Concept of Limiting Amino Acids
It is well known that methionine (Met) and lysine (Lys) are the two most limiting amino acids (AA) for maximizing milk and milk protein production in lactating dairy cows. This is largely because of their low concentrations in feed protein as compared to their concentrations in milk and ruminally synthesized bacterial protein (Table 1). Some dairy nutritionists are unaware of the amino acid content of commonly used feeds, let alone the amino acid content of bacterially synthesized crude protein, milk, or lean muscle tissue. However, when the amino acid content of commonly used feeds is compared to the amino acid content of the end products of feed digestion (e.g., bacterial protein, muscle tissue, and milk), it is readily apparent why Met and Lys are the two most limiting amino acids in dairy cow rations.

The NRC (2001) suggested concentrations of Lys and Met in metabolizable protein (MP) for maximal use of MP for milk and milk protein production are 7.2 and 2.4%, respectively. However, under almost all circumstances, these concentrations cannot be achieved. Therefore, more “practical recommendations” for Lys and Met in MP of 6.6 and 2.2%, respectively, have been suggested (Schwab et al., 2003). These concentrations can generally be achieved in corn-based rations by using a combination of high-Lys protein supplements (e.g., blood, fish, and processed soybean meals) and a rumen-protected Met (RPMet) product along with limiting intake of rumen-undegraded intake protein (RUP) to requirement levels. Not using a RPMet product requires the mix-and-matching of protein supplements to achieve the desired Lys:Met ratio in MP of 3:1 and, as a result, lowers the concentrations of both Lys and Met in MP that are achievable (Schwab et al., 2003).

Amino Acid Content of Feeds
The amino acid content of milk, lean muscle tissue, bacterially synthesized crude protein, and common feeds are summarized in Table 1. This data clearly demonstrates that the amino acid content of most feeds used in typical dairy rations are too low in Met and Lys to meet the requirements for milk production and lean tissue growth. It is also clearly evident that bacterially synthesized crude protein is a rich source of amino acids and is perhaps, the most complete source of amino acids for meeting the needs of the dairy cow for milk production and lean tissue growth.

Unfortunately, the high producing dairy cow cannot synthesize sufficient amounts of bacterial protein to satisfy the requirements for maintenance of body tissue and milk production. To help satisfy these requirements additional amino acids should be included in lactation rations. Unfortunately, supplementing additional amino acids in dairy rations is not an easy task, because rumen microorganisms tend to utilize ruminally available amino acids found in feed for their own needs. To overcome rumen breakdown, nutritionists can incorporate into dairy rations feedstuffs that have the ability to remain undegraded in the rumen, allowing passage to the small intestine for absorption. For reasons beyond the scope of this article, only a limited number of feedstuffs are available that can provide the needed amounts of Lys and Met to meet the needs of the high producing dairy cow. Because Met is available synthetically, this article will focus on the need for finding feedstuffs that will supply sufficient amounts of Lys to meet the needs of high producing dairy cows.

Many dairy nutritionists and producers are currently utilizing distillers grains, a protein-rich byproduct, in dairy rations due to its increasing availability and favorable cost. However, a common misconception about distillers grains exists; this being that distillers grains are high in Met content. This misconception often prompts nutritionists and producers to feed more bypass Lys in order to maintain a balanced Lys to Met ratio. It is important to note that distillers grains are not necessarily high in Met content, but rather it is simply that distillers grains are low in Lys content. In fact, the Lys content of distillers grains is still higher than the Met content, but overall, is low compared to other Lys-rich feeds, such as blood meal, fish meal, and soybean meal. Do not balance dairy rations when using distillers grains with the misconception that they are a rich source of RUP Met.

Plant Proteins Versus Animal Proteins
The use of plant protein sources versus animal protein sources as supplemental Lys sources for dairy rations needs evaluating. As shown in Table 1, animal protein sources, such as blood meal and fish meal, are much more concentrated sources of RUP-Lys compared to plant protein sources. It is extremely difficult to attain high levels of Lys required to meet the needs for milk and milk protein production of high producing dairy cows using only plant protein sources due to their relatively low content of Lys compared to animal protein sources. However, several inherent limitations exist when using animal protein sources. With the recent U.S. documented cases of bovine spongiform encephalopathy (i.e., Mad Cow disease), the use of animal proteins in rations for food animals or lactating animals has come under scrutiny by the government and general public. Beyond the negative public perception, problems associated with feeding animal proteins include the large variations that can exist in crude protein content, RUP content, RUP-digestibility, and amino acid content. Although these same problems exist when using plant protein sources they are of even greater concern with animal proteins. Also, palatability is often a concern when feeding animal proteins. Moderate levels of animal proteins can often be fed without a problem; however at higher levels, dry matter intake is often depressed.

