OSe groups.
Table 3

Effect of Dietary Selenium (Se) Supplementation on Tissue Se Concentration

Item

Se supplementationa

SEMb

P valuec

Control

ISe

OSe

Whole blood (µg/mL)

0.17a

0.20b

0.27c

0.009

<0.0001

Red blood cells (µg/mL)

0.26a

0.34b

0.42c

0.011

<0.0001

Plasma (µg/mL)

0.05

0.11

0.08

0.029

0.29

Liver (µg/g)d

0.26a

0.34b

0.47c

0.027

<0.0001

Values presented are least square means calculated from the 29 heifers. One heifer in the control group was lost.

aSe supplement treatments contained none (Control) or 3 mg Se/day as inorganic (sodium selenite, ISe) or organic (Sel-Plex®, OSe), and were mixed with enough of a common cracked corn/cottonseed hull-based diet (0.48 mg Se/day) to support 0.5 kg/day growth for 105 or 106 day. Means within a row that lack a common lowercase letter differ (P < 0.05 or 0.0001)

bSEM presented are the pooled standard error of the means. For the blood parameters, n = 9 in the control (no Se supplementation) group and n = 10 in either the OSe or the ISe supplementation group. For the liver tissues, n = 6 in the control group and n = 8 and 10 for the ISe and OSe supplementation groups, respectively

cP values presented were obtained from the ANOVA F test

dSe concentrations for liver tissue were calculated on a wet weight basis

Liver Se content (Table 3) was increased (P < 0.05) 31% and 81% with ISe and OSe supplementation, respectively, with the Se content of OSe heifers being 38% greater (P < 0.0001) than ISe heifers.

The finding of increased Se concentrations in whole blood and liver tissue with Se supplementation (at 3 mg/day) in this study is in agreement with previous reports [15, 16, 17, 31]. For example, Juniper et al. [17] reported greater Se concentrations in whole blood, liver, kidney, heart, and skeletal muscle in 20-month-old beef cattle supplemented with OSe (Sel-Plex®), compared to the cattle supplemented with ISe (sodium selenite) or no Se supplementation. From our results, as well as those in the literature, it can be concluded that a greater red blood cell and liver Se bioavailability results when Se-deficient cattle diets are supplemented with OSe (Sel-Plex®) versus ISe (sodium selenite).

The most effective way to determine cattle Se status is the analysis of blood or liver Se concentration [8]. According to Dargatz and Ross [1], whole blood Se concentrations of greater than 0.16 μg/mL are considered to be highly adequate. According to Surai [8], the liver Se concentration of 0.25 to 0.50 μg/g is considered to be adequate. According to the Food and Drug Administration standard, liver Se concentrations of 0.10 to 1.20 μg/g are considered “normal” (cited in [31]). In this study, the whole blood and liver Se concentrations of control heifers were 0.17 μg/mL and 0.26 μg/g, respectively (Table 3), and thus, the Se status of these heifers was at an adequate or highly adequate level. Given that none of the heifers were supplemented with Se for 75 days before Se treatments began, the control animals continued to receive no Se supplementation for the entire treatment period (105 or 106 days) and that the basal diet plus the basal mineral–vitamin premix (i.e., the control treatment diet) provided only 0.48 mg Se daily per animal, it is likely that the adequate Se status of the control heifers indicates a carryover effect from prior dietary management.

Genes Affected by Dietary Selenium Supplementation

Genomic microarray analysis has been conducted on a variety of animal tissues affected by diverse pathogenic or nutritional factors in an effort to document treatment effects on tissue transcriptome profiles. Nutrigenomic approaches using microarray technology have been employed to study Se nutrition. It has been established that dietary supplementation of selenomethionine can affect gene expression in mouse intestinal tissues by upregulating genes associated with cellular stress and cell cycling and downregulating genes associated with selenoprotein production, lipid transport, and detoxification mechanisms [32]. Another study comparing the effect of Se source, including sodium selenite (1.0 mg Se/kg diet) and Se-enriched yeast (1.0 mg Se/kg diet), on gene expression profile of mouse intestinal tissue found that nearly 11% of the 23,000 gene transcripts were influenced, with at least 100 being associated with animal reproductive functions (cited in [33]). However, there is a lack of data regarding the roles of different chemical forms of Se on the regulation of gene expression profile in beef cattle.

