animal
Animal (2014), 8:4, pp 542–554 © The Animal Consortium 2014 doi:10.1017/S1751731113002395
Meta-analysis of selenium accumulation and expression of antioxidant enzymes in chicken tissues E. Zoidis1†, N. Demiris2, A. Kominakis3 and A. C. Pappas1 1
Department of Nutritional Physiology and Feeding, Faculty of Animal Science and Aquaculture, Agricultural University of Athens, 75 Iera Odos, 11855 Athens, Greece; 2Department of Statistics, Athens University of Economics and Business, 76 Patission Str., 10434 Athens, Greece; 3Department of Animal Breeding and Husbandry, Faculty of Animal Science and Aquaculture, Agricultural University of Athens, 75 Iera Odos, 11855 Athens, Greece
(Received 6 September 2013; Accepted 9 December 2013; First published online 6 January 2014)
A meta-analysis integrating results of 40 selenium (Se) supplementation experiments that originated from 35 different controlled randomized trials was carried out in an attempt to identify significant factors that affect tissue Se accumulation in chicken. Examined factors included: Se source (12 different sources examined), type of chicken (laying hens or broilers), age of birds at the beginning of supplementation, duration of supplementation, year during which the study was conducted, sex of birds, number of chickens per treatment, method of analysis, tissue type, concentration of Se determined and Se added to feed. A correlation analysis was also carried out between tissue Se concentration and glutathione peroxidase activity. Data analysis showed that the factors significantly affecting tissue Se concentration include type of chicken ( P = 0.006), type of tissue ( P < 0.001) and the analytical method used ( P = 0.014). Although Se source was not found to affect tissue Se concentration (overall P > 0.05), certain inorganic (sodium selenite), calcium selenite, sodium selenate and organic sources (B-Traxim Se), Se-yeast, Se-malt, Se-enriched cabbage and Se-enriched garlic as well as background Se level from feed ingredients were found to significantly affect tissue Se concentration. The Se accumulation rate (estimated as linear regression coefficient of Se concentrations to Se added to feed) discriminated between the various tissues with highest values estimated in the leg muscle and lowest in blood plasma. Correlation analysis has also shown that tissue Se concentration (pooled data) was correlated to Se added to feed (r = 0.529, P < 0.01, log values) and to glutathione peroxidase activity (r = 0.332, P = 0.0478), with the latter not being correlated with Se added to feed. Although significant factors affecting Se concentration were reported in the present study, they do not necessarily indicate the in vivo function of the antioxidant system or the level of accumulated Se as other factors, not examined in the present study, may interact at the level of trace element absorption, distribution and retention. Keywords: antioxidant, broiler, chicken, hen, selenium
Implications
Introduction
A meta-analysis of selenium (Se) supplementation trials was performed to synthesize reported findings to arrive at a model for Se accumulation in various chicken tissues. Statistical analysis showed that the factors associated with tissue Se concentration are the type of chicken, the source of Se, the type of tissue and the analytical method used. Tissue Se concentration was correlated with Se added to feed and to glutathione peroxidase activity. The results of the present study can be useful to scientists as well as application areas, as meta-analysis findings are applicable to the totality of exposure situations.
Selenium (Se) is an essential trace element of fundamental importance for optimal animal and human health primarily because of its antioxidant activity. It has chemopreventive, anti-inflammatory, antiviral properties and is related in enhancing immunity (Rayman, 2012; Steinbrenner et al., 2013). The health-related properties of Se include but are not limited to protection against cancer, proper function of thyroid gland, and protection against cardiovascular and muscle disorders (Mao and Teng, 2013; Rocourt and Cheng, 2013). Se becomes cotranslationally incorporated into the polypeptide chain as part of the amino-acid selenocysteine (SeCys). Proteins that contain SeCys as an integral part of their polypeptide chain are defined as selenoproteins (Sel)
†
E-mail: [email protected]
542
Selenium accumulation in chicken. A meta-analysis and are present in all lineages of life (Schomburg, 2012). The major families of Sel include that of glutathione peroxidases, thioredoxin reductases (TRxR) and iodothyronine deiodinases (Pappas et al., 2008; Zoidis et al., 2010). In feed compounds of plant origin, Se occurs as part of an organic compound predominantly, selenomethionine (SeMet). Plant absorption of Se principally depends on the concentration and physicochemical forms existing in the soil. In chicken, to maintain high productive and reproductive performance, diets are usually supplemented with Se. This supplementation is an effective way to prevent Se deficiency and its associated problems, especially in combination with low vitamin E supply such as nutritional encephalomalacia, exudative diathesis and nutritional pancreatic atrophy (Pappas and Zoidis, 2012). Se is added either as an inorganic salt (sodium selenite, calcium selenite or sodium selenate) or as an organo-Se compound more often in the form of Se-yeast. SeMet is the predominant form of Se in most Se-enriched yeast products (Whanger, 2002). Other forms of organo-Se compounds include Se malt (Liu et al., 2009) and B-Traxim Se (Leeson et al., 2008). Absorbed Se can be incorporated into tissue proteins in place of methionine or can be further metabolized in the liver and used for the synthesis of specific Sel. The populations of many countries have a dietary Se intake below that of 55 μg/day, which is recommended by health regulatory bodies such as the Institute of Medicine in USA and the European Food Safety Authority (Institute of Medicine, Food and Nutrition Board, 2000; Combs, 2001; Rayman, 2005; European Food Safety Authority (EFSA), 2009; Fairweather-Tait et al., 2011). European countries such as Greece, (Pappa et al., 2006), Poland (Wasowicz et al., 2003), United Kingdom (Barclay et al., 1995), Spain (Díaz-Alarcón et al., 1996) and Croatia (Matec et al., 2000) have an average daily Se intake below 40 μg, and this seems to be the case for other parts of the world. For instance, it has been estimated that the average intake of Se for adult men and women in Argentina is 32 and 24 μg/day, respectively (Sigrist et al., 2012). To help meet the recommended dietary allowance (RDA), consumers should avail of functional foods use. Technology of production of Se-enriched eggs, meat and milk has been developed and successfully introduced in various countries worldwide. Indeed, Se-enriched eggs are produced in more than 25 countries worldwide (Surai, 2006). Se is added to laying hen diets (Pappas et al., 2005a) and/or broiler diets (Pappas et al., 2005b) and successfully deposited to eggs or broiler tissues. Many controlled randomized feeding trials have investigated the factors influencing accumulation of Se in eggs and various chicken tissues, with considerable variation in results. When controversial and/or variable results across individual studies are obtained, a meta-analysis can be carried out in an attempt to draw concrete conclusions by combining appropriately weighted studies in a coherent manner. The present study presents a meta-analysis of numerous reported studies aiming at: (a) undentifying significant factors that affect tissue Se accumulation in chickens after Se supplementation in feed and (b) estimating correlation(s)
between Se accumulation and the expression of antioxidant enzymes. Material and methods
Data sourcing and inclusion criteria Potential studies for use in the meta-analysis were found from a search of journals, conference proceedings, and book articles in abstract and other electronic databases (Academic Onefile, AGRICOLA, BIDS, Biochemistry and Biophysics Citation Index, BioInfoBank Library, Biological Abstracts, Biosis Previews, Cab Abstracts, Elsevier biobase-CABS, EMBASE, Current Contents/ Life Sciences, EMBiology, Google Scholar, IBIDS (International Bibliographic Information on Dietary Supplements), IngentaConnect, MEDLINE, NLM Gateway, OvidSP, PubMed, Science Direct (Journal), Scopus, Wilson Web), and in the libraries of the Universities of Cambridge (UK) and Athens (Greece). Indices used during the search were combinations and appropriate truncations and forms of the terms ‘selenium’, ‘Se’, ‘chicken’, ‘broiler’, ‘hen’, ‘egg’, ‘diet’, ‘dietary’, ‘feed’, ‘nutrition’, ‘poultry’ and any plurals thereof. Published information in English up to and including the publication year 2011 (3rd quartile) was considered. Experiments were sought on chickens fed fixed Se concentration on a daily basis throughout the experimental period examined. Allowed experimental designs involved controlled randomized feeding trials, with both serial slaughter and experiments, with only one time of slaughter for several groups of chickens receiving different doses and chemical forms of Se. From an initial database of 3497 articles on various aspects of Se and chicken, 35 feeding trials involving 837 chickens in a total of 140 treatment and control groups were identified for inclusion in the meta-regression. Most of the experiments include several treatment groups and one control group (The list of references used for the meta-analysis is given in Supplementary Material S1). Range of interest, data extraction and the data set The range of interest of this study was limited to exclude excessively low or high exposures to Se, because of the limited relevance in the field. It covers and exceeds (by a factor of 30) the maximum authorized total Se contents in feed in EU for farm animals (background Se plus supplemented one), which is 0.5 p.p.m. of complete feeding stuffs with a moisture content of 12% (European Union Commission (EU), 2004). The results apply to the same range of exposure situations: maximum values of 15 p.p.m. dry matter (DM) for the feed Se concentration and 7 to 175 days for the duration of supplementation. Whenever conversion from dry weight (DW, also DM) to wet weight (WW) was necessary, factors determined from a literature search and evaluation were used. WW to DW conversion factors for the chicken liver, kidney, yolk, albumen, muscle and liver protein used were 0.30, 0.26, 0.50, 0.20, 0.27 and 0.17, respectively. These are in agreement with factors reported by other authors as well (McCance, 1991; Solomon, 1991; Prankel et al., 2004). Data on amount 543
Zoidis, Demiris, Kominakis and Pappas of Se in whole egg usually presented as μg per egg could not be appropriately converted to concentration values (p.p.m.) as actual egg weight was not reported. Thus, only data of Se concentration of egg components were considered for analysis. Several data were recorded and used in the study. The components of the data set were as follows. The source of Se present in the diet grouped into four categories, namely, no supplementation, inorganic, organic and nano-Se. Control feeds were placed in the no supplementation category. Inorganic sources included sodium selenite, calcium selenite and sodium selenate, whereas organic sources included B-Traxim Se, SeMet, Se-yeast, Se-malt, Chlorella Algae, cabbage and garlic. In total, there were 12 Se source levels. Furthermore, there were two types of chicken (laying hens including broiler breeders or meat type birds i.e. broilers). Other components were the age of birds at the beginning of supplementation (young (⩽49 days), old (>49 days)); the duration of supplementation (short (⩽21 days), medium (>22, ⩽42 days), long (>42 days)); the year during which the study was conducted (1970 to 1979, 1980 to 1989, 1990 to 1999, 2000 onwards); the sex of the birds (male, female, ‘as hatched’), the number of chickens per experimental treatment (n), the method of Se determination (atomic absorption spectroscopy (AAS) – and its variations including hydride generation atomic absorption-, fluro-spectroscopy and inductively coupled plasma mass spectrometry (ICP-MS)). Cases of outsourcing of Se determination, that is, lack of analytical technique description, were recorded and grouped in an additional category named ‘Other’. Additional key parts of the data set included the Se added in the feed that was categorized into four levels, taking into account that the maximum concentration of Se added to chicken diets in US is 0.3 p.p.m. (US Food and Drug Administration (FDA), 2012) (no, normal (⩽0.3 p.p.m.), medium (>0.3, ⩽1 p.p.m.) and high (>1, ⩽15 p.p.m.); the Se concentrations in the organs and tissues (plasma, whole blood, liver, kidney, breast muscle tissue, leg muscle tissue, yolk, albumen); the type of tissue; and finally, the antioxidant enzyme glutathione peroxidase (GPx) activity. Some components (GPx activity in the whole blood, SOD activity in breast muscle and CAT activity in breast muscle and liver) were omitted from the data set owing to the low number of observations (i.e. 49 days) Duration Short (⩽21 days) Medium (>22, ⩽42 days) Long (>42 days) Year 1970 to 1979 1980 to 1989 1990 to 1999 2000 onwards Sex Male Female As hatched Method AAS Fluorometric assay ICP-MS Other Se source No supplementation Sodium selenite Calcium selenite Sodium selenate B-Traxim Se Selenomethionine Se yeast Se malt Chlorella Algae Cabbage (Se enriched) Garlic (Se enriched) Nano-Se Se added No Normal (⩽0.3 p.p.m.) Medium (>0.3, ⩽1 p.p.m.) High (>1, ⩽15 p.p.m.)
