08/21/2024
BOTTLENECKS AND SIRE SELECTION ON THE FARM
The University of California at Davis has a nice 2016 post entitled “How a Genetic Mutation From 1 Bull Caused the Loss of Half a Million Calves Worldwide”.
A bull born in 1962, by the name of Pawnee Farm Arlinda Chief, produced 16,000 daughters, 500,000 granddaughters, and more than 2 million great-granddaughters. His sons were also popular sires.
As a result, Chief’s chromosomes account for almost 14 percent of the genome in the current Holstein population in the United States.
It seems Chief was the source of a haplotype (a group of genes that are inherited from one parent) on chromosome 5 of Holstein cows that was associated with lower fertility rates and embryo loss.
Because Chief was such a popular sire, his genes alone were responsible for over 100,000 cumulative Holstein calf losses over 30 years in the United States alone, and about half a million worldwide.
What does this have to do with dogs? A bit.
When pressed about the poor genetic quality of today's ‘pure bred’ dogs, most Kennel Club breeders parrot the Kennel Club apologia: “We only register dogs, we don't breed them.”
In fact, the line is pure bunk.
The Kennel Club does far more than register dogs -- it sets the rules that guarantee more and more dogs will suffer serious (and often painful) genetic problems.
The problem, in a nutshell, is the closed registry system.
With all Kennel Club breeds, the ‘founding stock’ has always been small in number, and often fairly in**ed going in, since breed creation is a product of inbreeding and line breeding to ‘set’ the look of a dog.
Because a closed registry never adds new blood, it becomes progressively more in**ed over time.
Genetic diversity is never increased in the Kennel Club -- it is only reduced. In practice, it is often reduced quite rapidly due to the fact that show-winning males are in great demand to ‘cover’ as many bi***es as possible -- the so-called ‘popular sire effect.’....
How did the Kennel Club come to embrace a closed registry, and why does it maintain this system?
The adoption of a "closed registry" by the Kennel Club is an artifact of its history, while the continuation of this practice is driven by the economics of dog breeding and the political construct of the Kennel Club.
The Kennel Club was created in Victorian England in 1873, at a time when new theories about genetics were being promulgated by learned men who did not yet have a very good idea of what was going on in the natural world.
The "speciation" of domestic breeds of livestock began with the work of Robert Bakewell in the 18th Century, and the control of sires. Bakewell's work helped speed the rise of the Enclosure Movement, which in turn led to large estates, fox hunting, and the rise of terrier work.
Bakewell had no real knowledge of scientific genetics, and his breeding program was largely limited to the control of sires (made easier by enclosures) and the admonition that "like begats like" and that success was to be found by "breeding the best to the best".
The first stud book to document the breeding of animals was the General Stud Book of 1791 which tracked a small pool of racing horses. A stud book for Shorthorn Cattle was produced in 1822.
As more and more farmers followed the tenets of Robert Bakewell, sire selection became increasingly prevalent and inbreeding and line breeding more common. By selecting the best beef and milk producers, and pairing them, rapid improvements in cattle breeds were made.
What was different with farmers, than with dogs, however, was that down on the farm there was a clear axis of production.
Farmers inbreeding animals for improvement began to notice that fertility rates began to drop after a few generations. In some lines disease popped up, or defects such as weak hocks appeared. In**ed animals were not better if they remained increasingly in**ed, and so hybrids or out-crosses began to become the rule.
Because farm herds are large and often kept by families for generations, farmers were able to "tease out" data indicating drops in production, increases in mortality, declining fecundity, and a steady rise in disease and illness.
Inbreeding, which had initially boosted production, now appeared to be reducing it.
Because farmers had a clear "steak and eggs" axis for evaluation of stock, they were ready and willing to outcross to achieve the best results for their needs and their land. Consumers, after all, do not much care what breed of chicken their eggs come from, or what "champion" bull sired their steak.
Through experimentation, farmers discovered that outcrosses and hybrids of two "pure" types produce as well or better, while remaining more disease resistant, more fecund, and longer-lived than deeply homogeneous stock.
What may appear to be a pure Angus (the most common breed of beef cattle in the world) is likely to have a wide variety of cattle genes coursing through its system. In fact, entire breeds of cattle are now kept solely for their outcross potential. On today's farms the cattle in the field may be Brangus (Brahman-Angus crosses), Braford (Brahmam-Hereford crosses), Beefmasters (a cross of Hereford, Shorthorn and Brahman), or any other combination or mix.
In the case of the “popular sire” Holstein Pawnee Farm Arlinda Chief, the fecundity and mortality problems embedded in the genetics of this particular bull reared its heads through careful record-keeping over 50 years.
The good news is that the dairy industry had actual production statistics to reveal the problem *and* they were (and are) not restricted from outcrossing to solve this or any other production or health problem.
But with dogs, not only are there few meaningful metrics to evaluate stock, but data in general is poorly kept, if kept at all.
When lack of production and performance criteria is combined with little or no record-keeping, and when closed gene pools are mandated by the artificial scarcity economic model of the Kennel Club, the result is a relatively rapid canine devolution as more and more breeds get sicker and less fecund.
Is there a way out?
Yes, but it’s not with more testing, which simply reduces a breed’s already small gene pool.
The way forward is to devolve back to type (i.e. “dairy cow” in the Holstein case) and allow outcrossing as needed.
In the world of dogs, types include pointer-setters, retrievers, terriers, herding dogs, livestock guarding dogs, pulling dogs, etc.
Where the world of dogs took a wrong turn was when they decided to elevate just-invented breeds over long-established types.
The result was a bit like over-sharpening a pencil; it seemed like a good idea right up to the moment the pencil tip broke when it touched paper.
The way forward is not to keep over-sharpening the pencil; it’s to embrace whatever works to sustain a solid line.
As with pencils, so it is with dogs.
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UC Davis article at >> See >> https://www.ucdavis.edu/news/genetic-mutation-1-bull-caused-loss-half-million-calves-worldwide
