GENETIC CORRELATIONS
AMONG
SEX-LIMITED
TRAITS
IN B E E F C A T T L E 1
M. D. MacNeil 2'3, L. V. Cundiff 4 , C. A. Dinkel 3 and R. M. Koch 2
US Department of Agriculture, Clay Center, NE 68933 ;
South Dakota State University, Brookings 57007
and
University of Nebraska-Lincoln, Clay Center 68933
Summary
Data from a comprehensive germ plasm
evaluation program were used to estimate
genetic correlations of reproductive and maternal traits of beef females with growth and
carcass traits of their steer paternal half-sibs.
The data set consisted of 187 sires with approximately four female and five male progeny
each. Heritability estimates for age at puberty,
weight at puberty, conceptions/service, gestation
length, calving difficulty, progeny birth weight,
progeny preweaning daily gain and maturq
weight measured on females were .613 + .177,
.700 -+ .114, .026 -+ .126, .298 -+ .175, .217 -+
.175, .374 -+ .174, .094 -+ .161 and .540 +.150,
respectively. Postweaning daily gain, carcass
weight, fat trim weight and retail product
weight measured on male half-sibs had estimated
heritabilities of .363 -+ .090, .441 -+ .093, .502 -+
.093 and .451 -+ .093, respectively. The estimated genetic correlations suggest that selection
for postweaning daily gain would result in
increased age and weight at puberty, increased
mature weight, improved fertility, reduced
maternal gestation length, reduced maternal
calving difficulty, increased maternal birth
weight and reduced maternal preweaning gain.
Predicted correlated responses to selection for
reduced fat trim at a constant age were increased
age and weight at puberty, increased mature
weight, reduced maternal fertility, reduced
maternal preweaning gain and increased maternal gestation length, birth weight and calving
difficulty. Consequences of selection for
increased age constant retail product weight or
carcass weight appear to be increased age and
weight at puberty, increased mature weight,
improved fertility, increased maternal gestation
length and maternal birth weight but reduced
maternal difficulty and reduced maternal
preweaning gain.
(Key Words: Genetic Correlation, Heritability,
Sex-Limited Traits, Beef Cattle.)
I ntroduction
Knowledge of genetic correlations is needed
for multiple trait evaluation of individuals
(Hazel, 1943; Henderson and Quass, 1 9 7 6 ) a n d
prediction of correlated responses to selection
(Falconer, 1960). Correlations among components of merit modify the optimum weighting
of components and the overall effectiveness of
selection for merit (Dickerson, 1976). The
1Published in cooperation with and a contribution importance of these correlations in underfrom Regional Project NC-1, Improvement of Beef standing the effects of selection has been well
Cattle Through Breeding Methods. Published with the
approval of the Director of the South Dakota Agr. documented (Bell, 1974; Roberts, 1979).
For many pairs of economically important
Exp. Sta. as Publication No. 1936 of the Journal
Series and as Paper No. 7238 Journal Series, Nebraska growth and carcass characteristics, estimates of
Agr. Exp. Sta., Lincoln. Appreciation is expressed to the genetic correlations have been reported
Jeannie Pittam and Kathy Leising for secretarial
(reviews by Preston and Willis, 1974; Woldeassistance.
2Univ. of Nebraska, Roman L. Hruska U.S. Meat hawariat et al., 1977). However, there is a
paucity of estimates for which one trait must
Animal Research Center, Clay Center, NE 68933.
3Dept. of Anita. Sci., P.O. Box 2170, South be measured on females and the other on males.
Dakota State Univ., Brookings 57007.
This lack of information hinders the effective
4Roman L. Hruska U.S. Meat Animal Research
choice of selection objectives (Dickerson, 1976;
Center, Agr. Res. Service, Clay Center, NE 68933.
Niebel and Van Vleck, 1982). The objective of
Received July 22, 1983.
Accepted September 27, 1983.
this study was to estimate from experimental
1171
JOURNAL OF ANIMAL SCIENCE, Vol. 58, No. 5, 1984
1172
MacNEIL ET AL.
data the genetic correlations between reproductive and maternal traits of beef females and
growth and carcass traits of paternal half-sib
steers.
