I kept my turkey poults from dying by giving them neem leaf powder in their water every day.
I had a similar situation just this year. We had got some turkey poults mail order. In July (of all times!), the night temperature had dropped to the 50's and I think that helped chill them.
They were all living when we opened the box, but once they got in the brooder, the next day they started dropping dead! Every day at least one would die, and then it got to be where I was losing 2 or 3 a day. They would just sort of look all sad looking and wouldn't eat, but they would drink.
I was down to almost HALF of the turkeys and the ones still alive were looking not happy. I had just received some neem leaf powder in the mail as the turkeys were dying off. I took some of the powder and mixed it into their water (luckily most were at least still drinking). Guess what? IT SAVED THEM!! And, it's absolutely natural too!! I know it was the neem leaf powder because as they were recovering, a few days after that I stopped adding it to the water and they started to look sick again after one day. One wouldn't eat so I took some of the powder, mixed it in with a tiny bit of the mash I was giving them (I wetted it so it would be a tiny 'pill' with the mash and the powder) and got it down the poults throat. I also resumed putting the powder into their water. They pretty much perked right up and I did not lose another bird!
I then slowly (very slowly) withdrew the neem leaf powder. They're over a month old now and still kicking. We had a chick waterer (about a pint or so) and I only filled up the lower part of the waterer. I added about a teaspoon to start in about 3 ounces of water and I slowly cut back once they seemed to recover.