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Strains of White Plymouth Rocks for Specific Economic Purposes
Strains of White Plymouth Rocks for Specific Economic Purposes R. GEORGE JAAP
Oklahoma Agricultural Experiment Station, Stillwater (Received for publication September 26, 1942)
POPULARITY OF WHITE PLYMOUTH ROCKS IN OKLAHOMA
A
PPROXIMATELY 27 percent of all • birds banded in the flocks of 78 Oklahoma Poultry Improvement Association hatcheries are White Plymouth Rocks. This estimate is based on the data from 2,042 flocks containing 316,933 birds as included in the 1942 Yearbook of the Oklahoma Poultry Improvement Association.
binations, improve the value of the resulting strains. Four of the gene pairs are usually considered to be hypostatic in the White Plymouth Rock. PRODUCTION OF AN EARLY FEATHERING STRAIN
Warren (1925, 1930) has demonstrated a method of identifying a positive type of early feathering in the day old and 10-day chick. Since this gene responsible for early TABLE 1.—Popularity of five common varieties in appearance of feathers in the young chick Oklahoma* is sex-linked and recessive, it shall be designated by the symbol Zk. Feathers of Percent Percent chickens carrying the dominant allele (ZK) of of Variety flocks birds are not as numerous nor as long at hatching and during the first few weeks of the 27.0 30.1 White Plymouth Rock 20.8 14.2 Single Comb White Leghorn chick's life. It was apparent that the gene 12.9 13.2 Single Comb Rhode Island Red Zh was valuable not only for identifying 12.5 13.7 White Wyandotte 9.1 9.6 Barred Plymouth Rock the sex in appropriate matings (Warren, * Estimated from the records for 316,933 birds 1930) but also for improving the feathering banded in 2,042 flocks supplying 78 hatcheries. of the common breeds used for the producData summarized from the 1942 Yearbook of the tion of broiler and frying chickens. For this Oklahoma Poultry Improvement Association. latter reason this station undertook, in the Since these hatcheries are scattered over year 1936, the problem of developing the state, the figures in Table 1 probably strains of White and Barred Plymouth represent the nearest estimate of the dis- Rocks and Rhode Island Reds which would the positive type of early tribution of varieties in Oklahoma. Esti- breed true for k feathering. Z was identified in some inmating from the same source, there appear dividuals among the Rhode Island Reds and to be approximately twice as many flocks an early feathering strain was readily deof White Plymouth Rocks as flocks of any veloped in this variety. Radi and Warren other variety. Due to the prevalence of the (1938) have reported the development White Plymouth Rock, any strain differences which return an economic advantage of an early-feathering strain of Rhode Iscould be utilized to a greater extent than land Reds. No evidence of positive early in any other variety raised in Oklahoma. feathering was found among many White This paper reports a study of the action and Barred Plymouth Rock chicks obof five gene pairs which, in certain com- served in Oklahoma hatcheries. [209 1
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R. GEORGE JAAP
Due to the failure in locating Zk in the Plymouth Rock breed, this gene was secured from the Single Comb White Leghorn variety. A diagrammatic summary of the matings involved in developing the early-feathering White Plymouth Rock is presented in chart 1. The reasons for the specific matings given in this chart may be explained by the following statements.
In order to readily eliminate the dominant white (/) of the Leghorn and to utilize the first cross for the beginning of both the White and Barred varieties, a Barred Plymouth Rock male was crossed with Single Comb White Leghorn females. Forty-six males (group 1) were reared to approximately five months of age. Among these were four individuals having no
CHART 1 PRODUCTION OF EARLY FEATHERING WHITE PLYMOUTH ROCKS
Group Designation
Group Designation Sires
Dams
late,* Barred P. Rock $ iiCCZKZK
early,* White Leghorn 9 9
late, white splashed $ $ K
late, White P. Rock $ 9 iiccZKW
nccz z"
nccznv
late, White P. Rock £ iiccZKZK 3.
late, white $ $ HccZKZk
early, barred 9 $ iiCcZ"W late, White P. Rock 9 9 iiccZKW
late, White P. Rock $ ZKZK -late, white $ $ ZKZkt
2.
early, white 9 9 ZkW
4.
late, White P. Rock 9 $ ZKW
early, White P. Rock $ $ ZkZk early, White P. Rocks $ $ —ZkZk 9 9 —ZkW
early, white 9 $ ZkW
6. 7.
* The terms "early" and "late" refer to the presence or absence, respectively, of main tail feathers 10 days after hatching. t These sires were purchased in 1940 from a hatcheryman who had developed this stock. Group 5 males might have been used and the early feathering progeny selected for group 7.
