I have a three year old Orpington hen who is unable to get up on the perch with the other hens. She has been having trouble hopping up and over the entrance to the coop, and once in the yard, can't get up the ladder to get back in. Up until yesterday, she had been hopping up the ladder to the perch and sleeping there with the others, but the last couple of nights I've found her on the floor. The weakness seems to have gotten worse lately---she's been unable to do even short jumps for about six months, but she still somehow managed to get up on the perch every night. She is not underweight, she eats well and drinks well, looks healthy otherwise. Walks just fine, no sores on the feet. I wormed her, dusted her for mites, and checked her vent for stuck eggs or diarrhea, but nothing. No swelling in her abdomen or discharge of any kind. I'm not sure if she's laying---all of the hens have slowed down or stopped laying due to age, although a couple will lay every once in awhile. I'm at wits end trying to figure this out. Any guesses?