Thank you for your question.
Sudden lameness in a single hen can arise for a variety of reasons (just as it can in people). The most common cause is trauma (it does sound like this is leg localized but we can see trauma to the spine/neck/etc also cause lameness and discomfort) but we do sometimes see sudden lameness in hens arise if they have a more systemic issue (anemia, peritonitis, viral infections, toxins, nutritional issues, etc). So, if Charlie is feeling very poorly with it, we do have to appreciate that there are a lot of considerations here for her and that we may need her vet's assistance here (though not necessarily to put her down).
In regards XXXXX XXXXX and specific limb based lameness, we can consider a smaller list of differentials but do have to again consider that our approach does depend heavily on the type of lameness (ie bone based, muscle injury, or nerve damage). Most often this arises with trauma, and can be as dramatic as a predator attack but also as simple as a hen jumping off a perch or falling. As well, in cases of nerve based lameness, we can see it arise from nerve compression from within the body (ie from a retained egg, tumor, enlarged kidney, etc).
If we had a longer history of lameness or other birds affected, then we'd need to consider those nutritional and management issues that can cause lameness in a group of birds. But since this is a single hen, hopefully we can put this further down our list and focus on those acute causes of the individual.
Now it sounds like both legs are affected (which does again raise those concerns of the systemic issues I mentioned before and not just trauma). If if you haven't already, you want to have a thorough feel of the legs to rule out fracture. You also want to make sure the legs are not uneven (this + complete non-weight bearing can be a hint of hip dislocation), or found she has a loss of control or feeling in the leg (which would point us to nerve based disease). If we can rule those out, then our main focus for leg based issues at this stage would be muscular based injury.
If there is any doubt that one of the other issues may be afoot, then she would likely need veterinary intervention or culling (since fractures, dislocated hips, and nerve issues do often need vet help, of course to different degrees).
That said, if you rule those out and feel that muscle strain/sprain is our suspect, then there are some things you can do at home. First, this bird should be moved to a hospitalization pen. It should be a small enclosure with soft flooring (to prevent any additional damage). Her food/water should be easily accessible for her. This will remove any competition and stress of being outside with this injury, while it will allow you to closely monitor her (know if she is eating/drinking) and administer any supportive care measures. If she is struggling to eat and drink, you will know about it and be able to assist her.
If this is a strain/sprain, then treatment will be composed of supportive care but we also want to make sure we are addressing the discomfort angle here. To help soothe her sore muscles, you can apply warm compresses to the leg (if she will allow, since we don't want her to be stressed with our interventions). As well, we want her on a strong (and animal safe) pain relief, ie. meloxicam or carprofen. These are equally good choices and will likely help her with the pain she is suffering from. Both of these will likely require a veterinary visit for her, as they are not available over the counter. Some people do advocate baby aspirin in some cases (at a dose of 25 mg per pound of chicken's body weight once daily), but I would warn with this being a potential traumatic injury, we need to be very careful administering this drug. Aspirin, as you might be aware, is also a blood thinner. This means if she has any internal injuries or bleeds that haven't been appreciated, this could cause some potentially fatal side effects).
Overall, as I mentioned at the start, the cause can be quite a variety of issues. Therefore, if she is pale/collapsed/weak, then we'd have to lean towards the more sinister systemic issues that would really indicate veterinary intervention. Otherwise, if we are looking at leg limiting disease, then the lameness is subject to the type of tissue that has been injured. In this situation, if we are looking at a muscle basis of lameness then you can try supportive care for this wee one at home. So, do consider isolating her as I have outlined, double check your normal coop setup for risk factors, and see if she does respond and settle with supportive care. But to make sure you can rule out those bone or nerve based lameness with your wee examination, since these will often have poorer prognoses for them and afain would need her vet's help to either address the issue or to keep her from further suffering
And just as aside, if you don’t already have a specialist avian vet, you can check where you can find one by using the bird filter on the RCVS register to find a bird vet near you. You can find that here (LINK).
As well, you can find a few more avian vets listed via the Avian Web (http://www.avianweb.com/recommendedvets.htm#UK)
And there are a few more listed on the Parrot Society (LINK) website.
I hope this information is helpful.
Please do let me know if you have any further questions.
If you have no further questions, feedback is always appreciated.
All the best,
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