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Statistical Studies on the Inheritance of Rate of Laying in White Leghorns and Rhode Island Reds
Statistical Studies on the Inheritance of Rate of Laying in W h i t e Leghorns and Rhode Island Reds A. B. GODFREY AND MOELEY A. JULL Beltsville Research Center of the V. S. Department of Agriculture, Beltsville, Maryland (Received for Publication, February 21, 1935)
Jull (1934), in an investigation involving three years' data from Rhode Island Reds
and White Leghorns, obtained significant but relatively low correlation coefficients between the rate of laying of the dams and that of their daughters. He also found that the mean rate of the daughters whose dams were above the mean rate of all the dams mated to each male was not significantly higher than the mean rate of the daughters whose dams were below the mean rate of all the dams mated to each male. Jull concluded from his study that rate of laying is affected by a relatively large number of genes, some of which probably influence more than one character. Since egg production involves so many physiological characters it is very unlikely that rate of laying is determined by only two genes. If rate is determined by multiple genes, the number of genes involved probably never will be determined. Probably the best that one can do is to estimate the proportionate influence of heredity and environment on the observed differences. Such information will be almost as useful to the breeder in a practical way as would a definite catalogue of all the genes involved. From this point of view an analysis of variance was made of rate of laying among S.C. White Leghorns and Rhode Island Reds bred at the U. S. Animal Husbandry Experiment Station at Beltsville during the years 1925-1931, inclusive. The measure of rate used in this study was the percentage production from date of first egg to March 1, which was found by
[63]
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ALTHOUGH several investigators have -t^-found rate of laying to be an excellent criterion of total egg production, few investigators have attempted to explain its factorial inheritance. All of these investigators have not used the same measure of rate. However, Knox, Jull, and Quinn (1935) have stated that the different measures used by various investigators are all duplicate measures of rate. Pearl (1912) reported that the number of eggs produced before March 1 was determined by two dominant factors, one autosomal and the other sex-linked. Goodale and MacMullen (1919) reported results that were in agreement with Pearl's theory, but they also proposed an alternative theory that recognized two dominant, autosomal factors which could also account for Pearl's results. Goodale stated that the methods used by Pearl and himself were inadequate to solve the problem and concluded that the mode of inheritance of winter egg production remained to be determined. Hurst (1921) reported that the inheritance of percentage production from date of first egg to March 1 could be explained by Goodale's theory of two dominant autosomal factors. Hays (1924), using as a measure of rate the percentage production from date of first egg to March 1, obtained results that he reported could be explained by Goodale's proposed theory.
64
POULTRY
Knox, Jull, and Quinn to be the most suitable measure of rate of laying. The data were obtained from 54 pens of White Leghorns, involving 468 yearling dams and 2,428 daughters, and 55 pens of Rhode Island Reds, including 466 yearling dams and 2,226 daughters. The dams were
SCIENCE
at a greater rate but also were inclined to be less variable with respect to rate of laying. It is also to be noted that the mean rate of laying for the seven years was 52.4 percent for the White Leghorns and 55.5 percent for the Rhode Island Reds. The following components which con-
TABLE 1.—Mean rate of laying of the. daughters with standard deviation for each year White Leghorns
Rhode Island Red
of laying to Mar. 1
Standard deviation
No. of daughters
of laying to Mar. 1
Standard deviation
1925 1926 1927 1928 1929 1930 1931
278 406 415 307 355 350 317
Percent 44.8 50.3 53.1 55.2 54.5 51.9 56.1
Percent 16.5 15.3 13.9 14.2 14.1 13.8 12.8
212 303 341 373 350 303 344
Percent 48.0 54.4 55.0 55.1 54.1 59.8 59.6
Percent 16.9 16.4 14.5 15.8 16.2 15.1 12.4
Total
2,428
52.4
14.7
55.5
15.6
selected on the basis of having laid 200 or more eggs during the first laying year, and the sires were selected from dams that had laid 200 or more eggs during their first laying year, except that from 1928 to 1931, inclusive, in the White Leghorns the minimum number of eggs laid by each dam and sire's dam was 225 eggs. The daughters included all pullets that began laying before March 1. The daughters were hatched at approximately the same consecutive periods each year during the breeding season of 1925 to 1931, inclusive, and in the laying houses they were given as identical environmental conditions as it was practical to maintain. The mean rate of laying and standard deviation for each year are given in Table 1. It is apparent from the data in Table 1 that the method of selecting the dams and sires each year affected materially the rate of production of the pullets from year to year. The pullets raised during the subsequent years for the most part not only laid
2.226
tributed to the total variability was investigated: (1) Variability "between years." (2) Variability "between sires of the same year" (variability of pullets less related than half-sisters). (3) Variability "between dams of the same year with the same sire" (variability of half-sisters). (4) Variability "within dams" (variability of full sisters). The results of the entire analysis are summarized in Table 2. The significant points of the distribution of "z" were obtained by the procedure described by Fisher (1932). In each breed the variability "within dams" was significantly less than either the variability "between dams of the same year with the same sire" or the variability "between sires of the same year." This means that the variability of full sisters is significantly less than the variability of either
Downloaded from http://ps.oxfordjournals.org/ by guest on June 9, 2015
No. of daughters
JANUARY,
1936.
