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Selection for Chick Comb Weight with Androgen and Gonadotrophin Stimulation
PROTEIN AND LYSINE REQUIREMENTS
periment, but depressed growth in another. With the corn-soybean-fish meal rations used in these studies, female turkeys required no more than 18% protein from 8-12 weeks of age, 16% protein from 12-16 weeks of age, and 14% protein from 16-20 weeks of age. Male turkeys required higher levels of protein than the females.
Balloun, S. L., 1962. Lysine, arginine and methionine balance of diets for turkeys to 24 weeks of age. Poultry Sci. 4 1 : 417-424.
Balloun, S. L., and R. E. Phillips, 1957. Lysine and protein requirements of bronze turkeys. Poultry Sci. 36: 884-891. Jensen, L. S., L. H. Merrill, C. V. Reddy and J. McGinnis, 1962. Observations on eating patterns and rate of food passage of birds fed pelleted and unpelleted diets. Poultry Sci. 4 1 : 1414-1419. Kratzer, F. H., P. N. Davis and B. J. Marshall, 1956. The protein and lysine requirements of turkeys at various ages. Poultry Sci. 35: 197202. Reddy, C. V., L. S. Jensen, L. H. Merrill and J. McGinnis, 1962. Influence of mechanical alteration of dietary density on energy available for chick growth. J. Nutrition, 77: 428-432.
Selection for Chick Comb Weight with Androgen and Gonadotrophin Stimulation K. E. NESTOR AND R. G. JAAP Ohio Agricultural Research and Development Center, Columbus, Ohio (Received for publication December 10, 1964)
T
HE gonadotrophins and sex hormones are intimately involved in many important physiological processes, especially those concerned with reproduction. Undoubtedly, the genetic control of many of these processes is mediated, at least in part, through the gonadotrophins and sex hormones. Therefore, knowledge of the genetic control of production of, and response to, gonadotrophins and sex hormones is of great importance. The weight response of a target organ to a constant amount of a hormone may be influenced by two factors: (1) the amount of target organ tissue present upon which the hormone can act (Casida et al., 1952; and Jaap and Robertson, 1953); and (2) the sensitivity of the target organ tissue to the hormone. Comb weight of the young chick is highly heritable. Jaap et al. (1961) found the heritability of comb weight, as estimated
by covariance between full brother families, to be 0.76 and 0.68 at hatching and at 11 days of age, respectively. The additive genetic variance, based on analysis of diallel matings, was high at hatching but low at 11 days of age. Genetic differences in the sensitivity of the comb to androgens (Dorfman and Dorfman, 1948; and Jaap and Robertson, 1953) and to the injection of gonadotrophins (Munro et al., 1943) also exist. The heritability of comb weight in 11-day old chicks given a constant amount of either androgen or gonadotrophin is high, a large part of which is due to additive genetic variance (Jaap et al., 1961; and Jaap, 1962). At a similar age, Campos and Shaffner (1952) found that the heritability of comb weight of chicks treated with both androgen and estrogen to be low. Siegel and Siegel (1964 a,b) observed significant sire differences in the response
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REFERENCES
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K. E. NESTOR AND R. G. JAAP
MATERIALS AND METHODS
The base population for all of the selected lines was the North Central Regional Randombred White Leghorn (RL), designated as the U. S. A. Regional Randombred White Leghorn in the original report by Jaap (1962). Also, RL has been maintained as a randombred control population. The three hormone-response selected populations (Jaap, 1962) have been continued for five additional generations, seven in all. The selection criterion has been the weight response of the 10-day chick comb regressed to a constant body weight within each hatch and sex group. Chicks of two of the selected populations were injected subcutaneously with 2.5 mg. of testosterone propionate in sesame oil solution on the fifth and eighth days after hatching. One line, HTP, was selected for high and the other, LTP, for low
comb-weight response within sex at 10 days of age. The third population, PMS, has been selected for a high comb-weight response in male chicks subcutaneously injected with a constant amount of pregnant mares' serum gonadotrophin*. Each male chick received 2.5 Cartland-Nelson (1952) units on each of the fifth through the eighth days of age. Males were individually selected for highest comb-weight response at 10 days of age while females were selected on the basis of a superior response of their brothers. A system of paired matings, adapted from Gowe et al. (1959) and described by Jaap (1963), was used to reproduce the three selected lines and the randombred control. With this system, 40 pairs of males and females were mated, within all lines, by means of artificial insemination. The matings in all lines were at random with the exception that full sib matings were avoided. All lines were reproduced as soon as they attained an egg production of approximately fifty percent. To reproduce the RL control, two male and two female chicks were randomly selected from the offspring of each parental pair in an attempt to have one male and one female from each pair present at reproductive age. Some of the pairs, however, were not represented each generation due to mortality of their offspring or to a lack of reproduction by these pairs. In these cases, offspring were randomly selected from other families in order to keep the number of sires and dams constant at 40 of each sex. Approximately 55 progeny of each sex * The pregnant mares' serum gonadotrophin was obtained from The Upjohn Company, Kalamazoo, Michigan (Gonadogen) in generations 1 through 4 and from Organon, Inc., W. Orange, New Jersey (Gestyl-Organon) in generations five through seven.
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to various gonadotrophin preparations. Heritability of testes weight response to avian pituitary homogenates was estimated to be 0.24 from paternal half sib correlations. Similar estimates were obtained for response to equine LH and ovine LH. Heritability estimates for the response to equine FSH varied with the dosage employed. Jaap (1962), in a preliminary paper, reported the establishment of lines showing both high and low comb-weight response to testosterone propionate and high combweight response of male chicks to pregnant mares' serum gonadotrophin. The purpose of the present experiment was to determine the changes occurring in these lines with further selection and to determine if the difference between the lines was due to changes in size of the comb of non-treated chicks or to changes in sensitivity of the lines to the hormones, or to both.
SELECTION FOR COMB WEIGHT
RESULTS AND DISCUSSION
Genetic Variance in Comb-Weight Response to Androgen and Gonadotrophin. Heritability of comb-weight response to testosterone propionate in HTP and LTP and to pregnant mares' serum gonadotrophin in PMS was estimated in generations three through six. The method of parentoffspring regression was selected as the most desirable, since the magnitude of heritability estimates obtained in this way are not influenced by the use of selected parents (Falconer, 1961). Each regression was determined by repeating the parental record with each offspring value. This procedure was found by Bohren et al. (1961) to have greater precision than regressing the offspring mean on the parental value. In the case of the response to gonadotrophin, the regression of male offspring on male parent was used since the response was only measured in males. The regression was determined
within sex for the response to testosterone propionate due to an inequality of the comb-weight variance in the two sexes. The influence of body weight on the comb-weight response was removed prior to calculating the regressions. This was done by adjusting each individual comb weight to the mean body weight of each sex-hatch group. The deviations of adjusted comb weight values from their sex-hatch group means were the values used in determining the regression coefficients. This procedure should minimize the influence of hatch differences on the heritability estimates. The regression of offspring on parent contains one-half of the additive genetic variance (Falconer, 1961). Therefore, to estimate heritability in the narrow sense, the regression coefficient was doubled. Standard errors of the heritability estimates were determined by the method of Van Vleck et al. (1960). The heritability estimates of the combweight response to testosterone propionate are given in Table 1. The number of comparisons ranged from 132 to 241 per generation in HTP and from 166 to 269 in LTP. The generation estimates were quite variable. Based on all comparisons over the four generations, the comb-weight response was more heritable in the upward direction (HTP) than in the downward direction (LTP). This was partially due to the decline in the size of the estimate obtained in LTP in the last generation. The heritability estimates found in this study for the HTP agree closely with those reported by Jaap et al. (1961) and Jaap (1962) but not with the one reported by Campos and Shaffner (1952). However, Campos and Shaffner injected their chicks with both testosterone propionate and diethylstilbestrol. The heritability estimates of comb-
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were selected each generation in the HTP and LTP so that 40 pairs of parents would be available at reproductive age. The individuals in these lines having the highest selection differentials among those present at sexual maturity were used as parents. The proportion of offspring used to reproduce the HTP and LTP ranged from 21.2 to 25.4 percent and from 17.2 to 22.5 percent, respectively. The proportion of male offspring used to reproduce the PMS ranged from 18.5 to 23.4 percent. In this line, the males having the highest selection differentials were used to reproduce the line with the exception that a maximum of five males from one family was used. Female offspring from approximately one-half of the available families (34-38) were used as breeders. A maximum of five females was used from each family.
