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The Thyroxine Secretion Rate of Turkey Poults*
The Thyroxine Secretion Rate of Turkey Poults* J. ROBERT SMYTH, JR., AND THOMAS W. Foxf University of Massachttsetts, Amherst (Received for publication November 17, 1950)
ESULTS of recent studies involving • chickens and ducks suggest a possible close relationship between the secretory rate of the thyroid gland and growth rate and skeletal maturation. Schultze and Turner (1945) found the thyroxine secretion rate on a body weight basis to be higher for White Leghorn cockerels than for White Plymouth Rock cockerels. The growth patterns of the two breeds differ markedly as the White Leghorn has a more rapid early rate of growth and their growth curve levels off sooner. These investigators also found that under the conditions of their experiments Barred Plymouth Rocks had a higher secretion rate than did the White Plymouth Rocks which paralleled differences in their growth rate. However, as was pointed out, differences in the seasons in which the experiments were conducted makes the results of this latter comparison questionable. Also Glazener, Shaffner and Jull (1949) recently demonstrated that fast growing strains of chickens have an inherently higher thyroxine secretion rate than do slow growing strains of the same breed. The relationship of the thyroxine secretion rate to the extremely rapid growth rate and early skeletal maturation in the. duck was investigated by Hoffman (1950) * Contribution No. 787 from the Massachusetts Agricultural Experiment Station. t Present address: Department of Poultry Husbandry, Purdue University, Lafayette, Indiana. 607
who found the secretion rate to be much higher than it was for the domestic fowl. These results would be expected if a very close relationship exists between thyroidal activity and rate of growth. These results were confirmed independently by Biellier and Turner (1950). It appeared desirable to investigate the thyroxine secretion level of the turkey, which possesses another type of growth pattern and late skeletal maturation, to ascertain if relationships parallel those reported for the domestic fowl and the duck. An earlier attempt to accomplish this by Blakely, Anderson and MacGregor (1949) was unsuccessful because of considerable variability of thyroid weights as a function of body weight and because their exploratory levels of d,lthyroxine were found to be too low to provide an estimate of the normal thyroxine secretion level of their population. That thyroidal activity might be associated with the phenomena of hybrid vigor was considered by Mixner and Upp (1947). They found that "double cross" hybrid chicks produced from Rhode Island Red and White Leghorn inbred lines had a much higher thyroxine secretion rate than did "single cross" chicks produced by crosses of two inbred lines of the same breed or than did chicks resulting from a New Hampshire X Barred Plymouth Rock mating. Since matings were available by which
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J. ROBERT SMYTH, JR., AND THOMAS W. F O X
pure Jersey Buff, Broad-Breasted Bronze and crossbred offspring between the two varieties were being produced, a comparison of the thyroxine secretion rates of the three groups was undertaken. PROCEDURE
EXPERIMENTAL RESULTS
The results of the thyroxine secretion rate assays of Broad-Breasted Bronze, Jersey Buff and crossbred poults are presented in Table 1. A summary of the estimated thyroxine secretion rates on a per bird per day basis, body weight basis and for sexes for each group is presented in Table 2. Under the conditions of this experiment the daily thyroxine secretion rate of the Broad-Breasted Bronze male was 10.26 ng. per day or 2.71 ng. per 100 grams body weight. The females of this group appeared to secrete thyroxine at the rate of 10.03 fig. per day or 2.73 fig. per 100 grams body weight. Any sex difference in the thyroxine secretion rate is not apparent in these data for the BroadBreasted Bronze. The secretion rate per day for the smaller sized Jersey Buff poults was estimated at 8.56 fig. and 9.0 Hg. for males and females respectively, and at the rate of 2.62 fig. for males and 2.89 fig. for females per 100 grams body weight. A sex difference, although not statistically significant, favors the female which is similar to the results for growing chickens (Schultze and Turner, 1945) and growing ducks (Biellier and Turner, 1950).
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Jersey Buff, Broad-Breasted Bronze and crossbred poults were hatched on June 20 and sexed at this time by a commercial chick sexer. The crossbred poults were produced from reciprocal crosses of the two pure varieties studied. The poults were kept in a 16 compartment, 4-deck starting battery under a system of continuous lighting. The temperature under the hover portion of each compartment varied between 90 and 95°F. during the course of the experiment. The method used to determine the thyroxine secretion rate was the same as that used by Dempsey and Astwood (1943) with rats and applied to chickens by Mixner, Reineke and Turner (1944), Schultze and Turner (1945) and others. At hatching time 100 Jersey Buff poults were divided on the basis of body weight into five sub-groups. Each sub-group contained half males and half females. The 108 Broad-Breasted Bronze poults and the 54 crossbred poults were also assigned to five sub-groups by the same method. Each separate group had a control subgroup which received a conventional turkey starter ration, while the other four sub-groups were fed the same ration to which 0.1 percent thiouracil had been added. Three of the sub-groups of each group receiving the thiouracil ration were injected subcutaneously every day with three graded levels of d,l-thyroxine. These three levels were 5, 10 and 15 fxg. per day. The d,l-thyroxine solutions were prepared by dissolving the crystalline material in dilute alkali. This solution was then diluted with distilled water so that each
0.1 ml. of solution contained the daily dosage of thyroxine. At the end of three weeks, the poults were weighed and then killed and the thyroid glands immediately removed. The glands were quickly weighed on a milligram balance. The thyroid weights per 100 gm. body weight were then plotted against the amount of d,l-thyroxine injected daily in order to estimate the amount of thyroxine necessary to counteract the effects of the thiouracil. This amount is considered to represent the daily thyroxine secretion rate of the poults.
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THYROXINE SECRETION RATE or POULTS TABLE 1.—Thyroid secretion rale of 0-3 weeks of age Broad-Breasted Bronze, Jersey Buff and B.B.B.XJ.B. crossbred turkey poults Females
Males Treatment sub-group
Thyroid wt/100 gm. body wt. in mg.
18.7 100.3
5.10 45.77
376
77.7
20.65
7
363
18.5
.5.09
8
333
Ave. body wt. in gms.
