Effect of Selenium on Rat Growth, Growth Hormone and Diet Utilization1-2 RICHARD G. EWAN Department of Animal Science, Iowa State University, Ames, Iowa 50010 ABSTRACT Female rats were fed a selenium-deficient diet composed of Torula yeast, sucrose, vitamins (including tocopheryl acetate) and minerals from weaning and during breeding, gestation and lactation. The offspring were used to study the effects of selenium on growth, diet utiliza tion and growth hormone status. The Torula yeast diet containing 200 IU c/Z-a-tocopheryl acetate was fed alone or supplemented with 0.025 or 0.1 ppm of selenium as selenite. Rats fed the selenium-supplemented diets grew significantly faster and consumed significantly more diet than rats fed the unsupplemented diet. Anterior pituitary weights were lower in seleniumdeficient rats, but if expressed per unit of body weight, were similar to pituitary weights of selenium-supplemented animals. Total growth hormone in the anterior pituitary was reduced in selenium-deficient rats. A metab olism study indicated that rats allowed ad libitum access to supplemented diets consumed more diet and obtained more metabolizable energy from the diet than rats fed the deficient diet. If the intake of rats fed the supple mented diets was limited to that of rats allowed ad libitum access to de ficient diet, growth of rats was similar. However, metabolizable energy content of the diet increased quadratically and nitrogen digestibility in creased linearly as the level of selenium increased. Selenium deficiency reduced growth primarily by decreasing diet consumption, but also re duced the utilization of energy and nitrogen. J. Nutr. 106: 702-709, 1976. selenium •growth •diet utilization INDEXING KEY WORDS growth hormone Whanger and Weswig3 and McCoy and Weswig ( 1 ) first reported the symptoms of selenium deficiency in the rat in the pres ence of vitamin E. They observed that off spring of female rats fed a Torula yeast diet supplemented with 60 ppm of d-a-tocopheryl acetate grew slowly and had poor hair coat, pale iris and white retina. Supplemen tation of the diet with selenium (0.1 ppm) alleviated the deficiency symptoms. Mc Coy and Weswig ( 1 ) were unable to dem onstrate differences in levels of the plasma enzymes, glutamic-oxaloacetic transaminase or lactate dehydrogenase, or the in vitro uptake of "Se by erythrocytes. Hurt et al. (2) were able to confirm the observations of McCoy and Weswig and also demon strated a marked decrease in the selenium levels in blood, liver and muscle of rats fed
deficient diets when compared with rats fed diets containing 0.5 ppm of selenomethionine. Hurt et al. ( 2 ) did not observe histological changes in heart, liver, kidney, pancreas or skeletal muscle. Hurt et al. ( 2 ) reported a decrease in feed consumption by selenium deficient rats and an increase in feed:gain ratio. The objective of the present experiments was to determine the effect of selenium on growth, diet utilization and growth horHeceived for publication June 10, 1975. 1 Journal Paper No. J-8202 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 1943. »Presented in part at the Annual Meeting of the Federation of American Societies for Experimental Biology, Atlantic City, N.J., 1975. »Whanger, P. D. & Weswig, P. H. (1969) Se lenium responses in the rat independent of vitamin E. Federation Proc. 28, 809. (Abstr.) 702
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703
SELENIUM AND RAT RESPONSE
mone status of tne selenium-deficient and selenium-supplemented rat receiving ade quate amounts of a-tocopherol.
