NSFL description of conditions on a dairy farm:

I saw a lot of messed up stuff in those years,so it's hard to pick one thing, though there's a particularly tragic fate that befalls many egg-laying hens that stands out in my mind. On the vast majority of egg farms, hens are kept in stacks upon stacks of crowded wire cages, called "battery cages," where they never leave. Conveyor belts bring them feed and take their eggs, pipes give them water, and they basically sit their all day, 7 to 10 per cage, trampling each other and vying for space. They're bred to lay so many eggs that commonly, they "prolapse," which means that their oviduct basically inverts and spills outside of their body. It's a very painful condition, one that's common to animals that are intensively bred; I've seen it on dairy and pig farms before. However, with egg-laying hens, this organ can get tangled in the cage wires, causing extreme pain while depriving them of the ability to get food or water. So they basically starve or get trampled to death as their organs are slowly pulled out of their body. The craziest part is that in these facilities, there can be as little as one human worker per 300,000 birds. This means that most birds suffering this fate will never be noticed, and even worse, when they are, workers are not expected to help them. I was actually reprimanded by my supervisor for trying to help these birds and voicing concern for them. She said it was a distraction from my duties.

You can argue that an undercover investigator is a biased source. But it's a fact that the majority of animal food products come from factory farms and there's no denial that these are the methods used by the industry (except in countries that have already banned them).