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Is There an Egg-laying Type of the Domestic Fowl?
POULTRY S C I E N C E May, 1933, Vol. XII, No. 3
MORLEY A. JULL, JOSEPH P. QuiNN, AND A. B. GODFREY U. S. Department of Agriculture, Washington, D.C. (Received for Publication August 4, 1932)
T
HE phenotypic method of selecting layers and breeders based on the visible characters they possess constitutes the fundamental basis of judging fowls, whether in the showroom or in production classes. So long as the selection of breeding stock is based upon such an empirical method of procedure just so long will progress be retarded in the development of strains of fowls excelling in any particular. It is probably safe to say that there have been very few poultrymen anywhere in the world who have ever produced from year to year any more than a small percentage of their flock possessing reasonably good standard quality. The reason for such mediocre results in poultry breeding work is that the phenotypic instead of the genotypic method of selecting the breeders has been practised. If poultrymen breeding exhibition poultry had practised the progeny test, basing the selection of their breeding stock on the quality of progeny that a given mating produced, much better results would undoubtedly have been secured. The situation is not quite so backward among poultry men breeding for egg production because during recent years the
progeny test has been applied by a few breeders in the selection of breeding stock from year to year. At the same time, much of the selection of the breeding stock is still based upon appearance and pedigree rather than performance. So much has been said and written about body type in its relation to egg production that many poultrymen have assumed that material progress was likely to result if breeders were selected on appearance only. Most of the evidence available, however, suggests quite definitely that it is not possible for the human eye to separate good from poor breeders based on differences in so-called "body type." It is true, on the other hand, that there are certain physiological characters that are associated with egg production, most of them of value in estimating short-term production. The so-called "beefy" head in a layer is due apparently to the deposition of tissue, physiological factors rather than anatomical ones being involved. The so-called "handling quality" of a layer, involving, as it does, the texture and pliability of the skin, is associated with physiological rather than with anatomical characters. It should be pointed out at this time that it is very
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Is There an Egg-laying T y p e of the Domestic Fowl?
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HEAD SHAPE AND EGG PRODUCTION The importance of good head features has been emphasized, in connection with which it has been stated that the most desirable head features include flatness of skull from side to side, width of skull carried well for-
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ward, good depth of head in relation to its length, and levelness on the top of the skull from front to rear. A survey of the literature reveals the fact that apparently only two investigators have ever taken head measurements with the view of determining the significance of head type in relation to egg production.* Waters (1927), with 200 S.C. White Leghorns, found that the correlation between the width of cranium and egg production was —0.19+0.05 and that the correlation between depth of head and egg production was 0.10±0.05. Both correlations are very low, the latter having no significance, whereas the former indicates that the narrower the cranium the better the production in the birds that Waters examined. Fronda and Gamo (1931), in the case of 75 Cantonese pullets and 111 Cantonese hens, found that the width of the head was not significantly correlated with egg production, this being contrary to popular opinion. As a contribution toward a solution of the problem as to the significance of certain head measurements of live birds in relation to egg production, the authors present data secured from a flock of 52 S.C. White Leghorns and a flock of 50 Rhode Island Reds. Data are also presented concerning the relationship between skull measurements and egg production in a flock of 51 S.C. White Leghorns that were killed and had the skin and appendages removed from the skulls. In this flock brain weight in relation to egg production was also taken into consideration. The range in egg production in the 52 White Leghorns was from 73 to 256 eggs per bird and in the case of the 50 Rhode Island Reds from 11 to 273 eggs per bird. * Marble, D. R., 1932. The relationship of skull measurements to cycle and by production. POUL. SCI., 11:272-278; D. Marble's article was published shortly after this manuscript was sent to POULTRY SCIENCE.
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difficult indeed to measure differences between many characters of a physiological nature. Regarding the relationship between skeletal characters and egg production, however, it has become apparent that advice has been far in advance of knowledge obtained. Jull (1925) pointed out that the development and selection for breeding purposes of males * and females capable of transmitting high egg production presents a problem in the nature of a triangle, the inheritance of function, the inheritance of body form, and the correlation between form and function, each constituting one side of the triangle. Granting that there is inheritance of both form and function, the only remaining problem is to demonstrate a significant correlation between form and function. Does the evidence available give a definite answer to this problem? The more important skeletal characters that have been assumed to be associated with egg production are the shape of the head and the shape of the body. It has frequently been asserted that there is an egglaying type of fowl, but no conclusive evidence has ever been presented to justify the assertion. In order to secure definite evidence as to whether there is any significant relationship between the so-called type of laying fowl and its laying ability, a number of live bird measurements, carcass measurements, and bone measurements of dead birds have been made. It should be pointed out that the term "type" is used in this article with respect to the shape or form of the body of the bird as determined by skeletal structure.
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The mean egg production of the White Leghorns was 175.70+4.15 and that of the Rhode Island Reds 162.00±4.57, the difference being 13.70±6.17, which is not significant. The simple correlation coefficient between each of four different head meas-
birds varied from 20 to 283 eggs each, with a mean production of 195.67 eggs. The mean weight of eggs produced was 10,848.91 grams per bird and the mean egg weight per bird was 55.76 grams. The simple correlation coefficients between egg production
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TABLE 1. Simple correlation coefficients between each offour live-bird head measurements and egg production Character
urements and egg production is given in Table 1. The data in Table 1 show that in the case of the S.C. White Leghorns the correlations are all positive but low in value whereas in the case of the Rhode Island Reds they are all negative but low in value, indicating that in these two flocks the shape of head had little to do with egg producing ability. The only correlation having any significance is with respect to length from base of upper mandible to rear of head in the case of the S.C. White Leghorns, in
50 Rhode Island Reds
0.19 + 0.09 0.36 + 0.08 0.17 + 0.09
- 0 . 1 6 + 0.09 - 0 . 1 5 + 0.09 -0.05±0.09
0.26 + 0.09
-0.19±0.09
and total and mean egg weight per bird and each of the three skull measurements are given in Table 2. The data in Table 2 show that in not a single instance is there any significant correlation between any of the three skull measurements and egg production, total egg weight, and mean egg weight. Apparently, then, in this group of 51 White Leghorns neither length, nor breadth, nor depth of skull bore any relation to egg laying ability."The multiple correlation between length, breadth and depth of skull and egg produc-
TABLE 2. Simple correlation coefficients between each of three skull measurements and egg production and total and mean egg weight per bird in 51 S. C. White 'Leghorns Character Egg production Total egg weight Mean egg weight
Length of Skull
Breadth of skull
Depth of skull
0.13 + 0.09 0.20 + 0.09 0.20 + 0.09
0.08 + 0.09 0.09 + 0.09 0.01+0.09
0.08 + 0.09 0.07±0.07 - 0 . 0 3 + 0.09
which case the birds with the longest heads were inclined to be among the best layers. In order to determine any possible relationship between egg production and each of the three characters, length, breadth, and depth of skull, the heads of 51 S.C. White Leghorn yearling hens were boiled and the skin and appendages removed and measurements taken between certain fixed points. The first year egg production of these 51
tion was 0.14, which gives a multiple determination coefficient of 0.02, which means that the three skull characters accounted for only 2 percent of the variability in egg production in the group of 51 birds. This observation shows that the shape of the skull can hardly be used as a reliable guide in the selection of females to be used as breeders. The simple correlation coefficient between
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Length from base of upper mandihle to top of head Length from base of upper mandible to rear of head Greatest width over the top of head Depth from top of head to point directly below at base of head.
