Testing for elevated TCO2 as a result of milkshaking is best done as close to racetime as possible pre race and on a delay post race to allow the levels to rise again as a result of the administered alkalising agents. Testing all runners pre race only unless you have enough collectors would mean some horses could be tested before TCO2 levels had risen above the threshold.

For testing for other substances more pre race urine swabs could be collected and those choosen for testing could be determined post race. Don't see why testing should be limited to winners and big improvers, unexpectedly poor performances may warrant testing moreso then an expected winner. In the interests of animal welfare and integrity random testing should also occur amogst also rans to minimise the likelihood of horses on medication participating with connections confident that they won't be tested if they don't win.

But the biggest threat with regard to prohibited substances, as in human athletes these days, are substances administered during the course of training and eliminated well before raceday but from which the horse still has effects that are beneficial on raceday. Pre or post raceday testing won't detect these, indeed detection is not easy, but needs strategic unexpected out of competition testing.