A nutritious vegetable with one real catch
Broccoli is safe for guinea pigs in the sense that nothing in it is toxic to them, and it brings genuine benefits: vitamin C, which guinea pigs cannot make for themselves, plus fibre and a range of minerals. The catch is in the family it belongs to. Broccoli is a brassica, like cabbage and kale, and brassicas ferment as they digest, producing gas in the guinea pig's large and delicate gut. A little gas passes unnoticed; a lot can leave a pig bloated, tight-bellied and miserable, and true bloat is a painful condition. So the honest answer to whether guinea pigs can eat broccoli is yes, in the spirit of an occasional guest vegetable, not a resident one.
Which parts, and how much
The whole plant is usable: florets, the stalk peeled and sliced, and the leaves, which many pigs prefer to the florets themselves. Start with a single small floret, roughly thumbnail-sized pieces for an adult pig, and offer broccoli no more than a couple of times a week alongside that day's other vegetables rather than as the whole serving. Wash it first, and serve it raw, since cooking softens it into a form pigs handle less naturally and strips some of the vitamin C you are feeding it for. If your guinea pig has ever had a gassy or bloated episode, be more conservative still, keeping broccoli rare or skipping it in favour of peppers and leafy greens that deliver vitamin C without the fermentation.
Rotating broccoli among safer staples
The easiest way to keep broccoli in its proper place is to build the weekly menu around dependable daily vegetables and let broccoli visit. Bell peppers and leafy greens such as romaine or coriander can carry the daily vitamin C load, with broccoli, a little carrot, cucumber or a herb rotated in for interest across the week. Rotation also protects against the quieter issue that broccoli, fed heavily over time, contributes more calcium than a pig needs, and guinea pigs are prone to bladder sludge when calcium runs high. Thinking in weeks rather than days keeps every individual vegetable in sensible proportion without any measuring or fuss.
Signs you have overdone it
After broccoli days, glance at the pig as well as the bowl. A guinea pig who is hunched, quiet, off the rest of his food or producing a visibly rounded, drum-tight belly is a pig with too much gas, and one who stops eating or passing droppings needs a veterinarian promptly, because a guinea pig gut that stalls is an emergency, not a wait-and-see. Mild softness in the droppings after a first taste usually settles by simply offering less next time and spacing the servings further apart. Most pigs handle their small floret perfectly happily, and the watchfulness is about proportion, not fear: broccoli earns its place on the menu as long as it stays the occasional extra it should be.
An occasional food stays occasional when the feeding is shared and visible, and KinsLe's Care Teams let everyone who feeds your guinea pigs see what was served and when, so broccoli lands as the now-and-then extra rather than creeping onto the daily menu.