I think it is important to note that when using ACV you do not want just any AVC you want to make sure it is the kind of the mother in it.
People say it does a lot of things that there is no science to support so watch what you read when there are these long miracle list of benefits but that does not mean that there aren't real benefits -- the most important being to promote a healthy PH in the gut which promotes healthy bacteria. This has overall health benefits and a healthy gut is a harder place for parasites to reproduce.
This health benefit means it does a lot of things sort of/kind of indirectly I guess. People says it's a wormer.....well, no, It does not kill worms but chickens with healthy guts can combat worms a little better.....It does not actually help chickens make eggs but I guess you can argue that a healthy chicken lays more eggs?
It is very highly acidic so you do not want to give too much. Any strong acid also has it's negatives.
This is about people using ACV but I think it is still relevant and gives some history on its popularity: