b4breeding

Question came in recently from Kevin:  “I am looking for a list of Sires that carry the X Factor..Is there one, and where would i find it.”

I’d be interested in what others think or lists that people have found useful, but here is my views on the topic:

I don’t know of any list of standardbred sires that claims to identify current sires that carry the X factor. I am aware that Marianna Haun has published a list of galloping sires in her book “Understanding the Power of the X factor”, but she carefully defines what the list is – basically some current thoroughbred sires that possibly carry specific important heartlines and trace back to Eclipse (who was born in 1764) (See page 80 of her book).

It would be possible to do something similar for trotting and pacing, and there may be some pedigree/breeding consultancy services that will have databases that allow them to factor this into their evaluations of sires, damsires and mares. Such a list would be possible by either by tracing pedigrees back to Eclipse’s standardbred descendants or by listing current sires who are underpinned by proven producing mares and damsires – the great trotting and pacing families of the modern era.

There are pedigrees like that which maximise the chances of a sire inheriting a large heart. However even those lines can over time become diluted if mares are not matched with compatible sires that ‘bring out the best’ the mare has to offer and keep carryng those quality genes forward. Families “go off the boil” for a time, and often branches of them simply peter out. Even when matches are well considered, there is an element of ‘russian roulette’ about which X chromosome a foal will inherit.

In my view it is not as simple as labelling sires as ‘big hearted’ or not. The X factor usually refers to abnormally larger hearts, exceptional hearts. I’m not sure that an abnormally large heart is the ‘pot of gold’ some people think it is. In terms of heart scores, is a horse with an exceptional 150 score necessarily going to be that much better as a racehorse than one with a very good score of 120?  As in motor-racing, the car with the biggest engine has an advantage, but many other factors make a winner.

How can you tell if a sire potentially carries a large-heart gene?

• From their performance on the track. All other things being equal, big hearted horses have had a real advantage on the racetrack, and thus are more likely to achieve the consistent top level “stand out” racing performances that are required to become a commercial sires these days.
• From their performance in the breeding barn, those sires will soon start to build a reputation as a sire of good fillies, not just of colts.
• And in the longer run, from their performance as damsires, leaving females that go on to be good broodmares of both male and female offspring.

By their deeds you will know them – although it is much harder to gauge new boys hot off the track, as the more reliable signs will only be apparent later.

Some horses (male and female) will never get the chance to pass on their big heart genes because for some other reason they did not show enough potential as a racehorse or their family is not commercial enough.

A list of sires only tells half the story. If you agree that the big heart gene is carried on the X chromosome, then the mares served by a sire play a huge role in carrying and passing on good heart lines.

Firstly, if the larger heart gene is sex-specific (i.e. carried on the X chromosome) then a sire cannot pass this larger heart to his sons. Male foals are the product of a Y chromosome from their sires and an X chromosome from their dams. So the idea that In The Pocket passed on his own heart size to Courage Under Fire and Christian Cullen, for example, doesn’t stand up.

On the other hand, female foals receive an X chromosome from both parents. One of these is likely to be dominant or “expressed”.  It may (or may not) be one that carries a larger heart gene. A larger heart gene could be on the X chromosome from the sire (from his dam), or it could be on one or both of the two X chromosomes the mare carries. This is what is referred to as a single copy or double copy mare.

Marianna Haun explains this really well in Chapter 9 of Looking for the Great Heart (in “Understanding the Power of the X factor”) and describes how to look for the signs of the X factor in the productions statistics of mares and sires.

So there are no guarantees even by breeding a filly from a sire that is carrying a large heart gene, that the foal will express that gene. But of course it does help your chances.

My previous blogs about Nedda, Nedda Guy, Esther, Volomite and the link back to Eclipse might show an example of how quality lines and big hearts can endure through many generations and pop up in modern pedigrees in different places.

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