We had dogs in the Hav 100 study. The theory was that possibly not metabolizing cholesterol was a cause of CD. We weaned our dogs off of the egg a day after the study. Pam asked the egg expert if there was a possibility of over supplementing causing the dog to stop producing naturally, like has been found in horses, and he said he couldn't answer the question....so long story short, we didn't buy into it. Some claimed to see some sort of difference, but we never had problems before without it.
There are many who still believe that it's necessary, but there is no proof. Look at Twinkle's video of her 14th birthday on her page, and see if it looks like she's lacking anything.
Since then, the genes responsible for CD have been found (FGF4), so it's definately a genetic thing, and not a failure to properly metabolize cholesterol.
We do give ours eggs occasionally, but not even close to every day, or even every week.