1244
A. G. KHAN, R. G. JAAP AND A. K. KANOUN
dwarf dam strain should improve the growth rate of their normal-bodied crossbred progeny. REFERENCES
Distribution of Selenium in Egg White and Yolk after Feeding Natural and Synthetic Selenium Compounds J. D . LATSHAW AND M . OSMAN
Department of Poultry Science, Ohio Agricultural Research and Development Center, and Ohio State University, Columbus, Ohio 43210 (Received for publication November 25, 1974)
ABSTRACT Practical diets containing various selenium levels, with and without selenite supplementation, were fed to hens. Eggs were then collected over a 14-day period to determine how quickly changes in dietary selenium affected egg white and yolk selenium. Changes in egg white selenium content were rapid and essentially completed seven days after changing the selenium content of a practical diet. Changes in egg yolk were not yet completed by 14 days. When selenium from practical feedstuffs was fed, the selenium content of dried egg white was about equal to or greater than the selenium content of dried egg yolk. When selenite was fed, the selenium content of dried yolk was higher. Feeding selenomethionine resulted in more selenium in egg white than in egg yolk. Feeding selenocystine resulted in more selenium in egg yolk than egg white, a pattern similar to that from feeding selenite. The data suggest that selenocystine is not incorporated into protein but is metabolized to an inorganic selenium compound. POULTRY SCIENCE 54: 1244-1252, 1975
INTRODUCTION
S
from ingredients generally used for formulating practical diets, the selenium in a given
TUDIES with monogastric animals have shown that the form of selenium in the
diet has a significant effect on the amount of selenium which will be present in tissues of the body. If the dietary selenium comes
tissue is approximately proportional to the amount found in the diet (Ku et al., 1972b; Scott and Thompson, 1971; and Latshaw, 1975). If the dietary selenium is provided by sodium selenite, then the selenium content of tissues is not proportional to dietary sele-
Ohio Agricultural Research and Development Center Journal Article Series No. 113-74.
nium. Less selenium is retained from selenite, with the effect being especially prominent
Downloaded from http://ps.oxfordjournals.org/ at New York University on April 13, 2015
Chambers, J. R., A. D. Smith, I. McMillan and G. W. Friars, 1974. Comparison of normal and dwarf broiler breeder hens. Poultry Sci. 53: 864-870. Dev, D. S., R. G. Jaap and W. R. Harvey, 1969. Results of selection for eight-week body weight in three broiler populations of chickens. Poultry Sci. 48: 1336-1348. Khan, A. G., R. G. Jaap and W. R. Harvey, 1973. The effect of egg weight on eight-week body weight of normal and dwarf progeny from dwarf dams. Poultry Sci. 53: 211-218.
Mohammadian, M., and R. G. Jaap, 1972. Effect of the sex-linked dw dwarfing gene on body growth of chickens. Poultry Sci. 51: 1701-1707. Ricard, F. H., 1971. Growth rate and carcass characters of chicken broilers obtained from normal or dwarf (dw) dams. World's Poultry Sci. J. 27: 278279. Ricard, F. H., and L. P. Cochez, 1971. Effects of the sex-linked dwarf gene, dw, on performance of hens in a meat-type strain of domestic fowl. World's Poultry Sci. J. 27: 292. Ricard, F. H., and L. Conan, 1974. Performances zootechniques de poulets normaux fils de meres normales ou naines. Proc. XV World's Poultry Congress: 24-26. VanMiddlekoop, J. H., 1973. Influence of the dwarfing gene on egg laying pattern. 4th Europ. Poultry Conf., London: 563-567.