STRAINS OF WHITE PLYMOUTH ROCKS FOR SPECIFIC ECONOMIC PURPOSES
trace of white in the earlobes. One of these males was chosen for the series of back crosses (chart 1). As a result the enamelwhite earlobe color of the Leghorn was readily eliminated. By choosing the earlyfeathering, Barred females of group 2, dominant white was eliminated; and, by choosing the White males of group 3, recessive-white plumage was regained. During the back crosses from group 3 to group 6 a very vigorous selection was made to remove from the stock all White Leghorn characteristics other than the gene Zk. As a result groups 5 and 6 appeared to be good specimens of the White Plymouth Rock variety. Group 5 males might have been mated with group 6 females and the early feathering strain selected from their progeny. By obtaining three generations each two years, group 6 was hatched during the spring of 1940. By this time a hatcheryman had discovered Zk (positive early feathering) among the White Plymouth Rocks hatched in his hatchery and was producing a strain of this early-feathering stock. Male chicks were purchased from this hatcheryman and mated with group 6 pullets to produce the early feathering strain (group 7). During the 1941 and 1942 seasons over one thousand chicks of this strain have been observed. All have been fully feathered by six weeks after hatching, thus eliminating the problem of poor feathering at the broiler age. Darrow (1941) has stated that, in early feathering (Zk) strains of heavy breed stocks, probably the highest correlation is between well-developed tails at 10 days and good back feathering at the six weeks' age. All early feathering individuals used as illustrated in chart 1 were selected at 10 days of age by the presence of welldeveloped tail feathers. This probably accounts for the lack of the poor feathering types mentioned by Darrow (1941). Some
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of the incompleteness of feathering similar to that mentioned by Darrow has been observed in an early-feathering exhibition strain of Rhode Island Reds developed at the Oklahoma station. Recently Darrow (1942) has suggested selection for number of secondaries at hatching as a source of improving broiler feathering in Zk stock. GRAY DOWN COLOR AND SEXING
In practice the down color of White Plymouth Rocks varies due to the presence of pale-red and gray tints. Also, the amount and distribution of yellow tints in the down vary. A part of this variability may be environmental and due to varying amounts of xanthophyll in the egg. The American Poultry Association (1940) describes the standard color of the chicks as bluish gray, creamy white, or white. Chicks showing reddish tints in the down are, therefore, disqualified. Due to the variation that exists in the intensity of the gray pigmentation, some hatcherymen are culling the gray chicks to obtain uniformity among the baby chicks sold in boxes. Uniform down color would be useful as an aid in merchandising the chicks. The white chicken is white because very little pigment is placed in the growing feather. Its basic inheritance for color may vary greatly. A part of this basic inheritance is allowed to express itself in cross-breeding with colored varieties. As a result crossbreds from the White Plymouth Rock as one parent may vary from white to black in the same hatch. This is especially true when the other parent is red or buff in color. If all White Plymouth Rocks were "sports" from the Barred variety with the only change occurring in the genes for the presence or absence of color, the White variety when crossed with colored breeds should produce crossbreds with similar color to those from Barred parents. Any color inheritance which would
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R. GEORGE JAAP
promote uniformity in down color of the variety as well as its crossbreds would be beneficial. Possibilities of a dominant rather than a recessive white strain of White Plymouth Rocks will be discussed later. Jerome (1939) and later the Poultry Division of the Canadian Experimental Farms' Service (1941) have shown that sex differences in the color of Barred Plymouth Rock chicks are such that it is possible to indentify at least 95 percent of the pullets and cockerels. If the White variety had the same genes for down color pattern as those of the Barred, would it be possible to identify the sexes in gray chicks? The matings reported below were made to obtain the proper strain of stock to test this possibility. In addition, information which assists in explaining causes for variability in the White Plymouth Rock down color was collected from the segregation of the progenies produced as tests. The genes known to affect the degree of sexual dimorphism in the down of the Barred Plymouth Rock are E (black) and ZB (barring). The simplest method available to test for these genes in the White variety was to cross them with Rhode Island Reds and classify their progeny. Since the Red is e (not black) and Zh (not barred), all black or barred chicks obtained these dominant genes from the White Plymouth Rock parent. Tests were first obtained for 34 females and 4 males, the parents of group 7 in chart 1. Only one of the males had the desired genotype EEZBZB. Five of the females had gray down as chicks and had the genotype EeZBW. As a preliminary test, these were mated to the tested male during the summer of 1941 and an attempt was made to identify the males at hatching in a manner similar to that used for Barred Plymouth Rocks (Jerome, 1939). All of the 137 chicks hatched had gray down, al-
though the intensity varied from only a faint grayish tint along the sides of the body to a deep gray tone over the greater part of the dorsal surface. The sex of 96 or approximately 70 percent was classified correctly, indicating that some sexual dimorphism did exist. During the fall and winter of 19411942, 59 females and 22 males which were gray in color at hatching were tested in the same manner. All of these were either Ee or EE, indicating that the gene E (black) was necessary for the appearance of gray color in the chick down. Further proof of this hypothesis was obtained by a non-pedigreed flock test of their sisters which showed no visible grayish tints in the down at hatching. Out of the 376 chicks hatched, 319 or approximately 85 percent were ee. If all of their dams had been heterozygous, Ee, the expected number of ee chicks would have been 50 percent. These tests indicate that some nongray chicks may carry E but all gray chicks must be genetically Ee or EE. Since 20 out of the 59 gray-down females were genetically Zb, it was evident that the presence of gray in the down of the baby chick is not dependent on the barring gene. In the first mating of parents whose down color showed gray tints at hatching, all of the 137 chicks had some gray color. From similar matings in 1942, 703 chicks were produced. All chicks had some gray in the down although the amount varied from a slight tinge along the sides of the body to a deeply-pigmented chick closely approaching the color pattern of the Barred Plymouth Rock. Apparently the presence of gray down in E chicks is recessive to its absence. Density of the gray down color is either influenced by several modifying factors or has a high environmental variability. To measure the inherent variability of
STRAINS OF WHITE PLYMOUTH ROCKS FOR SPECIFIC ECONOMIC PURPOSES
color tone among the gray chicks, a series of 10 reference skins was prepared. These were given the arbitrary values of 1 for the weakest gray tint to 10 for the darkest chicks hatched. The scores of 349 chicks from EEZBZB males mated with EeZBW and EEZBW females averaged 4.61. Positive sex records are available for 163 males from this group. Their average score was 4.06. It is apparent from these records that the average score of the female chicks was slightly more than one grade darker than that of their brothers. Due to the variability in down color within each sex, no attempt was made to sex this group at hatching. A higher percentage of the sexes should have been identified if the method explained by Jerome (1939) and the Poultry Division of the Canadian Experimental Farms' Service (1941) had been practiced with only the more deeply pigmented chicks. Further matings of the darker types are planned to determine whether it is possible to secure a strain in which the down color of each sex is uniform. Reasoning from previous experience with the ZB-gene (Jaap, 1941), sexual dimorphism in the down color should be accentuated in the darker gray downs. RED TINTS IN THE DOWN
