Management
select for genetically improved
reproduction. This data also
reminds us that in any one
year, management is still the
key to successful pregnancy
rates in replacement heifers.
Remember, 87% of the
diļ¬erences in pregnancy rates
were due to the "environment."
Although reproductive
performance is a lowly heritable
trait, some heifers are born with
problems and they should be
identified as soon as possible
and removed from the herd.
Spring born heifers are in their
first breeding season now
and should be checked for
pregnancy about 60 days after
the end of their first breeding
season. Identifying and culling
open heifers early will remove
sub-fertile females from the
herd. Lifetime cow studies
from Montana indicated that
properly developed heifers
that were exposed to fertile
bulls but DID NOT become
pregnant were often sub-fertile
compared to the heifers that
did conceive. In fact, when the
heifers that failed to breed in
the first breeding season were
followed throughout their
lifetimes, they averaged a 55%
yearly calf crop. Therefore,
keeping them or rolling them
over to a fall-calving herd is
a bad bet. Selecting against
poor reproduction may be
painfully slow due to the
low heritability. However,
"painfully slow" progress is still
better than no progress! I
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