Infant Has Weight Loss After Switching To Cow's Milk From Formula, Frequent Motions. Is It Normal?

Hi My baby is 6+ month old, from starting baby is on formula milk, previously we were using NAN Pro 1 & now we started Nan Pro2. We also started giving him some solids twice a days, before some days we change the milk and start giving Cow Milk instead of Nan 2. After giving 2 days cow milk, we found that baby lost their half kg weight no loose motion at all, poops 2 times a day. then we stop giving cow milk & back to Nan2. My question is, it is normal baby loose weight first in when we change milk(cow milk) or should i start now giving whole(buffalo) milk. as i have read that cow milk don t have proper nutrition ? waiting for your reply. Thanks