Most strains of White Plymouth Rocks produce some chicks with distinct reddish tints. These off-colored chicks approach the pigmentation of the lighter colored variations in Rhode Island Reds. Although they seldom exceed 2 percent of the chicks hatched in hatchery flocks and at maturity appear pure white, their appearance causes a loss to the hatcheryman. Such chicks are not standard color and must be discarded or sold in mixed lots at a lower market price. Records available on the genetics of redin-the-down are limited at this time. Five
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females which had reddish down at hatching have been tested by mating with Rhode Island Red males. All of them proved to be genetically red (ee). However, not all of the ee White Plymouth Rocks had reddish tints. Down color records free from red pigment were available for four females and one male which, upon test, proved to be genetically ee. Additional information was obtained from the 1941 matings of White Plymouth Rocks involving the ee male described above, two Ee males, and an EE male. These males were mated to a random assortment of pullets of unknown down color. The ee male produced 11.2 percent red-tinted chicks, the Ee males 1.2 percent, and the EE male none. In 1942 all of the 703 chicks were at least heterozygous, Ee and none showed any reddish tints in the down. These data support the hypothesis that e may allow the presence of red color and E supresses it in chicks of White varieties. Among 547 White Wyandottes hatched during 1941, four chicks were described as purple (red plus gray). From their appearance the writer is inclined to believe that they were ee but genetically mahogany (Jaap, 1941). The gene for "silver" down (Punnett, 1923) changes some of the red to white and may be partially responsible for the suppression of the red in ee chicks. Since the color records for the above tests were taken from 18-day embryos, no attempt was made to differentiate the "silvers" from the "golds." GREEN- OR WILLOW-COLORED SHANKS
Green- or willow-colored shanks constitute a defect common to some strains of White Plymouth Rocks. This defective color is due to the presence of black pigment in the dermal layers of the shank skin underneath the yellow xanthophyll of
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R. GEORGE JAAP
the epidermis (Dunn, 1925; Knox, 1935). It appears to be more prevalent in females of the White Plymouth Rock than in any other White variety. The prevalence of the dark pigment in shanks of the White Plymouth Rock may be partially due to intermingling with the White variety of the Jersey Black Giant. Eye color and shank color are the only essential differences between these two varieties. The green-shank defect occurs occasionally in White Plymouth Rock males but is relatively rare in this sex. Occasionally the green color extends into the skin of the feathered areas, particularly around the hock and abdomen. In addition to being a standard disqualification the poultry packing industry has made serious price reductions for greenshanked birds. Since the green-shank defect cannot be identified at hatching the loss of pullets in egg producing and breeder flocks is much greater than in the case of the red down previously discussed. While sorting the White Plymouth Rock females tested for E and ZB, eight individuals with dark green shanks were observed to be E (black) and Z 6 (nonbarred). Upon a careful check of the 59 females, of the types EE and Ee, green color was observed in the shanks of all those that were genetically non-barred (ZlW). The shanks pf 38 females which carried the barring gene (ZBW) had no trace of the dermal pigment. Further evidence that the gene for barred feathers might be responsible for the absence of green shanks was obtained during the 1942 season. Eight females, having shanks with the deepest pigmentation were mated with a male which was homozygous for the barring gene (EEZBZB). From this mating 183 chickens have been observed at eight to nine weeks of age, none of which have had even the slightest trace of green color in the shanks or feet. These records
support the classification given by Knox (1935). By use of genetically barred (ZBZB) males the defect is permanently eliminated. Since Barred Plymouth Rock females usually have dark color in their shanks, it is apparent that the genes for recessive white plumage {cc) restrict the amount of black pigment in the shanks. Whether the elimination of green shanks is due to the barring gene itself or to the inhibitor of dermal pigment (Dunn, 1925) which is closely associated with barring, cannot be answered by matings included in this study. A few of the darkest gray chicks which at hatching approached the color of the Barred variety have shown a slight greenish shank color at eight weeks of age. Chicks as dark as these have never been found in commercial hatches. Evidence has been obtained that the gene for barred feathers is equally effective in preventing the appearance of green shanks in dominant-white (/) varieties. In developing a dominant-white strain of White Plymouth Rocks, a Barred Plymouth Rock male has been mated to White Plymouth Rock females which were heterozygous for dominant-white (Ii). All of the 65 dominant-white progeny (Ii) had clear yellow shanks. This indicates that the dominant-white gene plus the gene for barring, or its closely linked inhibitor of dermal pigment, elminates melanic pigment from the shanks. This conclusion is in agreement with that of Knox (1935). Since many of the White Leghorns have the barring gene this may be a partial explanation for the melanic pigment in the shanks of female crossbreds from Australorp males and White Leghorn females. Were the White Leghorn used as the sire and the Australorp as the dam, very few blue shanks would be expected under this hypothesis.
STRAINS OF WHITE PLYMOUTH ROCKS FOR SPECIFIC ECONOMIC PURPOSES
THE DOMINANT-WHITE PLYMOUTH ROCK
The majority of White Plymouth Rocks have recessive white plumage. When used in crosses with colored varieties the crossbreds are colored. Chickens of many different colors result when the other parent is red or buff. If the plumage color inheritance were dominant-white, crossbreds might be predominantly white. The majority of crossbreds at the present time are used for broiler and frying chickens. For this purpose a large white crossbred would be desirable. This phase of the problem is concerned with the development of a strain of White Plymouth Rocks suitable for producing white feathered crossbreds regardless of the color of the other parent. It is well known that the white of the Leghorn appears to be dominant only to black (Danforth, 1933). Crosses between White Leghorns and red or buff varieties often produce some predominantly red or buff individuals. The plan for producing the dominant-white strain of Plymouth Rocks is based on the assumption that the genes suppressing red color in dominant-white crossbreds are E (black), ZB (barring), and Zs (silver). If red or yellow would normally appear in the plumage, Zs would turn much of it to white. E replaces most of the reds and yellows with black and ZB reduces the amount of black by placing white bars across the feathers. A male with the genotype IIEEZB, SZB, s crossed with a red variety (iieeZb, sZl, s) should produce crossbreds whose adult plumage would have only slight flecks of black in a few of its feathers. Red color would be essentially absent. Since black would be entirely eliminated from the shanks, the green-shank defect would not occur. Only two generations have been obtained in the production of a desirable dominant-white
215
