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Thyroxine Secretion Rate and Growth In the White Pekin Duck
Thyroxine Secretion Rate and Growth In the White Pekin Duck EDMUND HOFFMANN
Department of Poultry Husbandry, The University of Georgia, Athens, Georgia (Received for publication July 29,1949)
HE phenomenally rapid rate of growth of the White Pekin duck is well known. Reported average weights at nine weeks of age are 4.85 and 5.77 pounds (Horton, 1928; Elford, 1925, 1927) as compared to 2.00 and 2.60 pounds (Hoffmann, 1946; Klein, 1949) for relatively rapid growing chickens. The marked difference in growth rate between the species is also reflected in the maximum size attained. A White Pekin drake attained the remarkable weight of 10.5 pounds at 68 days of age (Hunter and Scholes, 1943), as compared to a New Hampshire cockerel that weighed 5.12 pounds at 77 days (Jull, 1949). Recent work with chickens has established a relationship between rate of growth and thyroxine secretion. Fast growing strains have an inherently higher thyroxine secretion rate than slower growing strains (Glazener and Shaffner, 1949). The question naturally arises whether differences in growth rate between species can also be partially accounted for by differences in rate of thyroxine secretion. White Pekin ducks seem to be the ideal animals on which to test this hypothesis because they grow much more rapidly than any strain of chickens. Therefore, in the absence of any data for ducks, an experiment was undertaken to determine their thyroxine secretion rate. PROCEDURE
White Pekin ducklings hatched March 1 were divided, according to body weight
when one week old, into six groups of eight ducklings each. No attempt was made to obtain equal distribution of the sexes. The birds were kept in a conventional 4-deck starting battery located in a basement room without direct sunlight. Lights were kept on continuously. It is difficult to estimate the effective temperature of the birds' environment because they had free access to a "back-warmer" type hover maintained at a temperature of of about 95° F while room temperature varied within a few degrees of 80° F. Thyroxine secretion rate was determined by the method developed by Dempsey and Astwood (1943) which has been applied to chickens by Mixner, Reineke and Turner (1944) and others. Thiouracil was added to a conventional chick starting diet at a level of 0.1 percent as a goiterogen. Crystalline thyroxine1 was dissolved in an alkaline solution so that each 0.25 cc. contained an individual daily dose. This was injected subcutaneously for fourteen days at the graded dosage levels shown in Table 1. Fresh solutions were made up bi-weekly. At the end of the experiment, body weight was recorded, the ducklings were killed by decapitation, and the thyroid glands dissected out and their weight estimated to the nearest 0.1 mg. on a Roller-Smith balance. Average relative 1 The d, 1-thyroxine was kindly supplied by Dr. Erwin Schwenk, Schering Corporation, Bloomfield, New Jersey, and the thiouracil by Dr. Mark Welsh, Lederle Laboratories, Pearl River, New York.
109
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T
110
EDMUND HOFFMANN
TABLE 1.—Thyroxine secretion rate of White Pekin ducklings during period from one to three weeks of age Avg. thyroid wt. (mgs.)
i nyroia wt./100 gm. body weight
Treatment
No. of ducklings
Body wt. (gms.)
Normal controls 0.1 percent thiouracil no thyroxine 0.1 percent thiouracil + 5 gamma d, 1 thyroxine 0.1 percent thiouracil + 10 gamma d, 1 thyroxine 0.1 percent thiouracil + 2 0 gamma d, 1 thyroxine 0.1 percent thiouracil + 3 0 gamma d, 1 thyroxine
7
520.8±25.3
53.8+ 5.7
8
437.7 + 22.6
451.7 + 46.3
103.5+ 9.2
8
474.3±23.6
370.7 + 52.4
76.9 + 26.4
8
478.9+16.5
196.3±20.6
4 1 . 2 + 3.7
7
494.8 + 26.5
2 7 . 1 ± 5.5
5.8+
1.1
8
514.7±14.0
19.9+ 4.2
3.9+
.4
10.4+
1.0
XlOO
THYKOIO ENLARGEMENT 'RESULTING FKOM FEEDING THIOUKACIL TO DOCKS.
60
§
40
1
THYROID E.NLAOGLMENT ' RESULTING PttOM FECOINO THIOURACIL TO CHICKS
-IS.TS u. PEE 6 I E O PEK CAY "KOBMAt DUCK THYCOID a . I /A. F E U » I ( E O ct-K.
