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A horse rears in the Monmouth paddock | Bill Denver/Equi-Photo
A horse rears in the Monmouth paddock | Bill Denver/Equi-Photo

by Chris McGrath

Hot blood. What, if anything, does it mean? Not in the sense that divides different breeds, as with German “Warmbloods” and so on, but within the Thoroughbred itself. Can a racehorse inherit a fiery or neurotic temperament, or indeed a mild and calm one, with the genes of its parents? Or must the spectrum of behavior, for better or worse, also reflect environmental influences on the upbringing of a foal?

Many experienced and respected horsemen are adamant that temperament can be traced through a family tree. Tony Lacy of Four Stars Sales is one. In man and beast alike, he feels, “the personality of the offspring is generally a result of their parents, and others in the genetic line.”

As with all attempts to reduce developments in science to some kind of silver bullet, however, most traits still have to be traced along a spectrum between heritability and environment. And so long as an elusive equilibrium must be sought between pedigree and preparation, then horsemen will still have to rely on their own wit and wisdom.

To many of us, that is just as well. If we ever reach the stage where the full range of a horse’s potential can be predicted from a single hair, then every Kentucky Derby will be won by a sales-topper. The fulfilment of that potential, of course, would remain contingent on skilled horsemanship and other environmental factors. But without the dream of beating the odds, how sustainable would the rest of the business become?

Human nature being what it is, plenty of people have proved eager to conflate the rudiments of an evolving science with the possibility of immediate commercial advantage. But since the first sequencing of the equine genome-now over a decade ago, through a Thoroughbred mare owned by Cornell University and aptly named Twilight-most attention has been focused on such physical capacities as might be predicted from a horse’s genetic inheritance. (Or might not: genetic prediction is seldom clear-cut, varying with the heritability of a given trait.)

According to Dr. Brandon Velie, lecturer in the School of Life and Environmental Sciences at the University of Sydney, far less research has been conducted into the heritability (or otherwise) of behavioural traits in Thoroughbreds.

“Generally speaking, relatively little has been done compared to the typical-and much easier to measure-‘performance’ traits,” he says. “Some work has been done, and is currently being done, on stereotypies [i.e. ‘vices’], but I believe this has been very limited in size and scope thus far.”

That is hardly surprising, when “temperament” is such a loose concept, covering a multitude of sins. It’s difficult for scientists even to agree what they should be measuring, never mind how to measure it. And that makes it hard to distinguish possible genetic patterns, in behaviour, from environmental influences, such as the way a horse has been handled in infancy.

To take the example of ongoing research mentioned by Dr. Velie, nobody can yet say whether Thoroughbreds might be more prone than other breeds to “cribbing” and similar stable vices solely because they have inherited the propensity; or whether they develop it in response to a training regime typically in claustrophobic contrast with the roaming of other breeds?

“While temperament in a horse, to many, may be easily recognizable even in a foal-for instance, ‘bold’ versus ‘cautious’-where things get complicated is when you ask how this can be objectively measured, paired with genomic data, and subsequently analysed,” Dr. Velie explains. “Thoroughbreds and other ‘hot’ breeds may exhibit vices more often, and there is almost certainly a genetic component. However, the question often asked is whether or not the vice is a side-effect of having a high-performing animal cooped up for long periods of time, or if they would have the same vice if given the ability to run, graze freely and so on, in pastures and fields.

“Personally, I think it is a little of both. High-performing breeds need high levels of energy to perform their jobs. The likes of racehorses or dressage horses do jobs that take a lot of both physical and mental effort. When they are deprived of this outlet, or challenge, I think many of them struggle to cope and thus develop vices.”

Dr. Velie suspects that a parallel can be drawn from our own experience. “I imagine something similar would be seen in humans who are very active, but then are sidelined due to injury,” he says. “They often struggle as they no longer are receiving the positive feedback, both mental and physical, from everyday exercise.

“But I’m not aware of many genomic studies that have objectively looked at this, in Thoroughbreds; and those that have tend to be limited in size. Because these traits are generally considered complex, large sample sizes are needed to look at them thoroughly-and this can often be difficult, given the aversion of some industries to genomic profiling.”