9 12
379 224
Group I—Broad-Breasted Bronze 13 367 16.6 4.38 8 219 67.2 30.01
11
338
41.4
12.25
10
10
399
20.8
4.61
9
355
1.42
Ave. thyroid wt. in mg.
Thyroid wt./lOO gm. body wt. in mg.
5.02
No. of poults
Ave. body wt. in gm.
4.82
1.45
d,l-thyroxine per ]poult = 10.26 Mg- per day d,l-thyroxine per ]poult=10.03 Mg. per day d,l-thyroxine/100 gm. body wt. = 2.71 Mg- d,l-thyroxine/100 gms. body wt. = 2.73 Mgper day per day Normal controls 0.1% thiouracil 0.1% thiouracil+5 Mg. thyroxine 0.1% thiouracil+10 Mg. thyroxine 0.1% thiouracil+15 Mg. thyroxine
9 6
327 175
17.3 71.4
Group II—-Jersey Buff 8 311 5.25 12 166 40.73
7
279
28.9
10.36
9
10
292
10.7
3.67
261
4.8
1.83
7 .
18.2 79.4
5.85 47.90
263
38.7
14.72
9
272
11.5
4.25
10
265
4.7
1.77
d,l-thyroxine per poult=8.56 Mg. per day d,l-thyroxine per poult = 9.0 Mg. per day d,l-thyroxine per 100/gm. body wt.=2.62 d,l-thyroxine per 100/gm. body wt. = 2.89 Mg. per day <«g- per day Normal controls 0.1% thiouracil 0.1% thiouracil+5 fig. thyroxine 0.1% thiouracil+10 Mg- thyroxine 0.1% thiouracil+15 Mg. thyroxine
6 5
369 199
Group III—B.B.B.XJ.B. 4.52 16.7 44.05 87.5
5
337
63.2
18.78
5
356
21.0
5
373
9.36
crossbreds 330 6 192 6
18.2 67.9
5.49 35.43
4
257
36.0
14.02
5.89
5
305
15.4
5.03
2.51
5
280
5.88
2.10
d,l-thyroxine per poult = 11.0 Mg. per poult d,l-thyroxine per poult = 9.8 Mg- per poult per day per day d,l-thyroxine per 100/gm. body wt. = 2.98 d,l-thyroxine per 100/gm. wt. = 2.97 MgMg. per day per day
This sex difference was reversed in the case of the crossbred poults where the secretion rate per day was estimated at 11.0 ixg. per poult for the males and 9.8 fig. for the females. However, this difference disappeared when the data were converted to the thyroxine secreted per 100 grams body weight per day, or 2.98 fig. for the males and 2.97 fig. for the females. When the thyroxine secretion rates
for the three groups were compared, the crossbreds secreted slightly more thyroxine per bird per day and significantly more thyroxine per 100 grams body weight than did the other two groups. The percentages that the secretion rates of the other two groups are' of that of the crossbreds are presented in Table 2. When sexes are combined for each group, the secretion rate of Jersey Buff poults was
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Normal controls 0.1% thiouracil 0.1% thiouracil+5 Mg. thyroxine 0.1% thiouracil+10 Mg. thyroxine 0 . 1 % thiouracil+15 Mg. thyroxine
Ave. thyroid wt. in mg.
No. of poults
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J. ROBERT SMYTH, JR., AND THOMAS W. F O X
92.6 percent and that of the Bronze 91.4 percent of the crossbred value. The untreated females of all three groups of tukeys had larger thyroid glands than did the males of their respective group when thyroid weight was considered either as a function of body weight or on a per bird basis. The average thyroid weight for all females was 5.41 mg. per 100 grams body
been previously reported. Schultze and Turner (1945) reported that the thyroids of the White Rock chicken female were heavier than were those of the male at five weeks of age. Recently Biellier and Turner (1950) found the same sex relationship to exist for White Pekin ducks. When all poults of the thiouracil treated Broad-Breasted Bronze and Jersey Buff groups are combined, the resulting hyper-
Thyroxine secretion rate— Group
No. of poults and sex
Crossbreds
Males—26 Females—26 Both—52
11.00 9.80 10.40
Jersey Buff
Males—39 Females—48 Both—87
8.56 9.00 8.78
77.8 91.8 84.4
2.62 2.89 2.755
87.9 97.3 92.6
Broad-Breasted Bronze
Males—51 Females—46 Both—97
10.26 10.03 10.15
93.3 102.3 97.6
2.71 2.73 2.72 .