Plymouth Rock. The following explains the method used to date and suggests the necessary future matings. In establishing the strain with the positive type of early feathering, dominantwhite from the Leghorn was carefully removed by the procedure outlined in chart 1. Some time between this stage and the production of the group 6 included in that chart, dominant white was introduced into the stock through the White Plymouth Rock parents. As a result during the test for color genes in connection with the studies on gray down and green shanks, 16 out of 35 original tested females proved to be heterozygous for dominant white (li) and one homozygous (II). The best seven hens for egg production were chosen for the beginning of a desirable dominant-white strain. It would be advantageous if a dominantwhite strain of the type described above could be identified and kept separate from other existing strains of White Plymouth Rocks. Any known hereditary "markers" that could be readily identified on a white bird would be a defect or disqualification for the White Plymouth Rock variety. Having the genes /,. E, ZB and Zs in the stock a method for identifying crosses between this and common strains of White Plymouth Rocks is possible. The majority of existing White Plymouth Rocks are white because they are cc (lack the precursor of color). By making the new variety homozygous for color (CC) plus the genes /, E, ZB and Zs, practically all of the progeny from intravariety crosses with this strain would have black spots in the down as well as some black in the adult plumage (Brandt, 1936). This is a standard disqualification and, as such, should greatly facilitate the problem of isolation to maintain the proper genotype in the dominant-white strain. In view of the above comments the fol-
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R. GEORGE JAAP
lowing lists the procedure upon which the dominant white strain is being developed: 1. Identify the Ii White Plymouth Rock females by those which produce white chicks when crossed with a colored breed. 2. Mate the Ii females with Barred Plymouth males and keep only the splashed-white* female chicks. 3. Splashed-white females again mated with Barred Plymouth Rock males and the splashed-white progeny reared. 4. Identify which of these splashed-white males and females are CCEE; that is, homozygous for the ability to place color in the feathers and to extend the melanic pigment over the surface of the feathers. This is accomplished by mating with tested White Plymouth Rocks which produced only parti-colored (ee) chicks when tested in crosses with Reds. The desired individuals in this test will produce SO percent splashed-white and SO percent black or barred chicks. Undesirable individuals will produce some parti-colored chicks and/or 75 percent splashed-white and white chicks. For this reason a large number of progeny are needed to accurately identify the correct birds. 5. Mate the white-splashed males and females proven to be CCEE and retain only those white progeny which are free from black pigment in the down. 6. Test the pure white progeny to be certain that they are homozygous (II). When mated together these will form a strain in which the genotypes will be IICCEEZB, SZB, S for males and IICCEEZB, SW for females. DISCUSSION OF STRAIN POSSIBILITIES
tween inbred strains of poultry show promise of increased efficiency (Maw, 1942). Should the dominant-white and gray-down strains be developed as inbreds, the day-old progeny from crosses between these strains would have a different color (white with black spots) from that of either parental variety. If it is agreed that progeny from crosses between inbred strains should be used for production and not reproduction, the color of progeny from these strain crosses would facilitate their identification. SUMMARY 1. In 1942 approximately 27 percent of the birds in flocks of the Oklahoma Poultry Improvement Association were White Plymouth Rocks. This is greater than any other variety. 2. Data and theories are presented to explain: (a) the production of a strain positive for early feathering. (b) the reason for some sexual dimorphism in certain gray-down patterns and the possibility of sight-sexing White Plymouth Rock chicks. (c) the elimination of red tints from the down and in the adult plumage. (d) a cause for the occurrence of green- or willow-colored shanks and a simple method for eliminating this defect. (e) the production of a dominant-white strain to produce crossbreds with predominantely white plumage.
The early-feathering, dominant-white strain completely eliminates black in the down as well as adult plumage. Should the gray down prove useful in identifying sex at hatching, it would be necessary to maintain a gray-down, recessive-white strain as a separate variety. This has the disadvantage associated with the maintenance of two strains within a variety. The maintenance of two strains, however, may be an advantage. Crosses be-
3. Desirable strains should include the genes /, C, E, ZB, s, k; or, for sight sexing possibilities, i, c, E, ZB, s, le. 4. The advantage of maintaining two inbred strains of White Plymouth Rocks, dominant-white and gray-down, which would produce color-marked crosses is briefly discussed.
* The term splashed-white refers to those chicks or adults which are predominately white with small spots or flecks of black.
American Poultry Association, 1940. American standard of perfection. Amer. Poultry Assn., Davenport, Iowa.
REFERENCES
NEWS AND NOTES Brandt, A. E., 1936. A note on dominant white and crest in poultry. J. Hered. 27 :79-82. Danforth, C. H., 1933. The reaction of dominant white with yellow and black in the fowl. J. Hered. 24:301-307. Darrow, Merrit I., 1941. Relation of day-old chick wing feather development to feathering at the broiler age. (Abstract.) Poultry Sci. 20:458. , 1942. A study of modified expressions of sex-linked early feathering. (Abstract.) Poultry Sci. 21:468. Dunn, L. C , 1925. The genetic relation of some shank colors of the domestic fowl. (Abstract.) Anat. Rec. 31:343-344. Jaap, R. George, 1941. Auto-sex linkage in the domestic fowl. II. Auto-sexing accuracy with the gene for barred feathers in red to black down-color phenotypes. Poultry Sci. 20:317321. Jerome, Fred N., 1939. Auto-sex linkage in the
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Barred Plymouth Rock. Poultry Sci. 18:437440. Knox, C. W., 1935. The inheritance of shank color in chickens. Genetics 20:529-544. Maw, A. J. G., 1942. Crosses between inbred lines of the domestic fowl. Poultry Sci. 21:548-553. Poultry Division of the Canadian Experimental Farms' Service, 1941. Sight sexing Barred Rock baby chicks. Dominion Experimental Farm Bui., Ottawa. Punnett, R. C , 1923. Heredity in poultry. The Macmillan Company, London. Radi, M. H., and D. C. Warren, 1938. Studies on the physiology and inheritance of feathering in the growing chick. J. Agr. Res. 56:679-705. Warren, D. C , 1925. Inheritance of rate of feathering in poultry. J. Hered. 16:13-18. , 1930. Crossbred poultry. Kansas Agr. Exp. Sta. Bui. 252.
News and Notes The July issue of POULTRY SCIENCE will be bound in two parts. Part I will contain the usual papers and research notes, whereas Part II will consist of the alphabetical index of the first 20 volumes of POULTRY SCIENCE. The two parts will be mailed together, although they will be bound separately. In this way any member or subscriber who desires to file the Index for ready reference may do so. Others who may desire to incorporate it with the regular issues may either file or bind it in its regular place. Garry A. Miles (B.S., University of Connecticut, 1926), assistant extension poultryman and assistant garden specialist at the
University of Connecticut, has resigned effective March IS to take a position as extension poultryman at the University of Delaware where he will be responsible for poultry extension work and poultry club work. The position will be filled by Owen S. Trask (B.S., Massachusetts Agricultural College, 1936), who is now county club leader in Tolland County, Connecticut. Mr. Trask will take up his new work July 1, 1943. Dr. W. C. Tully is now associated with Lederle Laboratories, Pearl River, New York, as feed specialist. He will work with vitamin concentrates and other products for the feed trade.
