Reproduction
Commercial Replacement Heifer Selection
By Alison Van Eenennaam, UC Davis, and Darrh Bullock, University of Kentucky
Traits that are of the most economic
value to self-replacing herds are
reproductive traits including age at
first calving, reproductive success, and
reproductive longevity or stayability.
These maternal traits are sex-limited,
lowly heritable, and some are expressed
quite late in life. This has precluded
direct selection on these traits when
selecting commercial replacement
heifers, and impeded genetic progress.
In fact, the antagonism between
carcass traits and some maternal and
calving traits may have led to negative
progress (e.g. carcass weight is positively
correlated with mature weight), as
positive selection on the terminal
traits can result in negative selection
on the maternal traits. Improvements
in reproductive performance can
be up to four-fold more important
in terms of the bottom line than
improvements in end-product traits
in a conventional cow-calf operation
selling market calves at weaning.
Given the economic importance
of reproduction, commercial cow-
calf producers raising their own
replacement heifers should focus
some of their selection emphasis
on maternal traits. However, most
commercial producers have no EPD
information upon which to base their
replacement heifer selection decisions.
Selection is frequently driven by size,
as an indicator of age; smaller heifers
are often the ones that are born late(r)
in the calving season and are too
immature