Of course they lose more water than electrolytes; electrolytes weigh next to nothing.
Good point about the glycogen, although the flipside is that same hour window is when they burn fat if they don't get the glycogen ...
Wow, 3 lb of weight is a bunch; that is 48 oz of weight. I wonder if it would be a good idea give the water + electrolytes right after the work, wait an hour for processing, and then give the meal? You could even add the minor carb replacement that dogs need during that window (if you're not worried about fat loss). Just thinking out loud here, but this strategy might address all issues.
I think dogs WILL drink enough to keep themselves hydrated ... this is why (after the work) dogs will drink their asses off, and will continue to do so until they get re-hydrated. The problem, really, is OVER-drinking if they're hot and tired and the conditioner's dilemma of monitoring weight/intake, etc.
In point of fact, I actually believe that the critical weighing of the dog, before and after the work, pretty much signifies exactly how much they have lost during the work. But because they're burning calories, electrolytes, fluids, etc. it's hard to say exactly how much is water only, but I think adding Pedialyte rather than straight water is a better idea (in the same fashion that running a bag of saline is superior to just replenishing water).
Interesting discussion and observations.
If I were active, I would personally be trying to replace exactly the amount of weight lost after the work, or thereabouts, and then I would allow enough time for the replenished fluids (Pedialyte or equivalent) to dissipate before feeding. I don't think I would lump both that much water/fluid and his full meal all together at the same time myself.
Maybe you, or someone else, could provide some feedback on this eventually
Jack