Dairy crossbreeding was aggressively
studied by USDA in the 1940s-50s with the advent of A.I. ( This was done alongside inbreeding studies
in the purebred herds USDA maintained at Beltsville MD.) By the end of the 1950s crossbred research
was dropped as no cross combination seemed capable of milking more than a
Holstein or testing higher than a Jersey.
The inbreeding trials varied from breed to breed.
In that era, cows were more consistent
in fertility but slower maturing in productivity—pretty much the reverse of the
modern dairy cow after five decades of intense genetic selection.
Cross breeding core of support has widened in recent years
Crossbreeding had a core of support
within Red cattle breeds. One result
was formation of the Red & White Dairy Cattle Association in
1964. In a fairly short time,
however, Red Holstein bulls began to dominate the RWDCA through their acceptance
into commercial USA- A.I. systems.
Composite Red bulls are much more widely accepted in Europe, where Red
cattle widely outnumber Black in totals (even though Holstein has become the
largest dairy breed in Europe).
As some commercial Holstein herds expanded
rapidly without an abundance of labor, the crossbreeding expedient of breeding
Holstein heifers to Jersey sires insured calving ease in a way small-calf
Holstein sires could not, given pressure to breed heifers at younger ages. The resulting “HO-JO” cows proved popular
(milky, healthy, feed efficient) although often surprisingly low testing (the
fault of confusing hair color with bf% and pr% ability) and as cows could be
bred back to Holstein bulls.
At the same time, dairymen converting
to grazing were being advised that their success would depend on having a
smaller cow. The success of the HO-JO
was duplicated here, until promoters took over…
The argument for “hybrid vigor” and the
illusion crossbreeding could replace genetic selection
Declining fertility and health
characteristics leading to short commercial herdlife, and the nonadaptation of
the highest genetic value purebreds to intensive New Zealand-style grazing,
brought crossbreeding a new life from 2000 and ever since. LIC New Zealand (AI stud 190) brought their
sires to the USA, [first through CRI Genex, then Taurus-Service, and now
through Select Sires] promoting a two-breed criss-cross between shorter
Friesian-type Holsteins and Kiwi-type Jerseys (known as “KiwiCross”) and spring
season calving. The big selling point
to radical graziers was that Kiwi cows do not need grain. What we learned here was that if you fed
grain they don’t milk more, they just get fat and dry up early.
Creative Genetics of California is
promoting the “Pro Cross” [Holstein x Viking Red x Montbeliarde] concepts of Dr
Les Hanson (U-Minn) which was designed with high volume, lower Bf%, western
milk markets in mind where the only dairy income beyond fluid milk is beef cull
salvage. In the Midwest where Multiple
Component pricing exists and the cow replacement market is more robust but also
type conscious, old-fashion udders of Montbeliarde and narrow front ends of
Swedish Red do not compete.
Basically, what we should be learning
is that Crossbreeding hybrid vigor is not a substitute for sound genetic
selection. You still have to
select in any breed for needed production, reproduction, type and health
support traits. You still need to
consider mating effects so that you do not inadvertently produce the
physically inbred animal that results from selecting the same phenotypic
extremes from each breed.
Red Holstein x
Jersey x Fleckveih =
production + component $ value + durable feet & legs
= polled
+ A2A2 Beta Casein +
fertility/longevity
Why is this a superior three-breed
rotation? Because you have useful
genetic variety from the three largest globally distributed genetic pools. (Many alternative breeds promoted for crossbreeding
cannot identify enough variety to utilize “aAa” or avoid pedigree
inbreeding.) You have three breeds in
which cow fertility has been maintained.
You have three breeds with 50% to 66% frequency in the A2 Beta Casein
gene (a future factor in premium milk marketing). You have a number of polled bulls in Red
Holstein and Jersey that will carry over into the Fleckveih generation, polled
being a dominant trait. You have modern
type in udders, you have high function feet and legs, you have lactation
persistency, and you have a gene pool based in sufficient longevity that your
composite herd will be self-renewing.
You have high deacon calf values in
Red Holstein and Fleckveih which will carry over into the Jersey X
generation. If you feed steers, the
biggest premium market is currently grass fed, Jersey cross beef while the
growth rates and market prices for Fleckveih steers will compete with any
specialized beef breed.
Not interested in cross breeding ?