In this study, we employed Bovine GeneChip Genome Array (Affymetrix) that contains 24,016 bovine gene transcripts, representing approximately 19,000 UniGene Clusters (UniGene Build 57, March 24, 2004), to investigate the potential changes of bovine liver gene expression upon dietary supplementation of ISe (sodium selenite) and OSe (Sel-Plex®). All the microarray raw data (18 *.cel files) collected with the GCOS software plus the GCRMA-processed data analyzed with the Partek Genomics Suite [29] have been deposited into the Gene Expression Omnibus (National Center for Biotechnology Information, http://www.ncbi.nlm.nih.gov/geo) as accession number GSE19696.

ANOVA analyses of the microarray dataset found that 656 gene transcripts showed a treatment effect at P ≤ 0.05 level, of which 80 transcripts showed a treatment effect at P < 0.01 level. Of these 80 transcripts (58 being annotated), 56 were affected (P < 0.05) by ISe supplementation, 53 were affected (P < 0.05) by OSe supplementation (Table 4). For the ISe group, 30 of the 56 transcripts were upregulated by 2% to 57%, and 26 were downregulated by 9% to 167%, as compared to the control group. In the OSe group, 31 of the 53 transcripts were upregulated by 10% to 57% and 22 were downregulated by 5% to 100%.
Table 4

Genes or Gene Transcripts in Liver of Growing Beef Heifers Affected by Dietary Selenium (Se) Supplementation, Relative to Nonsupplemented Control Animals

Probe set ID

Gene name

Change (%)a

Common description of the gene

ISe

OSe

Bt.6027.1.A1_at

A1BG

−38*

−10

Alpha-1-B glycoprotein

Bt.12705.2.S1_at

ACTR8

40*

17

ARP8 actin-related protein 8 homolog (yeast)

Bt.23250.7.A1_x_at

AHSG

−4

4

Alpha-2-HS-glycoprotein

Bt.14993.3.S1_a_at

ARL6IP2

5

−18*

ADP-ribosylation factor-like 6 interacting protein 2

Bt.19311.1.A1_at

AZIN1

−20*

−4

Antizyme inhibitor 1

Bt.22344.1.S1_at

BHLHB2

−67*

−100*

Basic helix-loop-helix domain containing, class B, 2

Bt.23123.1.S1_at

BHLHB2

−39*

−80*

Basic helix-loop-helix domain containing, class B, 2

Bt.1194.1.S1_at

CANT1

−23*

−32*

Calcium-activated nucleotidase 1

Bt.3721.1.S1_at

CARHSP1

0

21*

Calcium-regulated heat stable protein 1, 24 kDa

Bt.26600.1.S1_at

CC2D1B

48*

15

Coiled-coil and C2 domain containing 1B

Bt.6571.1.A1_at

CCDC49

−3

26*

Coiled-coil domain containing 49

Bt.21978.1.S1_at

CCDC88C

−74*

−79*

Coiled-coil domain containing 88C

Bt.12980.3.S1_a_at

CL-43

−60*

−1

Collectin-43

Bt.892.1.S1_at

COX7A2L

3

−16*

Cytochrome c oxidase subunit VIIa polypeptide 2 like

Bt.11194.1.S1_at

DHRS4

−33*

−14

Dehydrogenase/reductase (SDR family) member 4

Bt.12194.1.S1_at

FBXW2

16*

26*

F-box and WD repeat domain containing 2

Bt.955.1.S1_at

GBF1

31*

26*

Golgi-specific brefeldin A resistant guanine nucleotide exchange factor 1

Bt.27844.1.S1_at

GCGR

−4

11*

Glucagon receptor

Bt.20267.1.S1_at

GCLM

3

−16*

Glutamate-cysteine ligase, modifier subunit

Bt.24621.1.S1_at

HAGHL

8

29*

Hydroxyacylglutathione hydrolase-like

Bt.15736.1.S1_at

HMHA1

−1

19*

Histocompatibility (minor) HA-1

Bt.7676.3.S1_at

IGF2

−6

22*

Insulin-like growth factor 2 (somatomedin A)

