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GENETICS
Genetic Variation in Pure Lines and Crosses of Large-Bodied Turkey Lines.
3. Growth-Related Measurements on Live Birds
1
K. E. Nestor,
2
J. W. Anderson, and S. G. Velleman
Department of Animal Sciences, Ohio Agricultural Research and Development Center,
The Ohio State University, Wooster, Ohio 44691
ABSTRACT An experimental line (F) selected over 34
generations for increased 16-wk BW was reciprocally
crossed with a primary breeding sire line (C) from a large
international turkey breeder to study the inheritance of
growth-related traits measured on live birds. All genetic
groups were grown intermingled in confinement with
sexes reared in different houses. The traits measured in-
cluded BW at 8, 16, and 20 wk of age and shank length,
shank width, shank depth, breast width, and walking
ability scores at 16 wk of age. Walking ability was rated
from 1 to 5 with 1 representing birds with no leg defects
and no difficulty walking and 5 indicating birds with
extreme lateral deviations of the legs and great difficulty
walking. Ratings of 2, 3, and 4 represented intermedi-
ate values.
The F line had a different growth pattern than the C
line with the F line being larger than the C line at 8 wk
of age, but the reverse was true at 16 and 20 wk of age.
The difference in BW between the C and F lines increased
from 16 to 20 wk of age. The C line had wider breasts
(Key words: turkey, body weight, breast width, inheritance, walking ability score)
2005 Poultry Science 84:1341–1346
INTRODUCTION
Commercial turkey breeders have made major im-
provements in growth characteristic of the modern turkey
(Havenstein et al., 2004a,b). Because commercial turkeys
are the result of a cross of a sire line (or sire line cross)
and a dam line (or dam line cross), the genetic gains could
be due to improvements within the primary breeding
lines (additive genetic variation) or heterosis (nonaddive
genetic variation) in the crosses used to produce the com-
mercial turkey.
Additive genetic variation is an important source of
variation for growth traits in turkeys. It has been shown
2005 Poultry Science Association, Inc.
Received for publication February 24, 2005.
Accepted for publication May 9, 2005.
1
Salaries and research support provided by state and federal funds
appropriated to the Ohio Agricultural Research and Development Cen-
ter, The Ohio State University.
2
To whom correspondence should be addressed: Nestor.1@osu.edu.
1341
than the F line at 16 wk of age. The F line had longer
shanks than the C line. Shank width was larger in the C
line than the F line for females but not males. No line
difference in shank depth was observed. Walking ability
scores at 16 wk of age were lower (better) in the C line
than in the F line for males but not females.
Significant heterosis in BW of the crosses of the F and
C lines was observed at all ages in males (range = 3.3 to
5.6%) and only at 8 wk of age in females (3.6%). These
results were similar to an earlier study in which the F
line was crossed with a primary-breeding sire line from
2 other international turkey breeders. No significant het-
erosis in the crosses of the C and F line was observed for
breast width and shank measurements. Heterosis was
significant for walking ability scores of females (−3.0%)
but not males. Reciprocal effects, a measure of sex linkage
and maternal influences, were noted only for shank length
and the direction of the difference was not the same in
the 2 sexes.
that large gains in BW (McCartney et al., 1968; Nestor,
1977, 1984; Nestor et al., 1996), breast width (Nestor et
al., 1969), and shank width (Nestor et al., 1985) can be
made by genetic selection within lines.
In general, earlier research suggested that nonadditive
genetic variation was not a major contributor to total
genetic variation for growth traits of turkeys. In earlier
studies, heterosis for BW was observed in some crosses
(Asmundson, 1942, 1948; Jerome et al., 1960; Friars et al.,
1963) but not in other crosses (Knox and Marsden, 1944;
Kondra and Shoffner, 1955; Jerome et al., 1960; Clark,
1961; Nestor, 1971). In some cases, heterosis was observed
only for BW at certain ages (Asmundson and Pun, 1954;
Friars et al., 1963). With diallel crosses, McCartney and
Chamberlin (1961) concluded that additive genetic vari-
ance was much more important that nonadditive genetic
variance for BW and body conformation measurements.
