How To determine which of your chickens may have worms??

For most, you are only guessing, by symptoms such as weight loss with good appetite and dull comb. If they happen to have tapeworm, you will see little white segments in the poop that look like rice. Occasionally a roundworm infestation is bad enough that some come out in the poop; they are long, thin and eaisly visible.

A vet can do a simple test on a poop sample, and many will do this for you for a modest fee, even if they don't treat chickens.

The truth is, worms and worm eggs are very common and found in most soils, and any animal that lives on the soil is almost certain to have some worms. Warm, wet soils like mine are very likely to have a high number of them. For this reason, I worm regularly, without testing. The first time I did it, the birds gained weight but if anything, ate less. Usually, worming is not done before one year of age.