Selenium enrichment of table eggs
D. C. Bennett1 and K. M. Cheng
Avian Research Centre, Faculty of Land and Food Systems, University of British Columbia,
2357 Main Mall, Vancouver, British Columbia, Canada, V6T 1Z4
ABSTRACT Selenium is an essential trace element with
a recommended dietary allowance for human adults of
55 μg/d. However, there is evidence that greater dietary intakes may have possible health benefits, including a reduction in the risk of cancer. Several studies
have shown the feasibility of enriching eggs using organic Se and that Se-enriched eggs are an effective way
to supplement human diets. However, few studies have
examined the response of egg Se concentration to high
(>1 μg/g) dietary organic Se intake by the laying hens.
The objective of the current study is to examine the
effect of higher dietary organic Se levels on production, egg mass, and egg Se levels. These were assessed
by feeding 3 breeds of laying hens (Barred Plymouth
Rock, Lohmann Brown, Lohmann White) a basal diet
containing 0.3 μg of Se/g of diet as Na2SeO3. Into this
diet, Se yeast (SelenoSource AF 600), an organic source
of Se, was added at 1.0, 2.4, or 5.1 μg of Se/g of diet for
4 wk. Feed consumption, egg production, and egg mass
were not affected by the dietary Se concentration in all
3 breeds. Within the range of Se levels employed in the
laying hens’ diet, egg Se content increased linearly as
dietary levels of Se increased. The results of this study
indicate that feeding up to 5.1 μg/g of Se will not affect
egg production and the welfare of the laying hen and
is a practical way of producing Se-enriched eggs for the
consumers.
Key words: selenium, laying hen, enriched egg
2010 Poultry Science 89:2166–2172
doi:10.3382/ps.2009-00571
INTRODUCTION
Selenium is an essential trace element that is indispensable for normal functioning of the body and thus
plays a critical role in the maintenance of optimal
health. Currently, the US and Canadian recommended
dietary allowance (RDA) for human adults is 55 μg/d
(Institute of Medicine, 2000). This recommendation is
based on the amount of dietary Se required to maximize
the activity of plasma glutathione peroxidase. However,
there is evidence that greater dietary Se intakes in the
range of 100 to 300 μg/d may have possible health benefits (Finley, 2007; Fisinin et al., 2009; Schrauzer, 2009;
Schrauzer and Surai, 2009). Schrauzer (2009) suggested
that the optimal Se intake for adults is in the range of
250 to 300 μg/d, which would require increasing the Se
intake by 100 to 200 μg/d for most North American
diets. This increased Se intake could be achieved either
through supplementation or through the consumption
of Se-enriched foods. It should be noted that although
Se is an essential nutrient, excess Se intake can have
toxic effects. However, the optimal Se intake proposed
©2010 Poultry Science Association Inc.
Received November 20, 2009.
Accepted June 27, 2010.
1 Corresponding author: [email protected]
by Schrauzer (2009) is lower than the no adverse effect
level of 800 μg/d proposed for Canada and the United
States (Institute of Medicine, 2000).
Several studies have examined the potential for enriching the Se content of various dietary items, including eggs. In fact, eggs have been shown to be an effective vehicle for supplementing Se in the diet (Surai
et al., 2007). The Se content of eggs is easily manipulated when hens are fed with organic forms of Se (i.e.,
selenomethionine). Selenium-enriched eggs have been
shown to be a good source of Se for humans (Surai
et al., 2007). Furthermore, eggs are a traditional and
affordable food in many countries and cultures; thus,
Se-enriched eggs should be really acceptable.
Most studies examining the Se enrichment of eggs
have fed hens diets only containing 0.3 to 0.5 μg of Se/g
of diet, the current legal limit in most jurisdictions.
Hens fed organic sources of Se at these levels produce
eggs containing 10 to 29 μg of Se, or 18 to 53% of the
US and Canadian RDA (Moksnes, 1983; Paton et al.,
2002; Payne et al., 2005; Chantiratikul et al., 2008).
