I don't really suspect vitamin deficiency because I would expect to see that in other members of the flock, especially since I have quite a few young pullets right now, including other white leghorns.
Individual genetics count in ALL things immune system related including the ability to uptake and process nutrients.
This is where people get SO confused as to if it's Marek's, vitamin deficit, influenza, or Covid 19.. why is only one showing symptoms.. Different genetics is the purest and simplest answer! Hidden roll of the DNA dice in combination with environmental input.
With all birds in my flock getting ONLY the same formulated (pelleted) ration.. hatching eggs showed individual hen weaknesses and strengths when monitored closely for nutritional differences.. according to the day an embryo may have failed to continue developing under controlled and acceptable incubator conditions. I a have a hint of extreme attention to detail, uhm "issues".
The pullets get a 15% pullet starter from a local organic feed mill along with my own custom grain mix of oats, barley, BOSS, and field peas. They all free range and the only treats they get are appropriate kitchen scraps, such as cucumber/carrot peels, leftover scrambled eggs, etc.
Can you come up with a nutritional analysis for your own custom mix? And also that 15% protein.. "starter"... HUH?!! Are all you other ingredient also organic, or what makes that one a good choice?
I would go out on a limb and say cut back on your "own mix".. individual ingredients are EASY to pick out and cause nutritional imbalance.. EASY, I say.. to happen to any individual.. by accident.
Also to be clear.. Marek's vaccinated birds just HIDE symptoms if/when they get exposed.. the vaccine does not stop them from getting OR spreading it.
Scrambled eggs and BOSS are both high fat.. eggs being 34% protein and 64% fat.. should be used minimally as a treat. Cucumbers and carrot peels.. many the things folks like to consider good for us.. are good enrichment for chickens.. but NOT helping their nutritional intake.. I'm not pointing fingers here.. I don't know your flock size or how much of each thing they get.. and even if I did, I'm still ONLY sharing information.. and hopefully in a friendly and uplifting manner.
It's *possible* she has an egg pressing that nerve getting ready to lay soon?? 20 weeks/5 months should be close!
My realist (cruddy) perspective suspects Marek's. But I'm always happy to be wrong.. noting that even if it goes away.. doesn't mean it wasn't Marek's per say or that it won't repeat.. many things work together to bring an individual down, NOT the least of which is hormonal surges. All we can do is our best, according to our current understanding, and switch it up if it isn't working or we learn something different.
I would definitely try the B complex.. Though I'd give it to everyone and return her to the flock, until seeing ANY change.. like separation, isolation, bullying, increased disability, not roosting, etc.
I also want to mention that when working with flighty or nervous birds, often the easiest time to catch them without any chasing (which also reduces stress) is once they've gone to roost and settled down.. after dark, using a flashlight, and keeping it dim. Everyone *usually* stays in their place.
The spur bump you describe sounds exactly like that, a spur bump. Most don't but some hens WILL grow spurs in their older age. Some also crow though it usually sounds a bit pathetic.
If you have space to add hay, shavings, dry leaves, grass clippings, etc. to the dirt floor.. it will invite good bacteria and bugs to an otherwise breeding ground for bad bacteria, add some enrichment, and soften the landing a bit, more like the forest floor is how I like to describe it.. called cold composting or SEMI deep litter.. Again I doubt injury, according to your description.. BUT, anything is possible.
If you do start to consider Marek's, I'm sure
@azygous can inform you of the live test routine if that's the way you wanna try and go to find out.
If she declines to where you decide to euthanize and send her in for a necropsy to try and get a more complete look or possible diagnosis the following link is to state poultry labs in the US.. often free or affordable to back yard keepers.. in Ca it was $25 for 2 birds and $17 overnight shipping through Fedex using UC Davis commercial account, after contacting them first as suggested in the thread linked after the labs..
State poultry labs
How to Send a Bird for a Necropsy
I'm not truly "Debbie Downer", just been in survival mode (bondage to the world) WAY to long
previously.
But, Life finds a way despite complications.. and I hope your gal mends quickly and thrives!