52 S. C. White Leghorns
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brain weight and egg production was found to be —0.03 ±0.09 and between brain weight and total egg weight, —0.001 + 0.094, and between brain weight and mean egg weight, 0.16+0.09. Since none of these three correlation coefficients is significant, it is apparent that total brain capacity bears no relation to egg laying ability. BODY FORM AND EGG PRODUCTION
of relatively little value in selecting females on the basis of egg producing ability. Furthermore, Sherwood and Godbey (1928) in the case of each of their flocks, found the value of the multiple correlation coefficient to be 0.65 ±0.04 for the characters, body weight, color of shank, handling quality, capacity, molt, length of back, width of back, and depth of body in front. In spite of the number of characters considered, the multiple correlation coefficient is relatively low and gives a multiple determination coefficient of 0.42, which leads Sherwood and Godbey to conclude that the
TABLE 3. Simple correlation coefficients between body measurements and egg production in S.C. White Leghorns, as determined by various investigators
Year
1921 1922 1923 1927 1928 1928
Investigator
Asmundson Sherwood Hall 1 Waters Sherwood and Godbey2 Sherwood and Godbey3
Correlation between egg production and each of the following characters Back length
Back width
. , —
0.36 + 0.04*
-0.16 + -0.03 + 0.20 + 0.18 +
0.07 0.05 0.07 0.07
—,
0.03 + 0.07
—
0.16 + 0.07 0.23±0.06*
Front depth 0.2S + 0.04* -0.03 + -0.03 + 0.41 + 0.42 +
0.07 0.05 0.06* 0.06*
Keel length 0.03 + 0.04 0.21+0.06* 0.15 + 0.07 - 0 . 0 7 + 0.05
— —
1
Hall (1923) also observed a correlation of —0.17 + 0.07 between shoulder width and egg production. and 3 represent two different flocks. * The six correlations thus marked are the only ones that are significant, since only in these six cases is the correlation value at least three times the value of its probable error. 2
relation coefficients determined between different body measurements and egg production are given in Table 3, the flock in the case of each investigator being S.C. White Leghorns. There are several interesting observations to be drawn from the data given in Table 3. There is considerable lack of uniformity among the observations of the different investigators; whereas some investigators secured positive correlations other investigators secured negative correlations for the same measurements. Out of 18 correlation determinations only 6 have any significance. All of the correlations are of relatively low value. The data in Table 3 show, therefore, that body measurements in themselves are
8 characters they considered accounted for about 42 percent of the total variability in egg production. This leaves 58 percent of the variability in egg production unaccounted for, due, as Sherwood and Godbey remark, either to errors in taking measurements and weights or to characters other than those they considered. Using a flock each of White Leghorns and Barnevelders, Scholten (1927) came to the conclusion that body measurements are of no practical value in selecting the most productive birds. Macht (1930) studied the relationship between certain body measurements and egg production in a group of White Leghorn pullets during the growing period as well as at maturity. It was found
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Several investigators have made measurements pertaining to body form in its relation to egg production, the measurements being made on live birds. The simple cor-
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that in both high and low producing birds skeletal growth was completed when the birds were approximately thirty-eight weeks of age and that the period from about fifteen to eighteen weeks of age was the best time to select the pullets on the basis of their laying ability. At that age the pullets with the longest and broadest backs and longest keels turned out to be among the best layers, so that Macht's observations confirm the opinion widely held that high egg production is associated with earliness of maturity. As a contribution toward a final solution of the problem of the relationship between egg production and body form, as determined by certain body measurements, the
The authors determined the relationship between each of five body measurements and egg production in the group of 52 White Leghorns and the group of 50 Rhode Island Reds mentioned previously, the correlation coefficients being given in Table 4. The measurements made include (1) length of back; (2) greatest width at shoulders; (3) greatest width over back, from femur joint to femur joint; (4) depth of body from shoulder to front of keel; (5) length of keel. All of the correlations in Table 4 are relatively low in value. All, except one in the case of the White Leghorns, are positive, whereas all in the case of the Rhode Island Reds are negative. Only one has any signifi-
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TABLE 4. Simple correlation coefficients between each of five live-bird body measurements and egg production Character Length of back Greatest width at shoulders Greatest width of back Front body depth Length of keel
52 S.C. White Leghorns 0.23 + 0.09 - 0 . 1 3 + 0.10 0.13 + 0.10 0.13+0.10 0.23 + 0.09
authors of this paper have obtained data from four different groups of birds. Five live bird body measurements are considered in relation to first-year egg production in a group of 52 S.C. White Leghorns and in a group of 50 Rhode Island Reds. The length and width of the backbone and the length of the keelbone is each considered in relation to egg production in 24 S.C. White Leghorns of the group of 52 mentioned previously and in another group of 51 S.C. White Leghorns. Finally, live bird, dressed carcass, and bone measurements of the length and width of back and the length of the keel are considered in their relation to first-year egg production in a flock of 237 S.C. White Leghorns, which were subdivided into a group of 54 highest producers, 132 intermediate producers, and 51 lowest producers.
