- Email: [email protected]
On the Problem of Correcting Albumen Quality Measures for Egg Weight1
42
M. G. KIDWELL, A. W. NORDSKOG AND R. H.
REFERENCES Coons, S., 1957. Analysis of covariance as a missing plot technique. Biometrics, 13: 387-405. Giesbrecht, F. G., 1961. Accuracy of estimating age at sexual maturity from pen records of egg production. Unpublished M.S. Thesis. Ames, Iowa, Library, Iowa State University. Goodman, B. L., and G. F. Godfrey, 1955. Genetic, phenotypic and environmental correlations between some egg quality traits and egg production and hatchability. Poultry Sci. 34: 1197. Johnson, A. S., and E. S. Merritt, 1955. Heritability of albumen height and specific gravity of eggs from White Leghorns and Barred Rocks and the correlations of these traits with egg production. Poultry Sci. 34: 578-587. Kilpatrick, L., A. W. Brant and H. L. Shrader,
1960. Equipment and methods for measuring egg quality. U. S. Dept. Agr. Agricultural Marketing Service Bui. 246. King, S. C , J. D. Mitchell, W. H. Kyle and W. J. Stadelman, 1961. Egg quality genetic variation and covariation. Poultry Sci. 40: 965-975. Lorenz, F. W., L. W. Taylor and H. J. Almquist, 1934. Firmness of albumen as an inherited characteristic. Poultry Sci. 13: 14-17. May, K. N., F. J. Schmidt and W. J. Stadelman, 1957. Strain variation in albumen quality decline of hen's eggs. Poultry Sci. 36: 1376-1379. McClary, C. F., and G. E. Bearse, 1956. The genetic correlation of albumen quality in fresh and stored eggs. Poultry Sci. 35: 1157. Mueller, W. J., 1959. Factors affecting the quality loss in egg albumen during storage. Poultry Sci. 38: 843-846. Nordskog, A. W., and O. Kempthorne, 1960. Importance of genotype-environment interactions in random sample poultry tests. International Symposium on Biometrical Genetics, Ottawa, 1958. Biometrical Genetics; proc, edited by Oscar Kempthorne: 159-168. Proudfoot, F. G., 1962. The decline of internal egg quality during storage at 30° and 70°F. among six strains of Leghorns reared in confinement and on range. Poultry Sci. 4 1 : 98-103. Wilcox, F. H., and H. R. Wilson, 1962. Changes in albumen quality with time. Poultry Sci. 4 1 : 883-886.
On the Problem of Correcting Albumen Quality Measures for Egg Weight1 MARGARET GALE KIDWELL, A. W. NORDSKOG AND R. H. FORSYTHE Department of Poultry Science, Iowa State University of Science and Technology, Ames, Iowa (Received for publication May 8, 1963)
F
OR the past decade or more, the Haugh unit has generally been regarded as the best criterion of albumen quality. This is 'Journal Paper No. J-4613 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1326. Part of a thesis submitted by the senior author to the Graduate School of Iowa State University in partial fulfillment of the requirements for the degree of Master of Science.
in a sense, as suggested by Brant et al. (1951) that the "best" criterion is one which is objective, is linearly related to observed albumen quality, and is quick and easy to measure. The Haugh unit is simply the logarithm of albumen height corrected to a standard 24 oz. egg weight. The logarithm transformation converts albumen height to a scale corresponding to subjective grades of broken-out eggs.
Downloaded from http://ps.oxfordjournals.org/ at National Institute of Education Library, Serials Unit on May 20, 2015
Haugh units were statistically significant for eggs broken out "fresh" and for eggs stored seven days. After twenty-one days storage, strain differences were not statistically significant. Repeatabilities for strains tested on different farms were highest for Haugh units fresh and lowest for Haugh unit loss. This investigation, although based on a moderately large sample of strains and eggs, failed to demonstrate that Haugh unit loss is genetically determined.
FORSYTHE
43
ALBUMEN QUALITY MEASURES
MATERIALS AND METHODS
The eggs for this study were produced by three Leghorn lines widely differing in egg size, developed at Iowa State University. (Nordskog and Festing, 1962). Line A, selected for high egg production, lays
standard or medium sized eggs. Line D has been selected solely for large egg size, and Line E has been selected solely for small egg size. Eggs were collected in March, April and May of 1961. After weighing on a Toledo scale between 12 and 36 hours after laying, eggs were assigned to weight classes with intervals of 1 gram. Samples of eggs, broken immediately after weighing, were measured for albumen height with a tripod screw micrometer (Kilpatrick, 1960). Other samples of eggs were stored for various lengths of time up to seven weeks. Albumen heights were then measured after a pre-assigned weight loss had been achieved. Samples of eggs were stored both in the open at a temperature of S6-58°F. and in desiccators containing anhydrous calcium chloride to induce rapid weight loss. From the observed albumen heights grouped in arrays according to initial egg weight classes, the linear regression of albumen height on the mean of each egg weight group was calculated. RESULTS
The distribution of individual eggs according to albumen height and egg weight is illustrated for the medium size egg line A in Figure 1. The results show a low-order relationship between the two variables. Averages for the three lines are summarized in Table 1. Line differences in albumen height are statistically significant as expected because these lines have been selected for wide differences in egg size. The regressions for each of the three lines are shown graphically in Figure 2. Here, the plotted points represent mean albumen height values for each weight class according to line. Differences between the regression coefficients proved to be statistically significant. From the combined data over the three
Downloaded from http://ps.oxfordjournals.org/ at National Institute of Education Library, Serials Unit on May 20, 2015
A recent study by Eisen et al. (1962) questioned the validity of the Haugh unit score as a measure of albumen quality. They reported that the Haugh unit measure did not completely adjust for differences in albumen height associated with egg weight. The regression of albumen height on egg weight was found to be essentially linear and was estimated to be .035. These workers concluded that the linear regression method was superior in correcting for differences in egg weight compared with the Haugh unit egg weight correction method. A question that seems not yet clarified in using the Haugh unit egg weight correction concerns the cause of egg weight differences. In particular, egg weight differences may be due to (I) inherent differences between hens and (II) environmental differences of time, temperature and other storage conditions. Conceivably the regression of albumen height on egg weight as specified by (I) might be quite different from that as specified by (II). This raises a question of the general validity of the Haugh unit correction when no specification is made concerning the causes of the differences in egg weights for which corrections are intended. The purpose of the present investigation was to compare the regression of albumen height on egg weight according to different lines of breeding and causes of egg weight differences as defined by I and II above. Implications to the Haugh unit method of measuring egg albumen quality will then be considered.
