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Heritability of Albumen Height and Specific Gravity of Eggs from White Leghorns and Barred Rocks and the Correlations of These Traits with Egg Production
Heritability of Albumen Height and Specific Gravity of Eggs from White Leghorns and Barred Rocks and the Correlations of These Traits with Egg Production A. S. JOHNSON AND E. S. MERRITT Poultry Division, Central Experimental Farm, Ottawa, Canada (Received for publication September 13, 1954)
C
Cavers (1948) and was considered to be in part due to high summer temperatures and poor holding conditions. Jeffrey (1941) attributed part of this decline to physiological changes in the bird with increasing age. The coincidence of the physiological decline, due to the aging of the spring-hatched pullet, and high summer temperatures increases the difficulty of maintaining high market quality in summer eggs. A seasonal decrease in shell strength which parallels that for albumen quality was observed by Wilhelm (1940), using shell thickness as a criterion, and also by O'Neil and Rae (1952) who employed the specific gravity method of measurement. In any selection program for egg quality, the effect of such selection on egg production is of importance. On the basis of rather limited data, Knox and Godfrey (1938) concluded that there was no relationship between the level of egg production and albumen quality as measured by percentage of firm white. Their report in 1940 on the results of selection of a high albumen line contained no mention of the effect of this selection on egg production. Jeffrey (1941) observed that the lowest producing hens tended to have the highest albumen quality. Brant et al. (1953) in a study of egg quality at two different egg laying trials, found, at one station, a significant negative correlation between egg production and albumen quality but no relationship at the other station. Miller and Bearse (1937) observed a significant negative correlation
578
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ONSIDERABLE attention has been focused on problems of egg quality in the past. The possibility of improving egg quality traits by breeding methods has been investigated and it has been found that the three main "components" of egg quality, namely albumen quality, shell strength, and freedom from blood and meat spots, are influenced to different degrees by heredity. The present report deals with an investigation of the first two of these traits. In this study albumen height was the criterion of albumen quality and specific gravity was used as a measure of shell strength. The effectiveness of selection in improving albumen quality has been shown by several workers, (Lorenz and Taylor, 1940; Knox and Godfrey, 1940). Taylor and Lerner (1939) demonstrated the genetic basis for shell strength by establishing two lines, differing in shell strength, from one population. McClary and Lerner (1950) reported a heritability estimate of .15 for specific gravity. Recently, data on sampling methods and some estimates of genetic parameters of egg quality traits have been presented by workers at Iowa State College. For example, Scheinberg el al. (1953) presented estimates of the heritability of albumen weight varying from .12 to .66, while Nordskog and Farnsworth (1953) estimated heritability of albumen height at .22. A seasonal decline in albumen quality of market eggs was found by Lorenz and Newlon (1944) and by Johnson and
EGG QUALITY AND EGG PRODUCTION
MATERIAXS AND METHODS
The data were obtained in 1948-49 from two flocks of pullets, one of White Leghorns and the other of Barred Rocks. In the fall of 1948, 452 and 526 pullets of each breed, respectively, were housed. Each flock was the progeny of 11 sires and 92 and 98 dams, respectively. They were
not closed flocks; limited introduction of outside stock had been made in 1944 in the White Leghorn flock and in 1947 in the case of the Barred Rocks. The pullets in each flock were produced from 2 separate hatches, the breeds being hatched alternately each week over a three-week period from March 25th to April 15th, 1948. They were reared together on range under relatively uniform conditions. The two breeds were housed in alternate pens in the same houses but at 'random within breed. Trapnest records were obtained on a seven-day-week basis. Beginning in November, 1948, all eggs laid in the first week of each month were gathered hourly and broken within two hours after collection to minimize the "post-laying" changes in albumen quality. Albumen height was measured with a tripod micrometer to the nearest .001 inch. In the second week of each month, all eggs laid were held overnight in an egg-holding room and tested the following morning for specific gravity. A series of ten salt solutions, ranging in specific gravity from 1.066 to 1.102 were made up in 10-gallon pails. About three dozen eggs at a time were placed in a wire egg basket and immersed in each solution starting with the lowest specific gravity solution. The specific gravity of the solution in which an egg first floated was recorded. Monthly records of albumen height and specific gravity were thus obtained from November 1948, to August, 1949, for every hen in production at the time of sampling. The total number of eggs tested for each trait was about 23,000. The average of two albumen height measurements on each egg was recorded. For each trait, the mean for every hen in each month was used, provided that she had measurements for at least two eggs. For purposes of analysis, the values for
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between egg production and albumen index, although their analysis does not exclude the possibility that this correlation was due to the nutritional treatments involved. Wilhelm (1940) reported that there was no correlation between egg shell thickness and level of egg production. The results of Brant et al. (1953) agree with this finding. It thus seems, from a study of the literature, that the relationship between albumen quality and egg production has not been clearly determined, while in the case of shell strength and egg production, no significant correlation has been found to exist. No reports of the magnitude or direction of genetic correlations between either of these egg quality traits and egg production have been observed in the literature. Recently, there has been some attention given to the encouragement of breeding for improved egg quality (Dawson et al., 1954). It would seem to be of primary importance to know the possible effect of such selection on egg production. For an egg quality selection program to be economically sound, it would seem necessary, at least under the present remunerative system, that this selection have no adverse effects on the egg producing ability of the strain. The study reported herein was carried out for the purpose of extending the information on the heritability of these egg quality traits and investigating their genetic relationship to egg production.
579
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A. S. JOHNSON AND E. S. MERRITT
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FIGS. 1 to 4: Seasonal trends in albumen height and specific gravity of eggs from White Leghorns and Barred Rocks, showing flock means (heavy line), sire means and corresponding final egg production.
each of two months were combined, resulting in five separate two-month periods. A hen was not represented in the analysis in any given period if she lacked a measure of albumen height or of specific gravity for that period, or if she had died.