50 Rhode Island Reds - 0 . 2 4 + 0.09 -0.03+0.09 - 0 . 2 6 + 0.09 • - 0 . 0 2 + 0.09 - 0 . 2 8 + 0.09
cance, length of keel in the case of the Rhode Island Reds, the birds with the shorter keels tending to be the better layers. Since Sherwood and Godbey (loc. cit.) have pointed out, however, that selection on the basis of live-bird measurements is for the most part unreliable, it is interesting to note that in the case of 24 S.C. White Leghorns examined by the authors the live-bird measurements varied considerably from the measurements of the bones of the same birds. The measurements of the length of back in the live birds was 120.91±1.20 percent of the length of the backbone itself, two-thirds of the birds showing a range of from approximately 111 to approximately 130 percent. The measurements of the breadth of back in the live birds was 142.52 percent of the breadth of the backbone itself, two-thirds of the birds showing a range
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multiple determination coefficient of 0.08, which means that the three characters measured accounted for approximately 8 percent of the variability in egg production, leaving approximately 92 percent of the variability in egg production unaccounted for. In the case of the group of 51 birds the multiple correlation coefficient between the three bone measurements and egg production was found to be 0.44, which gives a multiple correlation determination of 0.19, which means that the three characters measured accounted for approximately 19 percent of the variability in egg production in this group of 51 birds, leaving approximately 81 percent of the variability in egg production unaccounted for. The observations made on
TABLE 5. Simple correlation coefficients between each of three bone measurements and egg production Character Back length Back breadth Keel length
24 White Leghorns 0.20 + 0.12 - 0 . 1 5 + 0.13 0.28 + 0.10
indices of the actual length and breadth of the backbone, but the authors also observed that there was no significant correlation between each of the three bone measurements and egg production in the group of 24 S.C. White Leghorns. Simple correlation coefficients between each of the three same bone measurements and egg production were also determined in the case of the 51 S.C. White Leghorns mentioned previously. The data for both groups of White Leghorns are given in Table 5. It is apparent from the data in Table 5 that the only significant correlation is that between length of keel and egg production in the group of 51 birds, the birds with relatively short keels tending to be the better producers. In the case of the group of 24 birds the multiple correlation coefficient between the three bone measurements and egg production was found to be 0.29, which gives a
51 White Leghorns - 0 . 0 9 + 0.09 - 0 . 2 2 + 0.09 -0.49±0.07
these two groups of birds show, therefore, that the shape of the body apparently has little influence on egg production. The multiple correlation coefficient between the three bone measurements and total egg weight produced per bird was found to be 0.43 and the multiple correlation between the three bone measurements and mean egg weight per bird was found to be 0.42. These correlations are of relatively low value and indicate that neither the total weight of eggs produced by a bird in her first laying year nor the mean egg weight of her first year production are greatly influenced by the shape of the body of a bird. The flock of 237 S.C. White Leghorns represented an unselected flock of birds that completed their first year of laying out of an original flock of approximately 250, the balance having died during the year. The flock of 237 was subdivided into three groups: 54 of the highest producers, their
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from approximately 135 to approximately 150 percent. The keel length in the live birds was found to be 104.01 percent of the length of the keel bone itself, two-thirds of the birds showing a range from approximately 102 to approximately 106 percent. These observations show that the measurements of the length of keel in live birds served as a fairly reliable index of the actual length of keel bone but that live-bird measurements of the length and breadth of back did not serve as a reliable index of the length and breadth, respectively, of the backbone itself. Not only was it observed that the livebird measurements of back length and back breadth were apparently not very reliable
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mean egg production being 244.91 ±1.18 eggs; 132 intermediate producers, their mean egg production being 200.26±0.94 eggs; 51 of the lowest producers, their mean egg production being 153.43±2.76 eggs. The live bird and dressed carcass measurements of the highest, intermediate, and lowest producers are given in Table 6, as well as the bone measurements of the highest and lowest producers. The data in Table 6 show that the differences among the three groups in respect to live bird measurements are so slight as to
It is interesting to note that the highest producers were somewhat earlier maturing than the lowest producers. In the case of the highest producers the mean age in days that laying commenced was 163.11±1.28 days and in the case of the lowest producers it was 176.47±3.12 days. The difference is 13.36±3.37 days, thus indicating a significant difference in age in days that laying commenced in favor of the highest producers. One interesting feature should be observed in connection with the data in Table
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Measurements
54 highest producers
132 intermediate producers
51 lowest producers
Inches
Inches
birds: Length of back Width of back Length of keel
6.39 + 0.03 3.47 + 0.02 4.19 + 0.02
6.38 + 0.01 3.36 + 0.01 4.18 + 0.01
6.47 + 0.03 3.50 + 0.02 4.36 + 0.02
Dressed carcasses: 1. Length of back 2. Width of back 3. Length of keel
6.28 + 0.03 2.93 + 0.01 3.85 + 0.02
6.03 + 0.03 3.02 + 0.01 3.87 + 0.01
6.54±0.02 3.09 + 0.02 4.02 + 0.02
Bones: 1. Length of back 2. Width of back 3. Length of keel
5.45 + 0.02 2.12 + 0.01 3.60 + 0.03
Live 1. 2. 3.
indicate the impossibility of determining laying ability on the basis of live bird observations. The same is true of the dressed carcass measurements. The data regarding bone measurements show that the length of back in the highest and lowest groups was the same but that the width of backbone and length of keel was slightly greater in the lowest than in the highest producers. Judging from the data given in Table 6, it is apparent that the lowest producers were slightly larger than the highest producers. The mean weight of the highest producers was 1,934.25±24.01 grams per bird and the mean weight of the lowest producers was 2,037.25±34.31 grams, the difference not being significant.
