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Liver Lipid Content of Twenty Varieties of Laying Hens from Three Confinement Systems1,2,3
Liver Lipid Content of Twenty Varieties of Laying Hens from Three Confinement Systems 123 J. D . GARLICH, J. D . OLSON, W. E . H U F F AND P . B .
HAMILTON
Department of Poultry Science, North Carolina State University, Raleigh, North Carolina 27607 (Received for publication August 27, 1974)
POULTRY SCIENCE 54: 806-813, 1975
et al, 1969; Nesheim and Ivy, 1970; Wolford and Polin, 1972; Ivy and Nesheim, 1973). Excessive liver lipid has been associated with reduced egg production and mortality. In 1956 Couch described a "Fatty Liver Syndrome" (FLS). The symptoms included a sudden reduction in egg production, a yellow, friable liver which was high in lipid, and usually excessive abdominal fat. Flock mortality was sometimes increased. Nesheim et al. (1969) reported that sudden mortality in hens laying at a normal rate was the result of hemorrhage of the liver and that these livers were usually very high in lipid content (46 to 83% dry weight). The terminology "Liver Hemorrhage Syndrome" was proposed to describe the condition (Nesheim and Ivy, 1970). The association of the incidence of spontaneous liver hemorrhage with the high liver lipid values has been confirmed (Wolford and Polin, 1972; Wolford and Murphy, 1972).
INTRODUCTION
T
HE lipid content of the liver of normal growing chicks, adult cockerels, and non-laying pullets is low and the range of values is usually narrow (Balnave, 1972; Velu et al., 1971). The average liver lipid content expressed as a percent of dry weight were for: adult cockerels 12.9 (Wyatt et al, 1973); 15 nineteen week old Leghorn pullets (nonlaying; no developed ova) 19.8 ± 0.4, range 17.7 to 21.7 (unpublished observations). In contrast the liver lipid content of groups of laying hens may average from 24 to 76 percent (Griffith et al., 1969; Wolford and Polin, 1974). In other reports the range of individual values varied from 20 to 83 percent (Nesheim
1. Paper number 4458 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, North Carolina. 2. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Experiment Station nor criticism of similar products not mentioned. 3. A preliminary report of this work was presented at the sixty-third annual Poultry Science Association Meetings, Morgantown, West Virginia, August 1974.
The factors which may contribute to the accumulation of excessive liver lipid include aflatoxin (Hamilton and Garlich, 1971, 1972; Garlich et al, 1973), dietary deficiencies and environmental temperature (Schexnailder 806
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ABSTRACT Average liver lipid values were determined for 20 varieties of 71-week old laying hens managed in 3 confinement systems of the 1972-73 North Carolina Random Sample Laying Test. There were highly significant differences in liver lipid attributable to variety, to confinement system, and a significant variety x system interaction. Four varieties had consistently high and five had consistently low liver lipid values in all 3 confinement systems. Variety means ranged from 25.8 to 49.0% liver lipid on a dry weight basis. Hens confined 2/cage had slight but significantly higher liver lipid than hens 7/cage or in floor pens. Liver lipid was positively correlated with body weight in hens 2/cage and in floor pens. There were no significant correlations of liver lipid with egg production or mortality. A frequency distribution of individual liver lipid values revealed a continuous distribution from 15.4 to 65.4% with a pronounced skew to the right of the mean of 38.2%. Neither a fatty liver syndrome nor liver hemorrhage syndrome was reported for any of the flocks during the laying year. The normal range of liver lipid values for hens 71 weeks of age appears to be between 25 and 49 g. of lipid per 100 g. of dry liver weight.
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LIVER LIPID OF LAYING HENS
MATERIALS AND METHODS The 724 hens used in this study were obtained upon completion of the 1972-73 North Carolina Random Sample Laying Tests 4 on 14 August, 1973. They were 71 weeks of age. Twenty varieties of hens were represented in each of 3 confinement systems. The confinement systems were 2 birds per 25 x 45 cm. cage, 7 birds per 61 x 51 cm. cage, and 50 birds on half slats-half litter floor pens with 0.158 m.2 (1.7 sq. ft.) of floor space per bird. A total of 5840 hens began the laying year. All confinement systems were located on the same farm and all hens received feed of the same formulation. Twelve (or
4. Copies of the Fourteenth North Carolina Random Sample Test report may be obtained from Mr. T. R. Burleson, Jr., Piedmont Research Station, Route #6, Box 420, Salisbury, N.C. 28144.
in some cases 15) hens were selected at random from each variety in each confinement system. One variety was not represented in the 2 birds per cage system. Body weight and liver weight were determined. Liver lipid expressed as g. lipid/100 g. of dry liver weight was determined by the method described previously (Hamilton and Garlich, 1971) after homogenizing the entire liver. Data for egg production, feed efficiency, egg weight, blood and meat spots for the previous 80 day period were obtained from the records of the Random Sample Tests. Mortality figures covered all 350 days of the test. All birds which died during the Random Sample Test were necropsied and the cause of death assigned. Statistical analyses and correlations were obtained through use of the computerized Statistical Analysis System of the Department of Statistics and Biomathematics, North Carolina State University (Service, 1972). RESULTS The frequency distribution of the 724 individual values for liver lipid are shown in
28 r ~24
2 20 16
S 12 z ui
3 8
i±j
rr "• 4 1 0 13 21 29 37 45 53 61 LIVER LIPID (% of dry weight) FIG. 1. Frequency distribution of 724 individual liver lipid values.
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and Griffith, 1973), surfeit caloric intake (Nesheim and Ivy, 1970, Wolford and Polin, 1974) and quantity and source of dietary lipid (Weiss and Fisher, 1957; Bragg et al, 1973). A genetic predisposition may also contribute (Nesheim and Ivy, 1970). Griffith et al. (1969) observed that caged layers had higher liver lipid values than hens in floor pens. Few of the many publications concerning the liver lipid content of laying hens have indicated the variety of hen used. Similarly, several different confinement systems have been used in the various studies, but there is insufficient information to estimate the magnitude of the effects of this variable on liver lipid. The objectives of the survey reported here were (1) to determine whether there were differences in liver lipid attributable to variety, to confinement system, or an interaction between them, (2) to determine whether there were correlations between liver lipid and selected physiological and economic traits, and (3) to attempt to define a "normal" range of liver lipid values for hens in the latter part of their laying year.
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J. D . GARLICH, J. D . OLSON, W.
TABLE 1.—Liver lipid values for all varieties in each confinement system
E . H U F F AND P . B . HAMILTON
ranged from 25.8 to 49.0% lipid. T h e average w a s 38.2%. T h e r e were 4 varieties which w e r e consistently high and 5 which w e r e consistently low in liver lipid (Table 2). A variety w a s considered consistently high or low if t h e s e variety m e a n s in all 3 confinement s y s t e m s were either all a b o v e , or all below, the overall m e a n of 38.2%. T h e liver lipid values for the remaining varieties are s h o w n in Table 3.
