New harvests are generally oat laden, whereas later harvest such as Dec-Feb can be very light, minimal oats. Many people confuse Oat hay with Straw. The similarity is in the coloration. Straw is not a food source, but is typically used for bedding, mostly in the horse and farming communities. Oat hay is an excellent source of fiber.
Bunnies tend to enjoy the oats mostly, but munch on the hay portion sporadically.
If bun's diet is high in oat hay, the pellets she produces will be larger, lighter in color, and will look like sawdust if crushed. Many bunnies would benefit from eating more oat hay, excellent preventative for GI stasis. HRS boxed hay may contain oat hay or other fiber rich type to provide variety. Yes, it's that stuff you've been trying to get out of your flower bed since the beginning of time. Bermuda is less well known and not as easy to come by.