Oklahoma Agricultural Experiment Station, Stillwater (Received for publication September 26, 1942)
POPULARITY OF WHITE PLYMOUTH ROCKS IN OKLAHOMA
A
PPROXIMATELY 27 percent of all • birds banded in the flocks of 78 Oklahoma Poultry Improvement Association hatcheries are White Plymouth Rocks. This estimate is based on the data from 2,042 flocks containing 316,933 birds as included in the 1942 Yearbook of the Oklahoma Poultry Improvement Association.
binations, improve the value of the resulting strains. Four of the gene pairs are usually considered to be hypostatic in the White Plymouth Rock. PRODUCTION OF AN EARLY FEATHERING STRAIN
Warren (1925, 1930) has demonstrated a method of identifying a positive type of early feathering in the day old and 10-day chick. Since this gene responsible for early TABLE 1.—Popularity of five common varieties in appearance of feathers in the young chick Oklahoma* is sex-linked and recessive, it shall be designated by the symbol Zk. Feathers of Percent Percent chickens carrying the dominant allele (ZK) of of Variety flocks birds are not as numerous nor as long at hatching and during the first few weeks of the 27.0 30.1 White Plymouth Rock 20.8 14.2 Single Comb White Leghorn chick's life. It was apparent that the gene 12.9 13.2 Single Comb Rhode Island Red Zh was valuable not only for identifying 12.5 13.7 White Wyandotte 9.1 9.6 Barred Plymouth Rock the sex in appropriate matings (Warren, * Estimated from the records for 316,933 birds 1930) but also for improving the feathering banded in 2,042 flocks supplying 78 hatcheries. of the common breeds used for the producData summarized from the 1942 Yearbook of the tion of broiler and frying chickens. For this Oklahoma Poultry Improvement Association. latter reason this station undertook, in the Since these hatcheries are scattered over year 1936, the problem of developing the state, the figures in Table 1 probably strains of White and Barred Plymouth represent the nearest estimate of the dis- Rocks and Rhode Island Reds which would the positive type of early tribution of varieties in Oklahoma. Esti- breed true for k feathering. Z was identified in some inmating from the same source, there appear dividuals among the Rhode Island Reds and to be approximately twice as many flocks an early feathering strain was readily deof White Plymouth Rocks as flocks of any veloped in this variety. Radi and Warren other variety. Due to the prevalence of the (1938) have reported the development White Plymouth Rock, any strain differences which return an economic advantage of an early-feathering strain of Rhode Iscould be utilized to a greater extent than land Reds. No evidence of positive early in any other variety raised in Oklahoma. feathering was found among many White This paper reports a study of the action and Barred Plymouth Rock chicks obof five gene pairs which, in certain com- served in Oklahoma hatcheries. [209 1
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R. GEORGE JAAP
Due to the failure in locating Zk in the Plymouth Rock breed, this gene was secured from the Single Comb White Leghorn variety. A diagrammatic summary of the matings involved in developing the early-feathering White Plymouth Rock is presented in chart 1. The reasons for the specific matings given in this chart may be explained by the following statements.
In order to readily eliminate the dominant white (/) of the Leghorn and to utilize the first cross for the beginning of both the White and Barred varieties, a Barred Plymouth Rock male was crossed with Single Comb White Leghorn females. Forty-six males (group 1) were reared to approximately five months of age. Among these were four individuals having no
CHART 1 PRODUCTION OF EARLY FEATHERING WHITE PLYMOUTH ROCKS
Group Designation
Group Designation Sires
Dams
late,* Barred P. Rock $ iiCCZKZK
early,* White Leghorn 9 9
late, white splashed $ $ K
late, White P. Rock $ 9 iiccZKW
nccz z"
nccznv
late, White P. Rock £ iiccZKZK 3.
late, white $ $ HccZKZk
early, barred 9 $ iiCcZ"W late, White P. Rock 9 9 iiccZKW
late, White P. Rock $ ZKZK -late, white $ $ ZKZkt
2.
early, white 9 9 ZkW
4.
late, White P. Rock 9 $ ZKW
early, White P. Rock $ $ ZkZk early, White P. Rocks $ $ —ZkZk 9 9 —ZkW
early, white 9 $ ZkW
6. 7.
* The terms "early" and "late" refer to the presence or absence, respectively, of main tail feathers 10 days after hatching. t These sires were purchased in 1940 from a hatcheryman who had developed this stock. Group 5 males might have been used and the early feathering progeny selected for group 7.
