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Selection for Egg Mass in Different Social Environments 2. Estimation of Parameters in Selected Populations1,2
Selection for Egg Mass in Different Social Environments 2. Estimation of Parameters in Selected Populations1 ' 2 M. A. QUADEER and J. V. CRAIG Department of Dairy and Poultry Sciences, and K. E. KEMP and A. D. DAYTON Department of Statistics, Kansas State University, Manhattan, Kansas 66506 (Received for publication January 17, 1977)
Poultry Science 56:1536-1549, 1977 INTRODUCTION
The first paper of this series (Quadeer et al., 1977) presents background material and major objectives of the study. This article deals with egg production data of the foundation stock and four subsequent generations in selected strains. Estimates are presented for (a) additive genetic variance and heritabilities for the criterion of selection and associated traits, (b) genetic, environmental, and phenotypic correlations among those traits, and (c) changes in the genetic parameters associated with selection. PARAMETER ESTIMATES BY OTHERS Studies primarily involving White Leghorntype strains selected for egg production with trait measurements similar to those we studied
1 This investigation is part of the Kansas contribution to the NC-89 Regional Poultry Breeding Project. 2 Contribution No. 950J, Department of Dairy and Poultry Science, and No. 266-J Department of Statistics, Kansas Agricultural Experiment Station, Manhattan, Kansas.
are presented in Table 1. Few estimates involving egg mass are available. However, in a small flock of Sussex (12 and 144 degrees of freedom for sires and dams, respectively), Waring et al. (1962) reported heritability estimates of shortterm egg mass ranging from 0.04 ± .09 to 0.30 ±.11. Age at sexual maturity and early egg weight have mean heritability estimates of 0.33 and 0.48, respectively. Most egg weight estimates were based on averages of several eggs per pullet. Our survey indicates a mean heritability estimate for short-term rate of lay or production of 0.23. The genetic association between age at sexual maturity and short-term rate of production is unclear because of discrepancies between studies and that between maturity and early egg weight is apparently negligible. Estimates of the genetic correlation between egg weight and short-term egg production or rate were consistently negative and averaged —0.32. Environmental and phenotypic correlations among the traits were estimated to be small (absolute values ranged from 0.00 to 0.23).
1536
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ABSTRACT Data on hen-housed egg mass, the criterion of selection, and associated egg production traits were obtained from pullets of four strains selected over four generations in intermingled- or separated-family flocks. Data from the foundation stock also were used. Least squares estimates of phenotypic means, components of variance and covariance, heritabilities, and correlations (genetic, environmental, and phenotypic) were computed. Parameter estimates were regressed on generation number. No apparent time trends were found. Evidence was inconclusive for random genetic drift between strains within selection systems. Egg mass is estimated to be a lowly heritable trait (weighted means from sire component analyses ranged from 0.05 ± .03 to 0.16 ± .04). Egg weight is moderately heritable (sire component estimates of 0.32 ± .06 to 0.45 ± .04). Low heritability estimates (mean ranges of .05 to .13) were found for age at sexual maturity, hen-day, and hen-housed rates of lay. Genetic correlation estimates were high and positive between egg mass and rates of lay (sire component estimates ranged from .82 to 1.0). Egg mass and egg weight were moderately correlated genetically (.31 to .73). Genetic correlation estimates were low between age at sexual maturity and egg weight with mean ranges for estimates of —.06 to .12. Moderately large and negative genetic correlation estimates were obtained between age at sexual maturity and rates of lay.
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Early egg weight
populations
.23 .10 s , .06 t o . 5 6 7 .13 t o . 3 4 8 , .21 to .37' .48'°,.13" .14 to . 1 6 1 3 , . 1 0 t o .24 1 4 .14 to .24' 5 .15 .06 to .26
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Short-term rate of lay or production
7
Coded references: ' Abplanalp (1956, 1957). 2 Abplanalp et al. (1964). 3 Bray et al. (1960).'Clayton and Robertson (1966). s C r a i g « a / . (1969). "Dickerson (1957). Friars et al. (1962). 8 Hicks (1958). ' Jerome et al. (1956). ' ° King and Henderson (1954). l ' Kinney and Shoffner (1965). ' 2 Krueger et al. (1952). ' 3 Oliver et al. (1957). 14 Saadeh(1967). ' s Yamada
Off diagonal entries (in the upper right) are mean genetic correlation estimates (italics) and individual estimates with coded references, respectively; environmental (r e ) and phenotypic (r„) correlations with coded references are entered in the lower left.
* Diagonal entries are mean heritability estimates (italics), individual estimates or ranges with coded references, mean standard error (boldface) and the range of standard errors, respectively.
Short-term rate of lay or production
Early egg weight
.33* .12 to .17 to .23 to .16", .09 .07 to
Age at sexual maturity
. 1 5 ' , . 2 4 to .80 3 . 4 7 " , . 4 0 s , .22 to .31* . 3 5 ' , . 3 8 t o .55'° .07"
Age at sexual maturity
Traits
TABLE 1.—Estimates of beritabilities and correlations for some economic traits in selected
ded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015
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1538
M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON MATERIALS AND METHODS
Chicks of hatches 2 and 4, coded as Xi and X 2 , respectively, were moved to another laying house at 22 weeks. Pullets of those hatches also were placed in opposite sides of the house with each hatch in 3 adjacently-penned flocks. Each of those flocks included up to 10 females from each of the 18 sire families. Management Procedures. Hatching dates and space allowances per bird in each generation are given by Quadeer (1976). Chicks were vaccinated at hatching (against Newcastle and bronchitis) and were debeaked at 4 weeks of age and again when placed in laying-house pens. Only natural daylight was available during rearing, but artificial light was added at housing so there were at least 14 hours of light per day thereafter. The hatching season was changed from fall to spring in generation 4. An outbreak of coccidiosis occurred in generation 1 at about 6 1/2 months in the Y strains and was followed by enteritis and an E. coli infection. High mortality occurred in all strains because of Marek's disease in generation 2. Survival to reproductive age ranged from 39 to 54 percent in the various strains. Chicks were vaccinated against Marek's disease and 2 hatches were obtained per strain, in generation 3 only, because breeding stock in generation 2 had been severely depleted. From generation 1 onwards, each X strain was housed in 4 intermingled-family flocks in the laying house. Each of those flocks had up to 10 daughters from each sire family; sire families were subdivided nearly equally into those flocks. Y strain families were separated into small individual pens containing up to 40 daughters each in generation 0, 1, and 2. In generations 3 and 4, Y-strain families were subdivided into 2 small flocks each
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Foundation Stock. Four strains (Xi, X 2 , Y 2 , and Y 2 ) were selected from the Kentville Randombred Control population. Formation of those strains in generation 0 is described by Quadeer et al. (1977). Briefly, chicks from the same 18 single-sire matings (each male mated with 20 to 25 females) were produced in four hatches at weekly intervals. Hatch 1 and 3 chicks, designated as Yx and Y 2 , respectively, were housed at 22 weeks in opposite sides of the same house. Each sire family was placed in a separate pen. Each single-sire family pen contained up to 30 females.
with up to 25 daughters (usually <20) per flock. Selection Procedures. Generations 0 and I. Selection in all strains was based on sire family means of grams of egg per pullet housed per day (egg mass) for the period 30 to 37 weeks of age. Egg weights used to estimate egg mass were recorded during week 33. Six sire families were selected within each strain. Three sons of each of the selected sire families were subsequently mated to females from the other 5 selected sire families within each strain. Chicks thus produced constituted the next generation stock. The highest performing sire family within each of the 3 sire-related families then was selected to provide parents for the next generation. Selection pressure was somewhat reduced by this procedure; the selection differential for egg mass ranged from 54 to 77 percent of what it would have been without the restriction. The restriction was applied to minimize the rate of inbreeding and random drift. Generations 2, 3 and 4. The selection procedure was similar to that of previous generations except that the production period used for estimating egg mass was changed from 30 through 36 weeks to 30 through 39 weeks of age. Egg weights used to estimate egg mass were obtained during week 35. Traits Studied. The 5 traits were: henhoused egg mass (HHMAS), the criterion of selection; age at sexual maturity (SM); egg weight (EW); hen-day rate of lay (HDR); and hen-housed rate of lay (HHR). Descriptions of those traits are detailed by Quadeer et al. (1977). Statistical Methods. Models used for different generations are described by Quadeer (1976). The data were analyzed by the leastsquares procedure using Harvey's (1972) computer program involving a mixed model version (LSMLMM). Standard errors of estimates of least squares means, heritabilities and genetic correlations were computed by LSMLMM. Number of sires, dams, and pullet records used in analyses are presented in Table 2. Weighted estimates of parameters were obtained over generations by using the inverse of the square of their respective standard errors as weighting factors, following the method of Enfield et al. (1966). Such a weighting technique is desirable because the estimates with large standard errors contribute less than those having small standard errors.
SELECTION FOR EGG MASS
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RESULTS AND DISCUSSION
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Evidence of Random Drift. Least squares means for generations 0 through 4, their regressions on generation number, and weighted means along with their respective standard errors for intermingled- and separated-family selection systems are presented in Tables 3 and 4, respectively. Within the intermingled-family system (see Table 3), strain X 2 matured earlier, laid heavier eggs, but had inconsistent superiority over strain Xi for hen-day and hen-housed egg production and egg mass. Performance of strain X^ over all generations was superior as indicated by significantly greater egg mass, earlier age at sexual maturity, heavier eggs, and higher hen-day and henhoused rates of lay. In the separated-family system of selection (Table 4), strain Yt matured earlier in generations 0 through 2 but later in generation 3. Y t had significantly heavier egg weight in generations 0 through 2, but differed inconsistently over generations for hen-day and hen-housed rates of lay and egg mass. Weighted mean differences over all generations indicate that Yl matured earlier, had heavier eggs, and lower hen-day rate of lay. Y! and Y 2 did not differ for egg mass or henhoused rate of lay. The significant differences between strains within selection systems may be due to random genetic drift. However, random drift is confounded in these comparisons with effects of location (side of the house), hatch differences (usually one week), and level of exposure to diseases (Marek's disease, coccidiosis, and enteritis). None of the regressions of yearly means on generation number was significant in any of the 4 strains (Tables 3 and 4) except for hen-day rate of lay in strain X i . Examination of the time trends as evidence of effectiveness of selection is not justified because of confounding due to changes in season of hatch, length of production period, age at weighing of eggs, and outbreaks of disease. Our inability to detect significant regressions (perhaps due to limited degrees of freedom associated with tests of significance) is contrary to expectation in view of environmental changes over generations. Similary, changes over years as measured by strains Q and C 2 also derived from the Kentville Control popula-
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1539
0.58 ±0.02 0.61 ±0.02 -0.03
x, x2 x,--x 2
HHR
0.57 ±0.02 0.70 ± 0.02 -0.13**
0.66 ± 0.01 0.75 ± 0.01 -0.09**
54.1 ± 0.43 55.6 ± 0.42 -1.5*
0.55 ±0.02 0.60 ± 0.02 -0.05
0.67 ± 0.02 0.67 ± 0.02 0.00
51.3 ±0.45 55.3 ±0.42 -4.0*"
24.5 ±0.17 23.6 ±0.16 0.9**
31.0 ± 1.40 3 5.6 +1.30 -4.6*
Least squares means
Individual generation means were weighted by the inverse of their variances.
