Comparing tolerance of selenium (Se) as sodium selenite or Se yeast on blood and tissue Se concentrations of ruminants

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Comparing tolerance of selenium (Se) as sodium selenite or Se yeast on blood and tissue Se concentrations of ruminants
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2009 Florida Beef Report
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Davis, Paul
McDowell, Lee
Wilkinson, Nancy
Buergelt, Claus
Van Alstyne, Rachel
Weldon, Richard
Marshall, Tim
Matsuda-Fugisaki, Eric
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Institute of Food and Agricultural Sciences, University of Florida
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Gainesville, Fla.
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Comparing Tolerance of Selenium (Se) as Sodium Selenite or Se Yeast on
Blood and Tissue Se Concentrations of Ruminants

Paul Davis1
Lee McDowell
Nancy Wilkinson
Claus Buergelt
Rachel Van Alstyne
Richard Weldon
Tim Marshall
Eric Matsuda-Fugisaki

Selenium, whether in organic or inorganic forms, can be fed as high as 40 mg/kg for up to 60 wk
without inducing selenium toxicosis. Increasing dietary selenium level regardless of source is an
effective means of increasing selenium in blood and tissues.


Summary
The objective of this 60 wk study was to
determine the maximum tolerable level of
selenium (Se) by feeding Se as sodium selenite
or Se yeast at high dietary concentrations to
wether sheep. Twenty-eight, two-year-old,
Rambouillet-crossbred wethers (137.1 18.7 lb
initial body weight) were utilized in a 2 x 4
factorial arrangement with 0.2, 20, 30 and 40
mig kg dietary Se (as-fed) as either selenite or
yeast Se added to a corn-soybean meal basal
diet. Average body weight decreased linearly (P
< 0.10) as dietary Se level increased, ;bi,,gh/i
most wethers gained body weight. Serum Se,
whole blood Se, and wool Se concentrations
from wethers receiving organic Se were greater
(P < 0.01) than those from wethers receiving
inorganic Se. Selenium concentrations in brain,
diaphragm, heart, hoof kidney, liver and loin
muscle were affected (P < 0.05) by dietary Se
concentration, with higher Se concentrations
generally observed in tissues from wethers
receiving organic Se. Though Se concentrations
in serum, blood, wool, and major organs at most
times exceeded concentrations previously
reported in livestock ,,,iif, i-, from Se toxicosis,
a pattern of clinical signs ofSe toxicosis was not
observed in this experiment. Hi,,, ia '' ii igL ,,il.
microscopic evaluation of liver, kidney,
diaphragm, heart, andpsoas major muscle did


not reveal definitive evidence of Se toxicosis in
wethers on any dietary Se treatment. Wethers
under our experimental conditions tolerated up
to 40 mig kg dietary Se for 60 wk, ;1,ii,,gl
differences in Se source were observed.
Contrary to previous ;1i, Ight. the range between
optimal and toxic dietary levels is not narrow.

Introduction
Current estimates put the maximum tolerable
level of Se at 5 mg/kg for the major livestock
species (NRC, 2005) and no differentiation
exists for tolerable levels between ruminants and
monogastrics. However, Wright and Bell (1966)
reported that swine retained 77% and sheep
retained 29% of an oral dose of inorganic Se.
The NRC makes no distinction between
inorganic and organic (e.g., Se yeast or seleno-
methionine) forms of Se. Kim and Mahan
(2001) reported more accumulation of Se in the
plasma and tissues of swine fed high dietary
levels of Se as Se yeast compared to the same Se
levels as sodium selenite. They concluded that
greater than 5 mg/kg dietary Se, regardless of
source, did produce signs of Se toxicity in
growing swine. Based on these findings and the
increasing use of organic forms of Se for
supplementation to livestock, an experiment was
conducted to determine the maximum tolerable


2009 Florida BeefReport










level of Se by feeding Se as sodium selenite or
Se yeast at high dietary levels to ruminants.