STRAINS OF WHITE PLYMOUTH ROCKS FOR SPECIFIC ECONOMIC PURPOSES
trace of white in the earlobes. One of these males was chosen for the series of back crosses (chart 1). As a result the enamelwhite earlobe color of the Leghorn was readily eliminated. By choosing the earlyfeathering, Barred females of group 2, dominant white was eliminated; and, by choosing the White males of group 3, recessive-white plumage was regained. During the back crosses from group 3 to group 6 a very vigorous selection was made to remove from the stock all White Leghorn characteristics other than the gene Zk. As a result groups 5 and 6 appeared to be good specimens of the White Plymouth Rock variety. Group 5 males might have been mated with group 6 females and the early feathering strain selected from their progeny. By obtaining three generations each two years, group 6 was hatched during the spring of 1940. By this time a hatcheryman had discovered Zk (positive early feathering) among the White Plymouth Rocks hatched in his hatchery and was producing a strain of this early-feathering stock. Male chicks were purchased from this hatcheryman and mated with group 6 pullets to produce the early feathering strain (group 7). During the 1941 and 1942 seasons over one thousand chicks of this strain have been observed. All have been fully feathered by six weeks after hatching, thus eliminating the problem of poor feathering at the broiler age. Darrow (1941) has stated that, in early feathering (Zk) strains of heavy breed stocks, probably the highest correlation is between well-developed tails at 10 days and good back feathering at the six weeks' age. All early feathering individuals used as illustrated in chart 1 were selected at 10 days of age by the presence of welldeveloped tail feathers. This probably accounts for the lack of the poor feathering types mentioned by Darrow (1941). Some
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of the incompleteness of feathering similar to that mentioned by Darrow has been observed in an early-feathering exhibition strain of Rhode Island Reds developed at the Oklahoma station. Recently Darrow (1942) has suggested selection for number of secondaries at hatching as a source of improving broiler feathering in Zk stock. GRAY DOWN COLOR AND SEXING
In practice the down color of White Plymouth Rocks varies due to the presence of pale-red and gray tints. Also, the amount and distribution of yellow tints in the down vary. A part of this variability may be environmental and due to varying amounts of xanthophyll in the egg. The American Poultry Association (1940) describes the standard color of the chicks as bluish gray, creamy white, or white. Chicks showing reddish tints in the down are, therefore, disqualified. Due to the variation that exists in the intensity of the gray pigmentation, some hatcherymen are culling the gray chicks to obtain uniformity among the baby chicks sold in boxes. Uniform down color would be useful as an aid in merchandising the chicks. The white chicken is white because very little pigment is placed in the growing feather. Its basic inheritance for color may vary greatly. A part of this basic inheritance is allowed to express itself in cross-breeding with colored varieties. As a result crossbreds from the White Plymouth Rock as one parent may vary from white to black in the same hatch. This is especially true when the other parent is red or buff in color. If all White Plymouth Rocks were "sports" from the Barred variety with the only change occurring in the genes for the presence or absence of color, the White variety when crossed with colored breeds should produce crossbreds with similar color to those from Barred parents. Any color inheritance which would
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promote uniformity in down color of the variety as well as its crossbreds would be beneficial. Possibilities of a dominant rather than a recessive white strain of White Plymouth Rocks will be discussed later. Jerome (1939) and later the Poultry Division of the Canadian Experimental Farms' Service (1941) have shown that sex differences in the color of Barred Plymouth Rock chicks are such that it is possible to indentify at least 95 percent of the pullets and cockerels. If the White variety had the same genes for down color pattern as those of the Barred, would it be possible to identify the sexes in gray chicks? The matings reported below were made to obtain the proper strain of stock to test this possibility. In addition, information which assists in explaining causes for variability in the White Plymouth Rock down color was collected from the segregation of the progenies produced as tests. The genes known to affect the degree of sexual dimorphism in the down of the Barred Plymouth Rock are E (black) and ZB (barring). The simplest method available to test for these genes in the White variety was to cross them with Rhode Island Reds and classify their progeny. Since the Red is e (not black) and Zh (not barred), all black or barred chicks obtained these dominant genes from the White Plymouth Rock parent. Tests were first obtained for 34 females and 4 males, the parents of group 7 in chart 1. Only one of the males had the desired genotype EEZBZB. Five of the females had gray down as chicks and had the genotype EeZBW. As a preliminary test, these were mated to the tested male during the summer of 1941 and an attempt was made to identify the males at hatching in a manner similar to that used for Barred Plymouth Rocks (Jerome, 1939). All of the 137 chicks hatched had gray down, al-
though the intensity varied from only a faint grayish tint along the sides of the body to a deep gray tone over the greater part of the dorsal surface. The sex of 96 or approximately 70 percent was classified correctly, indicating that some sexual dimorphism did exist. During the fall and winter of 19411942, 59 females and 22 males which were gray in color at hatching were tested in the same manner. All of these were either Ee or EE, indicating that the gene E (black) was necessary for the appearance of gray color in the chick down. Further proof of this hypothesis was obtained by a non-pedigreed flock test of their sisters which showed no visible grayish tints in the down at hatching. Out of the 376 chicks hatched, 319 or approximately 85 percent were ee. If all of their dams had been heterozygous, Ee, the expected number of ee chicks would have been 50 percent. These tests indicate that some nongray chicks may carry E but all gray chicks must be genetically Ee or EE. Since 20 out of the 59 gray-down females were genetically Zb, it was evident that the presence of gray in the down of the baby chick is not dependent on the barring gene. In the first mating of parents whose down color showed gray tints at hatching, all of the 137 chicks had some gray color. From similar matings in 1942, 703 chicks were produced. All chicks had some gray in the down although the amount varied from a slight tinge along the sides of the body to a deeply-pigmented chick closely approaching the color pattern of the Barred Plymouth Rock. Apparently the presence of gray down in E chicks is recessive to its absence. Density of the gray down color is either influenced by several modifying factors or has a high environmental variability. To measure the inherent variability of
STRAINS OF WHITE PLYMOUTH ROCKS FOR SPECIFIC ECONOMIC PURPOSES
color tone among the gray chicks, a series of 10 reference skins was prepared. These were given the arbitrary values of 1 for the weakest gray tint to 10 for the darkest chicks hatched. The scores of 349 chicks from EEZBZB males mated with EeZBW and EEZBW females averaged 4.61. Positive sex records are available for 163 males from this group. Their average score was 4.06. It is apparent from these records that the average score of the female chicks was slightly more than one grade darker than that of their brothers. Due to the variability in down color within each sex, no attempt was made to sex this group at hatching. A higher percentage of the sexes should have been identified if the method explained by Jerome (1939) and the Poultry Division of the Canadian Experimental Farms' Service (1941) had been practiced with only the more deeply pigmented chicks. Further matings of the darker types are planned to determine whether it is possible to secure a strain in which the down color of each sex is uniform. Reasoning from previous experience with the ZB-gene (Jaap, 1941), sexual dimorphism in the down color should be accentuated in the darker gray downs. RED TINTS IN THE DOWN