DAY
w^^_j£mcKjrHYeoi»2_
s
io
to
d , JL - THYROXINE., MJCEOCeAMS, DAILY FIG. 1. Method of plotting data to determine thyroxine secretion rate in terms of d, 1-thyroxine per duck per day.
it
30
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120
THYROXINE SECRETION RATE AND GROWTH IN DUCKS
thyroid weight was then plotted against the amount of d, 1-thyroxine injected daily to permit an estimation of the thyroxine secreted per bird per day. RESULTS
111
The data are presented in Table 1 and Fig. 1. It will be noted that Fig. 1 includes a curve plotted from the data of Schultze and Turner (1945) for White Plymouth Rock cockerels assayed in the period from 4-7 weeks of age. It was necessary to use data obtained on older chickens in order to minimize difference in average body weight. This is an important point since thyroxine secretion rate is more closely correlated with body weight than with age during the period of rapid growth (Schultze and Turner, loc. cit.) The data indicate that under the conditions of this experiment the daily thyroxine secretion rate of White Pekin ducklings, from one to three weeks of age, was approximately 18.75 gamma per bird per day or 3.8 gamma per 100 gm. of body weight. Since Schultze and Turner's White Plymouth Rocks of comparable DISCUSSION weight secreted approximately 8.1 gamma per bird per day, or 1.98 gamma per 100 The marked enlargement of duck thygm. of body weight, it would seem that roid, which accompanies thiouracil-feedthe duck has an apparent thyroxine secre- ing, suggests that either the duck may tion rate about twice that of the chicken. have a higher thyrotropin secretion rate The number of individuals observed than the chicken, or that the duck thyroid was insufficient to permit a definitive com- may be more sensitive to thyrotropic parison between the thyroid weights of stimulation. Published reports too numerducks and chickens per unit of body ous to cite here suggest that thyrotropin weight. However, most of the published is the major factor involved in thyroid material assigns an average weight of 5 to enlargement and, in one case at least, this 8 mg. per 100 gm. body weight for the mechanism has been shown to exist in the thyroid of 3 week old chickens as com- duck (Schockaert, 1932). On the other pared to the 10.4 mg. reported here for hand, strain differences in thyroid response of chicks to thyrotropin has been the duck. Of more particular interest is the degree noted (Bates and Riddle, 1941). But reof compensatory thyroid enlargement ob- gardless of the mechanism involved, the tained in response to the inhibition of thy- more marked thyroid enlargement ob-
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 2, 2015
roxine formation by the feeding of thiouracil. Thyroid weights of the treated ducks were 10 times that of the controls, (103 and 10.4 mg., respectively). According to published reports and results obtained in this laboratory, thyroid weights of thiouracil-treated chickens range between 3 to 5 times heavier than "normal." (It is of interest that thiouracil-treatment of turkeys from 6 to 9 weeks of age resulted in a six-fold compensatory increase in thyroid weight. Blakely and Anderson, 1949.) Rate of gain was greatly reduced by feeding thiouracil to ducks for two weeks. This difference is statistically significant. However, as will be seen in Table 1, thyroxine therapy repaired this retardation in rough proportion to the amount of thyroxine administered. This in itself is evidence for the growth promoting action of thyroxine in the duck. In contrast, it has not been possible to obtain significant reductions in the growth rate of chickens fed thiouracil unless the treatment is continued for more than two weeks. (Schultze and Turner, 1943; others.)