Bt.422.1.S1_at

IGFBP3

30*

36*

Insulin-like growth factor-binding protein 3

Bt.9527.2.S1_at

KLF10

−60*

−70*

Kruppel-like factor 10

Bt.16916.3.S1_at

KLF11

−34*

−56*

Kruppel-like factor 11

Bt.4210.2.A1_at

KNG1

−13*

−10*

Kininogen 1

Bt.26572.1.S1_at

LEPREL1

53*

47*

Leprecan-like 1

Bt.14202.1.A1_at

LGI4

−38*

−7

Leucine-rich repeat LGI family, member 4

Bt.14202.2.S1_at

LGI4

−31*

−6

Leucine-rich repeat LGI family, member 4

Bt.22396.1.S1_at

LOC100139648

−6

10*

Similar to hepatocyte growth factor activator

Bt.6512.1.S1_at

LOC515356

−37*

−78*

Similar to cytochrome b5 domain containing 2

Bt.26568.2.S1_a_at

LOC531049

18*

27*

Similar to putative eukaryotic translation initiation factor 3 subunit (eIF-3)

Bt.3529.1.A1_at

LOC618094

−20*

9

Hypothetical LOC618094

Bt.14155.1.S1_at

LOC785119

12*

3

Similar to programmed cell death 10 (PDCD10)

Bt.5685.1.S1_at

MED22

32*

26*

Mediator complex subunit 22

Bt.22107.1.S1_at

MGC134282

29*

22*

Hypothetical protein LOC616423

Bt.9213.2.S1_at

MGC137368

36*

13

Fanconi anemia-associated protein, 24 kDa

Bt.17889.1.A1_at

MGC165939

−101*

−41

Hypothetical LOC517231

Bt.26410.1.A1_at

MTERF

16*

30*

Mitochondrial transcription termination factor

Bt.10999.1.A1_at

NCK2

−14*

3

NCK (Src homology 3 and 2 domain containing) adaptor protein 2

Bt.4381.1.A1_at

P4HA2

38*

−11

Procollagen-proline, 2-oxoglutarate 4-dioxygenase (proline 4-hydroxylase), alpha

Bt.20341.1.S1_at

PACSIN2

0

22*

Protein kinase C and casein kinase substrate in neurons 2

Bt.28047.1.A1_at

PRKCI

−18

−73*

Protein kinase C, iota

Bt.20546.1.S1_a_at

PTPN23

14*

16*

Protein tyrosine phosphatase, nonreceptor type 23

Bt.9571.2.S1_a_at

RBM3

−12

32*

RNA binding motif (RNP1, RRM) protein 3

Bt.26948.1.S1_at

RGS9

2*

0

Regulator of G-protein signaling 9

Bt.5119.1.S1_at

RPUSD3

9*

13*

RNA pseudouridylate synthase domain containing 3

Bt.18228.2.S1_at

SEC61A2

22*

21*

Sec61 alpha 2 subunit (Saccharomyces cerevisiae)

Bt.1976.1.S1_at

ST5

−24*

-3

Suppression of tumorigenicity 5

Bt.22144.2.S1_at

STARD5

37*

3

StAR-related lipid transfer (START) domain containing 5

Bt.20188.2.S1_at

STK3

30*

4

Serine/threonine kinase 3 (STE20 homolog, yeast)

Bt.12662.1.S1_at

SYNPO

5

18*

Synaptopodin

Bt.5082.1.S1_at

TLN1

−8

17*

Talin 1

Bt.22513.1.S1_at

VPS28

1

13*

Vacuolar protein sorting 28 homolog (Saccharomyces cerevisiae)