90.9 91.9 91.4
Micrograms per bird
weight, as compared to an average weight of 4.74 mg. per 100 grams body weight for the male thyroids. The average female thyroid weight was 18.4 mg., while those of the male averaged 16.9 mg. in weight. Blakely, Anderson and MacGregor (1949) reported in an abstract that a sex difference in the relative size of the thyroid as a function of body weight was noted in three week old turkey poults, but they did not point out whether the male or the female had the larger thyroids. However, previously Blakely and Anderson (1949) found that the thyroid glands of nine week old male turkeys were considerably heavier than were those of the females. When this difference is considered on a basis of weight per 100 grams body weight, it was only .18 mgs. in favor of the males. That the females of a species have larger thyroids than do the males has
Percent of crossbred level 100 100 100
Micrograms per 100 gm. body wt. 2.98 2.97 2.975
Percent of crossbred level 100 100 100
trophy of the thyroid glands per 100 grams body weight was approximately eight times that of the size of the thyroids of the control poults. This increase is intermediate between the three to fivefold increase reported for young growing chickens and the ten-fold increase found in two week old ducks by Hoffmann (1950). Blakely and Anderson (1949) found that the thyroid weights of nine week old poults fed thiouracil for three weeks increased six times over the weight of the control glands. This may represent the effect of increasing age on the degree of thyroid compensation to thiouracil induced thyroid inhibition as Schultze and Turner (1945) noted that older chicks tended to attain less thyroid enlargement when compared to the control size than did younger chicks following thiouracil treatment. This same relationship of com-
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TABLE 2.—-Summary of the thyroxine secretion rale for Broad-Breasted Bronze, Jersey Buff and crossbred turkeys
THYROXINE SECRETION RATE or POULTS
The effects of thiouracil fed at 0.1 percent level in the mash had a more marked effect on the growth rate of 0-3 week old turkeys than for any other avian species studied. The thiouracil treated sub-groups of poults were all 40 to 46 percent smaller at the end of the experiment than were the corresponding control sub-groups. No interaction between sex and thiouracil inhibition of growth was evident in the
present study. Using the 0-3 week data of Bielleir and Turner's (1950) study with ducks and combining the body weights of both sexes, the controls are seen to weigh approximately 12 percent more than the thiouracil fed ducks. Hoffmann (1950) also pointed out that the reduction in rate of growth for the 0-2 week old thiouracil treated ducks in his experiment was much greater than that observed previously in chickens. The data of Schultze and Turner (1945) show little effect of 'thiouracil on the early growth rate of chickens. DISCUSSION In order to compare the intergeneric thyroxine secretion rates and the relationships of thyroid activity to growth rate, it is important to know the comparative growth rates of chickens, ducks and turkeys. Milby and Henderson (1937) found that the growth rate of ducks was more rapid than that of chickens and turkeys during the period of growth preceding the major inflection of the growth curve. They employed the equation, W=Akt, established by Brody (1927) for this purpose. However, Milby and Henderson found that the chicken and the turkey grow at approximately the same rate during this period. The growth of the Bronze and White Holland turkeys studied by these investigators was less rapid than would be expected for average stock. In the present investigation we are primarily interested in the comparative growth rates during the one to fourweek growth period. The turkey growth data used by Milby and Henderson does not consider the growth during the first six weeks following hatching. The growth rates of different species are not easily compared. Brody (1927) has pointed out that the segment of the growth curve which precedes the major inflection consists of a number of epochs, each of which
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pensation to age can be demonstrated from the data on ducks of Biellier and Turner (1950). The females of the non-crossbred lots of poults showed a thiouracil induced increase in thyroid size of 8.6 times over the control females. A similar increase of 7.3 times was found for the treated males over the thyroid weights of the control males. This agrees with the results of Schultze and Turner (1945) who found that, in practically all cases, female chicks showed greater thyroid enlargement per 100 grams body weight than did the males. There is a similar tendency in favor of the females of the growing duck (from data of Biellier and Turner, 1950) but it is not exhibited until after the 0-3 week assay period. In connection with this, it has been shown that estrogens and thiouracil exhibit a synergistic effect on thyroid enlargement. Andrews and Bohren (1947), Selle and Selle (1948) and Detwiler, Andrews and Bohren (1950) all found that stilbestrol and thiouracil induced greater hypertrophy of the thyroid gland in growing chickens than did thiouracil alone. The reverse relationship between sex and thiouracil induced enlargement of the thyroids of the crossbred poults is not easily explained. Although the number of poults in each sub-group of the crossbred group were small, the greater enlargement of the male thyroid was also found in the sub-groups which were receiving 5 and 10 fig. of thyroxine daily in addition to the thiouracil feed.
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J. ROBERT SMYTH, JR., AND THOMAS W. FOX
Since ducks, turkeys and chicks all appear to be in the same early epoch of growth during the first few weeks following hatching, it would seem valid to compare their thyroxine secretion rates when body weights are as near similar as possible. The thyroxine secretion rate of 0-2 week old ducks was reported by Hoffmann (1950) to be 18.7 ng. per bird per day or 3.8 ng. per 100 grams body weight.
By combining the thyroxine secretion rates of the Jersey Buff and Bronze poults used in this study, the resulting figures of 9.46 /ug. per bird or 2.74 ng. per 100 grams body weight are obtained. These values indicate that the thyroxine secretion rate of the young growing turkey is lower than that of the young duck. However, this difference should be lessened if the advantage of weight for the ducks were eliminated, since Schultze and Turner (1945) have previously shown a rather close correlation between body weight and thyroxine secretion rate. White Plymouth Rock chicks of comparable size were found by these investigators to secrete 8.42 ixg. of thyroxine per day or 2.20 fig. per 100 grams body weight. Therefore, the thyroxine secretion rate of the young growing turkey would appear to be intermediate between that of ducks and chickens of similar size and age. Since growth rate data to four weeks of age were available for the three groups of turkeys studied, they can be compared to the results of the thyroxine secretion rate data. When growth rate was calculated by the formula -(lOOWi-Wd/Wu the crossbred, Jersey Buff and Bronze poults increased their weights at the rates of 257, 246, and 236 percent respectively during the one to three-week growth period. It is interesting to note that this group order of difference is identical to the results of the thyroxine assay. It would be desirable to know how this relationship compares with the rate of growth throughout the complete developmental period. That a close association exists between rate of growth and thyroidal activity in domestic birds has been previously pointed out (Schultze and Turner, 1945; Hoffmann, 1950). The fact that the relationship between the early growth rates of ducks, turkeys and chickens and the
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showed a constant rate of growth. Different species have characteristic epochs of growth which are correlated with the age of the individual. Therefore, at a given age two species may be in different epochs of growth. This difficulty is largely removed when comparisons are made between the growth rates of chickens and turkeys between the ages of one and three weeks, as both appear to be in their first growth epoch. One to three-week weights accumulated at this station for Broad-Breasted Bronze and Jersey Buff turkeys and a broiler strain of chickens were compared by use of the formula, percent rate of growth = 100(1^2— Wi)/W\. The percent increase in body weight between the ages of one and three weeks equaled 246 percent, 236 percent and 104 percent for Jersey Buff poults, Bronze poults and broiler chicks respectively. This same relationship holds true if the log poult and chick weights are plotted against age in weeks. By this method, the relative growth rate is directly proportional to the slope of the curves. Calculated slope or two-point ratio values in logarithms give results similar to the percent increase figures above. Therefore, in this study, the early post-embryonic increase in body size for the turkey is considered to be greater per week than for the chicken. The differences are even more marked, if the comparison includes growth data of the Rhode Island Red or similar "heavy" egg production breeds or strains.