Abbreviation Key: A, B, C, and N lines = commercial sire lines; F =
experimental line selected long term for increased 16-wk BW; and FL =
subline of F selected for increased shank width.
NESTOR ET AL.1342
More recent studies suggest that nonadditive genetic
variation is an important source of variation in growth
traits, particularly in offspring of crosses of lines differing
greatly in growth rate and body conformation. Emmerson
et al. (1991) observed significant heterosis for BW at older
ages and shank length in F
1
reciprocal crosses of an experi-
mental line (F) selected long term for increased 16-wk
BW and a commercial sire line (N) no longer in commer-
cial use. No heterosis for BW was observed in a cross of
an experimental egg line and the F line at 8, 16, or 20 wk
of age, and heterosis was observed only at 20 wk of age
in a cross of the egg and N lines (Nestor et al., 1997).
In crosses of an experimental line (FL) selected only for
increased shank width and an unimproved commercial
sire line, Ye et al. (1997) observed significant heterosis for
BW and shank length. When the FL line was crossed with
2 improved commercial sire lines (A and B), significant
heterosis in BW was observed for females of the cross
involving line A and for males of the cross involving line
B (Nestor and Anderson, 1998). When the F line was
crossed with commercial sire lines A and B, heterosis was
an important source of variation in BW of males and
percentage heterosis ranged from 3.1 to 7.5 (Nestor et al.,
2001a). For females of the reciprocal crosses of the F and
commercial sire lines, heterosis (range = 2.6 to 4.9%) was
only significant at younger ages (8 wk for the crosses of
the A and F lines and 8 and 16 wk for the crosses of the
B and F lines). At 16 wk of age, no significant heterosis
was observed for breast width and heterosis was sporadic
for shank measurements. The purpose of the present
study was to evaluate genetic variation of BW, breast
width, shank measurements, and walking ability in pure
lines and reciprocal crosses of the F and a sire line (C)
from a third major international turkey breeder.
MATERIALS AND METHODS
Genetic Stocks
The F line was started from a randombred control pop-
ulation by mass selection only for increased 16-wk BW.
Details of the maintenance of the F line and response to
selection have been previously reported (Nestor, 1977,
1984; Nestor et al., 1996, 2000). The F line had been se-
lected for 34 generations at the time of the study. A sample
of a sire line C was obtained from a major international
breeder as unpedigreed eggs.
Offspring from the pure F and C lines and reciprocal
crosses were produced in 2 hatches, each of which repre-
sented a 2-wk collection of eggs. The F line was produced
by weekly artificial mating of 36 sires to 72 dams with
each sire being mated to 2 dams. The number of offspring
produced was 262 males and 306 females. The pure C
line was produced from 20 dams artificially mated to 12
sires. Each week, the sire used for artificial insemination
of each hen was changed so that as large a genetic base
as possible was obtained. The number of offspring for
the C line was 50 males and 58 females. To produce the
cross involving F-line sires and C-line dams, the sires
were the same ones used in producing the pure F line,
and a different F-line sire was used to inseminate each
of 20 dams weekly in a manner so that all 36 F-line sires
were involved in the production of the cross. For the
reciprocal cross, 20 F-line dams were used and the same
sires used to produce the pure C line were also used in
the production of the crosses. The sire assigned to each
hen was changed weekly to insure as wide a genetic base
as possible. The number of offspring for the reciprocal
crosses ranged from 40 to 60 within each cross and sex
subgroup with an average of 48.8.
