.:. CiaoMilano answer
Thanks for writing to CiaoMilano :-)
Unfortunately, there is no offer of day trips from Milano to Zavattarello.
However, there are regular bus services between Pavia - which you can reach from Milano by train - and Zavattarello.
For the train trip from Milano to Pavia, please refer to the Trenitalia timetable by clicking on the Trenitalia link in our Railways
As for buses between Pavia and Zavattarello, the service is provided by Arfea. Buses start close to the railway station.
You find attached a relevant timetable. For example, you can start from Pavia at 10:50am to reach Zavattarello at 12:55pm. The last daily bus from Zavattarello to Pavia leaves at 6:05pm, to reach Pavia at 7:55pm.
Please take note that these bus services operate on working days (named FER, or feriali, in the attached timetable).
There are more options, only some of which are shown in the attached timetable (for instance, you can ride an Arfea bus even from Milano to Pavia, though not from the city center). But we believe the attached timetable refers to the most suitable option.
Hope this helps. In case it doesn't, do not hesitate to write back.
Welcome to Milano!