TABLE 1 Composition of basal diel Item
MATERIALS AND METHODS
Female, weanling Holtzman rats from a Torula yeast1 40.0 commercial supplier4 or from litters of fe Sucrose 51.9 males fed a stock diet5 were fed a Torula Stripped lard2 5.0 Vitamin premix3 yeast diet (table 1). The diet was supple 0.5 DL-Methionine 0.5 mented with 200 ppm of Ã-Ã-Z-a-tocopheryl Mineral premix4 2.1 acetate and contained 0.018 ppm of se lenium. Vitamins and minerals were added 1Type B, NF XIII, Lakes States Division, St. » Dis to supplement the composition of Torula Regis Paper Co., llhinelander, Wisconsin. Products, Inc., Rochester, N.Y., 14650. yeast and the diet met or exceeded the 3tillation Contributed the following per kilogram of diet: NRG (3) requirements for all nutrients 1,250 IU retinyl acetate, 120 IU eholecalciferol, 100 except selenium. At about 3 months of age, ¿igmenadione and 5/jg vitamin B12. 4 Contributed the females were mated with males that the following per kilogram of diet: 19.689 g calcium carbonate (CaCO3), 1.2 g sodium chloride (NaCl), had been fed stock diet. During breeding, mg manganese sulfate (MnSO4-H2O), and l mg gestation and lactation, the Torula diet was 60 potassium iodate (KIO3). fed. The offspring from the litters were used to study the effect of selenium sup ±SE). The treatments were the Torula plementation on growth and diet utiliza yeast diet, supplemented with 0.0, 0.025 or tion. Experiment 1. Thirty-three groups of 0.1 ppm of selenium as selenous acid, or three weanling rats from selenium-depleted the stock diet. One rat in each group was dams were selected by sex and litter. fed each diet. The stock diet was included Within groups, rats and treatments were to determine if differences in growth of assigned at random to cages. The average rats fed the stock diet and the supple initial weight of the rats was 44.2 ±0.5 g mented Torula diet were due to differences ( mean ±SE). The treatments were the in diet consumption or diet utilization. Eight groups were allowed ad libitum ac Torula yeast diet (table 1) supplemented with 0.0, 0.025 or 0.1 ppm of selenium as cess to the diets and, within each of the other eight groups, the intake of rats fed selenous acid. All rats were housed in sus pended wire-mesh cages and were allowed the supplemented Torula diets was re ad libitum access to feed and water. They stricted to the amount of food consumed by were housed in a room with a 12-hour light- the rat fed the unsupplemented diet. The intake of the rat fed the stock diet was re dark cycle and the temperature was main tained at 26°.Rats were weighed weekly stricted to the amount of food consumed by the rat fed the unsupplemented diet, and daily feed consumption was measured plus 10% to compensate for the lower in some groups for 2 weeks. At the end of the feeding period of 2, 3, digestibility of the stock diet. 4 or 5 weeks, rats were killed by decapita The rats were housed in stainless steel tion. Blood was collected and plasma was metabolism cages6 and total urine and retained for growth hormone assay. The feces were collected for the 14-day experi anterior pituitary was removed, weighed mental period. Urine was collected in a and frozen in distilled water for growth plastic bottle containing 5 ml of 5 N HC1 and was filtered before dilution to a known hormone assay (4). Experiment 2. Sixteen, littermate groups volume. Feces were dried at 70°,allowed of four rats of the same sex from selenium- to equilibrate at room temperature, depleted dams were used. The rats were weighed and ground through a 20-mesh weaned at 21 days and fed the Torula screen in a Wiley mill. yeast diet (table 1) for an average of 31 days before being allotted to treatments. * Small Animal Supply Co., Omaha, Nebraska. »Wayne Lab-Blox, Allied Mills Inc., Chicago, Illi At the time of allotment, the average nois. weight of the rats was 71.6 ±1.5 g ( mean 8 Hocltge, Inc., Cincinnati, Ohio 45238.
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704
RICHARD
At the conclusion of the feeding period, the rats were killed by decapitation; blood was collected and plasma was retained; the anterior pituitary was removed, weighed and frozen in distilled water for growth hormone assay (4). Urine and feces were analyzed for nitro gen by Kjeldahl procedures (5) and for energy by bomb calorimetry.7 Statistical analysis of the data was by least-squares analysis of variance for unequal numbers as described by Harvey (6). RESULTS
o o" UJ
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AND DISCUSSION
Experiment 1. Supplementation of the Tonila yeast diet with selenium resulted in a marked improvement in the growth of the offspring from selenium-depleted fe males (fig. 1). The linear and quadratic effects of selenium supplementation were significant after 1 week of the experiment and significant at each week thereafter. The significant quadratic effect suggests that the growth rates could be expressed as a quadratic function of selenium level and that growth rate was maximized by the Se, ppm 200
O
C. EWAN
».025
ISO-
X
o 100
o o CO 50
01234
5
WEEKS
Fig. 1 Experiment 1. Effect of selenium sup plementation on the growth of rats. Each point represents the mean of 33 rats at 1 and 2 weeks, 21 rats at 3 weeks, 12 rats at 4 weeks, and four rats at 5 weeks. Pooled SE were 1.35 g at 1 week, 2.00 g at 2 weeks, 3.38 g at 3 weeks, 5.29 g at 4 weeks, and 9.39 g at 5 weeks.
