I need to ask few more questions before answering your query. Early consultations can prevent complications. Kindly contact me on whatsapp chat  (84960595 six five) Dr Faisal Zoheb MBBS , MD PAEDIATRICS , PGPN (BOSTON), FELLOWSHIP IN NEONATOLOGY ( Newborn and vaccination specialist )

If you give cow milk or buffalo milk dilute it with water with 50 -50 . It will be better and most cases baby will accept it

Greetings It is common for some toddlers to have difficulty transitioning to cow's milk if they experience digestive discomfort or constipation. You might try introducing very small amounts of whole milk mixed with his current formula, gradually increasing the ratio over several weeks. Alternatively, goat's milk or lactose-free varieties may be easier for him to digest initially. Ensuring he consumes plenty of fiber-rich foods and water can also help manage the "tight" stools you mentioned.

It's common in few kids so you need to give small quantity of milk to sensitise their body and gradually increase quantity

Consult with Pediatrician physically for further evaluation and treatment

Some children take time to adjust to regular milk, and this may be due to mild lactose intolerance, sensitivity to milk protein, or simply difficulty digesting larger quantities at once. Constipation (tight potty) can also happen with buffalo milk because it is heavier and higher in fat.