THYROXINE SECRETION RATE OF POULTS
The higher thyroxine secretione rat of crossbred poults, as compared to the results found for offspring of the two parent turkey varieties, tends to substantiate the suggestion of Mixner and Upp (1947), who concluded from their chick data, that there was an association between hybrid vigor and thyroidal activity.
Their differences were in favor of doublecross inbred-hybrids in comparison to single-cross hybrids and crossbreds. These investigators did not compare the crossbred chickens used in their study with chicks from the stock used to make the cross. If thyroxine secretion rate is a measure of vigor or hybrid vigor, the results of this study would indicate that cross-breeding in turkeys could be employed to obtain heterosis. There is a possibility that the thyroxine secretion rates estimated in the present study are all lower than they would have been if the experiment had been conducted Earlier during the breeding season. It is commonly thought that late hatched poults are less vigorous than are those hatched earlier, Also, unpublished data from this station indicate that poults from breeders who have been in production for three or four months have less viability and a slower growth rate. This phenomena appears to be independent of the time of year. SUMMARY
The thyroxine secretion rates of 0—3 week old Jersey Buff, Broad-Breasted Bronze and crossbred poults were found to be intermediate between previously reported rates for chicks and ducks of similar weight and age. The secretion rates were estimated to be 10.15 /ug. per poult daily or 2.72 ng. per 100 gms. body weight daily for the Bronze poults; 8.78 ng. per poult or 2.76 ng. per 100 gms. body weight for the Jersey Buffs; and 10.40 Mg- per poult or 2.98 jug- per 100 gms. body weight for the crossbred poults. Although sex differences in the secretion rate of thyroxine were inconsistent, a marked sex difference was observed in regards to the compensatory hypertrophy of the thyroid gland following thiouracil administration at a 0.1 percent level in the feed. The females responded by great-
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estimated levels of thyroxine secretion rates of these species both show the same relative differences is added evidence for the growth rate-thyroxine secretion level relationship. This study does not answer the question of whether thyroxine stimulates growth in avian species, or whether the secretion rate is determined by the inherent growth rate. The thyroid gland may merely respond to the already determined needs of the growing tissues for thyroxine or thyroglobulin. From thyroxine secretion rate data and growth pattern observations in chickens and ducks Hoffmann (1950) made an interesting speculation concerning the possible role of the thyroid in skeletal maturation. This worker pointed out that since exogenous thyroxine accelerates skeletal maturation in growing rats and mice, while thiouracil treatment retards epiphyseal fusion, thyroxine may first stimulate skeletal growth and eventually inhibit it. However, the turkey has an early thyroxine secretion rate intermediate between that of the chicken and the duck but cessation of skeletal growth occurs comparatively later. Unfortunately, no data is available concerning the thyroidal activity of the turkey throughout the growing period. If the present, apparent, intergeneric differential rate of thyroxine secretion persists, the normal importance of the role of the thyroid in skeletal growth becomes questionable. Undoubtedly gonadal activity and its interrelationships with the thyroid and other endocrine glands play a major role in skeletal maturation.
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N E W S AND NOTES
REFERENCES Andrews, F . N., and B. B. Bohren, 1947. Influence of thiouracil and stilbestrol on growth, fattening, and feed efficiency in broilers. Poultry Sci. 26: 447-452. Biellier, H. V., and C. W. Turner, 1950. The thyroxine secretion rate of growing White Pekin ducks. Poultry Sci. 29: 248-257. Blakely, R. M., and R. W. Anderson, 1949. The influence of thiouracil on growth, fattening, feed
consumption and thyroid weight of turkey broilers. Poultry Sci. 28:185-188. Blakely, R. M., R. W. Anderson and H. I. MacGregor, 1949. Determination of thyroxine secretion rate of turkey poults. Poultry Sci. 28: 757. Brody, S., 1927. Growth and development. I I I . Growth rates, their evaluation and significance. University of Missouri Ag. Exp. Sta. Res. Bull. 97. Dempsey, E. W., and E. B. Astwood, 1943. Determination of the rate of thyroid hormone secretion at various environmental temperatures. Endocrinology 32:509-518. Detwiler, R. W., F. N. Andrews and B. B. Bohren, 1950: The influence of thiouracil and stilbestrol on broiler quality. Poultry Sci. 29: 513-519. Glazener, E. W., C. S. Shaffner and M. A. Jull, 1949. Thyroid activity as related to strain differences in growing chickens. Poultry Sci. 28: 834849. Hoffman, E., 1950. Thyroxine secretion rate and growth in the White Pekin duck. Poultry Sci. 29: 109-114. 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. Schultze, A. B., and C. W. Turner, 1945. The determination of the rate of thyroxine secretion by certain domestic animals. University of Missouri Ag. Exp. Sta. Res. Bull. 392. Seele, J. E., and R. M. Seele, 1948. Effect of diethylstilbestrol on the thyroid glands of chicks receiving thiouracil. Science 107:394-395.
News and Notes {Continued from page 606)
member of the staff of the Poultry Department and Secretary-Treasurer of the Poultry Science Association, won the allround judging honours at the 27th annual Mid-west Intercollegiate Judging Con-
test held in Chicago in November. Nineteen teams competed. The Kansas team won the Institute of American Poultry Industries' trophy for the third time which gives them permanent possession.
(Continued on page 620)
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er thyroid enlargement in the Jersey Buff and Bronze groups, while the reverse was found in the crossbred group. These differences were also present in the subgroups receiving 5 and 10 ng. d,l-thyroxine daily. Further confirmatory evidence was obtained for the previously reported relationship between thyroidal activity and rate of body growth. It was shown that the thyroxine secretion rates of young growing chicks, turkeys and ducks are correlated with their respective growth rates. A comparison of the differences in 1-3 week growth rates of the three groups of turkeys studied and their thyroxine secretion rates also substantiate this relationship. Crossbred offspring were found to have a higher rate of thyroxine secretion than did pure offspring from the two parent varieties. This is interpreted as evidence for the existence of hybrid vigor for the progeny of this varietal cross.