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K. E. NESTOR AND R. G. JAAP
TABLE 1.—Heritability estimates (h2) of comb-weight response to testosterone propionate and their standard errors h 2 ± Standard Error Generation
HTP Sire-male offspring
3 4 5 6 3 through 6
0.084 + 1.402 + 0.689 + 0.293 + 0.364 +
0.138 0.243 0.379 0.196 0.123
Dam-female offspring 0.257 + 0.965 + 0.708 + 0.633 + 0.528 +
0.117 0.345 0.101 0.160 0.097
0.441+0.079
weight response to gonadotrophin were also quite variable (Table 2). The estimate based on all data, 0.424 ± 0.108, is probably the most reliable since it was based on a larger number of observations and since there was no apparent trend in the magnitude of the estimate in successive generations. Non-additive genetic and/or maternal effects on the response of the male's comb following injection of gonadotrophin may be large. Much higher heritability estimates of 0.9S and 0.80 were obtained by Jaap et al. (1961) and Jaap (1962) from the covariance among full brothers in other populations. Jaap (1962) reported that the heritability of combweight response to gonadotrophin, as estimated from the sire component of the variance, was 0.42 in RL. Selection Response and Realized Heritabilities in HTP and LTP. The combweight response of testosterone-treated TABLE 2.—Heritability estimates (A2) of the combweight response to pregnant mares' serum gonadotrophin in PMS and their standard errors Generation 3 4 3
6 All data
No. of comparisons 171 213 208 188 780
h 2 ± Standard error 0.034 + 1.143 + 0.264 + 0.533 + 0.424 +
0.318 0.343 0.191 0.161 0.108
Sire-male offspring 0.220 + 0.789 + 0.927 + 0.136 + 0.285 +
0.114 0.216 0.538 0.173 0.099
Dam-female offspring 0.230 + 0.116 0.368 + 0.235 0.287 + 0.522 0.056±0.260 0.239 + 0.126
0.270 + 0.077
HTP and RL chicks is presented in Table 3. The linear regression coefficient of unadjusted comb weight (mg.) on generations was 38.4 and 26.8, respectively, in HTP males and females. A positive trend was present in the RL control, since the regression coefficients for males and females of this line were 9.1 and 5.8 respectively. After adjusting for the apparent positive trend in the environment, by subtracting, within sex, the RL coefficients from those of HTP, the regression coefficients for HTP were 29.3 and 21.0, respectively, for males and females. Similar regression coefficients were observed when combweight response was adjusted for differences in body weight by covariance analysis. The comb-weight response of LTP and its RL control is given in Table 4. The regression coefficients of comb-weight response of LTP on generations was 1.3 and 0.5 for males and females, respectively. After adjustment for the improvement in environment, the regression coefficients of change per generation in LTP became — 7.8 and —5.3, respectively, for males and females. Based on comb weights adjusted for body weight difference, the LTP regression coefficients were —0.5 and — 0.1, respectively, for males and females. These values became —9.8 and —6.8 when adjustment was made for the posi-
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3 through 6, both sexes
LTP
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SELECTION FOE COMB WEIGHT TABLE 3.—Changes in the comb-weight response to testosterone propionate in I1TP Adjusted comb weights (mg.)1
Actual comb weight (mg.) Generation
3 4 5 6 7
HTP
RL
HTP-RL
Gain from selection
61.9 65.3 108.9 76.0 101.9
Males 98.4 108.6 175.2 164.2 231.3
66.9 68.0 95.2 76.7 107.7
31.5 40.6 80.0 87.5 123.6
9.1 39.4 7.5 36.1
67.4 58.1 89.4 67.4 91.7
Females 93.7 97.5 145.8 147.3 224.9
HTP
RL control
95.4 101.9 199.5 163.0 208.1
—
3 4 5 6 7
90.4 91.1 159.7 138.8 200.2
71.3 61.1 86.3 73.7 100.3
—
22.4 36.4 59.5 73.6 124.6
14.0 23.1 14.1 51.0 102.2
Total
1 Comb weights were adjusted to a constant body weight of 79 grams by the use of the linear regression coefficient of comb weight on body weight.
tive environmental trend of the RL control. The gain from selection was higher in HTP (Table 3) than in LTP (Table 4). The total gains in HTP in generations three through six, as measured by the increase in size of the deviation from RL control (HTP-RL), was 92.1 and 102.2 TABLE 4.--Modification
milligrams, respectively, for males and females. In LTP, the total gain was —32.4 and —28.6 milligrams in males and females respectively. In order to determine whether the LTP was reaching a physiological barrier (i.e., minimum comb weight under stimulation), the frequency distribution for comb
:e to testosteronepropionate in LTF > i of comb-•weight •espons Adjusted comb weights (mg.)1
Actual comb weight (mg.) Generation
3 4 5 6 7
LTP
RL
47.9 43.8 75.1 47.7 51.8
61.9 65.3 108.9 76.0 101.9
LTP Males 54.5 45.3 62.3 44.8 52.9
RL
LTP-RL
Gain from selection
66.9 68.0 95.2 76.7 107.7
-12.4 -22.7 -32.9 -31.9 -44.8
-10.3 -10.2 + 1.0 -12.9
Total 3 4 5 6 7 Total
—
-32.4 47.8 43.3 61.5 44.4 49.9
67.4 58.1 89.4 67.4 91.7
Females 50.5 43.8 54.6 44.2 50.9
71.3 61.1 86.3 73.7 100.3
-20.8 -17.3 -31.7 -29.2 -49.4
—
+ 3.5 -14.4 + 2.5 -20.2 -28.6
1 Comb weights were adjusted to a constant body weight of 79 grams by the use of the linear regression coefficient of comb weight on body weight.
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92.1
Total
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K. E. NESTOR AND R. G. JAAP
ferential were determined. The intended selection differential was defined as the superiority of the parental values over the mean of the population from which they were selected. The actual selection differential was taken as the intended selection differential of each parent weighed according to the number of offspring produced. If natural selection is an important factor opposing artificial selection, the actual selection differential should be less than the intended selection differential (Falconer, 1961). The intended and actual selection differentials were essentially the same in both HTP and LTP (Table 5), indicating that natural selection did not oppose the selection practiced in these lines to a great extent. The magnitude of the selection differential is positively correlated with the amount of phenotypic variance (Falconer, 1961). The selection differentials were higher in males than in females for both HTP and LTP. This is a reflection of the larger phenotypic variance of comb-weight response in males. The selection differentials were larger in HTP than in
TABLE 5.—Selection differentials and realized heritabilities in HTP and LTP Selection differential (mg.) Generation
•
M
F
Ave.
M
F
3 4 5 6 Average
30.9 50.2 49.9 71.7 50.7
25.5 33.5 33.4 48.0 35.1
28.2 41.8 41.6 59.8 42.8
HTP Line 25.1 29.6 51.5 38.8 49.6 38.6 71.5 47.8 50.6 37.6
3 4 5 6 Average
12.4 15.5 14.5 21.7 16.0
13.5 13.9 12.5 18.0 14.5
12.9 14.7 13.5 19.8 15.2
LTP Line* 14.1 14.8 14.2 22.0 16.3
1 2
Selection response
Actual
Intended
12.8 14.5 12.5 18.2 14.5
(mg.)1
Realized heritability
Ave. 27.4 45.2 44.1 59.6 44.1
11.6 31.2 10.8 43.6 24.3
0.423 0.690 0.245 0.732 0.551
13.4 14.6 13.4 20.1 15.4
- 6.8 -12.3 + 2.8 -16.6 - 8.2
0.507 0.842 -0.209 0.826 0.535
Selection response was measured by the change in the deviations from RL control. All selection differentials in the LTP were negative.
