Kudos for the sharp eyes and sensitive fingers that know what is normal for your birds. As Chickens age they will go through changes just like people. Some old gals get reproductive problems-especially those turbo charged laying breeds that spit out nearly an egg a day. Just like a machine, parts that get worked hard wear out quicker. Some of these old gals develop certain types of cancer (chickens are often used in cancer research) that will make them lose weight. Some get peritonitis from internal laying (egg does not continue along the track like it should and ends up where it shouldn't) and will develop a doughy abdomen and a bony breast. Some will end up with kidney or liver problems that cause muscle loss. You will see more health issues in rare breeds as poor breeding practices creates inherited genetic issues.
Since you are not really into veterinarians, I'm not sure what advice I can give. Working as a LVT for 25 years, my advice will always be to get a veterinarian involved. I've seen a lot people waste a lot of money on stuff that don't work and ended up wishing they had spent money more effectively. Though I'm encouraging all backyard chicken owners to ask a vet for advice, I'm also encouraging the veterinary community to get involved with backyard chicken farmers. Remember, the veterinary community is very client oriented and when people start asking how to properly care for a backyard flock, the veterinary community will respond by expanding their knowledge.
Anyway, the most basic yet beneficial test you can do is have a fecal sample examined by a professional. I know you don't want to but this test can actually tell you what direction you need to go. The problem with holistic medicine is that some people will sell you anything and call it what they want. Since it's not a prescription drug, there are no forces regulating what is going in the product. We are all aware of the animal food industry putting questionable ingredients in their products. And as a horse owner I learned the hard way that all supplements are NOT equal. Some of the crap out there is simply dextrose with tree bark.
So, if you want to go holistic find you a holistic veterinarian that can supply you with products that are a safer than what you find elsewhere. Yes, there are holistic veterinarians out there. Just gotta find them.
Remember, backyard chicken medicine is relatively new and everybody is still learning. Never hurts to step outside your comfort zone in order to provide better care for your flock just as it never hurts a veterinarian to step outside their comfort zone to provide better care for their patient and client.
So, the most common reasons of weight loss in older birds are parasites, cancer, kidney liver issues and other various viral, bacterial,fungal diseases and diet. So many things can go wrong. So where do you start? With a trusted professional who knows your flock better than we do.