112
EDMUND HOFFMANN
Both the apparent higher thyrotropin secretion rate and the drastic reduction in growth rate following thyroid inhibition noted herein are circumstantial evidence for a relatively high thyroxine secretion rate in the duck. This does not in itself mean that a high thyroxine secretion rate is associated with rapid growth, but an impressive array of confirmatory evidence (although admittedly also circumstantial) can be assembled from the literature. It has been shown, from histological studies, that the thyroidal activity of the salmon is greatest during periods of rapid growth (Hoar, 1939). Biological assay of apparent thyroxine secret:on rates demonstrate that fast growing strains of chickens have a higher secretion rate than slow growing strains (Glazener and Shaffner, 1949). There is also evidence that an increased thyroxine secretion rate may be a factor contributing to the development of hybrid vigor in chicks (Mixner and Upp, 1947). All this evidence fits in very well with the data presented in this communication; ducks, a rapid growing species, have a thyroxine secretion rate of 3.8 gamma
per 100 gms. of body weight as compared to 1.98 gamma for the chicken, a relatively slower growing species. However, the question might be raised as to which is cause and which is effect. Does thyroxine actually stimulate growth or does rapid growth, in itself, result in a high thyroxine output? It is possible that during rapid growth utilization of thyroxine is accelerated to the extent that it disappears from the circulation fast enough to act as a stimulus for its own replacement through failure to reduce the secretion of thyrotropin. Examination of the growth pattern of the duck suggests an interesting speculation on the "maturation effect" of thyroxine. It is well known that exogenous thyroxine accelerates skeletal aging in growing animals (Noback, Barnett and Kupperman, 1949; Silverberg and Silverberg, 1942). Conversely, there is abundant evidence that thiouracil-feeding or thyroidectomy retards epiphyseal fusion. Thus, thyroxine has the paradoxical effects of stimulating growth and, by accelerating maturation rate, eventually inhibiting growth. If it is assumed that a high level of endogenous thyroxine has the same effect as exogenous thyroxine, then the higher thyroxine secretion rate of the duck might account for the difference in growth pattern between ducks and chickens. For instance, Milby and Henderson (1937) reported that ducklings grow approximately twice as fast as chicks during the first four weeks following hatching, but their growth curve tapers off markedly at about eight weeks of age. The same point in the curve for chickens occurs at 12 weeks of age. This pattern is also demonstrable in the chemical composition of ducks (Svetozarova and Shtraikl, 1939). As one might expect, early maturation of the duck is reflected in a difference
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 2, 2015
tained in these ducks is circumstantial evidence in support of an intrinsically higher thyroxine secretion rate. The severe reduction in rate of growth of ducks following only two weeks treatment with thiouracil, together with the progressive improvement in growth rate following thyroxine therapy, is perhaps the strongest evidence for a relationship between a high thyroxine secretion rate and rapid growth. An alternate hypothesis, that the thiouracil was in itself toxic, seems untenable since Mixner, Reineke and Turner (1944) reported that amounts up to 0.6 percent thiouracil in the ration were essentially non-toxic and Juhn (1946) fed individual birds 0.5 percent thiouracil for two years with no ill effect.
THYROXINE SECRETION RATE AND GROWTH IN DUCKS
SUMMARY
The thyroxine secretion rate of White Pekin ducklings for the period from one to three weeks of age was shown to be 18.7 gamma per bird per day or 3.8 gamma per 100 gms. of body weight. This is approximately double the thyroxine secretion rate of chickens of comparable weight. Circumstantial evidence for a relationship between thyroxine secretion rate and early rapid growth as well as early maturation is reviewed. It is suggested that the growth pattern of the duck is further evidence of an intrinsically high thyroxine secretion rate. REFERENCES Bates, R. W., O. Riddle, and E. L. Lahr, 1941. A strain difference in responsiveness of chick thyroids to thyrotropin and a step-wise increase during three years in thyroid weights of Carneau pigeons. Endocrinoloy 29: 492-497. Blakely, R. M. and R. W. Anderson, 1949: The influence of thiouracil on growth, feed consumption and thyroid weight of turkey broilers. Poultry Sci. 28:185-188. Connally, Howard and R. George Jaap, 1941. Rela-
