Danes use robots.
I've heard about a modern slaughterhouse built in Missouri - but now there's photos of the inside, available on the web. The most modern one I've seen is Danish Crown's, where they use robots for many tasks traditionally done by humans.
The reason the tracking of the meat is important is because of the labeling laws. To produce meat and label it a certain way (e.g. "USDA certified organic") , they have to meet legal obligations. Country of origin requirements likewise complicate things. Basically, every piece of meat that comes out of these slaughterhouses can be traced back to a load of pigs (or maybe even a particular pig), allowing one to ensure the label is correct.
For the producer, tracking carcass data back to a particular pig is very important - you can know what sows and boars produced the pigs that paid the most, figure out which ones are losing you money, and respond appropriately.
There's an important statement in the post:
Because people respond so directly to financial incentives, I think is important that consumers understand what they are funding. Margins are tiny in the hog business. An extra $7 a hog represents a huge increase in profit to the producer.For example, Maxwell tells a story about a potential meat customer that wanted antibiotic-free pork. Maxwell’s colleague tried to argue that antibiotics were not bad, and Maxwell kicked him under the table. “If I can do it and he will pay me $7 more? I’m doing it. When we talk about differentiating, it is about finding ways to differentiate, in this case, pork, from other producers.”