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DAYS
Fig. 2 Experiment 2. Effect of selenium sup plementation on feed consumption of rats. Each point is the mean of 21 rats. Pooled SE were 0.34, 0.19, 0.24, 0.26, 0.25, 0.26, 0.34, 0.50, 0.29, 0.38, 0.37, 0.34, 0.41, and 0.36 g for means at day 1 to day 14, respectively.
lowest level of selenium supplementation (0.025 ppm). The growth of the rats was similar to the response reported by McCoy and Weswig ( 1 ). Supplementation of the diet with 0.025 ppm of selenium resulted in growth similar to the response to addition of 0.1 ppm of selenium. The requirement of the rat for growth is less than 0.1 ppm and may be approximately 0.04 ppm if the selenium content of the diet and the sup plementary selenium are considered. This is consistent with the recommendations of NRC (3) for the selenium requirement of the growing rat. Growth responses to se lenium in the presence of tocopherol have been reported by several authors (1, 2, 7-9). In other studies in which rats were fed selenium-deficient diets, reduced growth was observed after several weeks (7-9) or not at all (10). Selenium-depleted rats fed supplemented diets consumed more diet during the first day than rats fed unsupplemented diets (fig. 2). The linear and quadratic effects of selenium levels were significant at each successive day. Hurt et al. (2) have re ported that rats fed an amino acid diet de ficient in selenium consume significantly less feed than controls fed a supplemented diet. Presumably, the reduction in food intake results in the reduction in growth 7 Oxygen bomb calorimetry and combustion meth ods. Manual No. 130. Parr Instrument Co., Moline, Illinois 61265.
SELENIUM AND RAT RESPONSE
rate. The mechanism by which selenium deficiency affects food intake is not clear. The rapid increase in feed intake after sup plemented diets are fed may suggest that metabolic changes occur in the seleniumdepleted rat that modify some factor that depresses feed consumption. The nature of the modification is not known. Selenium-depleted rats fed the unsupplemented Tonila diet require more feed per unit of gain (table 2) than rats fed supplemented diets. Improvements in ef ficiency of utilization of feed by seleniumsupplemented rats have been observed when amino acid diets and Torula diets were pair-fed (2). Because the major effect of selenium de ficiency was the reduction in growth rate, growth hormone (GH) levels were deter mined in the anterior pituitary and plasma. The size of the anterior pituitary and the total GH in the anterior pituitary were, except at 5 weeks of the experiment, sig nificantly increased when selenium-supple mented diets were fed (table 3). Pituitary weight was proportional to body size, but total GH was significantly reduced in rela tion to body size in the selenium-deficient rats after the supplemented diets were fed for 2, 3 or 4 weeks. Plasma GH levels were also reduced significantly after 2 and 4 weeks of the experiment. Thus, there seems to be a reduction in the production and circulating levels of growth hormone in selenium-deficient rats. Whether this is a cause or an effect of selenium deficiency cannot be determined at this time. Experiment 2. Selenium-depleted rats fed the stock diet grew significantly more rapidly than did rats fed the Torula diets
705
(table 4). Selenium supplementation of the Torula diet improved growth rate of both ad libitum and pair-fed rats, but the differences were not significant. Rats fed the stock diet consumed significantly more diet than rats fed Torula diets. Feed con sumption increased significantly if selenium was added to the Torula yeast diet and rats were allowed ad libitum access to the diets. Efficiency of feed utilization, as estimated by feed:gain ratio, improved when rats were allowed ad libitum access to seleniumsupplemented Torula diets. The response of rats in this study was similar to the re sponse of the rats in experiment 1. The growth response to selenium was not as marked, however, and this may be be cause the rats in this study were larger and older at the start of the experiment. Rats allowed ad libitum access to supple mented Torula diets obtained more di gestible energy and metabolizable energy from the diets than rats fed the unsupplemented diet (table 5). Thompson and Scott (11) have reported that seleniumdeficient chicks excrete more neutral lipids in the feces than do birds supplemented with selenium. The pancreatic Jipase activ ity decreased in the pancreas of seleniumdeficient chick (11). The selenium-deficient pig is unable to digest dietary ether extract (primarily soybean oil) as well as the se lenium-adequate animals.8 In seleniumdeficient rats, energy digestibility was re duced and may reflect a decrease in digestibility of dietary ether extract by the deficient rat. This may suggest that pan»Gllenke, L. R. & Ewan, R. C. (1974) Selenium in the nutrition of the young pig. J. Anlrn. Sci. 39, 975. (Abstr.)
