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Breeding a Low Producing Strain of Single Comb White Leghorns
Breeding a Low Producing Strain of Single Comb White Leghorns G. O. HALL Cornell University, Ithaca, New York (Received for Publication July 12, 1933)
B
METHOD OF PROCEDURE
Previous to 1914 only one line of breeding was followed at the Cornell Experiment Station. During the year 1913-14 two selections were made. One of these selections was called the low-line and that year the average production of the low birds was
99.5 eggs. The high producing birds laid 118.5 eggs per bird. During the first few years a small number of low producing individuals were selected from the high-line birds and placed in the low-line breeding pen. Since 1917 no outside blood has been introduced into this line, except one male from which only a few daughters were saved. Until 1924, hens and some pullets mated to cockerels were used as breeders. Since 1924 only hens have been used as breeding females and they have been mated to cockerels each year. The practices which have been followed have not been complicated. Each year eggs from the breeding pen were saved and set weekly in the same incubators with the general experimental plant eggs. All chicks were individually pedigreed. The chicks were brooded and raised in the same houses and on the same range as the other chicks on the experimental farm. The most promising cockerels were saved when the young birds were culled at the broiler age. They were selected for size, vigor, and general appearance. About the middle of October each year the pullets trapnested the previous year were handled and only those birds retained for breeding purposes which laid less than 120 eggs, providing there were enough available to fill the breeding pen after the old birds have been carefully culled. The maximum production of the breeding females was kept as low as possible. The pens usually contained 35 to 37 birds, and the pen with the old hens and yearlings became the
[123]
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on May 31, 2015
REEDING for low fecundity in the domestic fowl would seem to be a task very easy of accomplishment. Yet it is an interesting fact that it is almost as difficult a problem to produce a low fecundity strain of birds as it is a high fecundity strain, assuming that the environmental conditions, feed, and management are adequate and the same in both cases. Such a breeding project might be considered by some a waste of time. Certainly in the case of the practical poultry breeder it would be very unprofitable to follow such a line of breeding. However, from the standpoint of experimentation and of practical information, the experiment on low-line and high-line Single Comb White Leghorns has been quite fruitful. Marble and Hall (1931) give a comparison of the low-line high-line leghorns for a number of characters, covering the period 1908 to 1928. So far as the writer is aware no other experiment, exactly similar in nature to the low-line and high-line work, has been conducted over even a short period of time. Experiments in breeding for low production have been started by a few investigators but too close inbreeding was practiced and the line ran out after a few generations.
124 TABLE
POULTRY 1.—i
es in the low-line and high-line flocks with respect to production, davs to maturity, egg weight and body weight {1914-1932) High Line
Low Line Year
-SCIENCE
Mean
C.V.
Mean
C.V.
118.50 120.34 124.81 130.70 130.54 164.14 160.58 159.85 157.58 165.00 164.97 176.96 171.81 185.52 196.03 213.65 214.07 214.17 209.24
34.22 28.11 29.90 30.68 28.07 24.80 25.51 26.77 22.34 23.89 25.47 23.33 25.20 23.46 22.02 21.45 12.24 19.97 22.23
