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Selection for Egg Mass in Different Social Environments 1. Estimation of Some Parameters in the Foundation Stock1,2
Selection for Egg Mass in Different Social Environments 1. Estimation of Some Parameters in the Foundation Stock 1,2 M. A. QUADEER and J. V. CRAIG Department of Dairy and Poultry Science, 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 56:1522-1535, 1977
INTRODUCTION Social stress and peck-order status can significantly influence productivity of chickens (reviewed b y Biswas and Craig, 1 9 7 0 ) . Bidirectional selection e x p e r i m e n t s indicated social d o m i n a n c e ability t o be a heritable trait in t h r e e p o p u l a t i o n s studied (Guhl et al., I 9 6 0 ; and Craig et al., 1 9 6 5 ) . It appears t h a t chickens may be unconsciously selected for increased aggressiveness b y selecting for productivity u n der competitive conditions. T h e results of
1 This investigation is part of the Kansas contribution to the NC-89 Regional Poultry Breeding Project. 2 Contribution No. 948-J, Department of Dairy and Poultry Science, and No. 263-J, Department of Statistics, Kansas Agricultural Experiment Station, Manhattan, Kansas.
Lowry and Abplanalp ( 1 9 7 0 , 1 9 7 2 ) s u p p o r t t h a t hypothesis. Their strains selected u n d e r floor flock c o n d i t i o n s b e c a m e socially domin a n t t o b o t h t h o s e selected in single cages and t o unselected controls. Investigations at Kansas State University (Tindell and Craig, 1 9 5 9 ; Craig, 1 9 7 0 ; Biswas and Craig, 1 9 7 0 ) a n d theoretical considerations b y McBride ( 1 9 6 0 , 1962) suggested t h a t selection might well be based o n productivity of families k e p t in separate groups. Such a procedure presumably w o u l d p r o d u c e socially tolerant strains because t h o s e families with less agonistic behavior should p r o d u c e a less stressful e n v i r o n m e n t , be m o r e productive, and t h u s be selected. There is evidence t h a t early sexual m a t u r i t y is associated with increased aggressiveness a n d potential social d o m i n a n c e , at least during
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ABSTRACT Data on hen-housed egg mass and associated egg production traits were obtained from a sample of the Kentville Randombred Control White Leghorn population and from four subsequent unselected generations of two subpopulations. Pullets were kept in three social environments in the zero generation and in individual cages thereafter. Least-squares technique was used to obtain estimates of phenotypic means, components of variance and covariance, heritabilities, and correlations (genetic, environmental, and phenotypic). Weighted means and parameter estimates regressed on generation number were obtained and compared for the subpopulations to test for random genetic drift. In addition, performances of samples of the same sire families kept in intermingled- and separated-family environments were compared to test for sire family by social environment interactions. Sire family by social environment interactions were not detected, except for early egg weight. Heritability and genetic correlation estimates were usually associated with large standard errors. The results suggested that non-additive and/or maternal effects have some influence. Evidence of random genetic drift between the subpopulations was generally lacking. Heritability estimates suggested that egg mass, age at sexual maturity, hen-day, and hen-housed rates of lay either lacked additive genetic variance or were lowly heritable (estimates based on pooled sire components were all less than 0.15). Egg weight was estimated to be moderately heritable (sire component estimates of 0.38 and 0.55). Genetic correlation estimates were generally positive and significant between egg mass and egg weight and between egg mass and both measuresof rate of production (hen-day and hen-housed rate). Genetic correlation estimates involving age at sexual maturity, egg weight, and other traits appear to be unreliable as they were inconsistent in sign and/or magnitude when obtained from the foundation stock and from advanced generations of the unselected controls.
SELECTION FOR EGG MASS
PARAMETER ESTIMATES BY OTHERS Several heritability and correlation estimates, along with unweighted means and associated standard errors, for traits similar to those we studied, are presented in Table 1. Estimates are from egg-strain, randombred control populations. Heritability estimates (diagonal elements in Table 1) indicate, in general, that early egg weight is highly heritable while age at sexual maturity and short-term rate of lay or production appear to be moderately heritable. Estimates between and within populations vary widely (Table 1). Much of the within-populations variability is associated with lower estimates based on sire components as compared with those based on dam components. Estimates from the Kentville Control, source of our stock, suggest that its heritabilities are similar to or higher than those of the other stocks. Genetic correlation estimates in Table 1 (off-diagonal entries, upper right) are quite
variable, even within populations, presumably reflecting the usual imprecision associated with them. Few investigators reported standard errors. Age at sexual maturity and early egg weight appear to have low to moderate positive associations genetically and phenotypically and a high environmental correlation (single estimate). However, earlier sexual maturity appears to be negatively associated with rate of lay or egg production. Thus, earlier maturity appears to be somewhat associated with smaller but more eggs early in the laying year. Large number of eggs laid or high short-term rate of lay is estimated to have a moderately large negative genetic correlation with egg weight. In contrast, an opposite environmental correlation exists between early egg production and egg weight (one estimate); environmental conditions favoring increased egg production also favor heavier eggs. MATERIALS AND METHODS Genetic Stock. Go we et al. (1973) described the formation and methods of maintaining the Kentville Randombred Control population. Briefly, it was originated by crossing four leading commercial strains of White Leghorntype laying stock in 1959. It has been maintained by mating 80 males with 240 females in a restricted random manner since 1961. A sample of hatching eggs from that strain was introduced at this station in the spring of 1968 as foundation stock for the selection study. Our procedures with the Kentville Randombred Control over the next five generations were as follows: Comparison of Familes in Intermingled vs. Separated Flocks. Data used to estimate sire family by environment interactions were obtained from progeny of parent stock (generation 0) hatched from imported eggs. They were obtained from 18 single-sire matings (20—25 females with each male). Hatches 1 through 4 were obtained from them at weekly intervals. Those hatches constituted foundation stocks for our selected strains. All chicks were sexes and vaccinated (Newcastle and bronchitis) at hatching. Combs of males were removed at hatching. They were debeaked at 4 weeks and beaks were trimmed again at 20 weeks. Sire families within each hatch were brooded intermingled in 4 pens up to 20 weeks of age. Only natural daylight was
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adolescence (Craig, 1968, 1970; Craig and Toth, 1969; Biswas and Craig, 1970; Craig et al., 1975). It appears, therefore, that if selection is to be based on a trait such as part-year egg production, without increasing aggressiveness, selection for early sexual maturity should be avoided. Therefore, in designing the study, Craig and Dayton chose part-year egg mass, beginning at 30 weeks of age, as the criterion of selection. Previously collected data indicated that nearly all pullets begin laying sooner than 30 weeks, under our conditions. This study began in 1968. A major objective was to determine if changes in social behavior resulted from selecting for increased egg mass in intermingled-family and separated-family environments. We hypothesized (for reasons indicated above) that selection in the intermingledfamily environment would favor increased aggressiveness, whereas selection in the separatedfamily environment would favor increased social tolerance. This paper reports estimates of heritabilities and genetic, environmental, and phenotypic correlations of part-year egg mass and associated egg production traits in both the foundation stock and the unselected subpopulations derived from it. It also reports on performance of progenies of the same sire families of the original stock kept in two social environments (families intermingled and separated).
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M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON TABLE 1 .—Heritability and correlation estimates and associated standard errors for some economic traits in randombred control populations1
Traits
Age at sexual maturity
Age at sexual maturity CC:
RR: OC: KC:
.42* .26 to .57b .09 c .27 to .38 e .15 t o . 5 0 f .33d .20 to ,80a .45 to .73a .14 .06 to .23
Egg weight (early)
CC:
RR: .33 + .09 d OC: -.20 to .23 a KC: .21 to .24a
Egg weight (early) e r P
.62b .13b
CC:
RR: OC: KC:
Short term rate of lay (production)
r
e r P
.13b -.18b
r
e r P
.64 .60 to .51 to .51 to .39 to .72 d .48 to .54 to .16 .09 to .78b -.02°
.73b .64C .53e .80 f .94a .92 a
CC:
-.23 -.80 t o - . 1 5 b -.226
RR: -.05 ± .17 d OC: -.57 to -.09 a KC: -.15 to .03a
CC:
-.44 -.50 to -.06 b -.55 e
RR: -.58 + .10 d OC: -.70 to -.27a KC: -.46 to -.45a
.22 CC: RR: OC: KC:
.32 .06 to .15 to .18 d .18 to .21 to .11 .06 to
.43b .216 .39a .73a .20
1 CC = Cornell or Regional Cornell Control, RR •• Regional Red Control, OC = Ottawa Control, KC = Kentville Control.
*Diagonal elements consist of mean heritabilities (italics), estimates or ranges by particular investigators) (with coded references), mean standard errors (boldface), and range of standard errors, respectively. Off-diagonal elements, upper right, consist of mean genetic correlations (italics) and estimates by particular investigator(s) (with coded references), respectively; values in the lower left portion are environmental (r e ) and phenotypic (rp) correlations with coded reference. Coded references: a Gowe et al. (1973). b King (1961). c King et al. (1963). d Kinney and Lowe (1968). eKinney et al. (1968). f Vaccaro and Van Vleck (1972).
available during rearing. Cockerels were removed at about 16 weeks of age and placed in individual cages. At 22 weeks of age, pullets of each hatch were moved to adult-housing environments. Pullets of hatches 1 and 3 were moved into a laying house with each sire family assigned to a single small (150 cm. by 230 cm.) pen. Hatch 1 pullets were on one side of the house and hatch 3 on the other. Allotment of sire families to pens within hatches was random. Up to 30 daughters were kept from each sire family. Pullets from hatches 2 and 4 were placed in
another laying house with sire families intermingled. Within each hatch, a maximum of 10 pullets of each sire family was randomly assigned to 3 intermingled flocks. The intermingled flocks of hatches 2 and 4 were housed in pens on opposite sides of an aisle. Genetic Parameter Estimation. Data used to estimate heritabilities and genetic correlations in generation 0 were obtained from pullets of hatches 1 through 4 (described above) and from progeny of 2 additional hatches (5 and 6). Hatches 5 and 6 were obtained from 6 of the 18 single-sire matings. Those 6 were chosen
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r
.23+ .13 to .78b .32C .57^
Short term rate of lay (production)
SELECTION FOR EGG MASS
lated for the periods indicated above. It is the ratio of eggs laid to trapnesting days, i.e., 21 days for generations 0 and 1 and 30 days for generations 2, 3, and 4. This trait includes effects of late sexual maturity (after 29 weeks of age) and mortality, if either occurs. 4. Egg weight (EW). One egg (if available) was weighed for each pullet during week 33 of generations 0 and 1 and during week 3 5 in later generations. 5. Hen-housed egg mass (HHMAS). Grams of egg per bird housed per day was used to estimate egg mass, which was calculated for the periods indicated above as the product of egg weight and hen-housed rate of lay. Because individual pullets could lack records on some measures, heritability estimates were obtained for each trait separately and for pairs of traits for genetic correlations, in order to use as many data as possible. Number of sires, dams, and pullet records for each trait included in the analysis are shown in Table 2. Statistical Analyses. Analyses comparing sire families in intermingled vs. separated flocks were carried out using a mixed model version of least squares program (LSMLMM) developed by Harvey (1972). The model was detailed by Quadeer (1976). Variance and covariance components also were estimated by LSMLMM. Statistical models for different generations are detailed by Quadeer (1976). Heritability, genetic, environmental, and phenotypic correlation estimates were computed by the program using sire components, dam components, and sire and dam components combined. The standard errors of heritabilities and genetic correlations computed by the program were after Tallis (1959) and Swiger et al. (1964), respectively, as modified by Harvey for unequal sample sizes (see Harvey, 1972). Weighted estimates of parameters were obtained over generations by using the inverse of the square of the respective standard errors as weighting factors.