Bt.4534.1.S1_at

WDR46

14

42*

WD repeat domain 46

Bt.20351.1.S1_at

WDR79

4

16*

WD repeat domain 79

Bt.21258.1.A1_at

WRB

29*

11

Tryptophan-rich basic protein

Bt.13990.2.S1_at

ZCCHC8

15*

16*

Zinc finger, CCHC domain containing 8

Bt.10073.1.A1_at

---

−2

−22*

---

Bt.11909.1.A1_at

---

−23*

−11

---

Bt.15780.1.S1_at

---

17*

14*

---

Bt.16193.2.A1_at

---

−34*

−30*

---

Bt.16493.1.A1_at

---

−9*

−15*

---

Bt.16743.1.A1_at

---

29*

56*

---

Bt.17186.2.A1_at

---

−2

−5*

---

Bt.17205.2.S1_at

---

−10

−33*

---

Bt.22069.1.A1_at

---

15*

-4

---

Bt.23706.1.A1_at

---

4

−21*

---

Bt.23936.1.A1_at

---

30*

2

---

Bt.24051.1.S1_at

---

−17*

−16*

---

Bt.26403.1.A1_at

---

−29

−72*

---

Bt.28598.1.A1_at

---

20*

−1

---

Bt.29306.1.A1_at

---

−54*

−52*

---

Bt.4726.1.S1_at

---

16*

19*

---

Bt.7152.2.S1_at

---

23*

19*

---

Bt.7530.1.S1_at

---

57*

57*

---

Bt.7728.1.A1_at

---

−59*

−12

---

Bt.8518.1.S1_at

---

−107*

−51*

---

Bt.8962.2.S1_a_at

---

25*

13

---

Bt.9108.1.S1_at

---

−65*

−27

---

Se supplement treatments contained none (control) or 3 mg Se/day as inorganic (sodium selenite, ISe) or organic (Sel-Plex®, OSe) and were mixed with enough of a common cracked corn/cottonseed hull-based diet (0.48 mg Se/day) to support 0.5 kg/day growth for 105 or 106 days

--- indicates that no annotation has been made to the DNA or RNA sequence of bovine origin

aThe sign of (−) before the numbers denotes decreased mRNA expression, whereas no sign denotes increased mRNA expression, compared to the non-Se-supplemented control group. The sign of (*) indicates a significant change at P < 0.05 level tested by orthogonal contrasts

Besides the Se supplement-specific effects on liver gene expression presented in Table 4, a salient finding from this study was that 30 gene transcripts were commonly affected (P < 0.05) by both ISe and OSe treatments (Tables 4 and 5). Of these 30 transcripts, 17 were upregulated by 13% to 57% and 13 were downregulated by 10% to 100% (as seen in Table 4), regardless of whether Se was supplemented as ISe or OSe. Thus, these genes appear to be Se element-dependent and Se form-independent, when liver Se content is 26 µg/g (the Se content in the liver of control animals).
Table 5

Number of Transcripts Affected by Dietary Selenium (Se) Supplementation, Relative to Nonsupplemented Control Animals

 

Total affected

Solely affected

Commonly affected

ISe

OSe

ISe

OSe

Upregulated

 Total affected

30

31

13

14

17

 Annotated (gene)

21 (21)

26 (26)

9 (9)

14 (14)

12 (12)

Downregulated

 Total affected

26

22

13

9

13

 Annotated (gene)

17 (16)

12 (11)

9 (9)

4 (4)

8 (7)

Se supplement treatments contained none (control) or 3 mg Se/day as inorganic (sodium selenite, ISe) or organic (Sel-Plex®, OSe) and were mixed with enough of a common cracked corn/cottonseed hull-based diet (0.48 mg Se/day) to support 0.5 kg/day growth for 105 or 106 days. The number in the parenthesis denotes the number of unique genes encoding for the annotated transcripts

Besides these commonly affected gene transcripts, there were 26 transcripts that were solely altered by ISe but not OSe supplementation with 13 being upregulated and 13 being downregulated (Tables 4 and 5). The expression changes of these transcripts appear to be ISe-dependent (sodium selenite-dependent). There were also 23 gene transcripts that were solely altered by OSe but not ISe supplementation with 14 being upregulated and nine being downregulated, and apparently represent OSe-dependent (Sel-Plex-dependent) genes.