Blood
Mean
n
s.d.
Minimum
Maximum
Mean
n
s.d.
Minimum
Maximum
0.175
27
0.069
0.009
0.310
0.256
32
0.134
0.052
0.866
0.179 0.166
18 9
0.084 0.015
0.009 0.148
0.310 0.190
0.264 0.249
16 16
0.180 0.069
0.052 0.148
0.866 0.360
0.122 0.205
10 17
0.054 0.057
0.009 0.148
0.210 0.310
0.265 0.244
19 13
0.166 0.069
0.052 0.148
0.866 0.360
0.186 0.166 0.142
15 9 3
0.090 0.015 0.016
0.009 0.148 0.130
0.310 0.190 0.160
0.269 0.255 na
3 29 na
0.078 0.140 na
0.184 0.148 na
0.337 0.190 na
na 0.186 na 0.160
na 15 na 12
na 0.090 na 0.018
na 0.009 na 0.130
na 0.310 na 0.190
na na 0.257 0.256
na na 10 22
na na 0.068 0.157
na na 0.118 0.052
na na 0.337 0.866
0.186 0.166 0.142
15 9 3
0.090 0.015 0.016
0.009 0.148 0.130
0.310 0.190 0.160
0.190 0.249 0.298
5 16 11
0.091 0.069 0.203
0.052 0.148 0.088
0.264 0.360 0.866
na 0.175 na na
na 27 na na
na 0.069 na na
na 0.009 na na
na 0.310 na na
0.236 0.240 0.379 na
7 21 4 na
0.063 0.079 0.338 na
0.148 0.052 0.088 na
0.339 0.360 0.866 na
0.197 0.178 0.250 0.280 0.159 na 0.169 na na na na na
4 12 3 1 3 na 4 na na na na na
0.065 0.067 0.056 – 0.012 na 0.019 na na na na na
0.009 0.084 0.190 0.280 0.152 na 0.148 na na na na na
0.160 0.310 0.300 0.280 0.173 na 0.190 na na na na na
0.137 0.268 0.281 na 0.193 0.337 0.297 0.360 na na na na
6 10 3 na 1 1 10 1 na na na na
0.065 0.055 0.044 na – – 0.205 – na na na na
0.052 0.177 0.236 na 0.193 0.337 0.142 0.360 na na na na
0.230 0.350 0.324 na 0.193 0.337 0.866 0.360 na na na na
0.097 0.153 na 0.233
4 13 na 10
0.065 0.028 na 0.063
0.009 0.084 na 0.120
0.160 0.190 na 0.310
0.118 0.247 0.300 0.493
5 20 4 3
0.051 0.052 0.066 0.325
0.052 0.142 0.223 0.274
0.184 0.337 0.360 0.866
AAS = atomic absorption spectroscopy including hydride generation atomic fluorescence spectroscopy; ICP-MS = inductively coupled plasma mass spectroscopy; Other = outsourcing; No supplementation = naturally occurring Se; na = not applicable.
0.30 and 0.49 p.p.m., respectively (Table 1). Studies using Chlorella Algae, cabbage, garlic and nano-Se as a source of Se did not report any Se concentration in plasma and blood. Regarding the method of analysis used to determine Se concentration, no studies report atomic absorption or ICP-MS as the method used to acquire data on plasma Se concentration. The overall Se concentration in the liver and
kidney was 1.50 p.p.m. ranging from 0.09 to 10.56 p.p.m. and 1.76 p.p.m. (range: 0.24 to 7.62 p.p.m.), respectively (Table 2). The mean liver Se concentration was 0.44, 0.70, 0.74 and 4.16 for no, normal, medium and highly Se added level, respectively. Se concentration in the breast muscle tissue (Table 3) ranged from 0.05 to 14.10 p.p.m. (overall mean 0.74 p.p.m.), whereas that of the leg muscle from 545
Zoidis, Demiris, Kominakis and Pappas Table 2 Descriptive statistics of Se concentration (p.p.m.) in the liver and kidney of chicken Liver
Overall Subgrouping Chicken type Broilers Layers Age Young (⩽49 days) Old (>49 days) Duration Short (⩽21 days) Medium (>22, ⩽42 days) Long (>42 days) Year 1970 to 1979 1980 to 1989 1990 to 1999 2000 onwards Sex Male Female As hatched Method AAS Fluorometric assay ICP-MS Other Se source No supplementation Sodium selenite Calcium selenite Sodium selenate B-Traxim Se Selenomethionine Se yeast Se malt Chlorella Algae Cabbage (Se enriched) Garlic (Se enriched) Nano-Se Se added No Normal (⩽0.3 p.p.m.) Medium (>0.3, ⩽1 p.p.m.) High (>1, ⩽15 p.p.m.)
Kidney
Mean
n
s.d.
Minimum
Maximum
Mean
n
s.d.
Minimum
Maximum
1.499
74
2.154
0.090
10.560
1.762
37
1.937
0.240
7.620
1.970 0.678
47 27
2.577 0.419
0.210 0.090
10.560 2.420
2.605 0.873
19 18
2.386 0.537
0.380 0.240
7.620 2.540
1.021 2.031
39 35
1.182 2.801
0.210 0.090
5.290 10.560
1.001 2.226
14 23
0.895 2.253
0.380 0.240
3.610 7.620
2.897 0.858 0.964
23 46 5
3.276 0.865 0.961
0.210 0.240 0.090
10.560 5.290 2.420
3.130 0.730 1.170
15 17 5
2.432 0.144 1.005
0.380 0.390 0.240
7.620 0.990 2.540
0.964 3.257 1.053 0.773
5 20 11 38
0.961 3.373 1.414 0.601
0.090 0.210 0.340 0.240
2.420 10.560 5.290 3.271
1.170 3.751 0.643 0.792
5 12 10 10
1.005 2.328 0.147 0.118
0.240 0.380 0.390 0.551
2.540 7.620 0.801 0.990
2.782 0.671 0.989
26 28 20
3.100 0.413 1.183
0.210 0.090 0.240
10.560 2.420 5.290
3.751 0.873 0.641
12 18 7
2.328 0.537 0.137
0.380 0.240 0.390
7.620 2.540 0.800
0.850 1.687 1.617 na
16 51 7 na
1.191 2.458 1.054 na
0.240 0.090 0.491 na
5.290 10.560 3.271 na
0.752 1.998 na na
7 30 na na
0.102 2.086 na na
0.551 0.240 na na
0.863 7.620 na na
0.459 1.835 3.695 7.710 0.519 0.856 1.048 0.760 2.360 0.693 0.627 0.620
16 29 6 1 3 2 11 1 1 1 1 2
0.251 2.303 4.063 – 0.095 0.027 0.917 – – – – 0.099
0.090 0.330 0.550 7.710 0.450 0.837 0.044 0.760 2.360 0.693 0.627 0.550
1.110 10.270 10.560 7.710 0.628 0.876 3.271 0.760 2.360 0.693 0.627 0.690
0.553 1.846 3.078 5.690 na 0.801 0.753 0.900 na na na na
7 18 6 1 na 1 3 1 na na na na
0.300 1.692 3.001 – na – 0.046 – na na na na
0.240 0.340 0.570 5.690 na 0.801 0.700 0.900 na na na na
1.120 6.570 7.620 5.630 na 0.800 0.783 0.900 na na na na
0.439 0.507 0.738 4.160
14 33 9 18
0.256 0.457 0.100 3.086
0.090 0.330 0.627 0.540
1.110 2.410 0.880 10.560
0.517 0.683 0.884 3.359
6 12 4 15
0.310 0.131 0.086 2.233
0.240 0.340 0.783 0.775
1.120 0.801 0.900 7.620
AAS = atomic absorption spectroscopy including hydride generation atomic fluorescence spectroscopy; ICP-MS = inductively coupled plasma mass spectroscopy; Other = outsourcing; No supplementation = naturally occurring Se; na = not applicable.