RESULTS AND DISCUSSION Families in Intermingled and Separated Flocks Compared. Main effects. Analyses of variance (Table 3) suggested sire effects on all traits analyzed, social environment effects on egg weight and hen-day rate, and hatch effects within the separated-family environment on egg weight and egg mass. However, differences between social environments are suspect be-
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randomly and constituted foundation stock for the unselected control lines Q and C2, respectively. Two of the 6 single-sire matings were, by chance, common for Ci and C2. Data from Cj and C 2 in generations 1 through 4 also were used. Procedures used with the unselected Ci and C2 populations for generations 0 through 4 follow. Generation 0. Pullets of hatches 5 and 6 were reared as described for hatches 1—4 except that chicks were debeaked at 4 weeks only. They were placed in individual laying-hen cages at about 5 months of age. Portions of 5 back-to-back cage rows were used. Allotment of birds to cages was random, but pullets of hatches 5 and 6 were in different rows. Generation I. One male and 5 to 10 females were randomly chosen within each of the 6 sire families of lines Q and C2 in generation 0 as parents of generation 1. The single male from each sire family was mated to females of the other 5 sire families by artificial insemination. The same procedures for choosing and mating breeders within Q and C2 were followed in subsequent generations. Generation 2. Hatching, rearing, and housing details were similar to those of previous generations. Marek's disease reduced survival percentages until pullets were caged at 20 weeks to 55 and 52 in Q and C 2 , respectively. Mortality associated with this disease continued thereafter at a lower rate. Generation 3. Strains Q and C 2 were hatched separately with a week interval between hatches. Chicks were vaccinated against Marek's disease at hatching, and were debeaked at 4 and 20 weeks. Other details were the same as in generations 0—2. Generation 4. The hatching season was changed from fall to spring. Chicks of both strains were obtained from 4 weekly hatches. Rearing and housing procedures were similar to those of previous generations. Traits Studied. We studied 5 production traits: 1. Age at first egg in weeks (SM). 2. Hen-day rate of lay (HDR) from 30 to 37 weeks in generation 0 and 1 and from 30 to 40 weeks in later generations. Hen-day rate for each bird was calculated as the ratio of eggs laid to trapnesting days (3 per week) from first egg to end of period or until death. Hen-day rate was measured independently of sexual maturity and mortality. 3. Hen-housed rate of lay (HHR) was calcu-
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M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON
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Stability of Control Strains. Least squares means, weighted means, regressions on generation, and standard errors of 5 production traits are summarized in Table 4. Generally, strains Ci and C2 performed similarly as indicated by nonsignificant differences between their weighted means. Generation-by-generation comparisons of the strains indicated a few erratic differences; Cj had later sexual maturity and heavier egg weight in generation 0, greater egg mass in generation 2, and earlier maturity in generation 3. Differences in generation 0 were confounded by the strains having been produced in different hatches and housed after most pullets already were producing. Also, egg production was recorded from the same date for both strains, though Ci was a week older. The significant difference in egg mass between strains in generation 2 appears to be associated with different responses to Marek's disease, a major factor in that year. Lack of significant linear time trends suggested, contrary to our expectation, that environmental trends were not large. We expected time trends because we had changed length of period (30—37 to 30—40 weeks), season of hatch (fall to spring), and age of pullets when eggs were weighed (33 to 35 weeks). Perhaps the small size of the populations sampled or the
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I
il
cause hatch effects and house effects are confounded with social environment. Hatch effects are likewise confounded with location within houses. Interactions. Of the various interactions, our primary interest was in sire family by social environment interaction. That interaction was significant for egg weight (P<.05) only. Our generally negative results agree with those of Lowry et al. (1956), Tindell and Craig (1960), and McBride (1962), none of whom found sire family by housing environment interactions (for various housing conditions). However, Lowry and Abplanalp (1970) produced subpopulations particularly suited to individual cages or floor pens by selecting within those environments, a result not expected in view of their lack of significant sire family by social environment interactions in data analyzed before the subpopulations were formed. It appears, therefore, from their results, that genetic differences magnified by selection under different environmental conditions may yield genotype by environment interactions not previously evident.
59.9 222.3 182.1 283.3 3473.4" 276.5 306.2 508.2 100.6 209.8
DX E/S D X E/S R R R R R R R
1 17
XXX
1 1 17 17 2 2
XX
x = Range from 346 to 357, xx = Range from 253 to 283, xxx = Range from 900 to 1273.
**P<0.01
*P<0.05
1
1051.9'* 263.3
D/S R
17
X
Sires (S) Dams within sires (D/S) Social environment (intermingled vs. separated) (E) Sires X social environments (S X E) Dams X social environment/sires (D X E/S) Hatches within intermingled (H/E;) Hatches within separated (H/E 2 ) Sires X hatches/intermingled (S X H/E,) Sires X hatches/separated (S X H/E 2 ) Pens within hatch 2 Pens within hatch 4 Residual (R)
Egg mass
DF
Denominator for F-test
Source of variation
1
276.9** 24.7* 13.1 0.3 84.2* 18.1 19.6 11.1 7.7 12.8
242.7** 26.1
Egg weight
0.64** 0.04 0.05 0.02 0.02 0.05 0.04 0.08 0.03 0.05
0.22** 0.06
Hen-day rate
Mean squares for productivity measures
TABLE 3 .—Analyses of variance and least square means for comparison of sire families in intermingled and separated flocks
wnloaded from http://ps.oxfordjournals.org/ by guest on May 5, 2015 0.04 0.07 0.07 0.14 0.83 0.06 0.10 0.16 0.03 0.08
0.38** 0.10
Henhoused rate
to
C/3
o o
a
SO
z o
o
m r w
c, c,
c, c2
c, c2
EW
HDR
HHR
Generation means regressed on generations.
**P<.01.
*P<.05.
2
0.65 ± 0 . 0 4 0.60 ± 0.04 -0.05
0 . 7 0 + 0.03 0 . 7 2 ± 0.03 -0.02
55.0 ± 0 . 6 5 52.6 ± 0 . 6 7 2.4** ±0.85 ±0.91
±0.14 ±0.14
± 1.9 ± 2.1
0.69 ± 0 . 0 3 0.69 ± 0 . 0 3 0.00
0.75 ± 0 . 0 3 0.75 ± 0 . 0 3 0.00
54.2 54.6 -0.4
22.7 22.7 0.0
39.8 38.8 1.0
1
± 1.10 ± 1.60
±0.33 ±0.34
0.59 ± 0 . 0 4 0.60 ± 0 . 0 5 -0.01
0.65 ± 0 . 0 3 0.69 ± 0 . 0 4 -0.04
51.3 49.8 1.5
23.0 23.6 -0.6
3 2 . 4 . ± 2.4 15.8 ± 4 . 2 16.6**
2
Individual generation means were weighted by the inverse of their variances.
Diff.
Diff.
Diff.
Diff.
2 4 . 0 ± 0.16 22.7 ± 0.17 1.3**
3 7 . 8 ± 2.4 32.6 ± 2.4 5.2
0
Generation
± 1.4 ± 1.5
±0.79 ±0.82
0.69 ± 0.02 0 . 7 0 ± 0.03 -0.01
0.71 ± 0 . 0 3 0.70 ± 0 . 0 3 0.01
50.9 52.8 -1.9
20.4 ± 0 . 2 5 22.4 ± 0 . 2 5 -2.0**
36.3 39.2 -2.9
3
±0.62 ±0.61
±0.47 ±0.47
± 1.5 ±1.5
0.67 ± 0 . 0 3 0.65 ± 0 . 0 3 -0.02
0.70 ± 0 . 0 3 0.69 ± 0.03 -0.01
51.4 52.8 -1.4
22.7 23.2 -0.5
36.9 36.0 0.9
4
0.67 ± 0 . 0 1 0.66 ± 0 . 0 2 0.01 ± 0 . 0 2
0.70 ± 0 . 0 1 0.71 ± 0 . 0 1 -0.01 ± 0 . 0 2
52.7 ± 0 . 3 4 52.9 ± 0 . 3 5 -0.10 ± 0 . 4 9
22.8 ± 0 . 0 9 22.7 ± 0 . 0 9 0.07 ± 0 . 1 3
36.82 ± 0 . 8 0 36.24 ± 0 . 8 6 1.12 ± 1 . 1 8
Weighted' mean ± s.e.
traits
±0.33 ±0.62 ±0.42
±0.39 ±0.17 ±0.29
±0.94 ±3.51 ±2.65
2
0.004 ± 0.004 0.011 ± 0.016 0.005 ± 0.006
•O.004 ± 0 . 0 1 3 -0.011 ± 0 . 0 0 7 0.003 ± 0 . 0 0 7
-1.05 -0.14 -0.91
-0.49 0.23 -0.56
-0.53 0.72 -1.25
b ± s.e
m S
in
a
>
7>
< r>
> a 2°
>
a a
>
PANE
1
c, c2
SM
Diff.
c, c2
HHMAS
Trait
Least squares mean of
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TABLE 4.—Least square means, weighted means, and regressions on generations for productivity in control strains in generation 0-4
oo
M. A. QL
SELECTION FOR EGG MASS
limited. We shall investigate it further in subsequent analyses. Genetic Parameter Estimates. Heritability estimates. Heritability estimates based on sire, dam, and sire plus dam components of variance for generation 0 flocks kept in 3 social environments are presented in Table 5. For all traits except egg weight, estimates of heritability from the sire component in separated-family flocks were lower than the corresponding estimates in flocks where families were kept intermingled, suggesting that pen effects between separated families were of little consequence. Those effects, if present, should inflate the estimates. Combined estimates of heritability obtained by pooling sums of squares are presented in the last column of Table 5. Table 6 summarizes heritability estimates obtained for generations 0 through 4 for the Ci and C 2 caged control populations, regressions of those estimates on generation number, and their weighted means. The data indicate considerable fluctuation of heritability estimates from
TABLE 5.—Heritability estimates in generation 0
Trait
Heritability (h 2 ) 1
Individual cages
Intermingled flocks
Separated flocks
Pooled over all environments
HHMAS
h
0.25 ±0.21 0.38 ±0.27 0.13 0.32 ±0.12
0.18 +0.11 0.12 ±0.15 -0.06 0.15 ±0.06
0.10 ±0.07 0.10 ±0.14 0.0 0.10 ± 0.06
0.14 ±0.06 0.24 ±0.07 0.10 0.19 ±0.03
0.04 ± 0.09 0.68 ±0.27 0.64 0.36 ±0.13
0.04 ± 0.07 0.27 ± 0.20 0.23 0.15 ±0.08
-0.00 ± 0.03 0.21 ±0.15 0.21 0.10 ±0.06
0.01 ±0.02 0.16 ±0.07 0.15 0.08 ± 0.03
0.49 ± 0.34 0.53 ±0.32 0.04 0.51 ±0.15
0.48 ± 0.22 0.55 ±0.18 0.07 0.51 ± 0.09
0.62 ± 0.26 0.74 ±0.17 0.12 0.68 ± 0.09
0.55 ±0.19 0.60 ± 0.09 0.05 0.57 ± 0.06
-0.02 ± 0.06 -0.38 ±0.26 -0.36 -0.20 ± 0.08
0.17 ±0.10 0.07 ±0.15 -O.10 0.12 ±0.06
0.05 ± 0.05 0.46 ±0.15 0.41 0.25 ± 0.07
0.10 ± 0.05 0.15 ±0.06 0.05 0.12 ±0.03
0.15 ±0.15 0.26 ± 0.25 0.11 0.21 ±0.11
0.16 ± 0.09 0.13 ±0.14 -0.03 0.15 ±0.06
0.05 ± 0.05 0.16 ±0.13 0.11 0.11 ±0.05
0.11 ±0.05 0.21 ± 0.06 0.10 0.16 ± 0.03
S
hb hb-h| SM
h
S+D
h
S
hb hb-h S h
EW
S+D
h|
hb
hb"h| HDR
h
S+D
h
S
h
P b_hs
h h
HHR
S+D
h|
hb hb- h S h
S+D
= from sire component, D = from dam component, S + D = from sire plus dam component.
