Why mouldy grapes are a double threat
The blue-green fuzz you saw contains tremorgenic mycotoxins that attack the nervous system separately from grape toxicity. These can cause violent seizures within hours, sometimes before kidney symptoms appear. Meanwhile, the grapes themselves may have fermented into alcohol, adding disorientation risks.
Your 12 kg dog ate roughly half a typical toxic grape dose (the usual danger zone starts around 10 grapes for mid-sized dogs). But mould changes the math — even one mouldy grape could warrant emergency care. Watch for twitching eyelids or unsteady walking alongside typical grape toxicity signs like lethargy.
How long grapes sat out changes risks
Grapes left for days grow mould while also losing water content, concentrating their unknown toxic compound. Wrinkled skins suggest dehydration made them more potent than fresh fruit. If the bowl was in sunlight, heat could have broken down the grapes' natural acids into harsher irritants.
Dogs sometimes scavenge rotting fruit precisely because fermentation makes them smell sweeter. This means your dog may have eagerly eaten all six rather than spitting some out. Time matters here — mould toxins act fast, so don't wait for symptoms if ingestion was within the past two hours.
The 12 kg factor in treatment plans
At this weight, your dog is large enough to handle standard IV fluid rates but small enough that six grapes could overwhelm the kidneys. Vets calculate fluid doses by weight, aiming to maintain urine output at about 1-2 ml per kg hourly. They'll likely hospitalize for continuous monitoring.
Bloodwork will check liver enzymes alongside kidney values since mould toxins often target both organs. Your dog may get muscle relaxants if tremors start, but these won't prevent grape-related kidney damage — that requires separate treatment. Bring a photo of the mould if possible to help identify the strain.
When to escalate beyond your regular vet
If your dog develops seizures or can't stand, transfer to a 24-hour ER clinic immediately. Standard clinics may lack the equipment for round-the-clock care that severe mycotoxin cases need. Neurological signs typically peak within 6-12 hours but can recur days later.
Recovery depends on which toxin caused more damage — kidney injury from grapes often has longer consequences than mould's nervous system effects. Even after discharge, your dog may need weekly blood tests for a month to catch delayed kidney decline.
The full verdict, portion guidance and serving notes are collected on the Grapes food facts page.