114 R
.M. Herd, S.C. Bishop Livestock Production Science 63 2000 111 –119
model along with the fixed effects of birth year 10 lines. This meant that the design was unbalanced and
levels, rearing treatment three levels, age of dam results were therefore calculated as least-squares
10 levels and selection line three levels: two means.
selected lines plus an unselected control line. Al- though the data had been collected on animals
previously selected on the basis of LGR and LFCR,
3. Results
Bishop 1992 showed this to produce little bias in the genetic variances and covariances estimated for
3.1. Performance test results the traits he studied. For this reason, in this study it
was judged sufficient to include only LFCR in the The phenotypic and genetic correlations between
trivariate analyses of the other traits. As only males FI and MBW 0.6760.03 S.E. and 0.8960.08,
were performance tested, no animals had both per- respectively, and between FI and ADG 0.4760.04
formance and cow traits available. Calculation of and 0.7060.14 were medium to high, but less than
phenotypic correlations for COWWT with perform- one, indicating that there was both phenotypic and
ance test traits was therefore not possible. genetic variation in the relationship between FI and
Differences in test performance, resulting as a growth performance. RFI
had a heritability of
Reg
consequence of the three different pre-test nutritional 0.1660.08 and was phenotypically independent of
treatments i.e., ages of weaning, were analysed size and growth i.e., r with W200, W400, MBW
p
using a general linear model GLM procedure Proc and ADG were all zero; Table 1. RFI
was
Reg
GLM; SAS Institute, 1989. Data for 339 calves genetically independent of ADG, but the genetic
from years 1 to 6 of the selection experiment was correlations with size i.e., r with W200, W400 and
g
used, as in later years all calves were weaned at the MBW were not so close to zero, even though not
same age 84 days. The traits analysed were W200 statistically different from it. The large standard
as a measure of pre-test growth rate, and FI, ADG, errors were due to the small size of the dataset as
W400, LEAN, FCR, LFCR and RFI measured for
well as the low heritabilities of the component traits.
Reg
the 200-day performance tests. The GLM model RFI
was positively correlated with FCR and
Reg
included the fixed effects of year 1 to 6, rearing LFCR, both phenotypically and genetically, such that
treatment birth, 84 or 168 days of age, and line lower RFI
was associated with improved FCR and
Reg
control, LGR, LFCR, fitted sequentially. The inter- LFCR Table 1. RFI
was negatively associated
Reg
action of test year with rearing treatment was also with LEAN and LGR, implying that superior re-
included in the model. In years 1 and 2, calves were sidual feed intake was accompanied by a greater
not assigned to selection lines, and in year 3, all proportion of lean in the weight gain and final
calves were assigned to either the LGR or LFCR carcase of the calves. RFI
was phenotypically
Reg
Table 1 Means and heritabilities h for performance test traits, and their phenotypic r and genetic r correlations with RFI
2 p
g Reg
W200 FI
ADG MBW
W400 LEAN
LGR FCR
LFCR DEP
MAINT MMBW
0.75 0.75
kg kg 200 d
kg d kg
kg kg kg
kg d kg kg
kg kg MJ ME
MJ ME kJ kg
d Mean
166 1458
1.21 69.2
408 0.600
0.32 6.14
17.76 5327
9083 655
SD 30
176 0.18
50.6 41
0.024 0.04
1.07 3.24
818 1821
118 h
0.23 0.31
0.38 0.36
0.42 0.49
0.47 0.17
0.26 0.36
0.23 0.14
2
S.E. 0.08
0.08 0.10
0.09 0.10
0.11 0.10
0.09 0.09
0.10 0.08
0.08 r
0.00 0.70
2 0.01 2 0.01
2 0.01 2 0.22
2 0.33 0.61
0.63 0.06
0.78 0.91
p
S.E. 0.04
0.02 0.05
0.04 0.04
0.04 0.04
0.03 0.03
0.04 0.02
0.01 r
0.34 0.64
0.09 0.22
0.15 2 0.43
2 0.47 0.70
0.72 0.27
0.77 0.93
g
S.E. 0.34
0.16 0.29
0.29 0.28
0.23 0.17
0.22 0.18
0.30 0.13
0.06
R .M. Herd, S.C. Bishop Livestock Production Science 63 2000 111 –119
115
independent of feed energy required for gain of lean ues, with median values of 8.5 and 19.7 kg 200 d,
and fat DEP, although the genetic correlation was co-efficients of skewness equal to
2 0.25 and not so close to zero, even though not statistically
2 0.50, and Shapiro–Wilk statistics Proc Uni- different from it. RFI
was highly correlated, both variate; SAS Institute, 1989 of 0.98 and 0.97,
Reg
phenotypically and genetically, with variation in feed indicative of non-normality P , 0.05 and P , 0.01,
energy attributed to maintenance MAINT and to respectively.
maintenance energy expenditure per unit MBW MMBW.