With regard to the suggestion of Schrauzer (2009) that
adult humans should consume approximately 250 to
300 μg of Se/d, in order for a person to obtain an additional 100 to 200 μg of dietary Se/d, 2 eggs containing
50 to 100 μg of Se each would need to be consumed.
This would necessitate feeding hens a diet containing
2166
2167
SELENIUM ENRICHMENT OF TABLE EGGS
over 1 μg of Se/g of diet (Moksnes, 1983; Payne et
al., 2005; Vukasinovic et al., 2006; Chantiratikul et al.,
2008). However, given the relatively few studies conducted employing these dietary levels and the apparent
interstudy variability in egg Se, further work is needed
to better describe the response of egg Se content to high
dietary Se intake. The purpose of our current study
is to describe the relationship between dietary Se and
egg Se to determine the dietary Se requirement of hens
needed to produce eggs containing high levels of Se. To
achieve this, we conducted a feeding trial in which the
egg Se content of 3 breeds of laying hens, each supplemented with 3 high levels of dietary Se, were measured.
It should be noted that levels as high as 3 to 6 μg of
organic Se/g diet are not toxic to the hen and have
no effect on egg production (Moksnes, 1983; Payne et
al., 2005; Chantiratikul et al., 2008). The secondary
objective of the current study is to examine the effect
of higher dietary organic Se levels on feed intake, egg
mass, and egg production.
MATERIALS AND METHODS
Birds and Experimental Procedures
Hens were maintained in accordance with the guidelines of the Canadian Council on Animal Care. All procedures were approved by the animal care committees
of the Agassiz Research Centre (Agriculture and AgriFood Canada) and the University of British Columbia
(A07-0039).
One hundred fifty-two 60-wk-old laying hens of 3
breeds [48 Barred Plymouth Rocks (BR), 49 Lohmann
Browns (LB), and 55 Lohmann Whites (Lohmann Selected Longhorn Lites; LW)] were used in this experiment. Barred Plymouth Rocks were chosen to represent
a noncommercial heritage breed, whereas the LB and
LW are commercial brown and white egg layers, respectively. Hens were housed either 2 or 3 birds per cage
(mean = 2.5 ± 0.1 birds per cage, or 906 ± 50 cm2/
hen) for a total of 20 cages per breed. All hens were
initially fed a commercial wheat-soybean meal-canola
meal-based layer ration ad libitum [Unifeed (Viterra
Inc.), Chilliwack, British Columbia, Canada]. This diet
was formulated to meet NRC (1994) recommendations and contained 0.3 μg of Se/g of diet as inorganic
Na2SeO3 (see Table 1 for nutrient analysis). Into this
diet, Se yeast (SelenoSource AF 600, Diamond V Mills,
Cedar Rapids, IA) was added at 1.0, 2.4, or 5.1 μg of
Se/g of diet without substitution (see Table 2 for the
Se content and source for these diets). These 3 experimental diets were fed to 6, 7, and 7 cages of hens from
each breed, respectively, for 4 wk. Total feed intake
for each cage was measured weekly. At the end of the
experimental period (d 24 to 25), excreta output was
measured for 4 cages of LB on each of the 3 experimental diets. All excreta produced from each cage in the
24-h period were individually collected, dried at 60°C,
weighed, and stored until analyzed for Se content.
Table 1. Nutrient composition of base
diet1
(as-fed basis)
Item
Amount
Moisture (%)
Protein (%)
Fat (%)
Carbohydrates (%)
Ash (%)
Se2 (μg/g)
Energy
Gross energy, analyzed (kcal/kg)
AME, calculated (kcal/kg)
10.8
16.7
3.8
55.0
13.8
0.313
3,220
2,800
1Commercial layer ration supplied by Unifeed (Viterra Inc.), Chilliwack, British Columbia, Canada. Proximate analysis of diet determined
according to AOAC official methods (AOAC, 2000).
2Selenium supplied as Na SeO .
2
3
3Analyzed value.
