Why does anyone crossbreed?
(1) To gain added
performance from “hybrid vigor” [heterosis].
What is “hybrid vigor”?
(2) The
performance response we get from introducing some “warm”[outcross]
genes into a “cold”[closed] gene population.
Why do we wish to change the
performance [related behavior] of our animals?
(3) Because
current generations no longer respond as well as prior generations to trait
selection as practiced within our breed.
Let’s stop right there. “Crossbreeding” is tried when after
several generations of gaining performance from standardized methods of
selection [which today we call “index”] we no longer see any incremental
financial gains—ie, either cow life gets too short, or milk yields no longer
grow, or incremental costs are greater than incremental gains.
The problems that grow from believing “change” does not keep changing
The current fixation with “indexing”
for commercial herd propogation is based on a “race memory”—the window in time
that was the 1960s, when AI studs shifted from bloodline sire selection to
progeny data sire selection. While
this was done in a “purebred” context, the net result was we began a mating
process in which we “crossed” our herds—we bred “type” cows to “milk” bulls, we
bred linebred cows to outcross bulls.
We saw large leaps in productivity from the cow to the heifer
generation. We gave the +1000 PDM
figure 99% of the credit for this gain, and assumed this process would work
forever.
The 1960s was when all the “single
trait selection” ideas gained traction—ideas that later research have uniformly
proven to be laden with weaknesses—yet here we are in 2011, and we remain more
in love with “single trait selection” than ever, only instead of “PD Milk” we
look at “Genomic Net Merit”.
What goes wrong with single trait selection
The problem with single-trait
selection [any selection system in which you say, “no matter what, every sire I
use must be plus x pounds of milk/fat/protein”] is that you tend
to be going back to the same gene wells over multiple generations. Over time, the underlying gene possession
of your cows becomes the same as the gene possession of your mating sires. For some limited desired genes, a
“homozygous” [identical genes in each pairing] pattern is OK—as in gene
pairings that stimulate milk yield. But
for too many genes, a “heterozygous” pairing [maintaining the basis for a
“hybrid vigor” mating response] is more desirable—these being genes for traits
that we need but are not naturally associated with “milk” genes in the
mainstream of our breed.
In other words, think of the typical
experiences we have had for the “highest milk” bulls:
(1960) = If he is +2000m he will be minus for
udders and/or feet and legs.
(1970) = If he is +2000m he will be minus three or
four points on butterfat%.
(1980) = If he is +2000m he will be calving ease
and I will end up with small hard calving cows.
(1990) = If he is +2000m he will be minus for
Productive Life [sire short herdlife].
(2000) = If he is +2000m he will be too high on
expected future inbreeding.
(2010) = If he is +2000m he will be minus for
Daughter Pregnancy Rate [sire low natural fertility].
In each generation there would be an
exception close to the top, but in our fixation with “number one” it was always
possible to overlook him. Then we
would reap the negative effects of trusting only “rank”.
From generation to generation, the
negative effects of focusing on one main performance trait tend to accumulate,
and this accumulation reflects the trait weakness(es) of the ranking sire
line dominant in that generation.
This accumulation is more dangerous if a certain physique is preferred,
a further limiting of gene pools by qualitative as well as quantitative
selection, leading to extreme frail physiques.
Thus, graziers (who felt they
needed shorter, more mobile cows) and large confinement herd managers
(who were looking for easier calving heifers, more fertile cows, physiques
better adapted to the facility limitations, and more health in general) both
pursued crossbreeding as solutions to different problems.
But in fact, if by crossbreeding the
bull selected was defined merely by his breed, there is no guarantee of
“heterosis” [many Jersey bulls are just smaller, brown Holstein gene
accretions] [most Euro Red bulls are proven in single trait ranking “index”
systems very similar to our own].
Whether crossbreeding or outcrossing, the principles remain the same
In any multiple generation analysis,
the conclusions remain the same – there is no sustainable shortcut for
the full breeding process, IF your goal is to gain on both herd equity
and herd net income.
The insurmountable weakness of
crossbreeding as most have practiced it is that over time, milk yields will
decline. “Milk” genes get
replaced with “Beef” genes; “Cow capacity” genes get replaced with “small”
genes; Uniformity for adaptation to group feeding and handling is lost in
random variation.
Basically, because we are not taught
that the complexity of gene selection is manageable, and that any short cut
method (index selection) (crossbreeding) (linear mating) has declining
effectiveness after only three cow generations, we overlook some simple
alternatives.
What could have been done (but
usually was not):
We could limit our breed inclusions to one or two breeds, rotating back
to our “base” performance breed every second or third generation. This avoids the loss of productivity, but
if we also focus our outcross selection on sires in breed #2 and/or #3 on
changing the weaker traits of our base breed, there will be more of a true
“heterosis” response than if we pick the crossbreeding sires “the same way” as
we pick our performance breed sires.
You have to break the cycle of “likes to likes” matings.
We could stick
with our “pure” breed, but open up to using the very sires we usually turned
down, the “not enough milk” sires others found desirable—due to their
possession of the very traits we had been giving up consistently in our pursuit
of “single trait” [milk] selection.
Treat these as an “outcross”, ie, return to your “line” in the following
generation. This is how you find
heterosis within any breed. It is your
only way to avoid “inbreeding” today within any breed.
We could go
beyond the simply statistical (quantitative) level of bull “proofs” and include
a process for managing the physical (qualitative) level of mating— as we do
with the “aAa” breeding guide. If
you are unwilling to give up the index ranking selection (“likes to likes”) the
qualitative mating process still will impact on exactly those areas of physical
adaptation that lead so many to crossbreed initially.
The more successful crossbreeders I
know have usually found that at a certain point, saving their own bulls
representing the more successful crossed combinations, is more effective than
to continue to add new breeds. [Look
at the Kiwicross sires in the latest LIC New Zealand sire directory for
examples.]
CROSSBREEDING AND OUTCROSSING ARE (NOT) DIFFERENT
Crossbreeding assumes we get hybrid vigor because
different breeds means different genes.
In fact, under parallel selection systems, all breeds share many gene
patterns in common. The composite
(Euro Red) breeds actually offer less heterosis.
Outcrossing within a breed assumes we get hybrid
vigor because different bloodlines mean different genes. In fact, within most breeds, even more
gene patterns are in common than is true in crossbreeding, as a result of
highly focused trait selection.
“Hybrid vigor” today is thus a result of knowing how
to avoid “likes to likes” mating, whether within a breed or crossbreeding. More heterosis is available when we add in
the qualitative level of [physique-related] gene activity in our mating
process, and give up arbitrary selection levels on a “primary” trait to acquire
higher levels of performance in all our “secondary” traits—leading us to the
“different” bulls.
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