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Some Effects of Selecting for High and Low Thyroidal Response to Thiouracil Feeding in New Hampshire Chickens1,2
Some Effects of Selecting for High and Low Thyroidal Response to Thiouracil Feeding in New Hampshire Chickens1,2 WILLIAM E. SHAKLEE 3 AND C. S. SHAFFNER Poidlry Department, University of Maryland, College Park (Received for publication September 10, 1954)
HE fact that the activity of the thyroid glands of all adult vertebrates serves as a powerful metabolic regulator is well established, yet the extent to which altered thyroidal activity in animals can be utilized by man for more efficient animal production remains very limited. Reviews of the literature applicable to poultry have been provided by Blaxter el al. (1949), Sykes el al. (1953), and Sturkie (1954). A further review of the general subject at this time seems unnecessary. Shaklee and Shaffner (1952) demonstrated that the degree of response of the thyroid gland to thiouracil feeding was amenable to selection. By use of the sib test it was possible to develop lines of New Hampshires differing markedly in this respect. These selection experiments were initiated on the assumption that the weight of the thyroid gland after a period of thiouracil feeding might provide some indication of the activity of the thyroid gland. The effects of this selection experiment on other characteristics of chickens reported to be affected by variations in thyroid activity are reported herewith. 1
Scientific Paper No. A 479. Contribution No. 2570 of the Maryland Agricultural Experiment Station (Department of Poultry Husbandry). 2 Thiouracil was furnished through the courtesy of Dr. Mark Welsh, Lederle Laboratories, Pearl River, N . Y. 3 Present address: The Agricultural Research Center, Beltsville, Maryland.
EXPERIMENTAL PROCEDURE
One year after the original selection experiment was initiated for the high response and low response lines, hereafter referred to as the high and low lines, it was decided that too few families had been saved to avoid serious inbreeding. Accordingly, another selection experiment was initiated from the same random-bred population as used in the original experiment. It did not prove necessary, however, to cross the birds from the two selections, so in effect the experiments was replicated. Some of the data were collected on birds selected for two generations and some on birds selected for three generations. Each year, chicks from the two strains were reared together in conventional floor pens as a single population, then moved to range shelter. Family selection was practiced and was based on the thyroid gland weights of 4week-old chicks fed thiouracil as 0.2 percent of their ration from the time of hatching. The chicks were sacrified, and the thyroid glands were removed and weighed to the nearest milligram. At the time of thyroid removal, an estimate of the rate of feathering was obtained by removing and measuring the length of the longest tail feather to the nearest centimeter. Egg production data were obtained from August 17, 1952 to the end of February, 1953. Fertility and hatchability were recorded for the eggs set October
572
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T
SELECTION FOE THYROIDAL RESPONSE TO THIOURACIL
31, 1952 and December 3, 1952. Table 2 presents data from both treated and untreated chickens. Data on the thyroid weight, 4-week-body weight, rate of feathering, and mortality to four weeks of age were taken from birds fed thiouracil as 0.2 percent of the ration from the time of hatch until sacrificed at four weeks of age. All other data were taken from untreated birds.
573
TABLE 1.—Thyroid gland weights of thiouracil-treated chicks of two experiments after three generations and two generations of selection, respectively, for high and low response to thiouracil Low line
High line Thyroid No. Sire of wt. chicks (mg.)
C.of V.
(%)
N o . Thyroid Sire of wt. chicks (mg.)
C.of V.
(%)
After three generations of selection 22 23
23 24 47
540±57 446 ± 59
50 65
492±41
57
20 21
56 77
104±8 107 ± 5
55 43
133
106±4
48
After two generations of selection
Shaklee and Shaffner (1952) have reported results of the original experiment after two generations of selection, at which time the mean thyroid gland weight of treated birds of the high line was approximately four times that of the low line. Subsequent to the report cited above, a third generation of selection had separated the lines farther so that the mean of the high line was almost five times greater than that of the low line. The thyroid gland weights, coefficients of variation, and standard errors of the first and second experiments are presented in Table 1. In spite of the large difference in the response of these strains to thiouracil, it was not possible to demonstrate differences in their thyroxin-secretion rates. These were compared by determining the uptake of radioactive iodine4 (as described by Franklin et ah, 1944) and by the technique of simultaneous thiouracilthyroxin administration (Dempsey and Astwood, 1943). Any differences that may have existed in the thyroxin secretion rates of the high and low lines must have been of a very low order and must have had little or no relationship to the differences observed in thyroid size. 4
The authors are grateful to Dr. C. F. Winchester and V. C. Scarborough of the Agricultural Research Center, Beltsville, Maryland, for assistance in determining the radioactive iodine uptake.