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few data points used in testing significance of regression coefficients prevented environmental effects from being detected. Absence of time trends were reported by Dave et al. (1969) in broiler control strains, King et al. (1963) for sexual maturity in the Regional Cornell Control and by Gowe et al. (1959) for hen-housed and survivor's egg production, body weight at housing, March body weight, and laying house mortality over 6 generations in the Ottawa Control. King et al. (1963) found significant time trends for egg weight, as did Kinney et al. (1968) for age at first egg, egg weight at 32 and 55 weeks, and production percentages from 40 to 55 and 55 to 70 weeks. Gowe et al. (1959) reported a significant negative regression for age at sexual maturity for the Ottawa Control strain and suggested that general improvements in brooding, rearing facilities, and management were responsible. They also reported a significant increase in March egg weight. Clearly, our evidence for random genetic drift from the Q and C 2 populations is quite
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S+D
S+D
-0.05 ± 0.08 0.17 ±0.30 0.22 0.06 ±0.12
-0.06 ± 0.08 0.34 ±0.28 0.40 0.14 ±0.12
-0.02 ± 0.06 -0.38 ± 0.26 -0.36 O.20 ± 0.08
0.15 + 0.15 0.26 ± 0.25 0.11 0.21 ±0.11
0.06 ± 0.18 0.34 ±0.36 0.28 0.20 ±0.16
-0.06 ± 0.14 0.18 + 0.40 0.24 0.06 ± 0.16
*P<.05.
S = from sire component, D = from dam component, S+D = from sire plus dam component.
Unweighted means.
h
hb h b" h S
•>S
h|+D
hb" h S
S "D
h
h
0.03 ±0.14 -0.10 ±0.32 -0.13 -0.04 ±0.12
0.11 ±0.18 -0.31 ±0.32 -0.42 -0.10 ±0.10
0.67 ± 0.40 0.23 ±0.38 -0.44 0.45 ±0.18
0.93 ± 0.44 -0.27 ±0.32 -1.20 0.33 ±0.16
0.08 ±0.18 -0.15 ±0.36 -0.23 -0.04 ±0.12
3
-0.09 ±0.10 0.11 ±0.36 0.20 0.01 ±0.14
0.07 ± 0.20 0.10 ±0.38 0.03 0.08 ±0.16
0.03 ± 0.22 0.86 ± 0.46 0.83 0.44 ± 0.22
0.37 ±0.32 1.0 ±0.36 0.63 0.69 ±0.18
-0.09 ± 0.16 -0.23 ±0.46 -0.14 -0.16 ±0.16
4
-0.02 ± 0.05 0.20 ±0.14 0.22+ 0.10 ± 0.06
-0.02 ± 0.04 -0.10 ±0.14 -0.08+ -0.08 ±0.05
0.38 ±0.15 0.44 ±0.17 0.06+ 0.50 ± 0.08
-0.08 ± 0.04 0.12 ±0.13 0.20+ -0.36 ±0.02
-0.01 ±0.06 0.27 ±0.16 0.28+ 0.13 ±0.06
Weighted mean ± s.e.
-0.04 -0.07 -0.03 -0.06
0.03 0.05 0.01 0.04
-0.09 0.05 0.14 -0.02
0.17 0.11 -0.06 0.14
-0.05 -0.19 -0.14 -0.12
± 0.03 ± 0.05 ± 0.07 ± 0.02
±0.02 ±0.10 ±0.11 ± 0.04
±0.23 ±0.10 ±0.31 ± 0.04
±0.13 ±0.28 ± 0.29 ±0.17
± 0.04 ±0.07 ±0.10 ±0.03*
b ± s.e.
> a
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h
1.77 0.17 -1.60 0.70
0.64 ±0.38 0.36 ±0.34 -0.28 0.50 ±0.18
0.49 ± 0.34 0.53 ±0.32 0.04 0.51 ±0.15
±0.70 ±0.61 * ± 0.28
0.78 ± 0.46 1.0 ±0.38 0.22 0.91 ±0.18
0.05 ± 0.24 0.46 ± 0.48 0.41 0.26 ± 0.22
-0.13 ±0.04 -0.70 ±0.22 -0.57 -0.42 ± 0.02
-0.06 ± 0.08 0.57 ±0.30 0.63 0.25 ±0.14
2
0.04 + 0.09 0.68 ±0.27 0.64 0.36 +0.13
0.25 ± 0.21 0.38 + 0.27 0.13 0.32 ±0.12
1
MP AN DA. D
HHR
S
S+D
h
h
h
hb" S
"b h
s
S+D
h
h
n? h _n b s
"S
0
Generation
CRAIG,
HDR
EW
SM
HHMAS
Trait
Heritability (h2)'
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TABLE 6 .—Heritability estimates in control (caged) strains in generations 0-4, weighted heritability estimates and regression of h1 on the number of generations
•ER,
SELECTION FOR EGG MASS
Our heritability estimates based on sire components of variance from the 2 analyses were:
hg from
Traits
Generation 0 pooled over environments
Generations 0-4 weighted mean (caged pullets)
HHMAS SM EW HDR HHR
0.14 ± 0.06 0.01 ± 0.02 0.55 ±0.19 0.10 ± 0.05 0.11+0.05
-0.01 ± 0.06 -0.08 ± 0.04 0.38 ±0.15 -0.02 ± 0.04 -0.02+0.05
The negative weighted mean estimates of hg for hen-housed egg mass, sexual maturity, hen-day, and hen-housed rate of lay for caged pullets suggest that heritability of those traits is essentially zero. However, those same traits, except for age at maturity, were estimated to be heritable in generation 0 when data were pooled over all social environments. The discrepancies could be associated with the small number of sires used in the formation of the Q and C 2 strains and in each subsequent generation. The pooled estimate of hg for sexual maturity of 0.01 ± 0.02 in generation 0 is probably due to the fact that most pullets were laying before being housed in that generation. Our estimates of hg for egg weight of 0.55 ± 0.19 in generation 0 and 0.38 ± 0.15 for caged layers in generations 0—4 agree well with the estimate of Vaccaro and Van Vleck (1972), who obtained hg for 32-week egg weight as 0.39 ± 0 . 1 6 . Our estimates of heritability are considerably lower in general than corresponding estimates reported by Gowe et al. (1973) for the Kentville Control. However, our estimates, except for age at sexual maturity, are within the range of values reported in the literature (see Table 1). None of the estimates of linear regression of heritability on generation number was significant (except for hen-housed egg mass for hg + Q). King et al. (1963) found no important genetic trends in the Cornell Randombred Control during six generations for body weight, sexual maturity, egg production, and egg quality traits. Kinney et al. (1968) also failed to detect time trends of h 2 and sire variance component for sexual maturity, 32-week egg weight, and production percentage for 40—55 and 55—70 weeks. Correlation estimates: generation 0. Estimates of genetic, environmental, and phenotypic correlations for generation 0 flocks under different social environments are given in Table 7. Some estimates exceed their limits and most are associated with large standard errors. Hen-housed egg mass had large positive associations with hen-day and hen-housed rates of lay in intermingled and separated family flocks and in data pooled over all environments; pooled genetic correlations ranged from 0.83 to 0.96 (>3 standard errors), Table 7. Genetic correlation estimates based on data from individually caged pullets were erratic and associ-
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generations to generation. Estimates range from negative to above unity and their standard errors are often as large as, or larger than, the heritability estimate. Differences between estimates from sire and dam components were inconsistent from generation to generation. We met the requirement that unselected sires and dams be mated at random for valid variance component estimation; however, more sires, dams, and progeny apparently are required to obtain estimates with much reliability (Robertson, 1960). In general, our heritability estimates from dam components were larger than those from sire components (Tables 5 and 6). As suggested by King and Henderson (1954), maternal effects could cause higher values of ho- Jerome et al. (1956) found dominance variance to be 3.63 times as great as the additive genetic variance for egg production, which was an important source of bias when the dam component of variance was used to estimate heritability. King (1961) found the sire by dam interaction component of variance large in estimates from the Cornell Randombred Control population. He concluded that an upward bias in h 2 estimate could be caused when the dam component is estimated from a nested design. He also concluded that maternal effects must be important for sexual maturity, percentage egg production to January 1, and to 72 weeks of age. Vaccaro and Van Vleck (1972) also emphasized the sire by dam interaction in the component of variance. Our findings agree with those of Go we et al. (1973), who obtained considerably higher heritability estimates from dam components than from sire components, particularly for the Kentville Control, for sexual maturity and rate of production.