Thus, the population changed somewhat from one period to another due to non-production and mortality. The data were analyzed separately by breed. Egg production was recorded in 28-day periods. The total egg production to the
581
EGG QUALITY AND EGG PRODUCTION
TABLE 1.—Means of albumen height (in inches), specific gravity and egg production for White Leghorns and Barred Rocks by periods Period Breed Albumen height
Egg production
2 Jan.-Feb.
3 Mar-Apr.
4 May-June
5 July-August
.315+.043 .298±.042
.306 ±.045 .296 ±.041
.294±.045 .298+.044
W.L. 1.0886+.0044 B.R. 1.0837 ±.0050
l.O846±.0048 1.0809±.0049
1.0825 ±.0051 1.0800+.0049
1.0793+.0050 1.0776±.0051
1.0767 +.0050 1.0748 ±.0052
W.L. 60 ±16 B.R. 54 ±18
97 ±18 92 ±20
132 + 22 126 ±24
168 ±28 158 ±28
213 ±34 194 ±34
.337 ±.039 .324 ±.043
W.L.=White Leghorns, B.R. = Barred Rocks.
end of the period corresponding most closely to a period of quality measurement was used in calculation of correlations between the egg quality traits and production. Analyses of variance and covariance for estimating heritability and obtaining genetic and phenotypic correlations were carried out as described by Lerner (1950). The formula for the heritability calculation was 2(S+D)/S + D-|-A where S and D are sire and dam components of variance and the denominator is the phenotypic variance. RESULTS AND DISCUSSION
There was a seasonal decline in the albumen quality of the new-laid eggs of both breeds. The trend was noticeably different in the two breeds (Table 1, and Figures 1 and 2). The White Leghorns started at a higher level but their decline in albumen quality was more rapid than for the Barred Rocks and the difference between breeds had largely disappeared by July-August. The mean albumen height of the Barred Rocks had practically reached its minimum by period 3 (March-April), as illustrated in Figure 2. It stayed at essentially the same
level throughout the remainder of the test. In both breeds there was a considerable proportion of the birds laying eggs which, even when measured so soon after laying, were of only intermediate quality and would not have maintained this quality in storage. This was particularly so in the latter part of the season for the White Leghorns. The albumen quality of the sireprogeny groups in the lower range was dangerously close to a level which would result in a fairly large proportion of B grade eggs on marketing (Figures 1 and 2). Actually, a considerable number of the daughters of these sires, particularly White Leghorns Sires 7 and 8, were producing eggs in period 5 which were of quality equivalent to B grade when laid (Johnson, 1946). Others had eggs of such low quality that, with normal deterioration on holding, they would have been B grade when marketed. Johnson (1946), in a study of egg quality on Manitoba farms, found that the average albumen height of B grade eggs examined was .221 inch. He also observed that the decline in quality over a 3-day period under average farm holding conditions, as measured by a decrease in albumen
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.321 ±.039 .306± .041
W.L. B.R.
Specific gravity
1 Nov .-Dec.
582
A. S. JOHNSON AND E. S. MERRITT
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There were distinct differences between the sire means of the two egg quality traits, in both breeds, as shown by the analysis of variance in Table 2. The relative positions of the sire means were more or less maintained throughout the season in the case of albumen height; there was somewhat more change in ranking of the sires for specific gravity suggesting the possible need for testing
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height, was .040 inch. On this basis an egg with an albumen height of .261 inch or less when laid, would decline to the B grade average after three days under average farm holding conditions. Thus, a fairly large proportion of the low-grade eggs on the market in summer months may be due to initial low quality of albumen in the fresh-laid eggs as well as to the effects of high holding temperature. A seasonal decline also occurred in the specific gravity measurements and it was similar for both breeds (Table 1, and Figures 3 and 4). The White Leghorns stayed at a higher level throughout, although they dropped slightly more than the Barred Rocks, namely .0119 as against .0090. No experimental data are available to suggest the specific gravity level below which breakage in handling becomes a serious problem. The specific gravity method has been in wide use since Olsson (1934) found that most of the variation in the specific gravity of eggs was due to differences in percentage of shell. Novikoff and Gutteridge (1949) obtained a correlation of .75 between specific gravity and the force required to break the shell. The means and standard deviations in Table 1 as well as the sire means in Figures 3 and 4 show that a considerable proportion of the eggs in July-August had relatively poor shell quality as compared with the eggs in the first three periods, particularly in the Barred Rocks.
583
EGG QUALITY AND EGG PRODUCTION
TABLE 3.—Sire and dam variance components for albumen height, specific gravity and egg production, by periods Period Breed
Component
1 Nov.Dec.
2 JanFeb.
3 Mar.Apr.
4 MayJune
5 JulyAugust
W.L.
Sire Dam
207.7 290.0
246.6 246.7
264.3 181.6
274.8 201.6
336.0 149.1
B.R.
Sire Dam
79.7 106.3
39.1 156.7
28.3 52.3
48.3 61.3
72.4 117.3
W.L.
Sire Dam
5.53 -0.23
0.88 3.33
2.04 2.91
0.93 1.70
0.38 2.31
B.R.
Sire Dam
3.46 3.15
3.24 4.93
4.02 3.02
3.74 3.02
3.31 3.49
W.L.
Sire Dam
26.0 15.0
42.4 52.0
47.5 40.9
47.4 149.7
102.2 146.8
B.R.
Sire Dam
5.3 23.7
24.8 44.4
41.5 34.1
48.4 -13.1
112.6 -16.5
Albumen height*
Specific gravity*
Decode by multiplying by 10
breeds for all traits but particularly in the case of albumen height where the means of the estimates for the White Leghorns and Barred Rocks were .55 and .17 respectively. Scheinberg, Ward and Nordskog (1953) obtained heritability estimates of .66 and .12 of albumen weight in White Leghorns and Barred Rocks, respectively. Differences between breeds are also shown in the genetic variance components in Table 3 from which the heritability
for this trait at least twice during the year—once in the winter and once in the summer months. The sire means illustrated in Figures 1 to 4 include the two extremes in each breed and a representative number with intermediate values. The breed difference in range between the highest and lowest ranking sire for albumen height is particularly noticeable. The heritability estimates in Table 4 show a consistent difference between
TABLE 4.—Heritability estimates of albumen height, specific gravity and egg production of While Leghorns and Barred Rocks, by periods Period Breed
1 Nov.Dec.
2 Jan.Feb.
3 Mar.Apr.
4 MayJune
5 JulyAugust
Mean*
Albumen height
W.L. B.R.
.66 .20
.66 .23
.48 .09
.47 .13
.47 .19
.55 .17
Specific gravity
W.L. B.R.
.44 .52
.37 .68
.38 .60
.21 .52
.21 .50
.32 .56
Egg production
W.L. B.R.
