Also called stem lettuce, celery lettuce, asparagus lettuce, or Chinese lettuce, celtuce is a vegetable grown for its thick stem.
It is crisp, moist and mild flavoured and is usually stir fried with strong flavoured ingredients.
So can guinea pigs eat celtuce, and if they can how much of it can they eat?

Lets take a look at their nutritional data and find out a bit more about them.
In particular, their calcium, sugar, fat, phosphorus, and acidic content is particularly of interest.
Celtuce, raw
Nutritional value per 100 g (3.5 oz)
Energyt75 kJ (18 kcal)
Carbohydratest3.65 g
– Dietary fibert1.7 g
Fatt0.3 g
Proteint0.85 g
Vitamin A equiv.t175 μg (22%)
Thiamine (vit. B1)t0.055 mg (5%)
Riboflavin (vit. B2)t0.07 mg (6%)
Niacin (vit. B3)t0.55 mg (4%)
Pantothenic acid (B5)t0.183 mg (4%)
Vitamin B6t0.05 mg (4%)
Folate (vit. B9)t46 μg (12%)
Vitamin Ct19.5 mg (23%)
Calciumt39 mg (4%)
Iront0.55 mg (4%)
Magnesiumt28 mg (8%)
Manganeset0.688 mg (33%)
Phosphorust39 mg (6%)
Potassiumt330 mg (7%)
Sodiumt11 mg (1%)
Zinct0.27 mg (3%)
(source: Wikipedia)
As you can see celtuce contains a little phophorus and calcium, it is quite acidic,and has a hint of fat.
It is a has a nice amount of vitamin c in it.
With that in mind, guinea pigs can eat celtuce but only two to three times a week due to its acidic content. But it is still a very good veggie for piggies to eat