1245
SELENIUM IN EGGS
The predominant selenium compound in monogastric diets, therefore, is probably selenomethionine. This amino acid has been shown to be incorporated into protein (Ochoa-Solano and Gitler, 1968) presumably by peptide bonds and by substituting for methionine. If selenium is supplemented in diets, an inorganic form is generally used. Selenite is protein bound but is not incorporated by means of peptide bonds (Cummins and Martin, 1967; and Jenkins, 1968). Previous research has indicated that the egg is very useful in studying the distribution of selenium in tissues when various selenium compounds are fed. When natural selenium sources were fed, the selenium content of egg white was found to be equal to or higher than the yolk selenium. If selenite was fed, the distribution pattern was reversed so that more appeared in the yolk (Latshaw, 1975). The egg provides a method for following the incorporation of selenium into egg proteins over a period of time. Selenium sources can be used as non-radioactive tracers. Since the synthesis of egg white protein occurs in the oviduct (Anfinsen and Steinberg, 1951; Hendler, 1956), one would predict that egg white would begin to reflect a change in
dietary selenium status in one or two days. On the other hand, since egg yolk proteins are synthesized in the liver (Greengard et al., 1965) and the ovum requires approximately ten days for maturation, one would predict a longer period before dietary selenium changes are fully reflected in the yolk. These predictions were essentially confirmed. The resulting egg assay was then used to investigate various dietary selenium compounds. PROCEDURE All hens used in Experiment 1 were fed diet 1 (Table 1) from the onset of egg production until the start of the experiment. Hens were approximately 35 weeks old at the time and the rate of egg production was higher than 80%. For the experiment, various levels TABLE 1.—Composition of the diets Ingredients
Diet 1 % 65.35 23.00 — 2.00 7.45
Diet 2 % 71.55 14.00 5.00 2.00 5.00
Corn Soybean meal (44% protein) Meat scraps Alfalfa meal (17% protein) Limestone Mono- and dicalcium phosphate1 1.45 1.50 Iodized salt 0.30 0.50 Vitamin mix2 0.35 0.35 Trace mineral mix3 0.05 0.05 Methionine 0.05 0.50 'Biofos (not less than 21% P, not less than 15% or more than 18% Ca) manufactured by International Minerals and Chemical Corporation, IMC Plaza, Libertyville, 111. 2 Mix supplied per kilogram diet: retinyl palmitate, 4400 I.U.; cholecalciferol, 1100 I.C.U.; dlalpha tocopheryl acetate, 5.5 I.U.; (in mg.) menadione, 1.1; riboflavin, 4.4; calcium d-pantothenate, 8.8; niacin, 26.4; vitamin B i2 ,0.007; choline chloride, 110; butylated hydroxy toluene, 110. 3 Trace mineral mix supplied the following per kilogram diet: (mg.) manganese (MnS0 4 H 2 0), 50; iron (FeO), 50; copper (CuO), 5; cobalt (CoC0 3 ), 0.5; iodine (KI), 1.5; zinc (ZnS0 4 ), 50; calcium (CaCO,), 16.
Downloaded from http://ps.oxfordjournals.org/ at New York University on April 13, 2015
in tissues in which most of the dry matter is protein such as longissimus muscle (Ku et al, 1972a) and egg white (Latshaw, 1975). Most of the selenium which an animal takes in from a practical type of diet comes from plants. Studies by Olson et al. (1970) showed that approximately half of the radioactively labeled selenium present in wheat was incorporated into selenomethionine. The remaining selenium was scattered among a variety of compounds. Butler and Peterson (1967) also found a large percentage of plant selenium to be present as selenomethionine. However, in plants which accumulate selenium, much of the selenium is present in amino acids which are not protein bound, such as selenocystathione and methylselenocysteine (Virupaksha and Shrift, 1965).
1246
J. D. LATSHAW AND M. OSMAN
On day 0 of the experiment, the diets were placed in the feeders at approximately 4 P.M.
1.2-
P 1 *
-e -• n * *
0.08 008 0.18 0.18 0.28
mg/kg mg/kg mg/kg mg/kg mg/kg
Notural Natural Notural Natural Natural
Each diet was fed to 10 hens for 14 days. All eggs laid by the hens on days 2, 4, 7 and 14 of the experiment were collected and labeled. After the last collection, five eggs were randomly selected from each dietary treatment on each day. The yolk and white were separated, then frozen and lyophilized as soon as possible. Dry samples were stored in a desiccator until analyzed for selenium (Latshaw, 1975). In Experiment 2, synthetic selenium compounds were added to diet 1 (Table 1) to provide 0.1 or 0.2 mg. selenium per kg. of feed. The diets were fed for 14 days, and eggs were collected for selenium analysis on the 14th day. Pooled samples of four yolks
Se Se + 0.10 mg/kg Selenite Se Se Se + 0.10 mg/kg Selenite Se Se
i.o-
0.8-
0-6 -
z
uj
0.4
0.2 -
14 DAY
O N W H I C H EGG WAS
LAID
FIG. 1. Egg white selenium level as affected by type and level of dietary selenium, (Exp.l).
