I have had several chickens die off over the last several weeks and I'm at a loss. The first one wasn't vaccinated for Marek's, and I believe that's exactly what got her. She was a White Leghorn and died at approximately 9 months after she stopped laying a month prior. She stopped eating, drinking, walked with a limp for a short time, lost the limp, went blind, couldn't keep her balance to stand or walk, and died within hours of loss of balance. The second was a Delaware, a few weeks ago, when it was 118* for two days in a row. She laid consistently and did so the day she died. I found her in the late afternoon. No injuries, no blood, just dead. She was about 7 or 8 months. Vaccinated as a day old chick for Marek's. Today, I just discovered my Buff Orpington. It appears she just dropped straight off her roost in the coop. She was also about 8 months. No signs of illness or injury yesterday, she laid yesterday, no blood on her body now. Vaccinated as a day old chick for Marek's. Was hot a few days ago, around 110*, but it's been cooler the last few days (mid-low 90's). I'm at an absolute loss. Any ideas?