To improve handling characteristics and increase RUP characteristics, animal proteins are dried. Differences in drying procedures can greatly impact product quality. Products that are dried too long will have high RUP values, yet will have a low RUP-digestibility, and the Lys will be unavailable for use by the animal. Insufficient drying will result in low RUP values, enabling greater rumen degradation that prevents its passage to the small intestine for absorption and use by the animal. These two scenarios commonly occur with blood and meat and bone meal products where the method of processing has a significant impact on quality. Consequently, quality control is extremely important when processing animal proteins for use in dairy rations.

The ADM Alliance Nutrition Response
While ADM Alliance Nutrition recognizes that blood meal is the most concentrated source of Lys available, ADM researchers and feed technology scientists realize the potential quality control limitations of using blood meal as a source of digestible Lys. Unfortunately, poor quality control and improper processing techniques involved in producing blood meal may compromise expected performance in increasing milk protein production.

Equipped with this knowledge, ADM researchers applied extensive analytical research protocols to determine the nutritional content of blood meal from various suppliers. The process identified variations related to plant location and processing methods used in the blood meal manufacturing process. The results of ADM’s research efforts enabled ADM Alliance Nutrition to enhance the quality control of inputs, which ensure the proper amino acid content of feed ingredients is maintained on a continual basis. The result – ADM Alliance Nutrition can apply scientific knowledge and skill to formulate feed products and dairy rations which provide consistent quality and value, enabling dairy cows to perform to their genetic potential.

The ADM Alliance Nutrition Solution
ADM Alliance Nutrition developed the Dairy Solutions 6:1 Base to provide a 6:1 Lys to Met ratio. This ratio supplies the optimal balance of amino acids to compliment the growing use of distillers grains used in today’s dairy rations. The stringent quality control processes used in the manufacture of Dairy Solutions 6:1 Base provides ADM Alliance Nutrition dairy customers with the assurance that lactating cows receive the required amino acids for optimal milk and component production. The feeding of high-quality ingredients offers dairy producers the best return on their feed investment. Producers who fine-tune amino acid balance in lactating rations can reap the dividends of higher milk protein and milk production.

 

Table 1  A Comparison of the Essential Amino Acid Composition of Body Lean Tissue, Milk, and Ruminal Bacteria with that of Some Common Feeds1 (Adapted from Schwab and Ordway, 2005)
Item	Lysine	Methionine	Histidine
	───────────── (% of CP) ───────────
Lean tissue	6.4	2.0	2.5
Milk	7.6	2.7	2.7
Bacteria	7.9	2.6	2.0
Alfalfa silage	4.4	1.4	1.7
Corn silage	2.5	1.5	1.8
Grass silage	3.3	1.2	1.7
Barley	3.6	1.7	2.3
Corn	2.8	2.1	3.1
Oats	4.2	2.9	2.4
Wheat	2.8	1.6	2.4
Brewers grains	4.1	1.7	2.0
Canola meal	5.6	1.9	2.8
Corn DDG w/sol	2.2	1.8	2.5
Corn gluten meal	1.7	2.4	2.1
Cottonseed meal	4.1	1.6	2.8
Soybean meal	6.3	1.4	2.8
Sunflower meal	3.6	2.3	2.6
Blood meal	9.0	1.2	6.4
Feather meal	2.6	0.8	1.2
Fish meal	7.7	2.8	2.8
Meat meal	5.4	1.4	2.1
1 Amino acid values for lean tissue, milk, and ruminal bacteria are from O’Connor et al. (1993) and amino acid values for feeds are from NRC (2001).

References:

National Research Council. 2001. Nutrient Requirements of Dairy Cattle. 7th rev. ed. Natl. Acad. Sci., Washington, DC.

Schwab, C. G. and R. S. Ordway. 2005. Moving beyond protein: amino acid requirements of dairy cattle. In: Proc. 7th Intermountain Nutrition Conf., Salt Lake City, UT.

Schwab, C. G., R. S. Ordway, and N. L. Whitehouse. 2003. Amino acid balancing in the context of MP and RUP requirements. In: Proc Four-State Applied Nutrition and Management Conference.

 

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