Hi and welcome to BYC
So sorry it is through an illness with your hen that you have joined us but hope you will stick around to socialise and learn after we have(hopefully) helped you fix your girl.....that said, she does sound very poorly so taking action asap will be critical.
Being very light (emaciated), as you describe, can be caused by a number of things:-
blindness/poor eyesight... being unable to see food and water to eat and drink
broodiness
bullying
crop problems
tumour/disease like Marek's
worms
She will not lay eggs once her body condition becomes too poor, so the lack of eggs will almost certainly be due to her being so thin.
Lameness can be caused by
Bacterial infection like botulism
Bumblefoot or other localised infection
Coccidiosis
Diseases like Marek's or MS
Injury
Internal laying
Being broody could cause her to isolate herself, possibly lie around in odd spots if she was being bullied from the nest boxes, lose condition, feel unusually warm and not lay eggs and comb go pale, but I would expect you to have noticed some other broody symptoms that would indicate that condition.... most notably pooping one huge stinky broody poop each day, especially if you have her confined.
I would expect you to notice some signs of blindness, like pecking at food or water and missing.
You would also probably have noticed bullying assuming you spend a bit of time with your flock.... I appreciate she may have been getting bullied recently because she is sick, but prior to that, how was her status. BRs are usually quite high in the pecking order.
Have you checked her crop? Does it feel large/full or small/empty? Check on a morning before she has had the opportunity to eat anything.
Marek's is a possibility but less common in older, mature birds but could account for the lameness as well as being light weight. Cancer is not uncommon in chickens, so this is a possibility.
Worms and other internal parasites(coccidia) can be tested by most vets on a fresh poop sample.
As regards the list for causes of lameness.....
Botulism would have almost certainly progressed and killed her by now.
Bumblefoot, you should see a black scab and swelling on the underside of a foot.
Coccidiosis can be checked via a poop sample.
Marek's as discussed above....is common to both lists, so not to be ruled out. A short video of the way she moves can sometimes help to indicate if the lameness is neurological (paralysis) or pain motivated
Injury would usually show with some bruising (green in chickens) or swelling and as above might be identified by conscious favouring of one leg rather than uncoordinated hobbling.
Internal laying would be obvious because she would feel heavy rather than light and have a bloated abdomen.
So, I would suggest ruling out whatever you can by visual examination and observation.
Assuming her crop is not the problem, supporting her with good nutrition (scambled eggs, tuna, cat food, liver, live yoghurt , fermented feed) as well as a good poultry vitamin supplement like Nutri Drench or Save a Chick or Rooster Booster. Giving her moist mushy food rather than dry food will be important to ensure that she doesn't become dehydrated. You may need to consider tube feeding her to gen enough nourishment into her system. There are You Tube Video tutorials on this and
@casportpony has a good tutorial I believe or a vet should be able to show you how if you are not confident enough.
Getting a faecal test done by a vet (most should be able to perform the tests ven if they don't see chickens) or other laboratory (some labs offer a mail order service....in the UK they are called worm egg counts, but you would also want a check for coccidia and perhaps bacterial assessment)
If it is a crop problem then remove food and begin gentle massage and research to establish an appropriate treatment or come back to us with symptoms....ie hard or soft and squishy, bad breath or no smell etc.
Not sure if I have covered all the options but hopefully someone else will chip in with whatever I have missed.
As stated above a short video of how she moves/limps might give those of us who have experience of Marek's an indication of if that might be it and also a photo of her poop might be helpful.... poop can tell you a surprising amount, even though we can't smell it through the computer.... thank goodness!
Good luck
Barbara
We also have 4 chicks, and none of the other chickens seem to be showing any of the same symptoms.
Welcome To BYC
