I just raise this because many have grief with this sort of thing....
I have just found a kitsrus K145 temperature datalogger. I have never used it, I don't remember buying it, it is very old but it is still sold and supported, which itself says quite a bit.
The module has a PIC on board that reads four DS18B20 (only one supplied) and outputs serial via a 9-pin D socket. This last explains the 200m.
It is meant to feed direct to a PC terminal, no Arduino involvement, but I imagine an Arduino could be pursuaded to read it.
I assume it reads the sensors "by index" and all timing done at the receiving end.
Just the thing for the chookshed..........
Add RS485 converters which can do hundreds of meters if shielded wire and a not too high baud rate is used.
DS18B20 <> module <> RS232 <> RS485 <---- very long wire ----> RS485 <> PC or whatever
Yes, I forgtot to point out that this kit runs at 2400, which I'm sure isn't a problem.