My two cents on a post which for me more than achieved the author’s goal of being interesting:
As everybody knows, some vet scratches are due to cuts and bumps at the gate and have nothing to do with soundness.
Also, depending on the track, vet scratches are always or often lumped in with steward scratches, so that’s something you might also want to keep in mind when using this factor to handicap. For such tracks it is sometimes possible to read between the lines and figure out what kind of scratch it probably was, as when a horse just shipped into the track and was scratched before its first start. That’s usually but not always due to paperwork issues, since there are trainers who are known for shipping vet scratched horses to another state in the hope of getting a start before the vet scratch information becomes known.
In addition to the list on the link elkurzhal provided, the major tracks also used to mark an asterisk for each satisfactory work next to the name or workout time of horses which were on the vet’s list due to unsoundness. Thus, in California, where the rules used to require three supervised works to get off the list, you would see horses which had either one or two asterisks. I don’t know if they still do anything like that, even though that was often the only way I know of to distinguish between the types of vet scratches.
Finally, although it’s counterintuitive, I believe there is one specific and relatively rare instance where a vet scratch can be a potentially strong positive handicapping factor.
It is widely understood that a horse undergoes its most dramatic development between its two and three year old seasons, and as is often pointed out in the rotw analysis, a comparison of two “ancillary” items of data can be used to give one an idea of how much improvement might take place for specific sires.
What is not as widely understood or discussed is why this improvement takes place. As a very general proposition, this aspect of the growth process in horses is similar to the “growth spurts” which take place during human adolescence. Both involve the remodeling of bones, which is why it is sometimes said that an awkward teenager needs time to grow into his body.
For horses, a year or two ago there was a scientifically conducted study which proved to my satisfaction that the remodeling process and resultant development improves dramatically if the horse undergoes “serious” training at two, which was defined to include the kind of workout regimen necessary to be prepared to run a race, as well as the kind of training typically done for horses which are entered in two year old in training sales.
So, let’s say the horse you’re considering is a three year which is making its first start or has had one, two or three starts at three, and you’re interested in knowing whether the horse underwent “serious” training at two. In addition to a sales history which indicates whether the horse was an RNA or sold at a two year old in training sale, the only other way to find out is if you know whether the horse was a vet’s scratch at two.
In the right circumstances, such as long enough odds in a handicapping contest, I have interpreted the vet's scratch at two as a reason to play the horse, and after the fact had the opportunity to enjoy listening to the complaints that the play was nothing more than a clueless "stab."