0.28 to 12.00 p.p.m. (overall mean 1.63 p.p.m.). Studies using Se malt as a source of Se did not report any Se concentrations either in the breast or in leg muscle tissue (na, Table 3). Mean yolk and albumen Se concentration in layers was 1.50 (0.08 to 4.93 p.p.m.) and 1.62 p.p.m. (0.03 to 8.35 p.p.m.), respectively. No data were available for male birds indicating biological plausibility (Table 4). Furthermore, 546
the highest activity of GPx was recorded in the liver when compared with the other two tissues, that is, plasma and breast muscle (Table 5). The mean GPx activity in the breast muscle, plasma and liver was 0.03, 0.64 and 7.26 U per mg of protein, respectively (Table 5). Table 6 shows the correlations of Se concentration between the various tissues as well as correlations with GPx
Selenium accumulation in chicken. A meta-analysis Table 3 Descriptive statistics of Se concentration (p.p.m.) in the breast and leg muscle of chicken Breast
Overall Subgrouping Chicken type Broilers Layers Age Young (⩽49 days) Old (>49 days) Duration Short (⩽21 days) Medium (>22, ⩽42 days) Long (>42 days) Year 1970 to 1979 1980 to 1989 1990 to 1999 2000 onwards Sex Male Female As hatched Method AAS Fluorometric assay ICP-MS Other Se source No supplementation Sodium selenite Calcium selenite Sodium selenate B-Traxim Se Selenomethionine Se yeast Se malt Chlorella Algae Cabbage (Se enriched) Garlic (Se enriched) Nano-Se Se added No Normal (⩽0.3 p.p.m.) Medium (>0.3, ⩽1 p.p.m.) High (>1, ⩽15 p.p.m.)
Leg
Mean
n
s.d.
Minimum
Maximum
Mean
n
s.d.
Minimum
Maximum
0.740
55
1.955
0.050
14.100
1.635
11
3.457
0.280
12.000
1.103 0.153
34 21
2.429 0.043
0.110 0.050
14.100 0.249
1.635 na
11 na
3.457 na
0.280 na
12.000 na
1.089 0.428
26 29
2.801 0.391
0.110 0.050
14.100 1.190
1.874 0.997
8 3
4.095 0.456
0.280 0.470
12.000 1.270
0.569 0.293 2.340
15 30 10
0.399 0.250 4.350
0.110 0.110 0.050
1.190 1.090 14.100
na 0.602 6.258
na 9 2
na 0.408 8.082
na 0.280 0.570
na 1.270 12.000
0.132 0.670 0.165 0.901
5 12 3 35
0.694 0.382 0.073 2.431
0.050 0.110 0.116 0.110
0.210 1.190 0.249 14.100
na na na 1.635
na na na 11
na na na 3.457
na na na 0.280
na na na 12.000
0.604 0.153 1.735
19 21 15
0.384 0.043 3.599
0.110 0.050 0.110
1.190 0.249 14.100
0.732 na 2.387
5 na 6
0.487 na 4.714
0.280 na 0.307
1.270 na 12.000
0.196 0.609 3.426 0.237
13 33 5 4
0.095 0.830 5.974 0.030
0.110 0.050 0.390 0.209
0.430 4.330 14.100 0.278
0.335 0.438 3.112 na
2 4 5 na
0.078 0.254 4.982 na
0.280 0.307 0.470 na
0.390 0.819 12.000 na
0.378 0.385 0.963 0.920 0.155 0.549 2.081 na 1.090 0.314 0.323 0.365
11 21 3 1 2 2 10 na 1 1 1 2
0.389 0.470 0.212 – 0.001 0.424 4.416 na – – – 0.92
0.050 0.070 0.770 0.920 0.154 0.249 0.149 na 1.090 0.314 0.323 0.300
1.750 2.020 1.190 0.920 0.156 0.849 14.100 na 1.090 0.314 0.323 0.430
0.449 na na na na 0.819 3.480 na 1.270 0.321 0.307 na
3 na na na na 1 4 na 1 1 1 na
0.133 na na na na – 5.696 na – – – na
0.307 na na na na 0.819 0.280 na 1.270 0.321 0.307 na
0.570 na na na na 0.819 12.000 na 1.270 0.321 0.307 na
0.361 0.557 0.380 1.398
10 21 8 16
0.512 0.980 0.230 3.410
0.050 0.070 0.140 0.149
1.750 4.330 0.849 14.100
0.388 1.260 0.448 12.000
2 2 6 1
0.115 0.014 0.210 –
0.307 1.250 0.280 12.000
0.470 1.270 0.819 12.000
AAS = atomic absorption spectroscopy including hydride generation atomic fluorescence spectroscopy; ICP-MS = inductively coupled plasma mass spectroscopy; Other = outsourcing; No supplementation = naturally occurring Se; na = not applicable.
activity. Se concentrations in blood and plasma were positively correlated, implying that they could be used interchangeably. Se concentration in plasma was positively correlated with that in the liver (r = 0.845) and kidney (r = 0.953). Se concentration in blood was found to be positively correlated with that of the liver (r = 0.929), kidney (r = 0.802) and yolk (r = 0.999). Se in liver Se was also
positively correlated with that of the breast (r = 0.790), leg (r = 0.938) and kidney (r = 0.988). Se in the breast apart from its aforementioned correlation with the liver was additionally correlated with that of four other tissues, namely, the leg (r = 0.999), kidney (r = 0.926), yolk (r = 0.928), albumen (r = 0.899) as well as with GPx activity in the liver (r = 0.776) and plasma (r = 0.859) but not in the breast. 547
Zoidis, Demiris, Kominakis and Pappas Table 4 Descriptive statistics of Se concentration (p.p.m.) in the yolk and albumen of chicken Yolk
Overall Subgrouping Chicken type Broilers Layers Age Young (⩽49 days) Old (>49 days) Duration Short (⩽21 days) Medium (>22, ⩽42 days) Long (>42 days) Year 1970 to 1979 1980 to 1989 1990 to 1999 2000 onwards Sex Male Female As hatched Method AAS Fluorometric assay ICP-MS Other Se source No supplementation Sodium selenite Calcium selenite Sodium selenate B-Traxim Se Selenomethionine Se yeast Se malt Chlorella Algae Cabbage (Se enriched) Garlic (Se enriched) Nano-Se Se added No Normal (⩽0.3 p.p.m.) Medium (>0.3, ⩽1 p.p.m.) High (>1, ⩽15 p.p.m.)
Albumen
Mean
n
s.d.
Minimum
Maximum
Mean
n
s.d.
Minimum
Maximum
1.505
26
1.470
0.085
4.930
1.621
22
2.589
0.030
8.350
na 1.505
na 26
na 1.470
na 0.085
na 4.930
na 1.621
na 22
na 2.589
na 0.030
na 8.350
na 1.505
na 26
na 1.470
na 0.085
na 4.930
na 1.621
na 22
na 2.589
na 0.030
na 8.350
2.655 3.833 0.688
6 3 17
1.305 1.005 0.703
1.540 2.680 0.085
4.930 4.520 2.750
1.812 7.360 0.290
6 3 13
1.503 1.406 0.216
0.830 5.750 0.030
4.620 8.350 0.780
1.188 na 2.655 1.150
5 na 6 15
1.087 na 1.305 1.474
0.170 na 1.540 0.085
2.750 na 4.930 4.520
0.296 na 1.812 2.120
5 na 6 11
0.306 na 1.503 3.426
0.050 na 0.830 0.030
0.780 na 4.620 8.350
na 1.505 na
na 26 na
na 1.470 na
na 0.085 na
na 4.930 na
na 1.621 na
na 22 na
na 2.589 na
na 0.030 na
na 8.350 na
0.435 2.384 0.542 na
7 14 5 na
0.265 1.498 0.491 na
0.085 0.170 0.165 na
0.854 4.930 1.350 na
0.168 2.460 0.064 na
7 14 1 na
0.137 2.960 – na
0.030 0.050 0.064 na
0.404 8.350 0.064 na
0.668 2.252 na na na na 0.628 4.520 1.350 na na na
8 11 na na na na 5 1 1 na na na
0.942 1.517 na na na na 0.142 – – na na na
0.085 0.310 na na na na 0.505 4.520 1.350 na na na
2.680 4.930 na na na na 0.854 4.520 1.350 na na na
0.974 1.982 na na na na 0.263 7.980 na na na na
7 10 na na na na 4 1 na na na na
2.127 2.616 na na na na 0.097 – na na na na
0.030 0.050 na na na na 0.194 7.980 na na na na
5.750 8.350 na na na na 0.404 7.980 na na na na
0.413 1.045 2.066 2.648
6 8 6 6
0.556 0.937 1.868 1.434
0.085 0.184 0.505 0.790
1.540 2.680 4.520 4.930
0.205 1.370 3.032 1.597
5 5 6 6
0.350 2.468 3.988 1.680
0.030 0.041 0.207 0.200
0.830 5.750 8.350 4.620
AAS = atomic absorption spectroscopy including hydride generation atomic fluorescence spectroscopy; ICP-MS = inductively coupled plasma mass spectroscopy; Other = outsourcing; No supplementation = naturally occurring Se; na = not applicable.
Table 7 shows the results of mixed ANOVA along with least square means of Se concentration per class of factor included in the final model. The two chicken types were clearly discriminated (P < 0.0059) with regard to Se concentrations with layers displaying lower concentrations v. the broilers (−0.445 v. to 0.154, respectively). Fitting the duration of the experiment as a covariate did not improve the 548
model fit, implying no significance of this particular factor (P = 0.2268). In addition, the source of Se appeared not to significantly affect the Se concentration in the various tissues. However, a more thorough examination of least square (LS) class means showed that some Se sources may cause maximum (e.g. B-Traxim, Se yeast) or minimum (Garlic, cabbage) Se concentrations across the tissues.
Table 5 Descriptive statistics of GPx (glutathione peroxidase) concentration (U/mg protein) in the liver, plasma and breast muscle of chicken Liver GPx
Overall
Breast muscle GPx
Mean
n
s.d.
Minimum
Maximum
Mean
n
s.d.
Minimum
Maximum
Mean
n
s.d.