tive growth of the shank (tarso-metatarsus) in domestic ducks. Proc. Okla. Academy of Science 21: 15-16. Dempsey, E. W., and E. B. Astwood, 1943. Determination of the rate of thyroid hormone secretion at various environmental temperatures. Endocrinology 32: 509-518. Elford, F. C , 1926. Duck feeding experiments. Report of the Dominion Poultry Husbandman (1925): 49-52. Elford, F . C , 1928. Duck feeding experiments. Report of the Dominion Poultry Husbandman (1927): 38-43. Glazener, E. and C. S. Shaffner, 1949. Thyroid activity as related to strain differences in growing chickens. Poultry Sci. 28: 834-849. Hoar, W. S., 1939. The thyroid gland of the Atlantic salmon. J. of Morph. 65: 257-296. Hoffmann, Edmund, 1946. Standards of broiler production. Successful Broiler Growing. Watt Publishing Co., Mount Morris, 111. Horton, D. H., 1928. The growth of White Pekin ducklings. Poultry Sci. 7: 163-167. Hunter, J. M. and J. C. Scholes, 1943. Profitable Duck Management. The Beacon Milling Co., Cayuga, N . Y. Juhn, Mary, 1946. Spur growth in thiouracil treated fowl. Anat. Record 96: 589. Jull, M. A., 1949. Flock improvement. Hatchery and Feed 23: 42-43. Klein, G. T., 1949. Growth rate and feed consumption on the Connecticut broiler ration. Featheredfax Jan. 25,1949. Kroger, Marvin and C. W. Turner, 1943. The effect of mild hyperthyroidism on growing animals. University of Mo. Agr. Exp. Sta. Res. Bull. 377. Lerner, I. M., 1939. Predictibility of body weight from live shank measurements. Poultry Sci. 18: 378-380. Milby, T. T. and E. W. Henderson, 1937. The comparative growth rates of turkeys, ducks, geese, and pheasants. Poultry Sci. 16: 155-165. Mixner, J. P., E. P. Reineke and C. W. Turner, 1944. Effect of thiouracil and thiourea on the thyroid gland of the chick. Endocrinology 34:168-174. Mixner, J. P., and C. W. Upp, 1947. Increased rate of thyroxine secretion by hybrid chicks as a factor in heterosis. Poultry Sci. 26: 389-395. Noback, C. R., J. C. Barnett and B. S. Kupperman, 1949. The time of appearance of ossification centers in the rat as influenced by injections of thyroxine, thiouracil, estradiol and testosterone propionate. Anat. Record 103:49-64. Schockaert, J., 1932. Enlargement and hyperplasia of the thyroids in young ducks from the injection
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in the growth curve of the tarsometatarsus. Connally and Jaap (1941) have observed that "shank length is probably approaching its upper asymptote in growth after four weeks in females and five weeks in males," while it would appear from Lerner's data (1939) that this occurs in the chicken some time after 16 weeks of age. The data of Kroger and Turner (1943) illustrate these two effects of thyroxine on growth. Injection of crystalline thyroxine into mice increased the rate of early growth but mature size was not modified as a result of a concomitant increase in maturation rate. In the present instance, early rapid growth of the duck is associated with early incipient maturation, both of which are consistent with a high thyroxine secretion rate.
113
114
BOOK REVIEWS
of anterior pituitary. Amer. J. Anat. 49:379-409. Schultze, A. B. and C. W. Turner, 1945. The determination of the rate of thyroxine secretion by certain domestic animals. University of Mo. Ag. Exp. Sta. Res. Bull. 392. Silberberg, M. and R. Silberberg, 1943. Influence of
the endocrine glands on growth and aging of the skeleton. Arch. Path. 36: 512-534. Svetozarova, E. and G. Shtraikh, 1939. Changes in the chemical composition of birds during growth. Jour. Physiology (U.S.S.R.) 27: 610-615. Biological Abstracts 16:14373 (1942).
Book Reviews (Continued from page 108)
Lr, C. C , An Introduction to Population Genetics, National Peking University, Peiping, China, 1948, 321 pp. MATHER, K.., Biometrical Genetics, Dover Publications. 1949, ix+162 pp. WRIGHT, S., Systems of Mating and Other Papers. Offset reproduction by graduate students in Animal Breeding at Iowa State College, 1949. Genetics 6: 111-178 (1921); 16: 97-159 (1931); J. Agr. Res. 20: 557-585 (1921); Ann. Math. Stat. 5: 161-215 (1934). The subject of population genetics has in recent years assumed a major importance in investigations on animal breeding. Though none of the above publications deal directly with poultry, all three will make important additions to the library of any investigator in the field of poultry breeding.
Professor Li, trained in plant breeding at Cornell and in mathematical statistics at Columbia, provides an introduction to the principles of population genetics. The discussion is confined to situations involving one or two loci, and thus stops short of dealing with the basis of inheritance of most economically important traits, yet the clarity of the exposition, its development at a level of minimal prerequisite mathematical background compatible with the nature of the subject, the numerous examples and problems, all contribute towards making the book a most valuable vehicle of preparation for further study of population genetics. Particularly important in this connection is the lucid digest of the technique of path coefficients and of other methods developed by Sewall Wright. It is understood that arrangements are being made to make the book available for distribution in this country. The primary orientation of Professor Mather's book is on plant material, but at least one section of it is directly applicable to animal data. For the purpose of the present notice it may suffice to say that those already working in the field of population genetics, whether or not they agree with all of it, will find the book to be extremely stimulating and useful in many ways. Complete novices, may on the other hand, prefer to postpone its
(Continued, on page 121)
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decidedly enhance the value of the book. Another useful feature of the book are the many historical references which serve to provide a background for the reader. The author has written in an interesting and at times informal style thus putting much more of his personality than is customary into the book. Altogether this is a book which will be useful to everyone interested in poultry breeding and genetics whether as geneticist, teacher, student, or breeder. It deserves to be widely read and used.
