Also known as Chinese Cabbage, Bok choy is a leafy green chinese veggie that belongs to the cabbage family.
Its ribbed leaf stalks and oval green leaves are usually used for stir frying or being steamed.
But can guinea pigs eat bok choy, and if so how much can they eat?

Lets take a look at its nutritional data.
As usual, the things we are looking for are low amounts of phosphorus, calcium, fats, sugars, and oxelate acid.
A nice amount of vitamin a and c would be nice too.
image flickr
Total Fat 0.2 g 0%
Saturated fat 0 g 0%
Polyunsaturated fat 0.1 g
Monounsaturated fat 0 g
Cholesterol 0 mg 0%
Sodium 65 mg 2%
Potassium 252 mg 7%
Total Carbohydrate 2.2 g 0%
Dietary fiber 1 g 4%
Sugar 1.2 g
Protein 1.5 g 3%
Vitamin A 89%
Vitamin C 75%
Calcium 10%
Iron 4%
Vitamin D 0%
Vitamin B-6 10%
Vitamin B-12 0%
Magnesium 4%
source usda
As you can see it contains no phosphorus, oxelates, and a low amount of sugar, but it does contain a significantly high amount of calcium which is not good.
But as you can see its vitamin c and a content is amazingly good.
So going on the information provided, guinea pigs can eat bok choy but only sparingly, once or twice a week at the very most.
Can guinea pigs eat bok choy leaves?
Yes they can, again they have a terrific amount of vitamin a and c, but because of their calcium content only feed to them once or twice a week at the most.