The verb "feed" means to give food to someone or something. It is commonly used when talking about providing sustenance to animals or babies.
For example, if you give food to your pet dog, you can say "I fed my dog this morning." The past tense "fed" indicates that the action of providing food to the dog has already happened.
In the context of human infants, parents often use the verb "feed" when talking about giving milk or solid food to their babies. For instance, they might say "I fed my baby formula before bedtime." Here, "fed" shows that the action of nourishing the baby has been completed.
In conclusion, "feed" in the past tense is "fed" and it is used to describe the action of giving food to someone or something.