1531
1532
M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON TABLE 7.—Estimates of correlations among productivity
Traits
HHMAS X SM
Correlations 1
r
GS GD r G(S+D) r ES fED r E(S+D) r
r
HHMAS X EW
P
r
r
HHMAS X HDR
P
r
GS GD r G(S+D) r ES rED r E(S+D) r
r
HHMAS X HHR
r
GS GD r G(S+D) rES r ED r E(S+D) r
r
SM X EW
P
P
i"GS r GD r G(S+D) rES r ED r E(S+D) r
SM X HDR
P
r
GS GD r G(S+D) 'ES r ED r E(S+D) r
r
SM X HHR
r
P
GS fGD r G(S+D) fES rED r E(S+D)
Separated flocks
Pooled over all environments
Individually caged
Intermingled flocks
1.30 + 0 . 6 1 ' 0.0+ 0.0+ -0.12 0.12 0.00 0.03
-0.71 ± 0.53 -0.77 ± 0 . 6 2 -0.73 ± 0 . 3 3 * •O.04 0.19 0.06 -0.10
0.45 ± 0.49 0.0+ 0.0+ 0.20 0.32 0.26 0.24
0.29 ± 0 . 3 6 1.30 ± 0 . 5 1 * 0.90 ± 0 . 1 9 * * 0.37 -0.22 0.10 0.32
0 . 9 2 :± 0 . 1 3 * * 0 . 5 8 :± 0 . 1 3 * * 0.66 :± 0 . 0 9 * * 0.29 0.07 0.23 0.42
0.65 ± 0 . 1 7 * * 0.53 ± 0 . 1 3 * * 0.58 ± 0 . 0 8 * * 0.21 0.20 0.21 0.32
0.74 ± 0 . 3 1 * -1.30 + 4 . 6 0 -4.1 ± 4 8 . 0 0.95 0.97 0.96 0.93
0.76 ± 0 . 1 8 * * 0.98 ± 0 . 2 9 * * 0.83 ± 0 . 1 0 * * 0.95 0.94 0.95 0.93
0.57 ± 0 . 4 9 0.88 ± 0 . 0 5 * * 0.83 ± 0 . 0 5 * * 0.97 0.98 0.97 0.93
0.83 ± 0 . 1 0 * * 0.89 ± 0 . 0 5 * * 0.87 ± 0 . 0 4 * * 0.97 0.97 0.97 0.95
0.74 + 0.31* -1.30 ± 4 . 6 0 -4.10 ± 4 8 . 0 0.95 0.97 0.96 0.93
0.75 ± 0 . 1 8 * * 1.0 ± 0.52 0.81 ± 0 . 1 2 * * 0.96 0.95 0.95 0.93
0.55 ± 0 . 4 7 0.88 ± 0 . 0 4 * * 0.83 ± 0 . 0 5 * * 0.97 0.97 0.97 0.93
0.94 ± 0 . 0 3 * * 0.96 ± 0 . 0 1 * * 0.95 ± 0 . 0 1 * * 0.99 0.99 0.99 0.98
0 . 2 5 i 0.63 -0.38 + 0.63 -0.12 i 0.33 -0.06 0.22 0.07 0.02
-0.27 ± 0 . 4 2 -0.06 +: 0 . 2 8 -0.11 ±: 0 . 1 9 0.05 0.02 0.04 -0.02
-0.64 ± 0 . 3 5 -0.34 ± 0 . 5 0 -0.46 ± 0 . 2 8 0.09 0.09 0.09 -0.07
-0.43 ± 0 . 3 5 -0.17 ± 0 . 1 6 -0.22 ± 0 . 1 3 0.05 0.10 0.07 -0.03
1.20 + 0 . 6 9 0.0+ 0.0+ -0.10 0.05 -0.03 0.02
-0.47 ± 0 . 5 2 -1.20 +: 1.80 -0.80 + 0 . 4 4 -0.06 0.15 0.03 -0.11
-0.97 + 1.40 -0.93 ± 0 . 9 4 -0.81 ± 0.43 -0.03 0.17 0.06 -0.06
-0.18 ± 0 . 6 9 -0.86 ± 0 . 4 1 * -0.69 ± 0 . 2 4 * -0.09 0.05 -0.03 -0.09
1.20 + 0 . 6 9 0.0+ 0.0+ •0.10 0.05 -0.03 0.02
-0.47 i: 0 . 5 3 -1.50 i: 2 . 8 0 -0.90 i: 0 . 4 9 0.06 0.17 0.04 -0.11
-0.96 ± 1 . 2 0 -0.95 ± 0 . 9 5 -0.83 ± 0 . 4 3 -0.03 0.18 0.06 -0.06
-0.02 ± 0.64 -0.73 ± 0 . 3 9 * -0.56 ± 0 . 2 3 * -0.16 -0.05 -0.11 -0.15
-0.93 :± 0 . 4 4 * -0.97 :± 0 . 9 5 -0.93 :± 0 . 4 2 * -0.00 0.20 0.08 -0.08
-0.27 ± 0 . 4 5 -0.57 ± 0 . 3 3 -0.47 ± 0 . 1 9 * -0.10 0.00 -0.05 -0.11
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GS GD r G(S+D) r ES r ED fE(S+D) r
traits in generation 0
SELECTION FOR EGG MASS TABLE 7
Correlations
Traits
Individually caged
1533
-Continued
Intermingled flocks
Separated flocks
Pooled over all environments
TGS r GD r G(S+D) r ES r ED r E(S+D) r P
-0.39 ± 0.59 0.0+ 0.0+ -0.08 0.07 -0.01 -0.14
-0.39 ±0.35 1.40 ±1.90 0.41 ± 0.30 0.10 -0.52 -0.20 -0.03
0.20 ± 0.71 0.14 ±0.19 0.13 ±0.15 0.06 -0.15 0.01 0.06
-0.002 ± 0.29 -0.00 +0.17 -0.00 ±0.12 -0.04 -0.04 -0.04 -0.03
EW X HHR
'GS 'GD r G(S+D) 'ES TED r E(S+D) r P
•0.39 ± 0.59 0.0+ 0.0+ -0.08 0.07 -0.01 -0.14
-0.40 ±0.35 1.60 ± 2.8 0.41 ±0.31 0.10 -0.50 -0.19 -0.03
0.18 ±0.66 0.14 ±0.19 0.13 ±0.15 0.06 -0.17 0.00 0.06
0.005 ± 0.29 0.02 ± 0.16 0.01 +0.12 -O.04 -0.05 -0.05 -0.02
r
1.10 ±0.13** -1.00 ± 4.5 -0.55 ± 15.0 0.99 1.00 1.00 1.00
HDRX HHR
GS GD r G(S+D) fES 'ED r E(S+D) r P r
1.0 1.0 1.0 1.0 1.0 1.0 1.0
±0.0** ±0.19** ±0.01**
1.0 1.0 1.0 1.0 1.0 1.0 1.0
±0.01** ±0.0** ±0.0**
1.0 ±0.002** 0.99 ±0.008** 1.0 ±0.004** 0.98 0.98 0.98 0.98
1r GS = genetic correlation from sire component, rQD = genetic correlation from dam component, rc(S+D) = genetic correlation from sire plus dam component, r g s = environmental correlation from sire component, rgrj = environmental correlation from dam component, rE(g+D) = environmental correlation from sire plus dam component, r p = phenotypic correlation. t Negative variance component.
* r c ^ 2 s.e. **TQ>Z
s.e.
ated with larger standard errors, presumably because of smaller degrees of freedom and fewer pullet records from that environment. Hen-housed egg mass had a moderately large and positive genetic correlation with egg weight when estimated from data of pullets kept in flocks and from pooled data; overall estimates ranged from 0.53 to 0.65 (>3 standard errors). Associations of hen-housed egg mass and age at sexual maturity tended to be small and nonsignificant. Estimates of those correlations are somewhat dubious because of late housing of pullets in generation 0, as previously noted. The relative inaccuracy of sexual maturity data in generation 0 reduces confidence in other correlation estimates involving this variable. Egg weight at 3 3 weeks showed little association with variables other than egg mass.
Correlation estimates: caged pullets. Correlations were estimated from records of pullets kept in individual cages in generation 0 through 4. Single generation estimates showed large fluctuations in sign and magnitude (presumably caused by relatively small amounts of data within generations). Regressions of correlation estimates on generation number revealed no significant trends (Quadeer, 1976). However, only large changes would have been detected (if present) because of the relatively small quantity of data within generations. (Generation-bygeneration estimates and regressions on generation are available upon request.) Table 8 presents the weighted mean correlations based on data from all five generations. Hen-housed egg mass was estimated to have high and positive correlations with hen-day and
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EW X HDR
M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON hen-housed egg p r o d u c t i o n , a m o d e r a t e l y high and positive genetic correlation with egg weight, a n d an unclear association with age at sexual m a t u r i t y , Table 8. These results are consistent with t h o s e o b t a i n e d in generation 0 (Table 7 ) . Age at sexual m a t u r i t y of caged pullets appeared t o have little association with egg weight in o u r data and showed inconsistent genetic associations with hen-day and henhoused rates of lay (estimates based on sire and d a m covariances were of o p p o s i t e sign). Egg weight of caged pullets showed little association with traits o t h e r t h a n egg mass, as was also t h e case for generation 0 pullets in 3 different e n v i r o n m e n t s (see above).
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Biswas, D. K., and J. V. Craig, 1970. Genotypeenvironment interactions in chickens selected for high and low social dominance. Poultry Sci. 49:681-692. Craig, J. V., 1968. Correlated responses in body weight and egg production traits in chickens selected for social dominance. Poultry Sci. 47:1033-1035. Craig, J. V., 1970. Interactions of genotype and housing environment in White Leghorn chickens selected for high and low social dominance. XlVth World's Poultry Congress, Madrid, 2:37—4-2. Craig, J. V., M. L. Jan, C. R. Polley, A. L. Bhagwat and A. D. Dayton, 1975. Changes in relative aggressiveness and social dominance associated with selection for early egg production in chickens. Poultry Sci. 54:1647-1658. Craig, J. V., L. L. Ortman and A. M. Guhl, 1965. Genetic selection for social dominance ability in chickens. Anim. Behav. 13:114—131. Craig, J. V., and A. To'th, 1969. Productivity of pullets influenced by genetic selection for social dominance ability and by stability of flock membership. Poultry Sci. 48:1729-1736. Dave, D. S., R. G. Jaap and W. R. Harvey, 1969. Results of selection for eight-week body weight in three broiler populations of chickens. Poultry Sci. 48:1336-1348. Gowe, R. S., A. S. Johnson, J. H. Downs, R. Gibson, W. F. Mountain, J. H. Strain and B. F. Tinney, 1959. The value of a random-bred control strain in a selection study. Poultry Sci. 38:443—462. Gowe, R. S., W. E. Lentz and J. H. Strain, 1973. Long-term selection for egg production in several strains of White Leghorns: performance of selected and control strains including genetic parameters of two control strains. Fourth Europ. Poultry Conf., London:225—245. Guhl, A. M., J. V. Craig and C. D. Mueller, 1960. Selective breeding for aggressiveness in chickens. Poultry Sci. 39:970-980. Harvey, W. R., 1972. (a) General outline of computing procedures for six types of mixed models, (b)
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SELECTION FOR EGG MASS
Intra-flock genetic merit under floor and cage managements. Poultry Sci. 35:1034—1043. McBride, G., I960. Poultry husbandry and the peck order. Br. Poultry Sci. 1:65-68. McBride, G., 1962. The interactions between genotypes and housing environments in the domestic hen. Proc. Australian Soc. Animal Prod. 4:95—102. McCartney, M. G., 1962. Heritabilities and correlations for reproductive traits in a randombred population of turkeys. Poultry Sci. 41:168—174. Quadeer, M. A., 1976. Selection for egg mass in different social environments. Estimation of some parameters in selected and foundation stocks. Ph.D. dissertation, Kansas State University Library, Manhattan. Robertson, A., 1960. Experimental design in the evaluation of genetic parameters. Biometrics, 15:219-226. Swiger, L. A., W. R. Harvey, D. 0 . Everson and K. E. Gregory, 1964. The variance of intraclass correlation involving groups with one observation. Biometrics, 20:818-826. Tallis, G. M., 1959. Sampling errors of genetic correlation coefficients calculated from analyses of variance and covariance. Australian J. Stat. 1:35^3. Tindell, D., and J. V. Craig, 1959. Effects of social competition on laying house performance in the chicken. Poultry Sci. 38:95-105. Tindell, D., and J. V. Craig, 1960. Genetic variation in social aggressiveness and competition effects between sire families in small flocks of chickens. Poultry Sci. 39:1318-1320. Vaccaro, R., and L. D. Van Vleck, 1972. Genetics of economic traits in the Cornell Randombred Control population. Poultry Sci. 51:1556—1565.
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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. 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 , 1961. Inheritance of economic traits in the Regional Cornell Control population. Poultry Sci. 4 0 : 9 7 5 - 9 8 6 . King, S. C , andC. R. Henderson, 1954. Heritability studies of egg production in the domestic fowl. Poultry Sci. 33:155-169. King, S. C , L. D. Van Vleck and D. P. Doolittle, 1963. Genetic stability of the Cornell Randombred Control population of White Leghorns. Genetical Research, 4:290-304. Kinney, T. B., Jr., and P. C. Lowe, 1968. Genetic and phenotypic variation in the Regional Red Controls over nine years. Poultry Sci. 47:1105-1110. Kinney, T. B., P. C. Lowe, B. B. Bohren and S. P. Wilson, 1968. Genetic and phenotypic variation in randombred White Leghorn controls over several generations. Poultry Sci. 47:113—123. Lowry, D. C , and H. Abplanalp, 1970. Genetic adaptation of White Leghorn hens to life in single cages. Br. Poultry Sci. 1 1 : 1 1 7 - 1 3 1 . Lowry, D. C , and H. Abplanalp, 1972. Social dominance difference, given limited access to common food, between hens selected and unselected for increased egg production. Br. Poultry Sci. 13:365-376. Lowry, D. C , I. M. Lerner and L. W. Taylor, 1956.
