There are different types of whey: liquid whey and dried whey. Acid whey is generally a liquid whey. The production of cottage cheese yields acid whey. Its pH is about 4.0. Sweet whey is a by-product of the production of swiss, cheddar or mozzarella cheese. Its pH is approximately 6.0. The two kinds of whey differ somewhat in their usefulness. Sweet whey is less stable than acid whey during storage. It will lose up to 40% of it nutritional value if stored longer than 24 hours. Acid whey has a lower nutritional quality than sweet whey. Liquid acid whey can be successfully fed to pigs, but additional protein will be needed if good performance is expected. Acid liquid whey differs from sweet liquid whey in that it cannot replace supplemental protein in the diet.
Whey powder is a dried whey. Dried whey is a by-product of cheese manufacturing and a kilogram contains about the same amount of nutrients as 14 kg of liquid whey.
Dried whey is routinely added to diets of pigs weaned at an early age (21 days or less) as a source of milk protein and sugar (lactose). Numerous studies have demonstrated improved performance of pigs fed whey in starter diets.
While levels of 10% to 30% whey are commonly used in starter pig diets, some research has indicated that dietary levels of 30% to 45% dried whey can be added to the diet without depressing performance. A routine level of whey in pig starter diets in the U.S is 20%.
There are some differences between various sources of dried whey. If whey is excessively heated, it will result in a brownish color, indicating caramelization of the sugar (lactose). This lowers the feeding value of the product. White color is desirable, although some good quality whey may have a pinkish or yellowish color from carry-over of the cheese color. There are several forms of dried whey products such as partially delactosed whey, partially demineralized whey, and partially delactosed and partially demineralized whey. The amount of lactose and/or minerals removed from the dried whey will affect the actual amount of protein and ash present. Delactose whey is not recommended for use in baby pig diets.
There are some mechanical problems (such as bridging in the feeders and clogging in the feeding system because of moisture absorption) when feeding a 20 percent dried whey diet in meal form. Therefore, diets containing large amounts of milk products (> 20 percent) should be pelleted.
Dried whey and, to a lesser extent, dried skim milk are the most common milk products used in starter diets. Dried whey is high in lactose, has excellent quality protein, and is usually cheaper on a per unit of protein basis than dried skim milk. The level of protein in whey is lower than dried skim milk (12 vs 33 percent), so whey is not a direct substitute for dried skim milk. Levels of 20-25 percent edible grade dried whey maximize performance of starter pigs, but as little as 10 percent is beneficial. Levels higher than 10 percent tend to cause bridging in feeders when the diet is in meal form. When quality is an important consideration for weanling pigs. Human edible whey, rather than feed grade, is recommended for use in starter diets. The main quality factors to look for when buying whey are:
Lactose content --greater than 72 percent;
Protein content --greater than 12 percent;
Ash content --not greater than 9 percent;
Color --generally the lighter the better;
Salt --less than 3 percent;
Lysine --greater than 9 percent.