12 19 24
28 58 49
263 ± 2 7 193± 14 208 ± 14
55 54 46
135
214±10
53
13 25 26
107 49 61
107 ± 5 94 + 9 93±6
45 66 52
217
100 ± 4
52
Selection was practiced with no conscious regard for other characteristics. Thus, it was expected that, if the weight response of the thyroid gland to the feeding of thiouracil was directly related to thyroid gland activity, certain characteristics known to be influenced by thyroid gland activity would be adversely affected in one line and perhaps enhanced in the other. Table 2 presents the status of various characteristics of the two lines of New Hampshire chickens after two generations of selection in one experiment and three generations in the other. Numerous reports have appeared concerning the effect of hyperthyroidism, as induced by the feeding of thyroprotein, on egg production. While some of the reports have shown an increase in egg production from this treatment, a preponderance of the reports do not provide supporting evidence. Egg production was recorded during a part of the last year of the experiment reported herein. The data shown in Table 2 were obtained from August, 1952 to February, 1953. Many of the pullets were not yet laying during the first part of this period, and the percentage egg production was not high. The percentage egg production of the high line during this
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RESULTS AND DISCUSSION
574
W. E. S H A K L E E A N D C. S. SHAFFNER TABLE 2.—Status of various characteristics of New Hampshire chickens selected in two experiments for three and for two generations, respectively, for high and low thyroid gland weight response to the feeding of thiouracil
Sire
Thyroid wt.* (mg.)
Egg prod.
Fertility
Hatchability
(%)
(%)
(%)
Incubation period (days)
4 wk. body wt.* (gms.)
10 wk. body wt. (gms.) Male
Female
Adult body wt. (gms.)
R a t e of feath- Mortalering ity to (cm.)* 4 wks. length tail
Laying house mortality
(%)
After three generations of selection High Line
22 23 Unweighted Mean 20 21 Unweighted Mean
37.5 37.2
82.1 95.1
70.9 63.6
21.6 21.6
161 172
1,055 903
842 721
2,102 2,088
3.3 3.7
11.5 2.1
23 37
493
37.4
88.2
67.2
21.6
166
979
782
2,095
3.5
6.8
30
104 107
40.7 50.8
96.0 99.3
80.8 89.0
21.5 21.3
180 165
1,066 1,040
871 827
2,084 1,748
3.4 3.2
15.1 3.8
20 8
106
45.8
97.6
84.8
21.4
172
1,053
849
1,916
3.3
9.4
14
After two generations of selection High Line
12 19 24 Unweighted Mean
Low Line
13 25 26 Unweighted Mean
263 193 208
39.4 41.8 47.8
91.9 92.5 97.1
76.5 90.4 87.5
21.2 21.2 21.3
200 190 189
1,105 1,019 1,112
972 911 905
2,438 2,465 2,356
3.4 3.3 4.0
0.0 1.7 2.0
50 27 33
221
43.0
93.8
84.8
21.2
193
1,079
929
2,420
3.6
1.2
37
107 94 93
59.4 54.9 44.7
92.5 93.3 92.7
93.9 87.6 94.3
21.3 21.5 21.3
168 150 162
1,247 1,021 1,271
1,001 1,000 947
2,597 2,388 -2,193
3.1 3.1 1.0
4.5 15.5 3.2
26 14 25
98
53.0
92.8
91.9
21.4
160
1,180
983
2,393
2.4
7.7
22
* Chicks were treated by feeding thiouracil as 0.2% of the ration from date of hatch to 4 weeks of age.
