He’s done two posts on this. It’s quite interesting. He’s crunched all the numbers, and the youngest sires have far better results with their first crops than older sires by a rather large amount until a sire becomes well established. Their foals sell for more and do better on the track that even the most established sires.
https://ddink55.wordpress.com/
He postulates that first crop sires with good racing records get really good mares in the beginning for a couple of reasons: the popularity of the hot new thing, and the support they get from their stallion stations to try and establish them for a long run and a high fee.
Once that is over and new stallions arrive, their later crops are nowhere as near as good as their first ones until they have proved whether they can maintain their first crop magic.
A lot of sires do have excellent first crops, then not much else afterward, for whatever reasons. A striking recent example is Uncle Mo. His first crop was two-year-olds of 2015 and included seven two-year-old stakes winners (and 20 overall). Included among them was 2015 champion two-year-old and 2016 Kentucky Derby winner Nyquist. Uncle Mo got off to a great start at stud.
His second crop (two-year-olds of 2016) has been an entirely different story, however. So far it has produced ZERO stakes winners. That pattern has been entirely uncommon for a lot of sires.
An opposite example was Secretariat. His first crop was no great shakes. But his second crop included General Assembly and Terlingua. That pattern is not as common as the first pattern though (great first crop, not so great afterward).
That first pattern partially accounts for the slide in prices from 4-5 to 6-7 to 8-9. Prices then turn up with the 10-11 group. By then the original group of first-crop sires have enough progeny on the racetrack to determine their true worth as sires. Some will make the grade. Most will not. The former will have a lot fewer sales foals by age 10-11 or will have completely dropped out of the pool of sales sires, having been banished to some other (cheaper) locality.
It is the process of attrition. The truly good sires survive. Some even thrive and start receiving even better mares. Prices for their progeny perk up from the doldrums. But most sires do not survive this process of attrition, and their removal from the pool of sales sires causes prices to perk up for the remaining (surviving) sires around age 10-11.