Department of Poultry Husbandry, The University of Georgia, Athens, Georgia (Received for publication July 29,1949)
HE phenomenally rapid rate of growth of the White Pekin duck is well known. Reported average weights at nine weeks of age are 4.85 and 5.77 pounds (Horton, 1928; Elford, 1925, 1927) as compared to 2.00 and 2.60 pounds (Hoffmann, 1946; Klein, 1949) for relatively rapid growing chickens. The marked difference in growth rate between the species is also reflected in the maximum size attained. A White Pekin drake attained the remarkable weight of 10.5 pounds at 68 days of age (Hunter and Scholes, 1943), as compared to a New Hampshire cockerel that weighed 5.12 pounds at 77 days (Jull, 1949). Recent work with chickens has established a relationship between rate of growth and thyroxine secretion. Fast growing strains have an inherently higher thyroxine secretion rate than slower growing strains (Glazener and Shaffner, 1949). The question naturally arises whether differences in growth rate between species can also be partially accounted for by differences in rate of thyroxine secretion. White Pekin ducks seem to be the ideal animals on which to test this hypothesis because they grow much more rapidly than any strain of chickens. Therefore, in the absence of any data for ducks, an experiment was undertaken to determine their thyroxine secretion rate. PROCEDURE
White Pekin ducklings hatched March 1 were divided, according to body weight
when one week old, into six groups of eight ducklings each. No attempt was made to obtain equal distribution of the sexes. The birds were kept in a conventional 4-deck starting battery located in a basement room without direct sunlight. Lights were kept on continuously. It is difficult to estimate the effective temperature of the birds' environment because they had free access to a "back-warmer" type hover maintained at a temperature of of about 95° F while room temperature varied within a few degrees of 80° F. Thyroxine secretion rate was determined by the method developed by Dempsey and Astwood (1943) which has been applied to chickens by Mixner, Reineke and Turner (1944) and others. Thiouracil was added to a conventional chick starting diet at a level of 0.1 percent as a goiterogen. Crystalline thyroxine1 was dissolved in an alkaline solution so that each 0.25 cc. contained an individual daily dose. This was injected subcutaneously for fourteen days at the graded dosage levels shown in Table 1. Fresh solutions were made up bi-weekly. At the end of the experiment, body weight was recorded, the ducklings were killed by decapitation, and the thyroid glands dissected out and their weight estimated to the nearest 0.1 mg. on a Roller-Smith balance. Average relative 1 The d, 1-thyroxine was kindly supplied by Dr. Erwin Schwenk, Schering Corporation, Bloomfield, New Jersey, and the thiouracil by Dr. Mark Welsh, Lederle Laboratories, Pearl River, New York.
109
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T
110
EDMUND HOFFMANN
TABLE 1.—Thyroxine secretion rate of White Pekin ducklings during period from one to three weeks of age Avg. thyroid wt. (mgs.)
i nyroia wt./100 gm. body weight
Treatment
No. of ducklings
Body wt. (gms.)
Normal controls 0.1 percent thiouracil no thyroxine 0.1 percent thiouracil + 5 gamma d, 1 thyroxine 0.1 percent thiouracil + 10 gamma d, 1 thyroxine 0.1 percent thiouracil + 2 0 gamma d, 1 thyroxine 0.1 percent thiouracil + 3 0 gamma d, 1 thyroxine
7
520.8±25.3
53.8+ 5.7
8
437.7 + 22.6
451.7 + 46.3
103.5+ 9.2
8
474.3±23.6
370.7 + 52.4
76.9 + 26.4
8
478.9+16.5
196.3±20.6
4 1 . 2 + 3.7
7
494.8 + 26.5
2 7 . 1 ± 5.5
5.8+
1.1
8
514.7±14.0
19.9+ 4.2
3.9+
.4
10.4+
1.0
XlOO
THYKOIO ENLARGEMENT 'RESULTING FKOM FEEDING THIOUKACIL TO DOCKS.
60
§
40
1
THYROID E.NLAOGLMENT ' RESULTING PttOM FECOINO THIOURACIL TO CHICKS
-IS.TS u. PEE 6 I E O PEK CAY "KOBMAt DUCK THYCOID a . I /A. F E U » I ( E O ct-K.