Generation means regressed on generations.
**P<.01.
*P<.05.
2
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0.65 ± 0.02 0.65 ±0.02 0.00
x, x2 x,-- X ,
HDR
0.2
52.5 ±0.43 52.3 ±0.43
0.0
24.0 ±0.12 23.4 ±0.12 0.6**
23.6 ±0.12 23.6 ±0.14
x, x. x, -x 2
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x, -x2 x,
33.2 ±0.82 40.2 ±0.80 -7.0**
32.3 + 1.10 33.8 ± 1.10 -1.5
EW
SM
x,
HHMAS
X2
Strain
Trait
Generation
0.70 ± 0.02 0.62 ± 0.02 0.08**
0.72 ± 0.01 0.69 ± 0.01 0.03
51.3 ±0.30 53.7 ±0.31 -2.4**
21.7 ±0.13 21.3 ±0.13 0.4*
37.5 ±0.76 35.2 ±0.77 2.3*
0.70 ±0.02 0.68 ±0.02 0.02
0.74 ±0.01 0.74 ±0.01 0.00
53.2 ±0.44 55.6 ±0.46 -2.4**
0.3
23.1 ±0.19 22.8 ±0.20
37.8 ±0.82 38.9 ±0.86 -1.1
0.62 ±0.01 0.64 ±0.01 -0.02 ±0.01*
0.70 ±0.01 0.72 ±0.01 -0.02 ± 0.008*
52.28 ±0.18 54.37 ±0.18 -2.07 ±0.25**
23.34 ±0.06 22.90 ±0.06 0.42 ±0.09**
35.26 ±0.41 37.18 ±0.41 -2.00 ±0.58**
Weighted' mean ± s.e.
TABLE 3.—Least squares means, regressions on generation number, weighted means and their standard errors in intermingled-family selection system in generations 0 through 4
ded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015 ±0.34 ±0.28 ±0.12
±0.71 ±0.94 ± 1.16
0.037 ±0.016 0.006 ± 0.016 0.031 ± 0.022
0.024 ± 0.005 0.012 ±0.015 0.012 ±0.015
-0.14 ±0.44 0.47 ±0.46 -0.61 ±0.43
-0.33 -0.37 0.04
1.53 0.52 1.01
b ± s.e.2
Y, Y2 Y,-Y2
Y, Y2 Y.-Y,
Y, Y2 Y.-Y,
Y, Y, Y.-Y,
Y, Ya Y,-Y2
HHMAS
SM
EW
HDR
HHR
0.65 ± 0.02 0.58 ±0.02 0.07**
0.70 ± 0.01 0.69 ± 0.01 0.01
51.7 ±0.47 50.8 ±0.47 0.9**
23.4 ±0.08 24.0 ± 0.09 -0.6**
3 5.3 ±0.96 30.6 +0.96 4.7**
0
1
0.54 ± 0.02 0.60 ± 0.02 -0.06 0.48 ± 0.02 0.56 ± 0.03 -0.08*
0.58 ± 0.02 0.64 ± 0.02 -0.06*
53.9 ±0.37 50.8 ±0.37 3.1**
55.8 ± 0.40 53.7 ±0.42 2.1**
0.74 ± 0.02 0.72 ± 0.02 0.02
25.2 ±0.05 26.1 ±0.05 -0.9**
27.5 ± 1.60 30.8 ± 1.60 -3.3
Least squares means
2
Generation
23.9 ±0.13 24.4 ±0.14 -0.5*
31.0 ±1.30 36.9 ± 1.40 -5.9**
Note: Footnotes correspond to those of Table 3.
Strain
Trait
0.53 ±0.03 0.51 ±0.03 0.02
0.68 ± 0.01 0.72 ± 0.01 -0.04
53.4 ±0.50 53.0 ±0.49 0.4
22.3 ±0.18 21.3 ±0.18 1.0**
29.3 ± 1.60 28.2 ±1.60 1.1
3
0.58 ±0.02 0.59 ±0.02 -0.01
0.56 ± 0.01 0.58 ± 0.01 -0.01 + 0.01
0.67 ± 0.01 0.70 ±0.01 -0.01 ± 0.01
± 0.604 ±0.61 ± 0.40
±0.38 ±0.62 ±0.27
±1.55 ± 1.61 ±1.46
-0.015 ±0.02 -0.007 ± 0.014 -0.008 ± 0.02
-0.02 ± 0.02 -0.008 ± 0.014 -0.014 ± 0.01
0.86 1.09 -0.23
54.48 ± 0.19 52.78 ±0.20 1.65 ±0.27**
57.2 ±0.46 56.6 ±0.47 0.6 0.62 ±0.01 0.65 ±0.02 -0.03
-0.08 -0.21 0.13
0.33 0.81 -0.48
b ± s.e.2
24.50 ±0.04 25.27 ±0.04 -0.75 ±0.06**
34.14 ±0.51 34.20 ± 0.52 -0.16 ±0.73
Weighted1 mean ± s.e.
23.8 ±0.32 24.5 ±0.32 -0.7
37.8 ±0.85 39.0 + 0.88 -1.2
4
TABLE 4.—Least squares means, regressions on generation number, weighted means and their standard errors in separated-family selection system in generations 0 through 4
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1542
M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON
on those estimates in the following presentation. Egg mass appears to be of moderately low heritability with sire component estimates combined over generations ranging from 0.05 ± 0.03 to 0.16 ± 0.04. Our estimates are based on substantially more data compared wtih those of Waring et al. (1962), but fall within his range of estimates. Our mean estimates for heritability of age at sexual maturity (0.06 ± 0.02 to 0.07 ± 0.03) were at the low end of the range of estimates from the literature, Table 1. The estimates from generation 0, wherein most of the pullets were already in production when housed, apparently reduced somewhat the overall estimates. We obtained heritability estimates for egg weight of 0.32 + 0.06 to 0.45 ± 0.04. As indicated earlier, our estimates are based on a single egg weighed per pullet, whereas several of those reported in Table 1 involved means based on 2 or more. Hen-day and hen-housed rates of lay were estimated to be lowly heritable traits, with ranges of 0.05 ± 0.03 to 0.09 ± 0.03 and 0.08 ± 0.03 to 0.13 ± 0.02, respectively. Estimates of heritability presented in Table 1 for short-term rate of lay or production range from .06 to .56 with an average of 0.23. Those estimates are based on varying short-term periods, mostly extending from age at sexual maturity. However, our estimates closely agree with those reported by Craig et al. (1969) and Kinney and Shoffner(1965). Heritability estimates were generally lower from sire components in the intermingled- as compared to separated-family flocks. This suggests that pen effects may be confounded with sire variances when sire families are separated. None of the regressions of heritability estimates on generation number was significant except that based on dam components of variance for hen-day rate of lay in separated flocks. No other time trends were indicated. The inability to detect such trends may, however, be associated with the low power of the associated tests of significance. Our results agree with those of Friars et al. (1962), who found no strong evidence of change in heritabilities over nine years of selection for egg production and egg weight. Similarly, Craig et al. (1969) failed to detect depletion of additive genetic variance for partyear rate of lay resulting from 7 generations of selection.
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015
tion were not detected as significant (Quadeer etal, 1977). Hill (1971, 1972 a, b, c, d) showed that for most selection experiments the primary cause of variable response was genetic drift accumulating with each generation of selection, but the error due to sampling of individuals in successive generations is nonaccumulating and diminishes progressively with each generation of selection. Nordskog et al. (1974), studying 10 lines of chickens, found that drift variance was 9 to 20 times more important than sampling variance among individuals in each generation. They used average effective population sizes of 22 to 30 and average size of tested population per generation of 200 to 620 and concluded that number of individuals tested each generation was adequate to reduce sampling error, but effective population size was the limiting factor in controlling the drift variance. In our investigation, the possible relative importance of genetic drift is difficult to determine for reasons cited. Heritability Estimates. Heritability estimates based on sire, dam, and sire plus dam components of variance for selection systems involving intermingled and separated families, and for data pooled over control and selected strains for generations 0 through 4, are presented in Tables 5, 6, and 7, respectively. Regressions of heritability estimates on generation number and their weighted means along with standard errors also are presented. In general it appears that maternal and/or nonadditive genetic variance is of considerable importance as indicated by consistently higher weighted and pooled heritabilities based on dam components as compared with those based on sire components for all traits (except egg weight in separated-family flocks). Inconsistent generation-to-generation differences in heritability estimates from sire and dam components of variance are presumably due to sampling error as indicated by large standard errors associated with the relatively few degrees of freedom for sires and dams (Table 2). Our estimates, indicating that heritabilities based on dam components generally exceed those based on sire components agree with the results of Lerner and Cruden (1950), King and Henderson (1954), Friars et al. (1962, Yamada et al. (1958), and Hicks (1958). It appears that heritability estimates based on sire components are generally more reliable indicators of additive genetic variance. Therefore, we concentrate
.27 ± .20 2i .23 .08 .15 ±±.08 .15
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h|+D
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.16 ±± .09 .14 .13 ±±.14
.10 ..17 1 7 ±±.10 .07 ± .15 -.10 .12 ± .06
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.03 ± .04 .20 ± .10
.00 ± .04 .30 ±.12 .30 .15 ±.06
.47 ± .16 .67 ± .14 .20 .57 ± .08
.19 ± .06
25
.07 ± .06 .32 ± .12
.00 ± .04 .25 ± .12 .25 .13 ±.04
1
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.20 ± .08
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.12 ± .10 .27 ± .18
.04 ± .08 .30 ±.20 .26 .17 ± .08
.49 ± .22 .53 ± .24 .04 .51 ± .12
.30 ± .16 .28 ± .20 "°2 .29 ± .10
.14 ± .10 .26 ± .20 .12 .20 ±.08
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HHR
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Generation
.08 ± .04
--06
.11 ± .06 .05 ± .08
.08 ± .06 -.03 ± .08 -.11 .02 ± .04
.19 ± .08 .33 ± .12 .14 .26 ± .06
.06 ± .04 .26 ± .10 -20 .16 ± .04
.07 ± .06 .11 ± .10 .04 .09 ± .04
3
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.13 ± .08 .28 ± .12
.14 ± .08 .44 ± .14 .30 .29 ± .06
.53 ± .18 .50 ± .14 -.03 .52 ± .08
.08 ± .06 .98 ± .16 -90 .53 ± .08
.08 ± .06 .28 ± .14 .20 .18 ± .06
4
.13 ± .02
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.05 ± .03 .14 ± .05 .09+ .12 ± .02
.32 ± .06 .50 ± .07 .18+ .44 ± .04
.07 ± .03 .39 ± .06 -32+ .22 ± .03
.05 ± .03 .19 ± .06 .14+ .13 ± .02
,,, . . . • Weighted mean ± s.e.