Hen-day egg production was measured throughout
the experiment. All eggs laid at the start of the experiment (presupplementation) and on d 3, 10, 17, and
25 of the experiment were collected and stored at 5°C
until processed. Eggs were individually weighed and
broken out. The shell and shell membrane were dried,
weighed, and then discarded. The yolk and albumen
were weighed together and eggs collected from the same
cage were pooled, homogenized with a Polytron homogenizer (Brinkman Instruments, Westbury, NY), and
stored at −20°C until analyzed for Se content.
Samples of diets, excreta, and eggs were digested
according to AOAC official method 986.15 (AOAC,
2000), as outlined in Lambert and Turoczy (2000). This
method was chosen because facilities for using perchloric acid digestion were not available. Briefly, a 200- to
300-mg sample was weighed into a Teflon closed digestion vessel (Parr Instrument Company, Moline, IL),
and 5 mL of concentrated HNO3 and 2 antibumping
granules were added. The digestion vessel was sealed,
and the sample was allowed to predigest for 18 h at
room temperature. The digestion vessel was heated at
150°C for 2 h in a muffle furnace. After cooling, the
digest was transferred to a 50-mL crucible and 1 mL of
75 mg/mL of magnesium nitrate solution was added.
This mixture was dried slowly (2 to 3 h) on a hot plate
and then ashed at 500°C for 30 min in a muffle furnace.
After cooling, the residue was dissolved in 10 mL of
concentrated HCl and heated on a steam bath for 15
min. After cooling, the solution was transferred to a
Table 2. Selenium content of experimental diets (as-fed basis)
Se content (μg of Se/g of diet)
Diet
Na2SeO3
Se yeast1
Total2
Basal
1
2
3
0.31
0.31
0.31
0.31
0.00
1.03
2.38
5.12
0.31
1.34
2.69
5.43
1SelenoSource AF 600 (Diamond V Mills, Cedar Rapids, IA) containing 600 µg of Se/g of yeast.
2Total Se content of the diets was determined by analysis.
2168
Bennett and Cheng
Table 3. Feed intake and egg production of the 3 breeds of laying hens used in this study
Breed
Parameter
Feed intake (g/hen per d)
Hen-day egg production (%)
Weight (g/egg)
Whole egg
Eggshell
Yolk + albumen
Barred
Plymouth Rock
4.6B
4.0B
105.6 ±
63.9 ±
61.2 ± 0.9AB
5.1 ± 0.1C
56.1 ± 0.9A
Lohmann Brown
6.7A
2.7A
129.7 ±
86.2 ±
61.9 ± 0.9A
6.0 ± 0.1A
55.9 ± 0.9A
Lohmann White
112.8 ± 2.5B
87.7 ± 1.9A
58.4 ± 0.7B
5.5 ± 0.1B
52.9 ± 0.6B
A–CWithin-breed means within each row (parameter) with common superscripts are not significantly different
(P < 0.05). None of these parameters were affected by dietary Se levels. Each within-breed mean is the average
of 80 observations (20 cages, 4 wk).
volumetric flask and diluted to volume with distilled
water. The Se concentrations of the digests were then
determined using hydride generation atomic fluorescence spectroscopy (Millennium Excalibur PSA Model
10.055, PS Analytical Ltd., Kent, UK), as outlined in
Pappas et al. (2006).
Calculations and Statistical Analyses
Egg production, feed consumption, and egg Se concentrations ([SE]egg) were analyzed by repeated measures 2-way ANOVA with breed and dietary Se as main
effects. Excreta Se concentration and apparent Se absorption of the LB hens were analyzed by 1-way ANOVA with dietary Se as the main effect. When main effects were significant, differences were assessed by least
significance difference test. The relationships between
the dietary Se concentration ([SE]diet) and [SE]egg or
total egg Se were determined by linear regression. Data
are reported as means ± SEM. All statistical analyses
were performed using JMP statistical software (version
7, SAS Institute Inc., Cary, NC) and significance was
accepted when P < 0.05.
RESULTS
Lohmann Browns had significantly higher feed intake
than LW and BR (Table 3), but [SE]diet had no significant effect on feed intake. There was no significant diet
× breed interaction. Egg production and egg weight
were not significantly affected by the [SE]diet but did
vary significantly among breeds (Table 3).
