Interesting stuff here!
Seriously, I wouldn't be suprised if outdated candy made it to the feedlot. U R not going to find someone purchasing candy at your local Walmart to feed his cows though. That would be a misconception. I know of cases where feeders picked up outdated Hostes products (bread, ho hos, ding dongs, cherry pies, etc.; for free, otherwise thrown in the landfill by Hostes) and feed it to the cows. I used to dig through the piles myself and get my favorites before the cows got em. Also, used to dig through McDonalds dumpsters on the rodeo trail, but that's a different topic.
Often you will find feedlots and dairies in areas of high Ag. production and food processing locations. Byproducts are picked up by the operators and fed. Often ensilaged first if it is a vegetable product of some kind, but often just feed outright as well.
Overly simplified; cows need roughage, protein, and energy in their diet. Often the rougage comes in the form of ground straw. Protein can be added by good alfalfa hay (usually expensive to feed in a lot though; not so for dairies they pump up the alfalfa) silage, oh gosh many sources for protein, and carbohydrates; usually in the form of grain (corn most popular). The carbohydrates or energy can come from molassas, possibly candy, grain, beet pulp, thrown out bread, etc. With that over generalization you have to realize that ALL dairy rations are scientifically formulated from known values provided by forage tests. Dairy nutritionists are sticklers and rightly so for milk production. Most feedlot operators like to strictly calculate their rations as well, but are much more cost conscientious about the feed they buy. Candy, breads, and other processed carbs would be hard to calculate or formulate but I can see it happening when the price is right. I have seen it happen.
I am happy to see some of the points mentioned by others as to the benefits of feedlots and costs, etc.. Most anti-feedlot people don't like to see the postive aspects of feeding. One often overlooked aspect is the use of byporducts that would otherwise go to the landfill. These byproducts are turned into a terrific protein source for human consumption instead of going to the landfill.