VOL.
XV,
No.
half-sisters or less closely related birds. In each breed the variability "between dams of the same year with the same sire" was also significantly less than the variability "between sires of the same year." This shows that the variability of half-sisters was significantly less than the variability of the
1
65
dams and the rate of laying of daughters in White Leghorns and 0.154 between the rate of laying of dams and the rate of laying of daughters in Rhode Island Reds. It is apparent, therefore, that in the selected groups of dams under discussion the rate of laying of the dam could not be regarded as a cri-
TABLE 2.—Analysis of variance in rate of laying White Leghorns
Rhode Island Reds
Mean square
Degrees 5 Log.c of free- Sum of squares dom
Mean square
J Log.e
6
26,554
4,426
4.1976
6
24,291
4,049
4.1531
Between sires of the same year (pullets less related than half-sisters)
47
82,928
1,764
3.7377
48
45,099
940
3.4229
Between dams of the same year with the same sire (half-sisters)
414
104,831
253
2.7667
411
111,851
272
2.8029
1,960
313,323
160
2.5376
1,760 •362,585
206
2.6639
2,427
527,636
217
2.6899
2,225
244
2.7486
Between years
Within dams (full sisters) Total
less related birds. In each breed the mean square for "between years" is also significantly greater than the mean square for either of the other causes of variability. This variability "between years" is due not only to uncontrolled environmental conditions but also to the effect of indirect selection from year to year. As the variability "between sires of the same year" in both breeds was significantly greater than the variability "within dams," sires differ significantly in their ability to transmit rate of laying to their daughters. As the variability "between dams of the same year with the same sire" in both breeds was significantly greater than the variability "within dams," dams differ significantly in their ability to transmit rate of laying to their daughters. In dealing with some of the same birds Jull (1934) obtained an interclass correlation of 0.108 between the rate of laying of
543,826
terion of the transmitting ability of the dam in respect to this particular character. The results obtained in this study by the method of analysis of variance indicate, however, that the dams, selected on the basis of first year egg production, differed in their transmitting ability and that the selected sires also differed in their transmitting ability. The method of analysis of variance measures the segregation of the daughters for rate of laying from each sire or dam regardless of the phenotypic performance of the parents. For instance, if all birds of a pen laid at the same relative rate during their first laying year, it would be impossible to obtain a significant correlation between their rate and that of their daughters, but these dams may differ significantly in their ability to transmit high rate of laying to their daughters. Therefore, the analysis of variance is a more adequate method than the methods of correlation for
Downloaded from http://ps.oxfordjournals.org/ by guest on June 9, 2015
Degrees Sum of of free- squares dom
Source of variation
66
POULTRY
treating data on such problems as the one in this investigation. CONCLUSIONS
REFERENCES
Fisher, R. A., 1932. Statistical Methods for Research Workers. 4th ed. Oliver and Boyd, Edinburgh and London. Goodale, H. D. and Grace MacMullen, 1919. The bearing of ratios on theories of inheritance of winter egg production. Jour. Expt. Zool. 28:83124. Hays, F. A., 1924. Inbreeding the Rhode Island Red fowl with special reference to winter egg production. Amer. Nat. 58: 43-59. Hurst, C. C , 1921. Genetics of egg production in White Leghorns and White Wyandottes and its application to poultry breeding. Trans. First World Poultry Congress 1:3-20. Jull, M. A., 1934. Inheritance of sexual maturity, rate, and persistence of laying in the domestic fowl. Poul. Sci. 13 :286-289. Knox, C. W., M. A. Jull, and J. P. Quinn, 1935. Correlation studies of egg production and possible genetic interpretations. Jour. Agr. Res. 50: 573-589. Pearl, Raymond. 1912. The mode of inheritance of fecundity in the domestic fowl. Jour. Expt. Zool. 13: 153-268.