DAY
w^^_j£mcKjrHYeoi»2_
s
io
to
d , JL - THYROXINE., MJCEOCeAMS, DAILY FIG. 1. Method of plotting data to determine thyroxine secretion rate in terms of d, 1-thyroxine per duck per day.
it
30
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 2, 2015
120
THYROXINE SECRETION RATE AND GROWTH IN DUCKS
thyroid weight was then plotted against the amount of d, 1-thyroxine injected daily to permit an estimation of the thyroxine secreted per bird per day. RESULTS
111
The data are presented in Table 1 and Fig. 1. It will be noted that Fig. 1 includes a curve plotted from the data of Schultze and Turner (1945) for White Plymouth Rock cockerels assayed in the period from 4-7 weeks of age. It was necessary to use data obtained on older chickens in order to minimize difference in average body weight. This is an important point since thyroxine secretion rate is more closely correlated with body weight than with age during the period of rapid growth (Schultze and Turner, loc. cit.) The data indicate that under the conditions of this experiment the daily thyroxine secretion rate of White Pekin ducklings, from one to three weeks of age, was approximately 18.75 gamma per bird per day or 3.8 gamma per 100 gm. of body weight. Since Schultze and Turner's White Plymouth Rocks of comparable DISCUSSION weight secreted approximately 8.1 gamma per bird per day, or 1.98 gamma per 100 The marked enlargement of duck thygm. of body weight, it would seem that roid, which accompanies thiouracil-feedthe duck has an apparent thyroxine secre- ing, suggests that either the duck may tion rate about twice that of the chicken. have a higher thyrotropin secretion rate The number of individuals observed than the chicken, or that the duck thyroid was insufficient to permit a definitive com- may be more sensitive to thyrotropic parison between the thyroid weights of stimulation. Published reports too numerducks and chickens per unit of body ous to cite here suggest that thyrotropin weight. However, most of the published is the major factor involved in thyroid material assigns an average weight of 5 to enlargement and, in one case at least, this 8 mg. per 100 gm. body weight for the mechanism has been shown to exist in the thyroid of 3 week old chickens as com- duck (Schockaert, 1932). On the other pared to the 10.4 mg. reported here for hand, strain differences in thyroid response of chicks to thyrotropin has been the duck. Of more particular interest is the degree noted (Bates and Riddle, 1941). But reof compensatory thyroid enlargement ob- gardless of the mechanism involved, the tained in response to the inhibition of thy- more marked thyroid enlargement ob-
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 2, 2015
roxine formation by the feeding of thiouracil. Thyroid weights of the treated ducks were 10 times that of the controls, (103 and 10.4 mg., respectively). According to published reports and results obtained in this laboratory, thyroid weights of thiouracil-treated chickens range between 3 to 5 times heavier than "normal." (It is of interest that thiouracil-treatment of turkeys from 6 to 9 weeks of age resulted in a six-fold compensatory increase in thyroid weight. Blakely and Anderson, 1949.) Rate of gain was greatly reduced by feeding thiouracil to ducks for two weeks. This difference is statistically significant. However, as will be seen in Table 1, thyroxine therapy repaired this retardation in rough proportion to the amount of thyroxine administered. This in itself is evidence for the growth promoting action of thyroxine in the duck. In contrast, it has not been possible to obtain significant reductions in the growth rate of chickens fed thiouracil unless the treatment is continued for more than two weeks. (Schultze and Turner, 1943; others.)
