I agree that looks like Common Hogweed. I've no idea about the removal of veins and stems before drying, which is clearly a technical drying requirement
I feed all of it and it is extremely popular.
I agree with all j&b said about Giant Hogweed. I've never seen one and I think they are very uncommon.
If, the worst comes to the worst and you have picked Giant Hogweed instead of Common Hogweed, I think you would realise within a very short while because of the skin problems you would suffer and so the plant would never get anywhere near the rabbits.
From your picture the leaves look like Common Hogweed though. Pictures of Giant Hogweed show a much more feathery type leaf.