For all you know, if you don't know the difference, you may have been drinking catmilk all these years.
A simple test has been devised by an eminent biologist.
He has a miniature milking machine, based almost exactly on the standard cow milking machine. This can be bought or rented through Woolworths. This is best performed when the cat has kittens
Connect the machine to the cat. Always ensure that it is a female, as this could cause the male cat a great deal of embarrassment. Milk the cat as per the instruction leaflet.
Next prepare two bowls of weetabix. In one bowl, put the recently milked catmilk and in the other bowl, put in the cows milk.
Hold the kittens back until both bowls are equidistant apart. Then let the kittens go. The kittens will go to the bowl with the catmilk in. Hope this helps. P.S. If you have young children, see which bowl they go to. It's great fun.