Most pets are lactose intolerant when they reach adulthood. The reason is that, with age, they loose the ability to produce lactase, the enzyme that digests lactose, milk´s sugar. Lactose can cause vomiting, bloating and diarrhoea. When a dog or a cat has been unweaned and they eat solid foods, nutritionally speaking, they don’t need milk. However, if your pet enjoys the occasional bowl of milk, give it only lactose-free milk diluted in water. For cats, there are special formulas available in the market.