Infant formula can be used as a baby's sole food or in conjunction with breast milk when a baby is young, or with solids for older babies. Infant formula should always be prepared as directed, which means not using any type of milk in place of the water typically used for reconstituting formula. Whether you can safely add milk to prepared formula depends on the age of the baby and the type of milk you plan to mix in.
Infant formulas are designed to meet a baby's basic nutritional needs, although they lack some of the beneficial immune factors, enzymes and nutrients found in breast milk. If you choose to feed your baby formula, either as the sole food or as a supplement to breast milk, you can choose from ready-to-drink versions or concentrated liquid or powder forms that should be mixed with water to prepare them before feeding your baby.
Adding Cow's Milk
Always follow formula directions when preparing a bottle for your baby. This means adding only the specific amount of water required and nothing else, including cow's milk. Cow's milk is not nutritionally appropriate for babies under the age of 1, so it should never be used in place of water when making formula or mixed with already-prepared formula. Adding cow's milk could dilute your formula and cause nutrient deficiencies in your baby.
Mixing Breast Milk and Formula
For mothers who are both breastfeeding and supplementing with formula, mixing breast milk and prepared infant formula together is fine, since both contain adequate nutrition for a baby, but it might not be the best idea from a practical point of view. The goal when doing both breastfeeding and formula feeding is to maximize the amount of breast milk your child consumes, so if you mix the two, you might end up with some leftover milk-and-formula mix, which is a waste of precious breast milk. Instead, many mothers who use both foods try to offer the breast milk first and only feed formula after the baby has gotten her fill of breast milk. That way, any uneaten portion will be strictly from the formula bottle and no breast milk is wasted. You should also not make up formula using breast milk in place of water, since this can concentrate the nutrients, making it hard on your baby's kidneys.
Toddlers and Formula Mixing
Once your child is over the age of 1, you can mix prepared formula with cow's milk to make it more palatable for him if he doesn't like the taste of cow's milk. Gradually reduce the amount of formula and increase the amount of milk until he is willingly drinking cow's milk alone.