A supplement can be own's own expressed breast milk, infant formula or donor breast milk that's been screened and pasteurized.
Alternative Feeding: Supplementing a Breastfed Baby
The Best Ways to Transition From Breastmilk to Formula – The Baby's Brew
Supplementing Breastfeeding With Formula
Homemade Baby Formula: Your Ultimate Guide
Working Together: Breastfeeding and Solid Foods
How to Transition From Breastfeeding to Bottle
Supplementing With Formula: How to Combo Feed Your Baby
It's Okay Not to Breastfeed
Help! My Baby Refuses To Breastfeed But Will Take A Bottle — Milkology®
Alternative Feeding: Supplementing a Breastfed Baby