TABLE 2 Experiment 1. Effect of selenium on feed: gain ratio
Added selenium fl9^ppm3.083.273.13n innppm2.882.744.29Linear***NSQuadraticNS»*•*
Periodweeks0-11-22-3Ratsno212190.0005.686.965.84O
~l P < 0.05, *; P < 0.01, **; NS, not significant. Pooled SEMwere 0.75 at 0-1 weeks, 0.47 at 1 to 2 weeks and 0.81 at 2 to'Sjweeks.
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706
RICHARD
C. EWAN
TABLE 3 Experiment l. Effect of selenium on 'pituitary weight and growth hormone Weeks of ex periment23
selenium0.000g Pooled1ppm SEMNumber
ppm11
Quad-
rats118 of 4 5Added
840.025
g 7 40.100
84Significance2Linear
Pituitary 4 5
1.91 2.17 3.04 5.15
2.43 3.58 5.72 7.20 Pituitary 31.36 32.39 31.82 29.66
weight, mg 3.21 3.87 5.53 7.13
NS *
0.14 0.33 0.25 0.18
weight, mg/kg body wt 34.29 1.37 33.37 2.07 30.35 0.91 31.27 1.37
*** ***
**» ***
XS NS N>S XS
NS NS * NS
3 4 5
33.07 32.39 27.63 31.20
4 5
23.41 33.18 86.13 206.25
Total pituitary growth hormone, Mg 38.00 53.34 3.37 77.75 72.27 7.50 219.72 195.63 21.68 354.45 296.20 40.51
*** * *
NS ** ***
NS
NS
12.17 15.91 27.49 41.18
Pituitary growth hormone, /»g/mgpituitary 15.68 16.70 1.01 22.33 18.24 2.03 37.87 34.42 3.57 49.85 41.48 5.22
NS NS NS
NS * NS NS
2
2 3 4
Pituitary growth hormone, MgAg body wt 23452345401.7492.1758.41,260.34.1014.096.4034.47492.8 568.7706.9 603.21,208.1 1,048.71,464.3 1,288.8Plasma ng/ml13.86growth hormone, 26.6219.90 45.5460.87 43.9242.92 20.5234.247.9118.0170.86.0811.7812.1417.65**NSNSNS*NSNSNSNS***NSNSNS*NS
1Pooled SEMfor the treatment containing the largest number of rats. P < 0.005, ***; NS, not significant,
creatic lipase is reduced in the seleniumdeficient rat. The major effect on energy utilization was the excretion of energy in the urine. Rats fed the unsupplemented diet con sumed less energy, digested slightly less of the available energy and excreted less energy in the urine. Urinary energy was a greater fraction of the digestible energy, however, and metabolizable energy was
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deficient diets when compared with rats fed diets containing 0.5 ppm of selenomethionine. Hurt et al. ( 2 ) did not observe histological changes in heart, liver, kidney, pancreas or skeletal muscle. Hurt et al. ( 2 ) reported a decrease in feed consumption by selenium deficient rats and an increase in feed:gain ratio. The objective of the present experiments was to determine the effect of selenium on growth, diet utilization and growth horHeceived for publication June 10, 1975. 1 Journal Paper No. J-8202 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 1943. »Presented in part at the Annual Meeting of the Federation of American Societies for Experimental Biology, Atlantic City, N.J., 1975. »Whanger, P. D. & Weswig, P. H. (1969) Se lenium responses in the rat independent of vitamin E. Federation Proc. 28, 809. (Abstr.) 702
Downloaded from https://academic.oup.com/jn/article-abstract/106/5/702/4768817 by University of California School of Law (Boalt Hall) user on 01 August 2018
703
SELENIUM AND RAT RESPONSE
mone status of tne selenium-deficient and selenium-supplemented rat receiving ade quate amounts of a-tocopherol.
