mine get unlimited (because i dont have hay atm)

You can over feed it but if your bunny is coping ok with it then you can probably increase the amount. Just do it gradually.

I just recently discussed this with my rabbit-savvy vet  and she discourages grass clippings in large amount.   Moderate amounts INCLUDED  in the diet (not the main part of it though), should be okay.   She said that the reason for this is that excessive fresh, new grass can cause some muscular weakness in cows and horses — called “grass staggers”.  Though it’s not fully clear if rabbits get this, there is no reason to think at this time that rabbits would also not be suspectible.  

Posted By BinkyBunny on 07/31/2010 11:43 PM

I just recently discussed this with my rabbit-savvy vet  and she discourages grass clippings in large amount.   Moderate amounts INCLUDED  in the diet (not the main part of it though), should be okay.   She said that the reason for this is that excessive fresh, new grass can cause some muscular weakness in cows and horses — called “grass staggers”.  Though it’s not fully clear if rabbits get this, there is no reason to think at this time that rabbits would also not be suspectible.  

For what it’s worth, grass staggers is only caused by 2 specific species of grass, rye and paspalum.  So if you’re not feeding either of those, grass staggers is not an issue.  It’s caused by a fungus that grows on those two types of grass, that becomes toxic.  I’ve never actually even seen grass staggers in person, basic pasture management (avoiding those grasses in your pastures) eliminates that risk entirely.  In buns, it would be simply not giving them those types of grass.

In horses, the bigger issue with grass clippings is that grass clippings, due to their high water content, ferment VERY quickly, especially when exposed to heat.  Feeding the fermented grass can cause serious digestive problems like colic.  If the horse consumes ALL of the clippings within a short period of time, then you’re okay.  But if the clippings are allowed to sit, fermentation is a very high risk.

Interesting.
At any rate, never give fresh grass that sat, and grass clippings are really not suitable for rabbits at all. Fresh grass, if introduced gradually, and free from chemicals and noxious weeds can be fed but you should always be able to identify the grass species you are using to look up about issues such as the staggers or other phenomena.

I see your question really was how much to give: you can feed it like hay, unlimited, but only once your rabbit has gone through a gradual switch from hay to grass over a period of a few weeks. Do you know what kind of grass it is? It can be hard to tell sometimes if the grass has not grown seed pods yet.