Why your 4 kg dog will be fine after a cup of sprouts
Roasted Brussels sprouts break down into simpler compounds during cooking, which makes them far gentler on a dog's system than raw ones. For a small dog like yours, a cup is a sizable portion but not enough to cause more than mild digestive rumbling. The fiber content may lead to looser stools or extra gas over the next 12 hours—this is normal. Just ensure fresh water is available to help his gut process the extra roughage.
Watch for any unusual lethargy or refusal to eat his next meal, though this is unlikely. If he starts vomiting repeatedly (more than twice in an hour) or shows signs of abdominal pain like a hunched back, call your vet. These would be rare reactions but worth checking given his small size relative to the amount eaten. For now, skip his next scheduled snack to let his stomach settle.
How to keep curious cats out of dog food
Your 3 kg cat faced no risk here because she didn't ingest any sprouts, but their shared meals could become problematic. Cats often investigate dog bowls out of curiosity, especially if the food smells appealing like roasted vegetables. Unlike dogs, cats lack the enzymes to efficiently break down plant matter, so even small amounts could cause indigestion or diarrhea.
Feed your pets in separate rooms or at different times to prevent scavenging. If that's not possible, supervise mealtimes and remove the dog's bowl immediately after he finishes. Cats are more likely to steal food when the dog walks away leaving scraps behind. Consider elevating your dog's dish to counter height (if he can reach it safely) to create a physical barrier.
Spotting the difference between normal gas and trouble
Dogs digest fibrous vegetables more slowly than meat, so expect some audible gut sounds and perhaps a few extra odors over the next day. Normal gas from Brussels sprouts tends to be intermittent and doesn't distress the dog—he might seem slightly more restless than usual but will still play and nap normally. The gas should taper off within 24 hours as his system processes the fiber.
Concerning signs would include straining to pass gas without success, whimpering when his abdomen is lightly touched, or attempting to vomit without bringing anything up. These suggest possible gut irritation or a rare blockage, though the soft texture of roasted sprouts makes obstruction highly improbable. Trust your instinct—if his behavior seems off rather than just gassy, a vet check rules out complications.
When to relax and when to stay alert
Most dogs handle cooked Brussels sprouts without issues, especially one-off portions like this. By tomorrow, your pup should be back to his routine with no lingering effects. The real risk would come from making this a daily habit—regular large servings could disrupt his nutrient absorption over time due to the sprouts' goitrogenic compounds interfering with thyroid function.
For tonight, simply observe him as you would after any dietary change. No need to withhold water or food (unless he vomits), but do avoid giving treats or rich foods that could further challenge his digestion. If he sleeps peacefully through the night and greets you with his usual energy in the morning, the incident is safely behind you. Next time, maybe steam the sprouts without oil or seasoning to make them even gentler on his stomach.
The full verdict, portion guidance and serving notes are collected on the Brussels sprouts food facts page.