Thanks Womble - that's exactly what I'm saying. In fact, it was the vet that said it. So when the hens were ill (only a few months old, irrelevant of my yearly worming routine, they'd been wormed on arrival and were already high worm count just weeks later), the vet explained that if they were ill with something else, their immune systems were compromised and they would therefore find it harder to fight the worms. So it's chicken and egg - or in this case ill hen and worm.
I just object to the immediate leap from that point to the conclusion that I wait for all of my hens to get so ill with worms, they then come down with something else because there is absolutely no evidence of that. In respect to the original thread, my hens have a lot of space so their natural worm burden (as evidenced by vet testing) is extremely low to zero despite the yearly worming routine. My point was that if a hen gets ill with something else, it is worth worming them so that they have one less thing to compromise their immunity. So just to clarify - my chickens are all healthy, happy chucks. I can't remember when I last lost one - certainly none since last year - and many are now three or four. BUT if any of my birds get ill, the vet will normally give me a wormer in tandem with any other medicine they need so that we can be sure they are clear of worms. OK?
As for old thread, closed or not - that's not really up to you Eve. The joy of a forum like this is that it's possible to return to threads that are several years old to remind yourself of advice. In fact, I must go back to one on Fresias from years ago because I've found a solution to something I was requesting help on then!