I approach the worm situation differently. Every animal has intestinal parasites...even us. Yes, even you, so don't think you don't have them. But...you are walking around totally unaware that you have worms. Rarely do you actually see the adult worms shed from the intestines when they finally die because they are, by then, decayed and pretty much the color of your stool. Unless your health is already compromised or you are very young, you may never see the physical evidence of a worm load. Most doctors never test for this and will treat you three ways to Sunday to try and cure the symptoms you have that were ultimately caused by a worm load....no, you don't get skinnier with normal worms, you actually stay kind of fluffier. With tape worms you may see a weight loss but that is not the normal, every day round worm human parasite.
Dogs can be the same way. I rarely deworm my dogs as I never see any evidence that they have a heavy load of parasites(every once in awhile as an after thought I may give an older dog some horse wormer). What do feral animals do for worms? Some chew different plants and grasses to rid themselves and, if you ever saw your dog chewing on saw grass it was for the same reason. The sharp, serrated edges of that grass cuts the worm's skin, allow digestive acids to finish the job...sort of how folks use DE. Now I let my dog cure his own worm problem in just this manner....and it works.
I don't stare at poop to see if my birds have a problem. I look at the health of the birds. Any unhealthy looking/performing birds are cut from the flock when I do my yearly culling. Do they have an excess worm load? Who knows? I don't care. All I look for is general health and performance. If my birds can remain healthy and perform at peak with their existing worm load, this is the desired effect.
I WANT birds who can exist and thrive with the normal intestinal parasites and pathogens that are already there. This mimics more of conditions in nature and that is always what I am shooting for. A flock that is self-sustaining is less work, more profitable and will pass along stronger genetics.
When you constantly deworm, you create a flock that you can never reliably cull for hardiness~how would you know which birds were naturally healthy and parasite resistant if you give them all medicine across the board? Having to rely on medicine to stay healthy is not hardy...it's merely a bird that has to take chemicals into their system to thrive. A human that has to rely on medicine to thrive is generally not considered in optimal health.
Every once in awhile(as in every other year or so or even once a year) I might put a dab of garlic juice in the water just as a health tonic and general parasite dose. It's more of a~let's see if I can make them even glossier and perform even better than they do now~kind of thing. I never really notice a difference but I try it anyhow to see if I can...I'm always looking for ways to optimize health without creating a less natural environment. On the whole, if I felt like deworming, I'd use garlic, soap, etc. These are things that worms can't really build up a resistance to, though soap isn't the most natural thing...we use it to wash ourselves and our dishes, so that's good enough for me.
