Management
Heritability Estimates of Fertility in
Replacement Heifers
By Glenn Selk, Oklahoma State University
“Heritability” is that portion
of the difference in the
performance of cattle that
is due to genetics. The
remainder of the differences
are presumed to be due to
differences in the environment
(i.e. management, pastures,
weather, etc). Previous estimates
of the heritability of pregnancy
rates in heifers ranged from 0
to 0.28. Iowa State University
scientists studied records of
3144 heifers from 6 herds in 5
states. In the Iowa State study,
the heritability of pregnancy
rate was 0.13. Pregnancy
rate is the percentage of the
heifers exposed to artificial
or natural breeding that were
diagnosed pregnant after their
first entire breeding season.
First service conception rate is
the likelihood that the heifer
became pregnant on the first
artificial insemination attempt
to breed her. The heritability
of first service conception
rate was even lower at 0.03.
This implies that 97% of the
differences in the first service
conception rate are due to the
management environment in
which the heifers were raised.
(Source: Minick and co-workers.
2004 Iowa State University
Beef Research Report.)
These low heritability estimates
suggest that painfully slow
progress could be made by
selecting sires that produced
heifers with greater pregnancy
rates. Keeping heifers from
cows that calve early in the
calving season should also
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