Initial [SE]egg did not vary significantly among the
dietary treatments in any of the breeds (diet × breed
interaction, P < 0.56). When hens were fed the Sesupplemented diets, [SE]egg increased rapidly over the
first 10 d (P < 0.001) but continued to increase over
the last 2 wk (P < 0.001; Figure 1). By d 25, [Se]egg
varied significantly both among dietary treatments and
among breeds (diet × breed interaction, P < 0.002);
there were no breed differences at each of the 2 lower
[Se]diet, but at the highest [Se]diet, [Se]egg was significantly greater in the BR than in either of the 2 commercial breeds. Total egg Se followed the same response
pattern as [Se]egg (Figure 1). Overall, both [Se]egg and
total egg Se were significantly related to [Se]diet and to
daily Se intake (Figure 2).
As [Se]diet increased, excreta Se concentration also increased and consequently so did the total amount of Se
excreted (Table 4). However, the apparent Se absorption did not differ significantly between diets (mean =
70.2 ± 2.1%).
DISCUSSION
There is evidence that a dietary Se intake greater than the RDA may have possible health benefits
(Schrauzer, 2009). Although eggs have been shown to
be an effective vehicle for supplementing Se in the diet
(Surai et al., 2007), relatively few studies have fed hens
diets containing enough Se to produce eggs at these levels. Furthermore, the response of egg Se levels to high
dietary Se has been variable (Moksnes, 1983; Payne
et al., 2005; Na et al., 2006; Vukasinovic et al., 2006;
Chantiratikul et al., 2008).
Egg Se Levels
The [Se]egg due to the organic Se supplement in our
study were in agreement with those previously reported
in other studies (Moksnes, 1983; Payne et al., 2005; Na
et al., 2006; Vukasinovic et al., 2006; Chantiratikul et
al., 2008). We found that both [Se]egg and total egg Se
were linearly related to [SE]diet and intake (Figure 2).
This result is not surprising given that organic forms
of Se, such as selenomethionine (the major form of Se
in yeast Se products; Rayman, 2004), are absorbed by
active transport and are nonspecifically incorporated
into proteins in place of methionine (Schrauzer, 2003).
In contrast, inorganic Se sources, such as Na2SeO3, are
passively absorbed into the body and typically have
lower rates of absorption.
The current RDA of Se for human adults in the United States and Canada is 55 μg/d (Institute of Medicine, 2000). Based on the results of this study, hens
would require a diet containing 1.4 μg of organic Se/g
to produce an egg containing 55 μg of Se (Figure 2).
Given that most North American adults have a Se in-
SELENIUM ENRICHMENT OF TABLE EGGS
take greater than this RDA (Combs, 2001), producing Se-enriched eggs to meet this level is unwarranted.
However, in other regions of the world where there is
inadequate Se intake (e.g., parts of China, Europe, and
New Zealand), this target may be a desirable goal.
There is evidence that a Se intake greater than the
RDA may have possible health benefits (Finley, 2007;
Fisinin et al., 2009; Schrauzer, 2009; Schrauzer and Surai, 2009). Based on this evidence, Schrauzer (2009)
suggests that the optimal Se intake for human adults
is in the range of 250 to 300 μg/d. Assuming that the
average North American adult has a Se intake of 100 to
200 μg/d (Combs, 2001), this would require increasing
the Se intake by 50 to 200 μg/d. To produce an egg
containing 50, 100, or 200 μg of Se would necessitate
feeding hens diets containing 1.3, 2.8, or 5.7 μg of Se/g,
respectively (Figure 2). It should be noted that these
dietary levels are all greater than the current legal limit
for Se supplementation of livestock feeds in Canada and
the United States (0.3 μg of Se/g of diet).
