Greenleaf Farms

Skim milk may be used in place of water as a drink for poultry, it is always cheaper than whole milk unless one lives on a farm with milch cows; goat milk is always an expensive product unless again you are literally swimming in it.

Milk that sours during the day and turns to a semisolid form (clabber) is still satisfactory for supplying the moisture needs of poultry. 

Giving chickens nothing but milk as a drink is equivalent to the use of about thirteen pounds of dried milk in each hundred pounds of feed. This practice will reduce the other feed consumption by about 13 per cent. It also will supply all of the protein feedstuff needed for the laying, breeding, or fattening ration. 

Liquid skim milk and buttermilk are generally cheaper than the condensed and dried forms when compared on the basis of the same solid content, because the evaporation of water from milk is an expensive process. 

Condensed milk, also known as semisolid, is milk in which part of the water has been removed. It exists in a semisolid or paste form. Condensed milk varies greatly in moisture content. The products on the market generally contain 26 to 30 per cent solids, the remaining 70 to 74 per cent being water. The solids in condensed milk have about the same nutritive value as those in liquid or dried milk.

A gallon of liquid skim or buttermilk is equal to 3 pounds of condensed milk, which is very cost prohibitive to feed because the cost of removing all the water and the can.  Plus Carnation, has historically marketed as a substitute for heavy cream, see this ad from the classic Burns & Allen tv show.

Instead if you desire to feed your chooks milk, look for dried skim milk or dried buttermilk that is marketed for farm feeding purposes.  Typically more buttermilk than skim is used as most of the skim milk produced is marketed for human consumption.  The Vitamin G (B12) content of both kinds of milk will vary as well.  Remember Vitamin G is an essential vitamin for them.