Minimum
Maximum
7.63
27
16.14
0.01
50.00
0.64
28
1.71
0.01
5.74
0.03
10
0.02
0.01
0.04
11.40 0.08
18 9
18.80 0.02
0.01 0.06
50.00 0.13
0.78 0.13
22 6
1.91 0.03
0.01 0.11
5.74 0.17
0.01 0.04
4 6
0.01 0.01
0.01 0.04
0.01 0.04
11.40 0.08
18 9
18.80 0.02
0.01 0.06
50.00 0.13
0.78 0.13
22 6
1.91 0.03
0.01 0.11
5.74 0.17
0.01 0.04
4 6
0.01 0.01
0.01 0.04
0.01 0.04
30.00 6.76 na
1 26 na
– 15.82 na
30.00 0.01 na
30.00 50.00 na
na 0.06 5.49
na 25 3
na 0.06 0.22
na 0.01 5.31
na 0.17 5.74
na 0.03 na
na 10 na
na 0.02 na
na 0.01 na
na 0.04 na
0.06 0.09 0.01 10.27
2 4 1 20
0.01 0.01 – 18.12
0.05 0.07 0.01 0.01
0.06 0.10 0.01 50.00
0.02 0.11 0.01 1.92
14 4 1 9
0.03 0.02 – 2.68
0.01 0.09 0.01 0.11
0.11 0.13 0.01 5.74
0.01 na na 0.03
2 na na 8
0.01 na na 0.02
0.01 na na 0.01
0.01 na na 0.04
0.05 3.08 29.95
10 10 7
0.04 9.46 22.69
0.01 0.06 2.20
0.10 30.00 50.00
0.04 0.13 5.49
19 6 3
0.05 0.03 0.22
0.01 0.11 5.31
0.13 0.17 5.74
0.01 0.04 na
4 6 na
0.01 0.01 na
0.01 0.04 na
0.01 0.04 na
24.38 0.09 na 1.63
8 13 na 6
22.55 0.02 na 1.82
0.01 0.06 na 0.01
50.00 0.13 na 3.84
na 1.36 na 0.02
na 13 na 15
na 2.35 na 0.03
na 0.09 na 0.01
na 5.74 na 0.11
na 0.04 na 0.01
na 6 na 4
na 0.01 na 0.01
na 0.04 na 0.01
na 0.04 na 0.01
8.71 5.44 na na 0.08 0.05 0.77 na 47.50 na na na
6 10 na na 3 1 5 na 2 na na na
13.03 15.70 na na 0.04 – 1.58 na 0.70 na na na
0.01 0.01 na na 0.06 0.05 0.01 na 47.00 na na na
30.00 50.00 na na 0.13 0.05 3.60 na 48.00 na na na
1.38 0.65 na na 0.11 0.02 1.84 na na na na na
4 10 na na 2 9 3 na na na na na
2.69 1.79 na na 0.01 0.02 3.00 na na na na na
0.01 0.01 na na 0.11 0.01 0.11 na na na na na
5.41 5.74 na na 0.11 0.06 5.31 na na na na na
0.01 0.02 na na 0.38 0.01 0.04 na na na na na
1 4 na na 2 1 2 na na na na na
– 0.02 na na 0.03 – 0.01 na na na na na
0.01 0.01 na na 0.04 0.01 0.04 na na na na na
0.01 0.04 na na 0.04 0.01 0.04 na na na na na
4.46 6.77 48.00 0.10
5 20 1 1
8.74 15.76 – –
0.01 0.01 48.00 0.10
20.00 50.00 48.00 0.10
1.38 0.64 0.02 0.06
4 19 1 4
2.69 1.72 – 0.04
0.01 0.01 0.02 0.03
5.41 5.74 0.02 0.13
0.01 0.03 na na
1 9 na na
– 0.02 na na
0.01 0.01 na na
0.01 0.04 na na
549
AAS = atomic absorption spectroscopy including hydride generation atomic fluorescence spectroscopy; ICP-MS = inductively coupled plasma mass spectroscopy; Other = outsourcing; No supplementation = naturally occurring Se; na = not applicable.
Selenium accumulation in chicken. A meta-analysis
Subgrouping Chicken type Broilers Layers Age Young (⩽49 days) Old (>49 days) Duration Short (⩽21 days) Medium (>22, ⩽42 days) Long (>42 days) Year 1970 to 1979 1980 to 1989 1990 to 1999 2000 onwards Sex Male Female As hatched Method AAS Fluorometric assay ICP-MS Other Se source No supplementation Sodium selenite Calcium selenite Sodium selenate B-Traxim Se Selenomethionine Se yeast Se malt Chlorella Algae Cabbage (Se enriched) Garlic (Se enriched) Nano-Se Se added No Normal (⩽0.3 p.p.m.) Medium (>0.3, ⩽1 p.p.m.) High (>1, ⩽15 p.p.m.)
Plasma GPx
Zoidis, Demiris, Kominakis and Pappas Table 6 Pearson correlations between the Se concentration in various tissues and GPx (glutathione peroxidase) activity in chicken Se
GPx
Blood
Liver
Breast
Leg
Kidney
Yolk
Albumen
Liver
Plasma
0.956
0.845** 0.929**
0.091 0.564 0.790**
na na 0.938** 0.999**
0.953** 0.802** 0.988** 0.926** na
na 0.999* 0.392 0.928* na 0.343
na 0.980 −0.051 0.899* na −0.011 0.842**
0.241 0.000 0.043 0.776** na na na na
−0.596 na −0.523 0.859** na na na na
Breast
Se Plasma Blood Liver Breast Leg Kidney Yolk Albumen GPx Liver Plasma
0.660*
−0.186 na −0.463 −0.055 na na na na 0.634 0.906**
na = not applicable. *P ⩽ 0.05. **P ⩽ 0.01.
Overall, Se concentrations clearly discriminated across the various tissues (P < 0.001). In addition, here a thorough inspection of the estimated LS tissue means has shown highest concentrations in the yolk, albumen, kidney and liver, and lowest in plasma, blood and muscles (breast and leg). According to the estimated LS means of Se concentrations, the various tissues could thus be placed in ascending order as follows: plasma (lowest), blood, breast muscle, leg muscle, albumen and yolk (highest) (Table 7). Apart from differences in the Se concentrations in the various tissues, we have further detected different rates of Se accumulation across the various tissues (see values of linear regression coefficients (b) in Table 8). More specifically, highest accumulation rates were estimated in the leg muscle (b = 0.727, P < 0.001), liver (b = 0.570, P < 0.001) and kidney (b = 0.499, P < 0.001), and lowest or nil in blood (b = 0.326, P = 0.0074) and plasma (b = 0.106, P = 0.154). However, when s.e.s were taken into account, only differences in Se accumulation rates between the leg muscle and plasma (P = 0.0023) and between the leg muscle and breast muscle (P = 0.0274) could be confirmed statistically. Se accumulation rates between the leg muscle and blood tended (P = 0.0741) to differ significantly. Furthermore, statistically significant Se accumulation rates were noted between the liver and plasma (P < 0.001), liver and breast muscle (P = 0.001), and liver and blood (P = 0.05). Similarly, Se accumulation rates between albumen and plasma (P < 0.001) and albumen and breast muscle (P = 0.0368) differed significantly. Moreover, Se accumulation rates between the kidney and breast muscle (P < 0.001) and between the kidney and plasma (P < 0.001) could be statistically confirmed. Finally, statistically significant Se accumulation rates were observed between plasma and yolk (P = 0.0103), between plasma and breast muscle (P = 0.0130), and between plasma and egg (P = 0.0399). Finally, the analytical method applied to determine Se was found to be associated with significantly different 550
Se concentrations in the various tissues (P = 0.014) with lowest and highest values estimated for ICP-MS and AAS, respectively (Table 7). Further correlation analysis between Se concentration, Se added to feed and GPx activity showed Se concentration (pooled data) to be correlated (r = 0.529, P < 0.01) with Se added to feed and to GPx activity (r = 0.332, P = 0.0478), the latter not being correlated with Se added to feed (results not presented). Discussion The present study presents an attempt to evaluate the importance of various factors that are involved in Se accumulation in various chicken tissues as well as in the antioxidant enzyme activity. This meta-analysis identified significant factors, which affect Se accumulation, the source of Se, the type of tissue and the analytical method used. Regarding the Se source, the study revealed that certain Se sources such as sodium selenite, B-Traxim and Se yeast may cause maximum Se concentrations across the tissues. Chickens may receive Se via their typical diet and additionally via feed additives. With regard to the latter (feeding additives), the Commission of the European Communities has approved several forms including inorganic salts, sodium selenite or sodium selenate (EC, 2004), or organic salts including yeast strains Saccharomyces cerevisiae CNCM I-3060 (EC, 2006), NCYC R397 (EC, 2007) or CNCM I-3399 (EC, 2009). Yeast is able to bind element ions from the environment and then permanently incorporate them into its cellular structures. At present, S. cerevisiae, Candida utilis and Yarrowia lipolytica yeast species are mainly used in biotechnological investigations on mineral constituent incorporation (Kieliszek and Błażejak, 2013). SeMet is the predominant form of Se in most Seenriched yeast products usually ranging between 60% and 70% of the total Se (Whanger, 2002; Rayman, 2012). Among all Se yeast products available, large differences in quality and
Selenium accumulation in chicken. A meta-analysis Table 7 Level of significance of factors examined as well as least squares means (with standard errors) of classes within factor(s) of tissue Se concentration (log values) in chicken Factors examined Chicken type Overall Broilers Layers Duration Overall Se source Overall No supplementation Sodium selenite Calcium selenite Sodium selenate B-Traxim Se Selenomethionine Se yeast Se malt Chlorella Algae Cabbage (Se enriched) Garlic (Se enriched) Nano-Se Tissue Overall Plasma Blood Liver Kidney Breast muscle Leg muscle Yolk Albumen Method Overall AAS Fluorometric assay ICP-MS Other
LS mean
s.e.
– −0.154a −0.445b
– 0.089 0.112
–
–
Table 8 Linear regression coefficients ( b) of Se determined to Se added to feed across the various tissues of chicken Tissue
b1
s.e.
