Please help! My 7 month old chicken is very fatigued and can’t stand for very long

[Newchickenowner2021]

Hello everyone, I bought two chickens last august. One is doing absolutely fine, looks very healthy and alert and has started laying over the last month. The other looks much smaller in comparison, is lighter in weight, very pale and her comb is just not growing. She walks with a limp and cannot balance much on one leg. If they both try and run together, the other chicken sometimes pushes into her and she just collapses. Stays in a seated position for a few minutes and then gets back up. Aside from her normal feed I’ve started to feed them apple cider vinegar in some water, and garlic yoghurt once a week. Overall she is very fatigued and does not make much noise, is not very alert. I have attached some photos
Wonder if anyone could help please? Many thanks

 

[nuthatched]

Has she laid any eggs? How's her crop? How do her feet look? What is their main feed?

 

[Newchickenowner2021]

Thanks for your reply.
no she has not laid any eggs, I tried to bathe her in water a few times in case she was egg bound but it didn’t make a difference.
We feed them mostly mole valleys pellets poultry layers, that I bought from a farm. I feed them treats like berries sometimes too. I only have two chickens, the other is fine. Her feet look normal and pink, though they are feeling very cold today

 

[nuthatched]

Thanks for your reply.
no she has not laid any eggs, I tried to bathe her in water a few times in case she was egg bound but it didn’t make a difference.
We feed them mostly mole valleys pellets poultry layers, that I bought from a farm. I feed them treats like berries sometimes too. I only have two chickens, the other is fine. Her feet look normal and pink, though they are feeling very cold today

Hmm, any discharge from the eyes or nose?

 

[Newchickenowner2021]

Nope no discharge. Eats and drinks fine too.
Just the limp that is not going, comb pale and not growing, tiredness and not very alert