Management of Birds
and Measurements Made
Offspring from the pure lines and reciprocal crosses
were grown intermingled in confinement with the sexes
reared in separate houses. All birds were provided a de-
clining protein 5-ration system (Naber and Touchburn,
1970) based on the schedule for males. Continuous light-
ing was provided from hatching to 6 wk of age, when
the photoperiod was reduced to 12 h per day. At 16 wk
of age, the amount of light per day was reduced to 10 h
and remained at this level until 20 wk of age.
Body weight was recorded at 8, 16, and 20 wk of age.
At 16 wk of age, measurements of shank length, shank
width (laterally at the dew claw), shank depth (perpendic-
ular at the dew claw), and breast width were made. Breast
width was measured at 6.35 cm of body depth at a point
approximately 3.18 cm from the anterior point of the keel.
Walking ability at 16 wk of age was estimated by the
same person using the method of Nestor et al. (1985)
in which each bird was given a score of 1 to 5, with 1
representing birds with no leg defects and no difficulty
walking and 5 indicating birds with extreme lateral devia-
tions of the legs and great difficultly walking. Ratings of
2, 3, and 4 represented intermediate values.
Statistical Analysis
The data were analyzed using the GLM procedure of
SAS (SAS Institute, 1988) with genetic group (pure lines
and reciprocal crosses), sex, hatch, and the interaction of
genetic group and sex as source of variation. Orthogonal
contrasts (SAS Institute, 1988) were used to estimate addi-
tive genetic effects (contrast of F and C), heterotic effects
(contrast of average of the parental lines with the average
of the reciprocal crosses), and sex-linked and maternal
effects (contrast of reciprocal crosses). Percentage of heter-
osis was obtained by dividing the difference between the
average of the parental lines and that for the reciprocal
crosses by the average of the parental lines and multi-
plying by 100. Data for the 2 sexes were also analyzed
separately as above with genetic group and hatch as
sources of variation.
RESULTS
Hatch and Sex Effects
Hatch effects were significant for BW at 8 and 16 wk
of age and breast width in the analyses of the sexes sepa-
GENETIC VARIATION OF GROWTH TRAITS IN TURKEYS 1343
TABLE 1. Effect of reciprocally crossing a commercial sire line (C) and a line (F) selected
long term for increased 16-wk BW on performance of males
Parental lines Reciprocal crosses Additive
genetic Reciprocal Percentage
Variable C F F × CC× F effect
1
effect
2
heterosis
3
SEM
Body weight, kg
8 wk 4.90 5.13 5.12 5.24 *** NS 3.32** 0.120
16 wk 15.50 14.61 15.85 15.95 *** NS 5.61** 0.529
20 wk 20.47 18.84 20.41 20.85 *** NS 4.96** 1.166
Walking ability scores
4
2.43 2.85 2.35 2.53 ** NS −7.58 0.087
Shank
Length, cm 21.79 22.49 21.81 22.28 *** * −0.04 0.106
Width, mm 17.69 17.83 17.47 17.83 NS NS 0 0.115
Depth, mm 26.15 25.84 26.21 26.32 NS NS 1.04 0.113
Breast width, cm 15.43 12.65 14.16 14.04 *** NS 0.06 0.276
1
Measured by contrast of parental lines.
2
Measured by contrast of reciprocal crosses.
3
Percentage heterosis = [(average of reciprocal crosses − average of parental lines)/average of parental lines]
× 100.
4
Birds were subjectively rated at 16 wk of age from 1 to 5 with 1 representing birds whose legs did not have
any defects and had no difficulty walking and 5 indicating birds whose legs exhibited extreme lateral deviations
or had great difficulty walking. Ratings of 2, 3, and 4 represented intermediate values.
*P ≤ 0.05.
**P ≤ 0.01.
***P ≤ 0.001.
rate and sexes combined and for female BW at 20 wk of
age (data not shown). In general, hatch effects were not
significant for shank measurements and walking ability
scores with the only exception being shank length of
males (data not shown). In the combined analysis, the
sex effect was highly significant (P ≤ 0.001) for all traits
with the value for males being larger than that for females
measured except for breast width (data not shown). The
interaction between genetic group and sex was significant
for BW at 16 and 20 wk of age (P ≤ 0.001), shank length
(P ≤ 0.001), and walking ability scores (P ≤ 0.01). The
interactions in all cases were the result of scaling effects.