.34 .18
.59 .34
.36 .27
.49 .09
.42 .17
.44 .21
* Unweighted arithmetic mean of 5 estimates.
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Egg production
584
A. S. JOHNSON AND E. S. MEERITT
TABLE 5.—Sire and dam genetic covariance components for albumen height, specific gravity and egg production of White Leghorns and Barred Rocks Period
Egg production X albumen height*
Egg production X specific gravity*
W.L. B.R.
1 Nov.Dec.
2 JanFeb.
3 Mar.Apr.
4 MayJune
5 JulyAugust
Sire Dam
-30.87 -68.90
-52.46 -62.27
-95.82 -43.24
-107.70 -112.89
-148.00 -120.62
Sire Dam
-
0.75 0.25
11.33 -26.69
34.00 -13.68
-
Sire Dam
-
5.45 1.88
4.60 2.03
5.20 1.71
B.R.
Sire Dam
-
0.82 0.89
-
W.L.
Sire Dam
-
0.11 5.77
Sire Dam
-13.00 7.72
W.L.
B.R.
45.67 1.28
-
31.92 66.48
1.47 8.56
-
6.00 0.53
2.97 6.02
-
5.39 5.70
-
11.95 9.42
- 7.28 -11.37
-12.35 -14.24
-
3.30 7.49
-
10.32 6.17
-12.84 7.63
-12.01 16.08
-
12.77 15.31
-
12.86 3.48
3.54 0.11
-
* Decode by multiplying by 10~-63. t Decode by multiplying by 10 .
estimates were derived. The large sampling error of heritability estimates calculated by means of variance component analysis is recognized. Nevertheless the consistency of these differences over the five periods suggests that the possibility of actual breed differences in heritability exists in this case, particularly with reference to albumen height. It is unlikely that the differences in heritability in the case of this trait were due to peculiarities of this criterion of albumen quality, which is uncorrected for the effect of egg weight (Haugh, 1937). The mean egg weights measured in February, 1949, were 58.2 and 59.5 grams for the White Leghorns and Barred Rocks respectively. The heritability estimates of specific gravity were of a higher level for the Barred Rocks than for the White Leghorns, which is the reverse of the situation with albumen height. There was a drop in the heritability of specific gravity for White Leghorns from a level of .38 in March-April to .21 in May-June. The
estimates of heritability of shell strength obtained from these data are, for the most part, considerably higher than the estimate of .15 given by McClary and Lerner (1950). The heritability of survivor's egg production obtained here for the Barred Rocks was somewhat below, and for the White Leghorns slightly above, the average estimate of .30 which has been reported by Lerner (1950). King and Henderson (1954) reported heritability estimates of the same trait ranging from .48 in midseason to .31 at the end of the production year. The heritability estimates obtained in this study for White Leghorns in the early part of the season were similar to theirs in magnitude. The negative phenotypic correlations between albumen height and egg production, although low, were all significant at the 1% probability level except the one for the Barred Rocks in period 5, which was non-significant (Table 6). This agrees with the results of Brant et al. (1953) at
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Albumen height X specific gravity t
Breed
Component
EGG QUALITY AND EGG PRODUCTION
585
TABLE 6.—Genetic and phenotypic correlation coefficients for albumen height, specific gravity and egg production of White Leghorns and Barred Rocks, by periods Period Breed
Egg production X albumen height
Egg production X specific gravity
2 JanFeb.
3 Mar.Apr.
4 MayJune
5 JulyAugust
W.L.
Genetic Phenotypic
-.669 -.332f
-.532 -.1981
-.637 -.265f
-.720 -.233f
-.773 -.252f
B.R.
Genetic Phenotypic
-.014 -.290f
-.132 -.211f
.260 -.154f
.714 —. 153f
-.256 -.103
W.L.
Genetic Phenotypic
.269 -.088
.333 -.037
.330 -.057
.440 -.075
.211 -.213f
B.R.
Genetic Phenotypic
-.124 -.lSlf
-.144 -.081
-.390 -.118*
-.718 - .105*
-.836 - . 124*
W.L.
Genetic Phenotypic
-.122 .040
-.409 .016
-.449 .089
-.305 .041
-.456 .017
B.R.
Genetic Phenotypic
-.150 .043
-.130 .022
.171 .086
.093 .084
-.262 .043
Phenotypic correlations: * Significant at 5% probability level. f Significant at 1% probability level.
the Rhode Island Egg Laying Test. The genetic correlations between these two traits were consistently negative in the White Leghorns, at a level of about — .65. There was good agreement between the sire and dam covariance components, on which the correlations were based (Table 5). The corresponding components in the Barred Rocks were positive for the sires but negative for the dams, with the result that the correlations fluctuated considerably and were sometives negative and sometimes positive in value. An attempt to judge the exact nature of the relationship between the traits in this breed would be more difficult than in the White Leghorns. These results do not agree with those of Knox and Godfrey (1938) who found no relationship between egg production and albumen quality (measured as percentage of firm albumen) when they were correlated on the phenotypic level. Brant el al. (1953) obtained, in one case, a significant negative phenotypic correlation and, in another, no
correlation, between the two traits. No information on the genetic relationship of these traits was found in the literature. The consistency of the genetic covariance components for egg production and albumen height of the White Leghorns (Table 5) is strong evidence of a definite negative genetic relationship between egg number and albumen quality in this strain. This implies that, everything else being equal, any selection for albumen quality would tend to have an adverse effect on egg production and vice versa. Also, selection for both traits at the same time might result in more or less of a stand-still as far as any improvement in either trait was concerned. Egg production and specific gravity were significantly correlated on the phenotypic level in the Barred Rocks in all cases except in Period 2. The only phenotypic correlation which showed significance in the White Leghorns was the one in Period 5. These results are at variance with those of Wilhelm (1940) and Brant
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Albumen height X specific gravity
