Hey there.
first off, i want to offer you encouragement, please do not give up. I want to share my experience which is similar to yours, and i think it may uplift you a little.
Of my first backyard flock of 4 hens, I lost 3 hens within the first 4 months, 2 to mareks and one to mycoplasma. Both these diseases cause a really sad death to the birds, and can stay in your land for years. My problem was that this being my first time keeping chickens, i just wasn't as vigilant as i needed to be about where i got my hens from. The person i got 2 of them from was not a reliable source, lied about their history and vaccinations. The other 2 hens (one of which died of Mycoplasma) came from a feed store in livermore, CA, where i have since noticed what seems like a sneezing epidemic amongst their birds (and this is supposed to be a reputable source of birds). The ones that died of mareks were supposedly vaccinated for mareks, though i doubt it highly because the chances of that happening are very low.
Being the first few months of chicken keeping, dealing with these losses were really heartbreaking. My birds are free ranging in a lush organic garden (jungle) most of the time, and they have a good life here in oakland, CA so why was this happening? I think i gave myself a crash course on chicken husbandry with how much i read about chicken-keeping and chicken diseases during that time. I did my best to diagnose what was going on with them, but their symptoms were complex, atypical, and stretched out over 4 months.
I even tried taken them to the only avian vet there is around here, and hundreds of dollars (that i cannot afford) later, i learned nothing.I had to CULL 2 suffering birds with my own hands, and i've been a vegetarian all my life, so maybe you can imagine how difficult that was. I finally send 2 bodies out to necropsy at UCDAVIS and learned about the diseases that inflicted them.
My fourth hen (the remaining one) is a survivor, and supposedly now a carrier of MG and Mareks, so most folks recommended culling her if i wanted to have another flock - this is because the diseases are virulent and carriers can infect new birds and kill them.
But she is such a sweetheart, and strong and lively, that i just couldn't do it. Also, the diseases stay in the soil for years, so the new birds will be exposed whether we cull her or not. So we waited a couple months, disinfected the coop seriously 10 times over, took out the top layer of the soil, and got new birds.
Over the past 2 months, i've fretted and obsessed over whether i am seeing any symptoms of the diseases in my new flock. i watch them too closely for my own sanity. But I have to tell you, its been just fine!! They are not sick. they are healthy, happy birds so far. I have started to relax a little. I think i am seeing a light at the end of the tunnel.
When i was in the midst of my worries, i really couldn't imagine what it would be like if and when things were better and i had a healthy flock. But I am there now. And i learnt a lot along the way, and there were a lot of folks here on BYC that i PM-ed to get information, and they were super useful.
So please don't lose hope, you'll figure it out (necropsy is a good idea), and there is a way out of this heartache. If you'd like some help trying to diagnose the illness, i can maybe pick on some things i learnt along the way, and look in my books to find an answer for you. Let me know.