44
M. G. KIDWELL, A. W. NORPSKOG AND R. H. FORSYTHE TABLE 1.—Line means and regressions of c men height {II) and egg weight (W)
Line E (Small egg) A (Standard eg, D (Large egg)
No. of
Mean H (mm.)
Mean W (gm.)
Regression coefficient of H on W (mm./gm.)
193 272 125
4.76 5.70 6.30
47.31 58.13 65.76
.030+.009 . 0 4 7 ± .008 ,059±.015
lines, the range in egg size is 38 to 77 grams, and the over-all regression coefficient is .067 mm. of albumen height per gram of egg weight. The latter is greater than any of the three intra-line regression coefficients because the "between line" effect is included. It should be clearly understood that the above regressions pertain only to initial or "inherent" egg weight differences as defined under I above. However, the regression of albumen height on egg weight differences due to storage is also of interest.
8.0or. LU UJ
7.0• « • • •
2
* • •
Z »-
•
6.0
. • • • • • , ,• J•*---"' • —•• • • •
•
•
f •
•
a •
• * «
• • • • • • • • • •* •• • • • • •* » •
•
•
•
•
:
•
|
•
X CD UJ
z
2 5.0 2
•
*
•
4.0
45
_L 50
• • • • • •
JL
55
_
• • •
4
•. • 1 i
GO
•
« ^ — • * - * •
• • l--*--,» *^-*~***J • --)£"— * * • • • • • • £~*~~~~* * • • « • • • •• • • • 1 •• • • •• • • • • • • « • • • • • • •• • • • • • • • • • • • • • • • • • •• • • • • • • 1 • • • • • J •
60
65
_L 70
EGG WEIGHT IN GRAMS FIG. 1. Relationship of initial albumen height to egg weight in Line A.
75
Downloaded from http://ps.oxfordjournals.org/ at National Institute of Education Library, Serials Unit on May 20, 2015
Ordinarily the age of eggs sampled from the trade is not precisely known. Since eggs lose weight in storage, differences in egg weight clearly would influence any corrected measure of albumen heights. Regression coefficients for differing weight loss groups with initial egg weight constant were calculated. The analyses of variance presented in Table 2 were computed from the combined data on all three lines. Fresh eggs represent the zero weight loss class. The remaining three groups consisted of desiccator stored eggs. As expected, linear regression greater than zero proved to be statistically significant in all groups, but deviations from linearity were significant only in the 2 gram and 3 gram weight loss groups. The results suggest that curvilinear regression becomes well established only after a substantial period of storage.
45
ALBUMEN QUALITY MEASURES Y = I.77+.067X ? = 3.38 + .03 X $ = 2.97 •• .047X ? = 2 . 4 0 + .059X
(ALL (LINE (LINE (LINE
A LINE E • LINE A O LINE 0
LINES) E) A) D)
UJ
2
H X e> UJ
x UJ 2
m
4.0 L 35
40
45"
50
55
60
65
70
EGG WEIGHT IN GRAMS FIG. 2, Regression of initial albumen height on egg weight by lines of breeding.
The regressions of albumen height on egg weight according to causes of egg weight differences are presented in Table 3. The regressions denoted as bHw account for initial or inherent differences in egg weight. The differences between the four estimates are not statistically significant, and the over-all average was 0.065 ± .003. Thus, weight loss under the conditions of storage in this experiment apparently did not alter the initial relationship of albumen height to egg weight when the eggs compared were stored under the same condi-
tions. On the other hand, the regression of albumen height on egg weight loss bHL shows a more or less progressive decline with increase in initial egg weight classes. For the lowest egg weight class (44-56 grams), the regression is —0.488 ± .059, and for the highest egg weight class (6870 grams), the regression is —1.020 ± .134. The average regression is —0.636 ± 0.30. Differences in egg weight due to loss in storage, therefore, show about a 10-fold greater effect on albumen height as compared with the effect of inherent differences
TABLE 2.—Analysis of variance of albumen height of fresh and stored eggs Stored
Fresh Weight loss (gm.) 0 Source of variation Linear regression Deviations from linear regressions Error *P<.05. ** P < . 0 1 .