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weights of treated chicks in LTP was determined in the sixth generation of selection. The mode was compared with the mean within sex. If the distribution were normal, the mode should equal the mean (Snedecor, 1959). The modes in the male and female distributions of comb weight were 48 and 43 milligrams, respectively, for males and females. The mean combweight response was S3 and 49 milligrams, respectively, for males and females. These results suggest that the frequency distributions were skewed toward the smaller comb weights. Similar results were obtained in the seventh generation. The distributions of comb weight in treated male and female chicks of LTP were analyzed for skewness by the methods of Snedecor (1959). This analysis established the presence of skewness in both sexes (P < .01) as was indicated by the comparison of the modes and means. These results suggest that LTP is reaching a physiological barrier even though selection response was relatively large in the last generation. Two measures of the selection dif-
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SELECTION FOR COMB WEIGHT TABLE 6.—Changes in the comb-weight response to pregnant mares' gonadotrophs in PMS
Adjusted comb weights (mg.) 1
Unadjusted comb weights (mg.) Generation
3 4 5 6
PMS
RL
PMS
RL
PMS-RL
Gain from selection
61.8 86.1 103.8 101.8
56.9 62.3 61.5 48.0
61.1 89.6 102.9 104.1
55.7 62.9 60.2 59.9
5.4 16.7 42.7 45.2
11.3 26.0 3.5 31.8 72.6
Total Adjusted to a constant body weight of 84 grams by covariance analysis.
negative regression coefucient of —5.2 mg. A similar situation was present when comb-weight response was adjusted for differences in body weight. The response to selection, as measured by the increase in the size of the deviation from the randombred control (PMS minus RL), was 72.6 milligrams for generations three through six. The actual and intended selection differentials for PMS parents did not differ greatly (Table 7) which indicates that natural selection was not an important factor opposing artificial selection. The selection differentials were lower in females than in males. The selection differentials for females were those for families, not individuals. The realized heritability of combweight response to gonadotrophin was high (Table 7). Since the female selection differentials were those of family averages, realized heritability would be expected to
LTP, which indicates that the variance in comb-weight response may be correlated with the mean comb-weight response. The greater selection differential in HTP was probably responsible for its greater gains from selection relative to LTP. Realized heritabilities were determined by dividing the selection response by the actual selection differential. Heritability of comb-weight response to testosterone propionate was essentially the same in HTP and LTP. Selection Response and Realized Heritabilities in PMS. The comb-weight response of PMS and RL male chicks to pregnant mares' serum gonadotrophin is given in Table 6. The linear regression coefficient of unadjusted comb-weight response (mg.) on generations was 5.8 mg. per generation in PMS. A downward trend was evident in the RL control, as indicated by a small
TABLE 7.—Selection differentials, selection response and realized heritabilities in PMS Selection differential (mg.)
3 4 5 6 Average 1
- Selection response - (mg-)1
Actual
Intended
Generation M
F
Ave.
M
F
Ave
38.1 43.0 42.7 49.9 43.4
17.7 11.8 12.0 16.2 14.4
27.9 27.4 27.4 33.0 29.8
28.6 42.2 42.3 54.5 41.9
14.0 12.2 12.0 16.3 13.6
21.3 27.2 27.2 35.4 27.8
11.3 26.0 2.5 31.8 17.9
Selection response was measured by the change in the deviation from RL control.
Realized heritability 0.531 0.956 0.092 0.898 0.643
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1
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K. E. NESTOR AND R. G. JAAP TABLE 8.—Sensitivity of response to testosterone propionate in IITP, LTP, RL and PMS
Line
HTP LTP RL PMS
Comb wt. (mg.)1 of untreated chicks
Comb wt. (mg.)1 of treated chicks
Sensitivity index2
Males
Females
Males
Females
Males
Females
61.3** 23.6** 35.1 53.3**
47.4** 23.6** 31.2 41.1**
138.6** 57.2** 66.1 84.8**
132.7** 59.3** 69.3 83.9**
292.4 160.2 211.8 206.3
280.0 174.2 222.1 204.1
1
be higher than that estimated from individual father-son regressions only (Table 2). Sensitivity of Response to Androgen. Jaap and Robertson (1953) found that the comb-weight response to testosterone propionate was strongly correlated with the initial size of the comb. In order to determine whether the response to selection in all three selected lines was due to changes in the size of the non-stimulated comb or sensitivity to androgen, or to both, a test was conducted using chicks from selected parents of the sixth generation of selection. Since gonadotrophin exerts its influence on the testes causing them to produce androgen which in turn produces comb growth, the changes in comb-weight response by selection in PMS could have been due to an increase in sensitivity of the testes to gonadotrophin or to an increase in the sensitivity of the comb to the androgen produced, or to both. Also, initial size of the comb of non-treated chicks in this line could have increased which would probably have resulted in a greater comb-weight response to gonadotrophin in PMS. A random sample of chicks from each of the four lines was injected subcutaneously with 2.5 mg. of testosterone propionate on each of the fifth and eighth days of age. Another sample of chicks from these lines was maintained as non-treated controls.
Both groups were reared intermingled in battery brooders. Comb weights of nontreated chicks of each selected population were compared with the RL control to determine whether selection had produced changes in the size of the non-stimulated comb. Sensitivity of response to testosterone propionate was measured by dividing the comb weight of treated chicks by the corresponding comb weight of untreated female checks within each line. This value was converted to percentage units by multiplying by 100. The untreated females' combs were used in preference to making the determination within sex because the comb of non-treated male chicks was, presumably, stimulated by endogenous androgen during the injection period. Comb weight of untreated chicks was larger in HTP and PMS, and smaller in LTP, than in RL control. This was true for both males and females (Table 8). These results indicate that the size of the non-stimulated comb was changed by selection in all the selected lines. The comb weights of treated PMS, HTP or LTP deviated in the same direction from the treated RL control as did the comb weights of non-treated chicks. The sensitivity of response (sensitivity index) was higher in HTP and Lower in LTP than in the RL control. Thus, selection for total weight of the comb in testosterone-treated chicks resulted in changes in both the
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Comb weights were adjusted to a constant body weight of 70 grams by covariance analysis. Sensitivity index was calculated within lines by dividing the comb weight of treated chicks by the untreated female comb weight and multiplying by 100. ** Indicates difference from RL control was highly significant (P<.01). 2
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SELECTION FOR COMB WEIGHT
weight of the non-treated and the testosterone propionate stimulated comb. Although PMS had a greater comb-weight response than RL, the combs of PMS were slightly less sensitive to androgen than those of RL.
TABLE 9.—Sensitivity of PMS and RL to
pregnant mares' serum gonadotrophin Untreated chicks (99)
Treated chicks
Line
PMS RL
No.
Comb weight (mg.i)
No.
84 102
24.2» 22.1
75 86
Comb weight (mg.)" 100.9** 48.6
Sensitivity index 2
416.9 219.9
1 Comb weights were adjusted to a constant body weight of 75 grams by covariance analysis. 2 Sensitivity index was calculated by dividing the comb weight of treated male chicks by that of untreated female chicks and then multiplying by 100. * Indicates that line difference was significant (P<.05). ** Indicates that line difference was highly significant (P<.01).
Line
No. of chicks -
Unadjusted weight of: Body
PMS RL
73 70
75.7 74.1
Comb 86.3** 48.3
Adjusted weight of:"
Testes
Comb
46.3** 37.2
85.7** 48.8
Testes 46.1** 37.2
1 Adjusted to a constant body weight of 75 grams by covariance analysis. ** Indicates deviation from RL control was significant at the 1 percent level of confidence.
Both comb and testes weight responses to gonadotrophin were greater in PMS than in RL controls. This was true for both unadjusted weights and weights adjusted to a constant body weight by covariance analysis. A histological study was made of a sample of testes from both lines. The sample from each line consisted of the testes from five males. The testes from both lines showed evidence of interstitial cell and seminiferous tubule stimulation by the gonadotrophin but there was no apparent difference between the lines in this respect. The results of this study indicate that the selection criterion, comb-weight response, in PMS was a composite one, influenced by unstimulated comb weight and sensitivity of response to gonadotrophin. The change in sensitivity to pregnant mares' serum gonadotrophin in PMS was apparently entirely due to changes in the ability of the testes to produce androgen when given a constant amount of the hormone, since the combs of PMS were slightly less sensitive to androgen than those of RL (Table 8). Inbreeding in the Various Lines. The change in inbreeding per generation, as measured by one-half the reciprocal of the effective number of parents (Falconer, 1961), for generations three through six is presented in Table 11. Inbreeding was the highest in PMS and lowest in the ran-
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Sensitivity of Response to Gonadotropin. The sensitivity of comb-weight response to gonadotrophin was determined in PMS compared with RL in the sixth generation of selection. A sample of male chicks from both lines was assayed in the usual manner. A sample of female chicks from the same parents was used as controls. Sensitivity of response was estimated by dividing the comb weight of the treated male chicks by the comb weight of the corresponding untreated female chicks and multiplying by 100. The comb weight of untreated PMS female chicks (Table 9) was significantly larger than that of the controls. The combweight response to gonadotrophin and the sensitivity of response was much greater in PMS than in RL. The increase in testes weights in PMS over the control chicks treated with gonadotrophin was compared for offspring of selected males and females from third generation parents. The chicks were assayed with gonadotrophin as in the preceding test. The results are presented in Table 10.
