With Oxbow the back of the bag gives guidelines on how often the hay should be offered. I think Oxbow's information is fairly accurate. They state that chinchillas under a year of age can be free fed any of the hays they offer, even alfalfa. After a year they recommend only feeding alfalfa occasionally but still say all the others are fine to free fed. Some of the others have Timothy in their blend, for example Botanical Hay is a mix of Timothy Grass Hay, Chamomile, Lavender, Lemon Balm and Clover. The Oxbow label also tells you how sweet or hearty the hay is as well as how soft or crunchy it is, with a leveling system. Personally my girls are 3 months old and they get a mix of Timothy, Meadow Grass Hay, Botanical and Orchard Grass Hay. They seem to like the Meadow Grass Hay the best as it seems to disappear quicker. I typically shove a handful or so of two to three types of hay in their cage each day and let them decide what they eat. My girls have two large hay boxes, so they go through quite a bit of hay. I throw away most of what ends up on the bottom of the cage when I clean it.