Additive Genetic Effects
The C and F lines differed in BW at all ages for males
(Table 1), females (Table 2), and sexes combined (Table
3). At 8 wk of age, the F line was larger than the C line
but the reverse was true at 16 and 20 wk of age. The F
line had longer shanks than the C line at 16 wk of age
for males, females, and sexes combined. Shank width at
16 wk of age did not differ between lines for males, but
for females and sexes combined shank width was larger
in the C line than in the F line. Shank depth at 16 wk of
age was significantly (P ≤ 0.05) larger in the C line than
in the F line only in the combined analysis. The breast at
16 wk of age was wider in the C line than in the F line
in all analyses. Walking ability scores at 16 wk of age
were lower (birds walked better) for the C line than the
F line in males and sexes combined.
Reciprocal Effects
Reciprocal effects, a measure of sex linkage or maternal
influence, were not an important source of variation for
most traits (Tables 1 to 3). In the reciprocal crosses, the
sire is listed first. Reciprocal effects were significant (P ≤
0.05) for shank length in the males and females when
analyzed separately but not in the combined analysis.
The direction of the difference between reciprocal crosses
was different for males than for females.
Nonadditive Genetic Variation
Heterosis of BW at 8, 16, and 20 wk of age was a more
important source of variation in the analysis of males
separately (Table 1) and for sexes combined (Table 3).
For females, heterosis was significant (P ≤ 0.01) only at 8
wk of age (Table 2). For males and for both sexes com-
bined, percentage heterosis ranged from 3.32 to 5.61 and
3.14 to 3.53, respectively, at the various ages. Heterosis
was not an important source of variation for the shank
measurements or breast width in any analysis. The recip-
rocal crosses had lower average walking ability scores
than the pure lines in all analyses with the heterosis being
significant for females (P ≤ 0.05) (Table 2) and sexes com-
bined (P ≤ 0.01; Table 3). For males (Table 1), the percent-
age heterosis was large (−7.58) but not significant
DISCUSSION
The experimental F line was not closely related to pri-
mary breeding sire lines currently in use by 3 major inter-
national turkey breeders when based on DNA finger-
printing (Ye et al., 1998) or the frequency of MHC haplo-
types (Zhu et al., 1995, 1996b). In the study of Ye et al.
(1998), band sharing of DNA fingerprints was greater
among the commercial sire lines than between the F line
and commercial sire lines. One MHC class II haplotype
was predominant in all of the commercial lines (Zhu et
NESTOR ET AL.1344
TABLE 2. Effect of reciprocally crossing a commercial sire line (C) and a line (F) selected
long term for increased 16-wk BW on performance of females
Reciprocal
Additive
Parental lines crosses
genetic Reciprocal Percentage
Variable C F F × CC× F effect
1
effect
2
heterosis
3
SEM
Body weight, kg
8 wk 4.05 4.17 4.30 4.20 * NS 3.58** 0.035
16 wk 11.97 11.17 11.83 11.58 *** NS 1.17 0.068
20 wk 14.68 13.42 14.33 14.17 *** NS 1.42 0.176
Walking ability scores
4
2.30 2.22 1.99 2.20 NS NS −3.00* 0.060
Shank
Length, cm 17.75 18.15 18.04 17.79 *** * −0.02 0.046
Width, mm 16.49 15.83 16.26 16.15 *** NS 0.28 0.107
Depth, mm 22.60 22.35 22.66 22.36 NS NS 0.16 0.073
Breast width, cm 15.33 13.13 14.16 13.83 *** NS −1.65 0.103
1
Measured by contrast of parental lines.
2
Measured by contrast of reciprocal crosses.
