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Effect of Dietary Cholesterol on Serum and Egg Cholesterol Levels over a Period of Time12
Effect of Dietary Cholesterol on Serum and Egg Cholesterol Levels over a Period of Time1'2 H. M. EDWARDS, JR. AND VIVIAN JONES 3 Poultry Department, University of Georgia, Athens, Georgia (Received for publication December 27, 1963)
T
This study was conducted to determine the effect of feeding cholesterol to laying hens on serum and egg yolk cholesterol levels over a period of time. EXPERIMENTAL
Single Comb White Leghorn hens, housed individually in wire cages, were used in the two experiments reported. 1 Journal paper No. 334 of the College Experiment Station, University of Georgia, College of Agriculture Experiment Stations. 2 This investigation was supported in part by a Public Health Service research grant No. 6338 and a research career program award No. 18,411 from the Arthritis and Metabolic Disease Institute. 3 National Science Foundation Undergraduate Research Participant, Summer 1961 and 1962. Present address: Poultry Dept., North Carol'na State, Raleigh, North Carolina.
Experiment one had two dietary treatments, control diet and the control plus 1% of cholesterol. Experiment two had these two dietary treatments plus a third group receiving the control diet + 0 . 4 % dried hen bile. Since Edwards et al. (1962) have shown that feeding lithocholic acid to hens influences serum and egg cholesterol levels, it was thought desirable to determine the effect of feeding bile acids excreted by hens to laying hens. The dried hen bile used in experiment 2 was obtained from gall bladders of hens at a local slaughter plant, and freeze-dried. The basal diet used in these studies was a glucose monohydrate-isolated soybean protein type containing 6% corn oil. The detailed composition has been published previously, Marion and Edwards (1962). Fifteen hens received each of the experimental diets fed in both experiments. The hens used in experiment 1 had been in production approximately one year, while those used in experiment 2 had been in production approximately one month. Feed and water were supplied ad libitum. Egg production was recorded for five days before the hens were fed the experimental diets, and only laying hens were used for the experiments. Egg production, feed consumption and body weights were recorded for each hen. The weight of each egg was recorded in experiment 2. The hens were fed the experimental diets for 22 days in experiment 1 and 42 days in experiment 2. Five milliliters of blood were obtained by heart puncture after the hens had re-
877
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 14, 2015
HE influence of dietary cholesterol on the levels of serum and egg cholesterol of the laying hen was recently studied by Harris and Wilcox (1963) and the literature was critically reviewed. These workers found that after 11 days of feeding crystalline cholesterol to hens the serum and egg cholesterol levels were significantly increased. They interpreted their findings to suggest that laying hens are able to prevent a marked hypercholesteremia by excretion of cholesterol into the yolk. Since there is at least one report in the literature (Kurnick et al., 1958) in which no increase in yolk cholesterol was obtained when cholesterol was fed to laying hens, the possibility of time being a variable in these observations by various workers appeared possible.
878
H. M. EDWARDS, J R . AND V. J O N E S
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Serum Cholesterol
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FIG. 1. Effect of dietary cholesterol on serum and egg cholesterol over a period of time. Means bordered by the same adjacent vertical line are not significantly different (P<.05). Legend: (•) • X
(•) basal ration • 1% cholesterol X 0.4% dry hen bile
ceived the experimental diets for 0, 10 and 20 days in experiment 1 and 0, 10, 20 and 40 days in experiment 2. One egg produced by each hen during the experimental periods, —2 to 0 days, 10 to 12 days, 20 to 22 days and in experiment 2, 40 to 42 days was collected for cholesterol analysis. The blood and eggs were processed as previously described, Edwards el al. (1962). The data collected were subjected to a statistical analysis, and treatment significance was determined by the multiple range test of Duncan (1955) as modified by Kramer (1956). RESULTS AND DISCUSSION
Since only small and insignificant differences in hen weights, egg production, egg size and feed consumption existed between treatments in experiments 1 and 2, these d a t a are not presented. Large significant differences in serum and egg cholesterol were obtained in experiments 1 and 2 and these d a t a are presented in Figure 1. The data from experiments 1 and
The feeding of cholesterol caused the egg cholesterol level to be high at both 10 and 20 days in experiment 1. The feeding of cholesterol caused significantly higher egg cholesterol values at 10 days but not at 20 days in the second experiment. While the average cholesterol level of eggs from hens fed cholesterol was higher a t 20 and 40 days, the larger variation in cholesterol levels caused the differences not to be significant. The feeding of dried hen bile did not significantly influence serum or egg cholesterol levels. Comparisons of responses of serum and egg cholesterol levels with time are complicated by the time factor in development of the yolk. Warren and Conrad (1939) have shown t h a t approximately 10 days are required for the yolk to develop. I t would appear t h a t in the first experiment there was a large movement of dietary cholesterol into the egg from 0 to 20 days. However, since the serum cholesterol level of the hens fed cholesterol was high a t 10 days but had returned to the level of the controls at 20 days, it would appear t h a t maximum serum cho-
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 14, 2015
€gfi Ufwtl Cho* astero!