Procedure
This experiment was conducted from June 4,
2002 to July 29, 2003 at the University of
Florida Sheep Nutrition Unit located in
southwestern Alachua County, FL. Twenty-
eight, two-year-old, Rambouillet-crossbred
wethers were weighed (137.1 + 18.7 lb) and
randomly assigned to one of eight dietary
treatments for a 60 wk study. Dietary treatments
were arranged as a 2 x 4 factorial with 0.2, 20,
30 and 40 mg/kg Se (as-fed) as four dietary
levels and Se yeast (Sel-Plex; Alltech, Inc.) and
sodium selenite (Southeastern Minerals, Inc.) as
two Se sources added to a corn-soybean meal-
cottonseed hull basal diet. Blood was collected
periodically and samples of brain, diaphragm,
heart, hoof tip, kidney, liver, and psoas major
muscle were collected at slaughter for Se
analysis. At termination, blood was again
collected and analyzed for albumin and enzymes
suggestive of tissue breakdown. Analyses were
carried out using standardized procedures.

Brain, diaphragm, heart, hoof tip, kidney, liver,
and psoas major Se data were analyzed for
effects of treatment using PROC GLM in SAS
(SAS for Windows 8e; SAS Inst., Inc., Cary,
NC) in a 2 x 4 factorial arrangement. PROC
MIXED was used to analyze effects of
treatment, time, and the interaction of treatment
x time on body weight, serum Se, whole blood
Se, and wool Se as repeated measures with a
spatial power covariance structure with respect
to day and a subplot of animal nested within
treatment.

Results
Wether body weight was affected by dietary Se
level (P < 0.05). Body weights of wethers
receiving 30 or 40 mg/kg dietary Se as Se yeast
decreased from wk 0 to wk 60, whereas wethers
receiving all other dietary Se treatments gained
weight from wk 0 to wk 60.

Serum Se concentrations measured at wk 12, 24,
48 and 60 ranged from 110 to 3,922 .ig/L and
increased linearly (P < 0.05) as dietary Se level
increased, while a quadratic response (P < 0.05)


was observed at wk 36 (Table 1). Over the
entire trial, serum Se increased quadratically (P
< 0.05) as dietary Se level increased. Wethers
receiving organic Se had greater (P < 0.001)
serum Se than did selenite treated wethers
throughout the study. Cristaldi et al. (2004)
reported a linear increase in serum Se as dietary
Se was increased, however those authors used a
maximum level of 10 mg/kg dietary Se as
selenite. Our data show that at most collections
organic Se produced serum Se of more than
double the concentration produced by feeding
selenite Se at the same level.

Selenium concentration in new growth wool was
measured at wk 12, 24, 36, 48 and 60 (Table 2).
Dietary Se concentration, Se source, time,
dietary Se concentration x Se source, and dietary
Se source x time affected (P < 0.05) wool Se.
Wool Se ranged from 1.19 to 39.09 mg/kg and
increased linearly (P < 0.001) as dietary Se
increased. Wool Se from wethers receiving
organic Se was often more than three-fold
greater (P < 0.001) than from wethers receiving
selenite Se at the same dietary concentration.
Wool Se concentrations in the present study
were more than ten-fold higher than
concentrations of 2 to 2.5 mg/kg in wool from
wethers fed up to 10 mg/kg dietary Se as selenite
(Cristaldi et al., 2004), but never exceeded 40
mg/kg which is less than 45 mg/kg which was
described as the Se concentration in hair of
animals suffering from alkali disease (NAS,
1971).

Selenium concentrations, on a dry matter basis,
were greatest in liver followed by kidney, heart,
hoof, brain, loin, and diaphragm (Table 3).
Brain Se concentrations ranged from 1.28 to
32.3 mg/kg and brain Se concentrations from
wethers receiving organic Se were greater (P <
0.001) than brain Se from wethers receiving
selenite Se. These results suggest that Se does
cross the blood-brain barrier and that brain Se is
influenced by dietary Se source. Diaphragm Se
concentration ranged from 0.82 to 26.34 mg/kg
and tended to increase linearly (P = 0.089) as
dietary Se increased. Diaphragm Se
concentration was greater (P < 0.001) in wethers
receiving organic Se than from wethers
receiving selenite Se. Heart Se concentration