As such, the traditional association of fiery or excitable tendencies with a particular sire-line would seem rather too crude to be sustained by the available science. Of course, it is a besetting vice of the bloodstock industry to give disproportionate credit to sires in particular, and to sire-lines in general, purely because they benefit from a much greater statistical sample. In these days of huge commercial books, a successful sire can accumulate foals by the thousand; whereas even those mares with the most desirable genetic assets are confined to a single foal per annum. Sires duly tend to be identified with all heritable characteristics, never mind those on the margins of heritability.

Lacy resists that trap, actually crediting a stronger influence on temperament to mares. (As we’ll see in a moment, the actual process of maternity and nursing does give the dam behavioural influence unavailable to the sire.)

“The ‘legacy’ mares seem to have a dominant influence for generations, making them the force they are,” argues Lacy. “To produce a great racehorse, you need a mentally tough and genuine nature, along with a will to win. In my opinion, an extremely talented horse who is mentally weak is rarely a success on the track.

“Although the Thoroughbred is innately a high-spirited animal, I believe it is important to be aware of the temperament of your mare and what she may or may not need in a stallion. It is a piece in the puzzle that can often be overlooked. You are not trying to dull the spirit that often makes a good racehorse, you are however, attempting to channel it in the right direction. You need a balance.

“There are a number of sires/sire-lines that could be considered to have a hot or difficult nature. I think you want to avoid amplifying any negative aspects of their character in the potential foal.”

Coat color is one instance of a simple, agreed genetic inheritance. But how far can we attribute the broader brushstrokes of a horse’s genetic potential to the diminishing strands of what becomes, within four generations, just 1/16th of the genetic mix? (All genetic prediction is scaled proportionately to the expected contribution of each ancestor.)

“Simple traits, i.e. those attributed to a single gene, like many coat colours, typically can be easily traced down sire-/dam-lines,” explains Dr. Velie. “However complex traits, attributed to multiple genes, are typically more complicated and often require in-depth analyses.”

That very basic principle should perhaps be enough to get breeders to spend a little less time trying to imitate specific patterns through an endless genetic maze, and a little more thinking about the fundamental balance of matings: first and foremost to complement physical types, but also to redress other imbalances established in one or other parent during their own careers. That will most obviously apply to performance, as when you send a fast mare to Galileo; but it may conceivably extend to some aspects of behavior.

It would certainly do so, notes Dr. Velie, if you knew the extent to which a particular trait is inherited. But he stresses the importance of remembering the environmental element, too. “In Thoroughbreds, generally speaking, a ‘difficult’ mare will pass on half her genetic material to a foal that she will then raise,” he reasons. “The foal, like most foals, will have some of the same characteristics as the mare due to its genetic make-up, but will also learn certain behaviors and so on from the mare. We refer to this as a maternal effect.”

Ascription of heritable character to stallions notorious for their own fiery tempers, meanwhile, must plainly make allowance for the raised testosterone levels in those who graduate from racetrack to the covering shed. So while a lot of stallions have become notorious for their “savagery”, no automatic inference should necessarily be drawn regarding the co-operation likely in their stock in a normal training environment.

“If a stallion is more savage due to higher levels of testosterone, the trait could potentially be passed on to his progeny if those higher levels of testosterone are driven by a genetic anomaly,” Dr. Velie says. “But as Thoroughbred stallions don’t interact with their foals like mares do, there would be no paternal environment effect. So any influence the sire has on his foals must come from whatever genes he passed on to his foals.”

Once again, in other words, progress in scientific understanding leads to better questions, rather than to glib answers. In this specific instance, the question becomes whether an abnormal level of testosterone in a stallion itself reflects a genetic difference. Alleged and his son Law Society evidently had a fearsome reputation among handlers, for instance, but apparently not so Alleged’s sire and grandsire Hoist The Flag and Tom Rolfe.