T A B L E 10.—Body, comb and testes weights of chicks from PMS and RL which were given a constant amount of gonadotrophin
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K. E. NESTOR AND R. G. JAAP
F/Generation
HTP LTP RL PMS
Accumulated F
Generation
Line 3
4
5
6
1.89 0.87 0.35 1.20
0.85 1.21 0.37 2.09
1.18 1.56 0.37 1.19
0.73 0.73 0.42 0.81
4.65 4.37 1.51 5.29
dombred control (RL). However, inbreeding was not high in any line. These results, along with those presented by Jaap (1963), demonstrate that the paired mating system employed in this experiment was effective in keeping the inbreeding at a relatively low level. Therefore, changes due to inbreeding and genetic drift were probably negligible.
SUMMARY
Three populations originating with the North Central Regional Randombred Leghorn (RL) were selected for seven generations for response of the chick's comb to hormone stimulation prior to 10 days of age. Male chicks of selected population PMS were selected for a high response to the gonadotrophin from pregnant mares' serum. Testosterone propionate was the hormone used in HTP and LTP populations selected for high and low combweight response, respectively. Reproduction of each of the 4 lines was from 40 randomly-paired matings. The accumulated increase in the inbreeding coefficient, F, during generations 3 through 6 was 1.5, 5.3, 4.6 and 4.4 percent for RL, PMS, HTP and LTP, respectively. Highly significant comb-weight responses, as measured by deviations from
Influence of Body Weight on Combweight Response to Androgen and Gonadotropin. The results of this study indicate that there is a positive association between body weight and the comb-weight response to both androgen and gonadotrophin (Table 12). In chicks treated with testosterone propionate, the regression coefficients of comb weight response (mg.) on body weight (gm.) were highest in HTP and lowest in LTP with RL intermediate. While variance in body weight of all selected lines was similar to that of RL in early generations, the body weight vari-
TABLE 12.—The regression coefficients of comb weight (mg.) on body weight (gm.)+their standard errors in 10-day old chicks treated with testosterone propionate and pregnant mares' serum gonadotrophin Treated with: Testosterone propionate HTP
PMS gonadotrophin
LTP
M
F
M
1.48 + 0.32 1.98+0.39 2.34+0.81 3.09 + 0.84 3.22 + 0.52
0.89 + 0.37 0.95 + 0.52 2.58+0.61 2.17 + 0.52 3.46±0.40
0.83 + 0.24 0.52 + 0.14 1.01 + 0.20 0.82 + 0.12 0.44+0.14
RL F
0.59 + 0.10 + 1.12 + 0.32 + 0.46 +
M 0.20 0.14 0.21 0.17 0.08
PMS F
1.35 + 0.23 0.95 + 0.32 0.54+0.24 0.46+0.12 1.59 + 0.31 1.12 + 0.23 1.21±0.28 1.03 + 0.21 1.53 + 0.30 1.71 + 0.26
M 0.68 + 0.24 1.54+0.33 0.30 + 0.49 0.36+0.45 2.11 + 0.24
RL M 1.00 + 0.28 0.83 + 0.20 0.74+0.14 1.25 + 0.24 0.61 + 0.10
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ance of HTP chicks decreased in later generations. This could account for the significantly greater coefficient in the HTP (Table 12). The comb-weight variance appeared to be correlated with the mean in all lines. This could explain the line difference observed in the regression coefficients in androgen-treated chicks. However, on this basis, the regression coefficient of PMS should have been larger than that of RL when both lines were given gonadotrophin, which was not the case (Table 12).
TABLE 11.—Increase in inbreeding coefficient (&F) per generation and accumulated inbreeding coefficient (F) in generations 3 through 6
SELECTION FOR COMB WEIGHT
REFERENCES Bohren, B. B., H. E. McKean and Y. Yamada, 1961. Relative efficiencies of heritability estimates based on regression of offspring on parent. Biometrics, 17: 481-491. Campos, A. C , and C. S. Shaffner, 1952. The genetic control of chick comb and oviduct response to androgen and estrogen. Poultry Sci. 3 1 : 567-571. Cartland, G. F., and J. W. Nelson, 1952. The bioassay of mare serum hormone. Amer. J. Physiol. 122: 201-207. Casida, L. E., B. R. Casida and A. B. Chapman, 1952. Some differences between two strains of rats developed by selection to differ in their response to equine gonadotrophin. Endocrinology, 51: 148-151. Dorfman, R. I., and A. S. Dorfman, 1948. Studies
on the bioassay of hormones: The relative reactivity of the comb of various breeds of chicks to androgen. Endocrinology, 42: 7-14. Falconer, D. S., 1961. Introduction to Quantitative Genetics. Oliver and Boyd, London. Gowe, R. S., A. Robertson and B. D. H. Latter, 1959. Environment and poultry breeding problems. 5. The design of poultry control strains. Poultry Sci. 38: 462-471. Jaap, R. G., 1962. Genetics of the chick's response to gonadotrophin and androgen. Proc. 12th World's Poultry Congress, Sidney: 52-53. Jaap, R. G., 1963. Paired matings for control and selected populations of chickens. Poultry Sci. 42: 1027-1028. Jaap, R. G., and H. Robertson, 1953. The chick comb response to androgen in inbred Brown Leghorns. Endocrinology, 53: 512-519. Jaap, R. G., M. W. Murray and R. W. Temple, 1961. The genetic control of variance in comb and testes weights of young male chickens. Poultry Sci. 40: 354-363. Lerner, I. M., 1958. The Genetic Basis of Selection. John Wiley and Sons, Inc., New York. Munro, S. S., I. L. Kosin and E. L. McCartney, 1943. Quantitative genic-hormone interactions in the fowl. 1. Relative sensitivity of five breeds to an anterior pituitary extract possessing both thyrotropic and gonadotropic properties. Amer. Nat. 77: 256-273. Siegel, P. B., and H. S. Siegel, 1964a. Genetic variation in chick bioassays for gonadotrophins. I. Testes weight and response. The Virginia J. Sci. 15: 187-203. Siegel, H. S., and P. B. Siegel, 1964b. Genetic variation in chick bioassays for gonadotrophins. II. Histological and histochemical responses. The Virginia J. Sci. IS: 204-217. Snedecor, G. W., 1959. Statistical Methods. The Iowa State College Press, Ames, Iowa. Van Vleck, L. D., S. R. Searle and C. R. Henderson, 1960. The number of daughter-dam pairs needed for estimating heritability. J. Animal Sci. 19: 916-920.
NEWS AND NOTES NEBRASKA NOTES Dr. Theodore E. Hartung, formerly Associate Poultry Scientist, Poultry Section, Colorado Agricultural Experiment Station, Colorado State University, Fort Collins, has been appointed Head of the Department of Poultry Science, University of Nebraska, Lincoln.
He was born in Denver, Colorado, in 1929, and received a B.S. and a M.S. degree at Colorado State University in 1951 and 1953, respectively. In 1962 he received a Ph.D. at Purdue University, specializing in Food Technology. From 1951 to 1953 he was Instructor at Colorado State University (then Colorado A and M (Continued on page 1459)
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the RL control, were produced in all three selected populations. The responses were partly attributable to changes in the combweight of non-treated chicks and partly to changes in sensitivity of the chicks to the hormones. The greater comb-weight response in the PMS population was attributed to increased androgen production of the stimulated testes and not to an increase in androgneic sensitivity of the comb. Heritability of the comb-weight response estimated from regression of offspring on parents during generations 3 through 6 was 0.44 ± . 0 8 , 0.25 ± . 0 8 and 0.42 ± 0 . 1 1 in HTP, LTP and PMS, respectively. Realized heritabilities in generations three through six were 0.55 and 0.54, respectively, for HTP and LTP. In PMS, realized heritability with individual selection in males and family selection in females was 0.64.
