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Porter’s pedigrees
There was some credibility to bloodstock theories after all
The first of a three-part series by Alan Porter on the latest bloodstock and genetic research
THERE WAS AN extended period of time when theories of thoroughbred breeding were a matter of keen debate, spawning much discussion in sporting publications, as well as numerous books.
Although discourse began in the early days of the breed, when I first became involved in that side of the thoroughbred industry, back in the mid-1970s, there was still plenty of lively debate as to how different pedigree methodologies can be utilised to produce a great horse. Certainly over the last two decades, discussion on the best way from a pedigree standpoint to breed a runner has definitely been much less apparent.
This is probably down to several factors. One is that for those who are not private breeders, commercial considerations have probably become a much greater influence in the decision making process than any theory of breeding.
Another, at least in the US, is the predominance of automated on-line nicking programmes that rate a mating on the basis of the sire/broodmare sire, or sire-line/ broodmare sire line cross, with similar programmes offering a variation on the theme, popular in Europe and Australia.
Thirdly, and perhaps most importantly, is the progress made since the completion of the equine genome and greater awareness of genetics.
With regard to the latter, nature might abhor a vacuum, but speculative theory – of which there was much with regard to thoroughbred breeding – flourishes in one, at least when that vacuum is caused by a lack of empirical evidence. There’s no doubt that since awareness of genetics has increased, and data has become more readily available to create metrics to measure performance, scope for speculative philosophising, at least that with any credibility, has greatly diminished.
That said, many of those who propounded pedigree theories – even if reasoning behind those
theories doesn’t hold up to the scrutiny of current science or statistical analysis – were good observers. Although they may have “seen through a glass darkly” and been inclined to mistake the sign for the thing itself, more modern studies and genetic knowledge does show there was often something to what they had seen.
One of those theories, which holds a kernel of truth – but was dismissed, rather ironically, long before the modern advances in genetics – was the system devised by the Australian C. Bruce Lowe. In the late 1800s Lowe examined existing female lines back to their earliest documented sources. He discovered around 50 distinct founders, and then arranged those families in numerical order. That order was based upon the number of direct descendents of each founder that had won the Derby, Oaks
and St. Leger up to that time.
Number 1 was allocated to the Tregonwell’s Natural Barb family, whose foundation mare could claim the most winners of these three Classic races amongst her descendents in tail female at the time; the number 2 to the family with the second largest number of these Classic winners among its offspring; and so on down the scale.
Lowe then decided that families 1, 2, 4 and 5 produced good runners, but not good sires, and that horses descending from, or inbred to, families 8, 11, 12 and 14 produced good sires.
These two groups were designated “Running Families” and “Sire Families” family number 3 receiving the unique distinction of being in both groups.
Lowe died before his work could be made public, but prior to his passing, Lowe had entrusted his research to William Allison of The Sporting Life, and it was Allison who was eventually responsible for the publication of Lowe’s findings, in the form of a book, published in 1895 and called Breeding Racehorses by the Figure System.
For some considerable time, Lowe’s theories about combining what he viewed as the “core families” were held in high esteem, and were used by such as Colonel Hall Walker (Lord Wavertree), who founded the English (now Irish) National Stud and August Belmont II, breeder of the great Man O’ War.
Lowe’s concepts remained influential for most of the first half of the 20th century, but credibility was eroded in the 1940s when Timeform’s Phil Bull conducted a study which showed that success of the families in the Classics was proportional to their presence in the population, and family number 1, designated the best running family, also produced more horses which finished last in selling plates than did any other.
Although that was the beginning of the demise of the use of Lowe’s methodology in planning matings (and the rise of computerised nicking services), it didn’t mark the disappearance of his numbering system, which has endured until today as a system for organising the history of the breed with regard to its female descent.
It can be seen up to the present day in copies of the Bobinski Tables and its successors, and quite frequently in private stud books.
Of course, there was much that Lowe couldn’t know at the time. Given the time period – in some cases over 350 years back to founder mares – and the number of generations involved, the General Stud Book (GSB) is remarkably accurate, but the advent of genetic testing has also revealed that there are numerous significant errors in female lines (see “Thoroughbred
Bruce Lowe’s book outlining his work in the 1800s examining female thoroughbred lines and which he traced to their earliest documented sources and numbered according to their success rates in the Derby, the Oaks and the St Leger
The credibility of his work was eroded by Phil Bull of Timeform, and there are aspects of knowledge now available that Lowe could not have known.
However, recent research has shown that Lowe was indeed “on to something”
Photo by Simon Mockeridge
Kind: because MtDNA is “non-recombining” we can be sure the dam of Frankel is from Bruce Lowe’s number 1 family that first originated in the 1600s
racehorse mitochondrial DNA demonstrates closer than expected links between maternal genetic history and pedigree records” for reference).
What Lowe also couldn’t know is that a number of female lines (for example his family 4 and 13) are in fact genetically identical as far as the tail-female line is concerned. This means that before the advent of the GSB they had a common ancestor at some point preceding the earliest known founder by GSB records.
It also appears that Lowe’s concept of some female families being inherently superior to others is wide of the mark –a look at a population of nearly 200,000 horses revealed the percentages of elite performers produced by specific matrilineal lines vary little, one from another.
Lowe had an early inkling
What Lowe was almost certainly unaware of was the reason for his findings, and the genetics that differentiate one female line from another, a part of the genome called mitochondria.
