Can a 4 month old cocker spaniel be fed once a day?

It could but it is better to leave food down with it all the time because of how much he needs. If you persist in feeding him once a day, give him about 2 1/2 cups to make sure he isn't going hungry and leave it down all day because he will not eat it all at once. Dogs have a tendency to eat and then snack from time to time.