Interesting. I do something similar but on a much smaller scale.

I only give my cattle their once a week treat grain ( a couple pounds/head of sweet calf feed) in the corral. Every so often while they are eating their weekly or biweekly treat I just shut the gates and leave them in there for 20 minutes or so after they are done so they learn not to go crazy when in the corral.

Then after they are quiet being in the corral, I open all the internal corral gates, tub, alley and headgate and let them discover on their own that through the tub, alley, over the scale, etc is the way out back to their pasture.

So when I do need to work them or load, I just put some feed in the corral bunks, bang on a 5 gallon pail that I use to carry sweet feed and they recognize, and they will come at a run out of the woods or where ever maybe a 1/4 mile or more away, into the corral for a treat while I go around and close the gates behind them. Even the calves and ones that are not into sweet feed end up following the ones that are more interested in a sweet treat.

Then I wait for the vet or get the scale setup etc.  The only problem with this according to my vet, is that since they associate the tub with the way out, they sometimes all head for the tub at one time. Sorting them OUT of the tub is easier than collecting and chasing them in however.  And eventually they all come through almost on their own as you describe.

Life is a lot easier this way. Usually.  Thanks for the post and description.

Jim at Dawn