1
2
3
d.f. 1
M.S. 239.57"
d.f. 1
M.S. 71.24"
d.f. 1
M.S. 17.00"
d.f. 1
M.S. 11.08"
39 623
0.73 0.71
22 180
0.79 0.58
22 85
1.18" 0.54
8 26
0.58* 0.21
Downloaded from http://ps.oxfordjournals.org/ at National Institute of Education Library, Serials Unit on May 20, 2015
6.0-
46
M . G. KiDWELL, A. W . NORDSKOG AND R . H . FORSYTHE TABLE 3.—Regression of albumen height {H) on egg weight (W) and egg weight loss (L)
Initial egg
Classes Line
0
44-46
E
4.62 (44)*
47-49
E
50-52
1
2
3
4
All
bflL
Mean albumen height (mm.) 4.03 3.89 2.73 (32) (22) (6)
2.64 (S)
4.11 (109)
-0.488 ± .059
4.71 (42)
4.01 (32)
3.75 (18)
3.08 (5)
2.47 (9)
4.07 (106)
-0.538 + .043
E
4.92 (33)
4.27 (19)
3.63 (12)
2.82 (5)
4.37 (69)
-0.675 + .093
56-58
A
5.71 (46)
5.31 (29)
4.67 (15)
3.64 (5)
5.32 (95)
-0.583 + .086
59-61
A
5.94 (45)
5.35 (28)
4.86 (9)
4.13 (6)
5.52 (88)
-0.585 ± .095
62-64
D
6.28 (35)
5.34 (23)
4.75 (11)
4.47 (6)
5.62 (75)
-0.684 ± .098
65-67
D
6.03 (34)
5.47 (21)
4.99 (10)
4.57 (3)
5.64 (68)
-0.512 ± .106
68-70
D
6.52 (29)
5.41 (20)
4.36 (12)
3.47 (3)
5.62 (64)
-1.020 + .134
5.54 (308)
4.84 (204)
4.26 (109)
3.58 (39)
0.067 + .004
0.072 + .007
0.047 +.009
0.074 +.012
All t>HW
2.53 (14)
/-0.636 Av \ ± .030
1 0.0651 I + .003/AV
Figures in parenthesis are number of eggs.
7.0
x <2 uj i
z UJ
Z m
6.0-
DESICCATOR STORAGE
5.0 4.0 3.0
WEIGHT LOSS IN GRAMS
in egg weight. Mean albumen heights for two samples of eggs from line A kept in a desiccator and under room storage conditions are shown in Figure 3. The regression lines connecting the observations were not fitted statistically. Analyses of variance indicated that deviations from linear regression were not significant when storage was in desiccators. On the other hand, for storage in the open at room temperature, curvilinear
ROOM ST0RA8E
0
1
2
WEIGHT LOSS IN GRAMS
3
FIG. 3. Regression of albumen height on egg weight loss in desiccator and open room storage of two samples of eggs ( A , egg weight range 5658 gms, and • , egg weight range 59-61 gms.).
Downloaded from http://ps.oxfordjournals.org/ at National Institute of Education Library, Serials Unit on May 20, 2015
(gms.)
ALBUMEN QUALITY MEASURES
GU = 100 log [H - b (W - 56.7) ] Where H and W are defined as previously given and b = 0.067 is the combined linear regression coefficient shown in Figure 2. Correlation coefficients then were calculated between HU and GU for both fresh and stored eggs. The correlations came out to be r = .985 for fresh eggs and r = .988 for stored eggs. Thus, it is clear that for all practical purposes, the two methods of correction give identical results. The fact that the Haugh unit has been in common use over the past several years, would favor its continued use. Furthermore, the Haugh unit correction is data-independent and hence, has the property of a distribution-free statistic. DISCUSSION The results of this study show that the relation between albumen height and egg weight is essentially linear for new-laid eggs. This is in accord with the recent study reported by workers at Purdue University (Eisen et al., 1962). However, the present study also shows that the regression of albumen height on egg weight may
differ according to lines of breeding. The lowest regression was in the small egg line, and the highest regression was in the large egg line. Eisen et al. (1962) concluded that the Haugh unit method did not adequately adjust albumen height of individual eggs for egg weight in their data. They raised the question as to the validity and desirability of using the Haugh unit score as a measure of albumen quality. They reported a bias in the Haugh unit regression which resulted in over-estimating albumen height of smaller eggs and in under-estimating albumen height of larger eggs. The Purdue workers suggested that other populations should be studied to determine whether the regression of .035 which they reported is general. In the meantime, they suggested that a linear adjustment of albumen height for egg weight using the regression of .035 would be preferable to the adjustment provided by the Haugh unit formula. This recommendation appears not to be wholly justified from the results of their study. Eisen et al. (1962) compared a least squares derived regression coefficient (b = .035) with a "data-independent" regression coefficient, (b = .05). They pointed out that the latter closely approximates the Haugh unit regression which does not deviate greatly from linearity. Hence, in effect, they compared two linear regression coefficients as to their efficiency in correcting for egg weights. Clearly, the least squares estimate is bound to give a better fit to the data from which it is derived because this is a fundamental property of any least squares estimate. Consequently, the Haugh unit method as approximated by the value of b = .05, gives a poorer fit which they incorrectly interpreted as a bias. Corollary to this is the failure of the Haugh regression to completely remove the correlation between egg weight and adjusted albumen
Downloaded from http://ps.oxfordjournals.org/ at National Institute of Education Library, Serials Unit on May 20, 2015
regression proved to be highly significant. This is not to suggest, however, that any practical significance should be attached to the differences in the nature of the relationship of albumen height and weight losses between room and desiccator storage. The finding that albumen height and inherent egg weight are linearly related is in accord with the recent report by Eisen et al. (1962). However, to compare the net result • of a correction based on the least squares regression method, with the Haugh unit method, albumen heights for all eggs were converted to conventional HU and also into a modified HU (called GU) which contains the least squares egg weight correction defined as follows:
47
48
M. G. KIDWELL, A. W. NORDSKOG AND R. H. FORSYTHE
