First, I am sorry for your loss.
Once I bought chickens off Craigslist infested with worms. Ever since then, I have to deworm twice a year or I see worms in the poo. That was several years ago. This is even after a period of time having no chickens on that soil. The worm eggs are now in the soil and you will need to be vigilant in keeping your flock free from worms.
I'm always amazed at the amount of chicks/birds being sold on Craigslist. I called a guy once asking if he vaccinates his chicks for Marek's. He didn't even know what Marek's disease was. End of conversation there.
Using wormers are off-label for egglaying hens, and thus research is important, but this is a life-saving thing you can do for your flock. I have lost chickens to worms and even found a worm in an egg once. There is nothing like seeing my flock get depressed looking, me worming them, and then they perk up a few days later...back to normal.
There is a pelleted wormer made by Rooster Booster products which contains Hygromycin-B, and has no withdrawal period. It is pelleted and is added to feed. The trick would be insuring enough is eaten. I like direct fed wormers, then I know they are getting enough.
Same with mites/lice. They do prey upon weakened hens/cocks more. However, once there is an infestation of mites I have found that they even bite me and thus everyone will be infested. I have not dealt with lice. Make sure you repeat your wormers and mite/lice treatments to break the life cycle of these things.
Dusts are old-hat to me. An emulsified concentrate labeled for poultry like Permectrin II or Ravap EC has a residual of 28 days, which requires no secondary treatment.
Repeat your mite/lice treatments every 7 days or so, (x1 for mites, and for lice make sure you repeat x2 because that 14 day time frame is important). Worming- I repeat at 10 days.
Some wormers recommend 3 days in a row if there's a large infestation. Like you, I've found Spring and fall treatments (twice a year) prevents problems.
Some vets will do a fecal float for worms but false negatives are possible. I just watch my flock carefully and schedule my wormings for at least twice a year. Make sure that you toss eggs for an appropriate amount of time after deworming, too. Most say 14 days on BYC I have read.
I inquired with a vet for a fecal float about 5 years ago and he said it would cost $150, so I declined. What I find questionable about fenbendazole (Safeguard) is that there's no withdrawal time for Turkeys, yet folks claim there is for chickens. I eat eggs after worming with fenbendazole and never had any problems. That is just me though. It is always best to seek legitimate studies, such as those performed by poultry science departments at universities. i think it is a good idea to alternate wormers as to avoid worms becoming immune to the same solution year after year.
I hope this helps.
You always are helpful.
