|
Research documenting the value of crossbreeding in
production systems spans well over 30 years in many
different species. The value of using breed differences
to capture hybrid vigor (heterosis) has been well
established. We frequently find ourselves compared to
poultry or pork. How many straight-bred chickens are
marketed in retail stores? How about zero! The same
trend has been evident in the pork industry. All
commercial swine enterprises are based on crossbred
females and a large percentage use crossbred or hybrid
boars. I remember going to my first extension meeting
over 30 years ago (I was about six years old!!) and
hearing reports about the value of crossbreeding. The
importance of heterosis was inarguable-the data was
clear and consistent-not that I understood at that age.
Not long after that, I remember my dad introducing Angus
bulls for the first time in a predominately straight-
bred Hereford and Shorthorn herd.
It
is rare that I go to a meeting where someone doesn’t blame
crossbreeding for the “mongrelization” of the nation’s
cow herd. You can find the negatives of crossbreeding
in the popular press on a regular basis. Are we
sure we should blame crossbreeding for the variation
we see in cattle, or should we blame the crossbreeder?
If crossbreeding causes variation, why are broilers
(all hybrids) so uniform? Broilers are consistent
in age, weight, feed efficiency and carcass merit
at slaughter.
One of the major advantages poultry has in the
competition with beef for the animal protein dollar
is consistency. Perhaps we should review some simple
concepts. Crossing of two pure breeds results in
a calf superior to the average of the two parental
breeds. The superiority of this calf is called “individual heterosis”
or hybrid vigor. This does imply that crossing a
Charolais and a Hereford will result in a weaned calf
that is bigger than the Charolais, but the calf should
be somewhat above the average of the sire and dam is the
“percent heterosis”.
Second, and more importantly, if
that calf is a heifer that you keep as a replacement,
you capture “maternal heterosis” -the incredible value
of the crossbred cow! Recently, I have heard several
ranchers comment that they don’t see the value in
crossbreeding, saying there is “too much inconsistency
and you don’t really get that much more growth.”
Once
again, let’s look at how heterosis works. Heterosis does
not have a large effect on many of the easily measured
traits-like weaning weight or carcass traits. It’s about
4%. However heterosis has a small, but positive effect
on many traits that are critical to profitability.
Deceased age at puberty, increased conception rate,
greater calf livability and vigor, disease resistance
and increased longevity result in a substantial
cumulative effect-much of it realized from “maternal
heterosis”. If you look at any economic analysis of
ranch data, these less obvious traits are dramatically
important to the bottom line. It is a lot harder to brag
at the coffee shop about lower culling rates and more
cows in production at 10 years of age than it is about
the heaviest sale weights! Generally speaking, we get
our largest “kick” from hybrid vigor on traits that are
not highly heritable-primarily production traits. Traits
that are relatively highly heritable (growth and
carcass) will still exhibit heterosis, although to a
lesser degree. So, what is the value of a planned
crossbreeding system? Most studies like to measure the
value of heterosis in “the increase in pounds of calf
weaned per cow exposed.” Think about the measurement-it
is extremely powerful, encompassing fertility,
mothering ability, calf livability, milk production,
growth rate, longevity, etc. The data suggest an
8.5% increase in pounds of calf weaned per cow
exposed by simply crossing two pure breeds. If
you retain that crossbred heifer and put her into
a two-breed rotational system, you increase that
advantage to 14.8%. If you enter into a three-breed
rotation, the potential advantage becomes almost
23%! In these challenging economic times, it would
seem rather difficult for a rancher to ignore a
potential 15 to 20% in pounds at weaning-the combined
effect of 4% weaning weight plus all of the advantages
in the lowly heritable traits.
Remember my earlier reference to crossbreeding,
where I suggested the crossbreeder could be the
problem? The problem with crossbreeding is what
I call the “Breed of
the Month Club” where the producer tries one breed for
two years, switches to another based on his neighbor’s
advice, tries a different one because they are cheap at
the bull sale and switches again because of an order
buyers suggestion. What a way to plan a breeding
program! We end up with the classic “Heinz 57” herd and
blame crossbreeding! Cattle breeding is a very slow
process-to turn over a generation takes five to eight
years. Sometimes we switch breeds before we know if the
one we had was working. To make the process more
complicated, we often mix breeds of widely varying
biological type. “Biological type” basically refers
to the mature size, milk production and muscling
of a particular breed. Just picture running bulls
from a large breed in the same field as bulls of
a small breed. The daughters of these sires will
be highly variable, requiring extremely different
feed, management and marketing. We have complicated
our management and destroyed our consistency, not
by crossbreeding, but as the result of poor planning.
The other often overlooked advantage of crossbreeding
is the importance of breed complementarily. The
data is clear that different breeds are noted for
superiority in certain traits, whether it be growth,
carcass or reproductive fitness. The perfect example
is the general advantage that the Continental breeds
have in growth rate, muscling and leanness, while
the British breeds are noted for their adaptability
to the range, fleshing ability and maternal contribution.
The cross results in a hybrid that is intermediate
for many traits, providing the right “dose of genes” to produce an animal that fits
our entire industry from the cow/calf operator to the
packer. Using breed complementarity to improve a herd
can be just as important as the heterosis that is
obtained. The final piece of the puzzle that we call
crossbreeding is based on the ability to match your cow
herd to your environmental conditions and feed
resources. The genetic diversity between breeds allows
you to identify breeds best suited for your particular
environment. If we just remember that crossbreeding is a
way to capture individual and maternal heterosis,
utilized breed complementarity and match cattle to
specific environments, then the value to our industry is
unquestionable. Crossbreeding does not result in
increased variability! Clay Center, Nebraska has 20 plus
years of data indicating no more variability in the
crossbreed progeny than in the purebred parents.
Remember the variability is the result of poor planning
and life membership in “Breed of the Month Club”!
WRITTEN BY DAVID A. DALEY, PH.D. CALIFORNIA
STATE UNIVERSITY-CHICO
|