TABLE 1 Composition of basal diel Item
MATERIALS AND METHODS
Female, weanling Holtzman rats from a Torula yeast1 40.0 commercial supplier4 or from litters of fe Sucrose 51.9 males fed a stock diet5 were fed a Torula Stripped lard2 5.0 Vitamin premix3 yeast diet (table 1). The diet was supple 0.5 DL-Methionine 0.5 mented with 200 ppm of Ã-Ã-Z-a-tocopheryl Mineral premix4 2.1 acetate and contained 0.018 ppm of se lenium. Vitamins and minerals were added 1Type B, NF XIII, Lakes States Division, St. » Dis to supplement the composition of Torula Regis Paper Co., llhinelander, Wisconsin. Products, Inc., Rochester, N.Y., 14650. yeast and the diet met or exceeded the 3tillation Contributed the following per kilogram of diet: NRG (3) requirements for all nutrients 1,250 IU retinyl acetate, 120 IU eholecalciferol, 100 except selenium. At about 3 months of age, ¿igmenadione and 5/jg vitamin B12. 4 Contributed the females were mated with males that the following per kilogram of diet: 19.689 g calcium carbonate (CaCO3), 1.2 g sodium chloride (NaCl), had been fed stock diet. During breeding, mg manganese sulfate (MnSO4-H2O), and l mg gestation and lactation, the Torula diet was 60 potassium iodate (KIO3). fed. The offspring from the litters were used to study the effect of selenium sup ±SE). The treatments were the Torula plementation on growth and diet utiliza yeast diet, supplemented with 0.0, 0.025 or tion. Experiment 1. Thirty-three groups of 0.1 ppm of selenium as selenous acid, or three weanling rats from selenium-depleted the stock diet. One rat in each group was dams were selected by sex and litter. fed each diet. The stock diet was included Within groups, rats and treatments were to determine if differences in growth of assigned at random to cages. The average rats fed the stock diet and the supple initial weight of the rats was 44.2 ±0.5 g mented Torula diet were due to differences ( mean ±SE). The treatments were the in diet consumption or diet utilization. Eight groups were allowed ad libitum ac Torula yeast diet (table 1) supplemented with 0.0, 0.025 or 0.1 ppm of selenium as cess to the diets and, within each of the other eight groups, the intake of rats fed selenous acid. All rats were housed in sus pended wire-mesh cages and were allowed the supplemented Torula diets was re ad libitum access to feed and water. They stricted to the amount of food consumed by were housed in a room with a 12-hour light- the rat fed the unsupplemented diet. The intake of the rat fed the stock diet was re dark cycle and the temperature was main tained at 26°.Rats were weighed weekly stricted to the amount of food consumed by the rat fed the unsupplemented diet, and daily feed consumption was measured plus 10% to compensate for the lower in some groups for 2 weeks. At the end of the feeding period of 2, 3, digestibility of the stock diet. 4 or 5 weeks, rats were killed by decapita The rats were housed in stainless steel tion. Blood was collected and plasma was metabolism cages6 and total urine and retained for growth hormone assay. The feces were collected for the 14-day experi anterior pituitary was removed, weighed mental period. Urine was collected in a and frozen in distilled water for growth plastic bottle containing 5 ml of 5 N HC1 and was filtered before dilution to a known hormone assay (4). Experiment 2. Sixteen, littermate groups volume. Feces were dried at 70°,allowed of four rats of the same sex from selenium- to equilibrate at room temperature, depleted dams were used. The rats were weighed and ground through a 20-mesh weaned at 21 days and fed the Torula screen in a Wiley mill. yeast diet (table 1) for an average of 31 days before being allotted to treatments. * Small Animal Supply Co., Omaha, Nebraska. »Wayne Lab-Blox, Allied Mills Inc., Chicago, Illi At the time of allotment, the average nois. weight of the rats was 71.6 ±1.5 g ( mean 8 Hocltge, Inc., Cincinnati, Ohio 45238.
