Darn it! I don't know the post number....
Okay, okay...I'll tell it again but I'm just gonna get laughed at again.
This is the most complete explanation of the method...an earlier one wasn't quite as thorough but as this is the last time I'm going to talk about doing rectal exams on chickens, I'll put the entire messy business on the page.
I take each hen off the roost at night and gently insert a finger into her vent...if she is laying the next day you should be able to palpate an egg coming down.
No, it doesn't hurt them, it is only a part of your finger and mostly just the finger tip. Yes, I wear vinyl gloves and no it won't transmit disease or infection from one bird to the next....they are all flock mates and share the same intestinal flora.
If I don't feel an egg, I mark that bird with a zip tie on the leg~usually the right leg. The next night I palpate them all again. Those with another egg are left unmarked, those without an egg still are left with their zip ties in place. Those that were previously unmarked but don't have an egg I'll make a decision.... Do they appear in good health and condition? Are the other signs for good laying in place such as nice red combs, loose moist vent, etc? Are they one of my tried and true hens? If all the answers to these questions are "yes", then I won't palpate that bird on the third night. I've found that if they don't have an egg that second night it could be that I just caught them on the wrong day but more often than not, they are not laying every day or every other day.
If any of those answers are a "no", then she will be marked with a zip tie on the opposite leg of those who are doomed to die and will be palpated a third night...if she has an egg, she's a keeper, if she doesn't, she gets benched. That third night all birds with zip ties are trussed and laid down in the deep litter to await the next morning's butchering. The third night check on the left tie bird isn't really necessary but sometimes I keep hoping that my favorite birds are salvageable...I've not had any that were after that second night's check. The third night is just for sheer hope.
I like keeping a layer flock for as long as they are productive and healthy...if they are older than 2 years and lay every day or every other day during peak laying season, then they get to stay in the flock. If they don't at least lay every other day during peak months of lay, they are gone.