The majority of dairymen remain committed
to a purebred approach, where the possibilities of uniform herds and the focus
on one breed sire selection should be easier.
The reason this did not work out for so many who then entered into
crossbreeding was a result of “one size fits all” genetic selection where
evaluation trait index focuses lead us to extreme physiques and inbreeding
depression. An increasing number of
herds, both purebred or crossbred, confinement or grazing, prevent those
problems through the “aAa” Breeding Guide (Weeks Analysis) which
maintains balance in physical characteristics. The focus of “aAa” on the functioning
physique and avoidance of extreme “like to like” matings provides a hybrid
vigor mating response both within your chosen breed, and if you
crossbreed. No other mating system
is capable of bridging confinement TMR, grazing, purebreds and crossbreeds like
“aAa” does.
How to avoid inbreeding effects in the era of Genomics
Prior to Genomics the sires
of new bulls appeared to be the same everywhere, but their dams could
still provide some outcross vigor to your purebred matings. But what do you do in an era when over half
of the top 200 GTPI and GNM$ females are owned by four major AI
systems, producing most of their new sires, and all are siblings to ranking
AI sires? Farmer breeders are
being pushed out of the AI loop.
As has been pointed out by many
observers, the latest being Gordon Cook, President of Holstein USA (in the
December issue of Holstein International) – the beginnings of Genomics
came with the promise that “new outcross cow lines” could be found with this
technology. Instead, the application of
Genome evaluation has been to pile the ranking numbers as high as possible, as
fast as possible. Outcross went out
the window, because in any given generation, outcross ancestors did not rank
at the top. The effect they could
have had in the following generation (as a source of heterosis vigor) was never
estimated.
The role of “outcross” in protecting against inbreeding depression
The definition of “outcross” prior to
Genomics was, a different pedigree [either a different sire stack or a pedigree
more linebred in total than the weighted mix of pedigree influences in the
general population].
Under Genomics, an “outcross” (regardless
of pedigree) is an animal whose Genome is different from the
selection trend among ranking animals—ie, possessing different DNA combinations
and markers.
Inbreeding = the result of breeding “like to like” at the Genome level
Inbreeding is a process in which the
naturally heterozygotic pairing of gene alleles is transformed into homozygous
[identical] gene alleles. Inbreeding
is inherently good IF the genes being paired relate to desired
phenotypic responses (more milk, higher test %s, A2A2 Beta casein, homozygous
polled, etc).
But IF the genes being paired relate
to weaknesses or deficiencies (as in lethal recessives, or lost health and
fertility, or dysfunctional physical traits) then your animals exhibit
“selection depression”. In the days
before Genomics, we thought “pedigree inbreeding” caused these problems. In fact, ancestors in common was merely associative;
the creation of undesirable homozygous gene pairings was causative.
Physical evidence of
“inbreeding” among the elite Genomic population
One of my mentor Jersey breeders told me a story at the
beginning of popular Genomic testing, which involved his leading cow family
(from whom he was selling bulls to AI and heifers in national sales).
A particular mating, involving the
leading JPI sire onto his highest G value donor dam, produced four ET full
sisters. These Genomic tested all the
way from P2 (20th percentile) to P9 (90th
percentile). After calving and scoring,
the best of the four was the low ranking P2, who made 18,000 pounds in first
lactation, scored VG88%, and bred back easily. The high ranking P9 barely made 10,000
pounds (well below herd average), scored DS80%, and did not breed back, so was
culled. The other two performed around
pedigree expectations equal to their Genomic values. At the same time, major dairy magazines
were advising dairymen to G test all heifers and cull those at the lower P
levels, “don’t waste any feed on raising them”. The result of this kind of advice is that,
over time, your cow herd may reach a stage where their Genomes are near mirrors
of the available ranking AI sires, and “heterosis response” will slip away,
replaced by selection depression.
Every three generations, select
on a different index (ideally based on your current herd’s weaknesses)
In three generations it is a truism
that 87.5% of the original herd genes have been replaced. This is the level at which, if not already
present, research found “inbreeding [selection] depression” beginning to
occur. You need to throw in a
generation selected on a different basis, whose Genomes can offer a “hybrid vigor” effect. This will protect you from “mating effects”
that population genetics has never been able to anticipate, and keep you
producing vigorous, functional replacements.
No comments:
Post a Comment