Materials and Methods
This study includes data on calves born at
the Roman L. Hruska U.S. Meat Animal Research Center during 1970, 1971 and 1972.
Straightbred Hereford and Angus cows were
mated to either Hereford, Angus, Jersey, South
Devon, Limousin, Charolais or Simmental sires
to calve in the spring of each year. The sires of
each breed were assumed to be random samples
of the respective breeds. Calves were born in
the spring from late February to early May.
Bull calves were castrated within 24 h of birth,
and all calves had access to creep feed from
mid-July until weaning in late October at
approximately 215 d of age. Smith et al.
(1976c) have characterized the preweaning
performance of these breed types and reported
in more detail their preweaning management.
After weaning, heifers were fed ad libitum a
diet of approximately 50% corn silage (IFN
3-28-250) and 50% grass haylage (IFN 3-00-964)
with supplemental protein and minerals to meet
NRC (1963) requirements. Heifers were observed for estrous activity twice daily from
approximately 250 to 510 d of age, except in
1971 then estrous detection ceased at about
480 d of age. A breeding season of approximately 65 d duration was commenced when the
average age of all heifers was 430 d. During the
first two-thirds of the breeding season, all
heifers were artificially inseminated with
semen from either Hereford, Angus, Devon,
Holstein or Brahman bulls. In the latter one-third
of the breeding season, natural service Hereford
and Angus sires were used. Additional details
regarding the management of these heifers were
reported previously (Laster et al., 1976; Notter
et al., 1978).
Age at puberty was defined as the age of
first observed standing estrus. Weight at puberty
was calculated as the sum of weaning weight
and postweaning average daily gain times the
number of days from weaning to observed
estrus. Some individuals were not observed to
be in estrus and were excluded from the age
and weight at puberty data sets. Because the
number of individuals excluded was small
(< 7%) the impact on the estimates of heritability
and genetic correlation should be trivial.
F o r those heifers mated b y artificial insemination, the exact date of service was known, as
was calving date. If the interval between service
and calving was 285 + 10 d, it was assumed the
heifer conceived to that service. Fertility was
expressed as the ratio of numbers of conceptions
(either 0 or 1) to number of services. Conceptions/service has the advantage relative to
services/conception because data from all
individuals are used. Also relative to conception
to first service, all available information on each
individual is used. The interval from each
recorded breeding date to calving was calculated, and the length of the interval nearest 285
d was taken as gestation length. At calving, the
difficulty of birth was classified as either not
difficult (unobserved, no difficulty or minor
manual assistance) or difficult (assistance with
calf puller or surgery). Calving difficulty scores
for heifers with abnormally presented calves
were not used in this study. All calves were
weighed within 12 h of birth and again at
weaning. Daily gain was calculated as weaning
weight minus birth weight divided b y weaning
age. Only records from calves born when heifers
were 2 yr old were used in this study.
Cows were maintained continuously on
improved pastures and fed supplemental silage
and(or) hay as conditions warranted. All
females were weighed four times annually: at
brand clipping (approximately 60 d before
calving), at the beginning and end of breeding
(60 to 90 d and 100 to 140 d after calving,
respectively) and at weaning (approximately
200 d after calving). Mature weight was calculated as the average of these four weights taken
when each female was 7 yr old.
The postweaning management of steer calves
was different than that of their half-sib heifers.
After a 25- to 30-d adaptation period, steers
were implanted with 36 mg diethylstilbestrol
and assigned to feedlot pens replicated by sire
breed groups. Steers were fed ad libitum in
fenceline bunks for each pen. The diet was
changed periodically as the steers matured such
that the energy density of the diet increased
from approximately 2.61 Meal of metabolizable
energy after weaning to about 2.86 Meal of
metabolizable energy before slaughter. Details
of the feeding regimen have been presented by
Smith et al. (1976b). Steers were stratified by
age and breed group and within strata were
assigned randomly to one of three slaughter
groups at approximately monthly intervals. The
initial slaughter group was killed after 190 d on
GENETIC CORRELATIONS AMONG SEX-LIMITED TRAITS
feed in 1 9 7 1 , 169 d in 1 9 7 2 a n d 1 9 4 d in 1 9 7 3 .