In the case of windsucking and other vices, equally, there is evidence that grain levels in diet may be a non-genetic contributing factor: British ponies hardly ever windsuck, for instance, but nor do they tend to be fed concentrates.

There is an established variation of fear and reactivity between breeds: Thoroughbreds and Arabians are considered flightier than Quarterhorses or Warmbloods, but within each breed there will be a spectrum of docility. Moreover one man’s “temperament” will be another’s “responsiveness”, consistent with the tasks we have in mind when we breed horses selectively for sport. We might not want them too easily spooked, but we don’t want them too sluggish either.

Definition and measurement of temperament vary so much that even cursory exposure to the research introduces you to speculation that heritability, as opposed to environmental factors, accounts for as little as one percent of variation among horses in demeanour-or as much as 60 percent! The fact is that the research in this field, while ongoing, is still in its infancy so far as Thoroughbreds are concerned.

So perhaps we just need to avoid getting ahead of ourselves. Genomics will doubtless bring many benefits, but we shouldn’t expect or even ask science to reduce the mystique of breeding racehorses to simple formulae. It’s been a temptation forever: perhaps nothing will take us further than a tradition, tracing to primitive tribes, that you can signpost a highly-strung nature from the position of the whorl (or whorls) on a horse’s head.

Behavior, remember, is itself subject to change-for instance, according to empathy of handling, say, or traumatic experience. And environmental factors can mask or exaggerate heritable traits is. So the bottom line is that it is going to take more time and research for geneticists to unravel the complexities of temperament and highlight areas of risk.

Dr. Velie concludes with a resonant example. “A colt with a fiery temperament that is very trainable has a much greater chance of going on to win races if he is trained by a ‘good trainer,” he remarks. “After all, if his fiery disposition can be focused on its job as a racehorse, it may prove advantageous.

“However, if that same colt is given to a ‘bad’ trainer, he may become quite dangerous to handle. Trainability and temperament cut both ways as the horses is likely to learn good and bad behaviors equally quickly. In both scenarios the colt has the same genetic makeup, but the outcome differs based on the environment he is put in.”

Lacy can identify with that. He especially recalls working with a couple of Nijinsky fillies who daily challenged the skills of trainer and rider. “If they were with lesser horsemen, they would have been far less successful than they were,” he says.

But whatever the science eventually shows, he is a convinced spokesman for the anecdotal consensus among many horsemen.

“In my experience working not only with Thoroughbreds (both Flat and steeplechasers) in different parts of the world, but also with Arabians, I found that certain sire-lines had strong personality traits that could work in a positive, or negative, manner,” he insists.

“As an assistant trainer and rider, you had a good idea of what it would be like to manage a particular individual, based on what they were by. For example, I have always been an admirer of the Hail To Reason sire-line, through Roberto and Stop The Music. There is a consistently genuine and tough aspect that he has been pass on through the generations. They have in turn become a very effective in dam-sire lines.”

Interestingly, that focus on toughness takes us to a margin between mental and physical commitment, between the will to dominate and physiological capacity. It is always fascinating, for instance, to hear Aidan O’Brien talk about the patterns he observes in the stock of Galileo: how you nearly have to restrain his progeny from being reckless with their effort. The offspring of Montjeu, in contrast, often operated along another margin, between nerves and brilliance.

“Galileo is a classic example of a sire that has had an extremely positive effect on the gene pool,” agrees Lacy. “His classy and self-assured nature is passed down and improved many of the quality mares he was bred to. From what I have seen so far, I believe American Pharoah has passed to his offspring a calm and confident temperament that has impressed many. This could very well be an extremely important aspect to his potential success as a sire.”

And, given the role of the marketplace, perception can be more than half the battle. People reach their own conclusions in the sales ring without waiting for science to become a more helpful tool. And horses whose stock don’t hold up on the track, in terms of temperament, soon lose commercial viability. As Lacy says: “The selection process of the racing and sales industry often weeds out the weaker-natured stock.”

But even if science can one day distinguish between the weaker-natured and the weaker-nurtured, it seems that it will always observe a combination of both.

This article originally appeared on Thoroughbred Daily News and is published here with permission.

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