Data on young Charolais bulls were used to evaluate the effect of age of dam,
and provide genetic parameter estimates for growth and feed efficiency traits
in weaners compared with yearlings. Records on 510 performance test bulls born
from 1985 to 1989 and 792 progeny test bulls born from 1988 to 1997 were used,
plus available pedigree information (total n =
5493). After weaning (approximately 225 days of age), progeny test bulls were
housed in barns and tested until 15 months for all bulls and 19 months of age
for half of the bulls. From the records, the test period was artificially
partitioned into a weaner and a yearling test. Both tests were for 140 days,
with the weaner test commencing at approximately 274 days of age (6–8
weeks after weaning), and the yearling test commencing at approximately 430
days of age. For each test (weaner or yearling), average daily gain, daily
feed intake, feed conversion ratio (feed intake per unit weight gain), and
residual feed intake (feed intake net of the expected requirements for growth
and maintenance) were calculated. Liveweights at 12 and 18 months of age were
also studied.
Age of dam effect was significant (P < 0.05) for
weight at 12 and 18 months of age, and for all weaner traits except residual
feed intake. All the traits studied were moderately heritable
(0.20–0.46) except for feed conversion ratio in yearlings (0.10).
Genetic correlations for the same traits measured in weaners and later in
yearlings were less than unity (0.42–0.95), with the 3 highest
correlations obtained for weight (0.950.03), feed intake (0.900.07), and
residual feed intake (0.750.12). Therefore, for genetic improvement purposes,
traits measured in weaners should be considered different from those measured
in yearlings, except for weight and feed intake. However, the medium to very
high genetic correlations between weaner and yearling tests for most of the
traits studied indicate that selection based on weaners will have a positive
correlated response in yearlings and vice versa.