231.50 240.34 252.18 228.72 220.40 227.93 204.70 205.33 218.85 230.30 206.70 195.68 199.14 199.36 209.65 201.94 197.91 193.08 202.87
13.93 13.22 17.42 12.22 10.15 11.78 18.64 14.80 16.55 11.99 14.15 8.48 15.51 20.58 10.78 7.65 12.75 8.11 10.59
Production—first year 99.50 97.04 98.61 124.47 82.81 109.79 124.71 107.80 106.09 113.75 118.12 118.90 121.90 131.67 131.80 121.48 101.94 113.56 96.30
30.23 37.83 26.73 20.59 41.78 24.92 29.10 25.10 31.66 23.28 25.70 30.90 32.05 22.28 20.89 33.82 26.59 32.34 32.94 Days to Maturity
1913-14 14-15 15-16 16-17 17-18 18-19 19-20 20-21 21-22 22-23 23-24 24-25 25-26 26-27 27-28 28-29 29-30 30-31 31-32
251.50 242.27 261.67 231.32 252.40 264.84 224.90 241.00 295.73 265.42 267.19 222.83 240.20 244.33 231.60 268.21 290.42 249.19 253.61
11.19 11.51 16.33 5.81 16.89 10.67 25.17 17.41 14.48 12.23 19.84 16.88 13.42 11.44 10.92 18.48 12.50 18.58 12.72
breeding pen for the following year. Very low producing old hens were kept as long as they gave good hatching results. All the pullets from the low-line were brought together in the fall and a pen of 37 of the largest, most mature and vigorous pullets selected for the low-line pullet pen. These pullets were placed in a house 12 by 12 feet and fed, lighted, and managed in exactly the same manner as certain high-
line pens. They received the standard Cornell laying ration. The cockerels were selected in the fall and birds chosen whose dams have made a very low record. Most of the records of the dams whose sons have been used during the past few years have been under 100 eggs. Since full-brother matings have been used in the breeding pen for several years, preference was given them in the selection
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on May 31, 2015
1913-14 14-15 15-16 16-17 17-18 18-19 19-20 20-21 21-22 22-23 23-24 24-25 25-26 26-27 27-28 28-29 29-30 30-31 31-32
MARCH,
1934.
VOL.
XIII,
No. 2
TABLE 1. {Continued)
Egg weight—first year Low Line Year
C.V.
54.95 54.89 52.97 54.58 52.64 53.06 54.78 54.84 54.84 56.79 58.25 55.04 56.78 59.07 58.96 58.17 59.25 54.92 55.07
Mean
6.45 7.01 6.42 6.44 7.25 6.87 6.99 4.94 6.33 6.39 6.27 6.51 5.84 5.91 5.62 4.53 4.32 5.38 5.71
53.64 53.58 53.93 53.08 62.26 53.00 55.55 55.60 53.76 55.48 55.93 54.98 56.98 56.84 57.41 56.63 56.83 56.45 56.63
C.V. 7.41 7.12 6.26 6.33 7.40 5.85 6.15 7.25 6.56 6.86 7.09 6.33 6.94 6.86 6.35 6.94 6.22 6.61 6.57
Body weight—first year 1913-14 14-15 15-16 16-17 17-18 18-19 19-20 20-21 21-22 22-23 23-24 24-25 25-26 26-27 27-28 28-29 29-30 30-31 31-32
3.370 3.084 2.967 3.084 3.179 3.100 3.297 3.540 3.277 3.300 3.584 3.361 3.619 3.748 3.728 4.126 3.880 3.523 3.744
14.07 11.48 9.81 8.04 11.67 10.32 10.61 9.49 11.46 8.12 11.22 9.66 11.38 9.13 9.28 9.87 10.03 6.94 9.18
of cockerels. Vigor and body size have always been considered in selecting males as well as females. Egg size and egg color have not been given special consideration. RESULTS What changes have come about in this strain of birds as a result of such a breeding program? Table 1 gives the data covering four characters, average annual production, egg weight, body weight, and age at first
'
3.167 3.162 3.231 3.080 3.236 3.405 3.709 3.656 3.477 3.602 3.724 3.693 3.810 3.858 4.083 4.116 4.024 3.927 4.013
10.95 9.26 10.12 10.64 10.97 9.93 12.35 11.68 11.56 12.62 12.00 10.56 10.73 10.44 9.89 10.62 10.69 11.28 10.94
egg (sexual maturity). Similar data are given for the high-line birds. As stated previously, the average production of the low-line birds at the beginning of the experiment in 1913-14 was 99.5 eggs per bird. The maximum average production reached in 1927-28 was 131.8 eggs per bird, yet it is interesting to note that as early as 1916-17 the production reached 124.5 eggs per bird. Very little change has taken place in average egg production. The
