This is what we have been using- easy recovery for the horse and usually effective:
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pdfs.semanticscholar.org]
This brings up another interesting point for handicapping races- I'm guessing we would agree that the horses health impacts his performance and until its well understood what medicines they take and what procedures they've had as well as the anticipated outcomes from those procedures then there will be a big variable that is not accounted for in analysis. It also may not be quantifiable because the data around outcomes is limited.