ESULTS of recent studies involving • chickens and ducks suggest a possible close relationship between the secretory rate of the thyroid gland and growth rate and skeletal maturation. Schultze and Turner (1945) found the thyroxine secretion rate on a body weight basis to be higher for White Leghorn cockerels than for White Plymouth Rock cockerels. The growth patterns of the two breeds differ markedly as the White Leghorn has a more rapid early rate of growth and their growth curve levels off sooner. These investigators also found that under the conditions of their experiments Barred Plymouth Rocks had a higher secretion rate than did the White Plymouth Rocks which paralleled differences in their growth rate. However, as was pointed out, differences in the seasons in which the experiments were conducted makes the results of this latter comparison questionable. Also Glazener, Shaffner and Jull (1949) recently demonstrated that fast growing strains of chickens have an inherently higher thyroxine secretion rate than do slow growing strains of the same breed. The relationship of the thyroxine secretion rate to the extremely rapid growth rate and early skeletal maturation in the. duck was investigated by Hoffman (1950) * Contribution No. 787 from the Massachusetts Agricultural Experiment Station. t Present address: Department of Poultry Husbandry, Purdue University, Lafayette, Indiana. 607
who found the secretion rate to be much higher than it was for the domestic fowl. These results would be expected if a very close relationship exists between thyroidal activity and rate of growth. These results were confirmed independently by Biellier and Turner (1950). It appeared desirable to investigate the thyroxine secretion level of the turkey, which possesses another type of growth pattern and late skeletal maturation, to ascertain if relationships parallel those reported for the domestic fowl and the duck. An earlier attempt to accomplish this by Blakely, Anderson and MacGregor (1949) was unsuccessful because of considerable variability of thyroid weights as a function of body weight and because their exploratory levels of d,lthyroxine were found to be too low to provide an estimate of the normal thyroxine secretion level of their population. That thyroidal activity might be associated with the phenomena of hybrid vigor was considered by Mixner and Upp (1947). They found that "double cross" hybrid chicks produced from Rhode Island Red and White Leghorn inbred lines had a much higher thyroxine secretion rate than did "single cross" chicks produced by crosses of two inbred lines of the same breed or than did chicks resulting from a New Hampshire X Barred Plymouth Rock mating. Since matings were available by which
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608
J. ROBERT SMYTH, JR., AND THOMAS W. F O X
pure Jersey Buff, Broad-Breasted Bronze and crossbred offspring between the two varieties were being produced, a comparison of the thyroxine secretion rates of the three groups was undertaken. PROCEDURE
EXPERIMENTAL RESULTS
The results of the thyroxine secretion rate assays of Broad-Breasted Bronze, Jersey Buff and crossbred poults are presented in Table 1. A summary of the estimated thyroxine secretion rates on a per bird per day basis, body weight basis and for sexes for each group is presented in Table 2. Under the conditions of this experiment the daily thyroxine secretion rate of the Broad-Breasted Bronze male was 10.26 ng. per day or 2.71 ng. per 100 grams body weight. The females of this group appeared to secrete thyroxine at the rate of 10.03 fig. per day or 2.73 fig. per 100 grams body weight. Any sex difference in the thyroxine secretion rate is not apparent in these data for the BroadBreasted Bronze. The secretion rate per day for the smaller sized Jersey Buff poults was estimated at 8.56 fig. and 9.0 Hg. for males and females respectively, and at the rate of 2.62 fig. for males and 2.89 fig. for females per 100 grams body weight. A sex difference, although not statistically significant, favors the female which is similar to the results for growing chickens (Schultze and Turner, 1945) and growing ducks (Biellier and Turner, 1950).
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Jersey Buff, Broad-Breasted Bronze and crossbred poults were hatched on June 20 and sexed at this time by a commercial chick sexer. The crossbred poults were produced from reciprocal crosses of the two pure varieties studied. The poults were kept in a 16 compartment, 4-deck starting battery under a system of continuous lighting. The temperature under the hover portion of each compartment varied between 90 and 95°F. during the course of the experiment. The method used to determine the thyroxine secretion rate was the same as that used by Dempsey and Astwood (1943) with rats and applied to chickens by Mixner, Reineke and Turner (1944), Schultze and Turner (1945) and others. At hatching time 100 Jersey Buff poults were divided on the basis of body weight into five sub-groups. Each sub-group contained half males and half females. The 108 Broad-Breasted Bronze poults and the 54 crossbred poults were also assigned to five sub-groups by the same method. Each separate group had a control subgroup which received a conventional turkey starter ration, while the other four sub-groups were fed the same ration to which 0.1 percent thiouracil had been added. Three of the sub-groups of each group receiving the thiouracil ration were injected subcutaneously every day with three graded levels of d,l-thyroxine. These three levels were 5, 10 and 15 fxg. per day. The d,l-thyroxine solutions were prepared by dissolving the crystalline material in dilute alkali. This solution was then diluted with distilled water so that each
0.1 ml. of solution contained the daily dosage of thyroxine. At the end of three weeks, the poults were weighed and then killed and the thyroid glands immediately removed. The glands were quickly weighed on a milligram balance. The thyroid weights per 100 gm. body weight were then plotted against the amount of d,l-thyroxine injected daily in order to estimate the amount of thyroxine necessary to counteract the effects of the thiouracil. This amount is considered to represent the daily thyroxine secretion rate of the poults.
609
THYROXINE SECRETION RATE or POULTS TABLE 1.—Thyroid secretion rale of 0-3 weeks of age Broad-Breasted Bronze, Jersey Buff and B.B.B.XJ.B. crossbred turkey poults Females
Males Treatment sub-group
Thyroid wt/100 gm. body wt. in mg.
18.7 100.3
5.10 45.77
376
77.7
20.65
7
363
18.5
.5.09
8
333
Ave. body wt. in gms.
