I agree with our guest Snowdee.
The problem with using milk in a dough recipe is that there is something in the milk, either an enzyme or a protein, that interferes with the normal action of the yeast so that the end result is a soft, and slack dough. Those few pizza operators who do use milk usually use a specially processed milk using high heat. It is sold by bakery products suppliers and is called a high-heat or baker's grade milk. When using regular milk, the conventional advice is to scald it and let it cool before using. Apparently this is to disable the offending enzyme or protein in the milk. If a dry non-fat milk is to be used, the advice is to reconstitute it in water, scald it and let it cool before using. It's not clear whether scalding is necessary for pasteurized milk, but most people scald and cool it anyway.