Farming Magazine - December, 2009
Dairy Nutrition: The Missing Link
Improving and Managing Milk Protein
For nearly a decade now, in many areas of the country, milk prices have been based upon total pounds of milk components in your milk rather than percentages. What this means for dairy farmers is that the more pounds of components—milk fat, protein and other solids—that are in the fluid milk produced, the more money they receive for that milk. Of course, increasing total milk production per cow per day will also increase total pounds of components, as well. However, the most revenue for your milk will be realized by both increasing the percentage of components while at the same time increasing total volume per cow.
Just a few years back, we saw how valuable milk protein could become when worldwide demand quickly overwhelmed supply. The price U.S. dairy farmers were being paid for milk protein more than doubled overnight, topping an unprecedented $4 per pound. The sleeping beast had been awakened, and dairy farmers and nutritionists were scrambling to figure out ways to increase the protein component in their herd’s milk. Even though the economic bubble has burst for the time being, we should all continue feeding and managing our herds to maximize milk protein no matter what the price is, because even at $2 per pound, the milk protein still contributes to over half of the value of your milk.
Milk protein is difficult to manipulate. From a nutritional point of view, it’s highly dependent upon both a proper amino acid supply to the cow’s udder as well as dietary energy balance. Research has shown that protein production is usually limited by the amino acid that is in shortest supply in relation to the cow’s requirements. That amino acid is called the “first-limiting amino acid.” It’s the missing link of the protein chain, and when it is not available, protein production will be stopped.
The majority of the protein that a cow metabolizes and then finds its way into milk comes from the expired rumen microbes. The amino acid profile of microbial protein is about as near as we can get to delivering the perfect combination of amino acids to the cow. In other words, the lysine, methionine, arginine, etc. must be available in the proper quantities. The rumen microbes provide 50 to 75 percent of the amino acids and the rumen undegradable protein (dietary bypass protein) provides the rest. The efficiency of converting dietary nitrogen to milk protein by the cow is fairly low (25 to 30 percent). So, the more microbial protein that can be absorbed in a cow’s intestines, the greater the chances of increasing milk protein and milk value.
The first step towards increasing milk protein is to make sure that the rumen is working as efficiently as possible, growing as many rumen microbes as possible. Rumen microbes will proliferate by maximizing dry matter intakes with highly digestible forages and making sure there is adequate soluble and degradable protein in the diet. Fermentation in the rumen must remain at consistent levels throughout the day, every day, to maximize microbial population and activity. Any interruption through a lapse in feeding schedules or an abrupt change in ingredients will upset the balance of microbes and the fermentation process that creates metabolizable energy for the cow.
Between 25 and 50 percent of the protein that makes it to the small intestine comes from rumen undegradable protein (RUP). Diets should be balanced so that the amino acid profiles in RUP are close to that of the microbial protein. That’s been difficult to do with the typical high corn silage diets fed in the Northeast. The first and second limiting amino acids in many dairy cow diets are lysine and methionine. Corn products including corn silage, corn grain and corn distiller’s grains are all low in lysine. Legumes such as soybean meal and alfalfa have higher levels of lysin but are lower in methionine. Animal proteins such as meat, blood and bone meal have a more balanced lysine to methionine content. However, animal byproducts are often looked upon in disfavor. So, trying to balance RUP is often challenging.
Rumen-protected methionine products have been available for sometime, and a rumen-protected lysine product was introduced this past year. Both of these products included in diets that have carbohydrate fractions balanced correctly will aid in getting a more favorable amino acid profile into the cow’s blood stream. Over the years, yeast and other microbial enhancement products have shown promise in altering or stabilizing the rumen environment so that rumen microbes can thrive.
Energy is also necessary in maintaining adequate milk protein levels. Much of the energy in dairy rations comes from the grain and byproducts portion of the diet and starch is often the primary contributor. Degradation of starches varies in feedstuffs and must be closely matched with a comparable nitrogen source. In most cases, rumen microbes quickly degrade starches and sugars; so, in order to make the most efficient use of those carbs, a soluble source of protein needs to be available. The better job we do in matching the carbs to the proteins in diets, the more microbes are produced. A valuable tool for evaluating proper energy and protein balances in a ration is by testing the milk-urea-nitrogen levels (MUN). MUN levels should routinely stay in the 10 to 14 mg/dl range.
With the tough economic times our industry is currently experiencing, feeding high-quality forages in dairy cow diets should be a primary focus when attempting to improve milk protein. Rumen fermentation is most efficient when neutral detergent fiber—the fiber fraction of forages—is highly digestible. Grass hay and silages must be harvested at immature stages to increase the NDF digestibility. Now, laboratory analysis of forages is a necessity in determining the suitability of forages for dairy cow diets. NDF digestibility in both grasses and alfalfa vary from field to field, time of year, temperatures and growth rates.
Consistent feeding management practices on the dairy farm will have a major impact on the milk protein concentration in milk, as well. There are many non-nutritional factors that can affect milk protein such as genetics, environment, level of milk production, stage of lactation, disease, season of the year, cow comfort, facilities, and the age of the cow. All of these factors must be considered together when working to improve milk protein.
The author is a dairy nutritional consultant and works for Central Connecticut Farmer’s Cooperative in Manchester, Conn.