Range Mean of all of all Confinement Varieties varieties' varieties system (N) 7 hens/cage 20 36.6 a2 ± 4.7 25.8-48.4 Floor pens 20 37.8 a ±3.9 31.2-46.0 2 hens/cage 19 40.1 b ± 3.5 34.4 - 49.0 •Values in these columns are the mean liver lipid as percent of dry weight + S.D. 2 Means not followed by the same letter are significantly different (P < 0.05).
T h e r e w e r e highly significant differences in liver lipid a m o n g the 3 confinement systems (P < 0.0014), a m o n g the 20 varieties (P < 0.0003), and a significant system x variety interaction (P < 0.05). Table 1 shows the liver lipid values for each confinement system. H e n s confined to 2 bird cages had slight but significantly greater liver lipid than hens in the other 2 s y s t e m s . T h e variety m e a n s
different from each other. The correlations of liver lipid content, body weight and relative liver weight are shown in Table 4. The correlations were obtained from individual hen values across all varieties within each system. The number of hens (N)
TABLE 2.— Varieties which were consistently high or low in liver lipid in all confinement
Variety Thornber (808) Tatum (T-100) Colonial (365-B) Babcock (B-300)
7 hens/cage 40.01 39.5 39.4 39.0 39.5
Confinement system Floor pens 39.4 40.2 40.8 46.0
2 hens/cage 49.0 43.7 42.0 38.9
41.6
43.4
systems
Variety means 42.8 41.1 40.7 41.3
2
Overall mean 41.50, S.D. = 3.6, N = 12 Welps (971) Dekalb (171) Davis (Combiner) Anthony (W. Leg.) Tatum (T 111)
37.3 32.7 32.0 30.6 25.8 31.7
34.9 37.0 34.3 37.2 35.0 35.7 2
35.9 38.0 36.1 34.7 36.2
36.0 34.8 34.8 34.6 31.8
Overall mean 34.4 , S.D. = 3.2, N = 14 'Values in the table are the mean liver lipid expressed as percent of dry weight. 2 The overall means of the varieties that were consistently high differed significantly from the means of the varieties that were significantly low (P < 0.001).
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T h e 59 individual variety m e a n s w e r e ranked lowest to highest. D u n c a n ' s multiple range test w a s used to determine shortest significant ranges (P < 0.05). F r o m t h e low end of the range, m e a n s of 2 5 . 8 % through 4 1 . 1 % were not significantly different from each other. For the range which most closely b r a c k e t e d the overall mean of 3 8 . 2 % , m e a n s from 32.7% through 4 3 . 7 % were not different. F r o m the high end of the range, m e a n s from 3 8 . 1 % through 4 9 . 0 1 % were not significantly
Figure 1. T h e m e a n value was 38.2% with a standard deviation of 10.5. T h e median value was 40.2%. T h e r a n g e for individual birds was 10.3 t o 84.5%. T h e r e was a continuous distribution b e t w e e n 15.4 and 65.4%. There were only 3 values below 15.4 and 2 values a b o v e 65.4%.
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LIVER LIPID OF LAYING HENS
TABLE 3.—Mean liver lipid content for varieties of laying hens that were not consistently high or low Confinement system Variety
7 hens/cage
Floor pens
2 hens/cage
Variety means
Shaver (Exptl.) H & N (Nick Chick) Kimber (K-137) Ideal (236) Ind. Fm. Bu. (Du. 60) Hy-Line (W36) Shaver (288) Parks (Keystone) H & N (Exptl. A) Hubbard (Gld. C.) Babcock (B-390)
48.41 41.9 38.9 38.1 37.8 36.6 36.4 35.2 34.4 34.1 33.3
31.2 37.4 41.1 44.7 38.2 32.5 39.7 35.6 40.6 32.6 38.1
37.8 42.3 34.4 42.9 42.2 39.4 41.4 39.4 41.9 41.8 42.0
39.1 40.5 38.1 41.9 39.4 36.2 39.2 36.7 39.0 36.2 37.8
'Values in the table are the mean liver lipid of 9 to 15 hens expressed at percent of dry weight. 0.575 X 2 . For floor pens, N = 227 : Y = 25.48 - 3.20 X; + 0.38 X 2 . For two hens per cage, N = 266 : Y = 27.69 - 2.47 X , + 0.384 X 2 . For all three confinement systems combined, N = 724 : Y = 25.55 - 3.06 X, + 0.404 X 2 . Correlations of liver lipid content, liver weight and body weight with other economically important traits are shown in Table 5. The results are shown for each of the 3 confinement systems. Only for 7 hens/cage is liver lipid content significantly correlated with any of these traits. These are negative correlations of liver lipid content with kg. of feed per dozen eggs, and egg weight in kg. per dozen, and incidence of blood and meat spots. There was no significant correlation of liver lipid content with mortality in any of the 3 confinement systems.
TABLE 4.—Correlations of body weight, relative liver weight, and liver lipid within each confinement system 7 hens/cage 1 Liver weight 2 Body weight (kg.)
Liver lipid 3
-0.311 0.051 (P < 0.0001) (P < 0.55)
Liver weight (g./lOO g. body weight)
—
N
231
0.430 (P < 0.0001)
Floor pens Liver weight 2
Liver lipid 3
2 hens/cage Liver weight 2
Liver lipid 3
-0.128 0.140 -0.129 0.174 (P < 0.052) (P < 0.033) (P < 0.033) (P < 0.005) — 227
0.371 (P < 0.001)
—
0.396 (P < 0.001)
266
'Values in the table are the correlation coefficients between the indicated parameters followed in parentheses by the probability of the correlation coefficient being significant. 2 Liver weight expressed as g./lOO g. of body weight. 'Liver lipid expressed as percent of dry weight.