CONCLUSIONS 1. The linear regression of albumen height on initial egg weight may differ according to lines of breeding. 2. The regression of albumen height on weight loss of eggs due to storage is
about 10 times as great as due to initial or inherent differences in egg weight. 3. The Haugh unit method of adjusting albumen height adequately corrects for initial or inherent egg weight differences and is highly correlated with the least squares regression method of adjustment recommended by Eisen et al. (1962). 4. Correcting albumen height for egg weight appears to be a factor of secondary importance in measuring egg quality differences in trade channels. SUMMARY
The purpose of this investigation was to consider the importance of the egg weight correction as used in the Haugh unit (H.U.) measure of egg albumen quality. Measurements of albumen height and egg weight were taken on eggs from three different egg size strains of Leghorns. Eggs were stored under desiccator conditions for varying lengths of time to induce different amounts of weight loss. The linear regression of albumen height on initial egg weight (bHw) averaged 0.067 mm. per gram of egg but differed according to line of breeding. An egg quality unit, (GU), based on the linear regression of 0.067 but otherwise the same as H.U. was computed. The correlation between GU and H.U. was 0.985 and 0.988 for fresh and stored eggs, respectively, which suggests that the complicated egg weight correction in the Haugh unit is unnecessary. . The regression of albumen height on the egg weight loss in desiccator storage (bHi,) averaged —0.636 for eggs in the same initial egg weight classes. Evidently the Haugh unit corrects only for bHw and not for bHL even though in trade channels, for example, egg weight differences might be due both to genetic and environmental sources. Finally, the importance of egg weight
Downloaded from http://ps.oxfordjournals.org/ at National Institute of Education Library, Serials Unit on May 20, 2015
heights. Indeed, where two sets of variables are linearly related, any regression value other than the least squares estimate, will not completely remove all correlation between the independent variable and the corrected dependent variable. Thus, if a least squares regression of .035 is found in a set of data, but if albumen height is corrected using the regression of .05 (i.e. the Haugh unit correction), a residual correlation is bound to remain between the corcrected values of albumen height and egg weights. Hence, for any particular set of data, the Haugh unit correction cannot be expected to remove all of the correlation of albumen height on egg weight. The importance of an egg weight correction in the Haugh unit seems to have been over-emphasized. For special types of studies, where the age of eggs and other environmental factors can be properly controlled, the use of the Haugh unit as originally defined would seem to be quite justified. On the other hand, in connection with sampling eggs from the trade, the Haugh unit correction for egg weight is probably an unnecessary refinement in view of possible variability in egg weight due to storage-caused differences in egg weight. In fact, Haugh and Jasper (1962), in a recent popular article, concede that egg weight does not materially affect the accuracy of comparisons. Hence, for the trade, the only important feature of the Haugh unit is the logarithm transformation of the albumen height measurement which has long been recognized a useful objective measure corresponding to the USDA quality score.
ALBUMEN QUALITY MEASURES
REFERENCES Brant, A. W., A. W. Otte and K. H. Norris,
1951. Recommended standards for scoring and measuring opened egg quality. Food Technology, 5: 356-361. Eisen, E. J., B. B. Bohren and H. E. McKean, 1962. The Haugh unit as a measure of egg albumen quality. Poultry Sci. 41: 1461-1468. Haugh, R. R., and A. W. Jasper, 1962. It's new —The Haugh unit quality computer. Poultry Processing and Marketing, February: 116-119. Kilpatrick, L., A. W. Brant and H. L. Shrader. 1960. Equipment and methods for measuring egg quality. U.S.D.A. Agric. Marketing Serv. Bui. 246. Nordskog, A. W., and M. Festing, 1962. Selection and correlated responses in the fowl. Proc. X I I World's Poultry Congress, Sydney, Australia, 25-29.
Effect of Light Regime and Age on Reproduction of Turkeys1'2 3. RESTRICTED LIGHT ON YEARLING HENS A. T. LEIGHTON, JR. 3 AND R. N. SHOFFNER Department of Poultry Husbandry, University of Minnesota, St. Paul (Received for publication May 8, 1963)
I
T HAS been demonstrated by numerous investigators that the turkey female becomes refractory to photostimulation when exposed to 13 or more hours of continuous daily light for prolonged periods of time: Harper and Parker (1957, 1960, 1962), McCartney et al. (1961), Leighton and Shoffner (1961a, b), and Shoffner et al. (1962). It has also been demonstrated by 'Published as Paper No. 5121, Scientific Journal Series of the Minnesota Agricultural Experiment Station. 2 A portion of a thesis submitted by the senior author to the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Doctor of Philosophy. 3 Present address: Department of Poultry Science, Virginia Agricultural Experiment Station, Blacksburg, Virginia.
the above workers that the female turkey must be subjected to a period of short days followed by increased or increasing day length in order to be stimulated into satisfactory levels of egg production. Hens that are in egg production will, in most cases, cease production when subjected to a series of short days as shown by Harper and Parker (1957). Their data also showed that when yearling hens were restricted to 9 hours of light per day for a 4 week period and subsequently exposed to 17 hours of light per day, they did not produce eggs at a satisfactory rate. This study investigates further the photoperiodic reproductive responses of yearling female turkeys which had completed 6 months of lay.