1535
Poultry Science 56:1522-1535, 1977
INTRODUCTION Social stress and peck-order status can significantly influence productivity of chickens (reviewed b y Biswas and Craig, 1 9 7 0 ) . Bidirectional selection e x p e r i m e n t s indicated social d o m i n a n c e ability t o be a heritable trait in t h r e e p o p u l a t i o n s studied (Guhl et al., I 9 6 0 ; and Craig et al., 1 9 6 5 ) . It appears t h a t chickens may be unconsciously selected for increased aggressiveness b y selecting for productivity u n der competitive conditions. T h e results of
1 This investigation is part of the Kansas contribution to the NC-89 Regional Poultry Breeding Project. 2 Contribution No. 948-J, Department of Dairy and Poultry Science, and No. 263-J, Department of Statistics, Kansas Agricultural Experiment Station, Manhattan, Kansas.
Lowry and Abplanalp ( 1 9 7 0 , 1 9 7 2 ) s u p p o r t t h a t hypothesis. Their strains selected u n d e r floor flock c o n d i t i o n s b e c a m e socially domin a n t t o b o t h t h o s e selected in single cages and t o unselected controls. Investigations at Kansas State University (Tindell and Craig, 1 9 5 9 ; Craig, 1 9 7 0 ; Biswas and Craig, 1 9 7 0 ) a n d theoretical considerations b y McBride ( 1 9 6 0 , 1962) suggested t h a t selection might well be based o n productivity of families k e p t in separate groups. Such a procedure presumably w o u l d p r o d u c e socially tolerant strains because t h o s e families with less agonistic behavior should p r o d u c e a less stressful e n v i r o n m e n t , be m o r e productive, and t h u s be selected. There is evidence t h a t early sexual m a t u r i t y is associated with increased aggressiveness a n d potential social d o m i n a n c e , at least during
1522
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ABSTRACT Data on hen-housed egg mass and associated egg production traits were obtained from a sample of the Kentville Randombred Control White Leghorn population and from four subsequent unselected generations of two subpopulations. Pullets were kept in three social environments in the zero generation and in individual cages thereafter. Least-squares technique was used to obtain estimates of phenotypic means, components of variance and covariance, heritabilities, and correlations (genetic, environmental, and phenotypic). Weighted means and parameter estimates regressed on generation number were obtained and compared for the subpopulations to test for random genetic drift. In addition, performances of samples of the same sire families kept in intermingled- and separated-family environments were compared to test for sire family by social environment interactions. Sire family by social environment interactions were not detected, except for early egg weight. Heritability and genetic correlation estimates were usually associated with large standard errors. The results suggested that non-additive and/or maternal effects have some influence. Evidence of random genetic drift between the subpopulations was generally lacking. Heritability estimates suggested that egg mass, age at sexual maturity, hen-day, and hen-housed rates of lay either lacked additive genetic variance or were lowly heritable (estimates based on pooled sire components were all less than 0.15). Egg weight was estimated to be moderately heritable (sire component estimates of 0.38 and 0.55). Genetic correlation estimates were generally positive and significant between egg mass and egg weight and between egg mass and both measuresof rate of production (hen-day and hen-housed rate). Genetic correlation estimates involving age at sexual maturity, egg weight, and other traits appear to be unreliable as they were inconsistent in sign and/or magnitude when obtained from the foundation stock and from advanced generations of the unselected controls.
SELECTION FOR EGG MASS
PARAMETER ESTIMATES BY OTHERS Several heritability and correlation estimates, along with unweighted means and associated standard errors, for traits similar to those we studied, are presented in Table 1. Estimates are from egg-strain, randombred control populations. Heritability estimates (diagonal elements in Table 1) indicate, in general, that early egg weight is highly heritable while age at sexual maturity and short-term rate of lay or production appear to be moderately heritable. Estimates between and within populations vary widely (Table 1). Much of the within-populations variability is associated with lower estimates based on sire components as compared with those based on dam components. Estimates from the Kentville Control, source of our stock, suggest that its heritabilities are similar to or higher than those of the other stocks. Genetic correlation estimates in Table 1 (off-diagonal entries, upper right) are quite
variable, even within populations, presumably reflecting the usual imprecision associated with them. Few investigators reported standard errors. Age at sexual maturity and early egg weight appear to have low to moderate positive associations genetically and phenotypically and a high environmental correlation (single estimate). However, earlier sexual maturity appears to be negatively associated with rate of lay or egg production. Thus, earlier maturity appears to be somewhat associated with smaller but more eggs early in the laying year. Large number of eggs laid or high short-term rate of lay is estimated to have a moderately large negative genetic correlation with egg weight. In contrast, an opposite environmental correlation exists between early egg production and egg weight (one estimate); environmental conditions favoring increased egg production also favor heavier eggs. MATERIALS AND METHODS Genetic Stock. Go we et al. (1973) described the formation and methods of maintaining the Kentville Randombred Control population. Briefly, it was originated by crossing four leading commercial strains of White Leghorntype laying stock in 1959. It has been maintained by mating 80 males with 240 females in a restricted random manner since 1961. A sample of hatching eggs from that strain was introduced at this station in the spring of 1968 as foundation stock for the selection study. Our procedures with the Kentville Randombred Control over the next five generations were as follows: Comparison of Familes in Intermingled vs. Separated Flocks. Data used to estimate sire family by environment interactions were obtained from progeny of parent stock (generation 0) hatched from imported eggs. They were obtained from 18 single-sire matings (20—25 females with each male). Hatches 1 through 4 were obtained from them at weekly intervals. Those hatches constituted foundation stocks for our selected strains. All chicks were sexes and vaccinated (Newcastle and bronchitis) at hatching. Combs of males were removed at hatching. They were debeaked at 4 weeks and beaks were trimmed again at 20 weeks. Sire families within each hatch were brooded intermingled in 4 pens up to 20 weeks of age. Only natural daylight was
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adolescence (Craig, 1968, 1970; Craig and Toth, 1969; Biswas and Craig, 1970; Craig et al., 1975). It appears, therefore, that if selection is to be based on a trait such as part-year egg production, without increasing aggressiveness, selection for early sexual maturity should be avoided. Therefore, in designing the study, Craig and Dayton chose part-year egg mass, beginning at 30 weeks of age, as the criterion of selection. Previously collected data indicated that nearly all pullets begin laying sooner than 30 weeks, under our conditions. This study began in 1968. A major objective was to determine if changes in social behavior resulted from selecting for increased egg mass in intermingled-family and separated-family environments. We hypothesized (for reasons indicated above) that selection in the intermingledfamily environment would favor increased aggressiveness, whereas selection in the separatedfamily environment would favor increased social tolerance. This paper reports estimates of heritabilities and genetic, environmental, and phenotypic correlations of part-year egg mass and associated egg production traits in both the foundation stock and the unselected subpopulations derived from it. It also reports on performance of progenies of the same sire families of the original stock kept in two social environments (families intermingled and separated).
1523
1524
M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON TABLE 1 .—Heritability and correlation estimates and associated standard errors for some economic traits in randombred control populations1
Traits
Age at sexual maturity
Age at sexual maturity CC:
RR: OC: KC:
.42* .26 to .57b .09 c .27 to .38 e .15 t o . 5 0 f .33d .20 to ,80a .45 to .73a .14 .06 to .23
Egg weight (early)
CC:
RR: .33 + .09 d OC: -.20 to .23 a KC: .21 to .24a
Egg weight (early) e r P
.62b .13b
CC:
RR: OC: KC:
Short term rate of lay (production)
r
e r P
.13b -.18b
r
e r P
.64 .60 to .51 to .51 to .39 to .72 d .48 to .54 to .16 .09 to .78b -.02°
.73b .64C .53e .80 f .94a .92 a
CC:
-.23 -.80 t o - . 1 5 b -.226
RR: -.05 ± .17 d OC: -.57 to -.09 a KC: -.15 to .03a
CC:
-.44 -.50 to -.06 b -.55 e
RR: -.58 + .10 d OC: -.70 to -.27a KC: -.46 to -.45a
.22 CC: RR: OC: KC:
.32 .06 to .15 to .18 d .18 to .21 to .11 .06 to
.43b .216 .39a .73a .20
1 CC = Cornell or Regional Cornell Control, RR •• Regional Red Control, OC = Ottawa Control, KC = Kentville Control.
*Diagonal elements consist of mean heritabilities (italics), estimates or ranges by particular investigators) (with coded references), mean standard errors (boldface), and range of standard errors, respectively. Off-diagonal elements, upper right, consist of mean genetic correlations (italics) and estimates by particular investigator(s) (with coded references), respectively; values in the lower left portion are environmental (r e ) and phenotypic (rp) correlations with coded reference. Coded references: a Gowe et al. (1973). b King (1961). c King et al. (1963). d Kinney and Lowe (1968). eKinney et al. (1968). f Vaccaro and Van Vleck (1972).
available during rearing. Cockerels were removed at about 16 weeks of age and placed in individual cages. At 22 weeks of age, pullets of each hatch were moved to adult-housing environments. Pullets of hatches 1 and 3 were moved into a laying house with each sire family assigned to a single small (150 cm. by 230 cm.) pen. Hatch 1 pullets were on one side of the house and hatch 3 on the other. Allotment of sire families to pens within hatches was random. Up to 30 daughters were kept from each sire family. Pullets from hatches 2 and 4 were placed in
another laying house with sire families intermingled. Within each hatch, a maximum of 10 pullets of each sire family was randomly assigned to 3 intermingled flocks. The intermingled flocks of hatches 2 and 4 were housed in pens on opposite sides of an aisle. Genetic Parameter Estimation. Data used to estimate heritabilities and genetic correlations in generation 0 were obtained from pullets of hatches 1 through 4 (described above) and from progeny of 2 additional hatches (5 and 6). Hatches 5 and 6 were obtained from 6 of the 18 single-sire matings. Those 6 were chosen
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r
.23+ .13 to .78b .32C .57^
Short term rate of lay (production)
SELECTION FOR EGG MASS
lated for the periods indicated above. It is the ratio of eggs laid to trapnesting days, i.e., 21 days for generations 0 and 1 and 30 days for generations 2, 3, and 4. This trait includes effects of late sexual maturity (after 29 weeks of age) and mortality, if either occurs. 4. Egg weight (EW). One egg (if available) was weighed for each pullet during week 33 of generations 0 and 1 and during week 3 5 in later generations. 5. Hen-housed egg mass (HHMAS). Grams of egg per bird housed per day was used to estimate egg mass, which was calculated for the periods indicated above as the product of egg weight and hen-housed rate of lay. Because individual pullets could lack records on some measures, heritability estimates were obtained for each trait separately and for pairs of traits for genetic correlations, in order to use as many data as possible. Number of sires, dams, and pullet records for each trait included in the analysis are shown in Table 2. Statistical Analyses. Analyses comparing sire families in intermingled vs. separated flocks were carried out using a mixed model version of least squares program (LSMLMM) developed by Harvey (1972). The model was detailed by Quadeer (1976). Variance and covariance components also were estimated by LSMLMM. Statistical models for different generations are detailed by Quadeer (1976). Heritability, genetic, environmental, and phenotypic correlation estimates were computed by the program using sire components, dam components, and sire and dam components combined. The standard errors of heritabilities and genetic correlations computed by the program were after Tallis (1959) and Swiger et al. (1964), respectively, as modified by Harvey for unequal sample sizes (see Harvey, 1972). Weighted estimates of parameters were obtained over generations by using the inverse of the square of the respective standard errors as weighting factors.
