Often rye grass is used for hay and grazing for livestock as it is highly nutritious.
Additionally this grass is used for soil erosion control programs. There are 10 million kgs of certified seed are produced each year in New Zealand alone.
So can chinchillas eat rye grass?
Yes, but it needs to be dry and not fresh.
If a chinchilla was to eat too much fresh rye grass it may upset their stomach.
Ideally you want to only give them small amounts as too much of anything may be bad for their system.