1 Nov.Dec.
586
A. S. JOHNSON AND E. S. MERRITT
the standpoint of quality in the period from June to August. Heritability estimates for the two breeds were as follows: for albumen height, White Leghorns, .55, Barred Rocks, .17; for specific gravity, White Leghorns, .32, Barred Rocks, .56. Egg production was significantly correlated with both egg quality traits although at different levels for the two breeds. The outstanding results of the correlation analysis were: a significant negative phenotypic correlation between albumen height and egg production in both breeds, a genetic correlation between albumen height and egg production of the order of — .65 in the White Leghorns and .11 in the Barred Rocks, a genetic correlation between specific gravity and egg production averaging .28 for the White Leghorns and — .44 for the Barred Rocks. It is suggested that the problem of the improvement of strains for egg quality Albumen height and specific gravity traits has been oversimplified. Thorough showed no significant phenotypic correla- investigation of the genetic relationships tion in either breed. These traits had, of egg quality traits to egg production in however, a negative genetic correlation in various breeds and strains is important. the White Leghorns at an average level of Such information would be of considerable — .348. The Barred Rock correlations importance to anyone engaged in or conwere negative in three periods and positive templating selection for egg quality traits. in two. In this breed the sire and dam comACKNOWLEDGEMENT ponents were again opposite in sign (Table 5) but the dam components were positive The technical assistanceof Messrs. G. P. and the sire components negative, a reKavanagh, R. A. Lacroix and P. J. versal of the order for the breed in the McGann in taking the measurements was albumen height-egg number relationship. appreciated. SUMMARY
Data on albumen quality and shell strength were obtained monthly from November to August in two flocks of White Leghorn and Barred Rock pullets. More than 23,000 eggs were broken for albumen height measurement while an approximately similar number were tested for specific gravity. Seasonal trends showed these traits to be of main concern from
REFERENCES Brant, A. W., A. W. Otte and G. Chin, 1953. A survey of egg quality of two egg laying tests. U.S.D.A.. Tech Bull. 1066. Dawson, L. E., L. R. Champion, J. A. Davidson and H. C. Zindel, 1954. Improving egg quality through Michigan R.O.P. breeders—a progress report. Poultry Sci. 33: 293-297. Haugh, R. R., 1937. The Haugh unit for measuring egg quality. U. S. Egg Poultry Mag. 43: 760. Jeffrey, F. O., 1941. Changes in pullet year albumen
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et al. (1953) who found no significant phenotypic correlation between these two traits. The genetic correlations were positive for the White Leghorns, having a value of about .32; the corresponding correlations for the Barred Rocks were all negative, increasing progressively from - . 1 2 4 in Period 1 to - . 8 3 6 in Period 5. These correlations were quite consistent between periods in the White Leghorns and there was fairly good agreement between sire and dam estimates of covariance in both breeds. The fact that the correlations were positive in the White Leghorns but negative and of increasing magnitude in the Barred Rocks suggests that selection for egg production would have had quite different effects on shell strength in the two breeds, and vice-versa. The situation in the White Leghorns would be considered more favorable to improvement by selection.
LEUCINE AND FOWL ASCARIDS
chromosomal effects on the transmission of egg shell quality in chickens. Records Genet. Soc. Amer. 19: 113. Miller, M. W., and G. E. Bearse, 1937. Protein supplements for laying hens. Washington Agr. Exp. Sta. Bull. 347. Nordskog, A. W., and G. Farnsworth, Jr., 1953. The problem of sampling for egg quality in a breeding flock. Poultry Sci. 32:918. Novikoff, M., and H. S. Gutteridge, 1949. A comparison of certain methods of estimating shell strength. Poultry Sci. 28: 339-343. Olsson, N., 1934. Studies on Specific Gravity of Hens' Eggs. Otto Harrassowitz, Leipzig. O'Neil, J. B., and W. J. Rae, 1952. Changes in specific gravity of eggs during the laying year. Sci. Agr. 32:185-189. Scheinberg, S. L., H. Ward and A. W. Nordskog, 1953. Breeding for egg quality. 1. Heritability and repeatability of egg weight and its components. Poultry Sci. 32: 504-510. Taylor, L. W., and I. M. Lerner, 1939. Inheritance of egg shell thickness in White Leghorn pullets. J. Agr. Res. 58:383-396. Wilhelm, L. A., 1940. Some factors affecting variations in egg shell quality. Poultry Sci. 19: 246-253.
Leucine and Fowl Ascarids B E R N A R D B. R I E D E L
Department of Animal Disease, Mississippi Experiment Station, State College, Mississippi (Received for publication September 16, 1954)
I
T HAS been repeatedly shown that protein in a diet influences the degree of resistance of a fowl to parasitism (Ackert and Beach, 1933; Luttermoser and Allen, 1942; and Riedel and Ackert, 1950, 1951). Almquist and Grau (1944) presented some results which indicated that a mixture of amino acids in the diet of a growing chick could replace a protein supplement. Relative to parasites Riedel (1950) reported that lysine was not effective in protecting the fowl from the parasite Ascaridia galli, and Todd (1951) found more and larger roundworms when chicks were
fed a high methionine diet. Riedel (1954a) stated that sufficient tryptophane to promote host growth did not influence higher resistance to the chick ascarid. In another investigation it was found that glycine at a growth promoting level in the diet of a chick encouraged parasite length, but it did not alter the number of parasites harbored (Riedel, 1954b). Since leucine is indispensable from the diet of a chick (Almquist, 1947), data were taken to determine if the amino acid might affect the resistance of the chicken to the parasite, Ascaridia galli.
