Thoroughbred Genetics
Thoroughbred Genetics

Thoroughbred Genetics

(Image : UCSD / TBWP)

THOROUGHBRED BREEDING

“A NEW UNDERSTANDING”

annet becker - broodmare and foal manager
annet becker - broodmare and foal manager

Annet Becker Broodmare & Foal ManagerModern genetic theory as we know it, started with Gregor Johann Mendel, a German-Czech Augustinian monk and scientist, who studied the nature of inheritance in plants. The importance of Mendel’s work did not gain wide understanding until the 1890s, after his death, when other scientists, researching similar issues, re-discovered its value.

Currently, yields in the dairy and meat industries are being significantly enhanced through the application of molecular genetics in identifying breeding stock better able to pass on desired traits. It’s only logical then, that Thoroughbred breeders, so long plagued by confounding theories, should be looking in the same direction. Indeed, the most confounding thing is that it’s taken the racehorse community so long to “twig”, though it’s arguable we’ve chosen to be confused by a litany of outrageous (but romantically appealing) theories, as well as having little appreciation of the science behind genetics.

Very few articles on Thoroughbred breeding reveal an understanding of genetics. It remains the norm among readers of pedigrees, that the components are seen as names alone, and they’re only guessing at their importance. At the same time, many of us have been befuddled by the marketing impression generated by the page of a catalogue, into believing the female line is all-powerful, when it is in fact no more than a 50% contributor to the genetic composition of the animal.

In a recent publication on pedigree theories and genetics by one of the great turf writers of all time, Tony Morris and Dr. Matthew Binns (Thoroughbred Breeding - Pedigree Theories and the Science of Genetics), they provide a fresh insight into the correlation between genetics and pedigrees. “From a scientist’s perspective, genetics is really only another word for pedigree, but one that potentially provides more detailed and accurate information about the chances of producing the desired outcome than that of names on a page, the analyst’s usual stock-in-trade.”

In several scientific studies calculating the genetic contribution to race performance in Thoroughbreds, the results generally suggest that approximately one third is genetic, while the rest is attributable to an assortment of factors, labelled “environmental”, things such as horsemanship, nutrition, environmental management, veterinary care and training, amongst others. That’s encouraging for those of us who do not have piles of cash. The rich can always afford what they want genetically, but if you’re constrained by budgets, you have to rely upon your wits and energies in managing the remaining 67% better than most.

During the reproduction process, a shuffling of chromosomes takes place between the egg and the sperm cell, which creates a unique genetic entity. The possible combinations of chromosomes in identical matings are thus immense. The unrealistic expectations of most of us horse breeders are shown in the repetition of previously successful matings, whereas the average chromosomes shared between full siblings is at best only 50 per cent, but in reality closer to 25 per cent (1 in 4) in the practical scheme of things.

Breeders also seem to have a false idea of the exact contribution ancestors in a horse’s pedigree make to the actual individual; for example the names of famous horses in the fifth generation are often afforded reverential weight, simply because they’re famous.

CHROMOSOMAL AND GENETIC CONTRIBUTIONS

DOWN THE GENERATIONS

Generation

Ancestors in that Generation

Average % Contribution

from each

Average Number of Chromosome

transmitted per Ancestor

1

2

50.00*

32.00*

2

4

25.00

16.00

3

8

12.50

8.00

4

16

6.25

4.00

5

32

3.13

2.00

6

64

1.56

1.00

7

128

0.78

0.50

8

256

0.39

0.25

9

512

0.19

0.12

*Actual contribution

This table shows that at the parental generation, the number of chromosomes is fixed, but in the other generations the genetic contributions are based on average transmission. At the sixth generation, an individual has sixty-four ancestors, which on average will contribute just one chromosome to the individual. Studies have however, shown that at that level, some ancestors do not contribute any genetic material to an individual.

These studies reveal (for the first time really) the illogical nature of so many ‘breeding theories’ out there. In a sense, they expose the bare truth about the effectiveness (or relative lack of it,) which the deliberate coupling of ancestors several generations back, holds. That means inbreeding per se, can be pointless, unless it involves ancestors whose descendants are known to carry the factors we’re looking to reproduce; these nicks, if they exist at all, are far less common than many would like to believe.

This brings us back to the point that Thoroughbred breeding should be more about the matching of individuals, the parent stock, for rational reasons, than a game played with names on a page. Without wishing to be too smug about it, matching two individuals for the right reasons, with the aspiration of creating the best result from the two parents, has been Summerhill’s practice for years. The physical attributes, temperament, performance, soundness, speed, stamina, mental strength, physical durability, are the attributes that go into the making of a good horse; and oh! let’s not forget the instincts of the stockman, the one that’s closer to his animals, that understands their individuality and knows their idiosyncrasies, and how to bring them up. That’s all part of the other 67%!

summerhill stud, south africa
summerhill stud, south africa

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