RESULTS AND DISCUSSION Families in Intermingled and Separated Flocks Compared. Main effects. Analyses of variance (Table 3) suggested sire effects on all traits analyzed, social environment effects on egg weight and hen-day rate, and hatch effects within the separated-family environment on egg weight and egg mass. However, differences between social environments are suspect be-
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randomly and constituted foundation stock for the unselected control lines Q and C2, respectively. Two of the 6 single-sire matings were, by chance, common for Ci and C2. Data from Cj and C 2 in generations 1 through 4 also were used. Procedures used with the unselected Ci and C2 populations for generations 0 through 4 follow. Generation 0. Pullets of hatches 5 and 6 were reared as described for hatches 1—4 except that chicks were debeaked at 4 weeks only. They were placed in individual laying-hen cages at about 5 months of age. Portions of 5 back-to-back cage rows were used. Allotment of birds to cages was random, but pullets of hatches 5 and 6 were in different rows. Generation I. One male and 5 to 10 females were randomly chosen within each of the 6 sire families of lines Q and C2 in generation 0 as parents of generation 1. The single male from each sire family was mated to females of the other 5 sire families by artificial insemination. The same procedures for choosing and mating breeders within Q and C2 were followed in subsequent generations. Generation 2. Hatching, rearing, and housing details were similar to those of previous generations. Marek's disease reduced survival percentages until pullets were caged at 20 weeks to 55 and 52 in Q and C 2 , respectively. Mortality associated with this disease continued thereafter at a lower rate. Generation 3. Strains Q and C 2 were hatched separately with a week interval between hatches. Chicks were vaccinated against Marek's disease at hatching, and were debeaked at 4 and 20 weeks. Other details were the same as in generations 0—2. Generation 4. The hatching season was changed from fall to spring. Chicks of both strains were obtained from 4 weekly hatches. Rearing and housing procedures were similar to those of previous generations. Traits Studied. We studied 5 production traits: 1. Age at first egg in weeks (SM). 2. Hen-day rate of lay (HDR) from 30 to 37 weeks in generation 0 and 1 and from 30 to 40 weeks in later generations. Hen-day rate for each bird was calculated as the ratio of eggs laid to trapnesting days (3 per week) from first egg to end of period or until death. Hen-day rate was measured independently of sexual maturity and mortality. 3. Hen-housed rate of lay (HHR) was calcu-
1525
1526
M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON
I
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Stability of Control Strains. Least squares means, weighted means, regressions on generation, and standard errors of 5 production traits are summarized in Table 4. Generally, strains Ci and C2 performed similarly as indicated by nonsignificant differences between their weighted means. Generation-by-generation comparisons of the strains indicated a few erratic differences; Cj had later sexual maturity and heavier egg weight in generation 0, greater egg mass in generation 2, and earlier maturity in generation 3. Differences in generation 0 were confounded by the strains having been produced in different hatches and housed after most pullets already were producing. Also, egg production was recorded from the same date for both strains, though Ci was a week older. The significant difference in egg mass between strains in generation 2 appears to be associated with different responses to Marek's disease, a major factor in that year. Lack of significant linear time trends suggested, contrary to our expectation, that environmental trends were not large. We expected time trends because we had changed length of period (30—37 to 30—40 weeks), season of hatch (fall to spring), and age of pullets when eggs were weighed (33 to 35 weeks). Perhaps the small size of the populations sampled or the
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I
il
cause hatch effects and house effects are confounded with social environment. Hatch effects are likewise confounded with location within houses. Interactions. Of the various interactions, our primary interest was in sire family by social environment interaction. That interaction was significant for egg weight (P<.05) only. Our generally negative results agree with those of Lowry et al. (1956), Tindell and Craig (1960), and McBride (1962), none of whom found sire family by housing environment interactions (for various housing conditions). However, Lowry and Abplanalp (1970) produced subpopulations particularly suited to individual cages or floor pens by selecting within those environments, a result not expected in view of their lack of significant sire family by social environment interactions in data analyzed before the subpopulations were formed. It appears, therefore, from their results, that genetic differences magnified by selection under different environmental conditions may yield genotype by environment interactions not previously evident.
59.9 222.3 182.1 283.3 3473.4" 276.5 306.2 508.2 100.6 209.8
DX E/S D X E/S R R R R R R R
1 17
XXX
1 1 17 17 2 2
XX
x = Range from 346 to 357, xx = Range from 253 to 283, xxx = Range from 900 to 1273.
**P<0.01
*P<0.05
1
1051.9'* 263.3
D/S R
17
X
Sires (S) Dams within sires (D/S) Social environment (intermingled vs. separated) (E) Sires X social environments (S X E) Dams X social environment/sires (D X E/S) Hatches within intermingled (H/E;) Hatches within separated (H/E 2 ) Sires X hatches/intermingled (S X H/E,) Sires X hatches/separated (S X H/E 2 ) Pens within hatch 2 Pens within hatch 4 Residual (R)
Egg mass
DF
Denominator for F-test
Source of variation
1
276.9** 24.7* 13.1 0.3 84.2* 18.1 19.6 11.1 7.7 12.8
242.7** 26.1
Egg weight
0.64** 0.04 0.05 0.02 0.02 0.05 0.04 0.08 0.03 0.05
0.22** 0.06
Hen-day rate
Mean squares for productivity measures
TABLE 3 .—Analyses of variance and least square means for comparison of sire families in intermingled and separated flocks
wnloaded from http://ps.oxfordjournals.org/ by guest on May 5, 2015 0.04 0.07 0.07 0.14 0.83 0.06 0.10 0.16 0.03 0.08
0.38** 0.10
Henhoused rate
to
C/3
o o
a
SO
z o
o
m r w
c, c,
c, c2
c, c2
EW
HDR
HHR
Generation means regressed on generations.
**P<.01.
*P<.05.
2
0.65 ± 0 . 0 4 0.60 ± 0.04 -0.05
0 . 7 0 + 0.03 0 . 7 2 ± 0.03 -0.02
55.0 ± 0 . 6 5 52.6 ± 0 . 6 7 2.4** ±0.85 ±0.91
±0.14 ±0.14
± 1.9 ± 2.1
0.69 ± 0 . 0 3 0.69 ± 0 . 0 3 0.00
0.75 ± 0 . 0 3 0.75 ± 0 . 0 3 0.00
54.2 54.6 -0.4
22.7 22.7 0.0
39.8 38.8 1.0
1
± 1.10 ± 1.60
±0.33 ±0.34
0.59 ± 0 . 0 4 0.60 ± 0 . 0 5 -0.01
0.65 ± 0 . 0 3 0.69 ± 0 . 0 4 -0.04
51.3 49.8 1.5
23.0 23.6 -0.6
3 2 . 4 . ± 2.4 15.8 ± 4 . 2 16.6**
2
Individual generation means were weighted by the inverse of their variances.
Diff.
Diff.
Diff.
Diff.
2 4 . 0 ± 0.16 22.7 ± 0.17 1.3**
3 7 . 8 ± 2.4 32.6 ± 2.4 5.2
0
Generation
± 1.4 ± 1.5
±0.79 ±0.82
0.69 ± 0.02 0 . 7 0 ± 0.03 -0.01
0.71 ± 0 . 0 3 0.70 ± 0 . 0 3 0.01
50.9 52.8 -1.9
20.4 ± 0 . 2 5 22.4 ± 0 . 2 5 -2.0**
36.3 39.2 -2.9
3
±0.62 ±0.61
±0.47 ±0.47
± 1.5 ±1.5
0.67 ± 0 . 0 3 0.65 ± 0 . 0 3 -0.02
0.70 ± 0 . 0 3 0.69 ± 0.03 -0.01
51.4 52.8 -1.4
22.7 23.2 -0.5
36.9 36.0 0.9
4
0.67 ± 0 . 0 1 0.66 ± 0 . 0 2 0.01 ± 0 . 0 2
0.70 ± 0 . 0 1 0.71 ± 0 . 0 1 -0.01 ± 0 . 0 2
52.7 ± 0 . 3 4 52.9 ± 0 . 3 5 -0.10 ± 0 . 4 9
22.8 ± 0 . 0 9 22.7 ± 0 . 0 9 0.07 ± 0 . 1 3
36.82 ± 0 . 8 0 36.24 ± 0 . 8 6 1.12 ± 1 . 1 8
Weighted' mean ± s.e.
traits
±0.33 ±0.62 ±0.42
±0.39 ±0.17 ±0.29
±0.94 ±3.51 ±2.65
2
0.004 ± 0.004 0.011 ± 0.016 0.005 ± 0.006
•O.004 ± 0 . 0 1 3 -0.011 ± 0 . 0 0 7 0.003 ± 0 . 0 0 7
-1.05 -0.14 -0.91
-0.49 0.23 -0.56
-0.53 0.72 -1.25
b ± s.e
m S
in
a
>
7>
< r>
> a 2°
>
a a
>
PANE
1
c, c2
SM
Diff.
c, c2
HHMAS
Trait
Least squares mean of
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TABLE 4.—Least square means, weighted means, and regressions on generations for productivity in control strains in generation 0-4
oo
M. A. QL
SELECTION FOR EGG MASS
limited. We shall investigate it further in subsequent analyses. Genetic Parameter Estimates. Heritability estimates. Heritability estimates based on sire, dam, and sire plus dam components of variance for generation 0 flocks kept in 3 social environments are presented in Table 5. For all traits except egg weight, estimates of heritability from the sire component in separated-family flocks were lower than the corresponding estimates in flocks where families were kept intermingled, suggesting that pen effects between separated families were of little consequence. Those effects, if present, should inflate the estimates. Combined estimates of heritability obtained by pooling sums of squares are presented in the last column of Table 5. Table 6 summarizes heritability estimates obtained for generations 0 through 4 for the Ci and C 2 caged control populations, regressions of those estimates on generation number, and their weighted means. The data indicate considerable fluctuation of heritability estimates from
TABLE 5.—Heritability estimates in generation 0
Trait
Heritability (h 2 ) 1
Individual cages
Intermingled flocks
Separated flocks
Pooled over all environments
HHMAS
h
0.25 ±0.21 0.38 ±0.27 0.13 0.32 ±0.12
0.18 +0.11 0.12 ±0.15 -0.06 0.15 ±0.06
0.10 ±0.07 0.10 ±0.14 0.0 0.10 ± 0.06
0.14 ±0.06 0.24 ±0.07 0.10 0.19 ±0.03
0.04 ± 0.09 0.68 ±0.27 0.64 0.36 ±0.13
0.04 ± 0.07 0.27 ± 0.20 0.23 0.15 ±0.08
-0.00 ± 0.03 0.21 ±0.15 0.21 0.10 ±0.06
0.01 ±0.02 0.16 ±0.07 0.15 0.08 ± 0.03
0.49 ± 0.34 0.53 ±0.32 0.04 0.51 ±0.15
0.48 ± 0.22 0.55 ±0.18 0.07 0.51 ± 0.09
0.62 ± 0.26 0.74 ±0.17 0.12 0.68 ± 0.09
0.55 ±0.19 0.60 ± 0.09 0.05 0.57 ± 0.06
-0.02 ± 0.06 -0.38 ±0.26 -0.36 -0.20 ± 0.08
0.17 ±0.10 0.07 ±0.15 -O.10 0.12 ±0.06
0.05 ± 0.05 0.46 ±0.15 0.41 0.25 ± 0.07
0.10 ± 0.05 0.15 ±0.06 0.05 0.12 ±0.03
0.15 ±0.15 0.26 ± 0.25 0.11 0.21 ±0.11
0.16 ± 0.09 0.13 ±0.14 -0.03 0.15 ±0.06
0.05 ± 0.05 0.16 ±0.13 0.11 0.11 ±0.05
0.11 ±0.05 0.21 ± 0.06 0.10 0.16 ± 0.03
S
hb hb-h| SM
h
S+D
h
S
hb hb-h S h
EW
S+D
h|
hb
hb"h| HDR
h
S+D
h
S
h
P b_hs
h h
HHR
S+D
h|
hb hb- h S h
S+D
= from sire component, D = from dam component, S + D = from sire plus dam component.
