Wilbur is a pampered pig, treated like a baby by Fern, who saved him from being slaughtered. As the runt of the litter, poor little Wilbur was never going to get much in the way of tender loving care from his mother. But Fern's more than happy to take on the role of mother to this delightful piglet. As we're told at the beginning of chapter 2 of Charlotte's Web, she loves him more than anything.
Among other things, Fern's mothering of Wilbur involves feeding him with milk. In due course, Wilbur learns to love his milk, and he is never happier than when Fern's warming up another bottle. Wilbur receives his first bottle every morning when Fern gets up. She warms the milk and ties on his little bib before she holds the bottle for him.
Wilbur receives his second bottle from Mrs. Arable at around noontime, when Fern's at school. In the afternoon, when Fern returns home, she leaps off the school bus and makes a beeline for the kitchen, where she fixes another bottle of milk for her beloved piglet. She feeds him twice more each day, once at suppertime and again just before it's time for bed. All in all, Wilbur is fed milk five times a day, once by Mrs. Arable and four times by Fern.