period was 37.4 and that of the low line was 45.8 in the first experiment. The difference was only 8.4 percent and was not significant. In the second experiment, the egg production of the low line was 10.0 percentage points greater than that of the high line but again the difference was not significant. Selection for high and low thyroid gland-weight response to thiouracil feeding had no significant effect on egg production in these experiments. Fertility and hatchability have likewise been reported to be affected by treatment with thyroprotein or thiouracil but the data are not in agreement. In the first experiment, the fertility of the high line after three generations of selection for thyroid weight response to thiouracil was 88.2 percent, whereas that of the low line was 97.6 percent. The difference of 9.4 percent was not significant, and in the
previous generation the fertility of the high line was 8.1 percentage points higher than that of the low line. In the second experiment, the fertility of the high line was 1.0 percentage point higher than that of the low line. Apparently the selection practiced in this experiment had no effect on fertility of these New Hampshire chickens. The hatchability of fertile eggs was also recorded for each experiment during the hatching season. Hatchability was 67.2 percent for the high line and 84.9 percent for the low line in the first experiment. The difference of 17.7 percent was not significant and in the previous generation the situation was reversed, with the hatchability of the high line being 16.3 percentage points higher than that of the low line. In the second experiment, the hatchability of the low line was only 7.1
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Low Line
540 446
SELECTION FOE THYROIDAL RESPONSE TO THIOURACIL
Contradictory results have been reported concerning the effect of feeding thyroprotein on the growth of young chickens. On the other hand, there seems to be no doubt that the feeding of thiouracil depresses their rate of growth. Body weights were recorded at four weeks of age for the birds that were fed thiouracil. After three generations of selection for high and low thyroid gland weight response in thiouracil-fed birds, the low line averaged 172 grams compared with 166 for the high line. The difference of six grams was not significant. In the previous generation, the high-line chicks weighed six grams more than those of the low line. After two generations of selection in the second experiment, the high-line chicks
weighed 33 grams more than the low-line chicks. This selection experiment had no apparent effect on the four-week weights of the thiouracil-treated birds. Body weight at 10 weeks of age was recorded for the birds raised for breeding stock, the results being presented in Table 2. The body weights for males of the low line averaged 1,053 grams and the high-line males averaged 979 grams. Low-line females weighed 849 grams whereas high-line females weighed 782 grams. In the second experiment, the low-line males were 101 grams heavier and the females were 54 grams heavier than those of the high line. However, the difference between lines was not statistically significant. Mature body weights of the pullets selected for breeding were recorded. It should be recalled that body weight was not a factor in these selection experiments. In the 1952-53 season, the high-line pullets of the first experiment weighed 2,095 grams and the low-line pullets weighed 1,916 grams. The difference of 179 grams was not significant. In fact, in the previous generation, the low-line pullets weighed 64 grams more than those of the high line. In the second experiment, the high-line pullets weighed only 27 grams more than the low-line pullets. Here again, no effect of the selection experiment on mature pullet weight was demonstrated. It is well established that the rate of feathering in young birds is under the influence of thyroidal activity, thyroprotein increasing the rate and thiouracil depressing it. Rate of feathering in the present experiment was estimated by measuring the length in centimeters of the longest tail feathers of the four-weekold thiouracil-fed chicks. The average length of the longest tail feather was 3.5 ^centimeters in high-line chicks of the
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percentage points greater than that of the high line. Apparently the selection program had no effect on hatchability. Since it has been firmly established that the length of the incubation period can be altered by altering thyroid activity, it seemed of interest to investigate this characteristic for these two strains. An indication that the two lines in the present experiment might differ in incubation period occurred after two generations of selection, when, upon removing a hatch on the 21st day of incubation, only 70.8 percent of the high line eggs and 71.8 percent of the low line eggs had hatched. The unhatched chicks were replaced in the incubator and the following day an additional 24.1 percent hatched from the high line and only 6.8 percent from the low line. The following generation this point was checked further by counting the chicks which hatched during each six hour period during the hatching process. These data are presented in Table 2, there being essentially no difference between lines. Apparently, this selection experiment had no effect on length of the incubation period.
575
576
W. E. SHAKXEE AND C. S. SHAFFNER
TABLE 3.—Mortality of the untreated chicks within. sire families of high and low lines following an outbreak of Newcastle disease First hatch Sire No.
