While breast milk is the best, formula, in a way, is created specifically for babies while cow's milk is not. Infants cannot digest cow’s milk as completely or easily as they digest formula. Moreover, cow’s milk contains high concentrations of protein and minerals, which can put unwarranted stress on a baby's immature kidneys and cause fevers, diarrhoea etc. In addition, cow’s milk lacks the required amounts of iron, vitamin C, as well as other nutrients that babies need to grow strong and well. A lack of vitamin C could lead to low immunity and infections. In extreme cases, cow's milk may even cause iron-deficiency anaemia in some babies, since cow’s milk protein can irritate the lining of the stomach and intestines, leading to loss of blood into the stools. Cow’s milk also does not contain the healthiest types of fat for growing babies.
Based on the abovementioned reasons, your baby should not receive any regular cow’s milk for the first twelve months. You can start introducing cow's milk to baby's diet when he or she is older.
https://www.healthychildren.org/English/ages-stages/baby/feeding-nutrition/Pages/Why-Formula-Instead-of-Cows-Milk.aspx