2009 Florida BeefReport










ranged from 1.59 to 33.93 mg/kg and, like brain
and diaphragm Se was greater (P < 0.001) in
wethers receiving organic Se than from wethers
receiving selenite Se. Selenium concentrations
in the hoof tip increased linearly as dietary Se
concentration increased (P < 0.05), with wethers
receiving organic Se tending (P = 0.07) to be
greater than those receiving inorganic Se.
Kidney Se concentration tended (P = 0.07) to
respond linearly to increased dietary Se
concentration and ranged from 8.43 to 77.61
mg/kg. Kidney Se concentrations from wethers
receiving organic Se were greater (P < 0.01)
than from wethers receiving selenite Se.

Selenium concentrations in liver from wethers
receiving organic Se were not different (P
=0.34) than liver Se concentrations from wethers
receiving selenite Se. Selenium concentrations
in the loin muscle (psoas major), which is often
consumed ranged from 0.71 to 26.87 mg/kg and
tended (P = 0.12) to increase linearly as dietary
Se concentration was increased. Organic Se was
more effective (P < 0.001) at increasing Se
concentrations in edible tissue than was selenite
Se. As daily intake of Se by humans declines in
some parts of the world, increasing the Se
content of foods for human consumption by
manipulating source and level of Se
supplementation to livestock is now of interest
to food scientists.


Most of the heart, diaphragm, loin, liver, and
kidney tissues subjected to histopathological
evaluation were free from pathological changes.
No pattern associating abnormal pathology to
either dietary Se level or source could be
established.

Concentrations of albumin and activities of 5
enzymes associated with tissue damage in serum
collected at the termination of the experiment
were, in general, within or below the normal
range for adult sheep. In instances of Se
toxicosis, the activities of these enzymes would
have been increased due to tissue necrosis. The
lack of elevated enzymes, which are suggestive
of tissue necrosis, further indicates that the
wethers on our study were not suffering from Se
toxicosis.

The current estimate of the maximum tolerable
level of selenium in ruminants (5 mg/kg diet;
NRC, 2005) seems to be grossly underestimated.
Selenium, whether in organic or inorganic form,
can be fed as high as 40 mg/kg for up to 60 wks
without inducing Se toxicosis.


Literature Cited
Cristaldi et al., 2005. Small Rumin. Res. 56:205.
Kim and Mahan. 2001. J. Anim. Sci. 79:942.
National Academy of Science. 1971. Selenium in Nutrition. National Academy of Science, USA,
Washington, DC.
NRC, 2005. Mineral Tolerance of Domestic Animals. National Academy Press, Washington, DC.



'Paul Davis, Former Graduate Student; Lee McDowell, Professor; Nancy Wilkinson, Chemist; Rachel Van
Alstyne, Former Graduate Student; Tim Marshall, Professor; UF/IFAS, Department of Animal Sciences,
Gainesville, FL; Claus Buergelt, Professor, College of Veterinary Medicine, UF, Gainesville, FL; Richard
Weldon, Professor, Food and Resource Economics, UF, Gainesville, FL; Eric Matsuda-Fugisaki, Visiting
Researcher, Matsuda, Presidente Bernardes-S.P., Brazil.


2009 Florida BeefReport











Table 1. Serum Se concentrations of wethers fed four dietary levels of Se as sodium selenite or Se yeast

-------------Se source----------


----- Sodium selenite---
---------Dietary Se level, mg/kg-
0.2 20 30 40 0.2
-----------Serum Se, ig/L-
157 548 788 1,000 412
130 1,683 1,487 1,724 354
444 851 960 1,083 540
110 822 1,219 1,496 292
119 610 886 1,250 424
192 903 1,068 1,311 404


aData represent least squares means and pooled standard error (SE).
bDietary Se level response (P < 0.05).
CSelenium source response (P < 0.05).
dDietary Se level x Se source interaction (P < 0.05).
eDietary Se level linear response (P < 0.05).
fDietary Se level quadratic response (P < 0.05).