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on May 31, 2015
1913-14 14-15 15-16 16-17 17-18 18-19 19-20 20-21 21-22 22-23 23-24 24-25 25-26 26-27 27-28 28-29 29-30 30-31 31-32
Mean
High Line
126 ,
POULTRY
fluences are laying on the average about 100 eggs per bird more than the low-line individuals. Changes in Vigor The changes in natural vigor of these birds is no doubt of greater interest than the production records. Three measures of vigor have been used to illustrate these changes; namely, first year mortality (beginning in 1918), fertility, and hatchability records (commencing in 1919). New blood had been added up until 1917. Table 2 gives the means for three measures of vigor. As in the case with the other characters there are wide annual variations, but there are no distinct trends apparent. It may be assumed from these figures that these birds have not lost in vitality over a period of fifteen years under the methods of breeding which have been followed. They have not suffered under the effects of inbreeding as have been reported by many investigators where close inbreeding methods have been followed. According to the theory of the inheritance of egg production formulated by Hays (1929) and Hays and Sanborn (1926a, b, c, 1927a, b) it is the opinion of the writer that
TABLE 2.—Mortality, fertility and hatchability of low-line Single Comb White Leghorns {1918 to 1932)
Yes.r
Mortality first year (percent)
No. eggs set
Hatch (percent)
1917-18 18-19 19-20 20-21 21-22 22-23 23-24 24-25 25-26 26-27 27-28 28-29 29-30 30-31 31-32 32-33
31.6 21.1 13.9 13.9 6.9 28.6 14.3 37.1 25.7 8.6 30.6 20.0 16.2 24.3 35.1 18.2
131 97 273 181 455 680 625 294 734 433 649 492 625 511 601
51.1 40.2 77.3 43.6 55.8 58.8 50.6 71.0 36.8 55.9 67.9 54.1 59.2 67.9 65.2
Fertility (percent) 93.1 80.4 98.16 80.7 77.8 89.1 65.8 96.6 81.1 79.0 90.0 88.6 90.9 92.6 83.7
Hatchability (percent) 54.9 50.0 78.7 54.1 71.8 66.0 76.9 73.5 45.4 70.8 75.5 61.0 65.1 73.4 77.9
"
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on May 31, 2015
variability for egg production has remained practically constant. In connection with production it must be remembered that environmental conditions and influences have been improved constantly during the experimental period. There was a gradual increase in body weight until the year 1929-30, although there have been rather pronounced seasonal variations. The variability has been relatively low. Egg weight, although it has not been given much consideration, has changed in much the same manner as body weight. This would indicate that size of body has a rather intimate relationship with size of egg. This relationship has been rather well established by the Canadian Record of Performance work (1929) as well as by other investigations. The variability has been low from year to year and has not changed materially. Age at first egg, or sexual maturity, shows rather wide annual variations, although no distinct trends can be seen. The annual variability has not been as constant as in the case of egg weight. The figures presented show that the highline birds, under similar environmental in-
SCIENCE
MARCH,
1934.
VOL.
XIII,
No. 2
the majority of the low-line birds saved for breeding purposes are of the following genetic constitution, eee'e'WW rrrVaaccpp in which e and e' are recessive duplicate genes for late sexual maturity, W is the dominant gene for winter pause, r and r' are the complementary recessive genes for low rate of winter production a and c are the recessive genes giving non-broodiness and p is the recessive gene for low persistency. There is little or no evidence on the genes for egg size available.