Downloaded from http://ps.oxfordjournals.org/ at New York University on April 13, 2015
of natural and selenite selenium were fed. Diet 2 (Table 1) was composed of local feed ingredients which contained 0.08 mg. of selenium per kg. Another diet of identical formulation was obtained from a region high in selenium and contained 0.39 mg. selenium per kg. of feed. Blending the proper proportions of the two diets gave the desired levels of natural selenium. The following diets were prepared: diet A, 0.08 mg./kg. natural Se; diet B , as diet A plus 0.10 mg./kg. selenite Se; diet C, 0.18 mg./kg. natural Se; diet D, as diet C plus 0.10 mg./kg. selenite Se; diet E, 0.28 mg./kg. natural Se.
1247
SELENIUM IN EGGS
© •
& • -B -*•
0.08 0.08 0.18 0.18
mg/kg N a t u r a l mg/kg N a t u r a l mg/kg N a t u r a l mg/kg Natural
-*
0.28 mg/kg
Natural
DAY
Se Se + Se Se +
0.10
analysis. The total remaining fecal collection was then spread out on trays and dried at 100° C. in a forced air oven in order to determine dry matter content. The procedure used in Experiment 3 was identical to that used in Experiment 2. Practical diets (diet 2, Table 1) of identical feedstuff formulation but of different selenium content were blended to provide 0.1, 0.2, or 0.3 mg. of selenium per kg. of diet. In the remaining treatments, sources of natural selenium were included in the diet to provide 0.1 mg. selenium per kg. Sources and their selenium contents were as follows: Astragalus racemous leaves and stems, 150 mg./kg.; seleniferous wheat, 28 mg./kg.; menhaden fish meal, 1.93
mg/kg
Selenite
Se
0.10 mg/kg
Selenite
Se
Se
ON
WHICH
EGG
WAS
LAID
FIG. 2. Egg yolk selenium level as affected by type and level of dietary selenium, (Exp. 1).
Downloaded from http://ps.oxfordjournals.org/ at New York University on April 13, 2015
or whites were made before lyophilization, with two pooled samples per treatment. Several treatments had less than 8 eggs for that day, so 1 egg from the 15th day was included in each sample. Each treatment, therefore, contained 6 eggs from day 14 and 2 eggs from day 15. From days 8 through 14, feed consumption was recorded as well as fecal production. Droppings were collected by placing a wooden frame which was covered with plastic under each treatment group of ten hens. On day 14, the frame was removed and the week's total feces production was weighed. Approximately 100 grams of the pooled wet feces were lyophilized and saved for selenium
1248
J. D. LATSHAW AND M. OSMAN
mg./kg. The diet containing fish meal was adjusted so that the protein content was the same as for diet 1. Results from Experiment 1 were statistically analyzed according to procedures outlined in Steel and Torrie (1960). Treatment means were compared by the use of Duncan's multiple range test (Duncan, 1955). RESULTS Figure 1 shows the effect of different types and amounts of dietary selenium on the selenium content of egg white. When natural O
O W h i t e from 0.08
•
•
mg/kg N a t u r a l
B
B W h i t e from 0.18
if
A Yolk from 0.18 mg/kg N a t u r a l Se
Se +
Yolk from 0 0 8 mg/kg Natural Se + mg/kg N a t u r a l
0.10 mg/kg Selenite Se
0.10 mg/kg Selenite
Se
Se
1.0-
0.8Q
-
0.6H
S 3
0.4-
0.2-
T
1
4
7 DAY O N W H I C H
EGG
WAS
LAID
FIG. 3. Effect of dietary selenite and natural selenium on egg white and yolk selenium content, (Exp. 1).