112
EDMUND HOFFMANN
Both the apparent higher thyrotropin secretion rate and the drastic reduction in growth rate following thyroid inhibition noted herein are circumstantial evidence for a relatively high thyroxine secretion rate in the duck. This does not in itself mean that a high thyroxine secretion rate is associated with rapid growth, but an impressive array of confirmatory evidence (although admittedly also circumstantial) can be assembled from the literature. It has been shown, from histological studies, that the thyroidal activity of the salmon is greatest during periods of rapid growth (Hoar, 1939). Biological assay of apparent thyroxine secret:on rates demonstrate that fast growing strains of chickens have a higher secretion rate than slow growing strains (Glazener and Shaffner, 1949). There is also evidence that an increased thyroxine secretion rate may be a factor contributing to the development of hybrid vigor in chicks (Mixner and Upp, 1947). All this evidence fits in very well with the data presented in this communication; ducks, a rapid growing species, have a thyroxine secretion rate of 3.8 gamma
per 100 gms. of body weight as compared to 1.98 gamma for the chicken, a relatively slower growing species. However, the question might be raised as to which is cause and which is effect. Does thyroxine actually stimulate growth or does rapid growth, in itself, result in a high thyroxine output? It is possible that during rapid growth utilization of thyroxine is accelerated to the extent that it disappears from the circulation fast enough to act as a stimulus for its own replacement through failure to reduce the secretion of thyrotropin. Examination of the growth pattern of the duck suggests an interesting speculation on the "maturation effect" of thyroxine. It is well known that exogenous thyroxine accelerates skeletal aging in growing animals (Noback, Barnett and Kupperman, 1949; Silverberg and Silverberg, 1942). Conversely, there is abundant evidence that thiouracil-feeding or thyroidectomy retards epiphyseal fusion. Thus, thyroxine has the paradoxical effects of stimulating growth and, by accelerating maturation rate, eventually inhibiting growth. If it is assumed that a high level of endogenous thyroxine has the same effect as exogenous thyroxine, then the higher thyroxine secretion rate of the duck might account for the difference in growth pattern between ducks and chickens. For instance, Milby and Henderson (1937) reported that ducklings grow approximately twice as fast as chicks during the first four weeks following hatching, but their growth curve tapers off markedly at about eight weeks of age. The same point in the curve for chickens occurs at 12 weeks of age. This pattern is also demonstrable in the chemical composition of ducks (Svetozarova and Shtraikl, 1939). As one might expect, early maturation of the duck is reflected in a difference
Downloaded from http://ps.oxfordjournals.org/ at D H Hill Library - Acquis S on May 2, 2015
tained in these ducks is circumstantial evidence in support of an intrinsically higher thyroxine secretion rate. The severe reduction in rate of growth of ducks following only two weeks treatment with thiouracil, together with the progressive improvement in growth rate following thyroxine therapy, is perhaps the strongest evidence for a relationship between a high thyroxine secretion rate and rapid growth. An alternate hypothesis, that the thiouracil was in itself toxic, seems untenable since Mixner, Reineke and Turner (1944) reported that amounts up to 0.6 percent thiouracil in the ration were essentially non-toxic and Juhn (1946) fed individual birds 0.5 percent thiouracil for two years with no ill effect.
THYROXINE SECRETION RATE AND GROWTH IN DUCKS
SUMMARY
The thyroxine secretion rate of White Pekin ducklings for the period from one to three weeks of age was shown to be 18.7 gamma per bird per day or 3.8 gamma per 100 gms. of body weight. This is approximately double the thyroxine secretion rate of chickens of comparable weight. Circumstantial evidence for a relationship between thyroxine secretion rate and early rapid growth as well as early maturation is reviewed. It is suggested that the growth pattern of the duck is further evidence of an intrinsically high thyroxine secretion rate. REFERENCES Bates, R. W., O. Riddle, and E. L. Lahr, 1941. A strain difference in responsiveness of chick thyroids to thyrotropin and a step-wise increase during three years in thyroid weights of Carneau pigeons. Endocrinoloy 29: 492-497. Blakely, R. M. and R. W. Anderson, 1949: The influence of thiouracil on growth, feed consumption and thyroid weight of turkey broilers. Poultry Sci. 28:185-188. Connally, Howard and R. George Jaap, 1941. Rela-