No. of birds
Second hatch
Percent mortal- No. of birds ity
Percent mortality
79 38 61 63 53
16.5 36.8 8.2 4.8 17.0
78 50 61 70 53
15.4 36.0 24.6 28.6 5.7
ALL
294
15.0
312
21.8
Low Line 13 20 21 25 26
52 67 118 32 100
0.0 6.0 4.2 21.9 6.0
45 32 116 27 77
6.7 21.9 15.5 7.4 6.5
ALL
369
6.0
297
11.8
first experiment and 3.3 in low-line chicks. The difference of 0.2 centimeters was not significant nor was the difference of 1.2 centimeters in the second experiment. Apparently this selection experiment had no effect on rate of feathering in these thiouracil-treated New Hampshire chicks. The mortality of thiouracil-fed chicks to four weeks of age in the first experiment was 6.8 percent for the high-line and 9.4 percent for the low-line after three generations of selection. The difference of 2.6 percent was not significant. In the previous generation, the mortality of the high-line was 0.3 percentage points greater than that of the low-line. In the second experiment the mortality of the thiouracil-fed chicks of the low-line was 6.5 percentage points greater than that for the high-line. During the spring of 1952, an opportunity to study the relationship between thyroid response to thiouracil and resistance to Newcastle disease presented itself when an outbreak of this disease occurred in the University of Maryland poultry flock. Two hatches of replacement
SUMMARY AND CONCLUSION
Selection for high and low thyroid gland weight response at four weeks of age to the feeding of thiouracil to New Hampshire chicks resulted in a five-fold dif-
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High Line 12 19 22 23 24
chicks two and four weeks of age were being reared in a conventional brooder house with radiant-heated floors when the disease outbreak occurred. The high-line was represented by 606 chicks and the low line by 666 chicks. The usual symptoms of Newcastle disease were noted such as a wave of mortality, paralysis, etc. Many of the affected chicks were examined by a pathologist and the causative agent of Newcastle disease was found to be present. The mortality percentages of both hatches of the two lines are presented in Table 3. The pooled mortality for both hatches of the high-line was 18.5 percent while that of the low-line was only 8.6 percent. This difference of 9.9 percent appears to be important, but the variation within lines was quite large, and the difference between lines only approaches statistical significance. From the time the untreated breeding pullets were housed in the fall until the hatching season was over, mortality was recorded, as well as the culling of obviously undesirable pullets. The loss in the first experiment was 30 percent in the high-line and 14 percent in the low-line, as shown in Table 2, but the difference of 16 percent was not significant. In the second experiment the loss was 15 percentage points greater in the high-line than in the low-line. Although the differences in mortality between lines only approached significance, it is interesting to note that the chick losses from Newcastle disease and the adult mortality were considerably less in the low-line.
577
NEWS AND NOTES
explain the wide variations often observed in thyroid size. REFERENCES Blaxter, K. L., E. P. Reineke, E. W. Crampton and W. E. Petersen, 1949. The role of thyroidal materials and of synthetic goitrogens in animal production and an appraisal of their practical use. J. Animal Science, 8:307-352. Dempsey, E. W., and E. B. Astwood, 1943. Determination of the rate of thyroid hormone secretion at various environmental temperatures. Endocrinology, 32: 509-518. Franklin, A. L., S. R. Lerner and I. L. Chaikoff, 1944. The effect of thiouracil on the formation of thyroxine and diiodotyrosine by the thyroid gland of the rat with radioactive iodine as an indicator. Endocrinology, 34: 265-268. Shaklee, W. E., and C. S. Shaffner, 1952. High and low thyoridal response to the feeding of thiouracil to New Hampshire chickens. J. Heredity, 43: 238-242. Sykes, J. F., F. N . Andrews, F. W. Hill, F. W. Lorenz, J. W. Thomas and C. F. Winchester, 1953. Hormonal relationships and applications in the production of meats, milk and eggs. National Research Council Publication 266, 54 pp., Washington, D. C. Sturkie, P. D. 1954. Avian Physiology 423 pp. Cornstock Publishing Association, Ithaca, New York.
BOOK REVIEWS (Continued from page 571) who need have at least a reading knowledge of German the book will be especially useful.—W. D. Termohlen in the World's Poultry Science Journal PRIER, JAMES E. Turkey Diseases. Interstate Printers and Publishers, Danville, 111. 152 pp., $3.00. This book is a definite disappointment. The material is already available in better form and ap-
proximately the same number of pages in two other publications (Hinshaw and Rosenwald, 1951; Hinshaw in Biester and Schwarte, 1952). In fact a great deal of the material has been taken from these two sources. Since this is a late 1953 book, it should have been possible to quote the 1952 edition of Biester and Schwarte rather than the 1948 one. Many of the illustrations have been poorly reproduced, and others were apparently poor originals.—E.McN.