10
•••--'
2 indicate that when cholesterol is fed there is a rise in serum cholesterol levels, and then a decline such t h a t after 20 days it had returned to a normal level, or at least to the level of the controls. The older hens t h a t were used in experiment 1 appeared to respond to cholesterol feeding more than the young pullets used in experiment 2 as measured b y serum cholesterol level. While the pullets used in experiment 2 did show a significant increase in serum cholesterol after being fed cholesterol for 10 days, it was not the dramatic type of increase shown by the older hens in experiment 1. However, since only 10-day measurements were made, it is possible t h a t the pullets may have had a very high serum cholesterol at some time between 0 and 10 days but were able to adjust to a normal level rapidly.
879
SERUM AND EGG CHOLESTEROL
While the findings in these studies do not rule out the possibility that laying hens are able to prevent hypercholesteremia through excretion in the yolk as suggested by Harris and Wilcox (1963), the results certainly do not necessarily support this hypothesis. Also, in the work of Edwards et al. (1962) where a severe hypercholesteremia was produced by feeding lithocholic acid, only moderate increases in egg cholesterol were obtained (38 mg./gm. egg lipid to 55 mg./gm. egg lipid). In the present studies, the fact that both serum and egg cholesterol levels reached a maximum when cholesterol was fed and then rapidly returned to normal indicates that some other mechanism, such as: absorption, excretion or catabolism of cholesterol, is the dominant factor in regulating serum and egg cholesterol.
SUMMARY
Two experiments with Single Comb White Leghorn hens showed that feeding cholesterol caused increases in the serum and egg cholesterol levels resulting 10 days after feeding commenced. However, the hen appeared to adjust to the increased level of dietary cholesterol. In both experiments serum cholesterol levels had returned to normal by 20 days and, in one of the experiments, the egg cholesterol levels had also returned to normal. The differences in the responses obtained in the two experiments indicate that some other factors as yet unidentified are influencing the type of response obtained from cholesterol feeding. REFERENCES Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics, 11: 1-42. Edwards, H. M., Jr., V. Jones and J. E. Marion, 1962. Effect of bile acids on egg production, serum cholesterol and egg cholesterol in hens. J. Nutr. 77: 253-258. Harris, P. C , and F. H. Wilcox, 1963. Studies on egg yolk cholesterol. 3. Effect of dietary cholesterol. Poultry Sci. 42: 186-189. Kramer, C. Y., 1956. Extension of multiple range test to group means with unequal number of replications. Biometrics, 12: 307-310. Kurnick, A. A., J. B. Sutton, M. V. Pasvogel and A. R. Kemmerer, 1958. Effect of betaine, choline and methionine on the concentration of serum, tissue and egg yolk cholesterol. Poultry Sci. 37: 1218. Marion, J. E., and H. M. Edwards, Jr., 1962. The response of fat deficient laying hens to corn oil supplementation. Poultry Sci. 41: 1785-1792. Warren, D. C , and R. M. Conrad, 1939. Growth of the hen's ovum. J. Agric. Res. 58: 875.
NEWS AND NOTES {Continued from page 876) awards of $2,400 each were made in the animal science fields—3 in poultry science, 3 in dairy science and 3 in animal science—and one award of $5,500 for graduate study in the field of veterinary science.
The awards were made by a Committee consisting of: G. A. Young, University of Nebraska, representing the American Veterinary Medical Association; L. B. Howard, University of Illinois, representing the American Association of State
{Continued on page 918)
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 14, 2015
lesterol may have occurred at approximately 10 days. This of course, assumes that the level of cholesterol deposited is directly correlated with serum cholesterol. In experiment 2 the egg cholesterol level was initially high and when cholesterol was fed, the yolk formed during the first 10 days contained extremely high levels of cholesterol. The cholesterol content of the yolk formed between 10 and 20 days and 30 and 40 days was not significantly different for the three dietary treatments. The serum cholesterol was high only at 10 days. Therefore, using the same reasoning as was used above for experiment 2, it would appear that serum cholesterol reached a maximum before 10 days and was probably decreasing at 10 days.
