Also known as Boston lettuce, butterhead lettuce is known for its large, ruffle outer leaves and it’s blanched head.
It is tended to be grown a lot throughout Europe but is eaten around the world.
So can guinea pigs eat butterhead lettuce, and if they can how much of it can they eat?

Lets take a look at its nutritional data and find out more.
In particular, its calcium, fat, sugar, phosphourus, and acidic content is of interest as far as guinea pigs are concerned.
image source flickr
Lettuce (butterhead)
Nutritional value per 100 g (3.5 oz)
Energyt55 kJ (13 kcal)
Carbohydratest2.23 g
– Sugarst0.94
– Dietary fibret1.1 g
Fatt0.22 g
Proteint1.35 g
Watert95.63 g
Vitamin A equiv.t166 μg (21%)
– beta-carotenet1987 μg (18%)
– lutein and zeaxanthint1223 μg
Thiamine (vit. B1)t0.057 mg (5%)
Riboflavin (vit. B2)t0.062 mg (5%)
Pantothenic acid (B5)t0.15 mg (3%)
Vitamin B6t0.082 mg (6%)
Folate (vit. B9)t73 μg (18%)
Vitamin Ct3.7 mg (4%)
Vitamin Et0.18 mg (1%)
Vitamin Kt102.3 μg (97%)
Calciumt35 mg (4%)
Iront1.24 mg (10%)
Magnesiumt13 mg (4%)
Manganeset0.179 mg (9%)
Phosphorust33 mg (5%)
Potassiumt238 mg (5%)
Sodiumt5 mg (0%)
Zinct0.2 mg (2%)
source wikpedia
As you can see butterhead lettuce contains a little phosphorus and calcium, and a a little acidic, it contains a hint of fat and some sugar.
It’s vitamin c content is also not that high.
With that in mind, guinea pigs can eat butterhead lettuce but only one to two times a week due to its phosphorus and calcium content. It doesn’t offer that great a nutritinal benefit to gujnea pugs and there are definitely better veggies for them to eat.