Before slaughter, steers were f a s t e d 12 h,
t r a n s p o r t e d to a c o m m e r c i a l s l a u g h t e r p l a n t a n d
s l a u g h t e r e d t h e n e x t m o r n i n g . T h e right side o f
each carcass was t r a n s p o r t e d to Kansas S t a t e
University. Carcass sides were cut i n t o w h o l e s a l e
cuts w i t h n o t m o r e t h a n 8 m m e x t e r n a l fat. T h e
lean t r i m f r o m t h e w h o l e s a l e cuts was t h e n
t r i m m e d t o c o n t a i n a p p r o x i m a t e l y 25% fat a n d
retail cuts were f a b r i c a t e d . Details o f t h e
c u t t i n g p r o c e d u r e s have b e e n p r e s e n t e d previously ( K o c h et al., 1 9 7 6 ) .
P o s t w e a n i n g daily gain was c a l c u l a t e d f o r
each steer as t h e linear regression o f w e i g h t o n
age. O n l y t h o s e w e i g h t s (n = 8) t a k e n b e f o r e
t h e s l a u g h t e r o f t h e initial kill g r o u p each y e a r
were used. Retail p r o d u c t w e i g h t was t h e s u m
of lean t r i m a n d retail c u t weights. F a t t r i m was
t h e s u m o f e x t e r n a l fat f r o m t h e w h o l e s a l e cuts,
a d d i t i o n a l f a t t r i m m e d f r o m w h o l e s a l e cuts to
achieve 25% fat in t h e lean t r i m a n d t h e k i d n e y ,
h e a r t a n d pelvic fat ( k i d n e y i n c l u d e d ) .
S e p a r a t e analyses o f variance were c o n d u c t e d
f o r each heifer a n d steer sire b r e e d . F o r e a c h
sire b r e e d a n d trait, a n initial m o d e l t h a t
i n c l u d e d all m a i n effects t h o u g h possibly t o
affect t h a t t r a i t a n d t h e t w o - f a c t o r i n t e r a c t i o n s
of m a i n effects were f i t t e d ( t a b l e 1) a f t e r t h e
sire effects h a d b e e n a b s o r b e d . Covariates f o r
w e a n i n g age a n d days o n f e e d were i n c l u d e d in
t h e m o d e l s for carcass weight, retail p r o d u c t
w e i g h t a n d fat t r i m w e i g h t f o r a d j u s t m e n t to a
c o n s t a n t s l a u g h t e r age. O n l y t h e c o v a r i a t e
1173
w e a n i n g age was i n c l u d e d in t h e m o d e l for
p o s t w e a n i n g daily gain. T w o - f a c t o r intera c t i o n t e r m s were d e l e t e d o n e at a t i m e (least
s i g n i f i c a n t first) if t h e y d i d n o t a p p r o a c h
significance ( P > . 2 0 ) . Main effects were likewise
d e l e t e d if t h e y were n o t a t e r m in a n y t w o f a c t o r i n t e r a c t i o n t h a t r e m a i n e d in t h e m o d e l
a n d did n o t a p p r o a c h significance. O c c a s i o n a l l y
a s o u r c e o f v a r i a t i o n was o m i t t e d f r o m t h e
m o d e l f o r a p a r t i c u l a r t r a i t even if it a p p r o a c h e d
significance in o n e sire b r e e d b u t was u n i m p o r t a n t in t h e o t h e r s . In t h e analysis o f H e r e f o r d
a n d A n g u s h e i f e r a n d s t e e r sire b r e e d s a n y
m e a s u r e a b l e i n t e r a c t i o n o f b r e e d o f sire w i t h
b r e e d o f d a m was c o m p l e t e l y c o n f o u n d e d
with the breed of dam source of variation.
