Very good question dawg53. I did a bit more research on Piperazine and how it works, and although they (manufacturer) states that egg withdrawal is not necessary, this website http://parasitipedia.net/index.php?option=com_content&view=article&id=2524&Itemid=2797 states that "In laying hens piperazine residues can be detected in eggs up to 17 days after administration." So that does not make me feel great about continuing to eat the eggs :(. It's a very interesting read though and it explains how the worms are affected by the drug.
I have a LOT to learn about chickens, and am learning the hard way after just losing my beautiful rooster, Henry a week ago. I first noticed he wasn't well in mid November. He had runny stools and was lethargic, not going outside, not crowing. I immediately isolated him and on the vet's advice, treated him with Tetracycline 250 (Mfg - Vetoquinol). After 10 days he was not any better (although he went up, then crashed again, then up, then crashed again... did this about four times in four weeks). After talking to the vet again, she switched him to Baytril since she thought it may be a respiratory infection. He was mouth breathing at times and his breathing sounded a tiny bit raspy, but not all the time. I also gave him a tiny dose of Ivermectin after speaking to a friend who lost a good portion of her flock to a worm infestation (at least that is what she was told when she had two autopsied).
As a precaution, I treated all the hens with Piperazine about a week and a half ago. A couple days later I thoroughly cleaned their coop and then mixed DE with their bedding (sawdust, the same as we use for our horses). At the time they all looked fine, now some of them appear to be getting sick, runny stools, weight loss, and about half (of 14) of my hens are missing a lot of feathers on their chest/breast and one is missing some feathers around her vent. I can't see any mites or lice but then can they be seen by the human eye? Should I treat them for that "in case"? I'm at a loss as to what I should do next but my friend suggested I at least deworm with Fenbendazole, but all I have on hand this time of year for the horses is Ivermectin. It has a same spectrum as Fenbendazole but also does bots.
I read on here that I can apply Sudocrem on the bald spots so my husband is going to pick some up on his way home fro work. What I find confusing is that all the different things that can afflict chickens seem to have similar symptoms, so it's very difficult to know how to treat them (except I'm thinking the balding may or may not be related to their general condition). I'm wondering if I should put them on Tetracycline "just in case" they picked up something on the ground, but the product monograph (from the Vetoquinol website) says Chickens and turkeys: Chronic respiratory disease (CRD), bluecomb, cholera, enteritis and hexamitiasis. When I look up each one of those, it does not appear to be those symptoms. Back to square one, no idea what to do anymore.