As stated above, [Se]egg and total egg Se were significantly related to daily Se intake (Figure 2). However,
this response was variable among hens fed the highest
level of Se. Although BR hens had a lower feed intake
(Table 3), and hence Se intake, they produced eggs that
had a higher Se content than in either of the 2 commercial breeds (but only when hens were fed the highest level of Se yeast) (Figures 1 and 2). The BR hens
have a lower rate of egg production than commercial
2169
table egg layers (Table 3). This implies that when hens
with lower rates of egg production are fed high levels
of dietary Se, they may be able to build greater body
stores of Se (selenomethionine) that, when mobilized,
would allow for the production of eggs with a higher
Se content. This may have important implications for
breed selection if Se-enriched eggs are to be produced
commercially. For example, many niche market producers use heritage breeds, which have lower egg production rates.
Apparent Se Absorption
Few studies have examined the apparent absorption
of dietary organic Se by laying hens (Latshaw and Osman, 1975; Dobrzański and Jamroz, 2003; Richter et
al., 2006). Therefore, as part of this study, we conducted a balance study using LB hens. Although the total
amount of Se excreted increased as [Se]diet increased,
apparent Se absorption did not differ significantly between diets and averaged 70%. This value is somewhat
higher than the 60 to 65% apparent absorption previously reported (Latshaw and Osman, 1975; Dobrzański
and Jamroz, 2003; Richter et al., 2006). Together, these
results indicate that 30 to 40% of the ingested Se is excreted. Thus, future work should be undertaken to address potential environmental concerns associated with
feeding high levels of dietary Se to laying hens over a
full production cycle.
Figure 1. Time course of the effect of dietary Se on egg Se concentration ([Se]egg, upper panels) and total egg Se content (lower panels) in
3 breeds of laying hens. Base diet contained 0.3 μg of Se/g as inorganic Na2SeO3, which was supplemented with Se yeast at 1.0 (○), 2.4 (Δ), or
5.1 (□) mg of Se/kg of diet (see Table 2).
2170
Bennett and Cheng
Table 4. Apparent Se absorption of Lohmann Brown laying hens used in this study
Diet
Parameter
Feed
Se content (µg/g)
Feed intake (g/hen per d)
Se intake (µg/hen per d)
Excreta
Output (g of DM/hen per d)
Se content (µg/g)
Se output (µg/g)
Apparent Se absorption (%)
1
2
3
1.34
114.1 ± 11.7A
152.8 ± 15.7C
25.4 ± 1.4A
2.0 ± 0.1C
52.0 ± 3.2B
65.4 ± 2.8A
2.69
108.4 ± 3.6A
291.7 ± 9.6B
24.2 ± 1.7A
3.5 ± 0.1B
84.8 ± 4.5B
70.8 ± 2.1A
5.43
109.7 ± 3.8A
580.5 ± 6.1A
24.9 ± 3.6A
5.9 ± 0.4A
149.3 ± 27.7A
74.4 ± 4.6A
A–CMeans within each row (parameter) with common superscripts are not significantly different (P < 0.05).
Each mean is the average of 4 observations.
Figure 2. Relationships between egg Se content [egg Se concentration ([Se]egg) or total egg Se] and dietary Se concentration ([Se]diet) or total
Se intake in 3 breeds of laying hens [Barred Plymouth Rock (Δ), Lohmann Brown (□), and Lohmann White (○)] after 4 wk of supplementation.
Base diet contained 0.3 μg of Se/g as inorganic Na2SeO3, which was supplemented with Se yeast at 1.0, 2.4, or 5.1 mg of Se/kg of diet (see Table
2). Initial presupplement values are included.
SELENIUM ENRICHMENT OF TABLE EGGS
Effect of High Dietary Organic Se Levels
on Production
The high dietary Se levels used in this study did not
affect feed intake, egg production, or egg weight, which
is in agreement with previous studies (Moksnes, 1983;
Paton et al., 2002; Payne et al., 2005; Na et al., 2006;
Vukasinovic et al., 2006; Chantiratikul et al. 2008).
This lack of an effect on production indicates that high
dietary levels of organic Se do not negatively affect the
welfare of the hen.