Downloaded from http://ps.oxfordjournals.org/ at National Institute of Education Library, Serials Unit on May 20, 2015
correction in measuring albumen quality seems to have been over-emphasized. For special studies, where environmental factors can be adequately controlled, the use of the Haugh unit or a similar quality measure would be quite appropriate. On the other hand, for measuring albumen quality of eggs already graded for size, such as in the trade or where egg weights may vary due to differences in storage, correcting for egg weight is probably an unnecessary refinement.
49
M. G. KIDWELL, A. W. NORDSKOG AND R. H.
REFERENCES Coons, S., 1957. Analysis of covariance as a missing plot technique. Biometrics, 13: 387-405. Giesbrecht, F. G., 1961. Accuracy of estimating age at sexual maturity from pen records of egg production. Unpublished M.S. Thesis. Ames, Iowa, Library, Iowa State University. Goodman, B. L., and G. F. Godfrey, 1955. Genetic, phenotypic and environmental correlations between some egg quality traits and egg production and hatchability. Poultry Sci. 34: 1197. Johnson, A. S., and E. S. Merritt, 1955. Heritability of albumen height and specific gravity of eggs from White Leghorns and Barred Rocks and the correlations of these traits with egg production. Poultry Sci. 34: 578-587. Kilpatrick, L., A. W. Brant and H. L. Shrader,
1960. Equipment and methods for measuring egg quality. U. S. Dept. Agr. Agricultural Marketing Service Bui. 246. King, S. C , J. D. Mitchell, W. H. Kyle and W. J. Stadelman, 1961. Egg quality genetic variation and covariation. Poultry Sci. 40: 965-975. Lorenz, F. W., L. W. Taylor and H. J. Almquist, 1934. Firmness of albumen as an inherited characteristic. Poultry Sci. 13: 14-17. May, K. N., F. J. Schmidt and W. J. Stadelman, 1957. Strain variation in albumen quality decline of hen's eggs. Poultry Sci. 36: 1376-1379. McClary, C. F., and G. E. Bearse, 1956. The genetic correlation of albumen quality in fresh and stored eggs. Poultry Sci. 35: 1157. Mueller, W. J., 1959. Factors affecting the quality loss in egg albumen during storage. Poultry Sci. 38: 843-846. Nordskog, A. W., and O. Kempthorne, 1960. Importance of genotype-environment interactions in random sample poultry tests. International Symposium on Biometrical Genetics, Ottawa, 1958. Biometrical Genetics; proc, edited by Oscar Kempthorne: 159-168. Proudfoot, F. G., 1962. The decline of internal egg quality during storage at 30° and 70°F. among six strains of Leghorns reared in confinement and on range. Poultry Sci. 4 1 : 98-103. Wilcox, F. H., and H. R. Wilson, 1962. Changes in albumen quality with time. Poultry Sci. 4 1 : 883-886.
On the Problem of Correcting Albumen Quality Measures for Egg Weight1 MARGARET GALE KIDWELL, A. W. NORDSKOG AND R. H. FORSYTHE Department of Poultry Science, Iowa State University of Science and Technology, Ames, Iowa (Received for publication May 8, 1963)
F
OR the past decade or more, the Haugh unit has generally been regarded as the best criterion of albumen quality. This is 'Journal Paper No. J-4613 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1326. Part of a thesis submitted by the senior author to the Graduate School of Iowa State University in partial fulfillment of the requirements for the degree of Master of Science.
in a sense, as suggested by Brant et al. (1951) that the "best" criterion is one which is objective, is linearly related to observed albumen quality, and is quick and easy to measure. The Haugh unit is simply the logarithm of albumen height corrected to a standard 24 oz. egg weight. The logarithm transformation converts albumen height to a scale corresponding to subjective grades of broken-out eggs.
Downloaded from http://ps.oxfordjournals.org/ at National Institute of Education Library, Serials Unit on May 20, 2015
Haugh units were statistically significant for eggs broken out "fresh" and for eggs stored seven days. After twenty-one days storage, strain differences were not statistically significant. Repeatabilities for strains tested on different farms were highest for Haugh units fresh and lowest for Haugh unit loss. This investigation, although based on a moderately large sample of strains and eggs, failed to demonstrate that Haugh unit loss is genetically determined.