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.00 .04 .04 .02
.02 .04 .03 .03
.01 .14 .13 .07
.01 .02 .03 .00
.02 .03 .04 .02
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± ± ± ±
± ± ± ±
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.03 .07 .07 .03
.05 .04 .03 .04
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ed from http://ps.oxfordjournals.org/ at New York University on May 9, 2015
TABLE 5 .—Heritabilities, regressions on generation number, weighted means, and standard errors in intermingled-family selection system in generations 0 through 4
SELECTI ASS
.28 ± .10 .41 ±.12 .13 .35+ .06 .35 ± .14 .34 ±.14 -.01 .3 5 ± . 0 8 . 1 8 + .08
.38 ±.12 .20 .28 ±.06 .16 ± .08 .44 ± .10 .28 .30 ±.06
.03 -.00 ±±.03 .21 ± .15 .21 .10 ±±.06 .06
.62 ±±.26 .26 .17 .74 ±±.17 .12 .68 ± .09
.05 ±± ..05 .05 05
.15 .46 .46 ±±.15 .41 .41 .25 ±±.07 .07 .25
.05 ±± .05 .16 ± .13 .11 .11 ±± .05
h|
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S+D
Unweighted means.
h|+D
h|
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h|+D
h|
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.18 ± .08 .21 +.12 .03 .20 ± .06
1
.07 .10 ±±.07 .14 .10 ±±.14 .00 .10 ± .06
h| hf)
0
2
.24 ± .12 .38 ± .16 .14 .31 ±.08
.30 ± .18 .12 .24 ± .08
.18 ± .12
.21 ± .14 .28 ±.22 .07 .25 ± .10
.37 ± .16 -.16 ± .16 -.53 .10 ± . 0 8
.36 ± .16 .22 ±.18 -.14 .29 ± .08
Generation
*P<.05.
S = from sire component, D = from dam component, S+D = from sire plus dam component.
HHR
HDR
EW
SM
HHMAS
Trait
u •Hentability
.22 ± .08 .34 ± .10 .12 .28 ± .06
,21 ± .10 .16 .13 ± .04
.05 ± .06
.60 ± .18 .24 ± .12 -.36 .42 ± .08
.45 ± .14 .31 +.10 -.14 .38 ± .06
.24 ± .10 .33 ± .10 .09 .29 ± .06
3
.13 ± .06 .24 ± .12 .11 .19 ± .06
.22 ± .12 .08 .18 ± .06
.14 ± .08
.60 ± .20 .55 ± .16 -.05 .58 ± .08
.36 ± .12 .37 ±.12 .01 .37 ± .06
.12 ± .08 .09 ± .14 -.03 .10 ± .06
4
TABLE 6 .—Herttabutties, regressions on generation number, weighted means, and standard errors in separated-family selection system in generations 0 through 4
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.29 ± .06 .20+ .19 ± .03
.09 ± .03
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.07 ± .03 .27 ± .06 .20+ .28 ± .03
.16 ± .04 .21 ± .06 .05 + .19 ± .03
,,, . . , Weighted mean ± s.e.
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± .02 ± .04 ±.02 ± .03
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.01 ± .02
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.10
.17
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.18 ± .03
.00
.18 ± .05 .18 ± .06
.08 ± .04 .07 ± .07 -.01 .08 ± .03
.27 ± .07 .21 ± .06 -.06 .24 ± .07
.19 ± .05 .18 ± .07 -.01 .19 ± .03
.21 ± .08 .31 ±.13
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3
2
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Generation 1
0
S = from sire component, D = from dam component, S+D = from sire plus dam component.
HHR
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Heritability
Trait
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.09
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.08
.17 ± .06 .25 ± .09
.59 ±.12 .50 + .10 -.09 .55 ± .06
.40 * .05
.23
.29 ± .08 .52 ± .09
.15 ±.04
.10
.10 ± .05 .20 ± .09
4
TABLE 7.—Heritabilities, regressions on generation number, weighted means, and standard errors, pooled over control and selection systems in generations 0 through 4
ded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015 .13 ±.02 .24 ± .03 .11+ .19 ± .02
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.13 ± .02 .23 ± .04 .10+ .19 ± .02
Weighted mean ± s.e.
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M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON
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Correlation Estimates. Estimates of correlations (genetic, environmental, and phenotypic) among traits associated with the criterion of selection are presented for the 2 selection systems and for data pooled over systems in Table 8. It was shown by Bohren et al. (1966) that genetic correlations can change in magnitude and/or direction because of selection. Because egg mass is a compound trait, its selection amounts to simultaneous selection on component traits. Consequently, genetic correlations among them could change from positive to negative as generations advance (Lerner, 1958). However, Quadeer (1976) found that time trends were generally not significant for genetic, environmental, or phenotypic correlations among the traits studied. The general lack of time trends among correlations in the present investigation agrees with the results of Friars et al. (1962). (Generation-by-generation genetic correlation estimates and associated standard errors are available upon request). We found that most of the phenotypic correlations were smaller than corresponding genetic correlations in absolute magnitude which agrees with the results of Lerner and Cruden (1948) and Oliver et al. (1957). From evidence presented earlier, it appears that maternal effects and/or dominance deviations are of considerable magnitude for several traits associated with the criterion of selection. As hypothesized by King and Henderson (1954), changes in nonadditive and/or maternal effects could be considered independently of changes in additive genetic effects, particularly when selection is directed toward the latter. This may explain the lac k of a definite pattern between XQ S and TGDSome generalities are suggested, based on genetic correlations obtained from sire components. Egg weight apparently is rather important as a component of egg mass as indicated by genetic correlations of 0.31 ± 0.14, 0.73 ± 0.07, and 0.52 ± 0.07 from intermingled-family, separated-family, and pooled data, respectively. Genetic correlations are high and positive between hen-day and hen-housed rate of lay with magnitudes of 0.99 ± 0.02, 1.00 ± 0.01, and 1.00 ± 0.00 from intermingled-family, separated-family, and pooled data, respectively. These estimates suggest little or no confounding of age at sexual maturity and mortality with hen-housed rate of lay. Hen-housed egg mass is highly genetically correlated with rate of lay in
-.58 ± .31 -.41 ± .14* -.18 ± .12
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.99 ± . 0 2 * * 1.00 ± . 0 1 * * 1.00 ± . 0 0 * *
X Y Pooled
X Y Pooled
X Y Pooled
X Y Pooled
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-.08 ± .13 .13 ± .13 -.02 + .08
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-.01 ± .09 -.10 ± .08 -.08 + .05
.01 ± .09 -.12 ± .08 -.09 ± .05
-.37 ± . 1 1 * * -.18 ± . 0 8 * -.22 ± . 0 6 * *
-.29 ± . 1 1 * -.26 ± .09* -.26 ± . 0 7 * *
-.02 ± .08 .05 ± .08 .01 ± .05
.96 ± . 0 1 * * .98 ± . 0 1 * * .98 ± . 0 0 * *
.97 + .01 .93 ± .02 .95 + .01
.15 ± .03 -.01 + .04 .04 ± .03
.16 + .03 .02 + .03 .06 ± .03
-.10 + .05 -.02 + .07 -.12 + .03
-.09 ± .05 .02 ± .04 -.07 + .03
.01 ± .03 .15 ± .11 .04 ± .03
.98 ± .01 .98 ± .00 .99 ± .00
ed from http://ps.oxfordjournals.org/ at New York University on May 9, 2015 .96 ± . 0 1 .92 ± .02 .94 ± .02
-.25 ± . 1 2 .15 ± . 1 4 .03 + . 0 8
-.28 ± . 1 5 .14 ± . 1 3 .01 ± . 0 9
.26 ± .22 -.07 ± . 0 8 -.03 ± . 0 5
-.02 ± .07 -.01 ± . 0 9 .02 ± .04
.21 ± . 1 5 -.04 ± .08 .08 ± . 0 6
.98 ± . 0 1 .98 ± . 0 0 .99 ± . 0 0
.97 ± . 0 1 .93 ± .02 .95 ± . 0 1
-.03 ± . 0 5 .09 ± . 0 5 .03 ± . 0 4
-.04 ± . 0 7 .09 ± . 0 5 .03 ± . 0 5
-.03 ± . 0 5 -.04 ± . 0 6 -.09 ± . 0 3
-.03 ± . 0 5 .00 ± . 0 4 -.03 ± . 0 3
.06 ± . 0 4 .03 ± . 0 3 .05 ± . 0 3
.98 ± . 0 1 .98 ± . 0 0 .99 ± .00
.97 ± . 0 1 .94 ± .02 .95 ± . 0 1
.00 ± . 0 1 .02 ± . 0 3 .00 ± . 0 2
-.01 ± . 0 1 .02 ± . 0 4 .00 ± .02
-.12 ± . 0 2 -.09 ± . 0 6 -.11 ± . 0 3
-.10 ± . 0 3 -.06 ± . 0 2 -.08 ± . 0 3
.02 ± . 0 3 .02 ± . 0 4 .03 ± . 0 3
.97 ± . 0 1 .97 ± . 0 1 .98 ± . 0 0
**r G >3 s.e.
* r c > 2 s.e.
