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Feedstuffs, May 10, 2010

Nutrition & Health: Dairy

Amino acid balancing
Balancing for methionine and lysine is now practical and easily accomplished using effective rumen-protected products.
By BARBARA BARTON* HAT used to be inherent challenges to balancing amino acids in dairy rations has fallen to the wayside due to recent industry advances. Because it is easier to balance aminoacid levels with confidence now, lower crude protein levels can be fed without negatively affecting performance while reducing ration costs. Lactating dairy cows absorb and utilize individual amino acids. The cow has a specific requirement for 10 essential amino acids that she cannot produce in sufficient quantities to meet her needs. “Non-essential” amino acids are required as well, but the cow makesthem in sufficient quantities to meet her needs. The amino acid in the shortest supply becomes the “first-limiting” amino acid. In any given ration, the first-limiting amino acid depends on the amino acid profile of the ration feedstuffs. For lactating dairy cows, the first-limiting amino acid is usually lysine or methionine. Arginine and histidine may also be a concern in certain situations. Theamino acids available for digestion and absorption in the intestine come from three sources: microbial protein, undegraded dietary protein and endogenous protein from sloughed cells and secretions in the digestive tract. Microbial protein contributes approximately 55% of the total amino acids digested in the small intestine. Endogenous protein contributions are minimal at 5%. Consequently, dietaryundegraded proteins contribute 40% of the amino acids digested at the intestinal level. The protein absorbed in the small intestine from these three sources is called metabolizable protein (MP). Rations are formulated to supply MP with an amino acid makeup that is tailored to meeting the cow’s essential amino acid requirements.

1. Lysine, methionine and histidine content in animal products,bacteria and typical dairy feedstuffs expressed as a percentage of crude protein (Schwab, 2001)
Lean tissue Milk Rumen bacteria Alfalfa silage Corn silage Grass silage Barley Corn Oats Wheat Brewers grains Canola meal Corn dried distillers grains Corn gluten meal Cottonseed meal Soybean meal Sunflower meal Blood meal Feather meal Fish meal Meat meal Lysine 6.4 7.6 7.9 4.4 2.5 3.3 3.6 2.8 4.2 2.8 4.15.6 2.2 1.7 4.1 6.3 3.6 9.0 2.6 7.7 5.4 Methionine 2.0 2.7 2.6 1.4 1.5 1.2 1.7 2.1 2.9 1.6 1.7 1.9 1.8 2.4 1.6 1.4 2.3 1.2 0.8 2.8 1.4 Histidine 2.5 2.7 2.0 1.7 1.8 1.7 2.3 3.1 2.4 2.4 2.0 2.8 2.5 2.1 2.8 2.8 2.6 6.4 1.2 2.8 2.1

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Protein sources
The amino acid profile of microbial protein is similar to that of milk (Table 1). Because of this, microbial protein is considered a high-qualityprotein. Dairy rations should be balanced to optimize rumen microbial protein synthesis by taking into consideration rumen carbohydrate availability, synchronization of carbohydrate and protein availability, rumen pH, rumen content turnover and types of rumen microbes.

2. Summary of average milk and milk component responses to balancing methionine and lysine (% MP) in early-lactation dairy cowrations (based on results of seven research trials)
Item Milk yield, kg/day Milk protein, % Milk protein, g/day Milk fat, % Milk fat yield, g/day Response +1.7 +0.10 +90 +0.10 +96

*Dr. Barbara Barton (ACAN Dipl.) is a technical support specialist for Balchem Animal Nutrition & Health.

Rumen undegraded protein (RUP) contributes a significant amount of amino acids to the small intestine both inquality and quantity. The amino acid profile of RUP varies in makeup (quality) based on the

amino acid makeup of the feedstuffs fed. Variability in the RUP value of a feedstuff exists primarily due to inherent variability in the amino acid content of the feedstuff as well as to the variation in processing conditions that affect the extent of ruminal degradation of protein. The amino acid...