Toxic Effect of High Dietary Organic
Se Levels
The maximum tolerable dietary level of Se for poultry is currently set at 3 µg/g (NRC, 2005). This level
was determined based on the observations that the
threshold level of dietary Se for decreased egg hatchability and chick growth occurs at 5 µg/g. However,
no signs of toxicity were observed in the laying hens
used in this study or in those used in previous studies
that fed hens high levels (3 to 6 µg/g) of organic Se
(Moksnes, 1983; Payne et al., 2005; Vukasinovic et al.,
2006; Chantiratikul et al., 2008). Dietary Se levels of
5 to 6 µg/g have no effect on body mass, feed intake,
or egg production of laying hens when either organic
(Moksnes, 1983; Table 2) or inorganic (Ort and Latshaw, 1978; Moksnes and Norheim, 1982) sources of Se
are used. The threshold for decreased egg production
and egg weight is 8 to 9 µg of Se/g of diet (Arnold et
al., 1973; Ort and Latshaw, 1978). The levels of organic
Se proposed to be fed to hens in this study (1.3 to 5.7
µg/g) are below these levels. All Se studies except those
of Moksnes and Norheim (1982) and Moksnes (1983)
lasted 4 to 6 wk. The 2 studies fed hens Se for 18 wk.
Future research should be directed at longer term feeding trials to establish the safe dietary limits for organic
Se consumption in hens if Se-enriched eggs are to be
produced commercially.
Conclusions
In this study, we assessed the response of egg Se levels to high dietary levels of organic Se to determine
the dietary Se requirement of hens needed to produce
Se-enriched table eggs. The results of this study indicate that within the range of Se levels that we fed to
the hens, egg Se levels are linearly related to dietary
organic Se levels. This and previous studies have not
found any evidence of toxicity from organic Se to laying
hens, even at levels as high as 3 to 6 μg of organic Se/g
of diet. Future research should be directed at establishing the safe dietary limits for organic Se consumption
in hens if Se-enriched eggs are to be produced commercially.
2171
ACKNOWLEDGMENTS
This research was supported by funds from the British Columbia Ministry of Agriculture and Lands, administered by the UBC Speciality Bird Research Committee. We thank Ilkyu Yoon, Diamond V Mills, for the
Se yeast; Eduardo Jovel, Les Lavkulich and Gilles Galzi,
Faculty of Land and Food Systems, University of British Columbia, for discussions on selenium analysis and
use of equipment; Lisa Hedderson and Lee Struthers,
AAFC Agassiz Poultry Research Centre, for technical
assistance; and Fred Silversides, AAFC Agassiz Poultry Research Centre, Stewart Paulson, British Columbia Ministry of Agriculture and Lands, and Jennifer
Arthur, Avian Research Centre, University of British
Columbia, for valuable inputs.
REFERENCES
AOAC. 2000. Official Methods of Analysis. AOAC Interational, Arlington, VA.
Arnold, R. L., O. E. Olson, and C. W. Carlson. 1973. Dietary selenium and arsenic additions and their effects on tissue and egg
selenium. Poult. Sci. 52:847–854.
Chantiratikul, A., O. Chinrasri, and P. Chantiratikul. 2008. Effect of
sodium selenite and zinc-l-selenomethionine on performance and
selenium concentration in eggs of laying hens. Asian-australas.
J. Anim. Sci. 21:1048–1052.
Combs, G. F. Jr. 2001. Selenium in global food systems. Br. J. Nutr.
85:517–547.
Dobrzański, Z., and D. Jamroz. 2003. Bioavailability of selenium and
zinc supplied to the feed for laying hens in organic and inorganic
form. http://www.ejpau.media.pl/volume6/issue2/animal/art03.html Accessed Jul. 9, 2010.
Finley, J. W. 2007. Increased intakes of selenium-enriched foods may
benefit human health. J. Sci. Food Agric. 87:1620–1627.
Fisinin, V. I., T. T. Papazyan, and P. F. Surai. 2009. Producing
selenium-enriched eggs and meat to improve the selenium status
of the general population. Crit. Rev. Biotechnol. 29:18–28.
Institute of Medicine. 2000. Dietary Reference Intakes for Vitamin
C, Vitamin E, Selenium and Carotenoids. National Academy
Press, Washington, DC.