Functional analysis of the 80 Se-affected gene transcripts in Table 4 revealed that most transcripts are very important in that they are associated with a broad range of biological processes including (1) nutrient metabolism, (2) cellular growth, proliferation, and immune response, (3) cell communication or signaling, and (4) development and functions of various tissues and organs. For example, the expression of insulin-like growth factor binding protein 3 (IGFBP3) mRNA was increased by 30% and 36% upon ISe and OSe supplementation, respectively. Insulin-like growth factor (IGF) cell signaling pathway comprises a complex set of molecules including three polypeptide hormones (insulin, IGF1, IGF2), three receptors, and six binding proteins [34]. This signaling pathway regulates a diverse array of physiological functions including nutrient metabolism [35, 36, 37], cellular proliferation [38, 39], and tissue/organ development [40, 41]. As a member of IGFBP family, IGFBP3 forms a ternary complex with IGF and acid-labile subunit in the liver (a central organ in the GF-IGF axis). In this form, it circulates in the plasma, prolonging the half-life of IGF and altering their interaction with cell surface receptors [42]. Despite uncertainty about the mechanism involved, enhancement of IGF action by IGFBP3 appears to be a widely accepted phenomenon. The in vivo studies with hypophysectomized rats showed that coadministration of IGF1 with IGFBP3 was more effective than even a larger dose of IGF1 alone in eliciting weight gain and an increase in epiphysial width [43]. Recent IGFBP3 biological studies showed that IGFBP3, as a novel effector molecule, is not just another “binding protein” because it also exerts other IGF-independent actions on animal metabolism and cell growth [44, 45]. The upregulation of IGFBP3 mRNA by ISe and OSe supplementations may explain the tendency of improvement of gain:feed ratio observed in this study.

IGF2 mRNA expression also was increased by 22% by OSe supplementation, but not by ISe supplementation (Table 4). It has been reported that human-IGF2 protein increased IGFBP3 mRNA expression in cultured primary astroglia from cerebral cortex of newborn rat [46] and lymphoid tissues of transgenic mice [47]. IGF2 also can stimulate the healing of human wounds in at least the presence of recombinant IGFBP1 [43]. The upregulation of both IGFBP3 and IGF2 mRNA by OSe supplementation observed in this study is coincident with the reported enhanced growth performance of beef cattle when fed OSe versus ISe [18, 20].

Mitochondrial transcription termination factor (MTERF) mRNA content was increased by 16% and 30% with ISe and OSe supplementation, respectively (Table 4). In mammals, MTERF gene product has three leucine zipper motifs that participate in intra-molecular interactions to establish the three-dimensional structure required for DNA binding [48]. The binding of mitochondrial DNA at a region immediately downstream of the 16S rRNA gene can terminate the ribosomal transcription of mitochondrial DNA and therefore, provide a system for coordinating the passage of replication and transcription complexes [48, 49]. The upregulation of MTERF mRNA found in this study suggests that dietary supplementation of Se for growing heifers may safeguard the integrity of mitochondrial genome while facilitating its efficient expression.

