When you take the feed in at night the rats just switch to eating the chicken feed during the day. It is nearly impossible to trap or poison your way out of a rat infestation. Do a search on BYC for rats and chickens, there are hundreds of threads filled with advice and old wives tales on dealing with rats.
If you want the rats to leave you have to stop feeding the chicken feed to the rats. They cannot survive on herbs or veggies, not any sizeable population at least. And how do you stop feeding the rats? You either buy or build a treadle feeder. Do your research, don't trust most of the online reviews especially if they have a link and admit to getting a portion of the proceeds when you clink on their
amazon link. There are a few reviewer out there that are independent and a lot of blog sites that have done reviews without succumbing to shilling for dollars.
Some cats might mouse but few will take on actual rats. And if you do a forum search you will find folks whose hobby is trying to outwit rodents but the majority of the "solutions" will stop working once you kill a few rats as rats are very intelligent. But, removing their access to the feed always works. Always, always, always.
A proper feeder doesn't have a wide treadle for the rats to gang up on. It has a spring loaded door and a countertweight. It is all galvanized steel, nothing else will stop a rat from chewing into the feeder. It should have a swing inward door, not one of the guillotine style doors, for the simple reason that you HAVE to block those feeders open to train the birds and once the rats know where the feed is they will gang up on the feeder and just push the lid open. If you do go on
Amazon pay close attention to the negative reviews, 3 and below. There are always a few crazy people out there and those that refuse to follow much less read the directions, but the negative reviews ought to be single digits or you are reading a lot of reviews of people that bought a treadle feeder before they have rats. That is no real test, a real test is if you already have a rat infestation and need to solve it which is much, much, much harder to do.
Lastly, do a search for Howard E. and rats and you will find a wonderful post on dealing with rats, an exhaustively researched post, and another that has an old U.S. government treatise dealing with eliminating or controlling rodents. But the basics are sanitation, exclusion, then elimination in that specific order. A proper treadle feeder is sanitation as it prevents the rats from eating and if you do that you rarely ever need to spend a fortune trying to fence out rodents or poisoning them.