He's actually a very compassionate and empathic man... his exposure to the animal abuse as a child would have really [had an effect on him]. He probably had to grow a hard shell to protect himself from it and survive his childhood, and that kind of barricade doesn't come down overnight.

He was very expressive when he was describing his memories of those places... the sights, the sounds, the smells... [and it] sounds like it was pretty awful for him to experience and he's spent 41 years practising to block those thoughts and see animal flesh as food

So... tell him that!

And ask him if there was ever a moment or an early memory he has of questioning the legitimacy of using animals the way they were used on his ranch.

I think the default for behavior for some children is to be completely empathetic and compassionate, until the world or the society they grow up in forces us to be otherwise. We become desensitized to legitimate suffering and dysfunction because specific topics or sets of actions developed over time to try and ignore that specific type of dysfunction are normalized by whatever the particular culture we grow up under is.

Once he's seen the evidence for what actually goes on in the animal agriculture industries (which he has, at least for cows), ask him to practice seeing animal products for what they are. It doesn't really take a lot of time to make a hugely beneficial change in perception.

He doesn't give two shits about the environment, only recycles because I nag him. His whole philosophy in life is to do what makes you happy right now, because tomorrow you might be dead

Practical habit-changing advice:

He can be just as "lazy" doing habits that are good for the environment/himself/animals (I certainly am!), he just needs to get into the habit of doing them until they're as mindless and automatic as not doing them.

Yeah, getting into the routine takes a little effort at first, but after a while it becomes second nature.

That's how anyone can improve themselves without a lot of stress. Pick one, smaller thing to improve (ex: don't eat some kind of meat he already doesn't like a lot, perhaps seafood?), then do it until it fades into the background and doesn't even seem like an option anymore. Then do another one. Repeat until total bigger habit-changing goal is attained.