Dairy Initiatives

Dairy

Department of Animal Science

D A I R Y   I n i t i a t i v e s   N E W S L E T T E R
V o l u m e   8      I s s u e   2      F a l l   1 9 9 9

Understanding Milk Protein

JIM LINN, Department of Animal Science, University of Minnesota
DANA ALLEN, Department of Animal Science, University of Minnesota
PAUL NIERMAN, Dairy Quality Control Institute

The value of milk is based on its composition. This is not only true from the producer side, but the consumer side as well. Consumers are looking for milk that's nutritious, has good flavor, and is low in fat. Protein is a component that can contribute flavor and nutrition without increasing the fat or calorie content of milk. This article will look at a few ways the protein content of milk can be increased.

Kinds of Protein

Milk protein, like feed protein, consists of both true proteins (proteins composed of amino acids) and nonprotein nitrogen (NPN) compounds. Both true protein and NPN are included in the total or crude protein. This distinction between true and total protein in milk is important, because only about 94 percent of the total protein in milk is true protein. The other 6 percent is in NPN compounds such as milk urea nitrogen. The NPN compounds benefit neither consumers nor the processing industry, since cheese yields are related to the true protein in milk and not the total protein.

If you haven't experienced it yet, you most likely will see a drop in your milk protein reported from the milk plant. The reason is that, with passage of the new federal order reform, milk protein will no longer be reported as total protein, but as true protein (Total minus NPN). This will decrease the typical milk protein value by about 0.18 and 0.2 percent units in most herds. Instead of a 3.2 percent protein test, the new value based on true protein will be 3.0 percent.

Increasing True Milk Protein

It's important to distinguish between increasing true milk protein percent and increasing yield. Any increase in milk with no decrease in protein percent will increase milk protein yield. Likewise, any increase in milk protein percent with equal or increased milk yield will increase milk protein yield. This distinction is important because you are, and will continue to be, paid for milk on yield or amount of components produced and not percentage of the component in the milk. Ideally, you want both milk yield and protein percent to increase. The points below refer to ways you can increase milk protein percentages.

Consider Genetics.  Jerseys and Guernseys tend to have a higher true milk protein percent than other breeds. Thus, genetic selection will have a big influence on the percentage of true protein in milk.

Aim for Quality.  Somatic cell count above 350,000 can increase the total protein percent, but lowers true protein. Mastitis lowers the true protein in milk by decreasing casein, the largest single true protein fraction found in milk, and increasing NPN compounds. Also, any tissue damage caused by infections adds NPN.

Think Young.  First-lactation heifers may have a slightly higher true milk protein percent. This may be due to lower incidence of or exposure to mastitis compared to older cows.

Keep Cool.  Heat stress tends to reduce true milk protein as well as milk fat percent.

Watch the Diet.  Nutrition can change true milk protein slightly (0.1 to 0.3 percent units). To increase true milk protein percent, you can increase the amount of nonfiber carbohydrates (NFC) in the diet by adding more grain (corn or barley) or increasing the availability of NFC through grain processing (fine grinding, steam flaking). However, high NFC levels in the diet depress milk fat percent and can cause acidosis problems. You need to balance enough NFC for good milk and milk protein production with enough fiber to maintain an acceptable milk fat percent.

Adding fat to the diet generally decreases milk protein percent but increases milk yield. In most situations, the increase in milk yield is equal to or greater than the decrease in milk protein percent, resulting in an increase in total protein yield.

Increasing the amount of crude protein in the diet will not increase milk protein percent. Increasing the amount of rumen undegradable protein (RUP) in the diet may increase milk protein percent if the correct balance of amino acids becomes available to the mammary gland. Supplementation of rumen-protected methionine and lysine has been shown in some studies to increase true milk protein percent. A lysine:methionine ratio of about 3:1 as either the percent of metabolizable protein in the diet or as percent of essential amino acids is recommended as the desired ratio for optimum milk protein percent and yield.

Feed additives (buffers, yeasts, B vitamins) will not affect milk protein percent.

Summary

In summary, increasing milk protein percent along with increasing milk yield will result in the greatest economic benefit to the dairy.

D A I R Y    I n i t i a t i v e s    N E W S L E T T E R
Volume 8     Issue 2    Fall 1999

Dairy Initiatives

Dairy

Department of Animal Science