3
Percentage heterosis = [(average of reciprocal crosses − average of parental lines)/average of parental lines]
× 100.
4
Birds were subjectively rated at 16 wk of age from 1 to 5 with 1 representing birds whose legs did not have
any defects and had no difficulty walking and 5 indicating birds whose legs exhibited extreme lateral deviations
or had great difficulty walking. Ratings of 2, 3, and 4 represented intermediate values.
*P ≤ 0.05.
**P ≤ 0.01.
***P ≤ 0.001.
al., 1996b). In the F line, frequency of class II haplotypes
was more diverse (Zhu et al., 1995).
The F line apparently has a different growth pattern
than commercial sire lines. In the study of Nestor et al.
(2001a), BW at 8 wk of age of the F line was similar to,
or larger than, that from a primary breeding sire line from
2 of the 3 major international breeders but by 16 wk of
age, BW was larger in the commercial sire lines than the
F line and the line differences increased in magnitude at
20 wk of age. In the current study, the F line was larger
TABLE 3. Effect of reciprocally crossing a commercial sire line (C) and a line (F) selected
long term for increased 16-wk BW on performance of sexes combined
Reciprocal
Additive
Parental lines crosses
genetic Reciprocal Percentage
Variable C F F × CC× F effect
1
effect
2
heterosis
3
SEM
Body weight, kg
8 wk 4.48 4.65 4.71 4.71 *** NS 3.33*** 0.038
16 wk 13.88 12.90 13.84 13.78 *** NS 3.14*** 0.177
20 wk 17.57 16.14 17.38 17.54 *** NS 3.53*** 0.229
Walking ability scores
4
2.37 2.54 2.17 2.37 * NS −7.54** 0.061
Shank
Length, cm 19.76 20.32 19.93 20.04 *** NS −0.27 0.066
Width, mm 17.10 16.60 16.87 16.98 *** NS 0.45 0.096
Depth, mm 24.37 24.10 24.44 24.34 * NS 0.64 0.078
Breast width, cm 15.26 12.69 13.90 14.11 *** NS 0.03
1
Measured by contrast of parental lines.
2
Measured by contrast of reciprocal crosses.
3
Percentage heterosis = [(average of reciprocal crosses − average of parental lines)/average of parental lines]
× 100.
4
Birds were subjectively rated at 16 wk of age from 1 to 5 with 1 representing birds whose legs did not have
any defects and had no difficulty walking and 5 indicating birds whose legs exhibited extreme lateral deviations
or had great difficulty walking. Ratings of 2, 3, and 4 represented intermediate values.
*P ≤ 0.05.
**P ≤ 0.01.
***P ≤ 0.001.
than the C line at 8 wk of age but the reverse was true
at 16 and 20 wk of age and the difference between lines
increase from 16 to 20 wk of age. At 16 wk of age, the
commercial sire lines have wider breasts than the F line
(Nestor et al., 2001a; present study).
Additive genetic variation, as indicated by differences
among lines, was an important source of variation for
BW at 16 and 20 wk of age, shank length, shank width
(females only), and breast width in the study of Nestor
et al. (2001a) and the present study. It has been shown
GENETIC VARIATION OF GROWTH TRAITS IN TURKEYS 1345
that large gains in BW (McCartney et al., 1968; Nestor,
1977, 1984; Nestor et al., 1996), breast width (Nestor et
al., 1969), and shank width (Nestor et al., 1985) can be
made by genetic selection within a line.
Nonadditive genetic variation was a significant source
of variation in BW of males at all ages in crosses of the
F line and commercial sire lines (Nestor et al., 2001a;
present study). For females, heterosis for BW at 8 wk of
age was significant in all crosses of the F and commercial
sire lines (Nestor et al., 2001a; present study) but the only
significant heterosis at older ages was for 16 wk BW in
the crosses of the B and F lines (Nestor et al., 2001a). Age
specific heterosis for BW has been previously reported
(Asmundson, 1942; Asmundson and Pun, 1954).
