• Protection from infection. When a mother is unable to provide any or enough of her own breastmilk, donor breastmilk is often the preferred alternative to infant formula (or artificial milk). This is because donor breastmilk still contains many of the protective factors (such as immunoglobulins) which help protect premature babies from infection and are not present in formula which is prepared from cow’s milk.
• Protection from necrotising enterocolitis. Donor breastmilk may also have a protective role against the serious gut condition necrotising enterocolitis which mainly affects premature babies.
• Easier to digest. A preterm baby’s gut is very immature and is able to digest and absorb breastmilk more easily than formula milk. Premature babies are fed small amounts of breastmilk to help their gut mature and the volumes fed are increased gradually. This is also true for babies who have had gut surgery.

Useful link: http://www.unicef.org.uk/BabyFriendly/News-and-Research/Research/Miscellaneous-illnesses/Donor-breast-milk-versus-infant-formula-for-preterm-infants-systematic-review-and-meta-analysis/