P-value
0.106 0.326 0.570 0.499 0.295 0.727 0.428 0.543
0.074 0.120 0.054 0.068 0.063 0.191 0.101 0.102
0.1540 (ns) 0.0074
Animal (2014), 8:4, pp 542–554 © The Animal Consortium 2014 doi:10.1017/S1751731113002395
Meta-analysis of selenium accumulation and expression of antioxidant enzymes in chicken tissues E. Zoidis1†, N. Demiris2, A. Kominakis3 and A. C. Pappas1 1
Department of Nutritional Physiology and Feeding, Faculty of Animal Science and Aquaculture, Agricultural University of Athens, 75 Iera Odos, 11855 Athens, Greece; 2Department of Statistics, Athens University of Economics and Business, 76 Patission Str., 10434 Athens, Greece; 3Department of Animal Breeding and Husbandry, Faculty of Animal Science and Aquaculture, Agricultural University of Athens, 75 Iera Odos, 11855 Athens, Greece
(Received 6 September 2013; Accepted 9 December 2013; First published online 6 January 2014)
A meta-analysis integrating results of 40 selenium (Se) supplementation experiments that originated from 35 different controlled randomized trials was carried out in an attempt to identify significant factors that affect tissue Se accumulation in chicken. Examined factors included: Se source (12 different sources examined), type of chicken (laying hens or broilers), age of birds at the beginning of supplementation, duration of supplementation, year during which the study was conducted, sex of birds, number of chickens per treatment, method of analysis, tissue type, concentration of Se determined and Se added to feed. A correlation analysis was also carried out between tissue Se concentration and glutathione peroxidase activity. Data analysis showed that the factors significantly affecting tissue Se concentration include type of chicken ( P = 0.006), type of tissue ( P < 0.001) and the analytical method used ( P = 0.014). Although Se source was not found to affect tissue Se concentration (overall P > 0.05), certain inorganic (sodium selenite), calcium selenite, sodium selenate and organic sources (B-Traxim Se), Se-yeast, Se-malt, Se-enriched cabbage and Se-enriched garlic as well as background Se level from feed ingredients were found to significantly affect tissue Se concentration. The Se accumulation rate (estimated as linear regression coefficient of Se concentrations to Se added to feed) discriminated between the various tissues with highest values estimated in the leg muscle and lowest in blood plasma. Correlation analysis has also shown that tissue Se concentration (pooled data) was correlated to Se added to feed (r = 0.529, P < 0.01, log values) and to glutathione peroxidase activity (r = 0.332, P = 0.0478), with the latter not being correlated with Se added to feed. Although significant factors affecting Se concentration were reported in the present study, they do not necessarily indicate the in vivo function of the antioxidant system or the level of accumulated Se as other factors, not examined in the present study, may interact at the level of trace element absorption, distribution and retention. Keywords: antioxidant, broiler, chicken, hen, selenium
Implications
Introduction
A meta-analysis of selenium (Se) supplementation trials was performed to synthesize reported findings to arrive at a model for Se accumulation in various chicken tissues. Statistical analysis showed that the factors associated with tissue Se concentration are the type of chicken, the source of Se, the type of tissue and the analytical method used. Tissue Se concentration was correlated with Se added to feed and to glutathione peroxidase activity. The results of the present study can be useful to scientists as well as application areas, as meta-analysis findings are applicable to the totality of exposure situations.
Selenium (Se) is an essential trace element of fundamental importance for optimal animal and human health primarily because of its antioxidant activity. It has chemopreventive, anti-inflammatory, antiviral properties and is related in enhancing immunity (Rayman, 2012; Steinbrenner et al., 2013). The health-related properties of Se include but are not limited to protection against cancer, proper function of thyroid gland, and protection against cardiovascular and muscle disorders (Mao and Teng, 2013; Rocourt and Cheng, 2013). Se becomes cotranslationally incorporated into the polypeptide chain as part of the amino-acid selenocysteine (SeCys). Proteins that contain SeCys as an integral part of their polypeptide chain are defined as selenoproteins (Sel)
†
E-mail: [email protected]
542
Selenium accumulation in chicken. A meta-analysis and are present in all lineages of life (Schomburg, 2012). The major families of Sel include that of glutathione peroxidases, thioredoxin reductases (TRxR) and iodothyronine deiodinases (Pappas et al., 2008; Zoidis et al., 2010). In feed compounds of plant origin, Se occurs as part of an organic compound predominantly, selenomethionine (SeMet). Plant absorption of Se principally depends on the concentration and physicochemical forms existing in the soil. In chicken, to maintain high productive and reproductive performance, diets are usually supplemented with Se. This supplementation is an effective way to prevent Se deficiency and its associated problems, especially in combination with low vitamin E supply such as nutritional encephalomalacia, exudative diathesis and nutritional pancreatic atrophy (Pappas and Zoidis, 2012). Se is added either as an inorganic salt (sodium selenite, calcium selenite or sodium selenate) or as an organo-Se compound more often in the form of Se-yeast. SeMet is the predominant form of Se in most Se-enriched yeast products (Whanger, 2002). Other forms of organo-Se compounds include Se malt (Liu et al., 2009) and B-Traxim Se (Leeson et al., 2008). Absorbed Se can be incorporated into tissue proteins in place of methionine or can be further metabolized in the liver and used for the synthesis of specific Sel. The populations of many countries have a dietary Se intake below that of 55 μg/day, which is recommended by health regulatory bodies such as the Institute of Medicine in USA and the European Food Safety Authority (Institute of Medicine, Food and Nutrition Board, 2000; Combs, 2001; Rayman, 2005; European Food Safety Authority (EFSA), 2009; Fairweather-Tait et al., 2011). European countries such as Greece, (Pappa et al., 2006), Poland (Wasowicz et al., 2003), United Kingdom (Barclay et al., 1995), Spain (Díaz-Alarcón et al., 1996) and Croatia (Matec et al., 2000) have an average daily Se intake below 40 μg, and this seems to be the case for other parts of the world. For instance, it has been estimated that the average intake of Se for adult men and women in Argentina is 32 and 24 μg/day, respectively (Sigrist et al., 2012). To help meet the recommended dietary allowance (RDA), consumers should avail of functional foods use. Technology of production of Se-enriched eggs, meat and milk has been developed and successfully introduced in various countries worldwide. Indeed, Se-enriched eggs are produced in more than 25 countries worldwide (Surai, 2006). Se is added to laying hen diets (Pappas et al., 2005a) and/or broiler diets (Pappas et al., 2005b) and successfully deposited to eggs or broiler tissues. Many controlled randomized feeding trials have investigated the factors influencing accumulation of Se in eggs and various chicken tissues, with considerable variation in results. When controversial and/or variable results across individual studies are obtained, a meta-analysis can be carried out in an attempt to draw concrete conclusions by combining appropriately weighted studies in a coherent manner. The present study presents a meta-analysis of numerous reported studies aiming at: (a) undentifying significant factors that affect tissue Se accumulation in chickens after Se supplementation in feed and (b) estimating correlation(s)
between Se accumulation and the expression of antioxidant enzymes. Material and methods
Data sourcing and inclusion criteria Potential studies for use in the meta-analysis were found from a search of journals, conference proceedings, and book articles in abstract and other electronic databases (Academic Onefile, AGRICOLA, BIDS, Biochemistry and Biophysics Citation Index, BioInfoBank Library, Biological Abstracts, Biosis Previews, Cab Abstracts, Elsevier biobase-CABS, EMBASE, Current Contents/ Life Sciences, EMBiology, Google Scholar, IBIDS (International Bibliographic Information on Dietary Supplements), IngentaConnect, MEDLINE, NLM Gateway, OvidSP, PubMed, Science Direct (Journal), Scopus, Wilson Web), and in the libraries of the Universities of Cambridge (UK) and Athens (Greece). Indices used during the search were combinations and appropriate truncations and forms of the terms ‘selenium’, ‘Se’, ‘chicken’, ‘broiler’, ‘hen’, ‘egg’, ‘diet’, ‘dietary’, ‘feed’, ‘nutrition’, ‘poultry’ and any plurals thereof. Published information in English up to and including the publication year 2011 (3rd quartile) was considered. Experiments were sought on chickens fed fixed Se concentration on a daily basis throughout the experimental period examined. Allowed experimental designs involved controlled randomized feeding trials, with both serial slaughter and experiments, with only one time of slaughter for several groups of chickens receiving different doses and chemical forms of Se. From an initial database of 3497 articles on various aspects of Se and chicken, 35 feeding trials involving 837 chickens in a total of 140 treatment and control groups were identified for inclusion in the meta-regression. Most of the experiments include several treatment groups and one control group (The list of references used for the meta-analysis is given in Supplementary Material S1). Range of interest, data extraction and the data set The range of interest of this study was limited to exclude excessively low or high exposures to Se, because of the limited relevance in the field. It covers and exceeds (by a factor of 30) the maximum authorized total Se contents in feed in EU for farm animals (background Se plus supplemented one), which is 0.5 p.p.m. of complete feeding stuffs with a moisture content of 12% (European Union Commission (EU), 2004). The results apply to the same range of exposure situations: maximum values of 15 p.p.m. dry matter (DM) for the feed Se concentration and 7 to 175 days for the duration of supplementation. Whenever conversion from dry weight (DW, also DM) to wet weight (WW) was necessary, factors determined from a literature search and evaluation were used. WW to DW conversion factors for the chicken liver, kidney, yolk, albumen, muscle and liver protein used were 0.30, 0.26, 0.50, 0.20, 0.27 and 0.17, respectively. These are in agreement with factors reported by other authors as well (McCance, 1991; Solomon, 1991; Prankel et al., 2004). Data on amount 543
Zoidis, Demiris, Kominakis and Pappas of Se in whole egg usually presented as μg per egg could not be appropriately converted to concentration values (p.p.m.) as actual egg weight was not reported. Thus, only data of Se concentration of egg components were considered for analysis. Several data were recorded and used in the study. The components of the data set were as follows. The source of Se present in the diet grouped into four categories, namely, no supplementation, inorganic, organic and nano-Se. Control feeds were placed in the no supplementation category. Inorganic sources included sodium selenite, calcium selenite and sodium selenate, whereas organic sources included B-Traxim Se, SeMet, Se-yeast, Se-malt, Chlorella Algae, cabbage and garlic. In total, there were 12 Se source levels. Furthermore, there were two types of chicken (laying hens including broiler breeders or meat type birds i.e. broilers). Other components were the age of birds at the beginning of supplementation (young (⩽49 days), old (>49 days)); the duration of supplementation (short (⩽21 days), medium (>22, ⩽42 days), long (>42 days)); the year during which the study was conducted (1970 to 1979, 1980 to 1989, 1990 to 1999, 2000 onwards); the sex of the birds (male, female, ‘as hatched’), the number of chickens per experimental treatment (n), the method of Se determination (atomic absorption spectroscopy (AAS) – and its variations including hydride generation atomic absorption-, fluro-spectroscopy and inductively coupled plasma mass spectrometry (ICP-MS)). Cases of outsourcing of Se determination, that is, lack of analytical technique description, were recorded and grouped in an additional category named ‘Other’. Additional key parts of the data set included the Se added in the feed that was categorized into four levels, taking into account that the maximum concentration of Se added to chicken diets in US is 0.3 p.p.m. (US Food and Drug Administration (FDA), 2012) (no, normal (⩽0.3 p.p.m.), medium (>0.3, ⩽1 p.p.m.) and high (>1, ⩽15 p.p.m.); the Se concentrations in the organs and tissues (plasma, whole blood, liver, kidney, breast muscle tissue, leg muscle tissue, yolk, albumen); the type of tissue; and finally, the antioxidant enzyme glutathione peroxidase (GPx) activity. Some components (GPx activity in the whole blood, SOD activity in breast muscle and CAT activity in breast muscle and liver) were omitted from the data set owing to the low number of observations (i.e. 49 days) Duration Short (⩽21 days) Medium (>22, ⩽42 days) Long (>42 days) Year 1970 to 1979 1980 to 1989 1990 to 1999 2000 onwards Sex Male Female As hatched Method AAS Fluorometric assay ICP-MS Other Se source No supplementation Sodium selenite Calcium selenite Sodium selenate B-Traxim Se Selenomethionine Se yeast Se malt Chlorella Algae Cabbage (Se enriched) Garlic (Se enriched) Nano-Se Se added No Normal (⩽0.3 p.p.m.) Medium (>0.3, ⩽1 p.p.m.) High (>1, ⩽15 p.p.m.)
