The dehydrated stuff works in a pinch. Canz sells lamb liver too, and their stuff is more wholesome than the tub o' beef liver that you can get at big box stores. I do use that to supplement my dog's "real" liver intake.
Here's what I do though. I buy chicken liver in the little containers. (Beef liver is so much worse than chicken liver.
). Start a pot of boiling water. Empty the containers into the water (you never even have to touch it!) and boil. You don't have to boil it too long. Just til the meat turns pasty brown.
Then, spoon the meat out and stick into zip loc containers or something similar. Once the water/broth is cooled, let Mr. Ring-Dinger drink the water too.
Then, once the cooked liver has cooled, you can cut it into pieces. If it isn't cool, it will be really crumbly, so make sure it's cool.
You do know to feed teeny tiny pieces at a time, right? Or you'll have a dog with really nasty blobby runny poop.
Here is a website that gives you Iron-rich foods that aren't liver.
I sprinke thyme, parsley, and basil on all my dogs' meat. I cook up pork chops with cinnamon. I make a veggie stew out of mustard greens, turnip greens, kale, chard, Brussels sprouts, and romaine. (If you steam these, then stir in cooked sweet potato -- also high in iron -- or pumpkin -- add honey if he has a sweet tooth, he'll likely eat it). In other words, there are ways to supplement iron. Plant-based vitamins are harder for dogs' bodies to absorb, but it can be done -- at least so that you don't have to feed as much
You'll note that shrimp and venison (if you can afford it) are just as good sources of liver as calf liver.