Butterhead lettuce is also known as boston or bibb lettuce and is a head lettuce that has a loose arrangement of leaves. It is known for its sweet flavour and tender texture.
So can rabbits eat butterhead lettuce at all?
Lets take a look at its nutritional data in particular its calcium, sugar, fat, fibre, sodium, phosphorus, and acidic content is of most interest as far as bunnies are concerned.
Lettuce (butterhead)
Nutritional value per 100 g (3.5 oz)
Energy 55 kJ (13 kcal)
Carbohydrates
2.23 g
Sugars 0.94
Dietary fibre 1.1 g
Fat
0.22 g
Protein
1.35 g
Vitamins
Vitamin A equiv.
beta-carotene
lutein zeaxanthin
(21%) 166 μg
(18%) 1987 μg
1223 μg
Thiamine (B1) (5%) 0.057 mg
Riboflavin (B2) (5%) 0.062 mg
Pantothenic acid (B5)
(3%) 0.15 mg
Vitamin B6 (6%) 0.082 mg
Folate (B9) (18%) 73 μg
Vitamin C (4%) 3.7 mg
Vitamin E (1%) 0.18 mg
Vitamin K (97%) 102.3 μg
Trace metals
Calcium (4%) 35 mg
Iron (10%) 1.24 mg
Magnesium (4%) 13 mg
Manganese (9%) 0.179 mg
Phosphorus (5%) 33 mg
Potassium (5%) 238 mg
Sodium (0%) 5 mg
Zinc (2%) 0.2 mg
Other constituents
Water 95.63 g
source wikipedia
As you can see butterhead lettuce contains quite a bit of phosphorus, a little calcium, but a lot of acidic content. This means that although rabbits are renown for eating lettuce, and they absolutely love it, butterhead lettuce is not very good for them to eat.
They are fine to have a nibble at it, but because of the amount of acidic content that it has in it, rabbits should not eat any more than that.
Image "Lettuce (4988502260)" by Dwight Sipler from Stow, MA, USA - LettuceUploaded by Jacopo Werther. Licensed under CC BY 2.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Lettuce_(4988502260).jpg#mediaviewer/File:Lettuce_(4988502260).jpg