Se yeast


20 30 40 SE


2,583
2,639
3,283
2,428
1,699
2,526


3,210
3,922
2,086
2,076
2,712
2,801


2,458
1,585
1,409
1,831
2,549
1,966


249bcde
826be
250bcdf
253bce
331bce
395bcdf


Table 2. Wool Se concentrations of wethers fed four dietary levels of Se as sodium selenite or Se yeast

----------Se source-- -------


----- Sodium selenite---
---------Dietary Se level, mg/kg-
Week 0.2 20 30 40 0.2
---- ----Wool Se, mg/kg---
12 1.37 3.27 6.69 4.15 3.78
24 1.47 3.57 5.72 11.92 7.04
36 1.68 6.02 9.85 10.85 5.70
48 1.19 3.15 5.64 7.23 6.39
60 1.29 3.90 5.01 6.23 4.38
Average 1.40 3.98 6.58 8.08 5.46
aData represent least squares means and pooled standard error (SE).
bDietary Se level response (P < 0.05).
CSelenium source response (P < 0.05).
dDietary Se level x Se source interaction (P < 0.05).
eDietary Se level linear response (P < 0.10).
fTime response (P < 0.05).
gTime x Se source interaction (P < 0.05).


-Se yeast----

20 30 40


12.67
31.58
18.99
24.81
23.22
22.25


21.09
35.69
22.79
39.09
25.65
28.87


24.26
37.30
21.29
29.65
25.99
27.70


Week


12
24
36
48
60
Average


3.80bce
2.87bcd
4.72ce
2.22bcd
2.01bcd
3.38bcdefg


2009 Florida BeefReport











Table 3. Effects of four dietary levels of Se as sodium selenite or Se yeast on tissue Se of wethersa

--~------- -Se source--------


----- Sodium selenite- --
-- ------Dietary Se lev<
0.2 20 30 40
-----Se concentration
1.28 4.22 4.74 6.87
0.82 4.74 3.33 7.81
1.59 3.80 5.13 6.23
3.44 8.79 9.68 13.78
8.43 19.94 27.93 27.89
2.66 31.72 41.42 78.18
0.71 3.13 4.41 5.13


aData represent least squares means and pooled standard error (SE).
bDietary Se level response (P < 0.05).
CSelenium source response (P < 0.05).
dDietary Se level x Se source interaction (P < 0.05).
eDietary Se level linear response (P < 0.10).


