Whey has always been regarded as an acceptable fodder, mainly for pigs. However, the fluctuating supply and solids content have made the direct use problematic.

Tests made in Denmark more than 100 years ago with feeding pigs concluded that:

• 1 kg of skim milk could be replaced by 2 kg of whey
• 1 kg of barley could be replaced by 12 kg of whey
  Pigs of 50 kg or more can drink about 15 kg of whey per day.

However, the requirements to the quantity and quality of the bacon and the meat have been intensified, and breeding has provided pigs able to utilize a greater amount of protein from the food, which means that if the pigs should have whey as the only protein source, the amount of water from the whey would cause problems in the way of digestion. In order to meet these problems a mixture of whey and skim milk (50/50) has been used, either direct or evaporated to 20% TS.

Whey used for sows has proved to be a good idea, partly because they have a great need for liquids (15-25 kg/day), partly because of a great need for vitamin B, and whey contains a great amount of especially B₂ (riboflavin) and pantothenic acid.

For cattle feeding liquid whey has also proved to be valuable, however, when 2-4 months old a mixture of skim milk and whey is recommendable, and not until the calf is 4 months old, can it manage pure whey in an amount of 10-15 kg/day. It will be profitable to use liquid whey until they are 15 months old, as it can replace a great amount of concentrates or skim milk. It has even been proved that fatted calves had bigger daily growth, and the bodies and the yield were much better than for fatted calves fed on the same amount of feed units in the form of skim milk.

From the above it can be seen that liquid whey can easily be used for feeding pigs and calves. However, due to the big quantities needed and the way the whey has been treated at the consumer's place (very often the whey is days old, fermented and there-fore contains by-products leading to malnutrition), the use of liquid whey is not so attractive, especially in large stock holds.

Consequently, the factories are very often taking advantage of spray drying the whey thus transforming it into a powder. This means that the keeping quality of the whey is prolonged, the solids content of the dried product is constant, and seasonal variations in the supply are avoided.