Besides the 17 upregulated gene transcripts, 13 transcripts were downregulated by both ISe and OSe supplementations, with eight being annotated (Tables 4 and 5). Two annotated transcripts, Bt.22344.1.S1_at and Bt.23123.1.S1_at, are derived from a single gene, BHLHB2 (basic helix-loop-helix domain containing, class B, 2; a.k.a. BHLHE40 or Dec2) and were downregulated 67% to 39% or 100% to 67% by either ISe or OSe supplementation, respectively. As a transcription repressor, BHLHB2 plays a pivotal role in multiple cell signaling pathways that affects many biological processes, including tissue development, cell differentiation/growth, cell death, oncogenesis, immune systems, circadian rhythm, and homeostasis [50]. In terms of circadian rhythms, BHLHB2 functions as one of the clock-related genes [51] and may mediate synaptic function and neuronal excitability [52]. Fujimoto et al. [53] suggested that BHLHB2 employs multiple molecular mechanisms including DNA binding and protein–protein interactions to achieve its role via E-box-dependent transcriptional repressions. The physiological significance of the downregulation of BHLHB2 mRNA expression by Se supplementation observed in this study is unknown.

Genes Kruppel-like factor 10 (KLF10) and KLF11 are two of the 17 members in the family of Kruppel-like transcription factors, which are gene regulatory proteins implicated in many biological processes. In particular, KLF10 is known to induce and repress the expression of multiple genes in several cell types and to function as an inhibitor of cell proliferation and an inducer of apoptosis [54]. The correlation between levels of KLF10 protein and stage of breast cancer suggested that KLF10 may play a major role as a tumor suppressor for a variety of cancers [55]. Similar to KLF10 gene, KLF11 gene encodes a nuclear protein which also regulates multiple gene expression and inhibits cell proliferation. In some cases, KLF10 and KLF11 can regulate the same genes [56]. However, KLF10 knockout mice display defects in bone and skeletal muscle development, whereas KLF11 knockout mice appear phenotypically normal, with no apparent impact on viability, development, fertility, or lifespan [57]. The physiological significance of the downregulation of KLF10 and KLF11 mRNA in both ISe- and OSe-supplemented heifers warrants further investigation.

The product of collectin-43 (CL-43) gene is a serum conglutinin protein synthesized mainly in the liver of only Bovidae animals [58]. Involved in the innate immune defense, this conglutinin protein has dual function; CL-43 binds specifically to carbohydrate structures on the surface of a pathogen, and subsequently, recruits other cells and molecules to destroy the pathogen and impede pathogen infectivity [59, 60]. Within the ISe-dependent gene group identified in this study, CL-43 mRNA was downregulated by 60% (Table 4). We do not have evidence from this study to make connection between the downregulation of CL-43 mRNA in the liver and the reduced antiviral capacity of beef cattle. However, further investigation of this gene may be of interest because it would facilitate our understanding of the difference between Bovidae animals and humans in terms of innate anti-microbial immunity and between OSe versus ISe sources of supplemental Se.

As a cofactor of glutathione peroxidases and glutathione S-transferases, glutathione (γ-glutamyl-cysteinyl-glycine) is a cysteine-containing tripeptide with reducing and nucleophilic properties that play a key role in cellular detoxification or protection from oxidative damage of lipids, proteins, and nucleic acids [61]. Glutamate-cysteine ligase (GCL; γ-glutamylcysteine synthetase) is the first rate-limiting enzyme in GSH biosynthesis and is composed of catalytic (GCLC) and modifier (GCLM) subunits which are encoded by different genes. While GCLC catalyzes a unique γ-carboxyl linkage from glutamate to cysteine, GCLM increases the Vmax and Kcat of GCLC, decreases the Km for glutamate, and increases the Ki for GSH-mediated feedback inhibition of GCL [62]. Within the OSe-dependent gene group identified in this study, GCLM mRNA was downregulated by 16% (Table 4). Whether this downregulation results in more free hepatic cysteine, less GSH, or affects basal hepatic selenomethionine:selenocysteine ratio [11] remains to be determined. However, decreased levels of GCLM mRNA may be indicative of a lesser state of oxidative stress [63, 64].