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index as affected by age of bird. Poultry Sci. 20: 298-301. Johnson, A. S., 1946. Factors affecting the quality and grade of Manitoba eggs. Unpublished Master's thesis, Univ. of Manitoba Library, Winnipeg, Manitoba. Johnson, A. S., and J. R. Cavers, 1948. A survey of farm egg quality. Sci. Agr. 28: 533-544. King, S. C , and C. R. Henderson, 1954. Heritability studies of egg production in the domestic fowl. Poultry Sci. 33: 155-169. Knox, E. W., and A. B. Godfrey, 1938. Factors influencing the percentage of thick albumen of hens' eggs. Poultry Sci. 17:159-162. Knox, E. W., and A. B. Godfrey, 1940. Five years of breeding for high and low percentages of thick albumen in the eggs of Rhode Island Reds. Poultry Sci. 19: 291-294. Lerner, I. M., 1950. Population Genetics and Animal Improvement. 342 pp. Cambridge University Press, Cambridge, England. Lorenz, F. W., and W. E. Newlon, 1944. A field survey of ranch egg quality. Poultry Sci. 23:418-430. Lorenz, F. W., and L. W. Taylor, 1940. The inheritance of an albumen quality characteristic of chicken eggs. J. Agr. Res. 61:293-301. McClary, D. F., and I. M. Lerner, 1950. Extra
587
C
Cavers (1948) and was considered to be in part due to high summer temperatures and poor holding conditions. Jeffrey (1941) attributed part of this decline to physiological changes in the bird with increasing age. The coincidence of the physiological decline, due to the aging of the spring-hatched pullet, and high summer temperatures increases the difficulty of maintaining high market quality in summer eggs. A seasonal decrease in shell strength which parallels that for albumen quality was observed by Wilhelm (1940), using shell thickness as a criterion, and also by O'Neil and Rae (1952) who employed the specific gravity method of measurement. In any selection program for egg quality, the effect of such selection on egg production is of importance. On the basis of rather limited data, Knox and Godfrey (1938) concluded that there was no relationship between the level of egg production and albumen quality as measured by percentage of firm white. Their report in 1940 on the results of selection of a high albumen line contained no mention of the effect of this selection on egg production. Jeffrey (1941) observed that the lowest producing hens tended to have the highest albumen quality. Brant et al. (1953) in a study of egg quality at two different egg laying trials, found, at one station, a significant negative correlation between egg production and albumen quality but no relationship at the other station. Miller and Bearse (1937) observed a significant negative correlation
578
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ONSIDERABLE attention has been focused on problems of egg quality in the past. The possibility of improving egg quality traits by breeding methods has been investigated and it has been found that the three main "components" of egg quality, namely albumen quality, shell strength, and freedom from blood and meat spots, are influenced to different degrees by heredity. The present report deals with an investigation of the first two of these traits. In this study albumen height was the criterion of albumen quality and specific gravity was used as a measure of shell strength. The effectiveness of selection in improving albumen quality has been shown by several workers, (Lorenz and Taylor, 1940; Knox and Godfrey, 1940). Taylor and Lerner (1939) demonstrated the genetic basis for shell strength by establishing two lines, differing in shell strength, from one population. McClary and Lerner (1950) reported a heritability estimate of .15 for specific gravity. Recently, data on sampling methods and some estimates of genetic parameters of egg quality traits have been presented by workers at Iowa State College. For example, Scheinberg el al. (1953) presented estimates of the heritability of albumen weight varying from .12 to .66, while Nordskog and Farnsworth (1953) estimated heritability of albumen height at .22. A seasonal decline in albumen quality of market eggs was found by Lorenz and Newlon (1944) and by Johnson and
EGG QUALITY AND EGG PRODUCTION
MATERIAXS AND METHODS
The data were obtained in 1948-49 from two flocks of pullets, one of White Leghorns and the other of Barred Rocks. In the fall of 1948, 452 and 526 pullets of each breed, respectively, were housed. Each flock was the progeny of 11 sires and 92 and 98 dams, respectively. They were
not closed flocks; limited introduction of outside stock had been made in 1944 in the White Leghorn flock and in 1947 in the case of the Barred Rocks. The pullets in each flock were produced from 2 separate hatches, the breeds being hatched alternately each week over a three-week period from March 25th to April 15th, 1948. They were reared together on range under relatively uniform conditions. The two breeds were housed in alternate pens in the same houses but at 'random within breed. Trapnest records were obtained on a seven-day-week basis. Beginning in November, 1948, all eggs laid in the first week of each month were gathered hourly and broken within two hours after collection to minimize the "post-laying" changes in albumen quality. Albumen height was measured with a tripod micrometer to the nearest .001 inch. In the second week of each month, all eggs laid were held overnight in an egg-holding room and tested the following morning for specific gravity. A series of ten salt solutions, ranging in specific gravity from 1.066 to 1.102 were made up in 10-gallon pails. About three dozen eggs at a time were placed in a wire egg basket and immersed in each solution starting with the lowest specific gravity solution. The specific gravity of the solution in which an egg first floated was recorded. Monthly records of albumen height and specific gravity were thus obtained from November 1948, to August, 1949, for every hen in production at the time of sampling. The total number of eggs tested for each trait was about 23,000. The average of two albumen height measurements on each egg was recorded. For each trait, the mean for every hen in each month was used, provided that she had measurements for at least two eggs. For purposes of analysis, the values for
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between egg production and albumen index, although their analysis does not exclude the possibility that this correlation was due to the nutritional treatments involved. Wilhelm (1940) reported that there was no correlation between egg shell thickness and level of egg production. The results of Brant et al. (1953) agree with this finding. It thus seems, from a study of the literature, that the relationship between albumen quality and egg production has not been clearly determined, while in the case of shell strength and egg production, no significant correlation has been found to exist. No reports of the magnitude or direction of genetic correlations between either of these egg quality traits and egg production have been observed in the literature. Recently, there has been some attention given to the encouragement of breeding for improved egg quality (Dawson et al., 1954). It would seem to be of primary importance to know the possible effect of such selection on egg production. For an egg quality selection program to be economically sound, it would seem necessary, at least under the present remunerative system, that this selection have no adverse effects on the egg producing ability of the strain. The study reported herein was carried out for the purpose of extending the information on the heritability of these egg quality traits and investigating their genetic relationship to egg production.
579
580
(
A. S. JOHNSON AND E. S. MERRITT
MEANS OF SIRE PROGENY CROUPS 1948 • 49
MEANS OF SIRE PROGENY GROUPS 1141 . 49
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i JAR • FED.
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'MEAN EGG PRODUCTION
' MEAN EGG PRODUCTION i i
• NOV. • DEC.
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FIGS. 1 to 4: Seasonal trends in albumen height and specific gravity of eggs from White Leghorns and Barred Rocks, showing flock means (heavy line), sire means and corresponding final egg production.
each of two months were combined, resulting in five separate two-month periods. A hen was not represented in the analysis in any given period if she lacked a measure of albumen height or of specific gravity for that period, or if she had died.