—
•
— —
Inches
5.45 + 0.03 2.23 + 0.02 3.80 + 0.02
6. It will be noted that in the case of the group of 51 lowest producers, the length of back in the live birds is less than the length of back in the dressed carcasses. This indicates one of the difficulties involved in measuring live birds, assuming that dressed carcass measurements are more accurately determined than live bird measurements. However, it has been determined in the case of the group of highest producers and the group of lowest producers that certain dressed carcass measurements were not highly correlated with bone measurements, in fact, not as highly correlated as comparable live-bird measurements. Simple correlation coefficients were determined between the length of the backbone and the length of
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TABLE 6. Live bird, dressed carcass, and bone measurements in three groups of S.C. White Leghorns
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P O U L T R Y
back in live birds and the length of back in n dressed carcasses, between width of back:bone and width of back in live birds and d width of back in dressed carcasses, and be-:tween length of keelbone and length of keelil in live birds and length of keel in dressedd carcasses. These simple correlation coeffi-icients are given in Table 7. The data given in Table 7 show that inn three cases out of six the simple correlationi coefficient between a given bone measure-ment and a comparable measurement in livee
S C I E N C E
The data in Tables 6 and 7 regarding the body measurements of the three groups comprising the flock of 237 S.C. White Leghorns confirm the observations made previously regarding the other groups of S.C. White Leghorns and the group of Rhode Island Reds, two of the most important observations being that live-bird and dressed carcass measurements are not necessarily reliable indices of the skeletal structure of a bird and that the shape of a bird as determined by live-bird, dressed carcass, and
(White Leghorns) Highest producers
Lowest producers
Correlation between length of backbone and length of back in live birds
.47
.51
Correlation between length of backbone and length of back in dressed carcasses
.50
.70
Correlation between width of backbone and width of back in live birds
.74
.51
Correlation between width of backbone and width of back in dressed carcasses
.66
.36
Correlation between length of keelbone and length of keel in live birds
.86
.79
Correlation between length of keelbone and length of keel in dressed carcasses
.83
.94
birds was greater than the simple correla- bone measurements is not a reliable index tion coefficient between the same bone meas- of the bird's laying ability. urement and a comparable measurement in An observation made recently regarding dressed carcasses. Furthermore, practically the similarity between the skeletal structure all of the correlation coefficients given in of the beef and the dairy cow is of interest Table 7 are lower than might be expected, in this discussion. Swett, Graves, and Miller indicating that in the case of the two groups (1928) compared the conformation, anatof birds measured neither dressed carcass omy, and skeletal structure of a "highly spenor live bird measurements constituted a cialized Aberdeen Angus with that of a true index of the actual length and width of highly specialized Jersey" and drew the the backbone and of the length of the keel- following conclusions: "In external form the bone. The fact that accurate live-bird meas- two cows differed greatly. In weight and urements are so difficult to make probably size of internal organs, the differences were explains why the observations of various in- not sufficiently great to indicate significant vestigators given in Table 3 do not agree differences in function. In skeleton structure closely. the two cows varied somewhat but were
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TABLE 7. Simple correlation coefficients between bone measurements and comparable live bird, and dressed carcass measurements
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generally similar. This would indicate that the evolution of the dairy and beef types, which has been accomplished through breeding and selection, has not materially altered their skeletal structure, but rather that the difference in type is due to extreme fleshing on the one hand and to udder development and absence of fleshing on the other. Aside from the external form, the most marked difference noted between the cows compared was the quantity of secretory tissue in their udders." Apparently the outstanding difference between beef and dairy cows is in respect to the physiological aspects of flesh production and milk secretion, the physiological characters being transmitted through the agency of factors or genes, which are inherited. In the case of the domestic fowl the available evidence to date goes to show that flesh production and egg production are apparently inherited largely independently of skeletal structure. Kopec (1927) and Hutt (1929) have supplied evidence showing that while there are genes responsible for the development of the size of all parts of the body, there are also other genes affecting the development of the size of individual bones. If such is the case, then if skeletal structure is definitely associated with egg-laying ability there should be linkage between the genes determining bone size or length and the genes determining egg production. Such, however, has never been demonstrated; in fact, practically all of the available evidence indicates that type as determined by skeletal structure is not intimately associated with laying ability. It should be kept in mind, however, that in the selection of birds on the basis of their presumed laying ability, certain physiological characters should always be taken into consideration. The most important of these physiological characters include age in days that laying commences, the accumulation of excessive tissue over
various parts of the head, the accumulation of an excessive amount of fleshing in the abdomen, the bleaching of the yellow pigment from the beak and shanks as an indication of the approximate number of eggs laid during a given period, and the time of year and duration of the first annual molt. The relative importance of these characters in the selection of layers has been discussed fully by Rice, Hall, and Marble (1930). CONCLUSIONS Live-bird measurements, as usually taken, are not reliable indices of the shape or type of a bird. Live-bird measurements of the length, breadth and depth of head and of the length and breadth of back, greatest width at shoulders, and depth of body in front are of no value in the selection of birds according to their laying ability. In three out of six groups of birds those with the shortest keels were among the best layers. Dressed carcass measurements in the group of birds measured were not highly correlated with comparable bone measurements and cannot be considered as reliable indices of egg laying ability. There is no significant relationship between the length, breadth, or shape of skull and egg production. Neither the length nor the breadth nor the depth of the skull of a bird bears any relation to the total weight of eggs laid by the bird nor to her mean egg weight. Brain capacity bears no relation to the number, total weight, or mean weight of eggs laid by a bird. Simple correlation coefficients between egg production and each of three bone measurements, length of back, width of back from femur joint to femur joint, and length of keel, are of no significance, except possibly length of keel in certain flocks. The multiple correlation between egg production and the three bone measurements,
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REFERENCES
Asmundson, V. S., 1921. The relation of keel bone to egg production. Sci. Agr. 1:30-33, and 63-67. Fronda, Francisco M., and Felix S. Gamo, 1931. The relation of some head characters and egg production among Cantonese fowls. Philippine Agr. 20:261-268. Hall, G. O., 1923. A study of the relation between body conformation in laying fowls and size and shape of egg laid. Cornell Univ. Thesis. Cited by Rice, Hall, and Marble (1930). Hutt, F. B., 1921. Sex dimorphism and variability in the appendicular skeleton of the Leghorn fowl. Poul. Sci. 8:202-218.
Jull, Morley A., 1925. The selection of breeding stock in relation to the inheritance of form and function in the domestic fowl. Poul. Sci. 5 :1-19. Kopec, Stefan, 1927. Zur Kenntnis der Vererbung der Korperdimensionen und der Korperform beim Haushuhn. Zeitschrift fiir induktive Abstammungsund Vererbungslehre. Bd. 45, Heft Vi, 87-104. Macht, E., 1930. Wechselbeziehung zwischen Jugendentwicklung und Legeleistung. Die • Arbeiten der Kreisgeflugelzuchtanstalt fur Oberbayern Erding 1905-1930. Jubilaumsbericht, 66-101. Rice, J. E., G. O. Hall, and Dean R. Marble, 1930. Judging Poultry for Production, 425. John Wiley and Sons, New York. Scholten, Henry H., 1927. Correlation between external characteristics of a hen and her egg production. Rept. Proc. Third World's Poul. Congress, 141-143. Pub. by Canadian Dept. Agr., Ottawa, Canada. Sherwood, R. M., 1922. Correlation between external body characters and annual egg production in White Leghorn fowls. Texas Agr. Exp. Sta. Bui. 295. Sherwood, R. M., and C. B. Godbey, 1928. Construction of score card for judging for egg production. Poul. Sci. 7 :263-274. Swett, W. W., Graves, R. R., and F. W. Miller, 1928. Comparison of conformation, anatomy, and skeletal structure of a highly specialized dairy cow and a highly specialized beef cow. Jour. Agr. Res. 37:685-717. Waters, Nelson, F., 1927. The relation between body measurements and egg production in single comb White Leghorns. Poul. Sci. 6:167-173.
c
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length of back, width of back from femur joint to femur joint, and length of keel, is low and of no significance statistically. The same is true regarding the multiple correlation between total egg weight per bird and these three bone measurements and between mean egg weight per bird and those three bone measurements. Evidence is not only lacking to support the contention that there is an egg-laying type in the domestic fowl, type here being considered from the standpoint of skeletal structure, but all available evidence suggests that the type of the bird, as influenced by the skeleton, has no significant relationship to egg-producing ability.