2 X = strains selected on performance in intermingled-family flocks, Y = strains selected on performance in separated-family flocks, Pooled = involves all strains, unselected controls + X + Y.
' r GS = genetic correlation from sire component, r(jD = genetic correlation from dam component, rQ(g+D) = genetic correlation from sire plus dam component, rj?s = environmental correlation from sire component, r^D = environmental correlation from dam component, rjj(§+D) = environmental correlation from sire plus dam component, r„ = phenotypic correlation.
.12 ± .15 -.06 ± .12 .04 ± .09
X Y Pooled
S M X EW
.96 ± . 0 2 * * .98 ± . 0 1 * * .97 ± . 0 1 * *
X Y Pooled
HHMAS X HHR
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1548
M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON
Our very l o w estimates for t h e genetic correlation b e t w e e n age at sexual m a t u r i t y and egg weight, ranging from —.06 t o . 1 2 , agree with t h o s e of Clayton and R o b e r t s o n ( 1 9 6 6 ) a n d J e r o m e et al. ( 1 9 5 6 ) . Our pooled estimates of t h e genetic correlation b e t w e e n age a t sexual m a t u r i t y a n d rate of lay are m o d e r a t e and negative ( - 0 . 1 8 ± 0 . 1 2 , - 0 . 3 1 ± 0 . 1 1 , a n d - 0 . 2 6 ± 0.07 for r G S , r G D , and r G ( s + D ) , respectively, and are similar t o t h e o n e r e p o r t e d b y J e r o m e et al. ( 1 9 5 6 ) . Intermingled-family flocks had negative genetic correlations b e t w e e n egg weight and rate of lay ( - 0 . 4 5 ± 0 . 1 3 a n d - 0 . 4 6 ± 0 . 1 3 for hen-day rate and hen-housed rate, respectively), b u t separated-family flocks had positive and l o w c o r r e s p o n d i n g correlations ( 0 . 0 4 ± 0 . 1 4 a n d 0 . 0 9 ± 0 . 1 3 , respectively). Our estimates, ranging from - 0 . 4 6 ± 0 . 1 3 t o 0 . 0 9 ± 0 . 1 3 , for t h e genetic correlation b e t w e e n egg weight and r a t e of lay are n o t inconsistent with t h o s e of Craig et al. ( 1 9 6 9 ) , Hicks ( 1 9 5 8 ) , J e r o m e et al. ( 1 9 5 6 ) , and Kinney a n d Shoffner ( 1 9 6 5 ) . T i m e t r e n d s in covariance c o m p o n e n t s for all pairs of traits in b o t h selection systems a n d in pooled d a t a over s y s t e m s were generally nonsignificant (Quadeer, 1 9 7 6 ) .
REFERENCES Abplanalp, H., 1956. Selection procedures for poultry flocks w i t h m a n y hatches. Poultry Sci. 35:1285-1304. Abplanalp, H., 1957. Genetic and environmental correlations among production traits of poultry. Poultry Sci. 36:226-228.
Abplanalp, H., D. C. Lowry, I. M. Lerner and E. R. Dempster, 1964. Selection for egg number with X-ray induced variation. Genetics, 50:1083—1100. Bohren, B. B., W. G. Hill and A. Robertson, 1966. Some observations on asymmetrical correlated responses to selection. Genet. Res. 7:44—57. Bray, D. F., S. C. King and V. L. Anderson, 1960. Sexual maturity and the measurement of egg production. Poultry Sci. 39:590-601. Clayton, G. A., and A. Robertson, 1966. Genetics of changes in economic traits during the laying year. Brit. Poultry Sci. 7 : 1 4 3 - 1 5 1 . Craig, J. V., D. K. Biswas and H. K. Saadeh, 1969. Genetic variation and correlated responses in chickens selected for part-year rate of egg production. Poultry Sci. 48:1288-1296. Dickerson, G. E., 1957. Genetic variation in some economic characters of Leghorn type chickens. Poultry Sci. 36:1113. Enfield, F. D., R. E. Comstock and O. Braskerud, 1966. Selection for pupa weight in Tribolium Castaneum. I. Parameters in base populations. Genetics, 5 4 : 5 2 3 - 5 3 3 . Friars, G. W., B. B. Bohren and H. E. McKean, 1962. Time trends in estimates of genetic parameters in a population of chickens subjected to multiple objective selection. Poultry Sci.41:1773—1784. Harvey, W. R., 1972. (a) General outline of computing procedures for six types of mixed models, (b) Procedures used in computation of variances of least squares means for mixed models, (c) Instructions for use of LSMLMM (least squares and maximum likelihood general purpose program. 252K mixed model version). Mimeographed material from Ohio State University. Hicks, A. F., Jr., 1958. Heritability and correlation analysis of egg weight, egg shape and egg number in chickens. Poultry Sci. 37:967-975. Hill, W. G., 1971. Design and efficiency of selection experiments for estimating genetic parameters. Biometrics, 2 7 : 2 9 3 - 3 1 1 . Hill, W. G., 1972a. Estimation of realized heritabilities from selection experiments. Divergent selection. Biometrics, 2 8 : 7 4 7 - 7 6 5 . Hill, W. G., 1972b. Estimation of realized heritabilities from selection experiments. Selection in one direction. Biometrics, 28:767—780. Hill, W. G., 1972c. Estimation of genetic change. General theory and design of control populations. An. Breeding Absts. 40:1—5. Hill, W. G., 1972d. Estimation of genetic change. Experimental evaluation of control populations. An. Breeding Absts. 4 0 . 1 9 3 - 2 1 3 . Jerome, F. N., C. R. Henderson and S. C. King, 1956. Heritabilities, gene interactions and correlations associated with certain traits in the domestic fowl. Poultry Sci. 35:995-1013. King, S. C , and C. R. Henderson, 1954. Heritability studies of egg production in the domestic fowl. Poultry Sci. 33:155-169. Kinney, T. B., Jr., and R. N. Shoffner, 1965. Heritability estimates and genetic correlations among several traits in a meat type poultry population. Poultry Sci. 44:1020-1032. Krueger, W. F., G. E. Dickerson, Q. B. Kinder and H. L. Kempster, 1952. The genetic and environmental
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015
b o t h selection systems and in pooled data as indicated b y estimates ranging from 0.82 t o 0 . 9 8 . It should be k e p t in mind t h a t egg mass a n d rates of lay, as used h e r e , are largely i n d e p e n d e n t of sexual m a t u r i t y ; t h e y were based o n d a t a collected after 3 0 weeks of lay (nearly all pullets had m a t u r e d earlier). Results of t h e present investigation agree generally with those of Hicks ( 1 9 5 8 ) . His analysis of 3 8 5 4 records on White Leghorns over 3 generations indicated t h a t p h e n o t y p i c variation in egg n u m b e r was m o r e i m p o r t a n t in determining egg mass t h a n was variation in egg weight. He o b t a i n e d positive genetic correlations b e t w e e n egg mass a n d its c o m p o n e n t s ; estimates of t h e correlation b e t w e e n egg n u m b e r a n d egg mass were high, 0.8 t o 0.9. T h e heritability of egg mass was equivalent t o , o r slightly higher t h a n , t h e heritability of egg n u m b e r in his s t u d y .
SELECTION FOR EGG MASS
Ph.D. dissertation, Kansas State University Library, Manhattan. Quadeer, M. A., J. V. Craig, K. E. Kemp and A. D. Dayton, 1977. Selection for egg mass in different social environments. 1. Estimation of some parameters in the foundation stock. Poultry Sci. 56: 1522-153 5. Saadeh, H. K., 1967. Reciprocal recurrent selection versus family index selection, heritabilities and correlations associated with quantitative traits in the domestic fowl. Ph.D. dissertation, Kansas State University Library, Manhattan. Waring, F. J., P. Hunton and A. E. Maddison, 1962. Genetics of a closed poultry flock. I. Variance and covariance analysis of egg production, egg weight and egg mass. Brit. Poultry Sci. 3:151—160. Yamada, Y., B. B. Bohren and L. B. Crittenden, 1958. Genetic analysis of a White Leghorn closed flock apparently plateaued for egg production. Poultry Sci. 37:565-580.
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015
relationship of total egg production to its components and to body weights in the domestic fowl. Poultry Sci. 31:922. Lerner, I. M., 1958. The Genetic Basis of Selection. John Wiley and Sons, Inc., New York. Lerner, I. M., and D. M. Cruden, 1948. The heritability of accumulative monthly and annual egg production. Poultry Sci. 27:67—78. Lerner, I. M., and D. M. Cruden, 1950. The heritability of egg weight: the advantage of mass selection and of early measurements. Poultry Sci. 30:34—41. Nordskog, A. W., H. S. Tolman, D. W. Casey and C. Y. lin, 1974. Selection in small population of chickens. Poultry Sci. 53:1188-1219. Oliver, M. M., B. B. Bohren and V. L. Anderson, 1957. Heritability and selection efficiency of several measures of egg production. Poultry Sci. 36:395-402. Quadeer, M. A., 1976. Selection for egg mass in different social environments. Estimation of some parameters in selected and foundation stocks.
1549
Poultry Science 56:1536-1549, 1977 INTRODUCTION
The first paper of this series (Quadeer et al., 1977) presents background material and major objectives of the study. This article deals with egg production data of the foundation stock and four subsequent generations in selected strains. Estimates are presented for (a) additive genetic variance and heritabilities for the criterion of selection and associated traits, (b) genetic, environmental, and phenotypic correlations among those traits, and (c) changes in the genetic parameters associated with selection. PARAMETER ESTIMATES BY OTHERS Studies primarily involving White Leghorntype strains selected for egg production with trait measurements similar to those we studied
1 This investigation is part of the Kansas contribution to the NC-89 Regional Poultry Breeding Project. 2 Contribution No. 950J, Department of Dairy and Poultry Science, and No. 266-J Department of Statistics, Kansas Agricultural Experiment Station, Manhattan, Kansas.
are presented in Table 1. Few estimates involving egg mass are available. However, in a small flock of Sussex (12 and 144 degrees of freedom for sires and dams, respectively), Waring et al. (1962) reported heritability estimates of shortterm egg mass ranging from 0.04 ± .09 to 0.30 ±.11. Age at sexual maturity and early egg weight have mean heritability estimates of 0.33 and 0.48, respectively. Most egg weight estimates were based on averages of several eggs per pullet. Our survey indicates a mean heritability estimate for short-term rate of lay or production of 0.23. The genetic association between age at sexual maturity and short-term rate of production is unclear because of discrepancies between studies and that between maturity and early egg weight is apparently negligible. Estimates of the genetic correlation between egg weight and short-term egg production or rate were consistently negative and averaged —0.32. Environmental and phenotypic correlations among the traits were estimated to be small (absolute values ranged from 0.00 to 0.23).