T h e final m o d e l s for each b r e e d o f sire a n d
t r a i t are i n d i c a t e d in t a b l e 2. Sire e f f e c t s were
f i t t e d in t h e final m o d e l s r a t h e r t h a n a b s o r b e d
a n d a least-squares m e a n was e s t i m a t e d f o r each
sire. T h e b e t w e e n a n d w i t h i n sire c o m p o n e n t s
o f v a r i a n c e (o~ a n d O~v, r e s p e c t i v e l y ) were also
e s t i m a t e d in t h e final m o d e l s w i t h t h e d i r e c t
procedure of Harvey (1970).
H e r i t a b i l i t y was c o m p u t e d as:
4o~/(O2s +
O2w).
T h e h e r i t a b i l i t y o f calving d i f f i c u l t y was
a d j u s t e d to t h e n o r m a l basis w i t h t h e c o r r e c t i o n
derived b y R o b e r t s o n a n d L e r n e r ( 1 9 4 9 ) .
Subsequent examinations by Van Vleck (1972)
a n d O l a u s s o n a n d RiSnningen ( 1 9 7 5 ) d e m o n -
TABLE 1. FIXED MAIN EFFECTS AND COVARIATES INCLUDED IN
INITIAL ANALYSES OF VARIANCE MODELS a
Female trait b
Male trait c
Source of variation
AP
WP
CS
GL
CD
BW
MG
MW
DG
CW
FT
RP
Year
Breed of dam
Age of dam
Breed of service sire
Calf sex
b 1 (initial age)
b 2 (days fed)
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
aAU possible ~wo-factor interactions among main effects included in the model for each trait were also
included in the initial models. Sires were absorbed.
bAp = Age at puberty (d); WP = Weight at puberty (kg); CS = Conceptions/service; GL = Gestation length
(d); CD = Calving difficulty (0 = unassisted, i = assisted); BW = Birth weight (kg); MG = Preweaning daily gain of
progeny (kg); MW = Average of four weights taken at 7 yr of age (kg).
CDG = Postweaning daily gain (kg); CW = Carcass weight (kg); FT = Fat trim from one-half carcass (kg);
RP = Retail product from one-half carcass (kg).
1174
MacNEIL
TABLE
2. REDUCED
ET AL.
ANALYSIS
OF VARIANCE
MODELS
Female trait a
Male trait b
Source of variation
AP
WP
CS
GL
CD
BW
MG
MW
DG
CW
FT
RP
Sire
Year (Y)
Breed of dam (B)
Age of dam (A)
Breed of service
sire (S)
Sex (X)
x
x
x
x
x
x
x
x
X
X
X
X
X
X
X
X
X
X
X
X
IK
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Y*A
x
X
X
g
X
X
X
X
X
X
X
X
X
Y*B
X
Y*S
B*A
B*S
S*X
b 1 (initial age)
b~ (days fed)
X
X
aAp = Age at puberty (d); WP = Weight at puberty (kg); CS = Conceptions/service; GL = Gestation length
(d); CD = Calving difficulty (0 = unassisted, 1 = assisted); BW = Birth weight (kg); MG = Preweaning daily gain of
progeny (kg); MW = Average of four weights taken at 7 yr of age (kg).
bDG = Postweaning daily gain (kg); CW = Carcass weight (kg); FT = Fat trim from one-half carcass (kg);
RP = Retail product from one-half carcass (kg).
strated the utility of this procedure, particularly
when the incidence level is intermediate.