Blood
Mean
n
s.d.
Minimum
Maximum
Mean
n
s.d.
Minimum
Maximum
0.175
27
0.069
0.009
0.310
0.256
32
0.134
0.052
0.866
0.179 0.166
18 9
0.084 0.015
0.009 0.148
0.310 0.190
0.264 0.249
16 16
0.180 0.069
0.052 0.148
0.866 0.360
0.122 0.205
10 17
0.054 0.057
0.009 0.148
0.210 0.310
0.265 0.244
19 13
0.166 0.069
0.052 0.148
0.866 0.360
0.186 0.166 0.142
15 9 3
0.090 0.015 0.016
0.009 0.148 0.130
0.310 0.190 0.160
0.269 0.255 na
3 29 na
0.078 0.140 na
0.184 0.148 na
0.337 0.190 na
na 0.186 na 0.160
na 15 na 12
na 0.090 na 0.018
na 0.009 na 0.130
na 0.310 na 0.190
na na 0.257 0.256
na na 10 22
na na 0.068 0.157
na na 0.118 0.052
na na 0.337 0.866
0.186 0.166 0.142
15 9 3
0.090 0.015 0.016
0.009 0.148 0.130
0.310 0.190 0.160
0.190 0.249 0.298
5 16 11
0.091 0.069 0.203
0.052 0.148 0.088
0.264 0.360 0.866
na 0.175 na na
na 27 na na
na 0.069 na na
na 0.009 na na
na 0.310 na na
0.236 0.240 0.379 na
7 21 4 na
0.063 0.079 0.338 na
0.148 0.052 0.088 na
0.339 0.360 0.866 na
0.197 0.178 0.250 0.280 0.159 na 0.169 na na na na na
4 12 3 1 3 na 4 na na na na na
0.065 0.067 0.056 – 0.012 na 0.019 na na na na na
0.009 0.084 0.190 0.280 0.152 na 0.148 na na na na na
0.160 0.310 0.300 0.280 0.173 na 0.190 na na na na na
0.137 0.268 0.281 na 0.193 0.337 0.297 0.360 na na na na
6 10 3 na 1 1 10 1 na na na na
0.065 0.055 0.044 na – – 0.205 – na na na na
0.052 0.177 0.236 na 0.193 0.337 0.142 0.360 na na na na
0.230 0.350 0.324 na 0.193 0.337 0.866 0.360 na na na na
0.097 0.153 na 0.233
4 13 na 10
0.065 0.028 na 0.063
0.009 0.084 na 0.120
0.160 0.190 na 0.310
0.118 0.247 0.300 0.493
5 20 4 3
0.051 0.052 0.066 0.325
0.052 0.142 0.223 0.274
0.184 0.337 0.360 0.866
AAS = atomic absorption spectroscopy including hydride generation atomic fluorescence spectroscopy; ICP-MS = inductively coupled plasma mass spectroscopy; Other = outsourcing; No supplementation = naturally occurring Se; na = not applicable.
0.30 and 0.49 p.p.m., respectively (Table 1). Studies using Chlorella Algae, cabbage, garlic and nano-Se as a source of Se did not report any Se concentration in plasma and blood. Regarding the method of analysis used to determine Se concentration, no studies report atomic absorption or ICP-MS as the method used to acquire data on plasma Se concentration. The overall Se concentration in the liver and
kidney was 1.50 p.p.m. ranging from 0.09 to 10.56 p.p.m. and 1.76 p.p.m. (range: 0.24 to 7.62 p.p.m.), respectively (Table 2). The mean liver Se concentration was 0.44, 0.70, 0.74 and 4.16 for no, normal, medium and highly Se added level, respectively. Se concentration in the breast muscle tissue (Table 3) ranged from 0.05 to 14.10 p.p.m. (overall mean 0.74 p.p.m.), whereas that of the leg muscle from 545
Zoidis, Demiris, Kominakis and Pappas Table 2 Descriptive statistics of Se concentration (p.p.m.) in the liver and kidney of chicken Liver
Overall Subgrouping Chicken type Broilers Layers Age Young (⩽49 days) Old (>49 days) Duration Short (⩽21 days) Medium (>22, ⩽42 days) Long (>42 days) Year 1970 to 1979 1980 to 1989 1990 to 1999 2000 onwards Sex Male Female As hatched Method AAS Fluorometric assay ICP-MS Other Se source No supplementation Sodium selenite Calcium selenite Sodium selenate B-Traxim Se Selenomethionine Se yeast Se malt Chlorella Algae Cabbage (Se enriched) Garlic (Se enriched) Nano-Se Se added No Normal (⩽0.3 p.p.m.) Medium (>0.3, ⩽1 p.p.m.) High (>1, ⩽15 p.p.m.)
Kidney
Mean
n
s.d.
Minimum
Maximum
Mean
n
s.d.
Minimum
Maximum
1.499
74
2.154
0.090
10.560
1.762
37
1.937
0.240
7.620
1.970 0.678
47 27
2.577 0.419
0.210 0.090
10.560 2.420
2.605 0.873
19 18
2.386 0.537
0.380 0.240
7.620 2.540
1.021 2.031
39 35
1.182 2.801
0.210 0.090
5.290 10.560
1.001 2.226
14 23
0.895 2.253
0.380 0.240
3.610 7.620
2.897 0.858 0.964
23 46 5
3.276 0.865 0.961
0.210 0.240 0.090
10.560 5.290 2.420
3.130 0.730 1.170
15 17 5
2.432 0.144 1.005
0.380 0.390 0.240
7.620 0.990 2.540
0.964 3.257 1.053 0.773
5 20 11 38
0.961 3.373 1.414 0.601
0.090 0.210 0.340 0.240
2.420 10.560 5.290 3.271
1.170 3.751 0.643 0.792
5 12 10 10
1.005 2.328 0.147 0.118
0.240 0.380 0.390 0.551
2.540 7.620 0.801 0.990
2.782 0.671 0.989
26 28 20
3.100 0.413 1.183
0.210 0.090 0.240
10.560 2.420 5.290
3.751 0.873 0.641
12 18 7
2.328 0.537 0.137
0.380 0.240 0.390
7.620 2.540 0.800
0.850 1.687 1.617 na
16 51 7 na
1.191 2.458 1.054 na
0.240 0.090 0.491 na
5.290 10.560 3.271 na
0.752 1.998 na na
7 30 na na
0.102 2.086 na na
0.551 0.240 na na
0.863 7.620 na na
0.459 1.835 3.695 7.710 0.519 0.856 1.048 0.760 2.360 0.693 0.627 0.620
16 29 6 1 3 2 11 1 1 1 1 2
0.251 2.303 4.063 – 0.095 0.027 0.917 – – – – 0.099
0.090 0.330 0.550 7.710 0.450 0.837 0.044 0.760 2.360 0.693 0.627 0.550
1.110 10.270 10.560 7.710 0.628 0.876 3.271 0.760 2.360 0.693 0.627 0.690
0.553 1.846 3.078 5.690 na 0.801 0.753 0.900 na na na na
7 18 6 1 na 1 3 1 na na na na
0.300 1.692 3.001 – na – 0.046 – na na na na
0.240 0.340 0.570 5.690 na 0.801 0.700 0.900 na na na na
1.120 6.570 7.620 5.630 na 0.800 0.783 0.900 na na na na
0.439 0.507 0.738 4.160
14 33 9 18
0.256 0.457 0.100 3.086
0.090 0.330 0.627 0.540
1.110 2.410 0.880 10.560
0.517 0.683 0.884 3.359
6 12 4 15
0.310 0.131 0.086 2.233
0.240 0.340 0.783 0.775
1.120 0.801 0.900 7.620
AAS = atomic absorption spectroscopy including hydride generation atomic fluorescence spectroscopy; ICP-MS = inductively coupled plasma mass spectroscopy; Other = outsourcing; No supplementation = naturally occurring Se; na = not applicable.
