Being the researcher that I am, here is what I've found out and concluded based on replies received here and further inquiry (I am posting this for posterity): I spoke with a vet who is solely employed by a large egg producer in my area, he said that as long as chickens are on the ground, roundworms can be an issue. The only way to prevent roundworms is to get the birds off the ground. For backyard chicken farmers, this is not really an option. The vet indicated that they are generally not that hard to deal with and don't usually pose a serious problem to the health of the chicken, and that a regular routine (every 6 months or annually) of worm maintenance is a good idea. The bottom line message for me was that, yes those worms are gross, but there is no need to freak out.
It appears that the pepitas (pumpkin seeds) and buttermilk DOES paralyze the worms, causing them to be expelled. I think this is why I found worms this morning -- because yesterday I gave them a bunch of kitchen scraps that included various nuts and seeds (pine nuts, etc.) that I wanted to toss. Here is what I plan to do: for immediate control of the worms, I will use Verm-x which is herbal and has the benefit of no egg withdrawal period. For maintenance, I will add cayenne to feed and apple cider vinegar to the water on a regular basis (I'm not sure on the dose, so if anyone has advice, I'd appreciate it). I will also feed buttermilk and pepitas followed up with molasses in water (to aid passing) about once a month; and use Verm-x twice a year or as needed (re-treat after 10 days). I will also disinfect with a spray-solution of dilute Clorox twice a year.
As I indicated previously, I called Fleming Labs, makers of Wazine-17 and that product is not officially approved by the FDA for use in egg-laying chickens although a withholding period of 17 days following final dosage seems to be un-officially recommended. I also called Merial, makers of Ivomec Eprinex and they could not recommend their product for poultry because they have not done studies on the use of this product in poultry.
I keep thinking that people have kept chickens and had to deal with roundworm far longer than these livestock meds have been available. I think I'll go the control route (rather than the eradication route), especially since this is likely to be a continuous battle since the girls are free-range. Afterall, this is why I have chickens -- I want to provide my family with healthy , chemical-free food.
