While not directly toxic, most adult cats are lactose intolerant due to a lack of the enzyme lactase. Ingesting milk can lead to gastrointestinal upset as the undigested lactose ferments in their gut. It is best to avoid giving milk to cats.
How It Affects cats
Lack of lactase enzyme leads to undigested lactose fermenting in the gut.
Toxic Compound
Lactose
Disclaimer: This information is for educational purposes only. Always consult your veterinarian before making changes to your pet's diet.