tive growth of the shank (tarso-metatarsus) in domestic ducks. Proc. Okla. Academy of Science 21: 15-16. Dempsey, E. W., and E. B. Astwood, 1943. Determination of the rate of thyroid hormone secretion at various environmental temperatures. Endocrinology 32: 509-518. Elford, F. C , 1926. Duck feeding experiments. Report of the Dominion Poultry Husbandman (1925): 49-52. Elford, F . C , 1928. Duck feeding experiments. Report of the Dominion Poultry Husbandman (1927): 38-43. Glazener, E. and C. S. Shaffner, 1949. Thyroid activity as related to strain differences in growing chickens. Poultry Sci. 28: 834-849. Hoar, W. S., 1939. The thyroid gland of the Atlantic salmon. J. of Morph. 65: 257-296. Hoffmann, Edmund, 1946. Standards of broiler production. Successful Broiler Growing. Watt Publishing Co., Mount Morris, 111. Horton, D. H., 1928. The growth of White Pekin ducklings. Poultry Sci. 7: 163-167. Hunter, J. M. and J. C. Scholes, 1943. Profitable Duck Management. The Beacon Milling Co., Cayuga, N . Y. Juhn, Mary, 1946. Spur growth in thiouracil treated fowl. Anat. Record 96: 589. Jull, M. A., 1949. Flock improvement. Hatchery and Feed 23: 42-43. Klein, G. T., 1949. Growth rate and feed consumption on the Connecticut broiler ration. Featheredfax Jan. 25,1949. Kroger, Marvin and C. W. Turner, 1943. The effect of mild hyperthyroidism on growing animals. University of Mo. Agr. Exp. Sta. Res. Bull. 377. Lerner, I. M., 1939. Predictibility of body weight from live shank measurements. Poultry Sci. 18: 378-380. Milby, T. T. and E. W. Henderson, 1937. The comparative growth rates of turkeys, ducks, geese, and pheasants. Poultry Sci. 16: 155-165. Mixner, J. P., E. P. Reineke and C. W. Turner, 1944. Effect of thiouracil and thiourea on the thyroid gland of the chick. Endocrinology 34:168-174. Mixner, J. P., and C. W. Upp, 1947. Increased rate of thyroxine secretion by hybrid chicks as a factor in heterosis. Poultry Sci. 26: 389-395. Noback, C. R., J. C. Barnett and B. S. Kupperman, 1949. The time of appearance of ossification centers in the rat as influenced by injections of thyroxine, thiouracil, estradiol and testosterone propionate. Anat. Record 103:49-64. Schockaert, J., 1932. Enlargement and hyperplasia of the thyroids in young ducks from the injection
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in the growth curve of the tarsometatarsus. Connally and Jaap (1941) have observed that "shank length is probably approaching its upper asymptote in growth after four weeks in females and five weeks in males," while it would appear from Lerner's data (1939) that this occurs in the chicken some time after 16 weeks of age. The data of Kroger and Turner (1943) illustrate these two effects of thyroxine on growth. Injection of crystalline thyroxine into mice increased the rate of early growth but mature size was not modified as a result of a concomitant increase in maturation rate. In the present instance, early rapid growth of the duck is associated with early incipient maturation, both of which are consistent with a high thyroxine secretion rate.
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of anterior pituitary. Amer. J. Anat. 49:379-409. Schultze, A. B. and C. W. Turner, 1945. The determination of the rate of thyroxine secretion by certain domestic animals. University of Mo. Ag. Exp. Sta. Res. Bull. 392. Silberberg, M. and R. Silberberg, 1943. Influence of
the endocrine glands on growth and aging of the skeleton. Arch. Path. 36: 512-534. Svetozarova, E. and G. Shtraikh, 1939. Changes in the chemical composition of birds during growth. Jour. Physiology (U.S.S.R.) 27: 610-615. Biological Abstracts 16:14373 (1942).
Book Reviews (Continued from page 108)
Lr, C. C , An Introduction to Population Genetics, National Peking University, Peiping, China, 1948, 321 pp. MATHER, K.., Biometrical Genetics, Dover Publications. 1949, ix+162 pp. WRIGHT, S., Systems of Mating and Other Papers. Offset reproduction by graduate students in Animal Breeding at Iowa State College, 1949. Genetics 6: 111-178 (1921); 16: 97-159 (1931); J. Agr. Res. 20: 557-585 (1921); Ann. Math. Stat. 5: 161-215 (1934). The subject of population genetics has in recent years assumed a major importance in investigations on animal breeding. Though none of the above publications deal directly with poultry, all three will make important additions to the library of any investigator in the field of poultry breeding.
Professor Li, trained in plant breeding at Cornell and in mathematical statistics at Columbia, provides an introduction to the principles of population genetics. The discussion is confined to situations involving one or two loci, and thus stops short of dealing with the basis of inheritance of most economically important traits, yet the clarity of the exposition, its development at a level of minimal prerequisite mathematical background compatible with the nature of the subject, the numerous examples and problems, all contribute towards making the book a most valuable vehicle of preparation for further study of population genetics. Particularly important in this connection is the lucid digest of the technique of path coefficients and of other methods developed by Sewall Wright. It is understood that arrangements are being made to make the book available for distribution in this country. The primary orientation of Professor Mather's book is on plant material, but at least one section of it is directly applicable to animal data. For the purpose of the present notice it may suffice to say that those already working in the field of population genetics, whether or not they agree with all of it, will find the book to be extremely stimulating and useful in many ways. Complete novices, may on the other hand, prefer to postpone its
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decidedly enhance the value of the book. Another useful feature of the book are the many historical references which serve to provide a background for the reader. The author has written in an interesting and at times informal style thus putting much more of his personality than is customary into the book. Altogether this is a book which will be useful to everyone interested in poultry breeding and genetics whether as geneticist, teacher, student, or breeder. It deserves to be widely read and used.