NEWS AND NOTES TOM NEWMAN AWARD The Tom Newman International Award for 1954 has been made to Dr. W. Bolton of the Poultry Research Centre, Edinburgh, Scotland. The Award consists of a medal and £50 sterling. It is given for what, in the opinion of the Award Committee, is the
most important contribution to poultry husbandry research work published in the previous year. There are Corresponding Secretaries for the Award in every country where poultry husbandry is developed into an industry. The award was made to Dr. Bolton for work pub-
(Continued on page 597)
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ference in thyroid weight of the treated birds after three generations of selection. Concomitant observations on egg production, fertility, hatchability, incubation period, growth and body weight, rate of feathering, and mortality revealed no significant differences between birds of the high and low lines. Since many of these characteristics have been shown to be affected differently by induced hyperor hypothyroidism, it is concluded that the thyroid-gland activity of the two lines has not been changed by the process of selection for high and low thyroid gland weight response to the feeding of thiouracil. The fact that, following thiouracil treatment, the average thyroid gland weight of the high line is almost five times as large as that of the low line indicates that the two lines differ either in (1) the ability of the thyroid tissue to respond to a given quantity of thyrotrophic hormone, and/or (2) the amount of thyrotrophic hormone released by the anterior pituitary gland. These marked genetic differences may serve to partially
HE fact that the activity of the thyroid glands of all adult vertebrates serves as a powerful metabolic regulator is well established, yet the extent to which altered thyroidal activity in animals can be utilized by man for more efficient animal production remains very limited. Reviews of the literature applicable to poultry have been provided by Blaxter el al. (1949), Sykes el al. (1953), and Sturkie (1954). A further review of the general subject at this time seems unnecessary. Shaklee and Shaffner (1952) demonstrated that the degree of response of the thyroid gland to thiouracil feeding was amenable to selection. By use of the sib test it was possible to develop lines of New Hampshires differing markedly in this respect. These selection experiments were initiated on the assumption that the weight of the thyroid gland after a period of thiouracil feeding might provide some indication of the activity of the thyroid gland. The effects of this selection experiment on other characteristics of chickens reported to be affected by variations in thyroid activity are reported herewith. 1
Scientific Paper No. A 479. Contribution No. 2570 of the Maryland Agricultural Experiment Station (Department of Poultry Husbandry). 2 Thiouracil was furnished through the courtesy of Dr. Mark Welsh, Lederle Laboratories, Pearl River, N . Y. 3 Present address: The Agricultural Research Center, Beltsville, Maryland.
EXPERIMENTAL PROCEDURE
One year after the original selection experiment was initiated for the high response and low response lines, hereafter referred to as the high and low lines, it was decided that too few families had been saved to avoid serious inbreeding. Accordingly, another selection experiment was initiated from the same random-bred population as used in the original experiment. It did not prove necessary, however, to cross the birds from the two selections, so in effect the experiments was replicated. Some of the data were collected on birds selected for two generations and some on birds selected for three generations. Each year, chicks from the two strains were reared together in conventional floor pens as a single population, then moved to range shelter. Family selection was practiced and was based on the thyroid gland weights of 4week-old chicks fed thiouracil as 0.2 percent of their ration from the time of hatching. The chicks were sacrified, and the thyroid glands were removed and weighed to the nearest milligram. At the time of thyroid removal, an estimate of the rate of feathering was obtained by removing and measuring the length of the longest tail feather to the nearest centimeter. Egg production data were obtained from August 17, 1952 to the end of February, 1953. Fertility and hatchability were recorded for the eggs set October
572
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on May 29, 2015
T
SELECTION FOE THYROIDAL RESPONSE TO THIOURACIL
31, 1952 and December 3, 1952. Table 2 presents data from both treated and untreated chickens. Data on the thyroid weight, 4-week-body weight, rate of feathering, and mortality to four weeks of age were taken from birds fed thiouracil as 0.2 percent of the ration from the time of hatch until sacrificed at four weeks of age. All other data were taken from untreated birds.
573
TABLE 1.—Thyroid gland weights of thiouracil-treated chicks of two experiments after three generations and two generations of selection, respectively, for high and low response to thiouracil Low line
High line Thyroid No. Sire of wt. chicks (mg.)
C.of V.
(%)
N o . Thyroid Sire of wt. chicks (mg.)
C.of V.
(%)
After three generations of selection 22 23
23 24 47
540±57 446 ± 59
50 65
492±41
57
20 21
56 77
104±8 107 ± 5
55 43
133
106±4
48
After two generations of selection
Shaklee and Shaffner (1952) have reported results of the original experiment after two generations of selection, at which time the mean thyroid gland weight of treated birds of the high line was approximately four times that of the low line. Subsequent to the report cited above, a third generation of selection had separated the lines farther so that the mean of the high line was almost five times greater than that of the low line. The thyroid gland weights, coefficients of variation, and standard errors of the first and second experiments are presented in Table 1. In spite of the large difference in the response of these strains to thiouracil, it was not possible to demonstrate differences in their thyroxin-secretion rates. These were compared by determining the uptake of radioactive iodine4 (as described by Franklin et ah, 1944) and by the technique of simultaneous thiouracilthyroxin administration (Dempsey and Astwood, 1943). Any differences that may have existed in the thyroxin secretion rates of the high and low lines must have been of a very low order and must have had little or no relationship to the differences observed in thyroid size. 4
The authors are grateful to Dr. C. F. Winchester and V. C. Scarborough of the Agricultural Research Center, Beltsville, Maryland, for assistance in determining the radioactive iodine uptake.