9 12
379 224
Group I—Broad-Breasted Bronze 13 367 16.6 4.38 8 219 67.2 30.01
11
338
41.4
12.25
10
10
399
20.8
4.61
9
355
1.42
Ave. thyroid wt. in mg.
Thyroid wt./lOO gm. body wt. in mg.
5.02
No. of poults
Ave. body wt. in gm.
4.82
1.45
d,l-thyroxine per ]poult = 10.26 Mg- per day d,l-thyroxine per ]poult=10.03 Mg. per day d,l-thyroxine/100 gm. body wt. = 2.71 Mg- d,l-thyroxine/100 gms. body wt. = 2.73 Mgper day per day Normal controls 0.1% thiouracil 0.1% thiouracil+5 Mg. thyroxine 0.1% thiouracil+10 Mg. thyroxine 0.1% thiouracil+15 Mg. thyroxine
9 6
327 175
17.3 71.4
Group II—-Jersey Buff 8 311 5.25 12 166 40.73
7
279
28.9
10.36
9
10
292
10.7
3.67
261
4.8
1.83
7 .
18.2 79.4
5.85 47.90
263
38.7
14.72
9
272
11.5
4.25
10
265
4.7
1.77
d,l-thyroxine per poult=8.56 Mg. per day d,l-thyroxine per poult = 9.0 Mg. per day d,l-thyroxine per 100/gm. body wt.=2.62 d,l-thyroxine per 100/gm. body wt. = 2.89 Mg. per day <«g- per day Normal controls 0.1% thiouracil 0.1% thiouracil+5 fig. thyroxine 0.1% thiouracil+10 Mg- thyroxine 0.1% thiouracil+15 Mg. thyroxine
6 5
369 199
Group III—B.B.B.XJ.B. 4.52 16.7 44.05 87.5
5
337
63.2
18.78
5
356
21.0
5
373
9.36
crossbreds 330 6 192 6
18.2 67.9
5.49 35.43
4
257
36.0
14.02
5.89
5
305
15.4
5.03
2.51
5
280
5.88
2.10
d,l-thyroxine per poult = 11.0 Mg. per poult d,l-thyroxine per poult = 9.8 Mg- per poult per day per day d,l-thyroxine per 100/gm. body wt. = 2.98 d,l-thyroxine per 100/gm. wt. = 2.97 MgMg. per day per day
This sex difference was reversed in the case of the crossbred poults where the secretion rate per day was estimated at 11.0 ixg. per poult for the males and 9.8 fig. for the females. However, this difference disappeared when the data were converted to the thyroxine secreted per 100 grams body weight per day, or 2.98 fig. for the males and 2.97 fig. for the females. When the thyroxine secretion rates
for the three groups were compared, the crossbreds secreted slightly more thyroxine per bird per day and significantly more thyroxine per 100 grams body weight than did the other two groups. The percentages that the secretion rates of the other two groups are' of that of the crossbreds are presented in Table 2. When sexes are combined for each group, the secretion rate of Jersey Buff poults was
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Normal controls 0.1% thiouracil 0.1% thiouracil+5 Mg. thyroxine 0.1% thiouracil+10 Mg. thyroxine 0 . 1 % thiouracil+15 Mg. thyroxine
Ave. thyroid wt. in mg.
No. of poults
610
J. ROBERT SMYTH, JR., AND THOMAS W. F O X
92.6 percent and that of the Bronze 91.4 percent of the crossbred value. The untreated females of all three groups of tukeys had larger thyroid glands than did the males of their respective group when thyroid weight was considered either as a function of body weight or on a per bird basis. The average thyroid weight for all females was 5.41 mg. per 100 grams body
been previously reported. Schultze and Turner (1945) reported that the thyroids of the White Rock chicken female were heavier than were those of the male at five weeks of age. Recently Biellier and Turner (1950) found the same sex relationship to exist for White Pekin ducks. When all poults of the thiouracil treated Broad-Breasted Bronze and Jersey Buff groups are combined, the resulting hyper-
Thyroxine secretion rate— Group
No. of poults and sex
Crossbreds
Males—26 Females—26 Both—52
11.00 9.80 10.40
Jersey Buff
Males—39 Females—48 Both—87
8.56 9.00 8.78
77.8 91.8 84.4
2.62 2.89 2.755
87.9 97.3 92.6
Broad-Breasted Bronze
Males—51 Females—46 Both—97
10.26 10.03 10.15
93.3 102.3 97.6
2.71 2.73 2.72 .