1536
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015
ABSTRACT Data on hen-housed egg mass, the criterion of selection, and associated egg production traits were obtained from pullets of four strains selected over four generations in intermingled- or separated-family flocks. Data from the foundation stock also were used. Least squares estimates of phenotypic means, components of variance and covariance, heritabilities, and correlations (genetic, environmental, and phenotypic) were computed. Parameter estimates were regressed on generation number. No apparent time trends were found. Evidence was inconclusive for random genetic drift between strains within selection systems. Egg mass is estimated to be a lowly heritable trait (weighted means from sire component analyses ranged from 0.05 ± .03 to 0.16 ± .04). Egg weight is moderately heritable (sire component estimates of 0.32 ± .06 to 0.45 ± .04). Low heritability estimates (mean ranges of .05 to .13) were found for age at sexual maturity, hen-day, and hen-housed rates of lay. Genetic correlation estimates were high and positive between egg mass and rates of lay (sire component estimates ranged from .82 to 1.0). Egg mass and egg weight were moderately correlated genetically (.31 to .73). Genetic correlation estimates were low between age at sexual maturity and egg weight with mean ranges for estimates of —.06 to .12. Moderately large and negative genetic correlation estimates were obtained between age at sexual maturity and rates of lay.
.15' -.07'
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Early egg weight
populations
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Short-term rate of lay or production
7
Coded references: ' Abplanalp (1956, 1957). 2 Abplanalp et al. (1964). 3 Bray et al. (1960).'Clayton and Robertson (1966). s C r a i g « a / . (1969). "Dickerson (1957). Friars et al. (1962). 8 Hicks (1958). ' Jerome et al. (1956). ' ° King and Henderson (1954). l ' Kinney and Shoffner (1965). ' 2 Krueger et al. (1952). ' 3 Oliver et al. (1957). 14 Saadeh(1967). ' s Yamada
Off diagonal entries (in the upper right) are mean genetic correlation estimates (italics) and individual estimates with coded references, respectively; environmental (r e ) and phenotypic (r„) correlations with coded references are entered in the lower left.
* Diagonal entries are mean heritability estimates (italics), individual estimates or ranges with coded references, mean standard error (boldface) and the range of standard errors, respectively.
Short-term rate of lay or production
Early egg weight
.33* .12 to .17 to .23 to .16", .09 .07 to
Age at sexual maturity
. 1 5 ' , . 2 4 to .80 3 . 4 7 " , . 4 0 s , .22 to .31* . 3 5 ' , . 3 8 t o .55'° .07"
Age at sexual maturity
Traits
TABLE 1.—Estimates of beritabilities and correlations for some economic traits in selected
ded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015
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1538
M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON MATERIALS AND METHODS
Chicks of hatches 2 and 4, coded as Xi and X 2 , respectively, were moved to another laying house at 22 weeks. Pullets of those hatches also were placed in opposite sides of the house with each hatch in 3 adjacently-penned flocks. Each of those flocks included up to 10 females from each of the 18 sire families. Management Procedures. Hatching dates and space allowances per bird in each generation are given by Quadeer (1976). Chicks were vaccinated at hatching (against Newcastle and bronchitis) and were debeaked at 4 weeks of age and again when placed in laying-house pens. Only natural daylight was available during rearing, but artificial light was added at housing so there were at least 14 hours of light per day thereafter. The hatching season was changed from fall to spring in generation 4. An outbreak of coccidiosis occurred in generation 1 at about 6 1/2 months in the Y strains and was followed by enteritis and an E. coli infection. High mortality occurred in all strains because of Marek's disease in generation 2. Survival to reproductive age ranged from 39 to 54 percent in the various strains. Chicks were vaccinated against Marek's disease and 2 hatches were obtained per strain, in generation 3 only, because breeding stock in generation 2 had been severely depleted. From generation 1 onwards, each X strain was housed in 4 intermingled-family flocks in the laying house. Each of those flocks had up to 10 daughters from each sire family; sire families were subdivided nearly equally into those flocks. Y strain families were separated into small individual pens containing up to 40 daughters each in generation 0, 1, and 2. In generations 3 and 4, Y-strain families were subdivided into 2 small flocks each
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015
Foundation Stock. Four strains (Xi, X 2 , Y 2 , and Y 2 ) were selected from the Kentville Randombred Control population. Formation of those strains in generation 0 is described by Quadeer et al. (1977). Briefly, chicks from the same 18 single-sire matings (each male mated with 20 to 25 females) were produced in four hatches at weekly intervals. Hatch 1 and 3 chicks, designated as Yx and Y 2 , respectively, were housed at 22 weeks in opposite sides of the same house. Each sire family was placed in a separate pen. Each single-sire family pen contained up to 30 females.
with up to 25 daughters (usually <20) per flock. Selection Procedures. Generations 0 and I. Selection in all strains was based on sire family means of grams of egg per pullet housed per day (egg mass) for the period 30 to 37 weeks of age. Egg weights used to estimate egg mass were recorded during week 33. Six sire families were selected within each strain. Three sons of each of the selected sire families were subsequently mated to females from the other 5 selected sire families within each strain. Chicks thus produced constituted the next generation stock. The highest performing sire family within each of the 3 sire-related families then was selected to provide parents for the next generation. Selection pressure was somewhat reduced by this procedure; the selection differential for egg mass ranged from 54 to 77 percent of what it would have been without the restriction. The restriction was applied to minimize the rate of inbreeding and random drift. Generations 2, 3 and 4. The selection procedure was similar to that of previous generations except that the production period used for estimating egg mass was changed from 30 through 36 weeks to 30 through 39 weeks of age. Egg weights used to estimate egg mass were obtained during week 35. Traits Studied. The 5 traits were: henhoused egg mass (HHMAS), the criterion of selection; age at sexual maturity (SM); egg weight (EW); hen-day rate of lay (HDR); and hen-housed rate of lay (HHR). Descriptions of those traits are detailed by Quadeer et al. (1977). Statistical Methods. Models used for different generations are described by Quadeer (1976). The data were analyzed by the leastsquares procedure using Harvey's (1972) computer program involving a mixed model version (LSMLMM). Standard errors of estimates of least squares means, heritabilities and genetic correlations were computed by LSMLMM. Number of sires, dams, and pullet records used in analyses are presented in Table 2. Weighted estimates of parameters were obtained over generations by using the inverse of the square of their respective standard errors as weighting factors, following the method of Enfield et al. (1966). Such a weighting technique is desirable because the estimates with large standard errors contribute less than those having small standard errors.
SELECTION FOR EGG MASS
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Evidence of Random Drift. Least squares means for generations 0 through 4, their regressions on generation number, and weighted means along with their respective standard errors for intermingled- and separated-family selection systems are presented in Tables 3 and 4, respectively. Within the intermingled-family system (see Table 3), strain X 2 matured earlier, laid heavier eggs, but had inconsistent superiority over strain Xi for hen-day and hen-housed egg production and egg mass. Performance of strain X^ over all generations was superior as indicated by significantly greater egg mass, earlier age at sexual maturity, heavier eggs, and higher hen-day and henhoused rates of lay. In the separated-family system of selection (Table 4), strain Yt matured earlier in generations 0 through 2 but later in generation 3. Y t had significantly heavier egg weight in generations 0 through 2, but differed inconsistently over generations for hen-day and hen-housed rates of lay and egg mass. Weighted mean differences over all generations indicate that Yl matured earlier, had heavier eggs, and lower hen-day rate of lay. Y! and Y 2 did not differ for egg mass or henhoused rate of lay. The significant differences between strains within selection systems may be due to random genetic drift. However, random drift is confounded in these comparisons with effects of location (side of the house), hatch differences (usually one week), and level of exposure to diseases (Marek's disease, coccidiosis, and enteritis). None of the regressions of yearly means on generation number was significant in any of the 4 strains (Tables 3 and 4) except for hen-day rate of lay in strain X i . Examination of the time trends as evidence of effectiveness of selection is not justified because of confounding due to changes in season of hatch, length of production period, age at weighing of eggs, and outbreaks of disease. Our inability to detect significant regressions (perhaps due to limited degrees of freedom associated with tests of significance) is contrary to expectation in view of environmental changes over generations. Similary, changes over years as measured by strains Q and C 2 also derived from the Kentville Control popula-
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015
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0.58 ±0.02 0.61 ±0.02 -0.03
x, x2 x,--x 2
HHR
0.57 ±0.02 0.70 ± 0.02 -0.13**
0.66 ± 0.01 0.75 ± 0.01 -0.09**
54.1 ± 0.43 55.6 ± 0.42 -1.5*
0.55 ±0.02 0.60 ± 0.02 -0.05
0.67 ± 0.02 0.67 ± 0.02 0.00
51.3 ±0.45 55.3 ±0.42 -4.0*"
24.5 ±0.17 23.6 ±0.16 0.9**
31.0 ± 1.40 3 5.6 +1.30 -4.6*
Least squares means
Individual generation means were weighted by the inverse of their variances.
Generation means regressed on generations.
**P<.01.
*P<.05.
2
1
0.65 ± 0.02 0.65 ±0.02 0.00
x, x2 x,-- X ,
HDR
0.2
52.5 ±0.43 52.3 ±0.43
0.0
24.0 ±0.12 23.4 ±0.12 0.6**
23.6 ±0.12 23.6 ±0.14
x, x. x, -x 2
x, -xa
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x, -x2 x,
33.2 ±0.82 40.2 ±0.80 -7.0**
32.3 + 1.10 33.8 ± 1.10 -1.5
EW
SM
x,
HHMAS
X2
Strain
Trait
Generation
0.70 ± 0.02 0.62 ± 0.02 0.08**
0.72 ± 0.01 0.69 ± 0.01 0.03
51.3 ±0.30 53.7 ±0.31 -2.4**
21.7 ±0.13 21.3 ±0.13 0.4*
37.5 ±0.76 35.2 ±0.77 2.3*
0.70 ±0.02 0.68 ±0.02 0.02
0.74 ±0.01 0.74 ±0.01 0.00
53.2 ±0.44 55.6 ±0.46 -2.4**
0.3
23.1 ±0.19 22.8 ±0.20
37.8 ±0.82 38.9 ±0.86 -1.1
0.62 ±0.01 0.64 ±0.01 -0.02 ±0.01*
0.70 ±0.01 0.72 ±0.01 -0.02 ± 0.008*
52.28 ±0.18 54.37 ±0.18 -2.07 ±0.25**
23.34 ±0.06 22.90 ±0.06 0.42 ±0.09**
35.26 ±0.41 37.18 ±0.41 -2.00 ±0.58**
Weighted' mean ± s.e.