SCIEN'CE
MORLEY A. JULL, JOSEPH P. QuiNN, AND A. B. GODFREY U. S. Department of Agriculture, Washington, D.C. (Received for Publication August 4, 1932)
T
HE phenotypic method of selecting layers and breeders based on the visible characters they possess constitutes the fundamental basis of judging fowls, whether in the showroom or in production classes. So long as the selection of breeding stock is based upon such an empirical method of procedure just so long will progress be retarded in the development of strains of fowls excelling in any particular. It is probably safe to say that there have been very few poultrymen anywhere in the world who have ever produced from year to year any more than a small percentage of their flock possessing reasonably good standard quality. The reason for such mediocre results in poultry breeding work is that the phenotypic instead of the genotypic method of selecting the breeders has been practised. If poultrymen breeding exhibition poultry had practised the progeny test, basing the selection of their breeding stock on the quality of progeny that a given mating produced, much better results would undoubtedly have been secured. The situation is not quite so backward among poultry men breeding for egg production because during recent years the
progeny test has been applied by a few breeders in the selection of breeding stock from year to year. At the same time, much of the selection of the breeding stock is still based upon appearance and pedigree rather than performance. So much has been said and written about body type in its relation to egg production that many poultrymen have assumed that material progress was likely to result if breeders were selected on appearance only. Most of the evidence available, however, suggests quite definitely that it is not possible for the human eye to separate good from poor breeders based on differences in so-called "body type." It is true, on the other hand, that there are certain physiological characters that are associated with egg production, most of them of value in estimating short-term production. The so-called "beefy" head in a layer is due apparently to the deposition of tissue, physiological factors rather than anatomical ones being involved. The so-called "handling quality" of a layer, involving, as it does, the texture and pliability of the skin, is associated with physiological rather than with anatomical characters. It should be pointed out at this time that it is very
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Is There an Egg-laying T y p e of the Domestic Fowl?
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HEAD SHAPE AND EGG PRODUCTION The importance of good head features has been emphasized, in connection with which it has been stated that the most desirable head features include flatness of skull from side to side, width of skull carried well for-
SCIENCE
ward, good depth of head in relation to its length, and levelness on the top of the skull from front to rear. A survey of the literature reveals the fact that apparently only two investigators have ever taken head measurements with the view of determining the significance of head type in relation to egg production.* Waters (1927), with 200 S.C. White Leghorns, found that the correlation between the width of cranium and egg production was —0.19+0.05 and that the correlation between depth of head and egg production was 0.10±0.05. Both correlations are very low, the latter having no significance, whereas the former indicates that the narrower the cranium the better the production in the birds that Waters examined. Fronda and Gamo (1931), in the case of 75 Cantonese pullets and 111 Cantonese hens, found that the width of the head was not significantly correlated with egg production, this being contrary to popular opinion. As a contribution toward a solution of the problem as to the significance of certain head measurements of live birds in relation to egg production, the authors present data secured from a flock of 52 S.C. White Leghorns and a flock of 50 Rhode Island Reds. Data are also presented concerning the relationship between skull measurements and egg production in a flock of 51 S.C. White Leghorns that were killed and had the skin and appendages removed from the skulls. In this flock brain weight in relation to egg production was also taken into consideration. The range in egg production in the 52 White Leghorns was from 73 to 256 eggs per bird and in the case of the 50 Rhode Island Reds from 11 to 273 eggs per bird. * Marble, D. R., 1932. The relationship of skull measurements to cycle and by production. POUL. SCI., 11:272-278; D. Marble's article was published shortly after this manuscript was sent to POULTRY SCIENCE.
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difficult indeed to measure differences between many characters of a physiological nature. Regarding the relationship between skeletal characters and egg production, however, it has become apparent that advice has been far in advance of knowledge obtained. Jull (1925) pointed out that the development and selection for breeding purposes of males * and females capable of transmitting high egg production presents a problem in the nature of a triangle, the inheritance of function, the inheritance of body form, and the correlation between form and function, each constituting one side of the triangle. Granting that there is inheritance of both form and function, the only remaining problem is to demonstrate a significant correlation between form and function. Does the evidence available give a definite answer to this problem? The more important skeletal characters that have been assumed to be associated with egg production are the shape of the head and the shape of the body. It has frequently been asserted that there is an egglaying type of fowl, but no conclusive evidence has ever been presented to justify the assertion. In order to secure definite evidence as to whether there is any significant relationship between the so-called type of laying fowl and its laying ability, a number of live bird measurements, carcass measurements, and bone measurements of dead birds have been made. It should be pointed out that the term "type" is used in this article with respect to the shape or form of the body of the bird as determined by skeletal structure.
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The mean egg production of the White Leghorns was 175.70+4.15 and that of the Rhode Island Reds 162.00±4.57, the difference being 13.70±6.17, which is not significant. The simple correlation coefficient between each of four different head meas-
birds varied from 20 to 283 eggs each, with a mean production of 195.67 eggs. The mean weight of eggs produced was 10,848.91 grams per bird and the mean egg weight per bird was 55.76 grams. The simple correlation coefficients between egg production
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TABLE 1. Simple correlation coefficients between each offour live-bird head measurements and egg production Character
urements and egg production is given in Table 1. The data in Table 1 show that in the case of the S.C. White Leghorns the correlations are all positive but low in value whereas in the case of the Rhode Island Reds they are all negative but low in value, indicating that in these two flocks the shape of head had little to do with egg producing ability. The only correlation having any significance is with respect to length from base of upper mandible to rear of head in the case of the S.C. White Leghorns, in
50 Rhode Island Reds
0.19 + 0.09 0.36 + 0.08 0.17 + 0.09
- 0 . 1 6 + 0.09 - 0 . 1 5 + 0.09 -0.05±0.09
0.26 + 0.09
-0.19±0.09
and total and mean egg weight per bird and each of the three skull measurements are given in Table 2. The data in Table 2 show that in not a single instance is there any significant correlation between any of the three skull measurements and egg production, total egg weight, and mean egg weight. Apparently, then, in this group of 51 White Leghorns neither length, nor breadth, nor depth of skull bore any relation to egg laying ability."The multiple correlation between length, breadth and depth of skull and egg produc-
TABLE 2. Simple correlation coefficients between each of three skull measurements and egg production and total and mean egg weight per bird in 51 S. C. White 'Leghorns Character Egg production Total egg weight Mean egg weight
Length of Skull
Breadth of skull
Depth of skull
0.13 + 0.09 0.20 + 0.09 0.20 + 0.09
0.08 + 0.09 0.09 + 0.09 0.01+0.09
0.08 + 0.09 0.07±0.07 - 0 . 0 3 + 0.09
which case the birds with the longest heads were inclined to be among the best layers. In order to determine any possible relationship between egg production and each of the three characters, length, breadth, and depth of skull, the heads of 51 S.C. White Leghorn yearling hens were boiled and the skin and appendages removed and measurements taken between certain fixed points. The first year egg production of these 51
tion was 0.14, which gives a multiple determination coefficient of 0.02, which means that the three skull characters accounted for only 2 percent of the variability in egg production in the group of 51 birds. This observation shows that the shape of the skull can hardly be used as a reliable guide in the selection of females to be used as breeders. The simple correlation coefficient between
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Length from base of upper mandihle to top of head Length from base of upper mandible to rear of head Greatest width over the top of head Depth from top of head to point directly below at base of head.