90.9 91.9 91.4
Micrograms per bird
weight, as compared to an average weight of 4.74 mg. per 100 grams body weight for the male thyroids. The average female thyroid weight was 18.4 mg., while those of the male averaged 16.9 mg. in weight. Blakely, Anderson and MacGregor (1949) reported in an abstract that a sex difference in the relative size of the thyroid as a function of body weight was noted in three week old turkey poults, but they did not point out whether the male or the female had the larger thyroids. However, previously Blakely and Anderson (1949) found that the thyroid glands of nine week old male turkeys were considerably heavier than were those of the females. When this difference is considered on a basis of weight per 100 grams body weight, it was only .18 mgs. in favor of the males. That the females of a species have larger thyroids than do the males has
Percent of crossbred level 100 100 100
Micrograms per 100 gm. body wt. 2.98 2.97 2.975
Percent of crossbred level 100 100 100
trophy of the thyroid glands per 100 grams body weight was approximately eight times that of the size of the thyroids of the control poults. This increase is intermediate between the three to fivefold increase reported for young growing chickens and the ten-fold increase found in two week old ducks by Hoffmann (1950). Blakely and Anderson (1949) found that the thyroid weights of nine week old poults fed thiouracil for three weeks increased six times over the weight of the control glands. This may represent the effect of increasing age on the degree of thyroid compensation to thiouracil induced thyroid inhibition as Schultze and Turner (1945) noted that older chicks tended to attain less thyroid enlargement when compared to the control size than did younger chicks following thiouracil treatment. This same relationship of com-
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TABLE 2.—-Summary of the thyroxine secretion rale for Broad-Breasted Bronze, Jersey Buff and crossbred turkeys
THYROXINE SECRETION RATE or POULTS
The effects of thiouracil fed at 0.1 percent level in the mash had a more marked effect on the growth rate of 0-3 week old turkeys than for any other avian species studied. The thiouracil treated sub-groups of poults were all 40 to 46 percent smaller at the end of the experiment than were the corresponding control sub-groups. No interaction between sex and thiouracil inhibition of growth was evident in the
present study. Using the 0-3 week data of Bielleir and Turner's (1950) study with ducks and combining the body weights of both sexes, the controls are seen to weigh approximately 12 percent more than the thiouracil fed ducks. Hoffmann (1950) also pointed out that the reduction in rate of growth for the 0-2 week old thiouracil treated ducks in his experiment was much greater than that observed previously in chickens. The data of Schultze and Turner (1945) show little effect of 'thiouracil on the early growth rate of chickens. DISCUSSION In order to compare the intergeneric thyroxine secretion rates and the relationships of thyroid activity to growth rate, it is important to know the comparative growth rates of chickens, ducks and turkeys. Milby and Henderson (1937) found that the growth rate of ducks was more rapid than that of chickens and turkeys during the period of growth preceding the major inflection of the growth curve. They employed the equation, W=Akt, established by Brody (1927) for this purpose. However, Milby and Henderson found that the chicken and the turkey grow at approximately the same rate during this period. The growth of the Bronze and White Holland turkeys studied by these investigators was less rapid than would be expected for average stock. In the present investigation we are primarily interested in the comparative growth rates during the one to fourweek growth period. The turkey growth data used by Milby and Henderson does not consider the growth during the first six weeks following hatching. The growth rates of different species are not easily compared. Brody (1927) has pointed out that the segment of the growth curve which precedes the major inflection consists of a number of epochs, each of which
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pensation to age can be demonstrated from the data on ducks of Biellier and Turner (1950). The females of the non-crossbred lots of poults showed a thiouracil induced increase in thyroid size of 8.6 times over the control females. A similar increase of 7.3 times was found for the treated males over the thyroid weights of the control males. This agrees with the results of Schultze and Turner (1945) who found that, in practically all cases, female chicks showed greater thyroid enlargement per 100 grams body weight than did the males. There is a similar tendency in favor of the females of the growing duck (from data of Biellier and Turner, 1950) but it is not exhibited until after the 0-3 week assay period. In connection with this, it has been shown that estrogens and thiouracil exhibit a synergistic effect on thyroid enlargement. Andrews and Bohren (1947), Selle and Selle (1948) and Detwiler, Andrews and Bohren (1950) all found that stilbestrol and thiouracil induced greater hypertrophy of the thyroid gland in growing chickens than did thiouracil alone. The reverse relationship between sex and thiouracil induced enlargement of the thyroids of the crossbred poults is not easily explained. Although the number of poults in each sub-group of the crossbred group were small, the greater enlargement of the male thyroid was also found in the sub-groups which were receiving 5 and 10 fig. of thyroxine daily in addition to the thiouracil feed.
611
612
J. ROBERT SMYTH, JR., AND THOMAS W. FOX
Since ducks, turkeys and chicks all appear to be in the same early epoch of growth during the first few weeks following hatching, it would seem valid to compare their thyroxine secretion rates when body weights are as near similar as possible. The thyroxine secretion rate of 0-2 week old ducks was reported by Hoffmann (1950) to be 18.7 ng. per bird per day or 3.8 ng. per 100 grams body weight.
By combining the thyroxine secretion rates of the Jersey Buff and Bronze poults used in this study, the resulting figures of 9.46 /ug. per bird or 2.74 ng. per 100 grams body weight are obtained. These values indicate that the thyroxine secretion rate of the young growing turkey is lower than that of the young duck. However, this difference should be lessened if the advantage of weight for the ducks were eliminated, since Schultze and Turner (1945) have previously shown a rather close correlation between body weight and thyroxine secretion rate. White Plymouth Rock chicks of comparable size were found by these investigators to secrete 8.42 ixg. of thyroxine per day or 2.20 fig. per 100 grams body weight. Therefore, the thyroxine secretion rate of the young growing turkey would appear to be intermediate between that of ducks and chickens of similar size and age. Since growth rate data to four weeks of age were available for the three groups of turkeys studied, they can be compared to the results of the thyroxine secretion rate data. When growth rate was calculated by the formula -(lOOWi-Wd/Wu the crossbred, Jersey Buff and Bronze poults increased their weights at the rates of 257, 246, and 236 percent respectively during the one to three-week growth period. It is interesting to note that this group order of difference is identical to the results of the thyroxine assay. It would be desirable to know how this relationship compares with the rate of growth throughout the complete developmental period. That a close association exists between rate of growth and thyroidal activity in domestic birds has been previously pointed out (Schultze and Turner, 1945; Hoffmann, 1950). The fact that the relationship between the early growth rates of ducks, turkeys and chickens and the
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showed a constant rate of growth. Different species have characteristic epochs of growth which are correlated with the age of the individual. Therefore, at a given age two species may be in different epochs of growth. This difficulty is largely removed when comparisons are made between the growth rates of chickens and turkeys between the ages of one and three weeks, as both appear to be in their first growth epoch. One to three-week weights accumulated at this station for Broad-Breasted Bronze and Jersey Buff turkeys and a broiler strain of chickens were compared by use of the formula, percent rate of growth = 100(1^2— Wi)/W\. The percent increase in body weight between the ages of one and three weeks equaled 246 percent, 236 percent and 104 percent for Jersey Buff poults, Bronze poults and broiler chicks respectively. This same relationship holds true if the log poult and chick weights are plotted against age in weeks. By this method, the relative growth rate is directly proportional to the slope of the curves. Calculated slope or two-point ratio values in logarithms give results similar to the percent increase figures above. Therefore, in this study, the early post-embryonic increase in body size for the turkey is considered to be greater per week than for the chicken. The differences are even more marked, if the comparison includes growth data of the Rhode Island Red or similar "heavy" egg production breeds or strains.
