Why quantity matters less with plain barley
A quarter cup measurement sounds significant, but for plain cooked barley, it's more about volume than toxicity. That amount would weigh roughly 40 grams — substantial for a cat meal, but not dangerous as a one-time fiber source. Your 5 kg cat's digestive system will process this like an extra-large portion of roughage, not like a toxic dose.
Compare this to toxic foods where tiny amounts matter: a quarter cup of chocolate or grapes would be catastrophic. With barley, the main consequence is likely some digestive rumbling and possibly bulkier stools as her body moves the fiber through. There's no metabolic toxin at work here.
The weight difference that doesn't change risk
Your 3 kg cat avoided the barley entirely, but even if she'd nibbled some, her smaller size wouldn't increase concern. Unlike substances where body weight determines toxicity thresholds, plain barley's safety isn't dose-dependent in that way. A 3 kg cat could safely eat proportionally the same amount as her 5 kg companion.
The only weight-related factor would be stomach capacity — a quarter cup might make the smaller cat feel uncomfortably full faster. But with barley's high water content and swelling fibers, both cats would likely stop eating before reaching truly excessive amounts on their own.
Overnight digestion timeline clues
Since the barley was eaten hours ago, any immediate reaction would already be apparent. The lack of vomiting or diarrhea overnight is a good sign that your cat tolerated the unusual meal well. Barley's effects tend to manifest in stool changes rather than acute symptoms.
By now, the barley has moved from her stomach into the intestines, where fiber's benefits (or mild irritant effects) occur. You might notice increased litter box visits today as her system processes the bulk, but this isn't diarrhea — just more frequent elimination of normal stool with higher volume.
Preventing future grain raids
Cats remember food sources with remarkable precision, and your barley-eater now considers this a validated snack option. Unlike dogs, cats often prefer grazing to gorging, so she may return seeking smaller portions repeatedly. A truly cat-proof container is essential — many can open snap-lids or knock over unstable bins.
Consider storing cooked grains in the refrigerator behind a child-proof latch, as some determined cats learn to open standard fridge doors. For dry barley products, metal canisters with tight-fitting lids work better than plastic, which persistent cats can eventually chew through.
The full verdict, portion guidance and serving notes are collected on the Barley food facts page.