It does, but it's more than that, really...it's an increase in the health of the whole bowel that deters an infestation of the worms. The acidity is one determining factor but also the colonization of certain types yeasts from the acetobacter bacilli family that seem to create a hostile environment for intestinal parasites. I can't remember all that I've read on it and don't know if I have the information stored but I've read about it all and it's fascinating~if very dry~reading.
I would say, though, all sources agree that a bird with a low immune system is more susceptible to getting parasites and illnesses of all kinds, so if a person just kept all birds, no matter their condition..they are likely to wind up with some worms in their flocks. From what the biologists say, 90% of a flock's worm load is carried by 5% of the flock.
So, let's say you keep that 5% and rationalize, "Well, if they carry them and the other birds are healthy enough to resist them, there's really no harm in keeping just that bird and worming it every now and again or even worming the whole flock." But, at any given time a healthy bird can go through things that will stress even a healthy immune system....extremely cold weather, extremely hot weather, brooding, injury, or even a few days of diarrhea...then they are exposed to the oocysts the carrier bird is shedding at all times in her feces.
Then you have another bird that is carrying a worm load higher than normal....can she get her good health back with that added stress of the anemia caused by this load? Who knows? Will she then become a bird that is part of that 5%? But with each bird you keep that is a carrier and whom you try to keep worming to keep them healthy, is your 5% becoming more like 10% and pretty soon you have a flock problem and not a bird problem.
See how easy is the slippery slope of trying to manage a healthy flock while insisting on keeping weak and unhealthy birds in the middle of it? Pretty soon you have 90% carrier birds and only 5% who are healthy but...wait! You still have your worm medicine handy!
But, unfortunately, along the way you have bred worms that are resistant to your worm medicine because you have used it "regularly", just in case, to keep your birds free of worms. You now have super worms in a flock of birds with weak immune systems...you are basically up a certain creek without a paddle...it all gets increasingly brown and stinky from there on out. Not good.
Yessssssss, my preciousssssssss.... sssssssoooooooooo cruelzy, I am!