GROWTH OF CHICK EMBRYOS FROM HENS FED DIFFERENT PROTEIN LEVELS (Continued from page 18) Records were kept of infertile and dead in the shell on both lots of birds. Lot 1 contained 8.33 percent infertile and dead and Lot 2 contained 7.Q6 per cent infertile and dead in the shell. Due to the small number of dead embryos and infertile eggs no attempt was made to study the cause. SUMMARY Growth of embryos were observed from two lots of hens which had been fed on high and low protein levels. The embryos from the high protein lot were heavier between the seventh and seventeenth days, the period suggested by Needham (1927) when the chick embryo uses protein as a source of energy. An analysis of variance for this period revealed a greater variation within the groups than between the groups indicating the differences obtained to be insignificant. There is also a greater variation within the groups than between the groups when the total nitrogen of the embryos is considered.
Although the embryos from the high protein fed hens were heavier during the greater part of the incubation period as shown by both wet weight and dry weight, an analysis of variance shows these differences to be insignificant. The fact that both wet and dry weights obtained from the high protein group exceeded the group on the lower protein level suggests that a real difference may exist. It is possible that a larger number of embryos would yield significant values. ROBT. PENQUITE AND R. B. THOMPSON
Oklahoma A. & M. College, Stillwater REFERENCES
Dove, F. W., 1931. Exp. Sta. Bui. 360:174-175. Gerber, L. and R. H. Carr 1931. J. Nutr., 3:245. Henderson, E. W. 1930. Exp. Sta. Res. Bui. 149. McFarlane W. D., H. Lehman, and T. H. Jukes 1930 Biochem. J. 24:1611. Needham, Joseph, 1926. British J. Exp. Biol. 4:115. Titus, H. W., T. C. Byerly and N. R. Ellis, 1933. J. Nutr. 6:127
Downloaded from http://ps.oxfordjournals.org/ by guest on June 9, 2015
The results obtained seem to warrant the following conclusions: Sires differ significantly in their ability to transmit high rate of laying to their daughters. Dams differ significantly in their ability to transmit high rate of laying to their daughters. Full sisters lay more nearly at the same rate than half-sisters or less related pullets. Half-sisters lay more nearly at the same rate than less related pullets. The rate of laying of a flock can be increased materially by using the total first year egg production as a criterion for selecting and progeny testing the breeders.
SCIENCE
Jull (1934), in an investigation involving three years' data from Rhode Island Reds
and White Leghorns, obtained significant but relatively low correlation coefficients between the rate of laying of the dams and that of their daughters. He also found that the mean rate of the daughters whose dams were above the mean rate of all the dams mated to each male was not significantly higher than the mean rate of the daughters whose dams were below the mean rate of all the dams mated to each male. Jull concluded from his study that rate of laying is affected by a relatively large number of genes, some of which probably influence more than one character. Since egg production involves so many physiological characters it is very unlikely that rate of laying is determined by only two genes. If rate is determined by multiple genes, the number of genes involved probably never will be determined. Probably the best that one can do is to estimate the proportionate influence of heredity and environment on the observed differences. Such information will be almost as useful to the breeder in a practical way as would a definite catalogue of all the genes involved. From this point of view an analysis of variance was made of rate of laying among S.C. White Leghorns and Rhode Island Reds bred at the U. S. Animal Husbandry Experiment Station at Beltsville during the years 1925-1931, inclusive. The measure of rate used in this study was the percentage production from date of first egg to March 1, which was found by
[63]
Downloaded from http://ps.oxfordjournals.org/ by guest on June 9, 2015
ALTHOUGH several investigators have -t^-found rate of laying to be an excellent criterion of total egg production, few investigators have attempted to explain its factorial inheritance. All of these investigators have not used the same measure of rate. However, Knox, Jull, and Quinn (1935) have stated that the different measures used by various investigators are all duplicate measures of rate. Pearl (1912) reported that the number of eggs produced before March 1 was determined by two dominant factors, one autosomal and the other sex-linked. Goodale and MacMullen (1919) reported results that were in agreement with Pearl's theory, but they also proposed an alternative theory that recognized two dominant, autosomal factors which could also account for Pearl's results. Goodale stated that the methods used by Pearl and himself were inadequate to solve the problem and concluded that the mode of inheritance of winter egg production remained to be determined. Hurst (1921) reported that the inheritance of percentage production from date of first egg to March 1 could be explained by Goodale's theory of two dominant autosomal factors. Hays (1924), using as a measure of rate the percentage production from date of first egg to March 1, obtained results that he reported could be explained by Goodale's proposed theory.
