Unknown Illness in Chickens

[Gooseluv]

In September my friend purchased Plymouth Rocks from a breeder who is heavily involved in showing. She got 9 pullets and 1 rooster.
The first week of having them home a neighbour thought he was being helpful and let himself into their coop and left around 4 battery hens in with her new birds. Those birds stayed in the coop for a couple days before they were able to get the helpful neighbour to take them back.
Several weeks later one of her hens began to isolate herself, she would come out to eat and drink then back to her isolation. Her comb was pale and feathers puffed out, but would occasionally eat and drink. This went on for about 2 weeks and the hen got smaller and thinner. Once it was obvious that she was not going to recover, my friend put her in a crate and brought her in the house, within a couple days the hen died.
3 weeks later, another hen showed the same behaviour and within a week was dead.
It has been a month since and now a third hen is appearing to be displaying the same pattern of illness.
If it were viral, would it not take them all out fairly quickly or is it potentially a genetic weakness possibly due to over breeding practises?
We are both new to the hobby and she is feeling at a loss and a bit deflated.
Does anyone have an idea of what she might be dealing with?
Thank so much

 

[cafarmgirl]

If there is a complete lack of any respiratory disease symptoms then I would start with some of the other most common possibilities first and work my way out from there. That means ruling out internal and external parasites as well as the possibility of coccidiosis. These birds were not only exposed to a new environment but to the battery hens from the neighbor as well. It would be super easy for them to be exposed to a strain of coccidia that is completely new to them and that they are not resistant to. It would be well worth running a course of Corid to at least rule that out. Sometimes in older birds they will fight if off longer then a chick is capable of doing, then suddenly seem to be lethargic and just die.

The other thing to consider doing would be to have a bird necropsied by your state poultry pathology lab if another dies. Then you will know exactly what is going on in the flock.

 

[Gooseluv]

They haven't shown any respiratory symptoms nor runny poops.
Here is a copy of some info my friend has just sent me via e-mail:

" I have treated them with a round of antibiotics (in case respiratory or bacterial) as well as treated them for parasites/worms. It doesn't feel like that sort of issue as they would get sick together, not one at a time and several weeks apart. They've also been given a week of probiotics after the antibiotics to increase immune system. Since all of this, none have died, but the one bird looks similar to the others at the beginning of their 'illness'. There isn't anyone around here to perform autopsy, we'd have to ship to Guelph and it would cost over $100 for shipping and fees."

Just in case this is worth noting, she is feeding them a grain mix that she prepares, she is not feeding them "chicken feed". She is also providing them grit to supplement the whole grain diet they're on.

Any further ideas would be great, thanks