Se yeast


0.2 20 30 40 SE


21.90
10.30
23.77
12.53
33.96
23.42
14.69


32.30
26.34
28.71
29.20
77.61
132.73
23.51


18.71
20.71
33.93
23.66
36.28
41.24
26.87


0.99bcd
2.69bcde
2.43bcd
5.52ce
6.87bcde
18.17bde
1.05bed


2009 Florida BeefReport


Tissue


Brain
Diaphragm
Heart
Hoof
Kidney
Liver
Loin













































































140 2009 Florida BeefReport




Full Text

PAGE 1

Comparing Tolerance of Selenium (Se) as Sodium Selenite or Se Yeast on Blood and Tissue Se Concentrations of Ruminants Paul Davis 1 Lee McDowell Nancy Wilkinson Claus Buergelt Rachel Van Alstyne Richard Weldon Tim Marshall Eric Matsuda Fugisaki Summary The objective of this 60 wk study was to determine the maximum tolerable level of selenium (Se) by feeding Se as sodium selenite or Se yeast at high dietary concentrations to wether sheep. Twenty-eight, two-year-old, Rambouillet-crossbred wethers (137.1 18.7 lb initial body weight) were utilized in a 2 4 factorial arrangement with 0.2, 20, 30 and 40 mg/kg dietary Se (as-fed) as either selenite or yeast Se added to a corn-soybean meal basal diet. Average body weight decreased linearly (P < 0.10) as dietary Se level increased, though most wethers gained body weight. Serum Se, whole blood Se, and wool Se concentrations from wethers receiving organic Se were greater (P < 0.01) than those from wethers receiving inorganic Se. Selenium concentrations in brain, diaphragm, heart, hoof, kidney, liver and loin muscle were affected (P < 0.05) by dietary Se concentration, with higher Se concentrations generally observed in tissues from wethers receiving organic Se. Though Se concentrations in serum, blood, wool, and major organs at most times exceeded concentrations previously reported in livestock suffering from Se toxicosis, a pattern of clinical signs of Se toxicosis was not observed in this experiment. Histopathological, microscopic evaluation of liver, kidney, diaphragm, heart, and psoas major muscle did not reveal definitive evidence of Se toxicosis in wethers on any dietary Se treatment. Wethers under our experimental conditions tolerated up to 40 mg/kg dietary Se for 60 wk, though differences in Se source were observed. Contrary to previous thought, the range between optimal and toxic dietary levels is not narrow. Introduction Current estimates put the maximum tolerable level of Se at 5 mg/kg for the major livestock species (NRC, 2005) and no differentiation exists for tolerable levels between ruminants and monogastrics. However, Wright and Bell (1966) reported that swine retained 77% and sheep retained 29% of an oral dose of inorganic Se. The NRC makes no distinction between inorganic and organic (e.g., Se yeast or selenomethionine) forms of Se. Kim and Mahan (2001) reported more accumulation of Se in the plasma and tissues of swine fed high dietary levels of Se as Se yeast compared to the same Se levels as sodium selenite. They concluded that greater than 5 mg/kg dietary Se, regardless of source, did produce signs of Se toxicity in growing swine. Based on these findings and the increasing use of organic forms of Se for supplementation to livestock, an experiment was conducted to determine the maximum tolerable Selenium, whether in organic or inorganic forms, can be fed as high as 40 mg/kg for up to 60 wk without inducing selenium toxicosis. Increasing dietary selenium level regardless of source is an effective means of increasing selenium in blood and tissues.

PAGE 2

level of Se by feeding Se as sodium selenite or Se yeast at high dietary levels to ruminants. Procedure This experiment was conducted from June 4, 2002 to July 29, 2003 at the University of Florida Sheep Nutrition Unit located in southwestern Alachua County, FL. Twentyeight, two-year-old, Rambouillet-crossbred wethers were weighed (137.1 18.7 lb) and randomly assigned to one of eight dietary treatments for a 60 wk study. Dietary treatments were arranged as a 2 4 factorial with 0.2, 20, 30 and 40 mg/kg Se (as-fed) as four dietary levels and Se yeast (Sel-Plex; Alltech, Inc.) and sodium selenite (Southeastern Minerals, Inc.) as two Se sources added to a corn-soybean mealcottonseed hull basal diet. Blood was collected periodically and samples of brain, diaphragm, heart, hoof tip, kidney, liver, and psoas major muscle were collected at slaughter for Se analysis. At termination, blood was again collected and analyzed for albumin and enzymes suggestive of tissue breakdown. Analyses were carried out using standardized procedures. Brain, diaphragm, heart, hoof tip, kidney, liver, and psoas major Se data were analyzed for effects of treatment using PROC GLM in SAS (SAS for Windows 8e; SAS Inst., Inc., Cary, NC) in a 2 4 factorial arrangement. PROC MIXED was used to analyze effects of treatment, time, and the interaction of treatment time on body weight, serum Se, whole blood Se and wool Se as repeated measures with a spatial power covariance structure with respect to day and a subplot of animal nested within treatment. Results Wether body weight was affected by dietary Se level ( P < 0.05). Body weights of wethers receiving 30 or 40 mg/kg dietary Se as Se yeast decreased from wk 0 to wk 60, whereas wethers receiving all other dietary Se treatments gained weight from wk 0 to wk 60. Serum Se concentrations measured at wk 12, 24, 48 and 60 ranged from 110 to 3,922 g/L and increased linearly ( P < 0.05) as dietary Se level increased, while a quadratic response ( P < 0.05) was observed at wk 36 (Table 1). Over the entire trial, serum Se increased quadratically ( P < 0.05) as dietary Se level increased. Wethers receiving organic Se had greater ( P < 0.001) serum Se than did selenite treated wethers throughout the study. Cristaldi et al. (2004) reported a linear increase in serum Se as dietary Se was increased, however those authors used a maximum level of 10 mg/kg dietary Se as selenite. Our data show that at most collections organic Se produced serum Se of more than double the concentration produced by feeding selenite Se at the same level. Selenium concentration in new growth wool was measured at wk 12, 24, 36, 48 and 60 (Table 2). Dietary Se concentration, Se source, time, dietary Se concentration Se source, and dietary Se source time affected ( P < 0.05) wool Se. Wool Se ranged from 1.19 to 39.09 mg/kg and increased linearly ( P < 0.001) as dietary Se increased. Wool Se from wethers receiving organic Se was often more than three-fold greater ( P < 0.001) than from wethers receiving selenite Se at the same dietary concentration. Wool Se concentrations in the present study were more than ten-fold higher than concentrations of 2 to 2.5 mg/kg in wool from wethers fed up to 10 mg/kg dietary Se as selenite (Cristaldi et al., 2004), but never exceeded 40 mg/kg which is less than 45 mg/kg which was described as the Se concentration in hair of animals suffering from alkali disease (NAS, 1971). Selenium concentrations, on a dry matter basis, were greatest in liver followed by kidney, heart, hoof, brain, loin, and diaphragm (Table 3). Brain Se concentrations ranged from 1.28 to 32.3 mg/kg and brain Se concentrations from we thers receiving organic Se were greater ( P < 0.001) than brain Se from wethers receiving selenite Se. These results suggest that Se does cross the blood-brain barrier and that brain Se is influenced by dietary Se source. Diaphragm Se concentration ranged from 0.82 to 26.34 mg/kg and tended to increase linearly ( P = 0.089) as dietary Se increased. Diaphragm Se concentration was greater ( P < 0.001) in wethers receiving organic Se than from wethers receiving selenite Se. Heart Se concentration