Lambert, D. F., and N. J. Turoczy. 2000. Comparison of digestion
methods for the determination of selenium in fish tissue by cathodic stripping voltammetry. Anal. Chim. Acta 408:97–102.
Latshaw, J. D., and M. Osman. 1975. Distribution of selenium in
egg white and yolk after feeding natural and synthetic selenium
compounds. Poult. Sci. 54:1244–1252.
Moksnes, K. 1983. Selenium deposition in tissues and eggs of laying
hens given surplus of selenium as selenomethionine. Acta Vet.
Scand. 24:34–44.
Moksnes, K., and G. Norheim. 1982. Selenium concentrations in tissues and eggs of growing and laying chickens fed sodium selenite
at different levels. Acta Vet. Scand. 23:368–379.
Na, J. C., S. H. Kim, D. B. Jang, J. H. Kim, D. J. Yu, G. H. Kang,
H. K. Kim, D. S. Lee, S. J. Lee, J. C. Lee, and W. J. Lee. 2006.
Effects of dietary organic selenium levels on performance and
selenium retention in broiler chickens and laying hens. Korean J.
Poult. Sci. 33:255–262.
NRC. 1994. Nutrient Requirements of Poultry. 9th rev. ed. National
Academy Press, Washington DC.
NRC. 2005. Mineral Tolerance of Animals. 2nd rev. ed. National
Academy Press, Washington, DC.
Ort, J. F., and J. D. Latshaw. 1978. The toxic level of sodium selenite in the diet of laying chickens. J. Nutr. 108:1114–1120.
Pappas, A. C., F. Karadas, P. F. Surai, N. A. R. Wood, P. Casey, G.
R. Bortolotti, and B. K. Speake. 2006. Interspecies variation in
2172
Bennett and Cheng
yolk selenium concentrations among eggs of free-living birds: The
effect of phylogeny. J. Trace Elem. Med. Biol. 20:155–160.
Paton, N. D., A. H. Cantor, A. J. Pescatore, and C. A. Smith. 2002.
The effect of dietary selenium source and level on the uptake
of selenium by developing chick embryos. Poult. Sci. 81:1548–
1554.
Payne, R. L., T. K. Lavergne, and L. L. Southern. 2005. Effect of
inorganic versus organic selenium on hen production and egg
selenium concentration. Poult. Sci. 84:232–237.
Rayman, M. P. 2004. The use of high-selenium yeast to raise selenium status: How does it measure up? Br. J. Nutr. 92:557–573.
Richter, G., M. Leiterer, R. Kirmse, W. I. Ochrimenko, and W.
Arnhold. 2006. Comparative investigation of dietary supplements
of organic and inorganic bounded selenium in laying hens. Tierarztl. Umsch. 61:155–161.
Schrauzer, G. N. 2003. The nutritional significance, metabolism and
toxicology of selenomethionine. Adv. Food Nutr. Res. 47:73–
112.
Schrauzer, G. N. 2009. Selenium and selenium-antagonistic elements
in nutritional cancer prevention. Crit. Rev. Biotechnol. 29:10–
17.
Schrauzer, G. N., and P. F. Surai. 2009. Selenium in human and
animal nutrition: Resolved and unresolved issues. A partly historical treatise in commemoration of the fiftieth anniversary of
the discovery of the biological essentiality of selenium, dedicated
to the memory of Klaus Schwarz (1914–1978) on the occasion
of the thirtieth anniversary of his death. Crit. Rev. Biotechnol.
29:2–9.
Surai, P. F., T. T. Papazyan, B. K. Speake, and N. H. C. Sparks.
2007. Enrichment in selenium and other trace elements. Pages
183–190 in Bioactive Egg Compounds. R. Huopalahti, R. LopezFandinño, and M. Anton, R. Schade, ed. Springer-Verlag Berlin,
Germany.
Vukasinovic, M., R. Mihailovic, M. Sekler, V. Kaljevic, and V. Kurcubic. 2006. The impact of the selenium content of laying hen
feeds. Arch. Geflügelkd. 70:91–96.