52 S. C. White Leghorns
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brain weight and egg production was found to be —0.03 ±0.09 and between brain weight and total egg weight, —0.001 + 0.094, and between brain weight and mean egg weight, 0.16+0.09. Since none of these three correlation coefficients is significant, it is apparent that total brain capacity bears no relation to egg laying ability. BODY FORM AND EGG PRODUCTION
of relatively little value in selecting females on the basis of egg producing ability. Furthermore, Sherwood and Godbey (1928) in the case of each of their flocks, found the value of the multiple correlation coefficient to be 0.65 ±0.04 for the characters, body weight, color of shank, handling quality, capacity, molt, length of back, width of back, and depth of body in front. In spite of the number of characters considered, the multiple correlation coefficient is relatively low and gives a multiple determination coefficient of 0.42, which leads Sherwood and Godbey to conclude that the
TABLE 3. Simple correlation coefficients between body measurements and egg production in S.C. White Leghorns, as determined by various investigators
Year
1921 1922 1923 1927 1928 1928
Investigator
Asmundson Sherwood Hall 1 Waters Sherwood and Godbey2 Sherwood and Godbey3
Correlation between egg production and each of the following characters Back length
Back width
. , —
0.36 + 0.04*
-0.16 + -0.03 + 0.20 + 0.18 +
0.07 0.05 0.07 0.07
—,
0.03 + 0.07
—
0.16 + 0.07 0.23±0.06*
Front depth 0.2S + 0.04* -0.03 + -0.03 + 0.41 + 0.42 +
0.07 0.05 0.06* 0.06*
Keel length 0.03 + 0.04 0.21+0.06* 0.15 + 0.07 - 0 . 0 7 + 0.05
— —
1
Hall (1923) also observed a correlation of —0.17 + 0.07 between shoulder width and egg production. and 3 represent two different flocks. * The six correlations thus marked are the only ones that are significant, since only in these six cases is the correlation value at least three times the value of its probable error. 2
relation coefficients determined between different body measurements and egg production are given in Table 3, the flock in the case of each investigator being S.C. White Leghorns. There are several interesting observations to be drawn from the data given in Table 3. There is considerable lack of uniformity among the observations of the different investigators; whereas some investigators secured positive correlations other investigators secured negative correlations for the same measurements. Out of 18 correlation determinations only 6 have any significance. All of the correlations are of relatively low value. The data in Table 3 show, therefore, that body measurements in themselves are
8 characters they considered accounted for about 42 percent of the total variability in egg production. This leaves 58 percent of the variability in egg production unaccounted for, due, as Sherwood and Godbey remark, either to errors in taking measurements and weights or to characters other than those they considered. Using a flock each of White Leghorns and Barnevelders, Scholten (1927) came to the conclusion that body measurements are of no practical value in selecting the most productive birds. Macht (1930) studied the relationship between certain body measurements and egg production in a group of White Leghorn pullets during the growing period as well as at maturity. It was found
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Several investigators have made measurements pertaining to body form in its relation to egg production, the measurements being made on live birds. The simple cor-
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that in both high and low producing birds skeletal growth was completed when the birds were approximately thirty-eight weeks of age and that the period from about fifteen to eighteen weeks of age was the best time to select the pullets on the basis of their laying ability. At that age the pullets with the longest and broadest backs and longest keels turned out to be among the best layers, so that Macht's observations confirm the opinion widely held that high egg production is associated with earliness of maturity. As a contribution toward a final solution of the problem of the relationship between egg production and body form, as determined by certain body measurements, the
The authors determined the relationship between each of five body measurements and egg production in the group of 52 White Leghorns and the group of 50 Rhode Island Reds mentioned previously, the correlation coefficients being given in Table 4. The measurements made include (1) length of back; (2) greatest width at shoulders; (3) greatest width over back, from femur joint to femur joint; (4) depth of body from shoulder to front of keel; (5) length of keel. All of the correlations in Table 4 are relatively low in value. All, except one in the case of the White Leghorns, are positive, whereas all in the case of the Rhode Island Reds are negative. Only one has any signifi-
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TABLE 4. Simple correlation coefficients between each of five live-bird body measurements and egg production Character Length of back Greatest width at shoulders Greatest width of back Front body depth Length of keel
52 S.C. White Leghorns 0.23 + 0.09 - 0 . 1 3 + 0.10 0.13 + 0.10 0.13+0.10 0.23 + 0.09
authors of this paper have obtained data from four different groups of birds. Five live bird body measurements are considered in relation to first-year egg production in a group of 52 S.C. White Leghorns and in a group of 50 Rhode Island Reds. The length and width of the backbone and the length of the keelbone is each considered in relation to egg production in 24 S.C. White Leghorns of the group of 52 mentioned previously and in another group of 51 S.C. White Leghorns. Finally, live bird, dressed carcass, and bone measurements of the length and width of back and the length of the keel are considered in their relation to first-year egg production in a flock of 237 S.C. White Leghorns, which were subdivided into a group of 54 highest producers, 132 intermediate producers, and 51 lowest producers.
