How overnight mould changes the game
That green mould growing on bread left out overnight isn't just surface fuzz — it's likely producing mycotoxins throughout the entire slice. Unlike fresh bread where you can trim off bad spots, overnight exposure means the toxins have spread further into the food. For a 15 kg dog, even a full contaminated slice may not cause severe poisoning, but the risk depends on the mould type.
Different moulds produce different toxins, with some causing immediate vomiting while others trigger neurological symptoms like tremors or seizures hours later. The visible green patches are just the fruiting bodies — the invisible hyphae threads permeate the bread, making it impossible to judge safety by scraping off what you see.
The first 12 hours after ingestion
Mould toxins typically act fast if they're going to cause problems, with initial signs often appearing within 2-6 hours. For your dog's size, watch for excessive drooling, pawing at the mouth, or repeated swallowing — these suggest nausea building before actual vomiting occurs. The stomach may gurgle loudly as it reacts to the irritants.
Some dogs experience diarrhea before vomiting, while others just become unusually restless, pacing or seeking cool floor surfaces to lie on. These early signs are easy to mistake for general stomach upset, but with known mould ingestion, they warrant closer monitoring for progression to more severe symptoms.
When neurological symptoms raise the stakes
Certain moulds produce tremorgenic mycotoxins that affect the nervous system, usually manifesting 6-24 hours after eating. Early signs include fine muscle tremors (often starting in the face or legs), exaggerated reactions to sounds or touch, or difficulty standing steadily. These symptoms tend to worsen over several hours if untreated.
For a 15 kg dog, the dose from one mouldy slice may only cause mild tremors, but individual sensitivity varies greatly. Small breeds or dogs with pre-existing neurological conditions can react more severely to the same amount. Any twitching, uncoordinated movements, or apparent stiffness means immediate veterinary attention is needed.
Long-term monitoring after mould exposure
Even if your dog seems fine after 24 hours, monitor for delayed reactions like loss of appetite or unusual lethargy over the next few days. Some mycotoxins can cause liver inflammation that only becomes apparent through jaundice (yellow gums) or increased thirst and urination later on.
Dogs that recover from mould poisoning often have temporary digestive sensitivity, so offer bland food for several meals afterward. Prevent future incidents by storing bread in airtight containers and discarding questionable items immediately — dogs often counter-surf for stale bread left too close to the edge.
The full verdict, portion guidance and serving notes are collected on the Plain bread food facts page.