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in each system in indicated. Relative liver weight correlated positively and significantly with liver lipid content in all 3 systems. Relative liver weight was negatively and significantly correlated with body weight in all 3 systems. Liver lipid content was positively and significantly correlated with body weight for hens from floor pens and 2 bird cages, but not for 7 hens per cage. This latter observation corresponds to the relatively strong, very highly significant negative correlation of body weight with relative liver weight for the hens in 7 bird cages. The following regression equations relate liver lipid content to body weight and fresh liver weight. Y is liver lipid as % of dry weight, Xj is body weight in kg., X 2 is fresh liver weight in grams. For seven hens per cage, N = 231 : Y = 22.14 - 5.86 X, +
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TABLE 5. —Correlations of selected economic traits
Egg production' (eggs/ hen/day)
Feed conversion' Egg weight 1 (kg. feed/ (kg./ dozen dozen eggs) eggs) (7 hens/cage) 3 0.755 0.648 (0.0003) (0.002)
Blood, meat spots 1 (%of total eggs)
Mortality 2 (%of total)
0.837 (0.0001)
-0.129 (0.595)
- 0.4795 (0.031) 0.645 (0.002) 0.370 (0.105)
-0.747 (0.0003) -0.437 (0.052)
-0.699 (0.0009) -0.601 (0.005)
-0.789 (0.0001) -0.540 (0.013)
0.037 (0.870) -0.162 (0.502)
Body weight (kg.) P s Liver weight (g./lOOg. body weight Ps Liver lipid (%) P<
0.136 (0.574)
(Floor pens) 3 0.381 0.307 (0.095) (0.186)
0.729 (0.0005)
-0.267 (0.254)
0.365 (0.873) 0.189 (0.571)
-0.263 (0.261) -0.263 (0.262)
-0.471 (0.034) -0.285 (0.221)
-0.663 (0.002) 0.367 (0.108)
-0.154 (0.522) -0.159 (0.508)
Body weight (kg.) P s Liver weight (g./lOOg. body weight) P< Liver lipid (%) Ps
-0.245 (0.310)
(2 hens/cage) 4 0.684 0.450 (0.002) (0.051)
0.614 (0.005)
-0.114 (0.647)
-0.083 (0.734) -0.280 (0.245)
-0.271 (0.262) 0.130 (0.603)
-0.589 (0.008) -0.120 (0.628)
0.155 (0.534) -0.299 (0.211)
-0.437 (0.059) -0.080 (0.744)
Values for these parameters are based on the last 80 days of the random sample test. are based on the mortality during the last 350 days of the test.
2 Values for this parameter 3 N = 20 varieties. 4 N = 19 varieties. 5
Values in the table are the correlation coefficients between the indicated traits followed in parentheses by the probability level for the correlation coefficient. All hens which died during the 350 day laying year were necropsied by a veterinary pathologist. Fifty-five cases of liver hemorrhage were observed. The combined mortality from all causes was 736 out of the 5840 hens which started the laying year. Thus, mortality from all causes was 12.6% while mortality associated with hemorrhage was 0.74%, or stated another way, liver hemorrhage was observed in 7.47% of all cases of mortality. The laying year was divided into quarters with the first 3 quarters containing 90 days and the last 80 days. The cases of liver hemorrhage reported by quarters were 8, 7,
18, and 22 respectively. Thus 72% of the cases of liver hemorrhage were observed in the last half of the laying year. Tabulation by confinement system indicated 16, 22, and 17 cases respectively for 7 hens/cage, floor pens, and 2 hens/cage. Three of the 20 varieties of hens present had no case and 4 varieties had only 1 case of liver hemorrhage. Only 2 varieties had greater than 5 cases. One variety (Ind. Fm. Bu.) of 304 hens had 61 cases of mortality of which liver hemorrhage was associated with 9. The average liver lipid content determined for this variety was 39.4%. Another variety (Tatum,
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Body weight (kg.) P< Liver weight (g./lOOg. body weight) P< Liver lipid (%) P s
LIVER LIPID OF LAYING HENS
T-100) of 304 hens had 45 cases of mortality of which liver hemorrhage was associated with 10. Average liver lipid content determined for this variety was 41.1%. Liver lipid was not determined on the hemorrhaged livers observed at necropsy of hens which died during the laying year. The incidence of non-fatal liver hemorrhage is not known. A liver hemorrhage score (e.g. Wolford and Polin, 1974) was not determined on the livers of the hens killed for the liver lipid survey taken at the end of the laying year.
Hens confined 2/cage had significantly higher liver lipid content than hens in other confinement systems (P < 0.05; Table 1). Griffith et al. (1969) reported significantly greater liver lipid content in hens confined 2/cage as compared to floor pens. The degree of activity or inactivity as it relates to energy consumption and expenditure may play a role. Nesheim and Ivy (1970) and Wolford and Polin (1974) showed a relationship between energy intake, body weight, and liver lipid content. Our results indicate a significant, positive correlation between body weight and liver lipid for hens confined 2/cage and in floor pens but not 7/cage (Table 4). There were no significant correlations between liver lipid content and egg production (Table 5). There were very highly significant differences among varieties (P < 0.0003). The results shown in Table 2 indicate that some varieties have consistently low, and others consistently high liver lipid content regardless of the confinement. Nesheim and Ivy (1970) presented evidence which indicated possible genetic predisposition to the development of excessive liver lipid and death from liver hemorrhage. Of the many literature reports concerning factors which contribute to the accumulation of liver lipid, few identify the variety of hen. Genetic differences may account for the disparity among various investigations in the effectiveness of certain
lipotropic agents or in the magnitude of the differences in treatment response to the development of fatty livers. There was a statistically significant variety x confinement system interaction (P < 0.05). The mechanism whereby their interaction becomes manifest is not known. The effect of confinement and its interaction with variety deserves further study. There was no significant correlation of liver lipid content with rate of egg production, feed conversion, or mortality (Table 5). Nesheim et al. (1969) observed no correlation between liver lipid and rate of egg production in a flock with "Liver Hemorrhage Syndrome." The latter report and the report of Wolford and Polin (1972) indicated that high liver lipid content per se does not necessarily result in increased rate of mortality, although the hens laying at a normal rate that died from hemorrhage had a fatty liver. In the present study, there is no indication that the high liver lipid values adversely influenced the performance of any of the flocks studied except in the 7 hens/cage system where there was a significant negative correlation between liver lipid and egg weight. There was a positive correlation of liver lipid content with relative liver size as expected (Table 4). There was a negative correlation between body weight and relative liver weight. This indicates that as body weight increased, liver weight did not increase proportionately. The regression equations which relate liver lipid to body and liver weight are similar but not identical for the 3 systems. It is suggested that these equations may serve as a guide to the diagnosis of excessively fatty liver in hens in the latter half of their laying year. Whereas under field conditions it is often difficult or impractical to obtain a laboratory determination of liver lipid content, it is relatively easy to weigh both the hen and liver and from the appropriate equation obtain an estimate of liver lipid content.
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DISCUSSION
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J. D. GARLICH, J. D. OLSON, W. E. HUFF AND P. B. HAMILTON
Nesheim et al. (1969) and Griffith et al. (1969) observed that liver lipid content in their varieties of hens increased with age and were influenced by season of the year. The hens in the present report were 71 weeks of age and liver lipid values were obtained in August. We observed that 72% of the cases of liver hemorrhage occurred in the second half of the laying year.
