Well, if your birds stay healthy, then you may not have a variety of parasitic worms in the environment or strains Coccidiosis. I once knew a guy whose chickens had bloody stools. He asked me if worming with Lye could have done this!!! Yeah...unbelievably stupid. At least you won't kill them...
There's a reminder. I bought top soil one year and there were numerous bits of plastic mixed in it. I was annoyed since it wasn't noticeable until it was dumped. I saw a few pieces of plastic in some chicken droppings. I never bought soil from that outfit ever again.
Ivermectin only kills a couple types of worms. DE won't do anything for worms. Albendazole which is the content of Valbazen is a far better wormer. It kills them all and is safe at .5 cc for standards and .25 cc for Bantams. I used Wormazole and a few others over the years, but Valbazen is...
Here are some examples: http://chat.allotment.org/index.php?topic=17568.0
When you wormed your birds, were there evidence of worms, and what did you worm them with?