Buttermilk contains lactose, and many adult cats are lactose intolerant.
Consuming buttermilk can lead to gastrointestinal problems such as vomiting, diarrhea, and gas.
Suggestions
If you notice any signs of lactose intolerance in your cat after consuming buttermilk, such as vomiting or diarrhea, avoid giving it to them in the future.
Instead, consider safer alternatives like lean meats.
Note: even if labeled as safe, any food can potentially cause allergies. When introducing a new food, please feed a small amount and observe your cat for any allergic reactions.