Generally, kittens can drink their mother's milk, and their primary source of nutrition should be breast milk before they are weaned. However, feeding kittens cow's milk after weaning may not be suitable.
Here are some precautions to take when feeding kittens whole milk:
1. Lactose Intolerance: Adult cats typically lose the enzyme to digest lactose after weaning, a condition known as lactose intolerance. Therefore, most adult cats cannot digest the lactose in whole milk. Kittens may also gradually lose their ability to digest lactose after weaning, so feeding them whole milk may cause digestive problems such as diarrhea and abdominal pain.

2. Nutritional Imbalance: Pure milk is not a complete and balanced diet for kittens. Kittens need specific proportions of protein, fat, vitamins, and minerals to support their growth and development. Pure milk does not provide enough nutrients to meet these needs.
If your kitten needs a substitute after weaning, choose kitten formula specifically designed for kittens. These formulas are designed to mimic the composition and nutrition of a mother cat's milk, more closely matching the needs of kittens. If you have any questions about kitten feeding, it is recommended to consult a veterinarian for professional advice.