Rabbits can die if fed too much Iceberg lettuce - it contains something - can't remember what now - which is really harmful to them. Other lettuce is ok but doesn't give them anything nutritionally.
You've got me intrigued Taz so found the following:-
"Finally, it is often believed amoung rabbit breeders that
Rabbits should not eat some lettuces (such as iceberg) as they contain a substance called laudanum which can be harmful in large quantities.
RSPCA: Rabbit Diet Myths
But this is disputed because
Lettuce does not contain laudanum. Edible lettuce does contain a chemical called lactucin which is a component of lactucarian. Lactucarian is the milky fluid found in some species of lettuce and occurs in much larger amounts in wild lettuce, Lactuca virosa.
Lactucarium has sedative and analgesic effects. It creates a sense of mild euphoria. The milky exudate resembles that of opium and it can also be reduced to a thick substance which can be smoked in the same way as opium. As a result of which it acquired the name ‘lettuce opium’.
Edible lettuce, Lactuca sativa, does not even contain lactucarium although it does contain lactucin which is in lactucarium.
Lettuce for Rabbits and Guinea Pigs (note that rabbits and guinea pigs have different digestive systems, this link is included for the information on lettuce composition).
It is not known if lactucin turns into lactucarium during the digestive process in the rabbit, there are some accounts of rabbits appearing sedated after ingesting large quantities of lettuce. Regardless of the laudanum/lactucin status, there's no reason to feed iceberg because of the low nutrient value"
I'd no idea Iceberg lettuce was so potent!
Sorry for going off topic ladies
