On Breeding Values in Thoroughbreds - a letter to the TDN
The following letter appeared in the Thoroughbred Daily News in response to a column by noted industry observer Bill Oppenheim. It outlines the reason why the industry needs breeding values for genetic improvement to occur.
To the Editor
In Bill Oppenheim column (Near Miss, 6/13/12) he raises a fundamental issue that for far too long has been ignored by the thoroughbred breeding industry.
Since the time when the Sport of Kings was literally, the sport that kings participated in, thoroughbred breeding has been a non-random event, based on the belief that there is something to gain from the selection of mates that could not be obtained by random selection of mares and stallions. Seeking an improvement in the process of selection and breeding in thoroughbreds is founded on the belief that racing performance is inherited.
Heritability is a measure of the degree (0 to 100%) to which offspring resemble their parents for a specific trait, which broadly in our case is racing performance. Despite the intensity of selection carried out in the Thoroughbred, race times have not improved any further for at least the past 60 years (Hamori and Halasz, 1959; Cunningham, 1975). Research has however shown that many important traits in the horse are moderate to highly heritable (i.e can be passed on from parents to offspring) indicating that genetic progress from selection is possible if the methods of selection themselves are based on sound principles of inheritance.
My experience has been that in European countries, breeders and their agents place very little importance on the direct speed achievements like speed figures when selecting for breeding, rather their performance relative to their peers of the year and other generations before them with the use of Timeform figures. It seems their belief in subjective measures such as Timeform is well placed as Timeform has a relatively high known heritability of race performance at 35% (Cunningham, 2002). Thank you Phil Bull.
Somewhat conversely, North American breeders use two methods that are linked to that which is known to have low heritability for selection. Earnings, which statistics like the A.E.I are based on, are a very poor measure of racing performance as they have low heritability (<10%) and are not optimally distributed in that a horse running 7th in a Grade One gets no prize money while a horse running 3rd in a claimer at Finger Lakes does even though the horse running 7th is most likely a significantly better horse.
More importantly race time has also been used as a measure of performance in Thoroughbred racehorses but the heritability of race time has been reported as low as 9% to 16%, depending on the distance of the race (Moritsu et al., 1994, Oki et al 1995). This leads us to the crux of the problem, in the U.S in particular, that being the erroneous use of race time and race time based handicapping figures for selection of both breeding stock and matings. Noting above that race times as a whole are generally a lowly heritable measure, and with a caveat that the heritability of any time based speed figure is not known (itself a problem!), the use of a handicapping figure derived from race times such as Beyer numbers for breeding selection does not appear to be the most suitable method of genetic selection and could well partially explain why improvement in the North American thoroughbred has not been made and to a certain extent why European breeders, relying on the heritable Timeform figure, have continued to breed elite racehorses despite their breeding stock being significantly depleted at times of economic downturn.
As breeders we keep hearing year after year how each crop is getting slower in terms of the feature races such as the Kentucky Derby, Preakness and Belmont being won with lower and lower speed figures, yet we don’t think for a second that selecting our stallions and mares on speed figure numbers looks to be the cause! At its core it must be understood by breeders that the fact that a stallion ran a “1 on the sheets” or a “124 Beyer” should mean nothing to them when judging him as a stallion, or a mare as a potential broodmare for that matter, as the heritability of this figure is unknown but because it is based on time, most likely to be very low. Breeders certainly aren’t getting what they think they are paying for when they select a stallion or mare based on a speed figure. This leads us to what animal geneticist Dr. Betrand Langlois stated so clearly, “Why should one pay more for this or that pedigree or high performing sire if the performance itself is not heritable?”
Despite the fact that breeding and racing of thoroughbred horses has been a well-organized industry for well over a century now, it is a poor reflection on the industry at large that it has not yet come to an understanding of the best measure of racing performance or ability and the degree of inheritance of this racing ability. We use figures for selection that are built for handicapping, not breeding and because of this we are actually selecting on a measure with low heritability and act surprise when the breed doesn’t get an faster or sounder! Breeders worldwide are effectively trying to sculpt a masterpiece by using a chainsaw, all the time not even knowing what a masterpiece actually looks like.
Creating a universal breeding value/figure as opposed to using a handicapping figure for selection is not a difficult task, nor is it expensive and it should be very easy to disseminate to breeders worldwide. We have the data (we actually have one of the most data rich breeds in the world, why we don’t use this data more constructively is a mystery) and the methods have been thoroughly proven in other livestock and plant industries to great effect. Much, much smaller breeds such as The Danish Warmblood, Irish Sport Horse, Dutch Warmblood, French Sport Horse, Swedish Warmblood, Holstein, Hanoverian, Icelandic Toelter, German Trotter and Swedish Trotter Associations all use breeding values and have shown significant increase in genetic progress since their creation and implementation.
Thoroughbred registries around the world seem to have a similar mission statement – “dedication to the improvement of Thoroughbred breeding and racing.” While something like this will never make a Round Table for discussion or an expensive consultants report, and thus not get the attention it desperately deserves, actually having a scientifically sound framework of genetic merit is the essential starting point for any improvement of the thoroughbred to happen in the first place.
On the first Saturday in May and indeed each year on Belmont Stakes day for the “Test of Champions”, we can decry as much as we like about how we are not breeding horses to get a route of ground but only if we actually scientifically measure and disseminate these traits, and that could include not only speed over distances but also other traits like fertility and soundness, can we actually start to make progress. To get anywhere, you have to know where you are starting from and right now, by using speed figures for selection as a de-facto of a truly heritable measure, breeders have no idea where they are, where they are headed, and are probably doing the opposite of “improving the breed”.