My 5 mth old son doesn't drink a full bottle anymore, he was breasfed and had a big appetite.?

now he'll only drink 4 oz at a time, do you have any tips to help him to take more. I did introduce solids (rice, baby porridge) but cut back as my son cut back on his milk. also he seems to drink a good portion of his milk at night, how can I can get him to drink more milk during the day?