Flies and other insects that chickens eat can be tapeworm egg carriers, this is what is most likely happening and/or you've been underdosing with valbazen. See, when I tell folks that tapeworms are difficult to get rid of...you can now attest to that fact! It's time to stop the valbazen for the tapes. Save it for your regular worming schedule. Purchase Zimectrin Gold equine paste wormer at your feed store, see pic:
Zimectrin Gold contains praziquantel which kills tapeworms. Withhold feed for 24 hours. After 24 hours are up, give each bird a regular "pea" size amount of the paste orally. You can put it on a small piece of bread and give each piece of bread to each bird individually. It would be best to separate your birds and give the treated piece of bread to only one separated bird at a time. If you dont, others will steal the treated bread and run off with it, then you'll never know which ones got treated or not, and run the risk of overdosing or not getting dosed at all. Repeat this procedure in 10 days.
If your birds are penned, consider hauling in sand and putting it in the pen/run, about 5 to 6 inches deep. Sand helps deter insects and helps in keeping everything dry as you already know. It wont wash away like dirt and dries quicker than dirt after it rains. It will deter flies as well and it's easier to scoop poop, kinda like cat litter that clumps urine and feces.
![]()