I quoted this from the article, DO NOT USE POSION! It is terrible! Plus the rat has a painful death!
Poison
I’m going to say this right at the start: beware the use of poisons. This should be your last resort if nothing else is working. I know it seems like an easy fix to a big problem, but using poison to get rid of rodents could lead to bigger problems down the road. If a poisoned rodent were to die anywhere out in the open, it could be eaten by your chickens, your cat, your dog, or neighborhood wildlife. This means poisoning the rat is effectively poisoning other animals as well.
Another downside to poison is that over the years rats have developed immunity to many poisons, and others they’ve just learned not to eat it. This means you’ll have to frequently change the type of poison as one won’t work for long.
Even if you do manage to get the rats to eat the poison and they do die from it, they will likely die in a very hard to reach place, such as underneath the coop or within its walls, and you’ll be reminded daily of this horrible mistake by the stench.