THYROXINE SECRETION RATE OF POULTS
The higher thyroxine secretione rat of crossbred poults, as compared to the results found for offspring of the two parent turkey varieties, tends to substantiate the suggestion of Mixner and Upp (1947), who concluded from their chick data, that there was an association between hybrid vigor and thyroidal activity.
Their differences were in favor of doublecross inbred-hybrids in comparison to single-cross hybrids and crossbreds. These investigators did not compare the crossbred chickens used in their study with chicks from the stock used to make the cross. If thyroxine secretion rate is a measure of vigor or hybrid vigor, the results of this study would indicate that cross-breeding in turkeys could be employed to obtain heterosis. There is a possibility that the thyroxine secretion rates estimated in the present study are all lower than they would have been if the experiment had been conducted Earlier during the breeding season. It is commonly thought that late hatched poults are less vigorous than are those hatched earlier, Also, unpublished data from this station indicate that poults from breeders who have been in production for three or four months have less viability and a slower growth rate. This phenomena appears to be independent of the time of year. SUMMARY
The thyroxine secretion rates of 0—3 week old Jersey Buff, Broad-Breasted Bronze and crossbred poults were found to be intermediate between previously reported rates for chicks and ducks of similar weight and age. The secretion rates were estimated to be 10.15 /ug. per poult daily or 2.72 ng. per 100 gms. body weight daily for the Bronze poults; 8.78 ng. per poult or 2.76 ng. per 100 gms. body weight for the Jersey Buffs; and 10.40 Mg- per poult or 2.98 jug- per 100 gms. body weight for the crossbred poults. Although sex differences in the secretion rate of thyroxine were inconsistent, a marked sex difference was observed in regards to the compensatory hypertrophy of the thyroid gland following thiouracil administration at a 0.1 percent level in the feed. The females responded by great-
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estimated levels of thyroxine secretion rates of these species both show the same relative differences is added evidence for the growth rate-thyroxine secretion level relationship. This study does not answer the question of whether thyroxine stimulates growth in avian species, or whether the secretion rate is determined by the inherent growth rate. The thyroid gland may merely respond to the already determined needs of the growing tissues for thyroxine or thyroglobulin. From thyroxine secretion rate data and growth pattern observations in chickens and ducks Hoffmann (1950) made an interesting speculation concerning the possible role of the thyroid in skeletal maturation. This worker pointed out that since exogenous thyroxine accelerates skeletal maturation in growing rats and mice, while thiouracil treatment retards epiphyseal fusion, thyroxine may first stimulate skeletal growth and eventually inhibit it. However, the turkey has an early thyroxine secretion rate intermediate between that of the chicken and the duck but cessation of skeletal growth occurs comparatively later. Unfortunately, no data is available concerning the thyroidal activity of the turkey throughout the growing period. If the present, apparent, intergeneric differential rate of thyroxine secretion persists, the normal importance of the role of the thyroid in skeletal growth becomes questionable. Undoubtedly gonadal activity and its interrelationships with the thyroid and other endocrine glands play a major role in skeletal maturation.
613
614
N E W S AND NOTES
REFERENCES Andrews, F . N., and B. B. Bohren, 1947. Influence of thiouracil and stilbestrol on growth, fattening, and feed efficiency in broilers. Poultry Sci. 26: 447-452. Biellier, H. V., and C. W. Turner, 1950. The thyroxine secretion rate of growing White Pekin ducks. Poultry Sci. 29: 248-257. Blakely, R. M., and R. W. Anderson, 1949. The influence of thiouracil on growth, fattening, feed
consumption and thyroid weight of turkey broilers. Poultry Sci. 28:185-188. Blakely, R. M., R. W. Anderson and H. I. MacGregor, 1949. Determination of thyroxine secretion rate of turkey poults. Poultry Sci. 28: 757. Brody, S., 1927. Growth and development. I I I . Growth rates, their evaluation and significance. University of Missouri Ag. Exp. Sta. Res. Bull. 97. Dempsey, E. W., and E. B. Astwood, 1943. Determination of the rate of thyroid hormone secretion at various environmental temperatures. Endocrinology 32:509-518. Detwiler, R. W., F. N. Andrews and B. B. Bohren, 1950: The influence of thiouracil and stilbestrol on broiler quality. Poultry Sci. 29: 513-519. Glazener, E. W., C. S. Shaffner and M. A. Jull, 1949. Thyroid activity as related to strain differences in growing chickens. Poultry Sci. 28: 834849. Hoffman, E., 1950. Thyroxine secretion rate and growth in the White Pekin duck. Poultry Sci. 29: 109-114. 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. Schultze, A. B., and C. W. Turner, 1945. The determination of the rate of thyroxine secretion by certain domestic animals. University of Missouri Ag. Exp. Sta. Res. Bull. 392. Seele, J. E., and R. M. Seele, 1948. Effect of diethylstilbestrol on the thyroid glands of chicks receiving thiouracil. Science 107:394-395.
News and Notes {Continued from page 606)
member of the staff of the Poultry Department and Secretary-Treasurer of the Poultry Science Association, won the allround judging honours at the 27th annual Mid-west Intercollegiate Judging Con-
test held in Chicago in November. Nineteen teams competed. The Kansas team won the Institute of American Poultry Industries' trophy for the third time which gives them permanent possession.
(Continued on page 620)
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er thyroid enlargement in the Jersey Buff and Bronze groups, while the reverse was found in the crossbred group. These differences were also present in the subgroups receiving 5 and 10 ng. d,l-thyroxine daily. Further confirmatory evidence was obtained for the previously reported relationship between thyroidal activity and rate of body growth. It was shown that the thyroxine secretion rates of young growing chicks, turkeys and ducks are correlated with their respective growth rates. A comparison of the differences in 1-3 week growth rates of the three groups of turkeys studied and their thyroxine secretion rates also substantiate this relationship. Crossbred offspring were found to have a higher rate of thyroxine secretion than did pure offspring from the two parent varieties. This is interpreted as evidence for the existence of hybrid vigor for the progeny of this varietal cross.