T
This study was conducted to determine the effect of feeding cholesterol to laying hens on serum and egg yolk cholesterol levels over a period of time. EXPERIMENTAL
Single Comb White Leghorn hens, housed individually in wire cages, were used in the two experiments reported. 1 Journal paper No. 334 of the College Experiment Station, University of Georgia, College of Agriculture Experiment Stations. 2 This investigation was supported in part by a Public Health Service research grant No. 6338 and a research career program award No. 18,411 from the Arthritis and Metabolic Disease Institute. 3 National Science Foundation Undergraduate Research Participant, Summer 1961 and 1962. Present address: Poultry Dept., North Carol'na State, Raleigh, North Carolina.
Experiment one had two dietary treatments, control diet and the control plus 1% of cholesterol. Experiment two had these two dietary treatments plus a third group receiving the control diet + 0 . 4 % dried hen bile. Since Edwards et al. (1962) have shown that feeding lithocholic acid to hens influences serum and egg cholesterol levels, it was thought desirable to determine the effect of feeding bile acids excreted by hens to laying hens. The dried hen bile used in experiment 2 was obtained from gall bladders of hens at a local slaughter plant, and freeze-dried. The basal diet used in these studies was a glucose monohydrate-isolated soybean protein type containing 6% corn oil. The detailed composition has been published previously, Marion and Edwards (1962). Fifteen hens received each of the experimental diets fed in both experiments. The hens used in experiment 1 had been in production approximately one year, while those used in experiment 2 had been in production approximately one month. Feed and water were supplied ad libitum. Egg production was recorded for five days before the hens were fed the experimental diets, and only laying hens were used for the experiments. Egg production, feed consumption and body weights were recorded for each hen. The weight of each egg was recorded in experiment 2. The hens were fed the experimental diets for 22 days in experiment 1 and 42 days in experiment 2. Five milliliters of blood were obtained by heart puncture after the hens had re-
877
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 14, 2015
HE influence of dietary cholesterol on the levels of serum and egg cholesterol of the laying hen was recently studied by Harris and Wilcox (1963) and the literature was critically reviewed. These workers found that after 11 days of feeding crystalline cholesterol to hens the serum and egg cholesterol levels were significantly increased. They interpreted their findings to suggest that laying hens are able to prevent a marked hypercholesteremia by excretion of cholesterol into the yolk. Since there is at least one report in the literature (Kurnick et al., 1958) in which no increase in yolk cholesterol was obtained when cholesterol was fed to laying hens, the possibility of time being a variable in these observations by various workers appeared possible.
878
H. M. EDWARDS, J R . AND V. J O N E S
/ \ ,..,
J«0| |30o]
"!
JJ1
"I
/
-^
of — r
- ^
f i
_.™,
~ ~ ^ ..-,--.* -
,_
__ _ __,
.
Serum Cholesterol
»
:
•
t
I ,
^—-
* ^
-
t
T 6
U-.rtr-.t.-. |
p
10
20
6
r _ 20
,
_ 40
'
FIG. 1. Effect of dietary cholesterol on serum and egg cholesterol over a period of time. Means bordered by the same adjacent vertical line are not significantly different (P<.05). Legend: (•) • X
(•) basal ration • 1% cholesterol X 0.4% dry hen bile
ceived the experimental diets for 0, 10 and 20 days in experiment 1 and 0, 10, 20 and 40 days in experiment 2. One egg produced by each hen during the experimental periods, —2 to 0 days, 10 to 12 days, 20 to 22 days and in experiment 2, 40 to 42 days was collected for cholesterol analysis. The blood and eggs were processed as previously described, Edwards el al. (1962). The data collected were subjected to a statistical analysis, and treatment significance was determined by the multiple range test of Duncan (1955) as modified by Kramer (1956). RESULTS AND DISCUSSION
Since only small and insignificant differences in hen weights, egg production, egg size and feed consumption existed between treatments in experiments 1 and 2, these d a t a are not presented. Large significant differences in serum and egg cholesterol were obtained in experiments 1 and 2 and these d a t a are presented in Figure 1. The data from experiments 1 and
The feeding of cholesterol caused the egg cholesterol level to be high at both 10 and 20 days in experiment 1. The feeding of cholesterol caused significantly higher egg cholesterol values at 10 days but not at 20 days in the second experiment. While the average cholesterol level of eggs from hens fed cholesterol was higher a t 20 and 40 days, the larger variation in cholesterol levels caused the differences not to be significant. The feeding of dried hen bile did not significantly influence serum or egg cholesterol levels. Comparisons of responses of serum and egg cholesterol levels with time are complicated by the time factor in development of the yolk. Warren and Conrad (1939) have shown t h a t approximately 10 days are required for the yolk to develop. I t would appear t h a t in the first experiment there was a large movement of dietary cholesterol into the egg from 0 to 20 days. However, since the serum cholesterol level of the hens fed cholesterol was high a t 10 days but had returned to the level of the controls at 20 days, it would appear t h a t maximum serum cho-
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 14, 2015
€gfi Ufwtl Cho* astero!