FORSYTHE
43
ALBUMEN QUALITY MEASURES
MATERIALS AND METHODS
The eggs for this study were produced by three Leghorn lines widely differing in egg size, developed at Iowa State University. (Nordskog and Festing, 1962). Line A, selected for high egg production, lays
standard or medium sized eggs. Line D has been selected solely for large egg size, and Line E has been selected solely for small egg size. Eggs were collected in March, April and May of 1961. After weighing on a Toledo scale between 12 and 36 hours after laying, eggs were assigned to weight classes with intervals of 1 gram. Samples of eggs, broken immediately after weighing, were measured for albumen height with a tripod screw micrometer (Kilpatrick, 1960). Other samples of eggs were stored for various lengths of time up to seven weeks. Albumen heights were then measured after a pre-assigned weight loss had been achieved. Samples of eggs were stored both in the open at a temperature of S6-58°F. and in desiccators containing anhydrous calcium chloride to induce rapid weight loss. From the observed albumen heights grouped in arrays according to initial egg weight classes, the linear regression of albumen height on the mean of each egg weight group was calculated. RESULTS
The distribution of individual eggs according to albumen height and egg weight is illustrated for the medium size egg line A in Figure 1. The results show a low-order relationship between the two variables. Averages for the three lines are summarized in Table 1. Line differences in albumen height are statistically significant as expected because these lines have been selected for wide differences in egg size. The regressions for each of the three lines are shown graphically in Figure 2. Here, the plotted points represent mean albumen height values for each weight class according to line. Differences between the regression coefficients proved to be statistically significant. From the combined data over the three
Downloaded from http://ps.oxfordjournals.org/ at National Institute of Education Library, Serials Unit on May 20, 2015
A recent study by Eisen et al. (1962) questioned the validity of the Haugh unit score as a measure of albumen quality. They reported that the Haugh unit measure did not completely adjust for differences in albumen height associated with egg weight. The regression of albumen height on egg weight was found to be essentially linear and was estimated to be .035. These workers concluded that the linear regression method was superior in correcting for differences in egg weight compared with the Haugh unit egg weight correction method. A question that seems not yet clarified in using the Haugh unit egg weight correction concerns the cause of egg weight differences. In particular, egg weight differences may be due to (I) inherent differences between hens and (II) environmental differences of time, temperature and other storage conditions. Conceivably the regression of albumen height on egg weight as specified by (I) might be quite different from that as specified by (II). This raises a question of the general validity of the Haugh unit correction when no specification is made concerning the causes of the differences in egg weights for which corrections are intended. The purpose of the present investigation was to compare the regression of albumen height on egg weight according to different lines of breeding and causes of egg weight differences as defined by I and II above. Implications to the Haugh unit method of measuring egg albumen quality will then be considered.
44
M. G. KIDWELL, A. W. NORPSKOG AND R. H. FORSYTHE TABLE 1.—Line means and regressions of c men height {II) and egg weight (W)
Line E (Small egg) A (Standard eg, D (Large egg)
No. of
Mean H (mm.)
Mean W (gm.)
Regression coefficient of H on W (mm./gm.)
193 272 125
4.76 5.70 6.30
47.31 58.13 65.76
.030+.009 . 0 4 7 ± .008 ,059±.015
lines, the range in egg size is 38 to 77 grams, and the over-all regression coefficient is .067 mm. of albumen height per gram of egg weight. The latter is greater than any of the three intra-line regression coefficients because the "between line" effect is included. It should be clearly understood that the above regressions pertain only to initial or "inherent" egg weight differences as defined under I above. However, the regression of albumen height on egg weight differences due to storage is also of interest.
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60
65
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EGG WEIGHT IN GRAMS FIG. 1. Relationship of initial albumen height to egg weight in Line A.
75
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Ordinarily the age of eggs sampled from the trade is not precisely known. Since eggs lose weight in storage, differences in egg weight clearly would influence any corrected measure of albumen heights. Regression coefficients for differing weight loss groups with initial egg weight constant were calculated. The analyses of variance presented in Table 2 were computed from the combined data on all three lines. Fresh eggs represent the zero weight loss class. The remaining three groups consisted of desiccator stored eggs. As expected, linear regression greater than zero proved to be statistically significant in all groups, but deviations from linearity were significant only in the 2 gram and 3 gram weight loss groups. The results suggest that curvilinear regression becomes well established only after a substantial period of storage.
45
ALBUMEN QUALITY MEASURES Y = I.77+.067X ? = 3.38 + .03 X $ = 2.97 •• .047X ? = 2 . 4 0 + .059X
(ALL (LINE (LINE (LINE
A LINE E • LINE A O LINE 0
LINES) E) A) D)
UJ
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x UJ 2
m
4.0 L 35
40
45"
50
55
60
65
70
EGG WEIGHT IN GRAMS FIG. 2, Regression of initial albumen height on egg weight by lines of breeding.
The regressions of albumen height on egg weight according to causes of egg weight differences are presented in Table 3. The regressions denoted as bHw account for initial or inherent differences in egg weight. The differences between the four estimates are not statistically significant, and the over-all average was 0.065 ± .003. Thus, weight loss under the conditions of storage in this experiment apparently did not alter the initial relationship of albumen height to egg weight when the eggs compared were stored under the same condi-
tions. On the other hand, the regression of albumen height on egg weight loss bHL shows a more or less progressive decline with increase in initial egg weight classes. For the lowest egg weight class (44-56 grams), the regression is —0.488 ± .059, and for the highest egg weight class (6870 grams), the regression is —1.020 ± .134. The average regression is —0.636 ± 0.30. Differences in egg weight due to loss in storage, therefore, show about a 10-fold greater effect on albumen height as compared with the effect of inherent differences
TABLE 2.—Analysis of variance of albumen height of fresh and stored eggs Stored
Fresh Weight loss (gm.) 0 Source of variation Linear regression Deviations from linear regressions Error *P<.05. ** P < . 0 1 .