Downloaded from http://ps.oxfordjournals.org/ at New York University on April 13, 2015
selenium sources were fed, the change in selenium content of the white was rapid and was essentially complete by day 7. When selenium was fed as selenite, egg white showed a slow gradual increase in selenium content. At the two comparative levels shown, a unit of natural dietary selenium resulted in more egg white selenium than a unit of dietary selenite selenium. Values of egg yolk selenium are found in Figure 2. When hens were fed natural dietary selenium, the yolk selenium content increased gradually and almost linearly over the 14 day period. When hens were fed selenite seleni-
SELENIUM IN EGGS
TABLE 2.—Analysis of variance of egg selenium values, (Exp. 1) Component A (Dietary selenium) B (Egg white or yolk) C (Day 2, 4, 7 or 14) A x B A x C B x C A x B x C Residual
DF
Mean square
F1
4
1.3393
588.8
1 3 4 12 3 12 160
1.1310 0.7277 0.5358 0.0740 0.0244 0.0199 0.0023
497.3 319.9 235.5 32.5 10.7 8.7
'All F values greater than 3.84 are significant in this table (P < 0.05).
TABLE 3.—Distribution of selenium in egg white and yolk after feeding synthetic selenium compounds, (Exp. 2) Dietary selenium H.g. Se/g. dry Total matter in diet _ (mg./kg.) White Yolk" Source' 0.26a2 0.25a2 Diet 1 0.07 0.48b 0.34b + selenocystine 0.17 + selenomethio0.39b 0.65d nine 0.17 0.32b 0.44b + sodium selenite 0.17 0.40c 0.62c + sodium selenite 0.27 'See Table 1 for composition of the diet. 2 Means within a column not having the same letter are significantly different (P < 0.05).
Feeding selenomethionine resulted in more selenium in the egg white than in the yolk. The retention of selenium from the different synthetic selenium compounds is shown in Table 4. The lowest percentage of retention was recorded for hens fed diet 1 with no selenium supplement. Although the data were not statistically analyzed, the results suggest that the greatest retention occurred when selenium was fed in the form of selenomethionine. Higher egg selenium values from selenomethionine support the retention figures. Selenium retention was fairly similar when hens were fed selenocystine or the two levels of sodium selenite. Experiment 3 was designed to investigate the selenium content and distribution in eggs when hens were fed various natural sources of selenium. When diet 2 was fed, each increment in dietary selenium caused an increasing proportion of egg white selenium (Table 5). When 0.10 mg./kg. was fed, the egg white selenium was 0.18 jxg. / g . , or about twice the feed level. Egg white increased to 0.79 (xg./g. when 0.20 mg./kg. was fed (about 4 times feed level) and to 1.53 |xg./g. when 0.30 mg./kg. was fed (about 5 times feed level). At the lower selenium level, eggs from diet 2 had almost the same selenium content in white and yolk. Increases in dietary selenium resulted in increases in yolk sele-
Downloaded from http://ps.oxfordjournals.org/ at New York University on April 13, 2015
um, the yolk selenium content jumped rapidly between days four and seven and then continued a gradual increase. In the yolk, the selenium content from selenite fed hens was higher than from hens fed natural selenium. A comparison of egg white and yolk selenium values is shown in Figure 3, as summarized from Figures 1 and 2. When 0.18 mg./kg. natural selenium was fed, egg white selenium increased rapidly and contained more selenium per unit of weight than the yolk even at the end of 14 days. On the other hand, a diet containing 0.08 mg./kg. natural selenium plus 0.10 mg./kg. selenite selenium resulted in yolk selenium deposition which was larger than that present in the white. Table 2 shows the analysis of variance for Experiment 1. All the treatment factors and interactions were statistically significant (P < 0.05). In Experiment 2, diets containing various synthetic selenium compounds were fed for 14 days before analyzing the eggs for selenium. Feeding diet 1 resulted in an egg with almost equal selenium contents in the white and yolk (Table 3). Adding 0.10 mg./kg. selenocystine selenium to the diet produced an egg which contained more selenium in the yolk than in the white. The pattern of distribution and amounts of selenium were very similar to those of eggs from hens fed selenite.