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few data points used in testing significance of regression coefficients prevented environmental effects from being detected. Absence of time trends were reported by Dave et al. (1969) in broiler control strains, King et al. (1963) for sexual maturity in the Regional Cornell Control and by Gowe et al. (1959) for hen-housed and survivor's egg production, body weight at housing, March body weight, and laying house mortality over 6 generations in the Ottawa Control. King et al. (1963) found significant time trends for egg weight, as did Kinney et al. (1968) for age at first egg, egg weight at 32 and 55 weeks, and production percentages from 40 to 55 and 55 to 70 weeks. Gowe et al. (1959) reported a significant negative regression for age at sexual maturity for the Ottawa Control strain and suggested that general improvements in brooding, rearing facilities, and management were responsible. They also reported a significant increase in March egg weight. Clearly, our evidence for random genetic drift from the Q and C 2 populations is quite
1529
S+D
S+D
-0.05 ± 0.08 0.17 ±0.30 0.22 0.06 ±0.12
-0.06 ± 0.08 0.34 ±0.28 0.40 0.14 ±0.12
-0.02 ± 0.06 -0.38 ± 0.26 -0.36 O.20 ± 0.08
0.15 + 0.15 0.26 ± 0.25 0.11 0.21 ±0.11
0.06 ± 0.18 0.34 ±0.36 0.28 0.20 ±0.16
-0.06 ± 0.14 0.18 + 0.40 0.24 0.06 ± 0.16
*P<.05.
S = from sire component, D = from dam component, S+D = from sire plus dam component.
Unweighted means.
h
hb h b" h S
•>S
h|+D
hb" h S
S "D
h
h
0.03 ±0.14 -0.10 ±0.32 -0.13 -0.04 ±0.12
0.11 ±0.18 -0.31 ±0.32 -0.42 -0.10 ±0.10
0.67 ± 0.40 0.23 ±0.38 -0.44 0.45 ±0.18
0.93 ± 0.44 -0.27 ±0.32 -1.20 0.33 ±0.16
0.08 ±0.18 -0.15 ±0.36 -0.23 -0.04 ±0.12
3
-0.09 ±0.10 0.11 ±0.36 0.20 0.01 ±0.14
0.07 ± 0.20 0.10 ±0.38 0.03 0.08 ±0.16
0.03 ± 0.22 0.86 ± 0.46 0.83 0.44 ± 0.22
0.37 ±0.32 1.0 ±0.36 0.63 0.69 ±0.18
-0.09 ± 0.16 -0.23 ±0.46 -0.14 -0.16 ±0.16
4
-0.02 ± 0.05 0.20 ±0.14 0.22+ 0.10 ± 0.06
-0.02 ± 0.04 -0.10 ±0.14 -0.08+ -0.08 ±0.05
0.38 ±0.15 0.44 ±0.17 0.06+ 0.50 ± 0.08
-0.08 ± 0.04 0.12 ±0.13 0.20+ -0.36 ±0.02
-0.01 ±0.06 0.27 ±0.16 0.28+ 0.13 ±0.06
Weighted mean ± s.e.
-0.04 -0.07 -0.03 -0.06
0.03 0.05 0.01 0.04
-0.09 0.05 0.14 -0.02
0.17 0.11 -0.06 0.14
-0.05 -0.19 -0.14 -0.12
± 0.03 ± 0.05 ± 0.07 ± 0.02
±0.02 ±0.10 ±0.11 ± 0.04
±0.23 ±0.10 ±0.31 ± 0.04
±0.13 ±0.28 ± 0.29 ±0.17
± 0.04 ±0.07 ±0.10 ±0.03*
b ± s.e.
> a
P C
g >
<
"7-
m
W
^
>
O YTOl
1
P b~ h s
h
1.77 0.17 -1.60 0.70
0.64 ±0.38 0.36 ±0.34 -0.28 0.50 ±0.18
0.49 ± 0.34 0.53 ±0.32 0.04 0.51 ±0.15
±0.70 ±0.61 * ± 0.28
0.78 ± 0.46 1.0 ±0.38 0.22 0.91 ±0.18
0.05 ± 0.24 0.46 ± 0.48 0.41 0.26 ± 0.22
-0.13 ±0.04 -0.70 ±0.22 -0.57 -0.42 ± 0.02
-0.06 ± 0.08 0.57 ±0.30 0.63 0.25 ±0.14
2
0.04 + 0.09 0.68 ±0.27 0.64 0.36 +0.13
0.25 ± 0.21 0.38 + 0.27 0.13 0.32 ±0.12
1
MP AN DA. D
HHR
S
S+D
h
h
h
hb" S
"b h
s
S+D
h
h
n? h _n b s
"S
0
Generation
CRAIG,
HDR
EW
SM
HHMAS
Trait
Heritability (h2)'
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TABLE 6 .—Heritability estimates in control (caged) strains in generations 0-4, weighted heritability estimates and regression of h1 on the number of generations
•ER,
SELECTION FOR EGG MASS
Our heritability estimates based on sire components of variance from the 2 analyses were:
hg from
Traits
Generation 0 pooled over environments
Generations 0-4 weighted mean (caged pullets)
HHMAS SM EW HDR HHR
0.14 ± 0.06 0.01 ± 0.02 0.55 ±0.19 0.10 ± 0.05 0.11+0.05
-0.01 ± 0.06 -0.08 ± 0.04 0.38 ±0.15 -0.02 ± 0.04 -0.02+0.05
The negative weighted mean estimates of hg for hen-housed egg mass, sexual maturity, hen-day, and hen-housed rate of lay for caged pullets suggest that heritability of those traits is essentially zero. However, those same traits, except for age at maturity, were estimated to be heritable in generation 0 when data were pooled over all social environments. The discrepancies could be associated with the small number of sires used in the formation of the Q and C 2 strains and in each subsequent generation. The pooled estimate of hg for sexual maturity of 0.01 ± 0.02 in generation 0 is probably due to the fact that most pullets were laying before being housed in that generation. Our estimates of hg for egg weight of 0.55 ± 0.19 in generation 0 and 0.38 ± 0.15 for caged layers in generations 0—4 agree well with the estimate of Vaccaro and Van Vleck (1972), who obtained hg for 32-week egg weight as 0.39 ± 0 . 1 6 . Our estimates of heritability are considerably lower in general than corresponding estimates reported by Gowe et al. (1973) for the Kentville Control. However, our estimates, except for age at sexual maturity, are within the range of values reported in the literature (see Table 1). None of the estimates of linear regression of heritability on generation number was significant (except for hen-housed egg mass for hg + Q). King et al. (1963) found no important genetic trends in the Cornell Randombred Control during six generations for body weight, sexual maturity, egg production, and egg quality traits. Kinney et al. (1968) also failed to detect time trends of h 2 and sire variance component for sexual maturity, 32-week egg weight, and production percentage for 40—55 and 55—70 weeks. Correlation estimates: generation 0. Estimates of genetic, environmental, and phenotypic correlations for generation 0 flocks under different social environments are given in Table 7. Some estimates exceed their limits and most are associated with large standard errors. Hen-housed egg mass had large positive associations with hen-day and hen-housed rates of lay in intermingled and separated family flocks and in data pooled over all environments; pooled genetic correlations ranged from 0.83 to 0.96 (>3 standard errors), Table 7. Genetic correlation estimates based on data from individually caged pullets were erratic and associ-
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generations to generation. Estimates range from negative to above unity and their standard errors are often as large as, or larger than, the heritability estimate. Differences between estimates from sire and dam components were inconsistent from generation to generation. We met the requirement that unselected sires and dams be mated at random for valid variance component estimation; however, more sires, dams, and progeny apparently are required to obtain estimates with much reliability (Robertson, 1960). In general, our heritability estimates from dam components were larger than those from sire components (Tables 5 and 6). As suggested by King and Henderson (1954), maternal effects could cause higher values of ho- Jerome et al. (1956) found dominance variance to be 3.63 times as great as the additive genetic variance for egg production, which was an important source of bias when the dam component of variance was used to estimate heritability. King (1961) found the sire by dam interaction component of variance large in estimates from the Cornell Randombred Control population. He concluded that an upward bias in h 2 estimate could be caused when the dam component is estimated from a nested design. He also concluded that maternal effects must be important for sexual maturity, percentage egg production to January 1, and to 72 weeks of age. Vaccaro and Van Vleck (1972) also emphasized the sire by dam interaction in the component of variance. Our findings agree with those of Go we et al. (1973), who obtained considerably higher heritability estimates from dam components than from sire components, particularly for the Kentville Control, for sexual maturity and rate of production.