3.2. Associations with cow size RFI
calculated phenotypically for each test
Reg
had a high phenotypic correlation with RFI and
There was genetic variation in estimated mature
Phen
RFI 0.8860.01 and 0.7360.02 respectively, but
cow size COWWT as evidenced by its heritability
Gen
the correlations were less than unity implying that of 0.6960.11. Even though estimated from a small
RFI was phenotypically a different trait than
dataset this value is close to the weighted mean
Reg
RFI and RFI
. The genetic correlation of heritability for mature cow weight of 0.50 calculated
Phen Gen
RFI with RFI
0.7560.14 was also less than from 24 published estimates by Koots et al. 1994a.
Reg Phen
unity, although not statistically different from it. The Although estimated with a rather large standard
genetic correlation
of RFI
with RFI
error, COWWT appeared to be genetically indepen-
Reg Gen
0.4760.24 was considerably less than unity, imply- dent of RFI
measured during the postweaning
Reg
ing that they were genetically different traits. This performance test r 5 2 0.0960.26. The genetic
g
was unexpected as our preliminary calculations correlations between growth traits ADG, W400 and
based on expectations from the covariance com- LGR and COWWT were all positive 0.4060.18,
ponents indicated all these correlations should have 0.4060.16 and 0.4360.16, respectively. The ge-
been greater than 0.95. Two assumptions used in the netic correlations between measures of feed conver-
calculation of RFI and RFI
were that the sion efficiency FCR and LFCR and COWWT were
Phen Gen
component traits FI, MBW and ADG were normal- less than zero, although not significantly different
ly distributed, and that the regression coefficients for from it 20.2960.24 and 2 0.2360.22, respective-
FI with MBW and ADG were constant across years. ly.
With respect to the first assumption, FI and MBW for the 540 calves were normally distributed P .
3.3. Effect of pre-test weaning treatments 0.05 but ADG was not P , 0.01. To check the
second assumption, the relationships of FI to MBW The different rearing treatments resulted in differ-
and ADG across years were examined in a GLM, ent pre-test growth rates, as indicated by the sig-
with the interactions of MBW with year, and ADG nificantly lighter LW at the start of the performance
with year, fitted after year, MBW and ADG. The test W200 of the artificially-reared bulls, compared
interaction of MBW with year was not significant to the calves weaned at 84 and 168 days Table 2.
P . 0.2, indicating that the regression coefficients Across the six years i.e., six tests these differences
for the relationship of FI with MBW were similar in start-of-test LW were associated with a lower FI
across years. However, the interaction of ADG with during the subsequent 200-day performance test and
year was significant at P 5 0.08. Examination of final LW W400, and lean growth rate from birth to
regression indicated that in years 2 and 6 these 400 days of age LGR, but not with differences in
coefficients differed from those in the other years. ADG, LEAN, FCR, LFCR or RFI. However, there
Thus the two assumptions used to calculate RFI were significant year-by-rearing interactions such
Phen
and RFI appeared to have been violated. Finally,
that in some years there were differences in ADG,
Gen
although the three measures of residual feed intake FCR and LFCR between rearing-treatment groups. In
RFI , RFI
and RFI all had means of zero,
years 2 and 5, the 184-day weaned calves had a
Reg Phen
Gen
only RFI had a normal distribution for all 540
slower ADG, and a higher FCR, during the test, than
Reg
calves. The distributions for RFI and RFI
either the calves weaned at birth or 86 days. In year
Phen Gen
were skewed towards numerical more positive val- 5, LFCR was also worst for the 184-day weaned
116 R
.M. Herd, S.C. Bishop Livestock Production Science 63 2000 111 –119 Table 2
Least-squares means S.E.s for performance test results of bull calves weaned at birth, 84 or 168 days of age during the first six years of the selection experiment
Birth Rearing treatment
Interaction of rearing 3 test year
84 days 168 days
a b
b
W200 162 4
179 2 176 2
ADG 1.11 0.03
1.13 0.01 1.14 0.01
FI 1474 30
1520 15 1530 14
ns
a b
b
W400 385 7
405 3 404 3
ns LEAN
0.606 0.005 0.603 0.003
0.601 0.002 ns
a b
a,b
LGR 0.307 0.006
0.322 0.003 0.321 0.003
ns FCR
6.66 0.14 6.77 0.07
6.75 0.06 LFCR
19.1 0.5 19.5 0.2
19.5 0.2 RFI
1 22 2 12 11
4 10 ns
Reg
Means within a row with different superscripts differ P , 0.05. P , 0.001; P , 0.05; ns P . 0.05.
calves. The faster growth, and better FCR, of the increasing the size of the cow. This is an important
artificially-reared calves in years 2 and 5 was advantage over selection for growth rate, LGR or
evidence that compensatory gain in LW occurred LFCR. In this study these three traits were ge-
during their 200-day test in these two years. Feed netically correlated with COWWT indicating that
efficiency, as measured by RFI , was unaffected
selection to improve these traits would be accom-
Reg
each year i.e., over each test by differences in panied by an increase in cow size. Selection for
rearing treatment and pre-test growth rate. growth rate has been repeatedly associated with an
increase in cow size and its benefit to whole herd productivity has been seriously questioned Barlow,
4. Discussion 1984. Within the current selection experiment,
