In this section we will cover topics you probably learned in school or early in your dairy nutrition career. Our aim is to provide a review of information you might still need – but haven't studied recently.

Producers often say they are feeding “whey” to their herds, when in reality they are feeding a whey by-product.  As nutritionists, it is important to know what is being fed. All by-products vary in sugar, protein and solids, as well as their value to the dairy cow.

To better understand whey as a by-product, it is best to understand the process:

• Sweet whey comes from cheese making. Ten pounds of milk make about 1 pound of cheese and 9 pounds of whey. Sweet whey is very valuable for other products.

• Sour whey is the other broad category of whey, primarily resulting from the manufacture of Greek yogurt, sour cream, cream cheese and cottage cheese. Much of this gets spread on fields or fed to pigs – and occasionally cows.

Sweet whey starts out at approximately 8% solids, consisting of 11% protein and 70% lactose (milk sugar), with the balance being minerals. The food and feed industries have long seen value in whey’s protein and lactose, developing processes to isolate these materials.

For example, sweet whey is commonly run through a ultrafiltration (UF) membrane to extract the protein fraction from the lactose fraction. The protein can then be concentrated, yielding 34% whey protein concentrate (WPC 34), often used for calf milk replacers; and concentrations up to as high as 90%, used for human food products. 

What is left over from the UF is whey permeate. Although this is occasionally sold as dairy feed, the considerable value contained in its high lactose level means that’s normally not the case. The majority of whey permeate is sent to dryers, where the lactose is crystalized and dried into a powder, utilized in human products such as baby formula. 

Unconcentrated permeate is about 6% solids. Many processing plants will concentrate the permeate through reverse osmosis (RO) up to 20% solids or more. The lactose in permeate is in the 65% to 85% range, with protein in the 3% to 8% range.  It is important when formulating rations with permeate to have the source analyzed for components, so you can be certain of the total sugar and protein being fed. 

Lactose in permeate is made up of two molecules, glucose and galactose. The organic acids produced from feeding these sugar molecules vary depending on the base ration fed, but primarily increase propionate (1, 2, 3).  While lactose appears to help increase microbial protein in early lactation, there is also an increase in butyrate, which then leads to an increase in BHBA levels. It’s important to monitor herds fed this product to make sure there isn't an associated increase in clinical cases of ketosis.

Another use of whey permeate is to ferment the lactose into a product called Fermented Ammoniated Condensed Whey (FACW), a high-energy form of ammonium lactate salt sold as a liquid called Lacto Whey{4). This product no longer contains sugars, having converted them to ammonium lactate salt, which can be used directly as an energy source (5) without additional fermentation. In vitro studies show there is a considerable amount converted to propionate as well.

If the permeate has the lactose crystalized and removed, the product left over is called de-lactose whey permeate (DLP). This product has some residual lactose left over from the drying process, as well as a high level of minerals and ash. DLP is the most common whey by-product fed to cattle. A typical analysis is 30% to 40% solids (made up of 50% to 80% lactose) and 12% to 20% ash.

It is very important to have DLP tested, because every company has different abilities to extract the sugar. Also, it is often combined with other products to create something unique. There is no set analysis or standard for DLP, and many branded products sold as containing whey are actually DLP, plus some other ingredients.


As you work with your clients, on-farm considerations for the different products are important:

• All these products are fed as a liquid, so large tanks are needed.

• DLP must be agitated, as the high levels of minerals and ash settle out in a few days.

• DLP can also freeze in the winter.

• In a salt form, FACW does not need to be agitated, nor will it freeze.

• DLP is often fed in the range of 10 lbs. per cow per day, while FACW is fed from 2-3 lbs. per cow per day. Often both products are fed at the same time.


1/ Sutton, J. D. The fermentation of carbohydrates in rumen contents of cows given diets containing a large proportion of flaked maize. 1969. Br. J. Nutri. 23, 567,

2/ DeFrain, J. M. A. R. Hippen, K. F. Kalscheur, D. J. Schingoethe. 2004. Feeding Lactose Increases Ruminal Butyrate and Plasma B-hydroxybutyrate in Lactating Dairy Cows. J. Dairy Sci. 87:2486-2494

3/ DeFrain, J. M. A. R. Hippen, K. F. Kalscheur, D. J. Schingoethe. 2006. Feeding Lactose to Increase Ruminal Butyrate and the Metabolic Status of Transition Dairy Cows J. Dairy Sci. 89:267-276

4/ Marriott, T. A. 1985. Ammonium lactate – feedstuff and feedstock. J. Society of Dairy Tech, Vol. 38, No. 4

5/ R. S. Emery, L. D. Brown, C. F. Huffman, T. R. Lewis, J. P. Everett, C. A. Lassiter. 1961. Comparative Feeding Value of Lactic Acid and Grain for Dairy Cattle.  J. Anim. Sci. 20:159-162.



 Gerald Poppy, DVM, MBA, is President, Packerland Whey Products. Contact him via email: or phone: 970-215-8550