1451
periment, but depressed growth in another. With the corn-soybean-fish meal rations used in these studies, female turkeys required no more than 18% protein from 8-12 weeks of age, 16% protein from 12-16 weeks of age, and 14% protein from 16-20 weeks of age. Male turkeys required higher levels of protein than the females.
Balloun, S. L., 1962. Lysine, arginine and methionine balance of diets for turkeys to 24 weeks of age. Poultry Sci. 4 1 : 417-424.
Balloun, S. L., and R. E. Phillips, 1957. Lysine and protein requirements of bronze turkeys. Poultry Sci. 36: 884-891. Jensen, L. S., L. H. Merrill, C. V. Reddy and J. McGinnis, 1962. Observations on eating patterns and rate of food passage of birds fed pelleted and unpelleted diets. Poultry Sci. 4 1 : 1414-1419. Kratzer, F. H., P. N. Davis and B. J. Marshall, 1956. The protein and lysine requirements of turkeys at various ages. Poultry Sci. 35: 197202. Reddy, C. V., L. S. Jensen, L. H. Merrill and J. McGinnis, 1962. Influence of mechanical alteration of dietary density on energy available for chick growth. J. Nutrition, 77: 428-432.
Selection for Chick Comb Weight with Androgen and Gonadotrophin Stimulation K. E. NESTOR AND R. G. JAAP Ohio Agricultural Research and Development Center, Columbus, Ohio (Received for publication December 10, 1964)
T
HE gonadotrophins and sex hormones are intimately involved in many important physiological processes, especially those concerned with reproduction. Undoubtedly, the genetic control of many of these processes is mediated, at least in part, through the gonadotrophins and sex hormones. Therefore, knowledge of the genetic control of production of, and response to, gonadotrophins and sex hormones is of great importance. The weight response of a target organ to a constant amount of a hormone may be influenced by two factors: (1) the amount of target organ tissue present upon which the hormone can act (Casida et al., 1952; and Jaap and Robertson, 1953); and (2) the sensitivity of the target organ tissue to the hormone. Comb weight of the young chick is highly heritable. Jaap et al. (1961) found the heritability of comb weight, as estimated
by covariance between full brother families, to be 0.76 and 0.68 at hatching and at 11 days of age, respectively. The additive genetic variance, based on analysis of diallel matings, was high at hatching but low at 11 days of age. Genetic differences in the sensitivity of the comb to androgens (Dorfman and Dorfman, 1948; and Jaap and Robertson, 1953) and to the injection of gonadotrophins (Munro et al., 1943) also exist. The heritability of comb weight in 11-day old chicks given a constant amount of either androgen or gonadotrophin is high, a large part of which is due to additive genetic variance (Jaap et al., 1961; and Jaap, 1962). At a similar age, Campos and Shaffner (1952) found that the heritability of comb weight of chicks treated with both androgen and estrogen to be low. Siegel and Siegel (1964 a,b) observed significant sire differences in the response
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REFERENCES
1441
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K. E. NESTOR AND R. G. JAAP
MATERIALS AND METHODS
The base population for all of the selected lines was the North Central Regional Randombred White Leghorn (RL), designated as the U. S. A. Regional Randombred White Leghorn in the original report by Jaap (1962). Also, RL has been maintained as a randombred control population. The three hormone-response selected populations (Jaap, 1962) have been continued for five additional generations, seven in all. The selection criterion has been the weight response of the 10-day chick comb regressed to a constant body weight within each hatch and sex group. Chicks of two of the selected populations were injected subcutaneously with 2.5 mg. of testosterone propionate in sesame oil solution on the fifth and eighth days after hatching. One line, HTP, was selected for high and the other, LTP, for low
comb-weight response within sex at 10 days of age. The third population, PMS, has been selected for a high comb-weight response in male chicks subcutaneously injected with a constant amount of pregnant mares' serum gonadotrophin*. Each male chick received 2.5 Cartland-Nelson (1952) units on each of the fifth through the eighth days of age. Males were individually selected for highest comb-weight response at 10 days of age while females were selected on the basis of a superior response of their brothers. A system of paired matings, adapted from Gowe et al. (1959) and described by Jaap (1963), was used to reproduce the three selected lines and the randombred control. With this system, 40 pairs of males and females were mated, within all lines, by means of artificial insemination. The matings in all lines were at random with the exception that full sib matings were avoided. All lines were reproduced as soon as they attained an egg production of approximately fifty percent. To reproduce the RL control, two male and two female chicks were randomly selected from the offspring of each parental pair in an attempt to have one male and one female from each pair present at reproductive age. Some of the pairs, however, were not represented each generation due to mortality of their offspring or to a lack of reproduction by these pairs. In these cases, offspring were randomly selected from other families in order to keep the number of sires and dams constant at 40 of each sex. Approximately 55 progeny of each sex * The pregnant mares' serum gonadotrophin was obtained from The Upjohn Company, Kalamazoo, Michigan (Gonadogen) in generations 1 through 4 and from Organon, Inc., W. Orange, New Jersey (Gestyl-Organon) in generations five through seven.
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to various gonadotrophin preparations. Heritability of testes weight response to avian pituitary homogenates was estimated to be 0.24 from paternal half sib correlations. Similar estimates were obtained for response to equine LH and ovine LH. Heritability estimates for the response to equine FSH varied with the dosage employed. Jaap (1962), in a preliminary paper, reported the establishment of lines showing both high and low comb-weight response to testosterone propionate and high combweight response of male chicks to pregnant mares' serum gonadotrophin. The purpose of the present experiment was to determine the changes occurring in these lines with further selection and to determine if the difference between the lines was due to changes in size of the comb of non-treated chicks or to changes in sensitivity of the lines to the hormones, or to both.
SELECTION FOR COMB WEIGHT
RESULTS AND DISCUSSION
Genetic Variance in Comb-Weight Response to Androgen and Gonadotrophin. Heritability of comb-weight response to testosterone propionate in HTP and LTP and to pregnant mares' serum gonadotrophin in PMS was estimated in generations three through six. The method of parentoffspring regression was selected as the most desirable, since the magnitude of heritability estimates obtained in this way are not influenced by the use of selected parents (Falconer, 1961). Each regression was determined by repeating the parental record with each offspring value. This procedure was found by Bohren et al. (1961) to have greater precision than regressing the offspring mean on the parental value. In the case of the response to gonadotrophin, the regression of male offspring on male parent was used since the response was only measured in males. The regression was determined
within sex for the response to testosterone propionate due to an inequality of the comb-weight variance in the two sexes. The influence of body weight on the comb-weight response was removed prior to calculating the regressions. This was done by adjusting each individual comb weight to the mean body weight of each sex-hatch group. The deviations of adjusted comb weight values from their sex-hatch group means were the values used in determining the regression coefficients. This procedure should minimize the influence of hatch differences on the heritability estimates. The regression of offspring on parent contains one-half of the additive genetic variance (Falconer, 1961). Therefore, to estimate heritability in the narrow sense, the regression coefficient was doubled. Standard errors of the heritability estimates were determined by the method of Van Vleck et al. (1960). The heritability estimates of the combweight response to testosterone propionate are given in Table 1. The number of comparisons ranged from 132 to 241 per generation in HTP and from 166 to 269 in LTP. The generation estimates were quite variable. Based on all comparisons over the four generations, the comb-weight response was more heritable in the upward direction (HTP) than in the downward direction (LTP). This was partially due to the decline in the size of the estimate obtained in LTP in the last generation. The heritability estimates found in this study for the HTP agree closely with those reported by Jaap et al. (1961) and Jaap (1962) but not with the one reported by Campos and Shaffner (1952). However, Campos and Shaffner injected their chicks with both testosterone propionate and diethylstilbestrol. The heritability estimates of comb-
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were selected each generation in the HTP and LTP so that 40 pairs of parents would be available at reproductive age. The individuals in these lines having the highest selection differentials among those present at sexual maturity were used as parents. The proportion of offspring used to reproduce the HTP and LTP ranged from 21.2 to 25.4 percent and from 17.2 to 22.5 percent, respectively. The proportion of male offspring used to reproduce the PMS ranged from 18.5 to 23.4 percent. In this line, the males having the highest selection differentials were used to reproduce the line with the exception that a maximum of five males from one family was used. Female offspring from approximately one-half of the available families (34-38) were used as breeders. A maximum of five females was used from each family.
