The mothers milk carries antibodies to help protect the pups immune system it's called passive immunity and its passed to the pups from the first milk production by the mother. the milk is called colostrum and its a mix of protein, nutrients electrolytes and vitamins. This is important in new born as it helps the pups digestive system and enable them to fight of viruses and bacteria. The first 24 hours is vital that the pups feed and are one day old. after that the protection is gone. JMO seek advice from the vet