12 19 24
28 58 49
263 ± 2 7 193± 14 208 ± 14
55 54 46
135
214±10
53
13 25 26
107 49 61
107 ± 5 94 + 9 93±6
45 66 52
217
100 ± 4
52
Selection was practiced with no conscious regard for other characteristics. Thus, it was expected that, if the weight response of the thyroid gland to the feeding of thiouracil was directly related to thyroid gland activity, certain characteristics known to be influenced by thyroid gland activity would be adversely affected in one line and perhaps enhanced in the other. Table 2 presents the status of various characteristics of the two lines of New Hampshire chickens after two generations of selection in one experiment and three generations in the other. Numerous reports have appeared concerning the effect of hyperthyroidism, as induced by the feeding of thyroprotein, on egg production. While some of the reports have shown an increase in egg production from this treatment, a preponderance of the reports do not provide supporting evidence. Egg production was recorded during a part of the last year of the experiment reported herein. The data shown in Table 2 were obtained from August, 1952 to February, 1953. Many of the pullets were not yet laying during the first part of this period, and the percentage egg production was not high. The percentage egg production of the high line during this
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on May 29, 2015
RESULTS AND DISCUSSION
574
W. E. S H A K L E E A N D C. S. SHAFFNER TABLE 2.—Status of various characteristics of New Hampshire chickens selected in two experiments for three and for two generations, respectively, for high and low thyroid gland weight response to the feeding of thiouracil
Sire
Thyroid wt.* (mg.)
Egg prod.
Fertility
Hatchability
(%)
(%)
(%)
Incubation period (days)
4 wk. body wt.* (gms.)
10 wk. body wt. (gms.) Male
Female
Adult body wt. (gms.)
R a t e of feath- Mortalering ity to (cm.)* 4 wks. length tail
Laying house mortality
(%)
After three generations of selection High Line
22 23 Unweighted Mean 20 21 Unweighted Mean
37.5 37.2
82.1 95.1
70.9 63.6
21.6 21.6
161 172
1,055 903
842 721
2,102 2,088
3.3 3.7
11.5 2.1
23 37
493
37.4
88.2
67.2
21.6
166
979
782
2,095
3.5
6.8
30
104 107
40.7 50.8
96.0 99.3
80.8 89.0
21.5 21.3
180 165
1,066 1,040
871 827
2,084 1,748
3.4 3.2
15.1 3.8
20 8
106
45.8
97.6
84.8
21.4
172
1,053
849
1,916
3.3
9.4
14
After two generations of selection High Line
12 19 24 Unweighted Mean
Low Line
13 25 26 Unweighted Mean
263 193 208
39.4 41.8 47.8
91.9 92.5 97.1
76.5 90.4 87.5
21.2 21.2 21.3
200 190 189
1,105 1,019 1,112
972 911 905
2,438 2,465 2,356
3.4 3.3 4.0
0.0 1.7 2.0
50 27 33
221
43.0
93.8
84.8
21.2
193
1,079
929
2,420
3.6
1.2
37
107 94 93
59.4 54.9 44.7
92.5 93.3 92.7
93.9 87.6 94.3
21.3 21.5 21.3
168 150 162
1,247 1,021 1,271
1,001 1,000 947
2,597 2,388 -2,193
3.1 3.1 1.0
4.5 15.5 3.2
26 14 25
98
53.0
92.8
91.9
21.4
160
1,180
983
2,393
2.4
7.7
22
* Chicks were treated by feeding thiouracil as 0.2% of the ration from date of hatch to 4 weeks of age.