To the extent that the combined varieties of hens in our sample is representative of the general population, a discussion of "expected" values and definition of a normal range for liver lipid content is in order. The overall mean of the individual values was 38.2 g. of lipid per 100 g. dry liver weight
ACKNOWLEDGEMENTS The authors thank the following for their assistance: Dr. Grady A. Martin, Mr. T. R. Burleson, Jr., Mr. Clyde Z. McSwain, Mrs. Jolayne Service, Mr. John Gray, Mr. Gorum
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Wolford and Polin (1974) reported an increase in liver hemorrhage score with increased liver lipid. In the present study the incidence of liver hemorrhage during the year was determined from necropsy reports, since by definition birds with liver hemorrhage syndrome die from liver hemorrhage. The number of liver hemorrhages associated with mortality (53 out of 736 cases of mortality from a population of 5840 hens) was distributed over 17 varieties. This incidence was too low to obtain meaningful correlations with the other parameters which were measured. Nesheim and Ivy (1970) observed that of 39 cases of death due to the liver hemorrhage 11 were granddaughters of one sire and 6 were granddaughters of another. In the present study, the 2 varieties of hens which had the highest incidence of liver hemorrhage were not exceptional with regard to liver lipid content, body weight, or rate of lay. Other varieties had similar or higher values for body weight or liver lipid content, but a lower incidence of reported liver hemorrhage. In the present study the incidence of excessive liver lipid and reported liver hemorrhage was sufficiently low that it may be concluded that a "Fatty Liver Syndrome" or "Liver Hemorrhage Syndrome" had not occurred in any of the flocks.
with a S.D. of 10.5. Two thirds of the population is included in the range 27.5 to 48.7. The frequency distribution curve (Fig. 1) for the 724 individual values for liver lipid shows a rapid increase from 15% liver lipid to a peak near 30%. On the descending side there is a pronounced shoulder in the region between 37% and 45% liver lipid. Subsequently there is a rapid decrease in frequency of high liver lipid values. This distribution is probably explained by the significantly higher mean liver lipid content of hens confined 2 per cage (Table 1) and by the presence of 5 varieties with consistently low liver lipid values and 4 varieties with consistently high liver lipid values in all 3 confinement systems (Table 2). Nesheim et al. (1969) reported that of 21 hens which died of liver hemorrhage the range of liver lipid was 46 to 83% with a mean of 65.2%. Several factors reportedly cause elevated liver lipid values: e.g., dietary deficiency of lipotropic nutrients (Shexnailder and Griffith, 1973), 8% dietary tallow (Bragg et al., 1973), surfeit feed consumption (Wolford and Polin, 1972, 1974) and aflatoxin (Hamilton and Garlich, 1971, 1972). In all cases, these factors produce liver lipid values near or above 49 g. lipid/100 g. of dry liver weight. It would appear that a "normal" range of liver lipid values for a flock of laying hens should be between 25 and 49%. In consideration of the reported tendency toward liver hemorrhage in hens with liver lipid values near 46% and above (Nesheim et al., 1969; Wolford and Polin, 1972, 1974) flocks with average liver lipid values near or above the upper range should be investigated for the presence of factors which contribute toward the elevation of liver lipid content.
LIVER LIPID OF LAYING H E N S
W. Whitaker, M r s . Sharon W e s t and Miss N a n c y Goodwin. REFERENCES
fluencingthe liver fat content of laying hens. Poultry Sci. 52: 281-291. Nesheim, M. C , and C. A. Ivy, 1970. Factors influencing liver fat deposition in laying hens. Proc. Cornell Nutrition Conference, p. 43-49. Nesheim, M. C , C. A. Ivy and M. J. Norvell, 1969. Some observations on fatty livers in laying hens. Proc. Cornell Nutrition Conference, p. 36-41. Schexnailder, R., and M. Griffith, 1973. Liver fat and egg production of laying hens as influenced by choline and other nutrients. Poultry Sci. 52: 1188-1194. Service, J. A., 1972. A User's Guide to the Statistical Analysis System. Department of Statistics, North Carolina State University. Velu, J. G., D. H. Baker and H. M. Scott, 1971. Protein and energy utilization by chicks fed graded levels of a balanced mixture of crystalline amino acids. J. Nutrition, 101: 1249-1256. Weiss, H. S., and H. Fisher, 1957. Plasma lipid and organ changes associated with the feeding of animal fat to laying chickens. J. Nutrition, 61: 267-280. Wolford, J. H., and D. Murphy, 1972. Effect of diet on fatty liver-hemorrhagic syndrome incidence in laying chickens. Poultry Sci. 51: 2087-2094. Wolford, J. H., and D. Polin, 1972. Lipid accumulation and hemorrhage in livers of laying chickens. A study on fatty liver-hemorrhagic syndrome. Poultry Sci. 51: 1707-1713. Wolford, J. H., and D. Polin, 1974. Induced fatty liver-hemorrhagic syndrome and accumulation of hepatic lipid in force-fed laying chickens. Poultry Sci. 53: 65-74. Wyatt, R. D., D. M. Briggs and P. B. Hamilton, 1973. The effect of dietary aflatoxin on mature broiler breeder males. Poultry Sci. 52: 1119-1123.
NEWS AND NOTES (Continued from page 805) the inorganic substances, adaptation to the particular substance in excess, and storage of the excess in inedible and less metabolically active sites such as bone. "In addition, animals have a liver, a most remarkable organ that, in effect, filters the blood and removes waste products or foreign substances. These are either accumulated in the liver (as with heavy metals) or metabolized to a greater or lesser degree (as with organic substances). Most of the metabolized substances are then excreted.
"The combined action of all these mechanisms makes the animal very effective in excreting most substances it does not need, even though small quantities may be absorbed temporarily from the digestive tract. "As a consequence of the various selective and protective mechanisms in plants and animals, the linkage between the presence of a certain concentration of a toxic substance in irrigation water or in livestock drinking water and the toxicity of the resulting crop and animal products used as human food
(Continued on page 844)
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Balnave, D., 1972. The effects of temperature and length of exposure on liver composition and hepatic lipogenic enzyme activity in the immature male chick (Gallus domesticus). Comp. Biochem. Physiol. 43: 999-1007. Bragg, D. B., J. S. Sim and G. C. Hodgson, 1973. Influence of dietary energy source on performance and fatty liver syndrome in White Leghorn laying hens. Poultry Sci. 52: 736-740. Couch, J. R., 1956. Fatty livers in laying hens. A condition which may occur as a result of increased strain. Feedstuffs, 28(47): 46, 54. Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics 11: 1-42. Garlich, J. D., H. T. Tung and P. B. Hamilton, 1973. The effects of short term feeding of aflatoxin on egg production and some plasma constituents of the laying hen. Poultry Sci. 52: 2206-2211. Griffith, M., A. H. Olinde, R. Schexnailder, R. F. Davenport and W. F. McKnight, 1969. Effect of choline, methionine and vitamin B12 on liver fat, egg production and egg weight in hens. Poultry Sci. 48: 2160-2172. Hamilton, P. B., and J. D. Garlich, 1971. Aflatoxin as possible cause of fatty liver syndrome in laying hens. Poultry Sci. 50: 800-804. Hamilton, P. B., and J. D. Garlich, 1972. Failure of vitamin supplementation to alter the fatty liver syndrome caused by aflatoxin. Poultry Science 51: 689-692. Ivy, C. A., and M. C. Nesheim, 1973. Factors in-
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Department of Poultry Science, North Carolina State University, Raleigh, North Carolina 27607 (Received for publication August 27, 1974)
POULTRY SCIENCE 54: 806-813, 1975
et al, 1969; Nesheim and Ivy, 1970; Wolford and Polin, 1972; Ivy and Nesheim, 1973). Excessive liver lipid has been associated with reduced egg production and mortality. In 1956 Couch described a "Fatty Liver Syndrome" (FLS). The symptoms included a sudden reduction in egg production, a yellow, friable liver which was high in lipid, and usually excessive abdominal fat. Flock mortality was sometimes increased. Nesheim et al. (1969) reported that sudden mortality in hens laying at a normal rate was the result of hemorrhage of the liver and that these livers were usually very high in lipid content (46 to 83% dry weight). The terminology "Liver Hemorrhage Syndrome" was proposed to describe the condition (Nesheim and Ivy, 1970). The association of the incidence of spontaneous liver hemorrhage with the high liver lipid values has been confirmed (Wolford and Polin, 1972; Wolford and Murphy, 1972).
