Well, when it comes to large animals like cattle, you're never going to be able to feed the whole thing. I was really talking in approximations. Even if you could get a whole cow cut up into bits, and
had a freezer big enough to store it - there are parts of animals that size that are just too big for dogs to consume. Leg bones, for example, we talk of as "recreational" bones because they are too large to be consumable bones.
With big creatures like that, the best you can really do is feed an amount of meat, bone and offal that are roughly in the proportions of the whole animal. I wouldn't worry in this case about which part is which. With smaller animals though, you can just feed the whole range of bits. Or roughly the whole range of bits (there's no need to precise about it). In some cases, it will be more economical if you actually DO buy the whole thing (especially if you get a meal yourself out of it too). But in other cases, all you really need to aim for is an approximatation of the amount of meat, bone and offal that the whole carcass would contain. That's all
Just to illustrate - you'd never feed just chicken necks and wings because then the dog wouldn't be getting enough meat or offal (over time, I mean, it doesn't matter if an individual meal is those things). And at the other end of the scale, you wouldn't feed just meat or just offal either - because bone is needed as well. The simplest way of keeping a good balance between those three requirements is approximating (over the course of several meals) what makes up a whole carcass. Does that make sense?