Thus, the population changed somewhat from one period to another due to non-production and mortality. The data were analyzed separately by breed. Egg production was recorded in 28-day periods. The total egg production to the
581
EGG QUALITY AND EGG PRODUCTION
TABLE 1.—Means of albumen height (in inches), specific gravity and egg production for White Leghorns and Barred Rocks by periods Period Breed Albumen height
Egg production
2 Jan.-Feb.
3 Mar-Apr.
4 May-June
5 July-August
.315+.043 .298±.042
.306 ±.045 .296 ±.041
.294±.045 .298+.044
W.L. 1.0886+.0044 B.R. 1.0837 ±.0050
l.O846±.0048 1.0809±.0049
1.0825 ±.0051 1.0800+.0049
1.0793+.0050 1.0776±.0051
1.0767 +.0050 1.0748 ±.0052
W.L. 60 ±16 B.R. 54 ±18
97 ±18 92 ±20
132 + 22 126 ±24
168 ±28 158 ±28
213 ±34 194 ±34
.337 ±.039 .324 ±.043
W.L.=White Leghorns, B.R. = Barred Rocks.
end of the period corresponding most closely to a period of quality measurement was used in calculation of correlations between the egg quality traits and production. Analyses of variance and covariance for estimating heritability and obtaining genetic and phenotypic correlations were carried out as described by Lerner (1950). The formula for the heritability calculation was 2(S+D)/S + D-|-A where S and D are sire and dam components of variance and the denominator is the phenotypic variance. RESULTS AND DISCUSSION
There was a seasonal decline in the albumen quality of the new-laid eggs of both breeds. The trend was noticeably different in the two breeds (Table 1, and Figures 1 and 2). The White Leghorns started at a higher level but their decline in albumen quality was more rapid than for the Barred Rocks and the difference between breeds had largely disappeared by July-August. The mean albumen height of the Barred Rocks had practically reached its minimum by period 3 (March-April), as illustrated in Figure 2. It stayed at essentially the same
level throughout the remainder of the test. In both breeds there was a considerable proportion of the birds laying eggs which, even when measured so soon after laying, were of only intermediate quality and would not have maintained this quality in storage. This was particularly so in the latter part of the season for the White Leghorns. The albumen quality of the sireprogeny groups in the lower range was dangerously close to a level which would result in a fairly large proportion of B grade eggs on marketing (Figures 1 and 2). Actually, a considerable number of the daughters of these sires, particularly White Leghorns Sires 7 and 8, were producing eggs in period 5 which were of quality equivalent to B grade when laid (Johnson, 1946). Others had eggs of such low quality that, with normal deterioration on holding, they would have been B grade when marketed. Johnson (1946), in a study of egg quality on Manitoba farms, found that the average albumen height of B grade eggs examined was .221 inch. He also observed that the decline in quality over a 3-day period under average farm holding conditions, as measured by a decrease in albumen
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.321 ±.039 .306± .041
W.L. B.R.
Specific gravity
1 Nov .-Dec.
582
A. S. JOHNSON AND E. S. MERRITT
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There were distinct differences between the sire means of the two egg quality traits, in both breeds, as shown by the analysis of variance in Table 2. The relative positions of the sire means were more or less maintained throughout the season in the case of albumen height; there was somewhat more change in ranking of the sires for specific gravity suggesting the possible need for testing
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height, was .040 inch. On this basis an egg with an albumen height of .261 inch or less when laid, would decline to the B grade average after three days under average farm holding conditions. Thus, a fairly large proportion of the low-grade eggs on the market in summer months may be due to initial low quality of albumen in the fresh-laid eggs as well as to the effects of high holding temperature. A seasonal decline also occurred in the specific gravity measurements and it was similar for both breeds (Table 1, and Figures 3 and 4). The White Leghorns stayed at a higher level throughout, although they dropped slightly more than the Barred Rocks, namely .0119 as against .0090. No experimental data are available to suggest the specific gravity level below which breakage in handling becomes a serious problem. The specific gravity method has been in wide use since Olsson (1934) found that most of the variation in the specific gravity of eggs was due to differences in percentage of shell. Novikoff and Gutteridge (1949) obtained a correlation of .75 between specific gravity and the force required to break the shell. The means and standard deviations in Table 1 as well as the sire means in Figures 3 and 4 show that a considerable proportion of the eggs in July-August had relatively poor shell quality as compared with the eggs in the first three periods, particularly in the Barred Rocks.
583
EGG QUALITY AND EGG PRODUCTION
TABLE 3.—Sire and dam variance components for albumen height, specific gravity and egg production, by periods Period Breed
Component
1 Nov.Dec.
2 JanFeb.
3 Mar.Apr.
4 MayJune
5 JulyAugust
W.L.
Sire Dam
207.7 290.0
246.6 246.7
264.3 181.6
274.8 201.6
336.0 149.1
B.R.
Sire Dam
79.7 106.3
39.1 156.7
28.3 52.3
48.3 61.3
72.4 117.3
W.L.
Sire Dam
5.53 -0.23
0.88 3.33
2.04 2.91
0.93 1.70
0.38 2.31
B.R.
Sire Dam
3.46 3.15
3.24 4.93
4.02 3.02
3.74 3.02
3.31 3.49
W.L.
Sire Dam
26.0 15.0
42.4 52.0
47.5 40.9
47.4 149.7
102.2 146.8
B.R.
Sire Dam
5.3 23.7
24.8 44.4
41.5 34.1
48.4 -13.1
112.6 -16.5
Albumen height*
Specific gravity*
Decode by multiplying by 10
breeds for all traits but particularly in the case of albumen height where the means of the estimates for the White Leghorns and Barred Rocks were .55 and .17 respectively. Scheinberg, Ward and Nordskog (1953) obtained heritability estimates of .66 and .12 of albumen weight in White Leghorns and Barred Rocks, respectively. Differences between breeds are also shown in the genetic variance components in Table 3 from which the heritability
for this trait at least twice during the year—once in the winter and once in the summer months. The sire means illustrated in Figures 1 to 4 include the two extremes in each breed and a representative number with intermediate values. The breed difference in range between the highest and lowest ranking sire for albumen height is particularly noticeable. The heritability estimates in Table 4 show a consistent difference between
TABLE 4.—Heritability estimates of albumen height, specific gravity and egg production of While Leghorns and Barred Rocks, by periods Period Breed
1 Nov.Dec.
2 Jan.Feb.
3 Mar.Apr.
4 MayJune
5 JulyAugust
Mean*
Albumen height
W.L. B.R.
.66 .20
.66 .23
.48 .09
.47 .13
.47 .19
.55 .17
Specific gravity
W.L. B.R.
.44 .52
.37 .68
.38 .60
.21 .52
.21 .50
.32 .56
Egg production
W.L. B.R.
.34 .18
.59 .34
.36 .27
.49 .09
.42 .17
.44 .21
* Unweighted arithmetic mean of 5 estimates.