Mitochondria are small structures in cells that generate energy for the cell to use, and are hence referred to as the “powerhouses” of the cell.
What makes them unique in genome, and for the study of pedigrees, is that they exist outside of the nucleus of a cell, and effectively are inherited entirely through the female line.
Since mitochondrial DNA (mtDNA) is “non-recombining”, i.e. it means that it can only change through spontaneous mutation. So we can say, for example that Kind, the
GLOSSARY
Haplogroup
A very distinct group of mutations. Haplogroups are mtDNA sequence polymorphism (a common variant in a specific sequence of DNA) variations that occurred possibly 150,000 years ago and correlate with the geographic origins of populations traced through the maternal lineages They have evolved from different ancestries, so under different selection pressures. So, a haplogroup that developed in the East, such as L, has developed differently than the D haplogroup from which stems the Norwegian Fjord, Shetland Pony and Iceland Pony.
Haplotype
Is a sub-group that has the original mutations that define the haplogroup as well as further distinctions from other members of the haplogroup.
Amongst horses that have the mutations that distinguish the haplogroup, there can be a number of haplotypes.
For example, the L haplogroup has 10 haplotypes that have been found in the thoroughbred.
dam of Frankel, will have the same mtDNA as the founder of the family from which she stems (Bruce Lowe’s number 1 family), Tregonwell’s Natural Barb Mare, who was likely born in the mid-1600s.
In 2012 a scientific paper was published recording the establishment of the equine mitochondrial genome into 18 major haplogroups (annotated A through R), with a number of sub-groups under the broad haplotypes (now known as Achilli family identifiers, after the paper’s lead researcher).
To date through the work of people such as Dr Steve Harrison, Dr Mim Bower, Lyudmila Khrabrova, Judy Baugh, Ken McLean and Byron Rogers, 11 distinct haplogroups and a total of 36 haplotypes have been established within the thoroughbred (including most recently,
found by Byron Rogers, two Australian colonial families that weren’t previously known to exist in the thoroughbred population).
The largest group within the equine population in general and within the thoroughbred is the Achilli L haplogroup, which has 10 individual sub-haplotypes in the thoroughbred population.
To understand these haplogroups and haplotypes in terms of historical reference, it is most likely that the founder mare of a haplogroup lived 10,000+ years ago, while more recent mutations creating the unique haplotypes occurred 1000s of years ago, well before the establishment of the GSB.
Mitochondria: a key element
As far as athletic performance is concerned, mitochondria use aerobic respiration to generate most of the cells supply of adenosine triphosphate (ATP), which is used by the cell as a source of chemical energy, hence the description as the “powerhouses of the cell.”
An increase in both the size and number of mitochondria in the cells will result in improved performance all other things being equal (in humans, both steady distance running – aerobic training – and faster, more intensive interval training, have been shown to have a positive impact on mitochondrial density).
Mitochondria are, then, a key element in performance in any event that has a significant aerobic component.
While it’s well-known that, what for humans are described as middle and longdistance events, are primarily aerobic, it’s probably less realised that there is a major aerobic contribution to far shorter events.
The minimum distance over which top-class thoroughbreds race is 5f furlongs/1000m, and the duration of such events is in the region of 55secs.
In a study by Bond, et al “Assessment of two methods to determine the relative contributions of the aerobic and anaerobic energy systems in racehorses” a test of the relative anaerobic and aerobic contributions during three supramaximal treadmill runs (105, 115, and 125% V̇o2max) found that racehorses’ mean contributions were 81.4, 77.6, and 72.5 per cent (aerobic), and 18.5, 22.3, and 27.4 per cent (anaerobic) at 105, 115, and 125% V̇o2max, respectively.
So, as far as elite thoroughbreds are concerned, the aerobic system, and therefore the mitochondria, does play a major role in performance even at the minimum distance.
While his work had been discredited by Bull, later scientific papers have shown that Lowe was on to something.
He was correct in identifying the unique importance of the tail-female line, and was similarly correct in his observation that certain matrilineal lines combined well together.
Indeed, a recent paper by Lin, et al “Potential role of maternal lineage in the thoroughbred breeding
strategy” showed the heritability of race performance between dams and foals is much higher than that between sires and foals, and that this difference is statistically significant.
To further confirm the findings of Lin, and that the importance of mitochondria to thoroughbred performance isn’t just speculation, is confirmed in a more recent paper from the Journal of Animal Science. In a paper entitled “Select skeletal muscle mitochondrial measures in Thoroughbred weanlings are related to race earnings and sire”, Guy, et al found a statistically significant correlation between lifetime earnings and skeletal muscle mitochondrial capacity of Thoroughbreds (based on biological samples from the gluteus medius muscle of thoroughbred weanlings).
Early round-up
So, up to this point, we’ve established that mitochondria is a part of the genome which exists outside the nucleus of the cell; is effectively transmitted only in direct female line; plays a vital part in producing aerobic energy; and that aerobic energy makes a major contribution to performance even at the shortest distance over which elite thoroughbred compete. We’ve mentioned that there are 11 genetically distinct mitochondrial haplogroups found to date in the Thoroughbred breed, and 36 subgroups or haplotypes, but we’ve also noted that there isn’t any significant difference in the percentage of elite runners descending from each of these mitochondrial haplotypes.