birds gives a direct measure of the influence of heredity upon egg production. REFERENCES
Canadian National Poultry Record Association. Blue Book, 1929. Hays, F. A., 1929. Inbreeding in relation to egg production. Mass. Agr. Exp. Sta. Bui. 258. Hays, F. A. and Ruby Sanborn, 1926. Broodiness in relation to fecundity in the domestic fowl. Mass Agr. Exp. Sta. Tech. Bui. 7. , 1926b. Winter cycle and winter pause in relation to winter and annual egg production. Mass. Agr. Exp. Sta. Tech. Bui. 8. , 1926c. Annual persistency in relation to winter and annual egg production. Mass. Agr. Exp. Sta. Tech. Bui. 9. , 1927a. Intensity or rate of laying in relation to fecundity. Mass. Agr. Exp. Sta. Tech. Bui. 11. , 1927b. Net correlations of characters concerned in fecundity. Mass. Agr. Exp. Sta. Tech. Bui. 12. Marble, D. R. and G. O. Hall, 1931. A statistical analysis of the results of breeding high-line and low-line Leghorns. Cornell Univ. Agr. Exp. Sta. Bui. S33.
Reviews The book is divided into four parts with George W. Snedecor, Calculation and Interpretation of Analysis of Variance and twelve examples. For each example the Covariance, Ames: Collegiate Press, Inc., source and other information regarding the data used, together with the question to be 1934. 105 pages. $1.00. Many of the investigations with poul- answered, are first given. This is followed try require statistical treatment of the data by complete instructions for calculation, a collected before the results can be properly fairly full discussion, a brief interpretation evaluated, hence, any book that presents in and concluded with notes on theory. The a simple manner Fisher's recently developed, clear and complete instructions given under useful, statistical methods is sure to be wel- computation appear to the reviewer to be comed by both research workers and teach- an especially valuable feature. While only one of the examples deals with ers. Moreover, many have experienced difficulty in applying the analysis of variance to poultry, the application of the methods to the treatment of their own data and have data from different sources is obvious. This found some of the ideas puzzling. For these monograph by Professor Snedecor should, and others who have hesitated to attempt to therefore, prove useful to those who are conuse the analysis of variance because of cerned with poultry research. V. S. ASMUNDSON limited mathematical training the present volume should prove particularly useful. University of California
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on May 31, 2015
SUMMARY
It has been possible with a rather simple system of selecting and mating, which has avoided close inbreeding, to produce a strain of birds in which the production, mortality, age at first egg, fertility, and hatchability have not changed materially for fifteen years. A comparison between the production records of the low-line and high-line
127
B
METHOD OF PROCEDURE
Previous to 1914 only one line of breeding was followed at the Cornell Experiment Station. During the year 1913-14 two selections were made. One of these selections was called the low-line and that year the average production of the low birds was
99.5 eggs. The high producing birds laid 118.5 eggs per bird. During the first few years a small number of low producing individuals were selected from the high-line birds and placed in the low-line breeding pen. Since 1917 no outside blood has been introduced into this line, except one male from which only a few daughters were saved. Until 1924, hens and some pullets mated to cockerels were used as breeders. Since 1924 only hens have been used as breeding females and they have been mated to cockerels each year. The practices which have been followed have not been complicated. Each year eggs from the breeding pen were saved and set weekly in the same incubators with the general experimental plant eggs. All chicks were individually pedigreed. The chicks were brooded and raised in the same houses and on the same range as the other chicks on the experimental farm. The most promising cockerels were saved when the young birds were culled at the broiler age. They were selected for size, vigor, and general appearance. About the middle of October each year the pullets trapnested the previous year were handled and only those birds retained for breeding purposes which laid less than 120 eggs, providing there were enough available to fill the breeding pen after the old birds have been carefully culled. The maximum production of the breeding females was kept as low as possible. The pens usually contained 35 to 37 birds, and the pen with the old hens and yearlings became the
[123]
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on May 31, 2015
REEDING for low fecundity in the domestic fowl would seem to be a task very easy of accomplishment. Yet it is an interesting fact that it is almost as difficult a problem to produce a low fecundity strain of birds as it is a high fecundity strain, assuming that the environmental conditions, feed, and management are adequate and the same in both cases. Such a breeding project might be considered by some a waste of time. Certainly in the case of the practical poultry breeder it would be very unprofitable to follow such a line of breeding. However, from the standpoint of experimentation and of practical information, the experiment on low-line and high-line Single Comb White Leghorns has been quite fruitful. Marble and Hall (1931) give a comparison of the low-line high-line leghorns for a number of characters, covering the period 1908 to 1928. So far as the writer is aware no other experiment, exactly similar in nature to the low-line and high-line work, has been conducted over even a short period of time. Experiments in breeding for low production have been started by a few investigators but too close inbreeding was practiced and the line ran out after a few generations.