1
2
3
d.f. 1
M.S. 239.57"
d.f. 1
M.S. 71.24"
d.f. 1
M.S. 17.00"
d.f. 1
M.S. 11.08"
39 623
0.73 0.71
22 180
0.79 0.58
22 85
1.18" 0.54
8 26
0.58* 0.21
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6.0-
46
M . G. KiDWELL, A. W . NORDSKOG AND R . H . FORSYTHE TABLE 3.—Regression of albumen height {H) on egg weight (W) and egg weight loss (L)
Initial egg
Classes Line
0
44-46
E
4.62 (44)*
47-49
E
50-52
1
2
3
4
All
bflL
Mean albumen height (mm.) 4.03 3.89 2.73 (32) (22) (6)
2.64 (S)
4.11 (109)
-0.488 ± .059
4.71 (42)
4.01 (32)
3.75 (18)
3.08 (5)
2.47 (9)
4.07 (106)
-0.538 + .043
E
4.92 (33)
4.27 (19)
3.63 (12)
2.82 (5)
4.37 (69)
-0.675 + .093
56-58
A
5.71 (46)
5.31 (29)
4.67 (15)
3.64 (5)
5.32 (95)
-0.583 + .086
59-61
A
5.94 (45)
5.35 (28)
4.86 (9)
4.13 (6)
5.52 (88)
-0.585 ± .095
62-64
D
6.28 (35)
5.34 (23)
4.75 (11)
4.47 (6)
5.62 (75)
-0.684 ± .098
65-67
D
6.03 (34)
5.47 (21)
4.99 (10)
4.57 (3)
5.64 (68)
-0.512 ± .106
68-70
D
6.52 (29)
5.41 (20)
4.36 (12)
3.47 (3)
5.62 (64)
-1.020 + .134
5.54 (308)
4.84 (204)
4.26 (109)
3.58 (39)
0.067 + .004
0.072 + .007
0.047 +.009
0.074 +.012
All t>HW
2.53 (14)
/-0.636 Av \ ± .030
1 0.0651 I + .003/AV
Figures in parenthesis are number of eggs.
7.0
x <2 uj i
z UJ
Z m
6.0-
DESICCATOR STORAGE
5.0 4.0 3.0
WEIGHT LOSS IN GRAMS
in egg weight. Mean albumen heights for two samples of eggs from line A kept in a desiccator and under room storage conditions are shown in Figure 3. The regression lines connecting the observations were not fitted statistically. Analyses of variance indicated that deviations from linear regression were not significant when storage was in desiccators. On the other hand, for storage in the open at room temperature, curvilinear
ROOM ST0RA8E
0
1
2
WEIGHT LOSS IN GRAMS
3
FIG. 3. Regression of albumen height on egg weight loss in desiccator and open room storage of two samples of eggs ( A , egg weight range 5658 gms, and • , egg weight range 59-61 gms.).
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(gms.)
ALBUMEN QUALITY MEASURES
GU = 100 log [H - b (W - 56.7) ] Where H and W are defined as previously given and b = 0.067 is the combined linear regression coefficient shown in Figure 2. Correlation coefficients then were calculated between HU and GU for both fresh and stored eggs. The correlations came out to be r = .985 for fresh eggs and r = .988 for stored eggs. Thus, it is clear that for all practical purposes, the two methods of correction give identical results. The fact that the Haugh unit has been in common use over the past several years, would favor its continued use. Furthermore, the Haugh unit correction is data-independent and hence, has the property of a distribution-free statistic. DISCUSSION The results of this study show that the relation between albumen height and egg weight is essentially linear for new-laid eggs. This is in accord with the recent study reported by workers at Purdue University (Eisen et al., 1962). However, the present study also shows that the regression of albumen height on egg weight may
differ according to lines of breeding. The lowest regression was in the small egg line, and the highest regression was in the large egg line. Eisen et al. (1962) concluded that the Haugh unit method did not adequately adjust albumen height of individual eggs for egg weight in their data. They raised the question as to the validity and desirability of using the Haugh unit score as a measure of albumen quality. They reported a bias in the Haugh unit regression which resulted in over-estimating albumen height of smaller eggs and in under-estimating albumen height of larger eggs. The Purdue workers suggested that other populations should be studied to determine whether the regression of .035 which they reported is general. In the meantime, they suggested that a linear adjustment of albumen height for egg weight using the regression of .035 would be preferable to the adjustment provided by the Haugh unit formula. This recommendation appears not to be wholly justified from the results of their study. Eisen et al. (1962) compared a least squares derived regression coefficient (b = .035) with a "data-independent" regression coefficient, (b = .05). They pointed out that the latter closely approximates the Haugh unit regression which does not deviate greatly from linearity. Hence, in effect, they compared two linear regression coefficients as to their efficiency in correcting for egg weights. Clearly, the least squares estimate is bound to give a better fit to the data from which it is derived because this is a fundamental property of any least squares estimate. Consequently, the Haugh unit method as approximated by the value of b = .05, gives a poorer fit which they incorrectly interpreted as a bias. Corollary to this is the failure of the Haugh regression to completely remove the correlation between egg weight and adjusted albumen
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regression proved to be highly significant. This is not to suggest, however, that any practical significance should be attached to the differences in the nature of the relationship of albumen height and weight losses between room and desiccator storage. The finding that albumen height and inherent egg weight are linearly related is in accord with the recent report by Eisen et al. (1962). However, to compare the net result • of a correction based on the least squares regression method, with the Haugh unit method, albumen heights for all eggs were converted to conventional HU and also into a modified HU (called GU) which contains the least squares egg weight correction defined as follows:
47
48
M. G. KIDWELL, A. W. NORDSKOG AND R. H. FORSYTHE
CONCLUSIONS 1. The linear regression of albumen height on initial egg weight may differ according to lines of breeding. 2. The regression of albumen height on weight loss of eggs due to storage is