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M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON TABLE 7.—Estimates of correlations among productivity
Traits
HHMAS X SM
Correlations 1
r
GS GD r G(S+D) r ES fED r E(S+D) r
r
HHMAS X EW
P
r
r
HHMAS X HDR
P
r
GS GD r G(S+D) r ES rED r E(S+D) r
r
HHMAS X HHR
r
GS GD r G(S+D) rES r ED r E(S+D) r
r
SM X EW
P
P
i"GS r GD r G(S+D) rES r ED r E(S+D) r
SM X HDR
P
r
GS GD r G(S+D) 'ES r ED r E(S+D) r
r
SM X HHR
r
P
GS fGD r G(S+D) fES rED r E(S+D)
Separated flocks
Pooled over all environments
Individually caged
Intermingled flocks
1.30 + 0 . 6 1 ' 0.0+ 0.0+ -0.12 0.12 0.00 0.03
-0.71 ± 0.53 -0.77 ± 0 . 6 2 -0.73 ± 0 . 3 3 * •O.04 0.19 0.06 -0.10
0.45 ± 0.49 0.0+ 0.0+ 0.20 0.32 0.26 0.24
0.29 ± 0 . 3 6 1.30 ± 0 . 5 1 * 0.90 ± 0 . 1 9 * * 0.37 -0.22 0.10 0.32
0 . 9 2 :± 0 . 1 3 * * 0 . 5 8 :± 0 . 1 3 * * 0.66 :± 0 . 0 9 * * 0.29 0.07 0.23 0.42
0.65 ± 0 . 1 7 * * 0.53 ± 0 . 1 3 * * 0.58 ± 0 . 0 8 * * 0.21 0.20 0.21 0.32
0.74 ± 0 . 3 1 * -1.30 + 4 . 6 0 -4.1 ± 4 8 . 0 0.95 0.97 0.96 0.93
0.76 ± 0 . 1 8 * * 0.98 ± 0 . 2 9 * * 0.83 ± 0 . 1 0 * * 0.95 0.94 0.95 0.93
0.57 ± 0 . 4 9 0.88 ± 0 . 0 5 * * 0.83 ± 0 . 0 5 * * 0.97 0.98 0.97 0.93
0.83 ± 0 . 1 0 * * 0.89 ± 0 . 0 5 * * 0.87 ± 0 . 0 4 * * 0.97 0.97 0.97 0.95
0.74 + 0.31* -1.30 ± 4 . 6 0 -4.10 ± 4 8 . 0 0.95 0.97 0.96 0.93
0.75 ± 0 . 1 8 * * 1.0 ± 0.52 0.81 ± 0 . 1 2 * * 0.96 0.95 0.95 0.93
0.55 ± 0 . 4 7 0.88 ± 0 . 0 4 * * 0.83 ± 0 . 0 5 * * 0.97 0.97 0.97 0.93
0.94 ± 0 . 0 3 * * 0.96 ± 0 . 0 1 * * 0.95 ± 0 . 0 1 * * 0.99 0.99 0.99 0.98
0 . 2 5 i 0.63 -0.38 + 0.63 -0.12 i 0.33 -0.06 0.22 0.07 0.02
-0.27 ± 0 . 4 2 -0.06 +: 0 . 2 8 -0.11 ±: 0 . 1 9 0.05 0.02 0.04 -0.02
-0.64 ± 0 . 3 5 -0.34 ± 0 . 5 0 -0.46 ± 0 . 2 8 0.09 0.09 0.09 -0.07
-0.43 ± 0 . 3 5 -0.17 ± 0 . 1 6 -0.22 ± 0 . 1 3 0.05 0.10 0.07 -0.03
1.20 + 0 . 6 9 0.0+ 0.0+ -0.10 0.05 -0.03 0.02
-0.47 ± 0 . 5 2 -1.20 +: 1.80 -0.80 + 0 . 4 4 -0.06 0.15 0.03 -0.11
-0.97 + 1.40 -0.93 ± 0 . 9 4 -0.81 ± 0.43 -0.03 0.17 0.06 -0.06
-0.18 ± 0 . 6 9 -0.86 ± 0 . 4 1 * -0.69 ± 0 . 2 4 * -0.09 0.05 -0.03 -0.09
1.20 + 0 . 6 9 0.0+ 0.0+ •0.10 0.05 -0.03 0.02
-0.47 i: 0 . 5 3 -1.50 i: 2 . 8 0 -0.90 i: 0 . 4 9 0.06 0.17 0.04 -0.11
-0.96 ± 1 . 2 0 -0.95 ± 0 . 9 5 -0.83 ± 0 . 4 3 -0.03 0.18 0.06 -0.06
-0.02 ± 0.64 -0.73 ± 0 . 3 9 * -0.56 ± 0 . 2 3 * -0.16 -0.05 -0.11 -0.15
-0.93 :± 0 . 4 4 * -0.97 :± 0 . 9 5 -0.93 :± 0 . 4 2 * -0.00 0.20 0.08 -0.08
-0.27 ± 0 . 4 5 -0.57 ± 0 . 3 3 -0.47 ± 0 . 1 9 * -0.10 0.00 -0.05 -0.11
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GS GD r G(S+D) r ES r ED fE(S+D) r
traits in generation 0
SELECTION FOR EGG MASS TABLE 7
Correlations
Traits
Individually caged
1533
-Continued
Intermingled flocks
Separated flocks
Pooled over all environments
TGS r GD r G(S+D) r ES r ED r E(S+D) r P
-0.39 ± 0.59 0.0+ 0.0+ -0.08 0.07 -0.01 -0.14
-0.39 ±0.35 1.40 ±1.90 0.41 ± 0.30 0.10 -0.52 -0.20 -0.03
0.20 ± 0.71 0.14 ±0.19 0.13 ±0.15 0.06 -0.15 0.01 0.06
-0.002 ± 0.29 -0.00 +0.17 -0.00 ±0.12 -0.04 -0.04 -0.04 -0.03
EW X HHR
'GS 'GD r G(S+D) 'ES TED r E(S+D) r P
•0.39 ± 0.59 0.0+ 0.0+ -0.08 0.07 -0.01 -0.14
-0.40 ±0.35 1.60 ± 2.8 0.41 ±0.31 0.10 -0.50 -0.19 -0.03
0.18 ±0.66 0.14 ±0.19 0.13 ±0.15 0.06 -0.17 0.00 0.06
0.005 ± 0.29 0.02 ± 0.16 0.01 +0.12 -O.04 -0.05 -0.05 -0.02
r
1.10 ±0.13** -1.00 ± 4.5 -0.55 ± 15.0 0.99 1.00 1.00 1.00
HDRX HHR
GS GD r G(S+D) fES 'ED r E(S+D) r P r
1.0 1.0 1.0 1.0 1.0 1.0 1.0
±0.0** ±0.19** ±0.01**
1.0 1.0 1.0 1.0 1.0 1.0 1.0
±0.01** ±0.0** ±0.0**
1.0 ±0.002** 0.99 ±0.008** 1.0 ±0.004** 0.98 0.98 0.98 0.98
1r GS = genetic correlation from sire component, rQD = genetic correlation from dam component, rc(S+D) = genetic correlation from sire plus dam component, r g s = environmental correlation from sire component, rgrj = environmental correlation from dam component, rE(g+D) = environmental correlation from sire plus dam component, r p = phenotypic correlation. t Negative variance component.
* r c ^ 2 s.e. **TQ>Z
s.e.
ated with larger standard errors, presumably because of smaller degrees of freedom and fewer pullet records from that environment. Hen-housed egg mass had a moderately large and positive genetic correlation with egg weight when estimated from data of pullets kept in flocks and from pooled data; overall estimates ranged from 0.53 to 0.65 (>3 standard errors). Associations of hen-housed egg mass and age at sexual maturity tended to be small and nonsignificant. Estimates of those correlations are somewhat dubious because of late housing of pullets in generation 0, as previously noted. The relative inaccuracy of sexual maturity data in generation 0 reduces confidence in other correlation estimates involving this variable. Egg weight at 3 3 weeks showed little association with variables other than egg mass.
Correlation estimates: caged pullets. Correlations were estimated from records of pullets kept in individual cages in generation 0 through 4. Single generation estimates showed large fluctuations in sign and magnitude (presumably caused by relatively small amounts of data within generations). Regressions of correlation estimates on generation number revealed no significant trends (Quadeer, 1976). However, only large changes would have been detected (if present) because of the relatively small quantity of data within generations. (Generation-bygeneration estimates and regressions on generation are available upon request.) Table 8 presents the weighted mean correlations based on data from all five generations. Hen-housed egg mass was estimated to have high and positive correlations with hen-day and
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EW X HDR
M. A. QUADEER, J. V. CRAIG, K. E. KEMP AND A. D. DAYTON hen-housed egg p r o d u c t i o n , a m o d e r a t e l y high and positive genetic correlation with egg weight, a n d an unclear association with age at sexual m a t u r i t y , Table 8. These results are consistent with t h o s e o b t a i n e d in generation 0 (Table 7 ) . Age at sexual m a t u r i t y of caged pullets appeared t o have little association with egg weight in o u r data and showed inconsistent genetic associations with hen-day and henhoused rates of lay (estimates based on sire and d a m covariances were of o p p o s i t e sign). Egg weight of caged pullets showed little association with traits o t h e r t h a n egg mass, as was also t h e case for generation 0 pullets in 3 different e n v i r o n m e n t s (see above).
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Biswas, D. K., and J. V. Craig, 1970. Genotypeenvironment interactions in chickens selected for high and low social dominance. Poultry Sci. 49:681-692. Craig, J. V., 1968. Correlated responses in body weight and egg production traits in chickens selected for social dominance. Poultry Sci. 47:1033-1035. Craig, J. V., 1970. Interactions of genotype and housing environment in White Leghorn chickens selected for high and low social dominance. XlVth World's Poultry Congress, Madrid, 2:37—4-2. Craig, J. V., M. L. Jan, C. R. Polley, A. L. Bhagwat and A. D. Dayton, 1975. Changes in relative aggressiveness and social dominance associated with selection for early egg production in chickens. Poultry Sci. 54:1647-1658. Craig, J. V., L. L. Ortman and A. M. Guhl, 1965. Genetic selection for social dominance ability in chickens. Anim. Behav. 13:114—131. Craig, J. V., and A. To'th, 1969. Productivity of pullets influenced by genetic selection for social dominance ability and by stability of flock membership. Poultry Sci. 48:1729-1736. Dave, D. S., R. G. Jaap and W. R. Harvey, 1969. Results of selection for eight-week body weight in three broiler populations of chickens. Poultry Sci. 48:1336-1348. Gowe, R. S., A. S. Johnson, J. H. Downs, R. Gibson, W. F. Mountain, J. H. Strain and B. F. Tinney, 1959. The value of a random-bred control strain in a selection study. Poultry Sci. 38:443—462. Gowe, R. S., W. E. Lentz and J. H. Strain, 1973. Long-term selection for egg production in several strains of White Leghorns: performance of selected and control strains including genetic parameters of two control strains. Fourth Europ. Poultry Conf., London:225—245. Guhl, A. M., J. V. Craig and C. D. Mueller, 1960. Selective breeding for aggressiveness in chickens. Poultry Sci. 39:970-980. Harvey, W. R., 1972. (a) General outline of computing procedures for six types of mixed models, (b)
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SELECTION FOR EGG MASS
Intra-flock genetic merit under floor and cage managements. Poultry Sci. 35:1034—1043. McBride, G., I960. Poultry husbandry and the peck order. Br. Poultry Sci. 1:65-68. McBride, G., 1962. The interactions between genotypes and housing environments in the domestic hen. Proc. Australian Soc. Animal Prod. 4:95—102. McCartney, M. G., 1962. Heritabilities and correlations for reproductive traits in a randombred population of turkeys. Poultry Sci. 41:168—174. Quadeer, M. A., 1976. Selection for egg mass in different social environments. Estimation of some parameters in selected and foundation stocks. Ph.D. dissertation, Kansas State University Library, Manhattan. Robertson, A., 1960. Experimental design in the evaluation of genetic parameters. Biometrics, 15:219-226. Swiger, L. A., W. R. Harvey, D. 0 . Everson and K. E. Gregory, 1964. The variance of intraclass correlation involving groups with one observation. Biometrics, 20:818-826. Tallis, G. M., 1959. Sampling errors of genetic correlation coefficients calculated from analyses of variance and covariance. Australian J. Stat. 1:35^3. Tindell, D., and J. V. Craig, 1959. Effects of social competition on laying house performance in the chicken. Poultry Sci. 38:95-105. Tindell, D., and J. V. Craig, 1960. Genetic variation in social aggressiveness and competition effects between sire families in small flocks of chickens. Poultry Sci. 39:1318-1320. Vaccaro, R., and L. D. Van Vleck, 1972. Genetics of economic traits in the Cornell Randombred Control population. Poultry Sci. 51:1556—1565.
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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. 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 , 1961. Inheritance of economic traits in the Regional Cornell Control population. Poultry Sci. 4 0 : 9 7 5 - 9 8 6 . King, S. C , andC. R. Henderson, 1954. Heritability studies of egg production in the domestic fowl. Poultry Sci. 33:155-169. King, S. C , L. D. Van Vleck and D. P. Doolittle, 1963. Genetic stability of the Cornell Randombred Control population of White Leghorns. Genetical Research, 4:290-304. Kinney, T. B., Jr., and P. C. Lowe, 1968. Genetic and phenotypic variation in the Regional Red Controls over nine years. Poultry Sci. 47:1105-1110. Kinney, T. B., P. C. Lowe, B. B. Bohren and S. P. Wilson, 1968. Genetic and phenotypic variation in randombred White Leghorn controls over several generations. Poultry Sci. 47:113—123. Lowry, D. C , and H. Abplanalp, 1970. Genetic adaptation of White Leghorn hens to life in single cages. Br. Poultry Sci. 1 1 : 1 1 7 - 1 3 1 . Lowry, D. C , and H. Abplanalp, 1972. Social dominance difference, given limited access to common food, between hens selected and unselected for increased egg production. Br. Poultry Sci. 13:365-376. Lowry, D. C , I. M. Lerner and L. W. Taylor, 1956.
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