124 TABLE
POULTRY 1.—i
es in the low-line and high-line flocks with respect to production, davs to maturity, egg weight and body weight {1914-1932) High Line
Low Line Year
-SCIENCE
Mean
C.V.
Mean
C.V.
118.50 120.34 124.81 130.70 130.54 164.14 160.58 159.85 157.58 165.00 164.97 176.96 171.81 185.52 196.03 213.65 214.07 214.17 209.24
34.22 28.11 29.90 30.68 28.07 24.80 25.51 26.77 22.34 23.89 25.47 23.33 25.20 23.46 22.02 21.45 12.24 19.97 22.23
231.50 240.34 252.18 228.72 220.40 227.93 204.70 205.33 218.85 230.30 206.70 195.68 199.14 199.36 209.65 201.94 197.91 193.08 202.87
13.93 13.22 17.42 12.22 10.15 11.78 18.64 14.80 16.55 11.99 14.15 8.48 15.51 20.58 10.78 7.65 12.75 8.11 10.59
Production—first year 99.50 97.04 98.61 124.47 82.81 109.79 124.71 107.80 106.09 113.75 118.12 118.90 121.90 131.67 131.80 121.48 101.94 113.56 96.30
30.23 37.83 26.73 20.59 41.78 24.92 29.10 25.10 31.66 23.28 25.70 30.90 32.05 22.28 20.89 33.82 26.59 32.34 32.94 Days to Maturity
1913-14 14-15 15-16 16-17 17-18 18-19 19-20 20-21 21-22 22-23 23-24 24-25 25-26 26-27 27-28 28-29 29-30 30-31 31-32
251.50 242.27 261.67 231.32 252.40 264.84 224.90 241.00 295.73 265.42 267.19 222.83 240.20 244.33 231.60 268.21 290.42 249.19 253.61
11.19 11.51 16.33 5.81 16.89 10.67 25.17 17.41 14.48 12.23 19.84 16.88 13.42 11.44 10.92 18.48 12.50 18.58 12.72
breeding pen for the following year. Very low producing old hens were kept as long as they gave good hatching results. All the pullets from the low-line were brought together in the fall and a pen of 37 of the largest, most mature and vigorous pullets selected for the low-line pullet pen. These pullets were placed in a house 12 by 12 feet and fed, lighted, and managed in exactly the same manner as certain high-
line pens. They received the standard Cornell laying ration. The cockerels were selected in the fall and birds chosen whose dams have made a very low record. Most of the records of the dams whose sons have been used during the past few years have been under 100 eggs. Since full-brother matings have been used in the breeding pen for several years, preference was given them in the selection
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on May 31, 2015
1913-14 14-15 15-16 16-17 17-18 18-19 19-20 20-21 21-22 22-23 23-24 24-25 25-26 26-27 27-28 28-29 29-30 30-31 31-32
MARCH,
1934.
VOL.
XIII,
No. 2
TABLE 1. {Continued)
Egg weight—first year Low Line Year
C.V.
