Feeding for Milk Components and Milk Yield
Stephen M. Emanuele Ph.D., PAS
Westway Trading Corporation

At first glance feeding for milk components and milk yield may seem like a contradiction. After all, dairy nutritionists are taught that there is a negative correlation between the milk fat %, milk protein % and milk yield. As you increase milk yield, you expect the milk fat % and milk protein % to decline. This is referred to as a negative correlation. As one item increases the other correlated item decreases. One explanation for this phenomenon is that the increased volume of milk dilutes the quantity of milk fat and milk protein produced by the cow. This explanation assumes that the quantity of milk fat and milk protein produced by the cow does not change as milk volume increases. In this article, I will describe how you can increase both milk yield and milk components by feeding to optimize rumen function.

First, you can't increase milk yield and milk components simultaneously without increasing the amount of milk fat and milk protein produced by the cow. Your cows make milk fat from fatty acids. Fatty acids are the building blocks of fats. Fatty acids are classified according to the number of carbon atoms in their structure. For example, stearic acid is a fatty acid with 18 carbon atoms. Your cows get fatty acids from two processes. They can digest dietary fat and absorb fatty acids from their digestive tract. They can also synthesize more complex fatty acids from acetate and butyrate. Acetate and butyrate are short-chain fatty acids. They are by-products of fiber digestion (See diagram below). As you increase the amount of fiber digested by your cows, you increase the amount of acetate and butyrate produced in the rumen.

If you have a low butterfat test, two possible explanations are insufficient fiber in the diet and poor fiber digestion. Cows have a requirement for fiber. I balance the diet for the fiber requirement first, and then I worry about protein, energy and other nutrients. You should have at least 45% of the diet dry matter as forage and forage substitutes (cottonseed hulls) for high producing dairy cows. If forage quality is good, I can increase the percent forage in the diet dry matter from 45% to 50 - 55% percent. Poor fiber digestion can occur due to poor rumen function. A lack of effective fiber in the diet, a low rumen pH, excessive starch in the diet or over-feeding of certain types of fat can cause poor rumen function. Insufficient fiber in the diet and poor fiber digestion can lead to poor rumen fermentation which may result in insufficient acetate and butyrate production for optimal milk fat production.

You can optimize the digestion of fiber by feeding yeast culture and beet pulp in the close-up dry period and during lactation. Yeast culture can help to stabilize rumen pH, and increase the number of fiber digesting rumen bacteria. Beet pulp contains pectin and pectin is more digestible than cellulose and hemicellulose. Research with Westway Sweet Lac products has found that when you combine yeast culture, beet pulp and corn steep liquor, the number of fiber digesting rumen bacteria is increased compared to yeast culture alone (see table). A greater number of fiber-digesting bacteria will result in greater fiber digestion. The net result should be higher milk fat % and milk yield.

Table 1: Fiber Digesting Bacteria as a Percent of the Total Bacterial Population

In In Vitro Batch Culture

Incubation Time (hr.)

Control

Yeast Culture Only

Sweet Lac Lactation Formula

0

40

46.5

50

5

34

45

46

8

30

42

48

10

27.5

38

47

15

15

30

45

20

12

30

40

Source: Westway Sweet Lac Technical Presentation

If you want to increase milk protein, you are going to have to increase the supply of amino acids available to the cow. Your cows obtain amino acids from two sources. The bacteria in the rumen of the cow synthesize amino acids by combining ammonia and carbohydrates. These amino acids become part of bacterial protein. This bacterial protein is then digested in the small intestine and used to make milk protein in the udder (See diagram above). The second source of amino acids for the cow is dietary protein, which is not degraded in the rumen. This protein "bypasses" or escapes the rumen and is digested in the small intestine and used to make milk protein. The best way to increase milk protein is to increase the amount of microbial protein and high quality "bypass protein" available to the cow. You can increase the supply of microbial protein by optimizing rumen fermentation and replacing part of the starch in the diet with sugar. Sugar stimulates the growth of rumen bacteria. In some diets you may get a protein response with only 0.5-pound of supplemental sugar. In other diets it may require 0.75 to 1.25 pounds of supplemental sugar to get a milk protein response. Westway Sweet Lac Lactation formula is 39% sugar on an as fed basis. Feeding 2 pounds of that product would supply 0.78 pounds of supplemental sugar. In six feeding trials, replacing starch with Sweet Lac Lactation formula has increased milk yield an average of 5 pounds. The range in response was 3.3 to 7.8 pounds of additional milk. In the six trials, milk protein percent was increased between 0.05 and 0.2 points. Feeding sugar may also increase the glucose supply available to your cow. By increasing glucose you reduce the conversion of amino acids to glucose. It is unfortunate but true; your cow will use amino acids to make glucose when the glucose supply is insufficient. This reduces the amount of amino acids available to make milk protein.

In some diets, corn gluten meal will increase milk protein because it supplies the amino acid methionine, which is used to make milk protein. In other diets, the amino acid lysine may be limiting milk protein production. In those diets, you may get a protein response from feeding heat-treated soybean meal or canola meal. It appears the ratio of lysine to methionine in the diet can influence milk protein. A 3:1 ratio of lysine to methionine may help boost milk protein. Unfortunately, it is difficult to predict the ratio of lysine to methionine available to the cow. New products that provide "bypass amino acids" may be helpful in increasing milk protein. These products are expensive but may be justified in certain markets where dairy operations are paid a premium price for milk protein.

As you can see, it can be difficult to determine what may be limiting milk protein production on your farm. Sometimes it will just require a trial and error approach until you identify the limiting factor in your cow’s diet. If you optimize rumen function, increase the supply of glucose and increase the supply of amino acids you may be able to increase milk protein 0.1 to 0.2 points.