1443
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K. E. NESTOR AND R. G. JAAP
TABLE 1.—Heritability estimates (h2) of comb-weight response to testosterone propionate and their standard errors h 2 ± Standard Error Generation
HTP Sire-male offspring
3 4 5 6 3 through 6
0.084 + 1.402 + 0.689 + 0.293 + 0.364 +
0.138 0.243 0.379 0.196 0.123
Dam-female offspring 0.257 + 0.965 + 0.708 + 0.633 + 0.528 +
0.117 0.345 0.101 0.160 0.097
0.441+0.079
weight response to gonadotrophin were also quite variable (Table 2). The estimate based on all data, 0.424 ± 0.108, is probably the most reliable since it was based on a larger number of observations and since there was no apparent trend in the magnitude of the estimate in successive generations. Non-additive genetic and/or maternal effects on the response of the male's comb following injection of gonadotrophin may be large. Much higher heritability estimates of 0.9S and 0.80 were obtained by Jaap et al. (1961) and Jaap (1962) from the covariance among full brothers in other populations. Jaap (1962) reported that the heritability of combweight response to gonadotrophin, as estimated from the sire component of the variance, was 0.42 in RL. Selection Response and Realized Heritabilities in HTP and LTP. The combweight response of testosterone-treated TABLE 2.—Heritability estimates (A2) of the combweight response to pregnant mares' serum gonadotrophin in PMS and their standard errors Generation 3 4 3
6 All data
No. of comparisons 171 213 208 188 780
h 2 ± Standard error 0.034 + 1.143 + 0.264 + 0.533 + 0.424 +
0.318 0.343 0.191 0.161 0.108
Sire-male offspring 0.220 + 0.789 + 0.927 + 0.136 + 0.285 +
0.114 0.216 0.538 0.173 0.099
Dam-female offspring 0.230 + 0.116 0.368 + 0.235 0.287 + 0.522 0.056±0.260 0.239 + 0.126
0.270 + 0.077
HTP and RL chicks is presented in Table 3. The linear regression coefficient of unadjusted comb weight (mg.) on generations was 38.4 and 26.8, respectively, in HTP males and females. A positive trend was present in the RL control, since the regression coefficients for males and females of this line were 9.1 and 5.8 respectively. After adjusting for the apparent positive trend in the environment, by subtracting, within sex, the RL coefficients from those of HTP, the regression coefficients for HTP were 29.3 and 21.0, respectively, for males and females. Similar regression coefficients were observed when combweight response was adjusted for differences in body weight by covariance analysis. The comb-weight response of LTP and its RL control is given in Table 4. The regression coefficients of comb-weight response of LTP on generations was 1.3 and 0.5 for males and females, respectively. After adjustment for the improvement in environment, the regression coefficients of change per generation in LTP became — 7.8 and —5.3, respectively, for males and females. Based on comb weights adjusted for body weight difference, the LTP regression coefficients were —0.5 and — 0.1, respectively, for males and females. These values became —9.8 and —6.8 when adjustment was made for the posi-
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3 through 6, both sexes
LTP
144S
SELECTION FOE COMB WEIGHT TABLE 3.—Changes in the comb-weight response to testosterone propionate in I1TP Adjusted comb weights (mg.)1
Actual comb weight (mg.) Generation
3 4 5 6 7
HTP
RL
HTP-RL
Gain from selection
61.9 65.3 108.9 76.0 101.9
Males 98.4 108.6 175.2 164.2 231.3
66.9 68.0 95.2 76.7 107.7
31.5 40.6 80.0 87.5 123.6
9.1 39.4 7.5 36.1
67.4 58.1 89.4 67.4 91.7
Females 93.7 97.5 145.8 147.3 224.9
HTP
RL control
95.4 101.9 199.5 163.0 208.1
—
3 4 5 6 7
90.4 91.1 159.7 138.8 200.2
71.3 61.1 86.3 73.7 100.3
—
22.4 36.4 59.5 73.6 124.6
14.0 23.1 14.1 51.0 102.2
Total
1 Comb weights were adjusted to a constant body weight of 79 grams by the use of the linear regression coefficient of comb weight on body weight.
tive environmental trend of the RL control. The gain from selection was higher in HTP (Table 3) than in LTP (Table 4). The total gains in HTP in generations three through six, as measured by the increase in size of the deviation from RL control (HTP-RL), was 92.1 and 102.2 TABLE 4.--Modification
milligrams, respectively, for males and females. In LTP, the total gain was —32.4 and —28.6 milligrams in males and females respectively. In order to determine whether the LTP was reaching a physiological barrier (i.e., minimum comb weight under stimulation), the frequency distribution for comb
:e to testosteronepropionate in LTF > i of comb-•weight •espons Adjusted comb weights (mg.)1
Actual comb weight (mg.) Generation
3 4 5 6 7
LTP
RL
47.9 43.8 75.1 47.7 51.8
61.9 65.3 108.9 76.0 101.9
LTP Males 54.5 45.3 62.3 44.8 52.9
RL
LTP-RL
Gain from selection
66.9 68.0 95.2 76.7 107.7
-12.4 -22.7 -32.9 -31.9 -44.8
-10.3 -10.2 + 1.0 -12.9
Total 3 4 5 6 7 Total
—
-32.4 47.8 43.3 61.5 44.4 49.9
67.4 58.1 89.4 67.4 91.7
Females 50.5 43.8 54.6 44.2 50.9
71.3 61.1 86.3 73.7 100.3
-20.8 -17.3 -31.7 -29.2 -49.4
—
+ 3.5 -14.4 + 2.5 -20.2 -28.6
1 Comb weights were adjusted to a constant body weight of 79 grams by the use of the linear regression coefficient of comb weight on body weight.
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92.1
Total
1446
K. E. NESTOR AND R. G. JAAP
ferential were determined. The intended selection differential was defined as the superiority of the parental values over the mean of the population from which they were selected. The actual selection differential was taken as the intended selection differential of each parent weighed according to the number of offspring produced. If natural selection is an important factor opposing artificial selection, the actual selection differential should be less than the intended selection differential (Falconer, 1961). The intended and actual selection differentials were essentially the same in both HTP and LTP (Table 5), indicating that natural selection did not oppose the selection practiced in these lines to a great extent. The magnitude of the selection differential is positively correlated with the amount of phenotypic variance (Falconer, 1961). The selection differentials were higher in males than in females for both HTP and LTP. This is a reflection of the larger phenotypic variance of comb-weight response in males. The selection differentials were larger in HTP than in
TABLE 5.—Selection differentials and realized heritabilities in HTP and LTP Selection differential (mg.) Generation
•
M
F
Ave.
M
F
3 4 5 6 Average
30.9 50.2 49.9 71.7 50.7
25.5 33.5 33.4 48.0 35.1
28.2 41.8 41.6 59.8 42.8
HTP Line 25.1 29.6 51.5 38.8 49.6 38.6 71.5 47.8 50.6 37.6
3 4 5 6 Average
12.4 15.5 14.5 21.7 16.0
13.5 13.9 12.5 18.0 14.5
12.9 14.7 13.5 19.8 15.2
LTP Line* 14.1 14.8 14.2 22.0 16.3
1 2
Selection response
Actual
Intended
12.8 14.5 12.5 18.2 14.5
(mg.)1
Realized heritability
Ave. 27.4 45.2 44.1 59.6 44.1
11.6 31.2 10.8 43.6 24.3
0.423 0.690 0.245 0.732 0.551
13.4 14.6 13.4 20.1 15.4
- 6.8 -12.3 + 2.8 -16.6 - 8.2
0.507 0.842 -0.209 0.826 0.535
Selection response was measured by the change in the deviations from RL control. All selection differentials in the LTP were negative.