INTRODUCTION
T
HE lipid content of the liver of normal growing chicks, adult cockerels, and non-laying pullets is low and the range of values is usually narrow (Balnave, 1972; Velu et al., 1971). The average liver lipid content expressed as a percent of dry weight were for: adult cockerels 12.9 (Wyatt et al, 1973); 15 nineteen week old Leghorn pullets (nonlaying; no developed ova) 19.8 ± 0.4, range 17.7 to 21.7 (unpublished observations). In contrast the liver lipid content of groups of laying hens may average from 24 to 76 percent (Griffith et al., 1969; Wolford and Polin, 1974). In other reports the range of individual values varied from 20 to 83 percent (Nesheim
1. Paper number 4458 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, North Carolina. 2. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Experiment Station nor criticism of similar products not mentioned. 3. A preliminary report of this work was presented at the sixty-third annual Poultry Science Association Meetings, Morgantown, West Virginia, August 1974.
The factors which may contribute to the accumulation of excessive liver lipid include aflatoxin (Hamilton and Garlich, 1971, 1972; Garlich et al, 1973), dietary deficiencies and environmental temperature (Schexnailder 806
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ABSTRACT Average liver lipid values were determined for 20 varieties of 71-week old laying hens managed in 3 confinement systems of the 1972-73 North Carolina Random Sample Laying Test. There were highly significant differences in liver lipid attributable to variety, to confinement system, and a significant variety x system interaction. Four varieties had consistently high and five had consistently low liver lipid values in all 3 confinement systems. Variety means ranged from 25.8 to 49.0% liver lipid on a dry weight basis. Hens confined 2/cage had slight but significantly higher liver lipid than hens 7/cage or in floor pens. Liver lipid was positively correlated with body weight in hens 2/cage and in floor pens. There were no significant correlations of liver lipid with egg production or mortality. A frequency distribution of individual liver lipid values revealed a continuous distribution from 15.4 to 65.4% with a pronounced skew to the right of the mean of 38.2%. Neither a fatty liver syndrome nor liver hemorrhage syndrome was reported for any of the flocks during the laying year. The normal range of liver lipid values for hens 71 weeks of age appears to be between 25 and 49 g. of lipid per 100 g. of dry liver weight.
807
LIVER LIPID OF LAYING HENS
MATERIALS AND METHODS The 724 hens used in this study were obtained upon completion of the 1972-73 North Carolina Random Sample Laying Tests 4 on 14 August, 1973. They were 71 weeks of age. Twenty varieties of hens were represented in each of 3 confinement systems. The confinement systems were 2 birds per 25 x 45 cm. cage, 7 birds per 61 x 51 cm. cage, and 50 birds on half slats-half litter floor pens with 0.158 m.2 (1.7 sq. ft.) of floor space per bird. A total of 5840 hens began the laying year. All confinement systems were located on the same farm and all hens received feed of the same formulation. Twelve (or
4. Copies of the Fourteenth North Carolina Random Sample Test report may be obtained from Mr. T. R. Burleson, Jr., Piedmont Research Station, Route #6, Box 420, Salisbury, N.C. 28144.
in some cases 15) hens were selected at random from each variety in each confinement system. One variety was not represented in the 2 birds per cage system. Body weight and liver weight were determined. Liver lipid expressed as g. lipid/100 g. of dry liver weight was determined by the method described previously (Hamilton and Garlich, 1971) after homogenizing the entire liver. Data for egg production, feed efficiency, egg weight, blood and meat spots for the previous 80 day period were obtained from the records of the Random Sample Tests. Mortality figures covered all 350 days of the test. All birds which died during the Random Sample Test were necropsied and the cause of death assigned. Statistical analyses and correlations were obtained through use of the computerized Statistical Analysis System of the Department of Statistics and Biomathematics, North Carolina State University (Service, 1972). RESULTS The frequency distribution of the 724 individual values for liver lipid are shown in
28 r ~24
2 20 16
S 12 z ui
3 8
i±j
rr "• 4 1 0 13 21 29 37 45 53 61 LIVER LIPID (% of dry weight) FIG. 1. Frequency distribution of 724 individual liver lipid values.
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and Griffith, 1973), surfeit caloric intake (Nesheim and Ivy, 1970, Wolford and Polin, 1974) and quantity and source of dietary lipid (Weiss and Fisher, 1957; Bragg et al, 1973). A genetic predisposition may also contribute (Nesheim and Ivy, 1970). Griffith et al. (1969) observed that caged layers had higher liver lipid values than hens in floor pens. Few of the many publications concerning the liver lipid content of laying hens have indicated the variety of hen used. Similarly, several different confinement systems have been used in the various studies, but there is insufficient information to estimate the magnitude of the effects of this variable on liver lipid. The objectives of the survey reported here were (1) to determine whether there were differences in liver lipid attributable to variety, to confinement system, or an interaction between them, (2) to determine whether there were correlations between liver lipid and selected physiological and economic traits, and (3) to attempt to define a "normal" range of liver lipid values for hens in the latter part of their laying year.
808
J. D . GARLICH, J. D . OLSON, W.
TABLE 1.—Liver lipid values for all varieties in each confinement system
E . H U F F AND P . B . HAMILTON
ranged from 25.8 to 49.0% lipid. T h e average w a s 38.2%. T h e r e were 4 varieties which w e r e consistently high and 5 which w e r e consistently low in liver lipid (Table 2). A variety w a s considered consistently high or low if t h e s e variety m e a n s in all 3 confinement s y s t e m s were either all a b o v e , or all below, the overall m e a n of 38.2%. T h e liver lipid values for the remaining varieties are s h o w n in Table 3.