54.95 54.89 52.97 54.58 52.64 53.06 54.78 54.84 54.84 56.79 58.25 55.04 56.78 59.07 58.96 58.17 59.25 54.92 55.07
Mean
6.45 7.01 6.42 6.44 7.25 6.87 6.99 4.94 6.33 6.39 6.27 6.51 5.84 5.91 5.62 4.53 4.32 5.38 5.71
53.64 53.58 53.93 53.08 62.26 53.00 55.55 55.60 53.76 55.48 55.93 54.98 56.98 56.84 57.41 56.63 56.83 56.45 56.63
C.V. 7.41 7.12 6.26 6.33 7.40 5.85 6.15 7.25 6.56 6.86 7.09 6.33 6.94 6.86 6.35 6.94 6.22 6.61 6.57
Body weight—first year 1913-14 14-15 15-16 16-17 17-18 18-19 19-20 20-21 21-22 22-23 23-24 24-25 25-26 26-27 27-28 28-29 29-30 30-31 31-32
3.370 3.084 2.967 3.084 3.179 3.100 3.297 3.540 3.277 3.300 3.584 3.361 3.619 3.748 3.728 4.126 3.880 3.523 3.744
14.07 11.48 9.81 8.04 11.67 10.32 10.61 9.49 11.46 8.12 11.22 9.66 11.38 9.13 9.28 9.87 10.03 6.94 9.18
of cockerels. Vigor and body size have always been considered in selecting males as well as females. Egg size and egg color have not been given special consideration. RESULTS What changes have come about in this strain of birds as a result of such a breeding program? Table 1 gives the data covering four characters, average annual production, egg weight, body weight, and age at first
'
3.167 3.162 3.231 3.080 3.236 3.405 3.709 3.656 3.477 3.602 3.724 3.693 3.810 3.858 4.083 4.116 4.024 3.927 4.013
10.95 9.26 10.12 10.64 10.97 9.93 12.35 11.68 11.56 12.62 12.00 10.56 10.73 10.44 9.89 10.62 10.69 11.28 10.94
egg (sexual maturity). Similar data are given for the high-line birds. As stated previously, the average production of the low-line birds at the beginning of the experiment in 1913-14 was 99.5 eggs per bird. The maximum average production reached in 1927-28 was 131.8 eggs per bird, yet it is interesting to note that as early as 1916-17 the production reached 124.5 eggs per bird. Very little change has taken place in average egg production. The
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on May 31, 2015
1913-14 14-15 15-16 16-17 17-18 18-19 19-20 20-21 21-22 22-23 23-24 24-25 25-26 26-27 27-28 28-29 29-30 30-31 31-32
Mean
High Line
126 ,
POULTRY
fluences are laying on the average about 100 eggs per bird more than the low-line individuals. Changes in Vigor The changes in natural vigor of these birds is no doubt of greater interest than the production records. Three measures of vigor have been used to illustrate these changes; namely, first year mortality (beginning in 1918), fertility, and hatchability records (commencing in 1919). New blood had been added up until 1917. Table 2 gives the means for three measures of vigor. As in the case with the other characters there are wide annual variations, but there are no distinct trends apparent. It may be assumed from these figures that these birds have not lost in vitality over a period of fifteen years under the methods of breeding which have been followed. They have not suffered under the effects of inbreeding as have been reported by many investigators where close inbreeding methods have been followed. According to the theory of the inheritance of egg production formulated by Hays (1929) and Hays and Sanborn (1926a, b, c, 1927a, b) it is the opinion of the writer that
TABLE 2.—Mortality, fertility and hatchability of low-line Single Comb White Leghorns {1918 to 1932)
Yes.r
Mortality first year (percent)
No. eggs set
Hatch (percent)
1917-18 18-19 19-20 20-21 21-22 22-23 23-24 24-25 25-26 26-27 27-28 28-29 29-30 30-31 31-32 32-33
31.6 21.1 13.9 13.9 6.9 28.6 14.3 37.1 25.7 8.6 30.6 20.0 16.2 24.3 35.1 18.2
131 97 273 181 455 680 625 294 734 433 649 492 625 511 601
51.1 40.2 77.3 43.6 55.8 58.8 50.6 71.0 36.8 55.9 67.9 54.1 59.2 67.9 65.2
Fertility (percent) 93.1 80.4 98.16 80.7 77.8 89.1 65.8 96.6 81.1 79.0 90.0 88.6 90.9 92.6 83.7
Hatchability (percent) 54.9 50.0 78.7 54.1 71.8 66.0 76.9 73.5 45.4 70.8 75.5 61.0 65.1 73.4 77.9
"
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on May 31, 2015
variability for egg production has remained practically constant. In connection with production it must be remembered that environmental conditions and influences have been improved constantly during the experimental period. There was a gradual increase in body weight until the year 1929-30, although there have been rather pronounced seasonal variations. The variability has been relatively low. Egg weight, although it has not been given much consideration, has changed in much the same manner as body weight. This would indicate that size of body has a rather intimate relationship with size of egg. This relationship has been rather well established by the Canadian Record of Performance work (1929) as well as by other investigations. The variability has been low from year to year and has not changed materially. Age at first egg, or sexual maturity, shows rather wide annual variations, although no distinct trends can be seen. The annual variability has not been as constant as in the case of egg weight. The figures presented show that the highline birds, under similar environmental in-
SCIENCE
MARCH,
1934.