about 10 times as great as due to initial or inherent differences in egg weight. 3. The Haugh unit method of adjusting albumen height adequately corrects for initial or inherent egg weight differences and is highly correlated with the least squares regression method of adjustment recommended by Eisen et al. (1962). 4. Correcting albumen height for egg weight appears to be a factor of secondary importance in measuring egg quality differences in trade channels. SUMMARY
The purpose of this investigation was to consider the importance of the egg weight correction as used in the Haugh unit (H.U.) measure of egg albumen quality. Measurements of albumen height and egg weight were taken on eggs from three different egg size strains of Leghorns. Eggs were stored under desiccator conditions for varying lengths of time to induce different amounts of weight loss. The linear regression of albumen height on initial egg weight (bHw) averaged 0.067 mm. per gram of egg but differed according to line of breeding. An egg quality unit, (GU), based on the linear regression of 0.067 but otherwise the same as H.U. was computed. The correlation between GU and H.U. was 0.985 and 0.988 for fresh and stored eggs, respectively, which suggests that the complicated egg weight correction in the Haugh unit is unnecessary. . The regression of albumen height on the egg weight loss in desiccator storage (bHi,) averaged —0.636 for eggs in the same initial egg weight classes. Evidently the Haugh unit corrects only for bHw and not for bHL even though in trade channels, for example, egg weight differences might be due both to genetic and environmental sources. Finally, the importance of egg weight
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heights. Indeed, where two sets of variables are linearly related, any regression value other than the least squares estimate, will not completely remove all correlation between the independent variable and the corrected dependent variable. Thus, if a least squares regression of .035 is found in a set of data, but if albumen height is corrected using the regression of .05 (i.e. the Haugh unit correction), a residual correlation is bound to remain between the corcrected values of albumen height and egg weights. Hence, for any particular set of data, the Haugh unit correction cannot be expected to remove all of the correlation of albumen height on egg weight. The importance of an egg weight correction in the Haugh unit seems to have been over-emphasized. For special types of studies, where the age of eggs and other environmental factors can be properly controlled, the use of the Haugh unit as originally defined would seem to be quite justified. On the other hand, in connection with sampling eggs from the trade, the Haugh unit correction for egg weight is probably an unnecessary refinement in view of possible variability in egg weight due to storage-caused differences in egg weight. In fact, Haugh and Jasper (1962), in a recent popular article, concede that egg weight does not materially affect the accuracy of comparisons. Hence, for the trade, the only important feature of the Haugh unit is the logarithm transformation of the albumen height measurement which has long been recognized a useful objective measure corresponding to the USDA quality score.
ALBUMEN QUALITY MEASURES
REFERENCES Brant, A. W., A. W. Otte and K. H. Norris,
1951. Recommended standards for scoring and measuring opened egg quality. Food Technology, 5: 356-361. Eisen, E. J., B. B. Bohren and H. E. McKean, 1962. The Haugh unit as a measure of egg albumen quality. Poultry Sci. 41: 1461-1468. Haugh, R. R., and A. W. Jasper, 1962. It's new —The Haugh unit quality computer. Poultry Processing and Marketing, February: 116-119. Kilpatrick, L., A. W. Brant and H. L. Shrader. 1960. Equipment and methods for measuring egg quality. U.S.D.A. Agric. Marketing Serv. Bui. 246. Nordskog, A. W., and M. Festing, 1962. Selection and correlated responses in the fowl. Proc. X I I World's Poultry Congress, Sydney, Australia, 25-29.
Effect of Light Regime and Age on Reproduction of Turkeys1'2 3. RESTRICTED LIGHT ON YEARLING HENS A. T. LEIGHTON, JR. 3 AND R. N. SHOFFNER Department of Poultry Husbandry, University of Minnesota, St. Paul (Received for publication May 8, 1963)
I
T HAS been demonstrated by numerous investigators that the turkey female becomes refractory to photostimulation when exposed to 13 or more hours of continuous daily light for prolonged periods of time: Harper and Parker (1957, 1960, 1962), McCartney et al. (1961), Leighton and Shoffner (1961a, b), and Shoffner et al. (1962). It has also been demonstrated by 'Published as Paper No. 5121, Scientific Journal Series of the Minnesota Agricultural Experiment Station. 2 A portion of a thesis submitted by the senior author to the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Doctor of Philosophy. 3 Present address: Department of Poultry Science, Virginia Agricultural Experiment Station, Blacksburg, Virginia.
the above workers that the female turkey must be subjected to a period of short days followed by increased or increasing day length in order to be stimulated into satisfactory levels of egg production. Hens that are in egg production will, in most cases, cease production when subjected to a series of short days as shown by Harper and Parker (1957). Their data also showed that when yearling hens were restricted to 9 hours of light per day for a 4 week period and subsequently exposed to 17 hours of light per day, they did not produce eggs at a satisfactory rate. This study investigates further the photoperiodic reproductive responses of yearling female turkeys which had completed 6 months of lay.
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correction in measuring albumen quality seems to have been over-emphasized. For special studies, where environmental factors can be adequately controlled, the use of the Haugh unit or a similar quality measure would be quite appropriate. On the other hand, for measuring albumen quality of eggs already graded for size, such as in the trade or where egg weights may vary due to differences in storage, correcting for egg weight is probably an unnecessary refinement.
49