Range Mean of all of all Confinement Varieties varieties' varieties system (N) 7 hens/cage 20 36.6 a2 ± 4.7 25.8-48.4 Floor pens 20 37.8 a ±3.9 31.2-46.0 2 hens/cage 19 40.1 b ± 3.5 34.4 - 49.0 •Values in these columns are the mean liver lipid as percent of dry weight + S.D. 2 Means not followed by the same letter are significantly different (P < 0.05).
T h e r e w e r e highly significant differences in liver lipid a m o n g the 3 confinement systems (P < 0.0014), a m o n g the 20 varieties (P < 0.0003), and a significant system x variety interaction (P < 0.05). Table 1 shows the liver lipid values for each confinement system. H e n s confined to 2 bird cages had slight but significantly greater liver lipid than hens in the other 2 s y s t e m s . T h e variety m e a n s
different from each other. The correlations of liver lipid content, body weight and relative liver weight are shown in Table 4. The correlations were obtained from individual hen values across all varieties within each system. The number of hens (N)
TABLE 2.— Varieties which were consistently high or low in liver lipid in all confinement
Variety Thornber (808) Tatum (T-100) Colonial (365-B) Babcock (B-300)
7 hens/cage 40.01 39.5 39.4 39.0 39.5
Confinement system Floor pens 39.4 40.2 40.8 46.0
2 hens/cage 49.0 43.7 42.0 38.9
41.6
43.4
systems
Variety means 42.8 41.1 40.7 41.3
2
Overall mean 41.50, S.D. = 3.6, N = 12 Welps (971) Dekalb (171) Davis (Combiner) Anthony (W. Leg.) Tatum (T 111)
37.3 32.7 32.0 30.6 25.8 31.7
34.9 37.0 34.3 37.2 35.0 35.7 2
35.9 38.0 36.1 34.7 36.2
36.0 34.8 34.8 34.6 31.8
Overall mean 34.4 , S.D. = 3.2, N = 14 'Values in the table are the mean liver lipid expressed as percent of dry weight. 2 The overall means of the varieties that were consistently high differed significantly from the means of the varieties that were significantly low (P < 0.001).
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T h e 59 individual variety m e a n s w e r e ranked lowest to highest. D u n c a n ' s multiple range test w a s used to determine shortest significant ranges (P < 0.05). F r o m t h e low end of the range, m e a n s of 2 5 . 8 % through 4 1 . 1 % were not significantly different from each other. For the range which most closely b r a c k e t e d the overall mean of 3 8 . 2 % , m e a n s from 32.7% through 4 3 . 7 % were not different. F r o m the high end of the range, m e a n s from 3 8 . 1 % through 4 9 . 0 1 % were not significantly
Figure 1. T h e m e a n value was 38.2% with a standard deviation of 10.5. T h e median value was 40.2%. T h e r a n g e for individual birds was 10.3 t o 84.5%. T h e r e was a continuous distribution b e t w e e n 15.4 and 65.4%. There were only 3 values below 15.4 and 2 values a b o v e 65.4%.
809
LIVER LIPID OF LAYING HENS
TABLE 3.—Mean liver lipid content for varieties of laying hens that were not consistently high or low Confinement system Variety
7 hens/cage
Floor pens
2 hens/cage
Variety means
Shaver (Exptl.) H & N (Nick Chick) Kimber (K-137) Ideal (236) Ind. Fm. Bu. (Du. 60) Hy-Line (W36) Shaver (288) Parks (Keystone) H & N (Exptl. A) Hubbard (Gld. C.) Babcock (B-390)
48.41 41.9 38.9 38.1 37.8 36.6 36.4 35.2 34.4 34.1 33.3
31.2 37.4 41.1 44.7 38.2 32.5 39.7 35.6 40.6 32.6 38.1
37.8 42.3 34.4 42.9 42.2 39.4 41.4 39.4 41.9 41.8 42.0
39.1 40.5 38.1 41.9 39.4 36.2 39.2 36.7 39.0 36.2 37.8
'Values in the table are the mean liver lipid of 9 to 15 hens expressed at percent of dry weight. 0.575 X 2 . For floor pens, N = 227 : Y = 25.48 - 3.20 X; + 0.38 X 2 . For two hens per cage, N = 266 : Y = 27.69 - 2.47 X , + 0.384 X 2 . For all three confinement systems combined, N = 724 : Y = 25.55 - 3.06 X, + 0.404 X 2 . Correlations of liver lipid content, liver weight and body weight with other economically important traits are shown in Table 5. The results are shown for each of the 3 confinement systems. Only for 7 hens/cage is liver lipid content significantly correlated with any of these traits. These are negative correlations of liver lipid content with kg. of feed per dozen eggs, and egg weight in kg. per dozen, and incidence of blood and meat spots. There was no significant correlation of liver lipid content with mortality in any of the 3 confinement systems.
TABLE 4.—Correlations of body weight, relative liver weight, and liver lipid within each confinement system 7 hens/cage 1 Liver weight 2 Body weight (kg.)
Liver lipid 3
-0.311 0.051 (P < 0.0001) (P < 0.55)
Liver weight (g./lOO g. body weight)
—
N
231
0.430 (P < 0.0001)
Floor pens Liver weight 2
Liver lipid 3
2 hens/cage Liver weight 2
Liver lipid 3
-0.128 0.140 -0.129 0.174 (P < 0.052) (P < 0.033) (P < 0.033) (P < 0.005) — 227
0.371 (P < 0.001)
—
0.396 (P < 0.001)
266
'Values in the table are the correlation coefficients between the indicated parameters followed in parentheses by the probability of the correlation coefficient being significant. 2 Liver weight expressed as g./lOO g. of body weight. 'Liver lipid expressed as percent of dry weight.