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Egg production
584
A. S. JOHNSON AND E. S. MEERITT
TABLE 5.—Sire and dam genetic covariance components for albumen height, specific gravity and egg production of White Leghorns and Barred Rocks Period
Egg production X albumen height*
Egg production X specific gravity*
W.L. B.R.
1 Nov.Dec.
2 JanFeb.
3 Mar.Apr.
4 MayJune
5 JulyAugust
Sire Dam
-30.87 -68.90
-52.46 -62.27
-95.82 -43.24
-107.70 -112.89
-148.00 -120.62
Sire Dam
-
0.75 0.25
11.33 -26.69
34.00 -13.68
-
Sire Dam
-
5.45 1.88
4.60 2.03
5.20 1.71
B.R.
Sire Dam
-
0.82 0.89
-
W.L.
Sire Dam
-
0.11 5.77
Sire Dam
-13.00 7.72
W.L.
B.R.
45.67 1.28
-
31.92 66.48
1.47 8.56
-
6.00 0.53
2.97 6.02
-
5.39 5.70
-
11.95 9.42
- 7.28 -11.37
-12.35 -14.24
-
3.30 7.49
-
10.32 6.17
-12.84 7.63
-12.01 16.08
-
12.77 15.31
-
12.86 3.48
3.54 0.11
-
* Decode by multiplying by 10~-63. t Decode by multiplying by 10 .
estimates were derived. The large sampling error of heritability estimates calculated by means of variance component analysis is recognized. Nevertheless the consistency of these differences over the five periods suggests that the possibility of actual breed differences in heritability exists in this case, particularly with reference to albumen height. It is unlikely that the differences in heritability in the case of this trait were due to peculiarities of this criterion of albumen quality, which is uncorrected for the effect of egg weight (Haugh, 1937). The mean egg weights measured in February, 1949, were 58.2 and 59.5 grams for the White Leghorns and Barred Rocks respectively. The heritability estimates of specific gravity were of a higher level for the Barred Rocks than for the White Leghorns, which is the reverse of the situation with albumen height. There was a drop in the heritability of specific gravity for White Leghorns from a level of .38 in March-April to .21 in May-June. The
estimates of heritability of shell strength obtained from these data are, for the most part, considerably higher than the estimate of .15 given by McClary and Lerner (1950). The heritability of survivor's egg production obtained here for the Barred Rocks was somewhat below, and for the White Leghorns slightly above, the average estimate of .30 which has been reported by Lerner (1950). King and Henderson (1954) reported heritability estimates of the same trait ranging from .48 in midseason to .31 at the end of the production year. The heritability estimates obtained in this study for White Leghorns in the early part of the season were similar to theirs in magnitude. The negative phenotypic correlations between albumen height and egg production, although low, were all significant at the 1% probability level except the one for the Barred Rocks in period 5, which was non-significant (Table 6). This agrees with the results of Brant et al. (1953) at
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Albumen height X specific gravity t
Breed
Component
EGG QUALITY AND EGG PRODUCTION
585
TABLE 6.—Genetic and phenotypic correlation coefficients for albumen height, specific gravity and egg production of White Leghorns and Barred Rocks, by periods Period Breed
Egg production X albumen height
Egg production X specific gravity
2 JanFeb.
3 Mar.Apr.
4 MayJune
5 JulyAugust
W.L.
Genetic Phenotypic
-.669 -.332f
-.532 -.1981
-.637 -.265f
-.720 -.233f
-.773 -.252f
B.R.
Genetic Phenotypic
-.014 -.290f
-.132 -.211f
.260 -.154f
.714 —. 153f
-.256 -.103
W.L.
Genetic Phenotypic
.269 -.088
.333 -.037
.330 -.057
.440 -.075
.211 -.213f
B.R.
Genetic Phenotypic
-.124 -.lSlf
-.144 -.081
-.390 -.118*
-.718 - .105*
-.836 - . 124*
W.L.
Genetic Phenotypic
-.122 .040
-.409 .016
-.449 .089
-.305 .041
-.456 .017
B.R.
Genetic Phenotypic
-.150 .043
-.130 .022
.171 .086
.093 .084
-.262 .043
Phenotypic correlations: * Significant at 5% probability level. f Significant at 1% probability level.
the Rhode Island Egg Laying Test. The genetic correlations between these two traits were consistently negative in the White Leghorns, at a level of about — .65. There was good agreement between the sire and dam covariance components, on which the correlations were based (Table 5). The corresponding components in the Barred Rocks were positive for the sires but negative for the dams, with the result that the correlations fluctuated considerably and were sometives negative and sometimes positive in value. An attempt to judge the exact nature of the relationship between the traits in this breed would be more difficult than in the White Leghorns. These results do not agree with those of Knox and Godfrey (1938) who found no relationship between egg production and albumen quality (measured as percentage of firm albumen) when they were correlated on the phenotypic level. Brant el al. (1953) obtained, in one case, a significant negative phenotypic correlation and, in another, no
correlation, between the two traits. No information on the genetic relationship of these traits was found in the literature. The consistency of the genetic covariance components for egg production and albumen height of the White Leghorns (Table 5) is strong evidence of a definite negative genetic relationship between egg number and albumen quality in this strain. This implies that, everything else being equal, any selection for albumen quality would tend to have an adverse effect on egg production and vice versa. Also, selection for both traits at the same time might result in more or less of a stand-still as far as any improvement in either trait was concerned. Egg production and specific gravity were significantly correlated on the phenotypic level in the Barred Rocks in all cases except in Period 2. The only phenotypic correlation which showed significance in the White Leghorns was the one in Period 5. These results are at variance with those of Wilhelm (1940) and Brant
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Albumen height X specific gravity