The correlation of sire progeny means (r m)
was estimated separately for each breed of sire,
and these correlations were pooled by the
Z-transformation procedure originally described
by Fisher (1921). The correlations of sire
progeny means of male traits with calving
difficulty were subjected to adjustment to a
multivariate normal basis using the multiplicative correction developed by Olausson and
R6nningen (1975). An adaptation of the
method of path coefficients (Wright, 1934) was
used in this study to estimate genetic correlations. Essentially, this strategy was employed
by Calo et al. (1973) to estimate the genetic
correlations between growth traits of HolsteinFriesian bulls and milk production (kg) of
half-sib cows. Similar applications of path
coefficients have been made in the study of
genotype x environment interactions (Dickerson
1962; Yamada, 1962). Genetic correlations (rg)
among male and female traits were estimated
as:
/
.25h~k x
25h~ky
rg = r m / /
~/ 1 + ( k x - 1 ) ( h ~ / 4 )
1+ ( k y - 1 ) ( h ~ / 4 ) ,
where h2x and h~ are estimated heritabilities for
traits x and y, respectively, and k x and ky are
effective numbers of progeny/sire for traits x
and y.
The expression CRy = hyrgoy/h x, derived
from the formulas for direct and correlated
response to mass selection (Falconer, 1960),
was used to assess the magnitude and direction
of predicted correlated response in trait y
(CRy) per standard deviation of direct response
in trait x. Symbols used in the previous equation are defined as follows:
h x and hy = square roots of heritabilities for
traits x and y;
rg = genetic correlation of traits x and
y and
Oy = phenotypic standard deviation of
trait y.
Results and Discussion
Heritabilities. The average values of heritabilities and effective numbers of progeny for
the traits studied are presented in table 3. The
data for this study were generated from an
experiment whose primary objective was breed
evaluation. Therefore, more sires with fewer
progeny each were sampled than would be
GENETIC CORRELATIO1NS/~MONG SEX-LIMITED TRA,ITS
1175
TABLE 3. AVERAGE HERITABILITIES (h=), EFFECTIVE NUMBERS OF PROGENY PER SIRE (k),
TOTAL SIRE AND RESIDUAL DEGREE;S OF ~FtREEDOM(dfs AND df, RE[gPECTIVELY)
AND WITHIN SIRE COM~PONE~ff~I'SOF VARIANCE (a ~)
Traita
df s
k
df
o2
AP
WP
CS
GL
CD
BW
MG
MW
187
187
187
184
184
184
181
180
4.05
4.19
3.78
2.86
2.88
2.87
3.11
3.30
613
6,47
57'1
37t5
377
377
425
452
1710.
686.0
.1345
35.28
.1761
14.38
.0398
1901.
DG
CW
FT
RP
187
187
187
187
$,38
5.26
5,26
5.21
903
875
875
868
.0144
542.3
26.68
40.70
i
_
,
i
,
r
"
'
9 ....
--
.
h2
.
.
.613 •
.700 •
.026 •
.298 •
.217 •
.374 •
.094 •
.540 •
.363
.441
.502
.451
.126
.174
.161
.150
• .090
• .093
• .093
•
.
aFemale traits: AP = Age at puberty (d); WP = Weight at puberty (l~.g); CS = Conceptions/service; GL =
Gestation length (d); CD -- Calving difficulty (0 = unassisted, 1 = assisted)~ ~BW ~- Birth weight (kg); MG = Preweaning daily gain of progeny (kg); MW = Average of four waig'hts taken g 7 yr of age (ks). Male traits: DG =
Postweaning daily gain (ks); CW = Careus weight (kg); FT -- Fat trim from one-half carcass (kg); RP = Retail
product from one-half carcass (kg).
o p t i m u m for estimation of heritabilitiy and
genetic correlation. As a result, sampling
variances of estimated genetic statistics are large
relative to estimates from a population with the
same total number of individuals in fewer
families with more members per family.
Heritability estimates for age and weight ~
first observed estrus (puberty) estimated from
these data (.61 and .70, respectively) arc
somewhat higher than estimates previously
reported (average, ,31 and .64, respectively;
Arije and Wiltbank, 1971; Smith et al., 1976a;
Laster et al., 1979), A portion o f this difference
might be explained b y the reduction of preliminary models with a resultant decrease in the
residual component of variance. Other authors
have tended to utilize unreduced models in the
estimation of heritability.
Fertility, whether measured as calving rate,
conception/service or services/conception has
generally been found to be lowly heritable.