Most strains of White Plymouth Rocks produce some chicks with distinct reddish tints. These off-colored chicks approach the pigmentation of the lighter colored variations in Rhode Island Reds. Although they seldom exceed 2 percent of the chicks hatched in hatchery flocks and at maturity appear pure white, their appearance causes a loss to the hatcheryman. Such chicks are not standard color and must be discarded or sold in mixed lots at a lower market price. Records available on the genetics of redin-the-down are limited at this time. Five
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females which had reddish down at hatching have been tested by mating with Rhode Island Red males. All of them proved to be genetically red (ee). However, not all of the ee White Plymouth Rocks had reddish tints. Down color records free from red pigment were available for four females and one male which, upon test, proved to be genetically ee. Additional information was obtained from the 1941 matings of White Plymouth Rocks involving the ee male described above, two Ee males, and an EE male. These males were mated to a random assortment of pullets of unknown down color. The ee male produced 11.2 percent red-tinted chicks, the Ee males 1.2 percent, and the EE male none. In 1942 all of the 703 chicks were at least heterozygous, Ee and none showed any reddish tints in the down. These data support the hypothesis that e may allow the presence of red color and E supresses it in chicks of White varieties. Among 547 White Wyandottes hatched during 1941, four chicks were described as purple (red plus gray). From their appearance the writer is inclined to believe that they were ee but genetically mahogany (Jaap, 1941). The gene for "silver" down (Punnett, 1923) changes some of the red to white and may be partially responsible for the suppression of the red in ee chicks. Since the color records for the above tests were taken from 18-day embryos, no attempt was made to differentiate the "silvers" from the "golds." GREEN- OR WILLOW-COLORED SHANKS
Green- or willow-colored shanks constitute a defect common to some strains of White Plymouth Rocks. This defective color is due to the presence of black pigment in the dermal layers of the shank skin underneath the yellow xanthophyll of
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the epidermis (Dunn, 1925; Knox, 1935). It appears to be more prevalent in females of the White Plymouth Rock than in any other White variety. The prevalence of the dark pigment in shanks of the White Plymouth Rock may be partially due to intermingling with the White variety of the Jersey Black Giant. Eye color and shank color are the only essential differences between these two varieties. The green-shank defect occurs occasionally in White Plymouth Rock males but is relatively rare in this sex. Occasionally the green color extends into the skin of the feathered areas, particularly around the hock and abdomen. In addition to being a standard disqualification the poultry packing industry has made serious price reductions for greenshanked birds. Since the green-shank defect cannot be identified at hatching the loss of pullets in egg producing and breeder flocks is much greater than in the case of the red down previously discussed. While sorting the White Plymouth Rock females tested for E and ZB, eight individuals with dark green shanks were observed to be E (black) and Z 6 (nonbarred). Upon a careful check of the 59 females, of the types EE and Ee, green color was observed in the shanks of all those that were genetically non-barred (ZlW). The shanks pf 38 females which carried the barring gene (ZBW) had no trace of the dermal pigment. Further evidence that the gene for barred feathers might be responsible for the absence of green shanks was obtained during the 1942 season. Eight females, having shanks with the deepest pigmentation were mated with a male which was homozygous for the barring gene (EEZBZB). From this mating 183 chickens have been observed at eight to nine weeks of age, none of which have had even the slightest trace of green color in the shanks or feet. These records
support the classification given by Knox (1935). By use of genetically barred (ZBZB) males the defect is permanently eliminated. Since Barred Plymouth Rock females usually have dark color in their shanks, it is apparent that the genes for recessive white plumage {cc) restrict the amount of black pigment in the shanks. Whether the elimination of green shanks is due to the barring gene itself or to the inhibitor of dermal pigment (Dunn, 1925) which is closely associated with barring, cannot be answered by matings included in this study. A few of the darkest gray chicks which at hatching approached the color of the Barred variety have shown a slight greenish shank color at eight weeks of age. Chicks as dark as these have never been found in commercial hatches. Evidence has been obtained that the gene for barred feathers is equally effective in preventing the appearance of green shanks in dominant-white (/) varieties. In developing a dominant-white strain of White Plymouth Rocks, a Barred Plymouth Rock male has been mated to White Plymouth Rock females which were heterozygous for dominant-white (Ii). All of the 65 dominant-white progeny (Ii) had clear yellow shanks. This indicates that the dominant-white gene plus the gene for barring, or its closely linked inhibitor of dermal pigment, elminates melanic pigment from the shanks. This conclusion is in agreement with that of Knox (1935). Since many of the White Leghorns have the barring gene this may be a partial explanation for the melanic pigment in the shanks of female crossbreds from Australorp males and White Leghorn females. Were the White Leghorn used as the sire and the Australorp as the dam, very few blue shanks would be expected under this hypothesis.
STRAINS OF WHITE PLYMOUTH ROCKS FOR SPECIFIC ECONOMIC PURPOSES
THE DOMINANT-WHITE PLYMOUTH ROCK
The majority of White Plymouth Rocks have recessive white plumage. When used in crosses with colored varieties the crossbreds are colored. Chickens of many different colors result when the other parent is red or buff. If the plumage color inheritance were dominant-white, crossbreds might be predominantly white. The majority of crossbreds at the present time are used for broiler and frying chickens. For this purpose a large white crossbred would be desirable. This phase of the problem is concerned with the development of a strain of White Plymouth Rocks suitable for producing white feathered crossbreds regardless of the color of the other parent. It is well known that the white of the Leghorn appears to be dominant only to black (Danforth, 1933). Crosses between White Leghorns and red or buff varieties often produce some predominantly red or buff individuals. The plan for producing the dominant-white strain of Plymouth Rocks is based on the assumption that the genes suppressing red color in dominant-white crossbreds are E (black), ZB (barring), and Zs (silver). If red or yellow would normally appear in the plumage, Zs would turn much of it to white. E replaces most of the reds and yellows with black and ZB reduces the amount of black by placing white bars across the feathers. A male with the genotype IIEEZB, SZB, s crossed with a red variety (iieeZb, sZl, s) should produce crossbreds whose adult plumage would have only slight flecks of black in a few of its feathers. Red color would be essentially absent. Since black would be entirely eliminated from the shanks, the green-shank defect would not occur. Only two generations have been obtained in the production of a desirable dominant-white