1249
1250
J. D. LATSHAW AND M. OSMAN
TABLE 4.—Retention of dietary selenium from synthetic selenium compounds, (Exp. 2) Dietary selenium Fecal Retained Fecal Dry Se Total Feed Se loss Se Se feces in consump- intake diet tion (g./ (Mf-/ (M£-/g(M-g-/ (I*/
A. G. KHAN, R. G. JAAP AND A. K. KANOUN
dwarf dam strain should improve the growth rate of their normal-bodied crossbred progeny. REFERENCES
Distribution of Selenium in Egg White and Yolk after Feeding Natural and Synthetic Selenium Compounds J. D . LATSHAW AND M . OSMAN
Department of Poultry Science, Ohio Agricultural Research and Development Center, and Ohio State University, Columbus, Ohio 43210 (Received for publication November 25, 1974)
ABSTRACT Practical diets containing various selenium levels, with and without selenite supplementation, were fed to hens. Eggs were then collected over a 14-day period to determine how quickly changes in dietary selenium affected egg white and yolk selenium. Changes in egg white selenium content were rapid and essentially completed seven days after changing the selenium content of a practical diet. Changes in egg yolk were not yet completed by 14 days. When selenium from practical feedstuffs was fed, the selenium content of dried egg white was about equal to or greater than the selenium content of dried egg yolk. When selenite was fed, the selenium content of dried yolk was higher. Feeding selenomethionine resulted in more selenium in egg white than in egg yolk. Feeding selenocystine resulted in more selenium in egg yolk than egg white, a pattern similar to that from feeding selenite. The data suggest that selenocystine is not incorporated into protein but is metabolized to an inorganic selenium compound. POULTRY SCIENCE 54: 1244-1252, 1975
INTRODUCTION
S
from ingredients generally used for formulating practical diets, the selenium in a given
TUDIES with monogastric animals have shown that the form of selenium in the
diet has a significant effect on the amount of selenium which will be present in tissues of the body. If the dietary selenium comes
tissue is approximately proportional to the amount found in the diet (Ku et al., 1972b; Scott and Thompson, 1971; and Latshaw, 1975). If the dietary selenium is provided by sodium selenite, then the selenium content of tissues is not proportional to dietary sele-
Ohio Agricultural Research and Development Center Journal Article Series No. 113-74.
nium. Less selenium is retained from selenite, with the effect being especially prominent
Downloaded from http://ps.oxfordjournals.org/ at New York University on April 13, 2015
Chambers, J. R., A. D. Smith, I. McMillan and G. W. Friars, 1974. Comparison of normal and dwarf broiler breeder hens. Poultry Sci. 53: 864-870. Dev, D. S., R. G. Jaap and W. R. Harvey, 1969. Results of selection for eight-week body weight in three broiler populations of chickens. Poultry Sci. 48: 1336-1348. Khan, A. G., R. G. Jaap and W. R. Harvey, 1973. The effect of egg weight on eight-week body weight of normal and dwarf progeny from dwarf dams. Poultry Sci. 53: 211-218.
Mohammadian, M., and R. G. Jaap, 1972. Effect of the sex-linked dw dwarfing gene on body growth of chickens. Poultry Sci. 51: 1701-1707. Ricard, F. H., 1971. Growth rate and carcass characters of chicken broilers obtained from normal or dwarf (dw) dams. World's Poultry Sci. J. 27: 278279. Ricard, F. H., and L. P. Cochez, 1971. Effects of the sex-linked dwarf gene, dw, on performance of hens in a meat-type strain of domestic fowl. World's Poultry Sci. J. 27: 292. Ricard, F. H., and L. Conan, 1974. Performances zootechniques de poulets normaux fils de meres normales ou naines. Proc. XV World's Poultry Congress: 24-26. VanMiddlekoop, J. H., 1973. Influence of the dwarfing gene on egg laying pattern. 4th Europ. Poultry Conf., London: 563-567.