TABLE 3.—Least squares means, regressions on generation number, weighted means and their standard errors in intermingled-family selection system in generations 0 through 4
ded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015 ±0.34 ±0.28 ±0.12
±0.71 ±0.94 ± 1.16
0.037 ±0.016 0.006 ± 0.016 0.031 ± 0.022
0.024 ± 0.005 0.012 ±0.015 0.012 ±0.015
-0.14 ±0.44 0.47 ±0.46 -0.61 ±0.43
-0.33 -0.37 0.04
1.53 0.52 1.01
b ± s.e.2
Y, Y2 Y,-Y2
Y, Y2 Y.-Y,
Y, Y2 Y.-Y,
Y, Y, Y.-Y,
Y, Ya Y,-Y2
HHMAS
SM
EW
HDR
HHR
0.65 ± 0.02 0.58 ±0.02 0.07**
0.70 ± 0.01 0.69 ± 0.01 0.01
51.7 ±0.47 50.8 ±0.47 0.9**
23.4 ±0.08 24.0 ± 0.09 -0.6**
3 5.3 ±0.96 30.6 +0.96 4.7**
0
1
0.54 ± 0.02 0.60 ± 0.02 -0.06 0.48 ± 0.02 0.56 ± 0.03 -0.08*
0.58 ± 0.02 0.64 ± 0.02 -0.06*
53.9 ±0.37 50.8 ±0.37 3.1**
55.8 ± 0.40 53.7 ±0.42 2.1**
0.74 ± 0.02 0.72 ± 0.02 0.02
25.2 ±0.05 26.1 ±0.05 -0.9**
27.5 ± 1.60 30.8 ± 1.60 -3.3
Least squares means
2
Generation
23.9 ±0.13 24.4 ±0.14 -0.5*
31.0 ±1.30 36.9 ± 1.40 -5.9**
Note: Footnotes correspond to those of Table 3.
Strain
Trait
0.53 ±0.03 0.51 ±0.03 0.02
0.68 ± 0.01 0.72 ± 0.01 -0.04
53.4 ±0.50 53.0 ±0.49 0.4
22.3 ±0.18 21.3 ±0.18 1.0**
29.3 ± 1.60 28.2 ±1.60 1.1
3
0.58 ±0.02 0.59 ±0.02 -0.01
0.56 ± 0.01 0.58 ± 0.01 -0.01 + 0.01
0.67 ± 0.01 0.70 ±0.01 -0.01 ± 0.01
± 0.604 ±0.61 ± 0.40
±0.38 ±0.62 ±0.27
±1.55 ± 1.61 ±1.46
-0.015 ±0.02 -0.007 ± 0.014 -0.008 ± 0.02
-0.02 ± 0.02 -0.008 ± 0.014 -0.014 ± 0.01
0.86 1.09 -0.23
54.48 ± 0.19 52.78 ±0.20 1.65 ±0.27**
57.2 ±0.46 56.6 ±0.47 0.6 0.62 ±0.01 0.65 ±0.02 -0.03
-0.08 -0.21 0.13
0.33 0.81 -0.48
b ± s.e.2
24.50 ±0.04 25.27 ±0.04 -0.75 ±0.06**
34.14 ±0.51 34.20 ± 0.52 -0.16 ±0.73
Weighted1 mean ± s.e.
23.8 ±0.32 24.5 ±0.32 -0.7
37.8 ±0.85 39.0 + 0.88 -1.2
4
TABLE 4.—Least squares means, regressions on generation number, weighted means and their standard errors in separated-family selection system in generations 0 through 4
ded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015 C/5
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M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON
on those estimates in the following presentation. Egg mass appears to be of moderately low heritability with sire component estimates combined over generations ranging from 0.05 ± 0.03 to 0.16 ± 0.04. Our estimates are based on substantially more data compared wtih those of Waring et al. (1962), but fall within his range of estimates. Our mean estimates for heritability of age at sexual maturity (0.06 ± 0.02 to 0.07 ± 0.03) were at the low end of the range of estimates from the literature, Table 1. The estimates from generation 0, wherein most of the pullets were already in production when housed, apparently reduced somewhat the overall estimates. We obtained heritability estimates for egg weight of 0.32 + 0.06 to 0.45 ± 0.04. As indicated earlier, our estimates are based on a single egg weighed per pullet, whereas several of those reported in Table 1 involved means based on 2 or more. Hen-day and hen-housed rates of lay were estimated to be lowly heritable traits, with ranges of 0.05 ± 0.03 to 0.09 ± 0.03 and 0.08 ± 0.03 to 0.13 ± 0.02, respectively. Estimates of heritability presented in Table 1 for short-term rate of lay or production range from .06 to .56 with an average of 0.23. Those estimates are based on varying short-term periods, mostly extending from age at sexual maturity. However, our estimates closely agree with those reported by Craig et al. (1969) and Kinney and Shoffner(1965). Heritability estimates were generally lower from sire components in the intermingled- as compared to separated-family flocks. This suggests that pen effects may be confounded with sire variances when sire families are separated. None of the regressions of heritability estimates on generation number was significant except that based on dam components of variance for hen-day rate of lay in separated flocks. No other time trends were indicated. The inability to detect such trends may, however, be associated with the low power of the associated tests of significance. Our results agree with those of Friars et al. (1962), who found no strong evidence of change in heritabilities over nine years of selection for egg production and egg weight. Similarly, Craig et al. (1969) failed to detect depletion of additive genetic variance for partyear rate of lay resulting from 7 generations of selection.
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015
tion were not detected as significant (Quadeer etal, 1977). Hill (1971, 1972 a, b, c, d) showed that for most selection experiments the primary cause of variable response was genetic drift accumulating with each generation of selection, but the error due to sampling of individuals in successive generations is nonaccumulating and diminishes progressively with each generation of selection. Nordskog et al. (1974), studying 10 lines of chickens, found that drift variance was 9 to 20 times more important than sampling variance among individuals in each generation. They used average effective population sizes of 22 to 30 and average size of tested population per generation of 200 to 620 and concluded that number of individuals tested each generation was adequate to reduce sampling error, but effective population size was the limiting factor in controlling the drift variance. In our investigation, the possible relative importance of genetic drift is difficult to determine for reasons cited. Heritability Estimates. Heritability estimates based on sire, dam, and sire plus dam components of variance for selection systems involving intermingled and separated families, and for data pooled over control and selected strains for generations 0 through 4, are presented in Tables 5, 6, and 7, respectively. Regressions of heritability estimates on generation number and their weighted means along with standard errors also are presented. In general it appears that maternal and/or nonadditive genetic variance is of considerable importance as indicated by consistently higher weighted and pooled heritabilities based on dam components as compared with those based on sire components for all traits (except egg weight in separated-family flocks). Inconsistent generation-to-generation differences in heritability estimates from sire and dam components of variance are presumably due to sampling error as indicated by large standard errors associated with the relatively few degrees of freedom for sires and dams (Table 2). Our estimates, indicating that heritabilities based on dam components generally exceed those based on sire components agree with the results of Lerner and Cruden (1950), King and Henderson (1954), Friars et al. (1962, Yamada et al. (1958), and Hicks (1958). It appears that heritability estimates based on sire components are generally more reliable indicators of additive genetic variance. Therefore, we concentrate
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.11 ± .04
-17
.03 ± .04 .20 ± .10
.00 ± .04 .30 ±.12 .30 .15 ±.06
.47 ± .16 .67 ± .14 .20 .57 ± .08
.19 ± .06
25
.07 ± .06 .32 ± .12
.00 ± .04 .25 ± .12 .25 .13 ±.04
1
2
.20 ± .08
-15
.12 ± .10 .27 ± .18
.04 ± .08 .30 ±.20 .26 .17 ± .08
.49 ± .22 .53 ± .24 .04 .51 ± .12
.30 ± .16 .28 ± .20 "°2 .29 ± .10
.14 ± .10 .26 ± .20 .12 .20 ±.08
S = from sire component, D = from dam component, S+D = from sire plus dam component.
HHR
n
h£+D
h| hf)
0
Generation
.08 ± .04
--06
.11 ± .06 .05 ± .08
.08 ± .06 -.03 ± .08 -.11 .02 ± .04
.19 ± .08 .33 ± .12 .14 .26 ± .06
.06 ± .04 .26 ± .10 -20 .16 ± .04
.07 ± .06 .11 ± .10 .04 .09 ± .04
3
.20 ± .06
-15
.13 ± .08 .28 ± .12
.14 ± .08 .44 ± .14 .30 .29 ± .06
.53 ± .18 .50 ± .14 -.03 .52 ± .08
.08 ± .06 .98 ± .16 -90 .53 ± .08
.08 ± .06 .28 ± .14 .20 .18 ± .06
4
.13 ± .02
-07+
.08 ± .03 .15 ±.05
.05 ± .03 .14 ± .05 .09+ .12 ± .02
.32 ± .06 .50 ± .07 .18+ .44 ± .04
.07 ± .03 .39 ± .06 -32+ .22 ± .03
.05 ± .03 .19 ± .06 .14+ .13 ± .02
,,, . . . • Weighted mean ± s.e.
.00 .02 .01 .01
.00 .04 .04 .02
.02 .04 .03 .03
.01 .14 .13 .07
.01 .02 .03 .00
.02 .03 .04 .02
± ± ± ±
± ± ± ±
± ± ± ±
.02 .03 .04 .02
.03 .07 .07 .03
.05 .04 .03 .04
± .04 ± .08 ±.10 ± .04
± ± ± ±
b ± s.e.
