@NimsHouseGarden
So sorry to hear that you are dealing with Marek's Disease in your flock but you are not alone.
You've been given a lot of good sound advice here. I'll add a few things.
In my experience, once birds start being 'thin' it's hard to fatten them up when you are dealing with MD. It's just the nature of the disease I fear. I agree with the suggestions of upping the protein. Scrambled eggs, canned tuna or salmon, even mackerel. Whatever they will eat. For the longest time I had a problem keeping weight on my birds. I tossed out the book on feeding chickens and started feeding them scratch grain with cracked corn, BOSS and whatever else was mixed in with it. They plumped up and have held their weight.
I know there are a lot of folks out there that cringe at that but I had birds go from a low breast muscle ratio to as the old saying goes, fat and sassy in a few months time. You do what you have to do when you are dealing with MD.
I would recommend using a good probiotic and vitamin mix in their water at least once a week since you have active Marek's in your flock. I even added a few drops of food grade copper to my bird's water as it will suppress a lot of bacteria. Some even add a few drops of colloidal silver to their birds water. Do some research with Doctor Google and see what you can learn about nutrition in Marek's Disease. There is a lot of information out there.
The genie is out of the bottle though so you need to work towards fortifying your birds that are still health and simply carriers at this point. Close your flock. No unvaccinated birds in and none out. Unfortunately, Silkies are highly susceptible to Marek's and equally unfortunate, you are going to be fighting an uphill battle where it comes to fattening up the ones that are already presenting as being overly thin at this point in time. I hate to say that these are the birds you will probably lose, but I'm sorry, they are.
So work on the ones that are still good weight and acting normal at this point. I agree. Fermented feed and mash--let them have all they will eat. You want to be able to feel their breast muscles and keel bone and feel meat there. Think of how a whole chicken looks in the grocery store meat section. Granted, those are meat birds but you want to feel some substantial muscle there. Same with their legs.
When I feed mine wet mash (mostly in the winter when they need extra calories to keep warm) I will toss a few handfuls of cracked corn and black oil sunflower seeds to the mix. Corn will help fatten them up but you have to be careful not to overfeed them corn as it will contribute to fatty liver disease in chickens.
I won't lie to you. Things will get worse before they get better but they will get better. Just hang on and keep doing what you are doing. Good feed. Vitamins, good worming schedule and lots of prayers.
I'll be keeping you and your flock in mine.
Becky
PS. I want to invite you to read my article here on BYC:
https://www.backyardchickens.com/ar...-i-learned-to-deal-with-mareks-disease.76944/