1245
SELENIUM IN EGGS
The predominant selenium compound in monogastric diets, therefore, is probably selenomethionine. This amino acid has been shown to be incorporated into protein (Ochoa-Solano and Gitler, 1968) presumably by peptide bonds and by substituting for methionine. If selenium is supplemented in diets, an inorganic form is generally used. Selenite is protein bound but is not incorporated by means of peptide bonds (Cummins and Martin, 1967; and Jenkins, 1968). Previous research has indicated that the egg is very useful in studying the distribution of selenium in tissues when various selenium compounds are fed. When natural selenium sources were fed, the selenium content of egg white was found to be equal to or higher than the yolk selenium. If selenite was fed, the distribution pattern was reversed so that more appeared in the yolk (Latshaw, 1975). The egg provides a method for following the incorporation of selenium into egg proteins over a period of time. Selenium sources can be used as non-radioactive tracers. Since the synthesis of egg white protein occurs in the oviduct (Anfinsen and Steinberg, 1951; Hendler, 1956), one would predict that egg white would begin to reflect a change in
dietary selenium status in one or two days. On the other hand, since egg yolk proteins are synthesized in the liver (Greengard et al., 1965) and the ovum requires approximately ten days for maturation, one would predict a longer period before dietary selenium changes are fully reflected in the yolk. These predictions were essentially confirmed. The resulting egg assay was then used to investigate various dietary selenium compounds. PROCEDURE All hens used in Experiment 1 were fed diet 1 (Table 1) from the onset of egg production until the start of the experiment. Hens were approximately 35 weeks old at the time and the rate of egg production was higher than 80%. For the experiment, various levels TABLE 1.—Composition of the diets Ingredients
Diet 1 % 65.35 23.00 — 2.00 7.45
Diet 2 % 71.55 14.00 5.00 2.00 5.00
Corn Soybean meal (44% protein) Meat scraps Alfalfa meal (17% protein) Limestone Mono- and dicalcium phosphate1 1.45 1.50 Iodized salt 0.30 0.50 Vitamin mix2 0.35 0.35 Trace mineral mix3 0.05 0.05 Methionine 0.05 0.50 'Biofos (not less than 21% P, not less than 15% or more than 18% Ca) manufactured by International Minerals and Chemical Corporation, IMC Plaza, Libertyville, 111. 2 Mix supplied per kilogram diet: retinyl palmitate, 4400 I.U.; cholecalciferol, 1100 I.C.U.; dlalpha tocopheryl acetate, 5.5 I.U.; (in mg.) menadione, 1.1; riboflavin, 4.4; calcium d-pantothenate, 8.8; niacin, 26.4; vitamin B i2 ,0.007; choline chloride, 110; butylated hydroxy toluene, 110. 3 Trace mineral mix supplied the following per kilogram diet: (mg.) manganese (MnS0 4 H 2 0), 50; iron (FeO), 50; copper (CuO), 5; cobalt (CoC0 3 ), 0.5; iodine (KI), 1.5; zinc (ZnS0 4 ), 50; calcium (CaCO,), 16.
Downloaded from http://ps.oxfordjournals.org/ at New York University on April 13, 2015
in tissues in which most of the dry matter is protein such as longissimus muscle (Ku et al, 1972a) and egg white (Latshaw, 1975). Most of the selenium which an animal takes in from a practical type of diet comes from plants. Studies by Olson et al. (1970) showed that approximately half of the radioactively labeled selenium present in wheat was incorporated into selenomethionine. The remaining selenium was scattered among a variety of compounds. Butler and Peterson (1967) also found a large percentage of plant selenium to be present as selenomethionine. However, in plants which accumulate selenium, much of the selenium is present in amino acids which are not protein bound, such as selenocystathione and methylselenocysteine (Virupaksha and Shrift, 1965).
1246
J. D. LATSHAW AND M. OSMAN
On day 0 of the experiment, the diets were placed in the feeders at approximately 4 P.M.
1.2-
P 1 *
-e -• n * *
0.08 008 0.18 0.18 0.28
mg/kg mg/kg mg/kg mg/kg mg/kg
Notural Natural Notural Natural Natural
Each diet was fed to 10 hens for 14 days. All eggs laid by the hens on days 2, 4, 7 and 14 of the experiment were collected and labeled. After the last collection, five eggs were randomly selected from each dietary treatment on each day. The yolk and white were separated, then frozen and lyophilized as soon as possible. Dry samples were stored in a desiccator until analyzed for selenium (Latshaw, 1975). In Experiment 2, synthetic selenium compounds were added to diet 1 (Table 1) to provide 0.1 or 0.2 mg. selenium per kg. of feed. The diets were fed for 14 days, and eggs were collected for selenium analysis on the 14th day. Pooled samples of four yolks
Se Se + 0.10 mg/kg Selenite Se Se Se + 0.10 mg/kg Selenite Se Se
i.o-
0.8-
0-6 -
z
uj
0.4
0.2 -
14 DAY
O N W H I C H EGG WAS
LAID
FIG. 1. Egg white selenium level as affected by type and level of dietary selenium, (Exp.l).