64
POULTRY
Knox, Jull, and Quinn to be the most suitable measure of rate of laying. The data were obtained from 54 pens of White Leghorns, involving 468 yearling dams and 2,428 daughters, and 55 pens of Rhode Island Reds, including 466 yearling dams and 2,226 daughters. The dams were
SCIENCE
at a greater rate but also were inclined to be less variable with respect to rate of laying. It is also to be noted that the mean rate of laying for the seven years was 52.4 percent for the White Leghorns and 55.5 percent for the Rhode Island Reds. The following components which con-
TABLE 1.—Mean rate of laying of the. daughters with standard deviation for each year White Leghorns
Rhode Island Red
of laying to Mar. 1
Standard deviation
No. of daughters
of laying to Mar. 1
Standard deviation
1925 1926 1927 1928 1929 1930 1931
278 406 415 307 355 350 317
Percent 44.8 50.3 53.1 55.2 54.5 51.9 56.1
Percent 16.5 15.3 13.9 14.2 14.1 13.8 12.8
212 303 341 373 350 303 344
Percent 48.0 54.4 55.0 55.1 54.1 59.8 59.6
Percent 16.9 16.4 14.5 15.8 16.2 15.1 12.4
Total
2,428
52.4
14.7
55.5
15.6
selected on the basis of having laid 200 or more eggs during the first laying year, and the sires were selected from dams that had laid 200 or more eggs during their first laying year, except that from 1928 to 1931, inclusive, in the White Leghorns the minimum number of eggs laid by each dam and sire's dam was 225 eggs. The daughters included all pullets that began laying before March 1. The daughters were hatched at approximately the same consecutive periods each year during the breeding season of 1925 to 1931, inclusive, and in the laying houses they were given as identical environmental conditions as it was practical to maintain. The mean rate of laying and standard deviation for each year are given in Table 1. It is apparent from the data in Table 1 that the method of selecting the dams and sires each year affected materially the rate of production of the pullets from year to year. The pullets raised during the subsequent years for the most part not only laid
2.226
tributed to the total variability was investigated: (1) Variability "between years." (2) Variability "between sires of the same year" (variability of pullets less related than half-sisters). (3) Variability "between dams of the same year with the same sire" (variability of half-sisters). (4) Variability "within dams" (variability of full sisters). The results of the entire analysis are summarized in Table 2. The significant points of the distribution of "z" were obtained by the procedure described by Fisher (1932). In each breed the variability "within dams" was significantly less than either the variability "between dams of the same year with the same sire" or the variability "between sires of the same year." This means that the variability of full sisters is significantly less than the variability of either
Downloaded from http://ps.oxfordjournals.org/ by guest on June 9, 2015
No. of daughters
JANUARY,
1936.
VOL.
XV,
No.
half-sisters or less closely related birds. In each breed the variability "between dams of the same year with the same sire" was also significantly less than the variability "between sires of the same year." This shows that the variability of half-sisters was significantly less than the variability of the
1
65
dams and the rate of laying of daughters in White Leghorns and 0.154 between the rate of laying of dams and the rate of laying of daughters in Rhode Island Reds. It is apparent, therefore, that in the selected groups of dams under discussion the rate of laying of the dam could not be regarded as a cri-
TABLE 2.—Analysis of variance in rate of laying White Leghorns
Rhode Island Reds
Mean square
Degrees 5 Log.c of free- Sum of squares dom
Mean square
J Log.e
6
26,554
4,426
4.1976
6
24,291
4,049
4.1531
Between sires of the same year (pullets less related than half-sisters)
47
82,928
1,764
3.7377
48
45,099
940
3.4229
Between dams of the same year with the same sire (half-sisters)
414
104,831
253
2.7667
411
111,851
272
2.8029
1,960
313,323
160
2.5376
1,760 •362,585
206
2.6639
2,427
527,636
217
2.6899
2,225
244
2.7486
Between years
Within dams (full sisters) Total
less related birds. In each breed the mean square for "between years" is also significantly greater than the mean square for either of the other causes of variability. This variability "between years" is due not only to uncontrolled environmental conditions but also to the effect of indirect selection from year to year. As the variability "between sires of the same year" in both breeds was significantly greater than the variability "within dams," sires differ significantly in their ability to transmit rate of laying to their daughters. As the variability "between dams of the same year with the same sire" in both breeds was significantly greater than the variability "within dams," dams differ significantly in their ability to transmit rate of laying to their daughters. In dealing with some of the same birds Jull (1934) obtained an interclass correlation of 0.108 between the rate of laying of
