Genetic Selection
Cattle Genetics: Where’s Optimum?
By Aaron Berger, university of Nebraka-Lincoln
The use of genetic selection
percentage of calves weaned
tools by cattle breeders has
per cow exposed over the last
resulted in significant changes
15 years. This has to prompt
within the majority of major
the question why? How can it
breeds over the last 30 years.
be that there has been such
With a few exceptions, the
significant genetic change
overwhelming genetic trend
in several breeds that should
for milk, weaning weight, and
increase weaning weights, but
mature weight over that time
records from several commercial
has been for
cow-calf data
more. Without
sets would
How can it be that
question, the
indicate that
use of Expected
there has been
there has been
Progeny
relatively no
such significant
Differences (EPD)
change?
genetic change in
has enabled
several breeds that
In 2014, Dr. David
this change.
Lalman from
The question at
should increase
Oklahoma State
hand, however,
weaning weights, but
University made
is “have we
records
from
several
a presentation
selected towards
commercial cow-
at the Applied
that which is
calf
data
sets
would
Reproductive
optimal?” The
Strategies in Beef
late Dr. Bob
indicate that there
Cattle meeting
Taylor from
has been relatively no
titled “Matching
Colorado State
change?
Cows to Forage
University said it
Resources in a
well, “Profitable
World of Mixed
cattle are usually
Messages.” In that presentation,
productive, but productive
Dr. Lalman made the case
cattle are not always profitable.”
that the genetic potential of
Four different benchmark data
many cattle today are beyond
sets for commercial cow-calf
the nutrient levels that are
producers from the states of
provided by forage resources
Minnesota, North Dakota,
thus hindering the ability
Kansas, as well as Texas, New
of animals to express their
Mexico and Oklahoma have
genetic potential. He presented
shown little to no change in
data that would indicate
average weaning weights or calf
that the cost of maintaining
weaning rates in terms of the
larger cows with higher milk
32 | APRIL 2018
potential exceeds the value
produced by small increases
in calf weaning weights.
In 1988, Dr. Rick Bourdon,
wrote a paper titled “Bovine
Nirvana – From the Perspective
of a Modeler and Purebred
Breeder” where he presented
the case that genetic selection
should be toward the optimum
for what a set of resources or
environment could support.
Dr. Bourdon stated, “To breed
for optimum means to have a
target insight beyond which
you don’t want to go. If your
goal is to maintain an optimum
level for any trait, the evidence
of your accomplishment is not
visible change, but lack of it.”
Cow-calf producers have EPDs
and index tools to make genetic
selection decisions related
to traits that impact levels of
productivity and longevity.
Producers selecting sires from
which to develop replacement
heifers would be well served to
evaluate where their cow herd is
compared to what they believe
optimum to be. Producers
can work with beef cattle
genetic specialists and breed
association representatives to
help them identify what EPD
levels for milk, weaning weight
and mature weight best meet
their target. What a producer
identifies as optimum in terms