I wasn't trying to argue the pros and cons of milk and dairy consumption, I was trying to ridicule the argument that fast growth of new born mamals is due to milk consumption and your how the doctor arrived to that conclusion.
New borns are "programmed" to grow fast. They do need energy to allow this growth, but consumption of milk is not the reason. There are a lot of baby humans who are dairy intolerant, they are fed with non-dairy replacements, and surprise, they grow at the same rate as other babies.
How much do they consume? What else do they consume?
That saying has been around for ages, but strikes me as one of those superficially smart sounding but actually kind of fundamentally misguided phrases that sometimes become popular. Unless someone is suggesting an all cows milk diet, I suppose.
It's also for the species that conquered the world by relying on smart use of animal resources for survival.
I see two legitimate uses nowadays for "cow milk is for calves": raising awareness about the cruel aspects of our relation with other animals and promoting breast feeding.