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Russf,

Interesting comment. We may lose a couple of readers here as we go along discussing this, but I think that this is a very interesting line of thought, and certainly one worth further comment. Apologies in advance if you feel at any time that you have been misquoted and selectively referenced and feel free to do the same to me if I have missed a point that you are trying to make. Please also accept my apologies if the answer below is a little long.

The overriding question that you seek an answer to is if I “think that any rating bias exists when there is one prominent son of a sire who appears to behave very differently from the other sons.”

In our experience, borne out by the data we collected while creating TrueNicks, sirelines tend to operate in a similar way over several generations. To give an example, take a look at Fappiano/Unbridled/Unbridled’s Song with In Reality and his sons and grandsons, and you can appreciate that over time these two sirelines have generally worked well together. Right now if you mate a mare by Diktat (great-grandson of In Reality) to Zensational (great-grandson of Fappiano) it is an “A+.” Similarly, there are very few branches of In Reality that don’t rate well with sons of Unbridled's Song (grandson of Fappiano).

But just as Fappiano was a different type of Mr Prospector, and operated in some ways differently than most of that horses sons, so there are other sons of Fappiano who have created their own distinct branches. The Cryptoclearance branch, for instance doesn’t seem to work as well with In Reality, but that doesn’t mean he doesn’t share some common affinity with his general sireline. The few sons and grandsons of Cryptoclearance that are at stud have moved in a slightly different direction genetically, more towards another sireline that Unbridled’s Song has also shown affinity towards, for example Storm Bird/Storm Cat.

An example in reverse, where a son has shown a totally different affinity to his sireline, is Point Given. He doesn’t act at all like his sire or his grandsire. Neither Gulch nor Thunder Gulch have shown any particular affinity to Seattle Slew line mares, indeed they have underperformed with the Seattle Slew line mares to which they have been bred, but Point Given has been outstanding with the Seattle Slew line. He is an exception though, as other sons of Thunder Gulch have pretty much behaved like the sireline in general when crossed with Seattle Slew line mares.  Our feeling on this is that there are some other phenotypic interactions taking place here with Point Given that make him a unique son of the sireline.

Subsets based on number of times tried can be difficult, because at times it is neccessary to go back beyond of the most relevant subset to gain sufficient numbers to generate a rating. Alan and I discussed and researched the possibility of stopping at selective distinct ancestors but we found it is horrendously difficult to consistently apply, especially given that some crosses seem to be affected by the phenotypes involved and some less so. In other instances, phenotype seems to be a key to genotype behavior (for example Point Given, who is more physically reminiscent of his broodmare sire, Turkoman, emulating that stallion be crossing well with Seattle Slew) in the same way a mixed breed dog tends to have behavior traits most similar to the parent it most physically resembles.

As far as a bias existing, we have also seen examples where there is compensating data. If you take an unproven son of Storm Cat and mate him to a generic son of Mr Prospector it returns a C+. This rating includes the data of a son of Storm Cat that has done really well with Mr Prospector in Giant's Causeway (A+) and one that has not done so well in Forestry (D). In the abscence of any data to the contrary and give a relevant rating, TrueNicks, and for that matter any pedigree rating system that is based on sireline/broodmare sireline affinity, works on the presumption that a stallion will generally appreciate the same bloodlines that his own sire has been successful with. In the main, this is the correct assumption to make but there are exceptions and when there are exceptions, because TrueNicks uses live data that is updated daily from foals, starters and stakes winners from around the world we are quickly able to identify those stallions that are not behaving like a “normal son” and create their ratings based on their own results. We believe that this is the best way to handle the stallions, and for that matter broodmare sires, that don’t behave like the rest of the horses in particular circumstances with the latter word being the key. Getting back to Forestry as an example, while he is deplorable with Mr Prospector line mares in general, he is good with Fappiano line mares and like a lot of sons of Storm Cat, great with Damascus, so in some ways he is only "different" in certain circumstances, a nuance that helps breeders and stallion managers alike make informed decisions.

Byron