PAGE 3

ranged from 1.59 to 33.93 mg/kg and, like brain and diaphragm Se was greater ( P < 0.001) in wethers receiving organic Se than from wethers receiving selenite Se. Selenium concentrations in the hoof tip increased linearly as dietary Se concentration increased ( P < 0.05), with wethers receiving organic Se tending ( P = 0.07) to be greater than those receiving inorganic Se. Kidney Se concentration tended ( P = 0.07) to respond linearly to increased dietary Se concentration and ranged from 8.43 to 77.61 mg/kg. Kidney Se concentrations from wethers receiving organic Se were greater ( P < 0.01) than from wethers receiving selenite Se. Selenium concentrations in liver from wethers receiving organic Se were not different ( P =0.34) than liver Se concentrations from wethers receiving selenite Se. Selenium concentrations in the loin muscle (psoas major), which is often consumed ranged from 0.71 to 26.87 mg/kg and tended ( P = 0.12) to increase linearly as dietary Se concentration was increased. Organic Se was more effective ( P < 0.001) at increasing Se concentrations in edible tissue than was selenite Se. As daily intake of Se by humans declines in some parts of the world, increasing the Se content of foods for human consumption by manipulating source and level of Se supplementation to livestock is now of interest to food scientists. Most of the heart, diaphragm, loin, liver, and kidney tissues subjected to histopathological evaluation were free from pathological changes. No pattern associating abnormal pathology to either dietary Se level or source could be established. Concentrations of albumin and activities of 5 enzymes associated with tissue damage in serum collected at the termination of the experiment were, in general, within or below the normal range for adult sheep. In instances of Se toxicosis, the activities of these enzymes would have been increased due to tissue necrosis. The lack of elevated enzymes, which are suggestive of tissue necrosis, further indicates that the wethers on our study were not suffering from Se toxicosis. The current estimate of the maximum tolerable level of selenium in ruminants (5 mg/kg diet; NRC, 2005) seems to be grossly underestimated. Selenium, whether in organic or inorganic form, can be fed as high as 40 mg/kg for up to 60 wks without inducing Se toxicosis. Literature Cited Cristaldi et al., 2005. Small Rumin. Res. 56:205. Kim and Mahan. 2001. J. Anim. Sci. 79:942. National Academy of Science. 1971. Selenium in Nutrition. National Academy of S cience, USA, Washington, DC. NRC, 2005. Mineral Tolerance of Domestic Animals. National Academy Press, Washington, DC. 1 Paul Davis, Former Graduate Student; Lee McDowell, Professor; Nancy Wilkinson, Chemist; Rachel Van Alstyne Former Graduate Student; Tim Marshall, Professor; UF/IFAS, Department of Animal Sciences, Gainesville, FL; Claus Buergelt, Professor, College of Veterinary Medicine, UF, Gainesville, FL; Richard Weldon, Professor, Food and Resource Economics, UF, Gaines ville, FL; Eric Matsuda Fugisaki, Visiting Researcher, Matsuda, Presidente Bernardes S.P., Brazil.