Downloaded from http://ps.oxfordjournals.org/ at New York University on April 13, 2015
of natural and selenite selenium were fed. Diet 2 (Table 1) was composed of local feed ingredients which contained 0.08 mg. of selenium per kg. Another diet of identical formulation was obtained from a region high in selenium and contained 0.39 mg. selenium per kg. of feed. Blending the proper proportions of the two diets gave the desired levels of natural selenium. The following diets were prepared: diet A, 0.08 mg./kg. natural Se; diet B , as diet A plus 0.10 mg./kg. selenite Se; diet C, 0.18 mg./kg. natural Se; diet D, as diet C plus 0.10 mg./kg. selenite Se; diet E, 0.28 mg./kg. natural Se.
1247
SELENIUM IN EGGS
© •
& • -B -*•
0.08 0.08 0.18 0.18
mg/kg N a t u r a l mg/kg N a t u r a l mg/kg N a t u r a l mg/kg Natural
-*
0.28 mg/kg
Natural
DAY
Se Se + Se Se +
0.10
analysis. The total remaining fecal collection was then spread out on trays and dried at 100° C. in a forced air oven in order to determine dry matter content. The procedure used in Experiment 3 was identical to that used in Experiment 2. Practical diets (diet 2, Table 1) of identical feedstuff formulation but of different selenium content were blended to provide 0.1, 0.2, or 0.3 mg. of selenium per kg. of diet. In the remaining treatments, sources of natural selenium were included in the diet to provide 0.1 mg. selenium per kg. Sources and their selenium contents were as follows: Astragalus racemous leaves and stems, 150 mg./kg.; seleniferous wheat, 28 mg./kg.; menhaden fish meal, 1.93
mg/kg
Selenite
Se
0.10 mg/kg
Selenite
Se
Se
ON
WHICH
EGG
WAS
LAID
FIG. 2. Egg yolk selenium level as affected by type and level of dietary selenium, (Exp. 1).
Downloaded from http://ps.oxfordjournals.org/ at New York University on April 13, 2015
or whites were made before lyophilization, with two pooled samples per treatment. Several treatments had less than 8 eggs for that day, so 1 egg from the 15th day was included in each sample. Each treatment, therefore, contained 6 eggs from day 14 and 2 eggs from day 15. From days 8 through 14, feed consumption was recorded as well as fecal production. Droppings were collected by placing a wooden frame which was covered with plastic under each treatment group of ten hens. On day 14, the frame was removed and the week's total feces production was weighed. Approximately 100 grams of the pooled wet feces were lyophilized and saved for selenium
1248
J. D. LATSHAW AND M. OSMAN
mg./kg. The diet containing fish meal was adjusted so that the protein content was the same as for diet 1. Results from Experiment 1 were statistically analyzed according to procedures outlined in Steel and Torrie (1960). Treatment means were compared by the use of Duncan's multiple range test (Duncan, 1955). RESULTS Figure 1 shows the effect of different types and amounts of dietary selenium on the selenium content of egg white. When natural O
O W h i t e from 0.08
•
•
mg/kg N a t u r a l
B
B W h i t e from 0.18
if
A Yolk from 0.18 mg/kg N a t u r a l Se
Se +
Yolk from 0 0 8 mg/kg Natural Se + mg/kg N a t u r a l
0.10 mg/kg Selenite Se
0.10 mg/kg Selenite
Se
Se
1.0-
0.8Q
-
0.6H
S 3
0.4-
0.2-
T
1
4
7 DAY O N W H I C H
EGG
WAS
LAID
FIG. 3. Effect of dietary selenite and natural selenium on egg white and yolk selenium content, (Exp. 1).