period was 37.4 and that of the low line was 45.8 in the first experiment. The difference was only 8.4 percent and was not significant. In the second experiment, the egg production of the low line was 10.0 percentage points greater than that of the high line but again the difference was not significant. Selection for high and low thyroid gland-weight response to thiouracil feeding had no significant effect on egg production in these experiments. Fertility and hatchability have likewise been reported to be affected by treatment with thyroprotein or thiouracil but the data are not in agreement. In the first experiment, the fertility of the high line after three generations of selection for thyroid weight response to thiouracil was 88.2 percent, whereas that of the low line was 97.6 percent. The difference of 9.4 percent was not significant, and in the
previous generation the fertility of the high line was 8.1 percentage points higher than that of the low line. In the second experiment, the fertility of the high line was 1.0 percentage point higher than that of the low line. Apparently the selection practiced in this experiment had no effect on fertility of these New Hampshire chickens. The hatchability of fertile eggs was also recorded for each experiment during the hatching season. Hatchability was 67.2 percent for the high line and 84.9 percent for the low line in the first experiment. The difference of 17.7 percent was not significant and in the previous generation the situation was reversed, with the hatchability of the high line being 16.3 percentage points higher than that of the low line. In the second experiment, the hatchability of the low line was only 7.1
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Low Line
540 446
SELECTION FOE THYROIDAL RESPONSE TO THIOURACIL
Contradictory results have been reported concerning the effect of feeding thyroprotein on the growth of young chickens. On the other hand, there seems to be no doubt that the feeding of thiouracil depresses their rate of growth. Body weights were recorded at four weeks of age for the birds that were fed thiouracil. After three generations of selection for high and low thyroid gland weight response in thiouracil-fed birds, the low line averaged 172 grams compared with 166 for the high line. The difference of six grams was not significant. In the previous generation, the high-line chicks weighed six grams more than those of the low line. After two generations of selection in the second experiment, the high-line chicks
weighed 33 grams more than the low-line chicks. This selection experiment had no apparent effect on the four-week weights of the thiouracil-treated birds. Body weight at 10 weeks of age was recorded for the birds raised for breeding stock, the results being presented in Table 2. The body weights for males of the low line averaged 1,053 grams and the high-line males averaged 979 grams. Low-line females weighed 849 grams whereas high-line females weighed 782 grams. In the second experiment, the low-line males were 101 grams heavier and the females were 54 grams heavier than those of the high line. However, the difference between lines was not statistically significant. Mature body weights of the pullets selected for breeding were recorded. It should be recalled that body weight was not a factor in these selection experiments. In the 1952-53 season, the high-line pullets of the first experiment weighed 2,095 grams and the low-line pullets weighed 1,916 grams. The difference of 179 grams was not significant. In fact, in the previous generation, the low-line pullets weighed 64 grams more than those of the high line. In the second experiment, the high-line pullets weighed only 27 grams more than the low-line pullets. Here again, no effect of the selection experiment on mature pullet weight was demonstrated. It is well established that the rate of feathering in young birds is under the influence of thyroidal activity, thyroprotein increasing the rate and thiouracil depressing it. Rate of feathering in the present experiment was estimated by measuring the length in centimeters of the longest tail feathers of the four-weekold thiouracil-fed chicks. The average length of the longest tail feather was 3.5 ^centimeters in high-line chicks of the
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percentage points greater than that of the high line. Apparently the selection program had no effect on hatchability. Since it has been firmly established that the length of the incubation period can be altered by altering thyroid activity, it seemed of interest to investigate this characteristic for these two strains. An indication that the two lines in the present experiment might differ in incubation period occurred after two generations of selection, when, upon removing a hatch on the 21st day of incubation, only 70.8 percent of the high line eggs and 71.8 percent of the low line eggs had hatched. The unhatched chicks were replaced in the incubator and the following day an additional 24.1 percent hatched from the high line and only 6.8 percent from the low line. The following generation this point was checked further by counting the chicks which hatched during each six hour period during the hatching process. These data are presented in Table 2, there being essentially no difference between lines. Apparently, this selection experiment had no effect on length of the incubation period.
575
576
W. E. SHAKXEE AND C. S. SHAFFNER
TABLE 3.—Mortality of the untreated chicks within. sire families of high and low lines following an outbreak of Newcastle disease First hatch Sire No.
No. of birds
Second hatch
Percent mortal- No. of birds ity
Percent mortality
79 38 61 63 53
16.5 36.8 8.2 4.8 17.0
78 50 61 70 53
15.4 36.0 24.6 28.6 5.7
ALL
294
15.0
312
21.8
Low Line 13 20 21 25 26
52 67 118 32 100
0.0 6.0 4.2 21.9 6.0
45 32 116 27 77
6.7 21.9 15.5 7.4 6.5
ALL
369
6.0
297
11.8
first experiment and 3.3 in low-line chicks. The difference of 0.2 centimeters was not significant nor was the difference of 1.2 centimeters in the second experiment. Apparently this selection experiment had no effect on rate of feathering in these thiouracil-treated New Hampshire chicks. The mortality of thiouracil-fed chicks to four weeks of age in the first experiment was 6.8 percent for the high-line and 9.4 percent for the low-line after three generations of selection. The difference of 2.6 percent was not significant. In the previous generation, the mortality of the high-line was 0.3 percentage points greater than that of the low-line. In the second experiment the mortality of the thiouracil-fed chicks of the low-line was 6.5 percentage points greater than that for the high-line. During the spring of 1952, an opportunity to study the relationship between thyroid response to thiouracil and resistance to Newcastle disease presented itself when an outbreak of this disease occurred in the University of Maryland poultry flock. Two hatches of replacement
SUMMARY AND CONCLUSION
Selection for high and low thyroid gland weight response at four weeks of age to the feeding of thiouracil to New Hampshire chicks resulted in a five-fold dif-
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High Line 12 19 22 23 24
chicks two and four weeks of age were being reared in a conventional brooder house with radiant-heated floors when the disease outbreak occurred. The high-line was represented by 606 chicks and the low line by 666 chicks. The usual symptoms of Newcastle disease were noted such as a wave of mortality, paralysis, etc. Many of the affected chicks were examined by a pathologist and the causative agent of Newcastle disease was found to be present. The mortality percentages of both hatches of the two lines are presented in Table 3. The pooled mortality for both hatches of the high-line was 18.5 percent while that of the low-line was only 8.6 percent. This difference of 9.9 percent appears to be important, but the variation within lines was quite large, and the difference between lines only approaches statistical significance. From the time the untreated breeding pullets were housed in the fall until the hatching season was over, mortality was recorded, as well as the culling of obviously undesirable pullets. The loss in the first experiment was 30 percent in the high-line and 14 percent in the low-line, as shown in Table 2, but the difference of 16 percent was not significant. In the second experiment the loss was 15 percentage points greater in the high-line than in the low-line. Although the differences in mortality between lines only approached significance, it is interesting to note that the chick losses from Newcastle disease and the adult mortality were considerably less in the low-line.
