Two new studies concerning parental age at conception and gentic marker for racing ability

Probably better if I just link all the articles to read at your leisure. :slightly_smiling_face:

Here’s the original story I clicked on to read: (be sure to click “Read more” to open a more detailed version of the article with more pictures of pretty horses) :wink: Having a flutter on a horse? Better check how old its parents are! (

And the study about parental age: Evidence of maternal and paternal age effects on speed in thoroughbred racehorses | Royal Society Open Science (

And finally the study about genetic marker affecting racing ability: Higher levels of inbreeding significantly lower chances horses will race, new study finds (


Everyone who has racehorses would like to have faster/sounder ones so I was interested to read through those studies. I was particularly interested in how a horse’s “speed” was being measured. I wasn’t entirely reassured by what I read. This is a quote from the 2nd link:

“The dataset used comprised 906 027 finishing time records by 101 257 different (offspring) horses running across 88 385 individual races in Great Britain between 1996 and 2019. This only included races run ‘on the flat’ (as opposed to races involving jumps) and on turf (i.e. grass, not all-weather track surfaces). Finishing times were converted to running speed to provide a more intuitive performance trait.”

The idea of converting finishing times to running speed doesn’t in any way take into account what the horse was being asked to do by the jockey–nor the distance the horse was running. Six furlong races are almost always run at a faster rate of speed than mile ones. Horses racing a mile almost always cover that distance faster than ones racing 1 1/4m. By definition 6f horses are “faster” than those who race longer distances. That doesn’t seem to have been taken into consideration.

Another interesting quote (from the first link):
“…previous studies have suggested that first-born foals tend to be lighter and perform less well than subsequent offspring from the same mother.”

That may be true in Britain where the articles originated, but it isn’t true in the U.S. First foals are sometimes smaller than subsequent offspring, but (here) they are often the best performer that a mare ever produces. (This may be due to opportunity, in that a race mare’s first foal often has a higher stud fee than her subsequent foals until she has had a chance to prove herself.)

To me, it seems like the studies are more interesting than conclusive. But I’ll be watching my own mares in the future to see if they prove true.


Secretariat would have been an outlier (though the study only looked at British racing).

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From a casual, non-scientific standpoint, I don’t think there is a breeder or buyer in the US who didn’t already ascribe to the idea that there is a negative correlation between parental age and performance. Our entire sales market is built on it.

Ironically, the only way a horse overcomes it to maintain a breeding career is for it to be true. A horse has success early in their breeding career and they maintain their desirability and get to keep their job. No success early on means the horse will drop tax brackets until they land where they can be profitable, or they will lose their breeding career entirely.

(Warning: this is a major oversimplification of what goes into breeding decisions)


Very interesting, informative study.

Exactly. Secretariat’s dam was 18 and his sire was 16, so he is definitely an outlier.

I’m sure there are many factors in this study but one which occurs to me is that for mares, declining fertility can be associated with being bred to lower-class stallions. One example is if a mare miscarries or aborts a couple of years in a row, the owner might sell her to someone less inclined or able to pay for a top stallion, so the ability of later foals would be reflected.

I’m not saying there is no validity to the age thing, but I would question how definitive the study was.

That makes sense. It does seem that the variables would be difficult to build into a study, such as this one.

It would be interesting to see a study which compares mares who have a foal every year for many years with those who, after a few years, let’s say three or four, are bred every other year so their bodies get a chance to recharge.

In the University of Exeter graph shown in the first link which @Real_Rush posted, there is a marked drop in quality on the fifth foal. Now obviously, not every horse in the study at that age would have had four foals, one every year, by age six but I’ll bet a good number did. It could be that by the time that foal #5 is born, the first foal to show a decline in ability, it is simply a matter of breeding exhaustion. Maybe the mare just needs a break for a year to replenish her bodily resources after she’s had four foals.

Excellent point. I would imagine there are quite a few variables they did not control for.