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weights of treated chicks in LTP was determined in the sixth generation of selection. The mode was compared with the mean within sex. If the distribution were normal, the mode should equal the mean (Snedecor, 1959). The modes in the male and female distributions of comb weight were 48 and 43 milligrams, respectively, for males and females. The mean combweight response was S3 and 49 milligrams, respectively, for males and females. These results suggest that the frequency distributions were skewed toward the smaller comb weights. Similar results were obtained in the seventh generation. The distributions of comb weight in treated male and female chicks of LTP were analyzed for skewness by the methods of Snedecor (1959). This analysis established the presence of skewness in both sexes (P < .01) as was indicated by the comparison of the modes and means. These results suggest that LTP is reaching a physiological barrier even though selection response was relatively large in the last generation. Two measures of the selection dif-
1447
SELECTION FOR COMB WEIGHT TABLE 6.—Changes in the comb-weight response to pregnant mares' gonadotrophs in PMS
Adjusted comb weights (mg.) 1
Unadjusted comb weights (mg.) Generation
3 4 5 6
PMS
RL
PMS
RL
PMS-RL
Gain from selection
61.8 86.1 103.8 101.8
56.9 62.3 61.5 48.0
61.1 89.6 102.9 104.1
55.7 62.9 60.2 59.9
5.4 16.7 42.7 45.2
11.3 26.0 3.5 31.8 72.6
Total Adjusted to a constant body weight of 84 grams by covariance analysis.
negative regression coefucient of —5.2 mg. A similar situation was present when comb-weight response was adjusted for differences in body weight. The response to selection, as measured by the increase in the size of the deviation from the randombred control (PMS minus RL), was 72.6 milligrams for generations three through six. The actual and intended selection differentials for PMS parents did not differ greatly (Table 7) which indicates that natural selection was not an important factor opposing artificial selection. The selection differentials were lower in females than in males. The selection differentials for females were those for families, not individuals. The realized heritability of combweight response to gonadotrophin was high (Table 7). Since the female selection differentials were those of family averages, realized heritability would be expected to
LTP, which indicates that the variance in comb-weight response may be correlated with the mean comb-weight response. The greater selection differential in HTP was probably responsible for its greater gains from selection relative to LTP. Realized heritabilities were determined by dividing the selection response by the actual selection differential. Heritability of comb-weight response to testosterone propionate was essentially the same in HTP and LTP. Selection Response and Realized Heritabilities in PMS. The comb-weight response of PMS and RL male chicks to pregnant mares' serum gonadotrophin is given in Table 6. The linear regression coefficient of unadjusted comb-weight response (mg.) on generations was 5.8 mg. per generation in PMS. A downward trend was evident in the RL control, as indicated by a small
TABLE 7.—Selection differentials, selection response and realized heritabilities in PMS Selection differential (mg.)
3 4 5 6 Average 1
- Selection response - (mg-)1
Actual
Intended
Generation M
F
Ave.
M
F
Ave
38.1 43.0 42.7 49.9 43.4
17.7 11.8 12.0 16.2 14.4
27.9 27.4 27.4 33.0 29.8
28.6 42.2 42.3 54.5 41.9
14.0 12.2 12.0 16.3 13.6
21.3 27.2 27.2 35.4 27.8
11.3 26.0 2.5 31.8 17.9
Selection response was measured by the change in the deviation from RL control.
Realized heritability 0.531 0.956 0.092 0.898 0.643
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1
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K. E. NESTOR AND R. G. JAAP TABLE 8.—Sensitivity of response to testosterone propionate in IITP, LTP, RL and PMS
Line
HTP LTP RL PMS
Comb wt. (mg.)1 of untreated chicks
Comb wt. (mg.)1 of treated chicks
Sensitivity index2
Males
Females
Males
Females
Males
Females
61.3** 23.6** 35.1 53.3**
47.4** 23.6** 31.2 41.1**
138.6** 57.2** 66.1 84.8**
132.7** 59.3** 69.3 83.9**
292.4 160.2 211.8 206.3
280.0 174.2 222.1 204.1
1
be higher than that estimated from individual father-son regressions only (Table 2). Sensitivity of Response to Androgen. Jaap and Robertson (1953) found that the comb-weight response to testosterone propionate was strongly correlated with the initial size of the comb. In order to determine whether the response to selection in all three selected lines was due to changes in the size of the non-stimulated comb or sensitivity to androgen, or to both, a test was conducted using chicks from selected parents of the sixth generation of selection. Since gonadotrophin exerts its influence on the testes causing them to produce androgen which in turn produces comb growth, the changes in comb-weight response by selection in PMS could have been due to an increase in sensitivity of the testes to gonadotrophin or to an increase in the sensitivity of the comb to the androgen produced, or to both. Also, initial size of the comb of non-treated chicks in this line could have increased which would probably have resulted in a greater comb-weight response to gonadotrophin in PMS. A random sample of chicks from each of the four lines was injected subcutaneously with 2.5 mg. of testosterone propionate on each of the fifth and eighth days of age. Another sample of chicks from these lines was maintained as non-treated controls.
Both groups were reared intermingled in battery brooders. Comb weights of nontreated chicks of each selected population were compared with the RL control to determine whether selection had produced changes in the size of the non-stimulated comb. Sensitivity of response to testosterone propionate was measured by dividing the comb weight of treated chicks by the corresponding comb weight of untreated female checks within each line. This value was converted to percentage units by multiplying by 100. The untreated females' combs were used in preference to making the determination within sex because the comb of non-treated male chicks was, presumably, stimulated by endogenous androgen during the injection period. Comb weight of untreated chicks was larger in HTP and PMS, and smaller in LTP, than in RL control. This was true for both males and females (Table 8). These results indicate that the size of the non-stimulated comb was changed by selection in all the selected lines. The comb weights of treated PMS, HTP or LTP deviated in the same direction from the treated RL control as did the comb weights of non-treated chicks. The sensitivity of response (sensitivity index) was higher in HTP and Lower in LTP than in the RL control. Thus, selection for total weight of the comb in testosterone-treated chicks resulted in changes in both the
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Comb weights were adjusted to a constant body weight of 70 grams by covariance analysis. Sensitivity index was calculated within lines by dividing the comb weight of treated chicks by the untreated female comb weight and multiplying by 100. ** Indicates difference from RL control was highly significant (P<.01). 2
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SELECTION FOR COMB WEIGHT
weight of the non-treated and the testosterone propionate stimulated comb. Although PMS had a greater comb-weight response than RL, the combs of PMS were slightly less sensitive to androgen than those of RL.
TABLE 9.—Sensitivity of PMS and RL to
pregnant mares' serum gonadotrophin Untreated chicks (99)
Treated chicks
Line
PMS RL
No.
Comb weight (mg.i)
No.
84 102
24.2» 22.1
75 86
Comb weight (mg.)" 100.9** 48.6
Sensitivity index 2
416.9 219.9
1 Comb weights were adjusted to a constant body weight of 75 grams by covariance analysis. 2 Sensitivity index was calculated by dividing the comb weight of treated male chicks by that of untreated female chicks and then multiplying by 100. * Indicates that line difference was significant (P<.05). ** Indicates that line difference was highly significant (P<.01).
Line
No. of chicks -
Unadjusted weight of: Body
PMS RL
73 70
75.7 74.1
Comb 86.3** 48.3
Adjusted weight of:"
Testes
Comb
46.3** 37.2
85.7** 48.8
Testes 46.1** 37.2
1 Adjusted to a constant body weight of 75 grams by covariance analysis. ** Indicates deviation from RL control was significant at the 1 percent level of confidence.
Both comb and testes weight responses to gonadotrophin were greater in PMS than in RL controls. This was true for both unadjusted weights and weights adjusted to a constant body weight by covariance analysis. A histological study was made of a sample of testes from both lines. The sample from each line consisted of the testes from five males. The testes from both lines showed evidence of interstitial cell and seminiferous tubule stimulation by the gonadotrophin but there was no apparent difference between the lines in this respect. The results of this study indicate that the selection criterion, comb-weight response, in PMS was a composite one, influenced by unstimulated comb weight and sensitivity of response to gonadotrophin. The change in sensitivity to pregnant mares' serum gonadotrophin in PMS was apparently entirely due to changes in the ability of the testes to produce androgen when given a constant amount of the hormone, since the combs of PMS were slightly less sensitive to androgen than those of RL (Table 8). Inbreeding in the Various Lines. The change in inbreeding per generation, as measured by one-half the reciprocal of the effective number of parents (Falconer, 1961), for generations three through six is presented in Table 11. Inbreeding was the highest in PMS and lowest in the ran-
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Sensitivity of Response to Gonadotropin. The sensitivity of comb-weight response to gonadotrophin was determined in PMS compared with RL in the sixth generation of selection. A sample of male chicks from both lines was assayed in the usual manner. A sample of female chicks from the same parents was used as controls. Sensitivity of response was estimated by dividing the comb weight of the treated male chicks by the comb weight of the corresponding untreated female chicks and multiplying by 100. The comb weight of untreated PMS female chicks (Table 9) was significantly larger than that of the controls. The combweight response to gonadotrophin and the sensitivity of response was much greater in PMS than in RL. The increase in testes weights in PMS over the control chicks treated with gonadotrophin was compared for offspring of selected males and females from third generation parents. The chicks were assayed with gonadotrophin as in the preceding test. The results are presented in Table 10.
