Your rabbit is having diarrhea after eating lettuce because:
White or light-coloured lettuces are low in nutritional value and lead to diarrhea in rabbits, so they should be avoided.
Dark-coloured lettuces have lots of healthy nutrients for rabbits but if eaten too much or too often, they can lead to diarrhea, so they should be restricted in the rabbit's diet. Dark-coloured lettuces can be incorporated in the rotation of daily "salad" greens, but they shouldn't be fed every day and they should only make up one part of the salad (so, don't offer a salad of Green Leaf, Red Leaf, and Romaine -- instead choose just one lettuce, and mix it with other greens like carrot greens and dandelion. You can then feed that same lettuce for a few days, if you want to get rid of it, but then avoid lettuce entirely for another few days; and, for the sake of variety, next time you buy lettuce, buy a different sort).
Young rabbits under 12 weeks of age should not have any fresh foods: just hay, pellets, and water. From 7 to 12 months, the rabbit can transition to an adult's diet; but, from 12 weeks to 7 months, fresh dark-coloured leafy greens (like lettuce) should only make up a very small portion of the rabbit's diet.
by having romaine lettuce
My pet rabbit Billy Bob loves to eat fresh lettuce.I'm having a bacon, lettuce and tomato sandwich for lunch.I didn't eat the lettuce it had a slug on it.
Peter Rabbit
If you feed a small amount of lettuce to domestic rabbits, it will be fine. If you give a whole leaf, the rabbit will have an upset stomach and will have a temporary case of diarrhea.
That means your rabbit has a case of diarrhea. The most common reasons for diarrhea are,Your feeding it cold food (this is the most common cause)Your rabbit ate an unclean piece of foodYour rabbit ate too muchToo much fruitYou gave your rabbit houseplantsFed your rabbit tomato, lettuce, and/or cucumber (also very common diarrhea cause)Fed your rabbit old or wilted greensFed your rabbit a green part of a potato
Iceberg lettuce can NOT cause a rabbit death but it has no nutrients value and it COULD get your rabbit sick. Overall, iceberg lettuce for your rabbit should be avoided.
The person who got sick eating too much lettuce likely experienced symptoms related to excessive fiber intake, such as bloating, gas, and digestive discomfort. While lettuce is generally safe to eat, consuming it in large quantities can overwhelm the digestive system and lead to these issues. It's important to practice moderation when consuming high-fiber foods like lettuce.
Lettuce!! NEVER EVER feed a rabbit lettuce
Yes, rabbits can eat romaine lettuce, but only the dark-coloured parts (tear off the white/light-coloured bits and avoid entirely the heart or baby leaves). Too much romaine can lead to illness, so romaine can be included in the rabbit's "salad" but rabbits shouldn't eat lettuce every day. See the related question below for more details about the rabbit diet.
Anytime your rabbit develops diarrhea it's most likely because it's been eating too much food with a high water content, like fresh grass, lettuce, or fruit. Cut your rabbit's diet back to food pellets and dried hay, and you should notice the droppings becoming firmer and drier within a day or two. If this is not the case, you may need to get bunny into the vet for a check-up, since it could be a symptom of an illness. If all is well, you can carefully reintroduce a couple treat foods, watching closely each time to see if any cause a repeat of the diarrhea.
It is OK to give ANY rabbit a small amount of lettuce as a treat only, anytime. The only rabbit who can eat as much lettuce as they want is the wild rabbit who has access to herbs and minerals to counter balance the lettuce. Domestic rabbit owners should remember the tale of Peter Rabbit and what happened to him when he ate too much lettuce in Mr. MacGregor's garden.
There are a few human foods you can give a bunny: lettuce, apples, carrots, and pears, that's all I can think of right now. Only give the bunny tny, tiny portions at a time. Make these foods a treat, not a daily meal.