Lindley et al. (1958) and Milagres et al. (1979)
reported the heritability o f services/conception
to be .00 znd .64, respectively. Dearborn et al.
(1973) examined reproduction and fitness
traits, and reported heritability estimates
for conception on first service (.22), conceptions/estrous cycle exposed (.27) and pregnancy
rate at the end of the breeding season (.09). In
the present study, heritability for conceptions/
service was estimated to be .03.
Gestation length and calf birth weight have
been imp'licated in the incidence of dystocia
and result~ant calf mortality (Dickerson et al.,
1974; Cure,d i l l et al., 1975; Gravert, 1975;
Cundiff et al., 1982a). Heritability estimates for
gestation len~gth, birth weight and incidence of
dystocia, con'sidered as traits of the calf, have
been reported as .55, .33 and .30, respectively
(Cundiff et al., 1982b). Lindley et al. (1958)
estimated an a,verage heritability of .08 for
gestation length. Cundiff et al. (1975) reported
estimates of heritability for incidence of
dystocia to be very low (0 and - . 0 7 ) in Herefordand Angus-sired c~.lves out of 2- and 3-yr-old
Hereford and Angut~ cows. Other estimates of
hcritability for calving difficulty in first calf
h~jfers, also measured as a trait of the calf,
average .25 (Menissier, 1975). Estimates of
heritability for calf birth weight as a trait of the
call, summarized b y Woldehawariat et al.
(1977), averaged .4.
In the present study, gestation length, calf
birth weight, calving difficulty and preweaning
daily gain were treated as traits of the dam.
Maternal effects (gM), and to a lesser degree,
direc~ effects (gI) contribute to the expression
of these traits as (89 + gM). Therefore, interprel:ation of parameter estimates for these traits
should consider not only gI and gM, b u t also
any possible covariance of gI and gM.
In this study, heritability estimates were .30,
.37 and .22 for gestation length, calf birth
weight and calving difficulty, respectively.
1176
MacNEIL ET AL.
Some previous studies (Everett and Magee,
so,mewhat higher than the estimate reported
1965; Brown and Galvez, 1969) have found
here. However, in these data, the heritability of
direct and maternal components of birth weight
p'reweaning gain as a trait of the calf was also
to be at least moderately heritable. In contrast,
f o u n d to be low (Koch et al., 1982a).
Burfening et al. (1981) and Bourdon and
The amount of feed eaten by a cow is highly
Brinks (1982) fou, nd calving difficulty, birth
correlated with her weight. Therefore, an
weight and gestation length to be lowly heritable
indicator of cow size may be important in the
when measured as traits of the dam. Philipsson
evaluation of alternative selection objectives.
(1976) reported heritability estimates lot: Mature weight has been one commonly used
gestation length, birth weight and calving and highly heritable measure of size (h2=.74,
difficulty treated both as traits of the individual Brinks et al., 1962; h2=.55, Brinks et al., 1964;
and the dam. In that study, heritability esT:i- h2=.28, Brown et al., 1972; and h2=.42, Smith
mates for calving difficulty were essentially et al., 1976a). The estimated heritability of the
equal wether treated as a trait of the calf or of
average of four weights taken at 7 yr of age was
its dam and averaged approximately .10.
.54 in this study.
Heritability estimates for birth weight and
Heritability estimates for daily gain, carcass
gestation length treated as traits of the caTtf or
weight, retail product weight and trimmed fat
of its dam were .19 vs .06 and .50 vs .13,
weight found in this study (.36, .44, .45 and
respectively.