T A B L E 10.—Body, comb and testes weights of chicks from PMS and RL which were given a constant amount of gonadotrophin
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K. E. NESTOR AND R. G. JAAP
F/Generation
HTP LTP RL PMS
Accumulated F
Generation
Line 3
4
5
6
1.89 0.87 0.35 1.20
0.85 1.21 0.37 2.09
1.18 1.56 0.37 1.19
0.73 0.73 0.42 0.81
4.65 4.37 1.51 5.29
dombred control (RL). However, inbreeding was not high in any line. These results, along with those presented by Jaap (1963), demonstrate that the paired mating system employed in this experiment was effective in keeping the inbreeding at a relatively low level. Therefore, changes due to inbreeding and genetic drift were probably negligible.
SUMMARY
Three populations originating with the North Central Regional Randombred Leghorn (RL) were selected for seven generations for response of the chick's comb to hormone stimulation prior to 10 days of age. Male chicks of selected population PMS were selected for a high response to the gonadotrophin from pregnant mares' serum. Testosterone propionate was the hormone used in HTP and LTP populations selected for high and low combweight response, respectively. Reproduction of each of the 4 lines was from 40 randomly-paired matings. The accumulated increase in the inbreeding coefficient, F, during generations 3 through 6 was 1.5, 5.3, 4.6 and 4.4 percent for RL, PMS, HTP and LTP, respectively. Highly significant comb-weight responses, as measured by deviations from
Influence of Body Weight on Combweight Response to Androgen and Gonadotropin. The results of this study indicate that there is a positive association between body weight and the comb-weight response to both androgen and gonadotrophin (Table 12). In chicks treated with testosterone propionate, the regression coefficients of comb weight response (mg.) on body weight (gm.) were highest in HTP and lowest in LTP with RL intermediate. While variance in body weight of all selected lines was similar to that of RL in early generations, the body weight vari-
TABLE 12.—The regression coefficients of comb weight (mg.) on body weight (gm.)+their standard errors in 10-day old chicks treated with testosterone propionate and pregnant mares' serum gonadotrophin Treated with: Testosterone propionate HTP
PMS gonadotrophin
LTP
M
F
M
1.48 + 0.32 1.98+0.39 2.34+0.81 3.09 + 0.84 3.22 + 0.52
0.89 + 0.37 0.95 + 0.52 2.58+0.61 2.17 + 0.52 3.46±0.40
0.83 + 0.24 0.52 + 0.14 1.01 + 0.20 0.82 + 0.12 0.44+0.14
RL F
0.59 + 0.10 + 1.12 + 0.32 + 0.46 +
M 0.20 0.14 0.21 0.17 0.08
PMS F
1.35 + 0.23 0.95 + 0.32 0.54+0.24 0.46+0.12 1.59 + 0.31 1.12 + 0.23 1.21±0.28 1.03 + 0.21 1.53 + 0.30 1.71 + 0.26
M 0.68 + 0.24 1.54+0.33 0.30 + 0.49 0.36+0.45 2.11 + 0.24
RL M 1.00 + 0.28 0.83 + 0.20 0.74+0.14 1.25 + 0.24 0.61 + 0.10
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ance of HTP chicks decreased in later generations. This could account for the significantly greater coefficient in the HTP (Table 12). The comb-weight variance appeared to be correlated with the mean in all lines. This could explain the line difference observed in the regression coefficients in androgen-treated chicks. However, on this basis, the regression coefficient of PMS should have been larger than that of RL when both lines were given gonadotrophin, which was not the case (Table 12).
TABLE 11.—Increase in inbreeding coefficient (&F) per generation and accumulated inbreeding coefficient (F) in generations 3 through 6
SELECTION FOR COMB WEIGHT
REFERENCES Bohren, B. B., H. E. McKean and Y. Yamada, 1961. Relative efficiencies of heritability estimates based on regression of offspring on parent. Biometrics, 17: 481-491. Campos, A. C , and C. S. Shaffner, 1952. The genetic control of chick comb and oviduct response to androgen and estrogen. Poultry Sci. 3 1 : 567-571. Cartland, G. F., and J. W. Nelson, 1952. The bioassay of mare serum hormone. Amer. J. Physiol. 122: 201-207. Casida, L. E., B. R. Casida and A. B. Chapman, 1952. Some differences between two strains of rats developed by selection to differ in their response to equine gonadotrophin. Endocrinology, 51: 148-151. Dorfman, R. I., and A. S. Dorfman, 1948. Studies
on the bioassay of hormones: The relative reactivity of the comb of various breeds of chicks to androgen. Endocrinology, 42: 7-14. Falconer, D. S., 1961. Introduction to Quantitative Genetics. Oliver and Boyd, London. Gowe, R. S., A. Robertson and B. D. H. Latter, 1959. Environment and poultry breeding problems. 5. The design of poultry control strains. Poultry Sci. 38: 462-471. Jaap, R. G., 1962. Genetics of the chick's response to gonadotrophin and androgen. Proc. 12th World's Poultry Congress, Sidney: 52-53. Jaap, R. G., 1963. Paired matings for control and selected populations of chickens. Poultry Sci. 42: 1027-1028. Jaap, R. G., and H. Robertson, 1953. The chick comb response to androgen in inbred Brown Leghorns. Endocrinology, 53: 512-519. Jaap, R. G., M. W. Murray and R. W. Temple, 1961. The genetic control of variance in comb and testes weights of young male chickens. Poultry Sci. 40: 354-363. Lerner, I. M., 1958. The Genetic Basis of Selection. John Wiley and Sons, Inc., New York. Munro, S. S., I. L. Kosin and E. L. McCartney, 1943. Quantitative genic-hormone interactions in the fowl. 1. Relative sensitivity of five breeds to an anterior pituitary extract possessing both thyrotropic and gonadotropic properties. Amer. Nat. 77: 256-273. Siegel, P. B., and H. S. Siegel, 1964a. Genetic variation in chick bioassays for gonadotrophins. I. Testes weight and response. The Virginia J. Sci. 15: 187-203. Siegel, H. S., and P. B. Siegel, 1964b. Genetic variation in chick bioassays for gonadotrophins. II. Histological and histochemical responses. The Virginia J. Sci. IS: 204-217. Snedecor, G. W., 1959. Statistical Methods. The Iowa State College Press, Ames, Iowa. Van Vleck, L. D., S. R. Searle and C. R. Henderson, 1960. The number of daughter-dam pairs needed for estimating heritability. J. Animal Sci. 19: 916-920.
NEWS AND NOTES NEBRASKA NOTES Dr. Theodore E. Hartung, formerly Associate Poultry Scientist, Poultry Section, Colorado Agricultural Experiment Station, Colorado State University, Fort Collins, has been appointed Head of the Department of Poultry Science, University of Nebraska, Lincoln.
He was born in Denver, Colorado, in 1929, and received a B.S. and a M.S. degree at Colorado State University in 1951 and 1953, respectively. In 1962 he received a Ph.D. at Purdue University, specializing in Food Technology. From 1951 to 1953 he was Instructor at Colorado State University (then Colorado A and M (Continued on page 1459)
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the RL control, were produced in all three selected populations. The responses were partly attributable to changes in the combweight of non-treated chicks and partly to changes in sensitivity of the chicks to the hormones. The greater comb-weight response in the PMS population was attributed to increased androgen production of the stimulated testes and not to an increase in androgneic sensitivity of the comb. Heritability of the comb-weight response estimated from regression of offspring on parents during generations 3 through 6 was 0.44 ± . 0 8 , 0.25 ± . 0 8 and 0.42 ± 0 . 1 1 in HTP, LTP and PMS, respectively. Realized heritabilities in generations three through six were 0.55 and 0.54, respectively, for HTP and LTP. In PMS, realized heritability with individual selection in males and family selection in females was 0.64.
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