1 Nov.Dec.
586
A. S. JOHNSON AND E. S. MERRITT
the standpoint of quality in the period from June to August. Heritability estimates for the two breeds were as follows: for albumen height, White Leghorns, .55, Barred Rocks, .17; for specific gravity, White Leghorns, .32, Barred Rocks, .56. Egg production was significantly correlated with both egg quality traits although at different levels for the two breeds. The outstanding results of the correlation analysis were: a significant negative phenotypic correlation between albumen height and egg production in both breeds, a genetic correlation between albumen height and egg production of the order of — .65 in the White Leghorns and .11 in the Barred Rocks, a genetic correlation between specific gravity and egg production averaging .28 for the White Leghorns and — .44 for the Barred Rocks. It is suggested that the problem of the improvement of strains for egg quality Albumen height and specific gravity traits has been oversimplified. Thorough showed no significant phenotypic correla- investigation of the genetic relationships tion in either breed. These traits had, of egg quality traits to egg production in however, a negative genetic correlation in various breeds and strains is important. the White Leghorns at an average level of Such information would be of considerable — .348. The Barred Rock correlations importance to anyone engaged in or conwere negative in three periods and positive templating selection for egg quality traits. in two. In this breed the sire and dam comACKNOWLEDGEMENT ponents were again opposite in sign (Table 5) but the dam components were positive The technical assistanceof Messrs. G. P. and the sire components negative, a reKavanagh, R. A. Lacroix and P. J. versal of the order for the breed in the McGann in taking the measurements was albumen height-egg number relationship. appreciated. SUMMARY
Data on albumen quality and shell strength were obtained monthly from November to August in two flocks of White Leghorn and Barred Rock pullets. More than 23,000 eggs were broken for albumen height measurement while an approximately similar number were tested for specific gravity. Seasonal trends showed these traits to be of main concern from
REFERENCES Brant, A. W., A. W. Otte and G. Chin, 1953. A survey of egg quality of two egg laying tests. U.S.D.A.. Tech Bull. 1066. Dawson, L. E., L. R. Champion, J. A. Davidson and H. C. Zindel, 1954. Improving egg quality through Michigan R.O.P. breeders—a progress report. Poultry Sci. 33: 293-297. Haugh, R. R., 1937. The Haugh unit for measuring egg quality. U. S. Egg Poultry Mag. 43: 760. Jeffrey, F. O., 1941. Changes in pullet year albumen
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et al. (1953) who found no significant phenotypic correlation between these two traits. The genetic correlations were positive for the White Leghorns, having a value of about .32; the corresponding correlations for the Barred Rocks were all negative, increasing progressively from - . 1 2 4 in Period 1 to - . 8 3 6 in Period 5. These correlations were quite consistent between periods in the White Leghorns and there was fairly good agreement between sire and dam estimates of covariance in both breeds. The fact that the correlations were positive in the White Leghorns but negative and of increasing magnitude in the Barred Rocks suggests that selection for egg production would have had quite different effects on shell strength in the two breeds, and vice-versa. The situation in the White Leghorns would be considered more favorable to improvement by selection.
LEUCINE AND FOWL ASCARIDS
chromosomal effects on the transmission of egg shell quality in chickens. Records Genet. Soc. Amer. 19: 113. Miller, M. W., and G. E. Bearse, 1937. Protein supplements for laying hens. Washington Agr. Exp. Sta. Bull. 347. Nordskog, A. W., and G. Farnsworth, Jr., 1953. The problem of sampling for egg quality in a breeding flock. Poultry Sci. 32:918. Novikoff, M., and H. S. Gutteridge, 1949. A comparison of certain methods of estimating shell strength. Poultry Sci. 28: 339-343. Olsson, N., 1934. Studies on Specific Gravity of Hens' Eggs. Otto Harrassowitz, Leipzig. O'Neil, J. B., and W. J. Rae, 1952. Changes in specific gravity of eggs during the laying year. Sci. Agr. 32:185-189. Scheinberg, S. L., H. Ward and A. W. Nordskog, 1953. Breeding for egg quality. 1. Heritability and repeatability of egg weight and its components. Poultry Sci. 32: 504-510. Taylor, L. W., and I. M. Lerner, 1939. Inheritance of egg shell thickness in White Leghorn pullets. J. Agr. Res. 58:383-396. Wilhelm, L. A., 1940. Some factors affecting variations in egg shell quality. Poultry Sci. 19: 246-253.
Leucine and Fowl Ascarids B E R N A R D B. R I E D E L
Department of Animal Disease, Mississippi Experiment Station, State College, Mississippi (Received for publication September 16, 1954)
I
T HAS been repeatedly shown that protein in a diet influences the degree of resistance of a fowl to parasitism (Ackert and Beach, 1933; Luttermoser and Allen, 1942; and Riedel and Ackert, 1950, 1951). Almquist and Grau (1944) presented some results which indicated that a mixture of amino acids in the diet of a growing chick could replace a protein supplement. Relative to parasites Riedel (1950) reported that lysine was not effective in protecting the fowl from the parasite Ascaridia galli, and Todd (1951) found more and larger roundworms when chicks were
fed a high methionine diet. Riedel (1954a) stated that sufficient tryptophane to promote host growth did not influence higher resistance to the chick ascarid. In another investigation it was found that glycine at a growth promoting level in the diet of a chick encouraged parasite length, but it did not alter the number of parasites harbored (Riedel, 1954b). Since leucine is indispensable from the diet of a chick (Almquist, 1947), data were taken to determine if the amino acid might affect the resistance of the chicken to the parasite, Ascaridia galli.
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index as affected by age of bird. Poultry Sci. 20: 298-301. Johnson, A. S., 1946. Factors affecting the quality and grade of Manitoba eggs. Unpublished Master's thesis, Univ. of Manitoba Library, Winnipeg, Manitoba. Johnson, A. S., and J. R. Cavers, 1948. A survey of farm egg quality. Sci. Agr. 28: 533-544. King, S. C , and C. R. Henderson, 1954. Heritability studies of egg production in the domestic fowl. Poultry Sci. 33: 155-169. Knox, E. W., and A. B. Godfrey, 1938. Factors influencing the percentage of thick albumen of hens' eggs. Poultry Sci. 17:159-162. Knox, E. W., and A. B. Godfrey, 1940. Five years of breeding for high and low percentages of thick albumen in the eggs of Rhode Island Reds. Poultry Sci. 19: 291-294. Lerner, I. M., 1950. Population Genetics and Animal Improvement. 342 pp. Cambridge University Press, Cambridge, England. Lorenz, F. W., and W. E. Newlon, 1944. A field survey of ranch egg quality. Poultry Sci. 23:418-430. Lorenz, F. W., and L. W. Taylor, 1940. The inheritance of an albumen quality characteristic of chicken eggs. J. Agr. Res. 61:293-301. McClary, D. F., and I. M. Lerner, 1950. Extra
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