10
•••--'
2 indicate that when cholesterol is fed there is a rise in serum cholesterol levels, and then a decline such t h a t after 20 days it had returned to a normal level, or at least to the level of the controls. The older hens t h a t were used in experiment 1 appeared to respond to cholesterol feeding more than the young pullets used in experiment 2 as measured b y serum cholesterol level. While the pullets used in experiment 2 did show a significant increase in serum cholesterol after being fed cholesterol for 10 days, it was not the dramatic type of increase shown by the older hens in experiment 1. However, since only 10-day measurements were made, it is possible t h a t the pullets may have had a very high serum cholesterol at some time between 0 and 10 days but were able to adjust to a normal level rapidly.
879
SERUM AND EGG CHOLESTEROL
While the findings in these studies do not rule out the possibility that laying hens are able to prevent hypercholesteremia through excretion in the yolk as suggested by Harris and Wilcox (1963), the results certainly do not necessarily support this hypothesis. Also, in the work of Edwards et al. (1962) where a severe hypercholesteremia was produced by feeding lithocholic acid, only moderate increases in egg cholesterol were obtained (38 mg./gm. egg lipid to 55 mg./gm. egg lipid). In the present studies, the fact that both serum and egg cholesterol levels reached a maximum when cholesterol was fed and then rapidly returned to normal indicates that some other mechanism, such as: absorption, excretion or catabolism of cholesterol, is the dominant factor in regulating serum and egg cholesterol.
SUMMARY
Two experiments with Single Comb White Leghorn hens showed that feeding cholesterol caused increases in the serum and egg cholesterol levels resulting 10 days after feeding commenced. However, the hen appeared to adjust to the increased level of dietary cholesterol. In both experiments serum cholesterol levels had returned to normal by 20 days and, in one of the experiments, the egg cholesterol levels had also returned to normal. The differences in the responses obtained in the two experiments indicate that some other factors as yet unidentified are influencing the type of response obtained from cholesterol feeding. REFERENCES Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics, 11: 1-42. Edwards, H. M., Jr., V. Jones and J. E. Marion, 1962. Effect of bile acids on egg production, serum cholesterol and egg cholesterol in hens. J. Nutr. 77: 253-258. Harris, P. C , and F. H. Wilcox, 1963. Studies on egg yolk cholesterol. 3. Effect of dietary cholesterol. Poultry Sci. 42: 186-189. Kramer, C. Y., 1956. Extension of multiple range test to group means with unequal number of replications. Biometrics, 12: 307-310. Kurnick, A. A., J. B. Sutton, M. V. Pasvogel and A. R. Kemmerer, 1958. Effect of betaine, choline and methionine on the concentration of serum, tissue and egg yolk cholesterol. Poultry Sci. 37: 1218. Marion, J. E., and H. M. Edwards, Jr., 1962. The response of fat deficient laying hens to corn oil supplementation. Poultry Sci. 41: 1785-1792. Warren, D. C , and R. M. Conrad, 1939. Growth of the hen's ovum. J. Agric. Res. 58: 875.
NEWS AND NOTES {Continued from page 876) awards of $2,400 each were made in the animal science fields—3 in poultry science, 3 in dairy science and 3 in animal science—and one award of $5,500 for graduate study in the field of veterinary science.
The awards were made by a Committee consisting of: G. A. Young, University of Nebraska, representing the American Veterinary Medical Association; L. B. Howard, University of Illinois, representing the American Association of State
{Continued on page 918)
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on June 14, 2015
lesterol may have occurred at approximately 10 days. This of course, assumes that the level of cholesterol deposited is directly correlated with serum cholesterol. In experiment 2 the egg cholesterol level was initially high and when cholesterol was fed, the yolk formed during the first 10 days contained extremely high levels of cholesterol. The cholesterol content of the yolk formed between 10 and 20 days and 30 and 40 days was not significantly different for the three dietary treatments. The serum cholesterol was high only at 10 days. Therefore, using the same reasoning as was used above for experiment 2, it would appear that serum cholesterol reached a maximum before 10 days and was probably decreasing at 10 days.