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in each system in indicated. Relative liver weight correlated positively and significantly with liver lipid content in all 3 systems. Relative liver weight was negatively and significantly correlated with body weight in all 3 systems. Liver lipid content was positively and significantly correlated with body weight for hens from floor pens and 2 bird cages, but not for 7 hens per cage. This latter observation corresponds to the relatively strong, very highly significant negative correlation of body weight with relative liver weight for the hens in 7 bird cages. The following regression equations relate liver lipid content to body weight and fresh liver weight. Y is liver lipid as % of dry weight, Xj is body weight in kg., X 2 is fresh liver weight in grams. For seven hens per cage, N = 231 : Y = 22.14 - 5.86 X, +
810
J. D. GARLICH, J. D. OLSON, W. E. HUFF AND P. B. HAMILTON
TABLE 5. —Correlations of selected economic traits
Egg production' (eggs/ hen/day)
Feed conversion' Egg weight 1 (kg. feed/ (kg./ dozen dozen eggs) eggs) (7 hens/cage) 3 0.755 0.648 (0.0003) (0.002)
Blood, meat spots 1 (%of total eggs)
Mortality 2 (%of total)
0.837 (0.0001)
-0.129 (0.595)
- 0.4795 (0.031) 0.645 (0.002) 0.370 (0.105)
-0.747 (0.0003) -0.437 (0.052)
-0.699 (0.0009) -0.601 (0.005)
-0.789 (0.0001) -0.540 (0.013)
0.037 (0.870) -0.162 (0.502)
Body weight (kg.) P s Liver weight (g./lOOg. body weight Ps Liver lipid (%) P<
0.136 (0.574)
(Floor pens) 3 0.381 0.307 (0.095) (0.186)
0.729 (0.0005)
-0.267 (0.254)
0.365 (0.873) 0.189 (0.571)
-0.263 (0.261) -0.263 (0.262)
-0.471 (0.034) -0.285 (0.221)
-0.663 (0.002) 0.367 (0.108)
-0.154 (0.522) -0.159 (0.508)
Body weight (kg.) P s Liver weight (g./lOOg. body weight) P< Liver lipid (%) Ps
-0.245 (0.310)
(2 hens/cage) 4 0.684 0.450 (0.002) (0.051)
0.614 (0.005)
-0.114 (0.647)
-0.083 (0.734) -0.280 (0.245)
-0.271 (0.262) 0.130 (0.603)
-0.589 (0.008) -0.120 (0.628)
0.155 (0.534) -0.299 (0.211)
-0.437 (0.059) -0.080 (0.744)
Values for these parameters are based on the last 80 days of the random sample test. are based on the mortality during the last 350 days of the test.
2 Values for this parameter 3 N = 20 varieties. 4 N = 19 varieties. 5
Values in the table are the correlation coefficients between the indicated traits followed in parentheses by the probability level for the correlation coefficient. All hens which died during the 350 day laying year were necropsied by a veterinary pathologist. Fifty-five cases of liver hemorrhage were observed. The combined mortality from all causes was 736 out of the 5840 hens which started the laying year. Thus, mortality from all causes was 12.6% while mortality associated with hemorrhage was 0.74%, or stated another way, liver hemorrhage was observed in 7.47% of all cases of mortality. The laying year was divided into quarters with the first 3 quarters containing 90 days and the last 80 days. The cases of liver hemorrhage reported by quarters were 8, 7,
18, and 22 respectively. Thus 72% of the cases of liver hemorrhage were observed in the last half of the laying year. Tabulation by confinement system indicated 16, 22, and 17 cases respectively for 7 hens/cage, floor pens, and 2 hens/cage. Three of the 20 varieties of hens present had no case and 4 varieties had only 1 case of liver hemorrhage. Only 2 varieties had greater than 5 cases. One variety (Ind. Fm. Bu.) of 304 hens had 61 cases of mortality of which liver hemorrhage was associated with 9. The average liver lipid content determined for this variety was 39.4%. Another variety (Tatum,
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Body weight (kg.) P< Liver weight (g./lOOg. body weight) P< Liver lipid (%) P s
LIVER LIPID OF LAYING HENS
T-100) of 304 hens had 45 cases of mortality of which liver hemorrhage was associated with 10. Average liver lipid content determined for this variety was 41.1%. Liver lipid was not determined on the hemorrhaged livers observed at necropsy of hens which died during the laying year. The incidence of non-fatal liver hemorrhage is not known. A liver hemorrhage score (e.g. Wolford and Polin, 1974) was not determined on the livers of the hens killed for the liver lipid survey taken at the end of the laying year.
Hens confined 2/cage had significantly higher liver lipid content than hens in other confinement systems (P < 0.05; Table 1). Griffith et al. (1969) reported significantly greater liver lipid content in hens confined 2/cage as compared to floor pens. The degree of activity or inactivity as it relates to energy consumption and expenditure may play a role. Nesheim and Ivy (1970) and Wolford and Polin (1974) showed a relationship between energy intake, body weight, and liver lipid content. Our results indicate a significant, positive correlation between body weight and liver lipid for hens confined 2/cage and in floor pens but not 7/cage (Table 4). There were no significant correlations between liver lipid content and egg production (Table 5). There were very highly significant differences among varieties (P < 0.0003). The results shown in Table 2 indicate that some varieties have consistently low, and others consistently high liver lipid content regardless of the confinement. Nesheim and Ivy (1970) presented evidence which indicated possible genetic predisposition to the development of excessive liver lipid and death from liver hemorrhage. Of the many literature reports concerning factors which contribute to the accumulation of liver lipid, few identify the variety of hen. Genetic differences may account for the disparity among various investigations in the effectiveness of certain
lipotropic agents or in the magnitude of the differences in treatment response to the development of fatty livers. There was a statistically significant variety x confinement system interaction (P < 0.05). The mechanism whereby their interaction becomes manifest is not known. The effect of confinement and its interaction with variety deserves further study. There was no significant correlation of liver lipid content with rate of egg production, feed conversion, or mortality (Table 5). Nesheim et al. (1969) observed no correlation between liver lipid and rate of egg production in a flock with "Liver Hemorrhage Syndrome." The latter report and the report of Wolford and Polin (1972) indicated that high liver lipid content per se does not necessarily result in increased rate of mortality, although the hens laying at a normal rate that died from hemorrhage had a fatty liver. In the present study, there is no indication that the high liver lipid values adversely influenced the performance of any of the flocks studied except in the 7 hens/cage system where there was a significant negative correlation between liver lipid and egg weight. There was a positive correlation of liver lipid content with relative liver size as expected (Table 4). There was a negative correlation between body weight and relative liver weight. This indicates that as body weight increased, liver weight did not increase proportionately. The regression equations which relate liver lipid to body and liver weight are similar but not identical for the 3 systems. It is suggested that these equations may serve as a guide to the diagnosis of excessively fatty liver in hens in the latter half of their laying year. Whereas under field conditions it is often difficult or impractical to obtain a laboratory determination of liver lipid content, it is relatively easy to weigh both the hen and liver and from the appropriate equation obtain an estimate of liver lipid content.
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DISCUSSION
811
812
J. D. GARLICH, J. D. OLSON, W. E. HUFF AND P. B. HAMILTON
Nesheim et al. (1969) and Griffith et al. (1969) observed that liver lipid content in their varieties of hens increased with age and were influenced by season of the year. The hens in the present report were 71 weeks of age and liver lipid values were obtained in August. We observed that 72% of the cases of liver hemorrhage occurred in the second half of the laying year.