Protein kinase C iota (PRKCI) is a member of the atypical protein kinase C holoenzyme family, and under normal physiological conditions, is involved in the cell survival and proliferation and the formation of asymmetrical epithelial cell junction structures, which establishes cell polarity [65]. However, PRKCI is a known human oncogene, presumably through the onogenic Ras signaling pathway [66]. Over-expression of PRKCI mRNA and protein is common in cancerous tumors, whereas inhibition of PKRCI expression reduces migration and invasion of cancerous cells [66]. In human liver tissue, expression of PRKCI is positively correlated with development of hepatocellular carcinomas [67]. This pattern of PRKCI expression was accompanied by a parallel increase in β-catenin expression, but decreased expression of E-cadherin. These latter findings are consistent with tumor invasion and metastasis [67]. In the current study, supplementing Se as OSe reduced hepatic PRKCI mRNA expression by 73% relative to control animals, whereas ISe treatment did not affect expression. Because the animals displayed no signs of sickness, all liver biopsy samples appeared normal, and no alteration in β-catenin or E-cadherin was observed, the significance of this finding is unknown. However, given the decreased PRKCI mRNA content in the livers of heifers fed the OSe supplement, and the positive correlation between increased PRKCI expression and hepatic carcinomas, and although speculative, this finding may be of especial value.

This pilot study has identified genes individually or commonly affected by dietary supplementation of Se in the form of ISe (sodium selenite) or OSe (Sel-Plex®) to growing beef heifers that were of adequate Se status. Functional analysis of these genes revealed that a broad range of physiological functions might be affected by Se supplementation. Because there are differences in tissue Se concentrations and liver gene expression profiles between ISe and OSe supplementations, any dietary recommendation for the same level of supplementation of both forms should be questioned. Identification of key genes or biomarkers for different forms of Se can facilitate our designing of form-specific supplementation regimen for improved beef cattle health and productivity. However, further studies are required to resolve the key metabolic and signaling pathways that specifically underlie ISe and OSe functions. Only with a thorough understanding of the relationship between gene expression profile and Se form and concentration in diets, recommendations that delineate the concentration and length of time for ISe and OSe forms in diets can be given to beef cattle producers. In short, analysis of the dataset generated from this study provides the proof-of-concept that supplementing cattle diets with ISe (sodium selenite) or OSe (Sel-Plex®) at a same level (3 mg/day) results in different hepatic gene expression profiles, albeit with a common change in a core set of genes commonly affected by both forms of supplemental Se.

Summary

The data generated from this study demonstrated that more Se was retained in whole blood, red blood cells, and liver tissues, but not in plasma, of growing beef heifers upon dietary Se supplementation. Moreover, more Se was retained in these measured tissues (except for plasma) when Se was supplemented in OSe than ISe form. The study of liver gene expression profile by microarray analysis indicated the chemical form (inorganic versus organic) of supplemental Se matters. Functional analysis of these affected genes showed that they are associated with a broad range of physiological functions including (1) nutrient metabolism, (2) cellular growth, proliferation, and immune response, (3) cell communication or signaling, and (4) tissue/organ development and function. Regarding the effect of the supplemental Se forms, three distinct groups of genes were identified: those (1) commonly affected by ISe and OSe supplementation, (2) solely affected by ISe supplementation, and (3) solely affected by OSe supplementation. More specifically, both forms of supplementation appeared to upregulate mitochondrial gene expression capacity, whereas gene expression of a protein involved in antiviral capacity was downregulated in ISe-supplemented animals, and OSe-supplemented animals had reduced levels of mRNA encoding proteins known to be upregulated during oxidative stress and cancerous states.

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Copyright information

© Springer Science+Business Media, LLC 2010

Authors and Affiliations

  • Shengfa F. Liao
    • 1
  • Kelly R. Brown
    • 1
  • Arnold J. Stromberg
    • 2
  • Walter R. Burris
    • 1
  • James A. Boling
    • 1
  • James C. Matthews
    • 1
  1. 1.Department of Animal and Food SciencesUniversity of KentuckyLexingtonUSA
  2. 2.Department of StatisticsUniversity of KentuckyLexingtonUSA

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