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Plymouth Rock. The following explains the method used to date and suggests the necessary future matings. In establishing the strain with the positive type of early feathering, dominantwhite from the Leghorn was carefully removed by the procedure outlined in chart 1. Some time between this stage and the production of the group 6 included in that chart, dominant white was introduced into the stock through the White Plymouth Rock parents. As a result during the test for color genes in connection with the studies on gray down and green shanks, 16 out of 35 original tested females proved to be heterozygous for dominant white (li) and one homozygous (II). The best seven hens for egg production were chosen for the beginning of a desirable dominant-white strain. It would be advantageous if a dominantwhite strain of the type described above could be identified and kept separate from other existing strains of White Plymouth Rocks. Any known hereditary "markers" that could be readily identified on a white bird would be a defect or disqualification for the White Plymouth Rock variety. Having the genes /,. E, ZB and Zs in the stock a method for identifying crosses between this and common strains of White Plymouth Rocks is possible. The majority of existing White Plymouth Rocks are white because they are cc (lack the precursor of color). By making the new variety homozygous for color (CC) plus the genes /, E, ZB and Zs, practically all of the progeny from intravariety crosses with this strain would have black spots in the down as well as some black in the adult plumage (Brandt, 1936). This is a standard disqualification and, as such, should greatly facilitate the problem of isolation to maintain the proper genotype in the dominant-white strain. In view of the above comments the fol-
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lowing lists the procedure upon which the dominant white strain is being developed: 1. Identify the Ii White Plymouth Rock females by those which produce white chicks when crossed with a colored breed. 2. Mate the Ii females with Barred Plymouth males and keep only the splashed-white* female chicks. 3. Splashed-white females again mated with Barred Plymouth Rock males and the splashed-white progeny reared. 4. Identify which of these splashed-white males and females are CCEE; that is, homozygous for the ability to place color in the feathers and to extend the melanic pigment over the surface of the feathers. This is accomplished by mating with tested White Plymouth Rocks which produced only parti-colored (ee) chicks when tested in crosses with Reds. The desired individuals in this test will produce SO percent splashed-white and SO percent black or barred chicks. Undesirable individuals will produce some parti-colored chicks and/or 75 percent splashed-white and white chicks. For this reason a large number of progeny are needed to accurately identify the correct birds. 5. Mate the white-splashed males and females proven to be CCEE and retain only those white progeny which are free from black pigment in the down. 6. Test the pure white progeny to be certain that they are homozygous (II). When mated together these will form a strain in which the genotypes will be IICCEEZB, SZB, S for males and IICCEEZB, SW for females. DISCUSSION OF STRAIN POSSIBILITIES
tween inbred strains of poultry show promise of increased efficiency (Maw, 1942). Should the dominant-white and gray-down strains be developed as inbreds, the day-old progeny from crosses between these strains would have a different color (white with black spots) from that of either parental variety. If it is agreed that progeny from crosses between inbred strains should be used for production and not reproduction, the color of progeny from these strain crosses would facilitate their identification. SUMMARY 1. In 1942 approximately 27 percent of the birds in flocks of the Oklahoma Poultry Improvement Association were White Plymouth Rocks. This is greater than any other variety. 2. Data and theories are presented to explain: (a) the production of a strain positive for early feathering. (b) the reason for some sexual dimorphism in certain gray-down patterns and the possibility of sight-sexing White Plymouth Rock chicks. (c) the elimination of red tints from the down and in the adult plumage. (d) a cause for the occurrence of green- or willow-colored shanks and a simple method for eliminating this defect. (e) the production of a dominant-white strain to produce crossbreds with predominantely white plumage.
The early-feathering, dominant-white strain completely eliminates black in the down as well as adult plumage. Should the gray down prove useful in identifying sex at hatching, it would be necessary to maintain a gray-down, recessive-white strain as a separate variety. This has the disadvantage associated with the maintenance of two strains within a variety. The maintenance of two strains, however, may be an advantage. Crosses be-
3. Desirable strains should include the genes /, C, E, ZB, s, k; or, for sight sexing possibilities, i, c, E, ZB, s, le. 4. The advantage of maintaining two inbred strains of White Plymouth Rocks, dominant-white and gray-down, which would produce color-marked crosses is briefly discussed.
* The term splashed-white refers to those chicks or adults which are predominately white with small spots or flecks of black.
American Poultry Association, 1940. American standard of perfection. Amer. Poultry Assn., Davenport, Iowa.
REFERENCES
NEWS AND NOTES Brandt, A. E., 1936. A note on dominant white and crest in poultry. J. Hered. 27 :79-82. Danforth, C. H., 1933. The reaction of dominant white with yellow and black in the fowl. J. Hered. 24:301-307. Darrow, Merrit I., 1941. Relation of day-old chick wing feather development to feathering at the broiler age. (Abstract.) Poultry Sci. 20:458. , 1942. A study of modified expressions of sex-linked early feathering. (Abstract.) Poultry Sci. 21:468. Dunn, L. C , 1925. The genetic relation of some shank colors of the domestic fowl. (Abstract.) Anat. Rec. 31:343-344. Jaap, R. George, 1941. Auto-sex linkage in the domestic fowl. II. Auto-sexing accuracy with the gene for barred feathers in red to black down-color phenotypes. Poultry Sci. 20:317321. Jerome, Fred N., 1939. Auto-sex linkage in the
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Barred Plymouth Rock. Poultry Sci. 18:437440. Knox, C. W., 1935. The inheritance of shank color in chickens. Genetics 20:529-544. Maw, A. J. G., 1942. Crosses between inbred lines of the domestic fowl. Poultry Sci. 21:548-553. Poultry Division of the Canadian Experimental Farms' Service, 1941. Sight sexing Barred Rock baby chicks. Dominion Experimental Farm Bui., Ottawa. Punnett, R. C , 1923. Heredity in poultry. The Macmillan Company, London. Radi, M. H., and D. C. Warren, 1938. Studies on the physiology and inheritance of feathering in the growing chick. J. Agr. Res. 56:679-705. Warren, D. C , 1925. Inheritance of rate of feathering in poultry. J. Hered. 16:13-18. , 1930. Crossbred poultry. Kansas Agr. Exp. Sta. Bui. 252.
News and Notes The July issue of POULTRY SCIENCE will be bound in two parts. Part I will contain the usual papers and research notes, whereas Part II will consist of the alphabetical index of the first 20 volumes of POULTRY SCIENCE. The two parts will be mailed together, although they will be bound separately. In this way any member or subscriber who desires to file the Index for ready reference may do so. Others who may desire to incorporate it with the regular issues may either file or bind it in its regular place. Garry A. Miles (B.S., University of Connecticut, 1926), assistant extension poultryman and assistant garden specialist at the
University of Connecticut, has resigned effective March IS to take a position as extension poultryman at the University of Delaware where he will be responsible for poultry extension work and poultry club work. The position will be filled by Owen S. Trask (B.S., Massachusetts Agricultural College, 1936), who is now county club leader in Tolland County, Connecticut. Mr. Trask will take up his new work July 1, 1943. Dr. W. C. Tully is now associated with Lederle Laboratories, Pearl River, New York, as feed specialist. He will work with vitamin concentrates and other products for the feed trade.