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704
RICHARD
At the conclusion of the feeding period, the rats were killed by decapitation; blood was collected and plasma was retained; the anterior pituitary was removed, weighed and frozen in distilled water for growth hormone assay (4). Urine and feces were analyzed for nitro gen by Kjeldahl procedures (5) and for energy by bomb calorimetry.7 Statistical analysis of the data was by least-squares analysis of variance for unequal numbers as described by Harvey (6). RESULTS
o o" UJ
5 io
z o O
8
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AND DISCUSSION
Experiment 1. Supplementation of the Tonila yeast diet with selenium resulted in a marked improvement in the growth of the offspring from selenium-depleted fe males (fig. 1). The linear and quadratic effects of selenium supplementation were significant after 1 week of the experiment and significant at each week thereafter. The significant quadratic effect suggests that the growth rates could be expressed as a quadratic function of selenium level and that growth rate was maximized by the Se, ppm 200
O
C. EWAN
».025
ISO-
X
o 100
o o CO 50
01234
5
WEEKS
Fig. 1 Experiment 1. Effect of selenium sup plementation on the growth of rats. Each point represents the mean of 33 rats at 1 and 2 weeks, 21 rats at 3 weeks, 12 rats at 4 weeks, and four rats at 5 weeks. Pooled SE were 1.35 g at 1 week, 2.00 g at 2 weeks, 3.38 g at 3 weeks, 5.29 g at 4 weeks, and 9.39 g at 5 weeks.
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DAYS
Fig. 2 Experiment 2. Effect of selenium sup plementation on feed consumption of rats. Each point is the mean of 21 rats. Pooled SE were 0.34, 0.19, 0.24, 0.26, 0.25, 0.26, 0.34, 0.50, 0.29, 0.38, 0.37, 0.34, 0.41, and 0.36 g for means at day 1 to day 14, respectively.
lowest level of selenium supplementation (0.025 ppm). The growth of the rats was similar to the response reported by McCoy and Weswig ( 1 ). Supplementation of the diet with 0.025 ppm of selenium resulted in growth similar to the response to addition of 0.1 ppm of selenium. The requirement of the rat for growth is less than 0.1 ppm and may be approximately 0.04 ppm if the selenium content of the diet and the sup plementary selenium are considered. This is consistent with the recommendations of NRC (3) for the selenium requirement of the growing rat. Growth responses to se lenium in the presence of tocopherol have been reported by several authors (1, 2, 7-9). In other studies in which rats were fed selenium-deficient diets, reduced growth was observed after several weeks (7-9) or not at all (10). Selenium-depleted rats fed supplemented diets consumed more diet during the first day than rats fed unsupplemented diets (fig. 2). The linear and quadratic effects of selenium levels were significant at each successive day. Hurt et al. (2) have re ported that rats fed an amino acid diet de ficient in selenium consume significantly less feed than controls fed a supplemented diet. Presumably, the reduction in food intake results in the reduction in growth 7 Oxygen bomb calorimetry and combustion meth ods. Manual No. 130. Parr Instrument Co., Moline, Illinois 61265.
SELENIUM AND RAT RESPONSE
rate. The mechanism by which selenium deficiency affects food intake is not clear. The rapid increase in feed intake after sup plemented diets are fed may suggest that metabolic changes occur in the seleniumdepleted rat that modify some factor that depresses feed consumption. The nature of the modification is not known. Selenium-depleted rats fed the unsupplemented Tonila diet require more feed per unit of gain (table 2) than rats fed supplemented diets. Improvements in ef ficiency of utilization of feed by seleniumsupplemented rats have been observed when amino acid diets and Torula diets were pair-fed (2). Because the major effect of selenium de ficiency was the reduction in growth rate, growth hormone (GH) levels were deter mined in the anterior pituitary and plasma. The size of the anterior pituitary and the total GH in the anterior pituitary were, except at 5 weeks of the experiment, sig nificantly increased when selenium-supple mented diets were fed (table 3). Pituitary weight was proportional to body size, but total GH was significantly reduced in rela tion to body size in the selenium-deficient rats after the supplemented diets were fed for 2, 3 or 4 weeks. Plasma GH levels were also reduced significantly after 2 and 4 weeks of the experiment. Thus, there seems to be a reduction in the production and circulating levels of growth hormone in selenium-deficient rats. Whether this is a cause or an effect of selenium deficiency cannot be determined at this time. Experiment 2. Selenium-depleted rats fed the stock diet grew significantly more rapidly than did rats fed the Torula diets