577
NEWS AND NOTES
explain the wide variations often observed in thyroid size. REFERENCES Blaxter, K. L., E. P. Reineke, E. W. Crampton and W. E. Petersen, 1949. The role of thyroidal materials and of synthetic goitrogens in animal production and an appraisal of their practical use. J. Animal Science, 8:307-352. Dempsey, E. W., and E. B. Astwood, 1943. Determination of the rate of thyroid hormone secretion at various environmental temperatures. Endocrinology, 32: 509-518. Franklin, A. L., S. R. Lerner and I. L. Chaikoff, 1944. The effect of thiouracil on the formation of thyroxine and diiodotyrosine by the thyroid gland of the rat with radioactive iodine as an indicator. Endocrinology, 34: 265-268. Shaklee, W. E., and C. S. Shaffner, 1952. High and low thyoridal response to the feeding of thiouracil to New Hampshire chickens. J. Heredity, 43: 238-242. Sykes, J. F., F. N . Andrews, F. W. Hill, F. W. Lorenz, J. W. Thomas and C. F. Winchester, 1953. Hormonal relationships and applications in the production of meats, milk and eggs. National Research Council Publication 266, 54 pp., Washington, D. C. Sturkie, P. D. 1954. Avian Physiology 423 pp. Cornstock Publishing Association, Ithaca, New York.
BOOK REVIEWS (Continued from page 571) who need have at least a reading knowledge of German the book will be especially useful.—W. D. Termohlen in the World's Poultry Science Journal PRIER, JAMES E. Turkey Diseases. Interstate Printers and Publishers, Danville, 111. 152 pp., $3.00. This book is a definite disappointment. The material is already available in better form and ap-
proximately the same number of pages in two other publications (Hinshaw and Rosenwald, 1951; Hinshaw in Biester and Schwarte, 1952). In fact a great deal of the material has been taken from these two sources. Since this is a late 1953 book, it should have been possible to quote the 1952 edition of Biester and Schwarte rather than the 1948 one. Many of the illustrations have been poorly reproduced, and others were apparently poor originals.—E.McN.
NEWS AND NOTES TOM NEWMAN AWARD The Tom Newman International Award for 1954 has been made to Dr. W. Bolton of the Poultry Research Centre, Edinburgh, Scotland. The Award consists of a medal and £50 sterling. It is given for what, in the opinion of the Award Committee, is the
most important contribution to poultry husbandry research work published in the previous year. There are Corresponding Secretaries for the Award in every country where poultry husbandry is developed into an industry. The award was made to Dr. Bolton for work pub-
(Continued on page 597)
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ference in thyroid weight of the treated birds after three generations of selection. Concomitant observations on egg production, fertility, hatchability, incubation period, growth and body weight, rate of feathering, and mortality revealed no significant differences between birds of the high and low lines. Since many of these characteristics have been shown to be affected differently by induced hyperor hypothyroidism, it is concluded that the thyroid-gland activity of the two lines has not been changed by the process of selection for high and low thyroid gland weight response to the feeding of thiouracil. The fact that, following thiouracil treatment, the average thyroid gland weight of the high line is almost five times as large as that of the low line indicates that the two lines differ either in (1) the ability of the thyroid tissue to respond to a given quantity of thyrotrophic hormone, and/or (2) the amount of thyrotrophic hormone released by the anterior pituitary gland. These marked genetic differences may serve to partially