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SM
HHMAS
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„ . Heritability
ed from http://ps.oxfordjournals.org/ at New York University on May 9, 2015
TABLE 5 .—Heritabilities, regressions on generation number, weighted means, and standard errors in intermingled-family selection system in generations 0 through 4
SELECTI ASS
.28 ± .10 .41 ±.12 .13 .35+ .06 .35 ± .14 .34 ±.14 -.01 .3 5 ± . 0 8 . 1 8 + .08
.38 ±.12 .20 .28 ±.06 .16 ± .08 .44 ± .10 .28 .30 ±.06
.03 -.00 ±±.03 .21 ± .15 .21 .10 ±±.06 .06
.62 ±±.26 .26 .17 .74 ±±.17 .12 .68 ± .09
.05 ±± ..05 .05 05
.15 .46 .46 ±±.15 .41 .41 .25 ±±.07 .07 .25
.05 ±± .05 .16 ± .13 .11 .11 ±± .05
h|
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S+D
Unweighted means.
h|+D
h|
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h| hfj h})-h|
h|+D
h|
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.18 ± .08 .21 +.12 .03 .20 ± .06
1
.07 .10 ±±.07 .14 .10 ±±.14 .00 .10 ± .06
h| hf)
0
2
.24 ± .12 .38 ± .16 .14 .31 ±.08
.30 ± .18 .12 .24 ± .08
.18 ± .12
.21 ± .14 .28 ±.22 .07 .25 ± .10
.37 ± .16 -.16 ± .16 -.53 .10 ± . 0 8
.36 ± .16 .22 ±.18 -.14 .29 ± .08
Generation
*P<.05.
S = from sire component, D = from dam component, S+D = from sire plus dam component.
HHR
HDR
EW
SM
HHMAS
Trait
u •Hentability
.22 ± .08 .34 ± .10 .12 .28 ± .06
,21 ± .10 .16 .13 ± .04
.05 ± .06
.60 ± .18 .24 ± .12 -.36 .42 ± .08
.45 ± .14 .31 +.10 -.14 .38 ± .06
.24 ± .10 .33 ± .10 .09 .29 ± .06
3
.13 ± .06 .24 ± .12 .11 .19 ± .06
.22 ± .12 .08 .18 ± .06
.14 ± .08
.60 ± .20 .55 ± .16 -.05 .58 ± .08
.36 ± .12 .37 ±.12 .01 .37 ± .06
.12 ± .08 .09 ± .14 -.03 .10 ± .06
4
TABLE 6 .—Herttabutties, regressions on generation number, weighted means, and standard errors in separated-family selection system in generations 0 through 4
ed from http://ps.oxfordjournals.org/ at New York University on May 9, 2015 .12 ± .03 .32 ± .05 .20+ .22 ± .03
.29 ± .06 .20+ .19 ± .03
.09 ± .03
.41 ± .08 .40 ± .07 -.01+ .46 ± .04
.07 ± .03 .27 ± .06 .20+ .28 ± .03
.16 ± .04 .21 ± .06 .05 + .19 ± .03
,,, . . , Weighted mean ± s.e.
± .04 ± .04 ± .03 ± .03
.02 .01 -.02 .01
± .02 ± .04 ±.02 ± .03
-.06 ± . 0 1 * -.07 ± .02 -.03 ± .01
.01 ± .02
.02 ± .07 -.05 ± .07 -.07 ± .06 -.01 ± .06
.09 ± .04 .02 ± .08 -.07 ± .10 .06 ± .04
.01 .01 -.00 .01
b ± s.e.
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.25 ± .05
.09 ± .04 .34 + .07 .25
.22 ± .04
.11 ± .05 .21 + .06
.10
.16 ± .03
.20 ± .06
.07 ± .04 .32 + .08
.10 ± .05 .15 ± .06 .26
.46 ± .05
.57 ± .06
.20 ± .04
.07 + .06 .33 ± .13
.07
.05
.25
.42 ± .13 .3 5 ± .16 -.07 .39 ± .07
.43 ± .06 .50 ± .06
.55 ± .19 .60 + .09
.12 ± .03
.45 ± .06
.21 ± .04
.08 ± .03
.05
.23
.12
.33 ±.10 .56 ± .13
.15
.15 ± .05 .27 ± .08
.26 ± .06
.18 ± .04
.19 ± .03
.01 ± .02 .16 ± .07
.10
.17
.10
.41 ± .09 .28 ± .08 -.13 .34 ± .05
.18 ± .03
.00
.18 ± .05 .18 ± .06
.08 ± .04 .07 ± .07 -.01 .08 ± .03
.27 ± .07 .21 ± .06 -.06 .24 ± .07
.19 ± .05 .18 ± .07 -.01 .19 ± .03
.21 ± .08 .31 ±.13
.09 ± .04 .26 ± .08
3
2
.14 ± .06 .24 ± .07
Generation 1
0
S = from sire component, D = from dam component, S+D = from sire plus dam component.
HHR
HDR
EW
SM
hJS
HHMAS
hb hp-«S
Heritability
Trait
.18 ± .04
.09
.14 ± .05 .23 ± .08
.21 ± .04
.08
.17 ± .06 .25 ± .09
.59 ±.12 .50 + .10 -.09 .55 ± .06
.40 * .05
.23
.29 ± .08 .52 ± .09
.15 ±.04
.10
.10 ± .05 .20 ± .09
4
TABLE 7.—Heritabilities, regressions on generation number, weighted means, and standard errors, pooled over control and selection systems in generations 0 through 4
ded from http://ps.oxfordjournals.org/ at New York University on May 9, 2015 .13 ±.02 .24 ± .03 .11+ .19 ± .02
.09 ± .02 .19 ± .03 .10+ .14 ± .02
.45 ± .04 .46 ± .04 .01+ .46 ± .03
.06 ± .02 .28 ± .03 .22+ .21 ± .02
.13 ± .02 .23 ± .04 .10+ .19 ± .02
Weighted mean ± s.e.
.02 -.01 -.03 -.00
± .01 ± .03 ± .03 ± .01
± .01 ± .04 ± .04 ± .02
± .03 ± .04 ± .02 ± .03
.01 -.04 -.05 -.02 .02 -.01 -.02 .01
± .03 ± .06 ± .04 ± .04
± .02 ± .02 ± .02 ± .01 .07 .07 -.00 .07
.00 -.02 -.02 -.01
b ± s.e.
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Correlation Estimates. Estimates of correlations (genetic, environmental, and phenotypic) among traits associated with the criterion of selection are presented for the 2 selection systems and for data pooled over systems in Table 8. It was shown by Bohren et al. (1966) that genetic correlations can change in magnitude and/or direction because of selection. Because egg mass is a compound trait, its selection amounts to simultaneous selection on component traits. Consequently, genetic correlations among them could change from positive to negative as generations advance (Lerner, 1958). However, Quadeer (1976) found that time trends were generally not significant for genetic, environmental, or phenotypic correlations among the traits studied. The general lack of time trends among correlations in the present investigation agrees with the results of Friars et al. (1962). (Generation-by-generation genetic correlation estimates and associated standard errors are available upon request). We found that most of the phenotypic correlations were smaller than corresponding genetic correlations in absolute magnitude which agrees with the results of Lerner and Cruden (1948) and Oliver et al. (1957). From evidence presented earlier, it appears that maternal effects and/or dominance deviations are of considerable magnitude for several traits associated with the criterion of selection. As hypothesized by King and Henderson (1954), changes in nonadditive and/or maternal effects could be considered independently of changes in additive genetic effects, particularly when selection is directed toward the latter. This may explain the lac k of a definite pattern between XQ S and TGDSome generalities are suggested, based on genetic correlations obtained from sire components. Egg weight apparently is rather important as a component of egg mass as indicated by genetic correlations of 0.31 ± 0.14, 0.73 ± 0.07, and 0.52 ± 0.07 from intermingled-family, separated-family, and pooled data, respectively. Genetic correlations are high and positive between hen-day and hen-housed rate of lay with magnitudes of 0.99 ± 0.02, 1.00 ± 0.01, and 1.00 ± 0.00 from intermingled-family, separated-family, and pooled data, respectively. These estimates suggest little or no confounding of age at sexual maturity and mortality with hen-housed rate of lay. Hen-housed egg mass is highly genetically correlated with rate of lay in
-.58 ± .31 -.41 ± .14* -.18 ± .12
-.34 ± .26 -.46 ± . 1 2 * * -.16 ± .11
-.45 ± . 1 3 * * .04 ± .14 -.15 ± .09
-.46 ± . 1 3 * * .09 ± .13 -.13 ± .09
.99 ± . 0 2 * * 1.00 ± . 0 1 * * 1.00 ± . 0 0 * *
X Y Pooled
X Y Pooled
X Y Pooled
X Y Pooled
X Y Pooled
SM X H D R
SM X H H R
EW X HDR
EW X H H R
HDR X HHR 1.00* .01** .98 t . 0 2 * * .99 ± . 0 1 * *
.17 + .15 -.13 ± .13 -.06 ± .09
.15 ± .15 -.14 ± .13 -.07 + .09
-.39 ± . 1 9 * -.01 ± .13 -.24 ± . 1 1 *
-.21 + .14 -.15 ± .16 -.31 + . 1 1 *
-.08 ± .13 .13 ± .13 -.02 + .08
.98 ± . 0 1 * * .99 ± . 0 1 * * .98 ± . 0 0 * *
1.00 ± . 0 1 * * .98 ± . 0 1 * * 1.00 ± . 0 0 * *
-.01 ± .09 -.10 ± .08 -.08 + .05
.01 ± .09 -.12 ± .08 -.09 ± .05
-.37 ± . 1 1 * * -.18 ± . 0 8 * -.22 ± . 0 6 * *
-.29 ± . 1 1 * -.26 ± .09* -.26 ± . 0 7 * *
-.02 ± .08 .05 ± .08 .01 ± .05
.96 ± . 0 1 * * .98 ± . 0 1 * * .98 ± . 0 0 * *
.97 + .01 .93 ± .02 .95 + .01
.15 ± .03 -.01 + .04 .04 ± .03
.16 + .03 .02 + .03 .06 ± .03
-.10 + .05 -.02 + .07 -.12 + .03
-.09 ± .05 .02 ± .04 -.07 + .03
.01 ± .03 .15 ± .11 .04 ± .03
.98 ± .01 .98 ± .00 .99 ± .00
ed from http://ps.oxfordjournals.org/ at New York University on May 9, 2015 .96 ± . 0 1 .92 ± .02 .94 ± .02
-.25 ± . 1 2 .15 ± . 1 4 .03 + . 0 8
-.28 ± . 1 5 .14 ± . 1 3 .01 ± . 0 9
.26 ± .22 -.07 ± . 0 8 -.03 ± . 0 5
-.02 ± .07 -.01 ± . 0 9 .02 ± .04
.21 ± . 1 5 -.04 ± .08 .08 ± . 0 6
.98 ± . 0 1 .98 ± . 0 0 .99 ± . 0 0
.97 ± . 0 1 .93 ± .02 .95 ± . 0 1
-.03 ± . 0 5 .09 ± . 0 5 .03 ± . 0 4
-.04 ± . 0 7 .09 ± . 0 5 .03 ± . 0 5
-.03 ± . 0 5 -.04 ± . 0 6 -.09 ± . 0 3
-.03 ± . 0 5 .00 ± . 0 4 -.03 ± . 0 3
.06 ± . 0 4 .03 ± . 0 3 .05 ± . 0 3
.98 ± . 0 1 .98 ± . 0 0 .99 ± .00
.97 ± . 0 1 .94 ± .02 .95 ± . 0 1
.00 ± . 0 1 .02 ± . 0 3 .00 ± . 0 2
-.01 ± . 0 1 .02 ± . 0 4 .00 ± .02
-.12 ± . 0 2 -.09 ± . 0 6 -.11 ± . 0 3
-.10 ± . 0 3 -.06 ± . 0 2 -.08 ± . 0 3
.02 ± . 0 3 .02 ± . 0 4 .03 ± . 0 3
.97 ± . 0 1 .97 ± . 0 1 .98 ± . 0 0
**r G >3 s.e.
* r c > 2 s.e.