Downloaded from http://ps.oxfordjournals.org/ at New York University on April 13, 2015
selenium sources were fed, the change in selenium content of the white was rapid and was essentially complete by day 7. When selenium was fed as selenite, egg white showed a slow gradual increase in selenium content. At the two comparative levels shown, a unit of natural dietary selenium resulted in more egg white selenium than a unit of dietary selenite selenium. Values of egg yolk selenium are found in Figure 2. When hens were fed natural dietary selenium, the yolk selenium content increased gradually and almost linearly over the 14 day period. When hens were fed selenite seleni-
SELENIUM IN EGGS
TABLE 2.—Analysis of variance of egg selenium values, (Exp. 1) Component A (Dietary selenium) B (Egg white or yolk) C (Day 2, 4, 7 or 14) A x B A x C B x C A x B x C Residual
DF
Mean square
F1
4
1.3393
588.8
1 3 4 12 3 12 160
1.1310 0.7277 0.5358 0.0740 0.0244 0.0199 0.0023
497.3 319.9 235.5 32.5 10.7 8.7
'All F values greater than 3.84 are significant in this table (P < 0.05).
TABLE 3.—Distribution of selenium in egg white and yolk after feeding synthetic selenium compounds, (Exp. 2) Dietary selenium H.g. Se/g. dry Total matter in diet _ (mg./kg.) White Yolk" Source' 0.26a2 0.25a2 Diet 1 0.07 0.48b 0.34b + selenocystine 0.17 + selenomethio0.39b 0.65d nine 0.17 0.32b 0.44b + sodium selenite 0.17 0.40c 0.62c + sodium selenite 0.27 'See Table 1 for composition of the diet. 2 Means within a column not having the same letter are significantly different (P < 0.05).
Feeding selenomethionine resulted in more selenium in the egg white than in the yolk. The retention of selenium from the different synthetic selenium compounds is shown in Table 4. The lowest percentage of retention was recorded for hens fed diet 1 with no selenium supplement. Although the data were not statistically analyzed, the results suggest that the greatest retention occurred when selenium was fed in the form of selenomethionine. Higher egg selenium values from selenomethionine support the retention figures. Selenium retention was fairly similar when hens were fed selenocystine or the two levels of sodium selenite. Experiment 3 was designed to investigate the selenium content and distribution in eggs when hens were fed various natural sources of selenium. When diet 2 was fed, each increment in dietary selenium caused an increasing proportion of egg white selenium (Table 5). When 0.10 mg./kg. was fed, the egg white selenium was 0.18 jxg. / g . , or about twice the feed level. Egg white increased to 0.79 (xg./g. when 0.20 mg./kg. was fed (about 4 times feed level) and to 1.53 |xg./g. when 0.30 mg./kg. was fed (about 5 times feed level). At the lower selenium level, eggs from diet 2 had almost the same selenium content in white and yolk. Increases in dietary selenium resulted in increases in yolk sele-
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um, the yolk selenium content jumped rapidly between days four and seven and then continued a gradual increase. In the yolk, the selenium content from selenite fed hens was higher than from hens fed natural selenium. A comparison of egg white and yolk selenium values is shown in Figure 3, as summarized from Figures 1 and 2. When 0.18 mg./kg. natural selenium was fed, egg white selenium increased rapidly and contained more selenium per unit of weight than the yolk even at the end of 14 days. On the other hand, a diet containing 0.08 mg./kg. natural selenium plus 0.10 mg./kg. selenite selenium resulted in yolk selenium deposition which was larger than that present in the white. Table 2 shows the analysis of variance for Experiment 1. All the treatment factors and interactions were statistically significant (P < 0.05). In Experiment 2, diets containing various synthetic selenium compounds were fed for 14 days before analyzing the eggs for selenium. Feeding diet 1 resulted in an egg with almost equal selenium contents in the white and yolk (Table 3). Adding 0.10 mg./kg. selenocystine selenium to the diet produced an egg which contained more selenium in the yolk than in the white. The pattern of distribution and amounts of selenium were very similar to those of eggs from hens fed selenite.
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TABLE 4.—Retention of dietary selenium from synthetic selenium compounds, (Exp. 2) Dietary selenium Fecal Retained Fecal Dry Se Total Feed Se loss Se Se feces in consump- intake diet tion (g./ (Mf-/ (M£-/g(M-g-/ (I*/