50 Rhode Island Reds - 0 . 2 4 + 0.09 -0.03+0.09 - 0 . 2 6 + 0.09 • - 0 . 0 2 + 0.09 - 0 . 2 8 + 0.09
cance, length of keel in the case of the Rhode Island Reds, the birds with the shorter keels tending to be the better layers. Since Sherwood and Godbey (loc. cit.) have pointed out, however, that selection on the basis of live-bird measurements is for the most part unreliable, it is interesting to note that in the case of 24 S.C. White Leghorns examined by the authors the live-bird measurements varied considerably from the measurements of the bones of the same birds. The measurements of the length of back in the live birds was 120.91±1.20 percent of the length of the backbone itself, two-thirds of the birds showing a range of from approximately 111 to approximately 130 percent. The measurements of the breadth of back in the live birds was 142.52 percent of the breadth of the backbone itself, two-thirds of the birds showing a range
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multiple determination coefficient of 0.08, which means that the three characters measured accounted for approximately 8 percent of the variability in egg production, leaving approximately 92 percent of the variability in egg production unaccounted for. In the case of the group of 51 birds the multiple correlation coefficient between the three bone measurements and egg production was found to be 0.44, which gives a multiple correlation determination of 0.19, which means that the three characters measured accounted for approximately 19 percent of the variability in egg production in this group of 51 birds, leaving approximately 81 percent of the variability in egg production unaccounted for. The observations made on
TABLE 5. Simple correlation coefficients between each of three bone measurements and egg production Character Back length Back breadth Keel length
24 White Leghorns 0.20 + 0.12 - 0 . 1 5 + 0.13 0.28 + 0.10
indices of the actual length and breadth of the backbone, but the authors also observed that there was no significant correlation between each of the three bone measurements and egg production in the group of 24 S.C. White Leghorns. Simple correlation coefficients between each of the three same bone measurements and egg production were also determined in the case of the 51 S.C. White Leghorns mentioned previously. The data for both groups of White Leghorns are given in Table 5. It is apparent from the data in Table 5 that the only significant correlation is that between length of keel and egg production in the group of 51 birds, the birds with relatively short keels tending to be the better producers. In the case of the group of 24 birds the multiple correlation coefficient between the three bone measurements and egg production was found to be 0.29, which gives a
51 White Leghorns - 0 . 0 9 + 0.09 - 0 . 2 2 + 0.09 -0.49±0.07
these two groups of birds show, therefore, that the shape of the body apparently has little influence on egg production. The multiple correlation coefficient between the three bone measurements and total egg weight produced per bird was found to be 0.43 and the multiple correlation between the three bone measurements and mean egg weight per bird was found to be 0.42. These correlations are of relatively low value and indicate that neither the total weight of eggs produced by a bird in her first laying year nor the mean egg weight of her first year production are greatly influenced by the shape of the body of a bird. The flock of 237 S.C. White Leghorns represented an unselected flock of birds that completed their first year of laying out of an original flock of approximately 250, the balance having died during the year. The flock of 237 was subdivided into three groups: 54 of the highest producers, their
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from approximately 135 to approximately 150 percent. The keel length in the live birds was found to be 104.01 percent of the length of the keel bone itself, two-thirds of the birds showing a range from approximately 102 to approximately 106 percent. These observations show that the measurements of the length of keel in live birds served as a fairly reliable index of the actual length of keel bone but that live-bird measurements of the length and breadth of back did not serve as a reliable index of the length and breadth, respectively, of the backbone itself. Not only was it observed that the livebird measurements of back length and back breadth were apparently not very reliable
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mean egg production being 244.91 ±1.18 eggs; 132 intermediate producers, their mean egg production being 200.26±0.94 eggs; 51 of the lowest producers, their mean egg production being 153.43±2.76 eggs. The live bird and dressed carcass measurements of the highest, intermediate, and lowest producers are given in Table 6, as well as the bone measurements of the highest and lowest producers. The data in Table 6 show that the differences among the three groups in respect to live bird measurements are so slight as to
It is interesting to note that the highest producers were somewhat earlier maturing than the lowest producers. In the case of the highest producers the mean age in days that laying commenced was 163.11±1.28 days and in the case of the lowest producers it was 176.47±3.12 days. The difference is 13.36±3.37 days, thus indicating a significant difference in age in days that laying commenced in favor of the highest producers. One interesting feature should be observed in connection with the data in Table
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Measurements
54 highest producers
132 intermediate producers
51 lowest producers
Inches
Inches
birds: Length of back Width of back Length of keel
6.39 + 0.03 3.47 + 0.02 4.19 + 0.02
6.38 + 0.01 3.36 + 0.01 4.18 + 0.01
6.47 + 0.03 3.50 + 0.02 4.36 + 0.02
Dressed carcasses: 1. Length of back 2. Width of back 3. Length of keel
6.28 + 0.03 2.93 + 0.01 3.85 + 0.02
6.03 + 0.03 3.02 + 0.01 3.87 + 0.01
6.54±0.02 3.09 + 0.02 4.02 + 0.02
Bones: 1. Length of back 2. Width of back 3. Length of keel
5.45 + 0.02 2.12 + 0.01 3.60 + 0.03
Live 1. 2. 3.
indicate the impossibility of determining laying ability on the basis of live bird observations. The same is true of the dressed carcass measurements. The data regarding bone measurements show that the length of back in the highest and lowest groups was the same but that the width of backbone and length of keel was slightly greater in the lowest than in the highest producers. Judging from the data given in Table 6, it is apparent that the lowest producers were slightly larger than the highest producers. The mean weight of the highest producers was 1,934.25±24.01 grams per bird and the mean weight of the lowest producers was 2,037.25±34.31 grams, the difference not being significant.