In earlier studies, nonadditive genetic variation in BW
weight was not an important source of variation (Kondra
and Shoffner, 1955; Clark, 1961; McCartney and Chamber-
lin, 1961; Nestor, 1971), except in some crosses in which
the parents differed greatly in body conformation (As-
mundson, 1945, 1948). More recent studies in which the
parental strains differed greatly in body conformation,
heterosis was an important source of variation (Emmer-
son et al., 1991; Ye et al., 1997; Nestor and Anderson,
1998; Nestor et al., 2001a). The F line differed from the
A, B, and C sire lines in breast width (Nestor et al., 2001a;
present study) and body shape (Nestor et al., 2001b; un-
published data). The differences in breast width and body
shape between the experimental F line and the commer-
cial sire lines might have been responsible for the hetero-
sis in BW observed. It is unknown why heterosis was
expressed to a greater extent in males than in females.
Inbreeding, as measured by band sharing of DNA fin-
gerprints (Kuhnlein et al., 1990; Zhu et al., 1996a), was
greater in the commercial sire lines than in the F line (Ye
et al., 1998). Accumulated inbreeding in the F line, as
calculated by variation in family size, was 30.1% (unpub-
lished data) when the crosses were made with sire line
C. Because the commercial sire lines and the F line are
moderately inbred, the heterosis observed in BW may
have been due to elimination of inbreeding effects by
crossing relatively unrelated lines. A linear relationship
is expected between the degree of heterosis and level of
inbreeding (Hill, 1982) and the magnitude of the heterosis
should be inversely related to the degree of genetic resem-
blance between parental populations (Wilhelm and Pol-
lak, 1985).
Nonadditive genetic variation in shank measurements
was not a consistent source of variation in the crosses of
the F line and commercial sire lines. No significant hetero-
sis was observed in the current study for any shank mea-
surements for crosses of the F and C line. In the study of
Nestor et al. (2001a), heterosis was a more important
source of variation for shank width and depth in males
than in females in crosses of the F and A and F and B lines.
No heterosis was observed in shank length for crosses of
A and F but significant, but small in magnitude, heterosis
was observed in crosses of B and F.
No heterosis in breast width was observed in crosses
of the F and commercial sire lines (Nestor et al., 2001a;
present study). Similarly, Asmundson (1948), Ye et al.
(1997), and Nestor and Anderson (1998) did not observe
heterosis in crosses of lines differing greatly in breast
width.
Heterosis in walking ability scores (−7.54%) was sig-
nificant for females but not males. Nestor et al. (2001a) did
not observed any significant heterosis in walking ability
scores in crosses of the F and A lines but heterosis was
significant for males (−12.9%) but not females in the
crosses of the F and B lines. Negative heterosis for walking
ability scores has been observed previously in reciprocal
crosses of the N and F lines (Emmerson et al., 1991) and
in a cross of an unimproved commercial sire line and the
FL line (Ye et al., 1997). When the FL line was reciprocally
crossed with the A and B lines, heterosis was negative
and significant for only males of 1 of the crosses (Nestor
and Anderson, 1998). The results of the present study and
those in the literature indicate that nonadditive genetic
variation in walking ability scores may be an important
source of variation in certain crosses.
Reciprocal effects, indicating sex linked or maternal
influences were not a consistent source of variation for
any trait. Maternal effects might have been expected be-
cause average egg weight different greatly in the F (95.4
g) and C (102.1 g) lines (unpublished data).
In summary, the F line had a different growth pattern
than the C line and heterosis was an important source of
variation in BW of males at 8, 16, and 20 wk of age. For
females, heterosis was significant in reciprocal crosses of
the F and C lines only at 8 wk of age. No significant
heterois was observed for breast width and width, depth,
or length of the shank. Significant negative heterosis in
walking ability scores was observed for females but not
males of the F and C crosses.
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