To the extent that the combined varieties of hens in our sample is representative of the general population, a discussion of "expected" values and definition of a normal range for liver lipid content is in order. The overall mean of the individual values was 38.2 g. of lipid per 100 g. dry liver weight
ACKNOWLEDGEMENTS The authors thank the following for their assistance: Dr. Grady A. Martin, Mr. T. R. Burleson, Jr., Mr. Clyde Z. McSwain, Mrs. Jolayne Service, Mr. John Gray, Mr. Gorum
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Wolford and Polin (1974) reported an increase in liver hemorrhage score with increased liver lipid. In the present study the incidence of liver hemorrhage during the year was determined from necropsy reports, since by definition birds with liver hemorrhage syndrome die from liver hemorrhage. The number of liver hemorrhages associated with mortality (53 out of 736 cases of mortality from a population of 5840 hens) was distributed over 17 varieties. This incidence was too low to obtain meaningful correlations with the other parameters which were measured. Nesheim and Ivy (1970) observed that of 39 cases of death due to the liver hemorrhage 11 were granddaughters of one sire and 6 were granddaughters of another. In the present study, the 2 varieties of hens which had the highest incidence of liver hemorrhage were not exceptional with regard to liver lipid content, body weight, or rate of lay. Other varieties had similar or higher values for body weight or liver lipid content, but a lower incidence of reported liver hemorrhage. In the present study the incidence of excessive liver lipid and reported liver hemorrhage was sufficiently low that it may be concluded that a "Fatty Liver Syndrome" or "Liver Hemorrhage Syndrome" had not occurred in any of the flocks.
with a S.D. of 10.5. Two thirds of the population is included in the range 27.5 to 48.7. The frequency distribution curve (Fig. 1) for the 724 individual values for liver lipid shows a rapid increase from 15% liver lipid to a peak near 30%. On the descending side there is a pronounced shoulder in the region between 37% and 45% liver lipid. Subsequently there is a rapid decrease in frequency of high liver lipid values. This distribution is probably explained by the significantly higher mean liver lipid content of hens confined 2 per cage (Table 1) and by the presence of 5 varieties with consistently low liver lipid values and 4 varieties with consistently high liver lipid values in all 3 confinement systems (Table 2). Nesheim et al. (1969) reported that of 21 hens which died of liver hemorrhage the range of liver lipid was 46 to 83% with a mean of 65.2%. Several factors reportedly cause elevated liver lipid values: e.g., dietary deficiency of lipotropic nutrients (Shexnailder and Griffith, 1973), 8% dietary tallow (Bragg et al., 1973), surfeit feed consumption (Wolford and Polin, 1972, 1974) and aflatoxin (Hamilton and Garlich, 1971, 1972). In all cases, these factors produce liver lipid values near or above 49 g. lipid/100 g. of dry liver weight. It would appear that a "normal" range of liver lipid values for a flock of laying hens should be between 25 and 49%. In consideration of the reported tendency toward liver hemorrhage in hens with liver lipid values near 46% and above (Nesheim et al., 1969; Wolford and Polin, 1972, 1974) flocks with average liver lipid values near or above the upper range should be investigated for the presence of factors which contribute toward the elevation of liver lipid content.
LIVER LIPID OF LAYING H E N S
W. Whitaker, M r s . Sharon W e s t and Miss N a n c y Goodwin. REFERENCES
fluencingthe liver fat content of laying hens. Poultry Sci. 52: 281-291. Nesheim, M. C , and C. A. Ivy, 1970. Factors influencing liver fat deposition in laying hens. Proc. Cornell Nutrition Conference, p. 43-49. Nesheim, M. C , C. A. Ivy and M. J. Norvell, 1969. Some observations on fatty livers in laying hens. Proc. Cornell Nutrition Conference, p. 36-41. Schexnailder, R., and M. Griffith, 1973. Liver fat and egg production of laying hens as influenced by choline and other nutrients. Poultry Sci. 52: 1188-1194. Service, J. A., 1972. A User's Guide to the Statistical Analysis System. Department of Statistics, North Carolina State University. Velu, J. G., D. H. Baker and H. M. Scott, 1971. Protein and energy utilization by chicks fed graded levels of a balanced mixture of crystalline amino acids. J. Nutrition, 101: 1249-1256. Weiss, H. S., and H. Fisher, 1957. Plasma lipid and organ changes associated with the feeding of animal fat to laying chickens. J. Nutrition, 61: 267-280. Wolford, J. H., and D. Murphy, 1972. Effect of diet on fatty liver-hemorrhagic syndrome incidence in laying chickens. Poultry Sci. 51: 2087-2094. Wolford, J. H., and D. Polin, 1972. Lipid accumulation and hemorrhage in livers of laying chickens. A study on fatty liver-hemorrhagic syndrome. Poultry Sci. 51: 1707-1713. Wolford, J. H., and D. Polin, 1974. Induced fatty liver-hemorrhagic syndrome and accumulation of hepatic lipid in force-fed laying chickens. Poultry Sci. 53: 65-74. Wyatt, R. D., D. M. Briggs and P. B. Hamilton, 1973. The effect of dietary aflatoxin on mature broiler breeder males. Poultry Sci. 52: 1119-1123.
NEWS AND NOTES (Continued from page 805) the inorganic substances, adaptation to the particular substance in excess, and storage of the excess in inedible and less metabolically active sites such as bone. "In addition, animals have a liver, a most remarkable organ that, in effect, filters the blood and removes waste products or foreign substances. These are either accumulated in the liver (as with heavy metals) or metabolized to a greater or lesser degree (as with organic substances). Most of the metabolized substances are then excreted.
"The combined action of all these mechanisms makes the animal very effective in excreting most substances it does not need, even though small quantities may be absorbed temporarily from the digestive tract. "As a consequence of the various selective and protective mechanisms in plants and animals, the linkage between the presence of a certain concentration of a toxic substance in irrigation water or in livestock drinking water and the toxicity of the resulting crop and animal products used as human food
(Continued on page 844)
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Balnave, D., 1972. The effects of temperature and length of exposure on liver composition and hepatic lipogenic enzyme activity in the immature male chick (Gallus domesticus). Comp. Biochem. Physiol. 43: 999-1007. Bragg, D. B., J. S. Sim and G. C. Hodgson, 1973. Influence of dietary energy source on performance and fatty liver syndrome in White Leghorn laying hens. Poultry Sci. 52: 736-740. Couch, J. R., 1956. Fatty livers in laying hens. A condition which may occur as a result of increased strain. Feedstuffs, 28(47): 46, 54. Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics 11: 1-42. Garlich, J. D., H. T. Tung and P. B. Hamilton, 1973. The effects of short term feeding of aflatoxin on egg production and some plasma constituents of the laying hen. Poultry Sci. 52: 2206-2211. Griffith, M., A. H. Olinde, R. Schexnailder, R. F. Davenport and W. F. McKnight, 1969. Effect of choline, methionine and vitamin B12 on liver fat, egg production and egg weight in hens. Poultry Sci. 48: 2160-2172. Hamilton, P. B., and J. D. Garlich, 1971. Aflatoxin as possible cause of fatty liver syndrome in laying hens. Poultry Sci. 50: 800-804. Hamilton, P. B., and J. D. Garlich, 1972. Failure of vitamin supplementation to alter the fatty liver syndrome caused by aflatoxin. Poultry Science 51: 689-692. Ivy, C. A., and M. C. Nesheim, 1973. Factors in-
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