by Dr. Tonya Amen
Geneticist for North American Limousin Foundation
I
f you’ve been breeding cattle long, you are aware of the costs
associated with either raising or buying replacement females. Yet,
through the years, we’ve often placed more emphasis on bull selection.
This is not without reason, of course, as bulls do contribute heavily to
the genetic value of the herd each year. But, over her lifetime, a female
can also leave a big mark on the genetics of an operation.
DNA tests that generate the genotypes used in genomic-enhanced
expected progeny differences (GE-EPD) serve two primary purposes
in seedstock production: 1) to improve the accuracy selection through
improved accuracy of EPDs or 2) for marketing purposes. Due to the
impact of sires on genetic improvement and because, in seedstock
operations, selling bulls is often the main income source, most
breeders who decide to invest in genomic technology understandably
start with the bulls. However, I’d like to present the case that females
are also important candidates for testing.
Table 1 shows the progeny equivalents for traits currently evaluated
by International Genetic Solutions for all partner breed organizations
(of which NALF is one). Progeny equivalents illustrate the average
number of progeny that would have to be measured for a particular
trait in order to achieve the level of accuracy delivered on by a genomic
test on young, genotyped, non-parents. For example, for a non-parent
bull to achieve the level of accuracy delivered by a genomic test for
CED, a breeder would have to submit calving scores on more than 25
first-calf heifers whose calves were sired by him. For yearling weight,
on average, a breeder would need to submit more than 25 yearling
weights on his progeny to achieve the level of accuracy expected by
genomic testing.
TABLE 1
Progeny Equivalents for GE-EPDs powered by BOLT
Trait
Progeny
Trait
Progeny
Equivalents
Equivalents
CED
25+
STAY
15
CEM
4
DOC
25+
BW
22
CW
5
WW
25+
Marb
8
YW
25+
REA
6
MILK
19
BF
8
KEEP INFORMED
If we were to think about genomic testing heifers instead of the
non-parent bull, it becomes apparent that for most traits, a genomic
test will deliver more accuracy on her EPDs than if you submitted
performance data for all the natural-service calves she has in her
88
lifetime. What a tremendous investment in the genetic future of
your herd! Not only will testing your females improve the accuracy
of selection when it comes time to make your replacement heifer
choices, but it will also help insure you make the best mating choices
when breeding time rolls around. By adding accuracy to her EPDs
before the heifer is bred, you’ll get a truer picture of her genetic
strengths and weaknesses, which will give you better information
when you select the bull to breed her to. Additionally, the inclusion
of parent verification with all HD and LD tests will help avoid
inbreeding by ensuring the accuracy of the pedigree.
I’d like to direct your attention back to Table 1. You may have
noticed that compared to the rest of the traits, calving-ease maternal
looks low. This is due to lack of genotypes on females—especially
2-year-old females. The majority of the genomic impact you see for
CEM actually comes through its relationship with CED. Not only
does genotyping females offer real benefits within your herd, those
genotypes are also necessary for the breed to have more accurate
selection tools for maternal calving-ease.
Of course, all of this is not meant to suggest you should not use all
the current tools in your heifer selection tool box (performance data,
birth dates, visual appraisal)—all of these remain a very important
part of your arsenal in heifer selection and cattle breeding. In fact,
collecting performance data is more important than ever, as it is
necessary to insure the efficacy of genomic tests as well. As always,
we should remain vigilant in adding new tools that help add accuracy
and efficiency to management decisions to ensure we are raising the
best seedstock possible and supplying the best tools for selection and
breeding to our commercial customers.
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• APRIL 2020