—
•
— —
Inches
5.45 + 0.03 2.23 + 0.02 3.80 + 0.02
6. It will be noted that in the case of the group of 51 lowest producers, the length of back in the live birds is less than the length of back in the dressed carcasses. This indicates one of the difficulties involved in measuring live birds, assuming that dressed carcass measurements are more accurately determined than live bird measurements. However, it has been determined in the case of the group of highest producers and the group of lowest producers that certain dressed carcass measurements were not highly correlated with bone measurements, in fact, not as highly correlated as comparable live-bird measurements. Simple correlation coefficients were determined between the length of the backbone and the length of
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TABLE 6. Live bird, dressed carcass, and bone measurements in three groups of S.C. White Leghorns
160
P O U L T R Y
back in live birds and the length of back in n dressed carcasses, between width of back:bone and width of back in live birds and d width of back in dressed carcasses, and be-:tween length of keelbone and length of keelil in live birds and length of keel in dressedd carcasses. These simple correlation coeffi-icients are given in Table 7. The data given in Table 7 show that inn three cases out of six the simple correlationi coefficient between a given bone measure-ment and a comparable measurement in livee
S C I E N C E
The data in Tables 6 and 7 regarding the body measurements of the three groups comprising the flock of 237 S.C. White Leghorns confirm the observations made previously regarding the other groups of S.C. White Leghorns and the group of Rhode Island Reds, two of the most important observations being that live-bird and dressed carcass measurements are not necessarily reliable indices of the skeletal structure of a bird and that the shape of a bird as determined by live-bird, dressed carcass, and
(White Leghorns) Highest producers
Lowest producers
Correlation between length of backbone and length of back in live birds
.47
.51
Correlation between length of backbone and length of back in dressed carcasses
.50
.70
Correlation between width of backbone and width of back in live birds
.74
.51
Correlation between width of backbone and width of back in dressed carcasses
.66
.36
Correlation between length of keelbone and length of keel in live birds
.86
.79
Correlation between length of keelbone and length of keel in dressed carcasses
.83
.94
birds was greater than the simple correla- bone measurements is not a reliable index tion coefficient between the same bone meas- of the bird's laying ability. urement and a comparable measurement in An observation made recently regarding dressed carcasses. Furthermore, practically the similarity between the skeletal structure all of the correlation coefficients given in of the beef and the dairy cow is of interest Table 7 are lower than might be expected, in this discussion. Swett, Graves, and Miller indicating that in the case of the two groups (1928) compared the conformation, anatof birds measured neither dressed carcass omy, and skeletal structure of a "highly spenor live bird measurements constituted a cialized Aberdeen Angus with that of a true index of the actual length and width of highly specialized Jersey" and drew the the backbone and of the length of the keel- following conclusions: "In external form the bone. The fact that accurate live-bird meas- two cows differed greatly. In weight and urements are so difficult to make probably size of internal organs, the differences were explains why the observations of various in- not sufficiently great to indicate significant vestigators given in Table 3 do not agree differences in function. In skeleton structure closely. the two cows varied somewhat but were
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TABLE 7. Simple correlation coefficients between bone measurements and comparable live bird, and dressed carcass measurements
161
generally similar. This would indicate that the evolution of the dairy and beef types, which has been accomplished through breeding and selection, has not materially altered their skeletal structure, but rather that the difference in type is due to extreme fleshing on the one hand and to udder development and absence of fleshing on the other. Aside from the external form, the most marked difference noted between the cows compared was the quantity of secretory tissue in their udders." Apparently the outstanding difference between beef and dairy cows is in respect to the physiological aspects of flesh production and milk secretion, the physiological characters being transmitted through the agency of factors or genes, which are inherited. In the case of the domestic fowl the available evidence to date goes to show that flesh production and egg production are apparently inherited largely independently of skeletal structure. Kopec (1927) and Hutt (1929) have supplied evidence showing that while there are genes responsible for the development of the size of all parts of the body, there are also other genes affecting the development of the size of individual bones. If such is the case, then if skeletal structure is definitely associated with egg-laying ability there should be linkage between the genes determining bone size or length and the genes determining egg production. Such, however, has never been demonstrated; in fact, practically all of the available evidence indicates that type as determined by skeletal structure is not intimately associated with laying ability. It should be kept in mind, however, that in the selection of birds on the basis of their presumed laying ability, certain physiological characters should always be taken into consideration. The most important of these physiological characters include age in days that laying commences, the accumulation of excessive tissue over
various parts of the head, the accumulation of an excessive amount of fleshing in the abdomen, the bleaching of the yellow pigment from the beak and shanks as an indication of the approximate number of eggs laid during a given period, and the time of year and duration of the first annual molt. The relative importance of these characters in the selection of layers has been discussed fully by Rice, Hall, and Marble (1930). CONCLUSIONS Live-bird measurements, as usually taken, are not reliable indices of the shape or type of a bird. Live-bird measurements of the length, breadth and depth of head and of the length and breadth of back, greatest width at shoulders, and depth of body in front are of no value in the selection of birds according to their laying ability. In three out of six groups of birds those with the shortest keels were among the best layers. Dressed carcass measurements in the group of birds measured were not highly correlated with comparable bone measurements and cannot be considered as reliable indices of egg laying ability. There is no significant relationship between the length, breadth, or shape of skull and egg production. Neither the length nor the breadth nor the depth of the skull of a bird bears any relation to the total weight of eggs laid by the bird nor to her mean egg weight. Brain capacity bears no relation to the number, total weight, or mean weight of eggs laid by a bird. Simple correlation coefficients between egg production and each of three bone measurements, length of back, width of back from femur joint to femur joint, and length of keel, are of no significance, except possibly length of keel in certain flocks. The multiple correlation between egg production and the three bone measurements,
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REFERENCES
Asmundson, V. S., 1921. The relation of keel bone to egg production. Sci. Agr. 1:30-33, and 63-67. Fronda, Francisco M., and Felix S. Gamo, 1931. The relation of some head characters and egg production among Cantonese fowls. Philippine Agr. 20:261-268. Hall, G. O., 1923. A study of the relation between body conformation in laying fowls and size and shape of egg laid. Cornell Univ. Thesis. Cited by Rice, Hall, and Marble (1930). Hutt, F. B., 1921. Sex dimorphism and variability in the appendicular skeleton of the Leghorn fowl. Poul. Sci. 8:202-218.
Jull, Morley A., 1925. The selection of breeding stock in relation to the inheritance of form and function in the domestic fowl. Poul. Sci. 5 :1-19. Kopec, Stefan, 1927. Zur Kenntnis der Vererbung der Korperdimensionen und der Korperform beim Haushuhn. Zeitschrift fiir induktive Abstammungsund Vererbungslehre. Bd. 45, Heft Vi, 87-104. Macht, E., 1930. Wechselbeziehung zwischen Jugendentwicklung und Legeleistung. Die • Arbeiten der Kreisgeflugelzuchtanstalt fur Oberbayern Erding 1905-1930. Jubilaumsbericht, 66-101. Rice, J. E., G. O. Hall, and Dean R. Marble, 1930. Judging Poultry for Production, 425. John Wiley and Sons, New York. Scholten, Henry H., 1927. Correlation between external characteristics of a hen and her egg production. Rept. Proc. Third World's Poul. Congress, 141-143. Pub. by Canadian Dept. Agr., Ottawa, Canada. Sherwood, R. M., 1922. Correlation between external body characters and annual egg production in White Leghorn fowls. Texas Agr. Exp. Sta. Bui. 295. Sherwood, R. M., and C. B. Godbey, 1928. Construction of score card for judging for egg production. Poul. Sci. 7 :263-274. Swett, W. W., Graves, R. R., and F. W. Miller, 1928. Comparison of conformation, anatomy, and skeletal structure of a highly specialized dairy cow and a highly specialized beef cow. Jour. Agr. Res. 37:685-717. Waters, Nelson, F., 1927. The relation between body measurements and egg production in single comb White Leghorns. Poul. Sci. 6:167-173.
c
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length of back, width of back from femur joint to femur joint, and length of keel, is low and of no significance statistically. The same is true regarding the multiple correlation between total egg weight per bird and these three bone measurements and between mean egg weight per bird and those three bone measurements. Evidence is not only lacking to support the contention that there is an egg-laying type in the domestic fowl, type here being considered from the standpoint of skeletal structure, but all available evidence suggests that the type of the bird, as influenced by the skeleton, has no significant relationship to egg-producing ability.
SCIEN'CE