.50, respectively) were comparable with other
Estimated with these data, the herit'ability literature estimates. In a larger study from
for preweaning gain of the calf as a trait, of the
which these steers are a subsample, Koch et al.
dam was .09. Heritability of preweani.ng gain
(1982a) also estimated heritability for daily
measured as a trait of the dam could b e lower gain, half carcass weight, retail product weight
than heritability of either direct effects or
and trimmed fat weight (.57, .43, .58 and .48,
maternal effects on preweaning gairi, possibly respectively). Earlier studies (Cundiff et al.,
due to a negative covariance between the direct
1971; Dinkel and Busch, 1973; Koch, 1978)
and maternal effects (Koch and Clark, 1955,
also confirm the intermediate to high heritability
Deese and Koger, 1967; Hoherlboken and
of these traits. Therefore, selection to increase
Brinks, 1971; Koch, 1972). Even so, previous
(or decrease) any of these traits measured on
studies (Deese and Koger, 1967.; Hohenboken
steers should be effective.
and Brinks, 1971) suggest the total heritability
Genetic Correlations. Presented in table 4
(Willham, 1972) lies in the range .17 to .34,
are estimated genetic correlations of male and
TABLE 4. ES'rIMATED GENETIC CORRELATIONS BETWEEN GROWTH
AND COMPOSITION TRAITS MEASURED ON MALES AND
REPRODUCTION AND PRODUCTIVITY TRAITS
MEASURED ON FEMALE HALF-SIBS
Male traita
Female traitsb
DG
CW
FT
RP
AP
WP
CS
GL
CD
BW
MG
MW
.16
.07
1.33
-.10
-.60
.17
.07
.61
.03
--.31
--.29
--.31
.21
--.07
--.36
.30
.08
.28
.13
--.02
.30
--.26
.25
.34
-1.02
.07
. .37
--1.00
.21
--.07
--1.25
--.09
aMale traits: DG = Postweaning daily gain (kg); CW = Carcass weight (kg); FT = Fat trim from one-half
carcass (kg); RP = Retail product from one-haif carcass (kg).
bFemaie traits: AP = Age at puberty (d); WP = Weight at puberty (kg); CS = Conceptions/service; GL =
Gestation length (d); CD = Calving difficulty (0 = unassisted, 1 = assisted); BW = Birth weight (kg); MG = Preweaning daily gain of progeny (kg); MW = Average of four weights taken at 7 yr of age (kg).
GENETIC CORRELATIONS AMONG SEX-LIMITED TRAITS
female traits studied. The sampling variances of
these estimates are unknown but presumed
high.
Postweaning daily gain, carcass weight and
retail product weight at a constant age appear
to have similar genetic associations with the
complex of female reproductive and productivity traits studied. Previous studies have found
the genetic correlations among daily gain,
carcass weight and retail product weight at the
same age to be positive and large (Cundiff
et al., 1971; Dinkel and Busch, 1973; Koch et
al., 1982b). Therefore, this result was not
unexpected.
The weight of trimmed fat from steer
carcasses at a constant age appeared t o have
genetic associations with puberty and weight
traits of females opposite those of daily gain
and retail product weight. Dinkel and Busch
(1973) reported genetic correlations at constant
age and weight of - . 8 1 and - . 8 8 for fat trim
weight with postweaning daily gain and retail
product weight, respectively. Koch et al.
(1982b) estimated the genetic correlation of
postweaning daily gain and fat trim weight to
be .40 and the correlation of retail product
weight and fat trim weight to be - . 1 1 . Cundiff
et al. (1969) estimated the genetic correlation
for retail product and fat trim at constant age
to be +.55, hut at constant weight to be - . 9 0 .
The correlations of progeny birth weight and
calving difficulty with postweaning daily gain
1177
pose an anomaly. At the phenotypic level,
increases in birth weight generally have been
associated with increases in calving difficulty
(Bellows et al., 1971; Notter et al., 1978;
Nelson and Beavers, 1982). Likewise, the
genetic correlation between direct effects for
birth weight and calving difficluty is generally
accepted as being positive (Cundiff et al.,
1982b). These data suggest that selection based
on postweaning daily gain would tend to
increase maternal birth weight and decrease
maternal calving difficulty simulatneously (table
5).
There is ample evidence to show that genetic
correlation of direct effects on pre- and postweaning gain is positive (Preston and Willis,
1974; Woldehawriat et al., 1977), supposedly
due to pleiotropic effects of genes for growth.