VOL.
XIII,
No. 2
the majority of the low-line birds saved for breeding purposes are of the following genetic constitution, eee'e'WW rrrVaaccpp in which e and e' are recessive duplicate genes for late sexual maturity, W is the dominant gene for winter pause, r and r' are the complementary recessive genes for low rate of winter production a and c are the recessive genes giving non-broodiness and p is the recessive gene for low persistency. There is little or no evidence on the genes for egg size available.
birds gives a direct measure of the influence of heredity upon egg production. REFERENCES
Canadian National Poultry Record Association. Blue Book, 1929. Hays, F. A., 1929. Inbreeding in relation to egg production. Mass. Agr. Exp. Sta. Bui. 258. Hays, F. A. and Ruby Sanborn, 1926. Broodiness in relation to fecundity in the domestic fowl. Mass Agr. Exp. Sta. Tech. Bui. 7. , 1926b. Winter cycle and winter pause in relation to winter and annual egg production. Mass. Agr. Exp. Sta. Tech. Bui. 8. , 1926c. Annual persistency in relation to winter and annual egg production. Mass. Agr. Exp. Sta. Tech. Bui. 9. , 1927a. Intensity or rate of laying in relation to fecundity. Mass. Agr. Exp. Sta. Tech. Bui. 11. , 1927b. Net correlations of characters concerned in fecundity. Mass. Agr. Exp. Sta. Tech. Bui. 12. Marble, D. R. and G. O. Hall, 1931. A statistical analysis of the results of breeding high-line and low-line Leghorns. Cornell Univ. Agr. Exp. Sta. Bui. S33.
Reviews The book is divided into four parts with George W. Snedecor, Calculation and Interpretation of Analysis of Variance and twelve examples. For each example the Covariance, Ames: Collegiate Press, Inc., source and other information regarding the data used, together with the question to be 1934. 105 pages. $1.00. Many of the investigations with poul- answered, are first given. This is followed try require statistical treatment of the data by complete instructions for calculation, a collected before the results can be properly fairly full discussion, a brief interpretation evaluated, hence, any book that presents in and concluded with notes on theory. The a simple manner Fisher's recently developed, clear and complete instructions given under useful, statistical methods is sure to be wel- computation appear to the reviewer to be comed by both research workers and teach- an especially valuable feature. While only one of the examples deals with ers. Moreover, many have experienced difficulty in applying the analysis of variance to poultry, the application of the methods to the treatment of their own data and have data from different sources is obvious. This found some of the ideas puzzling. For these monograph by Professor Snedecor should, and others who have hesitated to attempt to therefore, prove useful to those who are conuse the analysis of variance because of cerned with poultry research. V. S. ASMUNDSON limited mathematical training the present volume should prove particularly useful. University of California
Downloaded from http://ps.oxfordjournals.org/ at University of Georgia on May 31, 2015
SUMMARY
It has been possible with a rather simple system of selecting and mating, which has avoided close inbreeding, to produce a strain of birds in which the production, mortality, age at first egg, fertility, and hatchability have not changed materially for fifteen years. A comparison between the production records of the low-line and high-line
127