Wednesday, August 2, 2017

The Ultimate “Three Way” Cross – have we found it yet ?

From the Jan-Feb 2016 Dairy Route Letter

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.

1 comment:

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