0.28 to 12.00 p.p.m. (overall mean 1.63 p.p.m.). Studies using Se malt as a source of Se did not report any Se concentrations either in the breast or in leg muscle tissue (na, Table 3). Mean yolk and albumen Se concentration in layers was 1.50 (0.08 to 4.93 p.p.m.) and 1.62 p.p.m. (0.03 to 8.35 p.p.m.), respectively. No data were available for male birds indicating biological plausibility (Table 4). Furthermore, 546
the highest activity of GPx was recorded in the liver when compared with the other two tissues, that is, plasma and breast muscle (Table 5). The mean GPx activity in the breast muscle, plasma and liver was 0.03, 0.64 and 7.26 U per mg of protein, respectively (Table 5). Table 6 shows the correlations of Se concentration between the various tissues as well as correlations with GPx
Selenium accumulation in chicken. A meta-analysis Table 3 Descriptive statistics of Se concentration (p.p.m.) in the breast and leg muscle of chicken Breast
Overall Subgrouping Chicken type Broilers Layers Age Young (⩽49 days) Old (>49 days) Duration Short (⩽21 days) Medium (>22, ⩽42 days) Long (>42 days) Year 1970 to 1979 1980 to 1989 1990 to 1999 2000 onwards Sex Male Female As hatched Method AAS Fluorometric assay ICP-MS Other Se source No supplementation Sodium selenite Calcium selenite Sodium selenate B-Traxim Se Selenomethionine Se yeast Se malt Chlorella Algae Cabbage (Se enriched) Garlic (Se enriched) Nano-Se Se added No Normal (⩽0.3 p.p.m.) Medium (>0.3, ⩽1 p.p.m.) High (>1, ⩽15 p.p.m.)
Leg
Mean
n
s.d.
Minimum
Maximum
Mean
n
s.d.
Minimum
Maximum
0.740
55
1.955
0.050
14.100
1.635
11
3.457
0.280
12.000
1.103 0.153
34 21
2.429 0.043
0.110 0.050
14.100 0.249
1.635 na
11 na
3.457 na
0.280 na
12.000 na
1.089 0.428
26 29
2.801 0.391
0.110 0.050
14.100 1.190
1.874 0.997
8 3
4.095 0.456
0.280 0.470
12.000 1.270
0.569 0.293 2.340
15 30 10
0.399 0.250 4.350
0.110 0.110 0.050
1.190 1.090 14.100
na 0.602 6.258
na 9 2
na 0.408 8.082
na 0.280 0.570
na 1.270 12.000
0.132 0.670 0.165 0.901
5 12 3 35
0.694 0.382 0.073 2.431
0.050 0.110 0.116 0.110
0.210 1.190 0.249 14.100
na na na 1.635
na na na 11
na na na 3.457
na na na 0.280
na na na 12.000
0.604 0.153 1.735
19 21 15
0.384 0.043 3.599
0.110 0.050 0.110
1.190 0.249 14.100
0.732 na 2.387
5 na 6
0.487 na 4.714
0.280 na 0.307
1.270 na 12.000
0.196 0.609 3.426 0.237
13 33 5 4
0.095 0.830 5.974 0.030
0.110 0.050 0.390 0.209
0.430 4.330 14.100 0.278
0.335 0.438 3.112 na
2 4 5 na
0.078 0.254 4.982 na
0.280 0.307 0.470 na
0.390 0.819 12.000 na
0.378 0.385 0.963 0.920 0.155 0.549 2.081 na 1.090 0.314 0.323 0.365
11 21 3 1 2 2 10 na 1 1 1 2
0.389 0.470 0.212 – 0.001 0.424 4.416 na – – – 0.92
0.050 0.070 0.770 0.920 0.154 0.249 0.149 na 1.090 0.314 0.323 0.300
1.750 2.020 1.190 0.920 0.156 0.849 14.100 na 1.090 0.314 0.323 0.430
0.449 na na na na 0.819 3.480 na 1.270 0.321 0.307 na
3 na na na na 1 4 na 1 1 1 na
0.133 na na na na – 5.696 na – – – na
0.307 na na na na 0.819 0.280 na 1.270 0.321 0.307 na
0.570 na na na na 0.819 12.000 na 1.270 0.321 0.307 na
0.361 0.557 0.380 1.398
10 21 8 16
0.512 0.980 0.230 3.410
0.050 0.070 0.140 0.149
1.750 4.330 0.849 14.100
0.388 1.260 0.448 12.000
2 2 6 1
0.115 0.014 0.210 –
0.307 1.250 0.280 12.000
0.470 1.270 0.819 12.000
AAS = atomic absorption spectroscopy including hydride generation atomic fluorescence spectroscopy; ICP-MS = inductively coupled plasma mass spectroscopy; Other = outsourcing; No supplementation = naturally occurring Se; na = not applicable.
activity. Se concentrations in blood and plasma were positively correlated, implying that they could be used interchangeably. Se concentration in plasma was positively correlated with that in the liver (r = 0.845) and kidney (r = 0.953). Se concentration in blood was found to be positively correlated with that of the liver (r = 0.929), kidney (r = 0.802) and yolk (r = 0.999). Se in liver Se was also
positively correlated with that of the breast (r = 0.790), leg (r = 0.938) and kidney (r = 0.988). Se in the breast apart from its aforementioned correlation with the liver was additionally correlated with that of four other tissues, namely, the leg (r = 0.999), kidney (r = 0.926), yolk (r = 0.928), albumen (r = 0.899) as well as with GPx activity in the liver (r = 0.776) and plasma (r = 0.859) but not in the breast. 547
Zoidis, Demiris, Kominakis and Pappas Table 4 Descriptive statistics of Se concentration (p.p.m.) in the yolk and albumen of chicken Yolk
Overall Subgrouping Chicken type Broilers Layers Age Young (⩽49 days) Old (>49 days) Duration Short (⩽21 days) Medium (>22, ⩽42 days) Long (>42 days) Year 1970 to 1979 1980 to 1989 1990 to 1999 2000 onwards Sex Male Female As hatched Method AAS Fluorometric assay ICP-MS Other Se source No supplementation Sodium selenite Calcium selenite Sodium selenate B-Traxim Se Selenomethionine Se yeast Se malt Chlorella Algae Cabbage (Se enriched) Garlic (Se enriched) Nano-Se Se added No Normal (⩽0.3 p.p.m.) Medium (>0.3, ⩽1 p.p.m.) High (>1, ⩽15 p.p.m.)
Albumen
Mean
n
s.d.
Minimum
Maximum
Mean
n
s.d.
Minimum
Maximum
1.505
26
1.470
0.085
4.930
1.621
22
2.589
0.030
8.350
na 1.505
na 26
na 1.470
na 0.085
na 4.930
na 1.621
na 22
na 2.589
na 0.030
na 8.350
na 1.505
na 26
na 1.470
na 0.085
na 4.930
na 1.621
na 22
na 2.589
na 0.030
na 8.350
2.655 3.833 0.688
6 3 17
1.305 1.005 0.703
1.540 2.680 0.085
4.930 4.520 2.750
1.812 7.360 0.290
6 3 13
1.503 1.406 0.216
0.830 5.750 0.030
4.620 8.350 0.780
1.188 na 2.655 1.150
5 na 6 15
1.087 na 1.305 1.474
0.170 na 1.540 0.085
2.750 na 4.930 4.520
0.296 na 1.812 2.120
5 na 6 11
0.306 na 1.503 3.426
0.050 na 0.830 0.030
0.780 na 4.620 8.350
na 1.505 na
na 26 na
na 1.470 na
na 0.085 na
na 4.930 na
na 1.621 na
na 22 na
na 2.589 na
na 0.030 na
na 8.350 na
0.435 2.384 0.542 na
7 14 5 na
0.265 1.498 0.491 na
0.085 0.170 0.165 na
0.854 4.930 1.350 na
0.168 2.460 0.064 na
7 14 1 na
0.137 2.960 – na
0.030 0.050 0.064 na
0.404 8.350 0.064 na
0.668 2.252 na na na na 0.628 4.520 1.350 na na na
8 11 na na na na 5 1 1 na na na
0.942 1.517 na na na na 0.142 – – na na na
0.085 0.310 na na na na 0.505 4.520 1.350 na na na
2.680 4.930 na na na na 0.854 4.520 1.350 na na na
0.974 1.982 na na na na 0.263 7.980 na na na na
7 10 na na na na 4 1 na na na na
2.127 2.616 na na na na 0.097 – na na na na
0.030 0.050 na na na na 0.194 7.980 na na na na
5.750 8.350 na na na na 0.404 7.980 na na na na
0.413 1.045 2.066 2.648
6 8 6 6
0.556 0.937 1.868 1.434
0.085 0.184 0.505 0.790
1.540 2.680 4.520 4.930
0.205 1.370 3.032 1.597
5 5 6 6
0.350 2.468 3.988 1.680
0.030 0.041 0.207 0.200
0.830 5.750 8.350 4.620
AAS = atomic absorption spectroscopy including hydride generation atomic fluorescence spectroscopy; ICP-MS = inductively coupled plasma mass spectroscopy; Other = outsourcing; No supplementation = naturally occurring Se; na = not applicable.
Table 7 shows the results of mixed ANOVA along with least square means of Se concentration per class of factor included in the final model. The two chicken types were clearly discriminated (P < 0.0059) with regard to Se concentrations with layers displaying lower concentrations v. the broilers (−0.445 v. to 0.154, respectively). Fitting the duration of the experiment as a covariate did not improve the 548
model fit, implying no significance of this particular factor (P = 0.2268). In addition, the source of Se appeared not to significantly affect the Se concentration in the various tissues. However, a more thorough examination of least square (LS) class means showed that some Se sources may cause maximum (e.g. B-Traxim, Se yeast) or minimum (Garlic, cabbage) Se concentrations across the tissues.
Table 5 Descriptive statistics of GPx (glutathione peroxidase) concentration (U/mg protein) in the liver, plasma and breast muscle of chicken Liver GPx
Overall
Breast muscle GPx
Mean
n
s.d.
Minimum
Maximum
Mean
n
s.d.
Minimum
Maximum
Mean
n
s.d.