2 X = strains selected on performance in intermingled-family flocks, Y = strains selected on performance in separated-family flocks, Pooled = involves all strains, unselected controls + X + Y.
' r GS = genetic correlation from sire component, r(jD = genetic correlation from dam component, rQ(g+D) = genetic correlation from sire plus dam component, rj?s = environmental correlation from sire component, r^D = environmental correlation from dam component, rjj(§+D) = environmental correlation from sire plus dam component, r„ = phenotypic correlation.
.12 ± .15 -.06 ± .12 .04 ± .09
X Y Pooled
S M X EW
.96 ± . 0 2 * * .98 ± . 0 1 * * .97 ± . 0 1 * *
X Y Pooled
HHMAS X HHR
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M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON
Our very l o w estimates for t h e genetic correlation b e t w e e n age at sexual m a t u r i t y and egg weight, ranging from —.06 t o . 1 2 , agree with t h o s e of Clayton and R o b e r t s o n ( 1 9 6 6 ) a n d J e r o m e et al. ( 1 9 5 6 ) . Our pooled estimates of t h e genetic correlation b e t w e e n age a t sexual m a t u r i t y a n d rate of lay are m o d e r a t e and negative ( - 0 . 1 8 ± 0 . 1 2 , - 0 . 3 1 ± 0 . 1 1 , a n d - 0 . 2 6 ± 0.07 for r G S , r G D , and r G ( s + D ) , respectively, and are similar t o t h e o n e r e p o r t e d b y J e r o m e et al. ( 1 9 5 6 ) . Intermingled-family flocks had negative genetic correlations b e t w e e n egg weight and rate of lay ( - 0 . 4 5 ± 0 . 1 3 a n d - 0 . 4 6 ± 0 . 1 3 for hen-day rate and hen-housed rate, respectively), b u t separated-family flocks had positive and l o w c o r r e s p o n d i n g correlations ( 0 . 0 4 ± 0 . 1 4 a n d 0 . 0 9 ± 0 . 1 3 , respectively). Our estimates, ranging from - 0 . 4 6 ± 0 . 1 3 t o 0 . 0 9 ± 0 . 1 3 , for t h e genetic correlation b e t w e e n egg weight and r a t e of lay are n o t inconsistent with t h o s e of Craig et al. ( 1 9 6 9 ) , Hicks ( 1 9 5 8 ) , J e r o m e et al. ( 1 9 5 6 ) , and Kinney a n d Shoffner ( 1 9 6 5 ) . T i m e t r e n d s in covariance c o m p o n e n t s for all pairs of traits in b o t h selection systems a n d in pooled d a t a over s y s t e m s were generally nonsignificant (Quadeer, 1 9 7 6 ) .
REFERENCES Abplanalp, H., 1956. Selection procedures for poultry flocks w i t h m a n y hatches. Poultry Sci. 35:1285-1304. Abplanalp, H., 1957. Genetic and environmental correlations among production traits of poultry. Poultry Sci. 36:226-228.
Abplanalp, H., D. C. Lowry, I. M. Lerner and E. R. Dempster, 1964. Selection for egg number with X-ray induced variation. Genetics, 50:1083—1100. Bohren, B. B., W. G. Hill and A. Robertson, 1966. Some observations on asymmetrical correlated responses to selection. Genet. Res. 7:44—57. Bray, D. F., S. C. King and V. L. Anderson, 1960. Sexual maturity and the measurement of egg production. Poultry Sci. 39:590-601. Clayton, G. A., and A. Robertson, 1966. Genetics of changes in economic traits during the laying year. Brit. Poultry Sci. 7 : 1 4 3 - 1 5 1 . Craig, J. V., D. K. Biswas and H. K. Saadeh, 1969. Genetic variation and correlated responses in chickens selected for part-year rate of egg production. Poultry Sci. 48:1288-1296. Dickerson, G. E., 1957. Genetic variation in some economic characters of Leghorn type chickens. Poultry Sci. 36:1113. Enfield, F. D., R. E. Comstock and O. Braskerud, 1966. Selection for pupa weight in Tribolium Castaneum. I. Parameters in base populations. Genetics, 5 4 : 5 2 3 - 5 3 3 . Friars, G. W., B. B. Bohren and H. E. McKean, 1962. Time trends in estimates of genetic parameters in a population of chickens subjected to multiple objective selection. Poultry Sci.41:1773—1784. Harvey, W. R., 1972. (a) General outline of computing procedures for six types of mixed models, (b) Procedures used in computation of variances of least squares means for mixed models, (c) Instructions for use of LSMLMM (least squares and maximum likelihood general purpose program. 252K mixed model version). Mimeographed material from Ohio State University. Hicks, A. F., Jr., 1958. Heritability and correlation analysis of egg weight, egg shape and egg number in chickens. Poultry Sci. 37:967-975. Hill, W. G., 1971. Design and efficiency of selection experiments for estimating genetic parameters. Biometrics, 2 7 : 2 9 3 - 3 1 1 . Hill, W. G., 1972a. Estimation of realized heritabilities from selection experiments. Divergent selection. Biometrics, 2 8 : 7 4 7 - 7 6 5 . Hill, W. G., 1972b. Estimation of realized heritabilities from selection experiments. Selection in one direction. Biometrics, 28:767—780. Hill, W. G., 1972c. Estimation of genetic change. General theory and design of control populations. An. Breeding Absts. 40:1—5. Hill, W. G., 1972d. Estimation of genetic change. Experimental evaluation of control populations. An. Breeding Absts. 4 0 . 1 9 3 - 2 1 3 . Jerome, F. N., C. R. Henderson and S. C. King, 1956. Heritabilities, gene interactions and correlations associated with certain traits in the domestic fowl. Poultry Sci. 35:995-1013. King, S. C , and C. R. Henderson, 1954. Heritability studies of egg production in the domestic fowl. Poultry Sci. 33:155-169. Kinney, T. B., Jr., and R. N. Shoffner, 1965. Heritability estimates and genetic correlations among several traits in a meat type poultry population. Poultry Sci. 44:1020-1032. Krueger, W. F., G. E. Dickerson, Q. B. Kinder and H. L. Kempster, 1952. The genetic and environmental
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b o t h selection systems and in pooled data as indicated b y estimates ranging from 0.82 t o 0 . 9 8 . It should be k e p t in mind t h a t egg mass a n d rates of lay, as used h e r e , are largely i n d e p e n d e n t of sexual m a t u r i t y ; t h e y were based o n d a t a collected after 3 0 weeks of lay (nearly all pullets had m a t u r e d earlier). Results of t h e present investigation agree generally with those of Hicks ( 1 9 5 8 ) . His analysis of 3 8 5 4 records on White Leghorns over 3 generations indicated t h a t p h e n o t y p i c variation in egg n u m b e r was m o r e i m p o r t a n t in determining egg mass t h a n was variation in egg weight. He o b t a i n e d positive genetic correlations b e t w e e n egg mass a n d its c o m p o n e n t s ; estimates of t h e correlation b e t w e e n egg n u m b e r a n d egg mass were high, 0.8 t o 0.9. T h e heritability of egg mass was equivalent t o , o r slightly higher t h a n , t h e heritability of egg n u m b e r in his s t u d y .
SELECTION FOR EGG MASS
Ph.D. dissertation, Kansas State University Library, Manhattan. Quadeer, M. A., J. V. Craig, K. E. Kemp and A. D. Dayton, 1977. Selection for egg mass in different social environments. 1. Estimation of some parameters in the foundation stock. Poultry Sci. 56: 1522-153 5. Saadeh, H. K., 1967. Reciprocal recurrent selection versus family index selection, heritabilities and correlations associated with quantitative traits in the domestic fowl. Ph.D. dissertation, Kansas State University Library, Manhattan. Waring, F. J., P. Hunton and A. E. Maddison, 1962. Genetics of a closed poultry flock. I. Variance and covariance analysis of egg production, egg weight and egg mass. Brit. Poultry Sci. 3:151—160. Yamada, Y., B. B. Bohren and L. B. Crittenden, 1958. Genetic analysis of a White Leghorn closed flock apparently plateaued for egg production. Poultry Sci. 37:565-580.
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relationship of total egg production to its components and to body weights in the domestic fowl. Poultry Sci. 31:922. Lerner, I. M., 1958. The Genetic Basis of Selection. John Wiley and Sons, Inc., New York. Lerner, I. M., and D. M. Cruden, 1948. The heritability of accumulative monthly and annual egg production. Poultry Sci. 27:67—78. Lerner, I. M., and D. M. Cruden, 1950. The heritability of egg weight: the advantage of mass selection and of early measurements. Poultry Sci. 30:34—41. Nordskog, A. W., H. S. Tolman, D. W. Casey and C. Y. lin, 1974. Selection in small population of chickens. Poultry Sci. 53:1188-1219. Oliver, M. M., B. B. Bohren and V. L. Anderson, 1957. Heritability and selection efficiency of several measures of egg production. Poultry Sci. 36:395-402. Quadeer, M. A., 1976. Selection for egg mass in different social environments. Estimation of some parameters in selected and foundation stocks.
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