PAGE 4

Table 1. Serum Se concentrations of wethers fed four dietary levels of Se as sodium selenite or Se yeast a Se source Sodium selenite Se yeast Dietary Se level, mg/kg Week 0.2 20 30 40 0.2 20 30 40 SE Serum Se, g/L 12 157 548 788 1,000 412 2,583 3,210 2,458 249 bcde 24 130 1,683 1,487 1,724 354 2,639 3,922 1,585 826 be 36 444 851 960 1,083 540 3,283 2,086 1,409 250 bcdf 48 110 822 1,219 1,496 292 2,428 2,076 1,831 253 bce 60 119 610 886 1,250 424 1,699 2,712 2,549 331 bce Average 192 903 1,068 1,311 404 2,526 2,801 1,966 395 bcdf a Data represent least squares means and pooled standard error (SE). b Dietary Se level response ( P < 0.05). c Selenium source response ( P < 0.05). d Dietary Se level Se source interaction ( P < 0.05). e Dietary Se level linear response ( P < 0.05). f Dietary Se level quadratic response ( P < 0.05). Table 2. Wool Se concentrations of wethers fed four dietary levels of Se as sodium selenite or Se yeast a Se source Sodium selenite Se yeast Dietary Se level, mg/kg Week 0.2 20 30 40 0.2 20 30 40 SE Wool Se, mg/kg 12 1.37 3.27 6.69 4.15 3.78 12.67 21.09 24.26 3.80 bce 24 1.47 3.57 5.72 11.92 7.04 31.58 35.69 37.30 2.87 bcd 36 1.68 6.02 9.85 10.85 5.70 18.99 22.79 21.29 4.72 ce 48 1.19 3.15 5.64 7.23 6.39 24.81 39.09 29.65 2.22 bcd 60 1.29 3.90 5.01 6.23 4.38 23.22 25.65 25.99 2.01 bcd Average 1.40 3.98 6.58 8.08 5.46 22.25 28.87 27.70 3.38 bcdefg a Data represent least squares means and pooled standard error (SE). b Dietary Se level response ( P < 0.05). c Selenium source response ( P < 0.05). d Dietary Se level Se source interaction ( P < 0.05). e Dietary Se level linear response ( P < 0.10). f Time response ( P < 0.05). g Time Se source interaction ( P < 0.05).

PAGE 5

Table 3 Effects of four dietary levels of Se as sodium selenite or Se yeast on tissue Se of wethers a Se source Sodium selenite Se yeast Dietary Se level, mg/kg Tissue 0.2 20 30 40 0.2 20 30 40 SE Se concentration, mg/kg Brain 1.28 4.22 4.74 6.87 6.12 21.90 32.30 18.71 0.99 bcd Diaphragm 0.82 4.74 3.33 7.81 5.28 10.30 26.34 20.71 2.69 bcde Heart 1.59 3.80 5.13 6.23 6.35 23.77 28.71 33.93 2.43 bcd Hoof 3.44 8.79 9.68 13.78 6.26 12.53 29.20 23.66 5.52 ce Kidney 8.43 19.94 27.93 27.89 22.26 33.96 77.61 36.28 6.87 bcde Liver 2.66 31.72 41.42 78.18 15.67 23.42 132.73 41.24 18.17 bde Loin 0.71 3.13 4.41 5.13 5.73 14.69 23.51 26.87 1.05 bcd a Data represent least squares means and pooled standard error (SE). b Dietary Se level response ( P < 0.05). c Selenium source response ( P < 0.05). d Dietary Se level Se source interaction ( P < 0.05). e Dietary Se level linear response ( P < 0.10).