Minimum
Maximum
7.63
27
16.14
0.01
50.00
0.64
28
1.71
0.01
5.74
0.03
10
0.02
0.01
0.04
11.40 0.08
18 9
18.80 0.02
0.01 0.06
50.00 0.13
0.78 0.13
22 6
1.91 0.03
0.01 0.11
5.74 0.17
0.01 0.04
4 6
0.01 0.01
0.01 0.04
0.01 0.04
11.40 0.08
18 9
18.80 0.02
0.01 0.06
50.00 0.13
0.78 0.13
22 6
1.91 0.03
0.01 0.11
5.74 0.17
0.01 0.04
4 6
0.01 0.01
0.01 0.04
0.01 0.04
30.00 6.76 na
1 26 na
– 15.82 na
30.00 0.01 na
30.00 50.00 na
na 0.06 5.49
na 25 3
na 0.06 0.22
na 0.01 5.31
na 0.17 5.74
na 0.03 na
na 10 na
na 0.02 na
na 0.01 na
na 0.04 na
0.06 0.09 0.01 10.27
2 4 1 20
0.01 0.01 – 18.12
0.05 0.07 0.01 0.01
0.06 0.10 0.01 50.00
0.02 0.11 0.01 1.92
14 4 1 9
0.03 0.02 – 2.68
0.01 0.09 0.01 0.11
0.11 0.13 0.01 5.74
0.01 na na 0.03
2 na na 8
0.01 na na 0.02
0.01 na na 0.01
0.01 na na 0.04
0.05 3.08 29.95
10 10 7
0.04 9.46 22.69
0.01 0.06 2.20
0.10 30.00 50.00
0.04 0.13 5.49
19 6 3
0.05 0.03 0.22
0.01 0.11 5.31
0.13 0.17 5.74
0.01 0.04 na
4 6 na
0.01 0.01 na
0.01 0.04 na
0.01 0.04 na
24.38 0.09 na 1.63
8 13 na 6
22.55 0.02 na 1.82
0.01 0.06 na 0.01
50.00 0.13 na 3.84
na 1.36 na 0.02
na 13 na 15
na 2.35 na 0.03
na 0.09 na 0.01
na 5.74 na 0.11
na 0.04 na 0.01
na 6 na 4
na 0.01 na 0.01
na 0.04 na 0.01
na 0.04 na 0.01
8.71 5.44 na na 0.08 0.05 0.77 na 47.50 na na na
6 10 na na 3 1 5 na 2 na na na
13.03 15.70 na na 0.04 – 1.58 na 0.70 na na na
0.01 0.01 na na 0.06 0.05 0.01 na 47.00 na na na
30.00 50.00 na na 0.13 0.05 3.60 na 48.00 na na na
1.38 0.65 na na 0.11 0.02 1.84 na na na na na
4 10 na na 2 9 3 na na na na na
2.69 1.79 na na 0.01 0.02 3.00 na na na na na
0.01 0.01 na na 0.11 0.01 0.11 na na na na na
5.41 5.74 na na 0.11 0.06 5.31 na na na na na
0.01 0.02 na na 0.38 0.01 0.04 na na na na na
1 4 na na 2 1 2 na na na na na
– 0.02 na na 0.03 – 0.01 na na na na na
0.01 0.01 na na 0.04 0.01 0.04 na na na na na
0.01 0.04 na na 0.04 0.01 0.04 na na na na na
4.46 6.77 48.00 0.10
5 20 1 1
8.74 15.76 – –
0.01 0.01 48.00 0.10
20.00 50.00 48.00 0.10
1.38 0.64 0.02 0.06
4 19 1 4
2.69 1.72 – 0.04
0.01 0.01 0.02 0.03
5.41 5.74 0.02 0.13
0.01 0.03 na na
1 9 na na
– 0.02 na na
0.01 0.01 na na
0.01 0.04 na na
549
AAS = atomic absorption spectroscopy including hydride generation atomic fluorescence spectroscopy; ICP-MS = inductively coupled plasma mass spectroscopy; Other = outsourcing; No supplementation = naturally occurring Se; na = not applicable.
Selenium accumulation in chicken. A meta-analysis
Subgrouping Chicken type Broilers Layers Age Young (⩽49 days) Old (>49 days) Duration Short (⩽21 days) Medium (>22, ⩽42 days) Long (>42 days) Year 1970 to 1979 1980 to 1989 1990 to 1999 2000 onwards Sex Male Female As hatched Method AAS Fluorometric assay ICP-MS Other Se source No supplementation Sodium selenite Calcium selenite Sodium selenate B-Traxim Se Selenomethionine Se yeast Se malt Chlorella Algae Cabbage (Se enriched) Garlic (Se enriched) Nano-Se Se added No Normal (⩽0.3 p.p.m.) Medium (>0.3, ⩽1 p.p.m.) High (>1, ⩽15 p.p.m.)
Plasma GPx
Zoidis, Demiris, Kominakis and Pappas Table 6 Pearson correlations between the Se concentration in various tissues and GPx (glutathione peroxidase) activity in chicken Se
GPx
Blood
Liver
Breast
Leg
Kidney
Yolk
Albumen
Liver
Plasma
0.956
0.845** 0.929**
0.091 0.564 0.790**
na na 0.938** 0.999**
0.953** 0.802** 0.988** 0.926** na
na 0.999* 0.392 0.928* na 0.343
na 0.980 −0.051 0.899* na −0.011 0.842**
0.241 0.000 0.043 0.776** na na na na
−0.596 na −0.523 0.859** na na na na
Breast
Se Plasma Blood Liver Breast Leg Kidney Yolk Albumen GPx Liver Plasma
0.660*
−0.186 na −0.463 −0.055 na na na na 0.634 0.906**
na = not applicable. *P ⩽ 0.05. **P ⩽ 0.01.
Overall, Se concentrations clearly discriminated across the various tissues (P < 0.001). In addition, here a thorough inspection of the estimated LS tissue means has shown highest concentrations in the yolk, albumen, kidney and liver, and lowest in plasma, blood and muscles (breast and leg). According to the estimated LS means of Se concentrations, the various tissues could thus be placed in ascending order as follows: plasma (lowest), blood, breast muscle, leg muscle, albumen and yolk (highest) (Table 7). Apart from differences in the Se concentrations in the various tissues, we have further detected different rates of Se accumulation across the various tissues (see values of linear regression coefficients (b) in Table 8). More specifically, highest accumulation rates were estimated in the leg muscle (b = 0.727, P < 0.001), liver (b = 0.570, P < 0.001) and kidney (b = 0.499, P < 0.001), and lowest or nil in blood (b = 0.326, P = 0.0074) and plasma (b = 0.106, P = 0.154). However, when s.e.s were taken into account, only differences in Se accumulation rates between the leg muscle and plasma (P = 0.0023) and between the leg muscle and breast muscle (P = 0.0274) could be confirmed statistically. Se accumulation rates between the leg muscle and blood tended (P = 0.0741) to differ significantly. Furthermore, statistically significant Se accumulation rates were noted between the liver and plasma (P < 0.001), liver and breast muscle (P = 0.001), and liver and blood (P = 0.05). Similarly, Se accumulation rates between albumen and plasma (P < 0.001) and albumen and breast muscle (P = 0.0368) differed significantly. Moreover, Se accumulation rates between the kidney and breast muscle (P < 0.001) and between the kidney and plasma (P < 0.001) could be statistically confirmed. Finally, statistically significant Se accumulation rates were observed between plasma and yolk (P = 0.0103), between plasma and breast muscle (P = 0.0130), and between plasma and egg (P = 0.0399). Finally, the analytical method applied to determine Se was found to be associated with significantly different 550
Se concentrations in the various tissues (P = 0.014) with lowest and highest values estimated for ICP-MS and AAS, respectively (Table 7). Further correlation analysis between Se concentration, Se added to feed and GPx activity showed Se concentration (pooled data) to be correlated (r = 0.529, P < 0.01) with Se added to feed and to GPx activity (r = 0.332, P = 0.0478), the latter not being correlated with Se added to feed (results not presented). Discussion The present study presents an attempt to evaluate the importance of various factors that are involved in Se accumulation in various chicken tissues as well as in the antioxidant enzyme activity. This meta-analysis identified significant factors, which affect Se accumulation, the source of Se, the type of tissue and the analytical method used. Regarding the Se source, the study revealed that certain Se sources such as sodium selenite, B-Traxim and Se yeast may cause maximum Se concentrations across the tissues. Chickens may receive Se via their typical diet and additionally via feed additives. With regard to the latter (feeding additives), the Commission of the European Communities has approved several forms including inorganic salts, sodium selenite or sodium selenate (EC, 2004), or organic salts including yeast strains Saccharomyces cerevisiae CNCM I-3060 (EC, 2006), NCYC R397 (EC, 2007) or CNCM I-3399 (EC, 2009). Yeast is able to bind element ions from the environment and then permanently incorporate them into its cellular structures. At present, S. cerevisiae, Candida utilis and Yarrowia lipolytica yeast species are mainly used in biotechnological investigations on mineral constituent incorporation (Kieliszek and Błażejak, 2013). SeMet is the predominant form of Se in most Seenriched yeast products usually ranging between 60% and 70% of the total Se (Whanger, 2002; Rayman, 2012). Among all Se yeast products available, large differences in quality and
Selenium accumulation in chicken. A meta-analysis Table 7 Level of significance of factors examined as well as least squares means (with standard errors) of classes within factor(s) of tissue Se concentration (log values) in chicken Factors examined Chicken type Overall Broilers Layers Duration Overall Se source Overall No supplementation Sodium selenite Calcium selenite Sodium selenate B-Traxim Se Selenomethionine Se yeast Se malt Chlorella Algae Cabbage (Se enriched) Garlic (Se enriched) Nano-Se Tissue Overall Plasma Blood Liver Kidney Breast muscle Leg muscle Yolk Albumen Method Overall AAS Fluorometric assay ICP-MS Other
LS mean
s.e.
– −0.154a −0.445b
– 0.089 0.112
–
–
Table 8 Linear regression coefficients ( b) of Se determined to Se added to feed across the various tissues of chicken Tissue
b1
s.e.
P-value
0.106 0.326 0.570 0.499 0.295 0.727 0.428 0.543
0.074 0.120 0.054 0.068 0.063 0.191 0.101 0.102
0.1540 (ns) 0.0074