705
(table 4). Selenium supplementation of the Torula diet improved growth rate of both ad libitum and pair-fed rats, but the differences were not significant. Rats fed the stock diet consumed significantly more diet than rats fed Torula diets. Feed con sumption increased significantly if selenium was added to the Torula yeast diet and rats were allowed ad libitum access to the diets. Efficiency of feed utilization, as estimated by feed:gain ratio, improved when rats were allowed ad libitum access to seleniumsupplemented Torula diets. The response of rats in this study was similar to the re sponse of the rats in experiment 1. The growth response to selenium was not as marked, however, and this may be be cause the rats in this study were larger and older at the start of the experiment. Rats allowed ad libitum access to supple mented Torula diets obtained more di gestible energy and metabolizable energy from the diets than rats fed the unsupplemented diet (table 5). Thompson and Scott (11) have reported that seleniumdeficient chicks excrete more neutral lipids in the feces than do birds supplemented with selenium. The pancreatic Jipase activ ity decreased in the pancreas of seleniumdeficient chick (11). The selenium-deficient pig is unable to digest dietary ether extract (primarily soybean oil) as well as the se lenium-adequate animals.8 In seleniumdeficient rats, energy digestibility was re duced and may reflect a decrease in digestibility of dietary ether extract by the deficient rat. This may suggest that pan»Gllenke, L. R. & Ewan, R. C. (1974) Selenium in the nutrition of the young pig. J. Anlrn. Sci. 39, 975. (Abstr.)
TABLE 2 Experiment 1. Effect of selenium on feed: gain ratio
Added selenium fl9^ppm3.083.273.13n innppm2.882.744.29Linear***NSQuadraticNS»*•*
Periodweeks0-11-22-3Ratsno212190.0005.686.965.84O
~l P < 0.05, *; P < 0.01, **; NS, not significant. Pooled SEMwere 0.75 at 0-1 weeks, 0.47 at 1 to 2 weeks and 0.81 at 2 to'Sjweeks.
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706
RICHARD
C. EWAN
TABLE 3 Experiment l. Effect of selenium on 'pituitary weight and growth hormone Weeks of ex periment23
selenium0.000g Pooled1ppm SEMNumber
ppm11
Quad-
rats118 of 4 5Added
840.025
g 7 40.100
84Significance2Linear
Pituitary 4 5
1.91 2.17 3.04 5.15
2.43 3.58 5.72 7.20 Pituitary 31.36 32.39 31.82 29.66
weight, mg 3.21 3.87 5.53 7.13
NS *
0.14 0.33 0.25 0.18
weight, mg/kg body wt 34.29 1.37 33.37 2.07 30.35 0.91 31.27 1.37
*** ***
**» ***
XS NS N>S XS
NS NS * NS
3 4 5
33.07 32.39 27.63 31.20
4 5
23.41 33.18 86.13 206.25
Total pituitary growth hormone, Mg 38.00 53.34 3.37 77.75 72.27 7.50 219.72 195.63 21.68 354.45 296.20 40.51
*** * *
NS ** ***
NS
NS
12.17 15.91 27.49 41.18
Pituitary growth hormone, /»g/mgpituitary 15.68 16.70 1.01 22.33 18.24 2.03 37.87 34.42 3.57 49.85 41.48 5.22
NS NS NS
NS * NS NS
2
2 3 4
Pituitary growth hormone, MgAg body wt 23452345401.7492.1758.41,260.34.1014.096.4034.47492.8 568.7706.9 603.21,208.1 1,048.71,464.3 1,288.8Plasma ng/ml13.86growth hormone, 26.6219.90 45.5460.87 43.9242.92 20.5234.247.9118.0170.86.0811.7812.1417.65**NSNSNS*NSNSNSNS***NSNSNS*NS
1Pooled SEMfor the treatment containing the largest number of rats. P < 0.005, ***; NS, not significant,
creatic lipase is reduced in the seleniumdeficient rat. The major effect on energy utilization was the excretion of energy in the urine. Rats fed the unsupplemented diet con sumed less energy, digested slightly less of the available energy and excreted less energy in the urine. Urinary energy was a greater fraction of the digestible energy, however, and metabolizable energy was
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