543,826
terion of the transmitting ability of the dam in respect to this particular character. The results obtained in this study by the method of analysis of variance indicate, however, that the dams, selected on the basis of first year egg production, differed in their transmitting ability and that the selected sires also differed in their transmitting ability. The method of analysis of variance measures the segregation of the daughters for rate of laying from each sire or dam regardless of the phenotypic performance of the parents. For instance, if all birds of a pen laid at the same relative rate during their first laying year, it would be impossible to obtain a significant correlation between their rate and that of their daughters, but these dams may differ significantly in their ability to transmit high rate of laying to their daughters. Therefore, the analysis of variance is a more adequate method than the methods of correlation for
Downloaded from http://ps.oxfordjournals.org/ by guest on June 9, 2015
Degrees Sum of of free- squares dom
Source of variation
66
POULTRY
treating data on such problems as the one in this investigation. CONCLUSIONS
REFERENCES
Fisher, R. A., 1932. Statistical Methods for Research Workers. 4th ed. Oliver and Boyd, Edinburgh and London. Goodale, H. D. and Grace MacMullen, 1919. The bearing of ratios on theories of inheritance of winter egg production. Jour. Expt. Zool. 28:83124. Hays, F. A., 1924. Inbreeding the Rhode Island Red fowl with special reference to winter egg production. Amer. Nat. 58: 43-59. Hurst, C. C , 1921. Genetics of egg production in White Leghorns and White Wyandottes and its application to poultry breeding. Trans. First World Poultry Congress 1:3-20. Jull, M. A., 1934. Inheritance of sexual maturity, rate, and persistence of laying in the domestic fowl. Poul. Sci. 13 :286-289. Knox, C. W., M. A. Jull, and J. P. Quinn, 1935. Correlation studies of egg production and possible genetic interpretations. Jour. Agr. Res. 50: 573-589. Pearl, Raymond. 1912. The mode of inheritance of fecundity in the domestic fowl. Jour. Expt. Zool. 13: 153-268.
GROWTH OF CHICK EMBRYOS FROM HENS FED DIFFERENT PROTEIN LEVELS (Continued from page 18) Records were kept of infertile and dead in the shell on both lots of birds. Lot 1 contained 8.33 percent infertile and dead and Lot 2 contained 7.Q6 per cent infertile and dead in the shell. Due to the small number of dead embryos and infertile eggs no attempt was made to study the cause. SUMMARY Growth of embryos were observed from two lots of hens which had been fed on high and low protein levels. The embryos from the high protein lot were heavier between the seventh and seventeenth days, the period suggested by Needham (1927) when the chick embryo uses protein as a source of energy. An analysis of variance for this period revealed a greater variation within the groups than between the groups indicating the differences obtained to be insignificant. There is also a greater variation within the groups than between the groups when the total nitrogen of the embryos is considered.
Although the embryos from the high protein fed hens were heavier during the greater part of the incubation period as shown by both wet weight and dry weight, an analysis of variance shows these differences to be insignificant. The fact that both wet and dry weights obtained from the high protein group exceeded the group on the lower protein level suggests that a real difference may exist. It is possible that a larger number of embryos would yield significant values. ROBT. PENQUITE AND R. B. THOMPSON
Oklahoma A. & M. College, Stillwater REFERENCES
Dove, F. W., 1931. Exp. Sta. Bui. 360:174-175. Gerber, L. and R. H. Carr 1931. J. Nutr., 3:245. Henderson, E. W. 1930. Exp. Sta. Res. Bui. 149. McFarlane W. D., H. Lehman, and T. H. Jukes 1930 Biochem. J. 24:1611. Needham, Joseph, 1926. British J. Exp. Biol. 4:115. Titus, H. W., T. C. Byerly and N. R. Ellis, 1933. J. Nutr. 6:127
Downloaded from http://ps.oxfordjournals.org/ by guest on June 9, 2015
The results obtained seem to warrant the following conclusions: Sires differ significantly in their ability to transmit high rate of laying to their daughters. Dams differ significantly in their ability to transmit high rate of laying to their daughters. Full sisters lay more nearly at the same rate than half-sisters or less related pullets. Half-sisters lay more nearly at the same rate than less related pullets. The rate of laying of a flock can be increased materially by using the total first year egg production as a criterion for selecting and progeny testing the breeders.
SCIENCE