Progeny preweaning daily gain expressed as a
trait of the dam is influenced by both direct
and maternal effects, while postweaning daily
gain of paternal half-sibs of the dam is indicative
only of direct effects. Therefore, the negative
genetic correlation of maternal preweaning
daily gain with postweaning daily gain observed
in this study suggests an antagonism of direct
and maternal effects for growth. Willham
(1972) suggested a possible negative correlation
of direct and maternal effects on preweaning
growth. However, these findings appear to be in
disagreement with the report of Calo et al.
(1973). Among Holstein-Fresian bulls pedigree
TABLE 5. PREDICTED CORRELATED RESPONSES IN FEMALE REPRODUCTION AND
PRODUCTIVITY TRAITS PER STANDARD DEVIATION OF DIRECT RESPONSE
IN GROWTH AND COMPOSITION TRAITS
Female traitb
(mean)
AP
WP
CS
GL
CD
BW
MG
MW
(374)
(284)
(.512)
(238)
(.377)
(31.6)
(.641)
(537)
DG (.126)
9.34
2.81
c
--.559
--.201
1.37
c
3.99
Selection criteriaa and (standard deviation)
CW (16.6)
FT (5.52)
9.43
2.63
.061
.166
-.102
1.46
c
11.5
14.4
10.5
-.018
.333
.101
.241
c
.438
RP (6.77)
15.7
2.86
.024
.652
--.007
1.08
-.024
12.8
aDG = Postweaning daily gain (kg); CW = Carcass weight (kg); FT -- Fat trim from one-half carcass (kg);
RP = Retail product from one-half carcass (kg). Selection applied to increase daily gain, carcass weight and
retail product weight and decrease fat trim weight.
bAp = Age at puberty (d); WP = Weight at puberty (kg); CS -- Conceptions/service; GL =
Gestation length (d); CD = Calving difficulty (0 = unassisted, 1 -- assisted); BW = Birth weight (kg); MG = Preweaning daily gain of progeny (kg); MW = Average of four weights taken at 7 yr of age (kg).
CEstimated genetic correlation has absolute value greater than 1.0.
1178
MacNEIL ET AL.
selected for increased milk production, low but
positive genetic correlations of estimated
merit for milk production and average daily
gain were found.
Retail product weight and carcass weight at
a constant age, as would be expected from the
high genetic correlation between them (Cundiff
et al., 1971; Koch et al., 1982b), had similar
genetic correlations with each of the female
traits measured (table 4). As both retail product
weight and carcass weight also had essentially
equal heritabilities, the predicted correlated
responses (table 5) to selection for either trait
are also similar. The predicted correlated
responses to selection for either retail product
weight or carcass weight are greater in magnitude
than those for daily gain selection, due primarily to the higher heritabilities of the former
traits.
Selection for increased carcass weight or
retail product weight of steers at a constant
slaughter age should result in heifers older and
heavier at puberty and that have improved
fertility. The gestation length of heifers would
increase slightly as would calf birth weight,
although parturition would occur with less
difficulty. The inconsistency of a larger calf and
less calving difficulty is perhaps explained by
the increased size of the heifer herself.
The notion of selection for decreased fat
recently has received considerable attention
(Van Demark, 1976). While this course of
action may result in more desirable carcasses,
the genetic correlation found in this study
foretell of possible genetic antagonisms. Females
from sires selected for reduced fat trim of steer
progeny would be expected to reach puberty
later and at a heavier weight, have reduced
fertility and be larger at 7 yr of age (table 5).
These data also suggest a longer first gestation
with the resultant calf born heavier and with
greater difficulty.
The preceding results document the existence
of unfavorable genetic correlations between
component traits of female productivity and
progeny carcass value. Therefore, the concept
of specialized sire and dam lines (Smith, 1964)
appears to have some merit in beef production.
Alternatively, selection indexes that incorporate
both carcass value traits and maternal productivity traits provide logical selection objectives
in general purpose populations. Genetic progress
in index-selected general purpose populations
would be reduced relative to progress that
could be made from crossing specialized sire
and dam lines (Smith, 1964).
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