*Dr. Charles Sniffen is with Fencrest LLC. Dr. Essi Evans is with Technical Advisory Services Inc. Dr. Elliot Block is research fellow, animal nutrition, at Arm & Hammer Animal Nutrition. This is part 2 of a two-part series. Part 1 appeared in the June 10 issue of Feedstuffs.
AMINO acid balancing has gained more traction in the past five to six years due to increased concerns about the environment, volatile ingredient prices and the continued development of more precise nutritional models.
Previously, the research and discoveries that led to current models and methods were explained to offer a history of amino acid balancing and how the industry reached its current level of understanding (Feedstuffs, June 10). The following is additional explanation as well as how amino acid balancing fits into ration formulation.
Because of the complexity of the rumen environment, emphasis has been placed on sorting out events occurring in the rumen and assessment methods. The next important step is to determine what occurs beyond the rumen — and to discuss appropriate analytical methods.
The intestines are presented with a combination of escape proteins, escape peptides, free amino acids, microbes and microbial debris. This must be broken down by chemical and enzymatic means to free amino acids and small peptides for absorption.
The bulk of the amino acids entering the intestine are from microbial protein. If a consistent amino acid profile is assumed, the next step is to assign a digestibility value to this amino acid source. Available data suggest that the digestibility of the true protein fraction hovers at around 80% (Salter and Smith, 1972; Hvelplund, 1985; National Research Council, 2001). This is generally subtracted from the calculated requirements.
In order to meet a cow's amino acid needs, the portion of her requirement that is not covered by microbial protein must come from the escape portion of feed. Two approaches have been taken to assess this availability:
1. Estimate the digestible component by determining the indigestible part.
2. Attempt to determine what gets absorbed.
To estimate indigestibility, the mobile nylon bag technique involves placing samples previously incubated in sacco into a low-pH pepsin solution and then into a duodenal cannula and, finally, recovering the bags from the feces (De Boer et al., 1987; Frydrych, 1992). This gives a fair estimate of the indigestible fraction, although some secondary fermentation can occur in the large intestine.
To get around the secondary fermentation aspect, several other methods were developed (Tomankova and Homolka, 1995; Jarosz et al., 1994; Calsamiglia and Stern, 1995).
Finally, Stern et al. (1997) introduced the concept of comparing proteins on the basis of their intestinally absorbable dietary protein. This compares the rumen undegradable protein and amino acid component.
Rather than recovering the indigestible components of proteins or their fractions, attempts have been made to evaluate the uptake of the nutrients entering the duodenum directly. This has resulted in substantial frustration as the gut tissues themselves gain first access to the nutrient supply and may alter the profile through their use (Huntington and Prior, 1985).
If this utilization by gut and splanchnic tissues is not taken into account, absorption estimates will be inaccurate.
In a 2010 study at the Atlantic Dairy & Forage Institute (Block, Hendel, Clark and Evans, unpublished), it was demonstrated that lysine is used by gut tissues as it is being absorbed and may not appear in blood.
In that experiment, 50.0 g of lysine from lysine hydrochloride were infused in control animals and compared to 37.5 g, 50.0 g and 62.5 g of lysine from a commercial product (MEGAMINE L, Church & Dwight Inc.). The calculated relative intestinal availability increased with supply (57.5%, 67.2% and 70.3%, for the 37.5 g, 50.0 g and 62.5 g treatments, respectively). Because the intestinal availability varied with supply, it indicated that the technique has limitations.
These limitations were detailed by the following research:
* Weekes et al. (2006) infused highly different ratios of amino acids and found only slight changes in plasma levels, not at all representative of the infusate. These researchers also found no relationship between plasma levels of amino acids and mammary uptake.
* Blood that is not deproteinized immediately continues to increase in free amino acid concentration (Li et al., 2009) and reduces the sensitivity of assays. Thus, plasma levels may not be a good reflection of absorption status. The indirect technique of quantifying the indigestible fraction and subtracting it from the total remains the most robust.
The net uptake of amino acids into the portal system and their conversion into non-essential amino acids and energy-yielding compounds remains elusive. Where an amino acid ends up is highly dependent upon the needs and priorities of various types of tissues. Amino acids leaving the liver pass to somatic tissues, where the uptake efficiency of amino acids varies among different amino acids.
Amino acid metabolism is further complicated because certain amino acids have multiple functions, including acting on receptors. This affects hormonal shifts in the animal. Adding another level of complication are genetic differences, coupled with the stage of growth and the stage of pregnancy or lactation, which significantly affects changes in efficiency. These factors are largely ignored in current models.
While not taken into account, such uses of amino acids are being studied, and modeling techniques are being developed to optimize nutrient utilization on a more integrated basis.
Lapierre et al. (2005) recommended evaluating all sequential metabolic uses of amino acids in order to better assess utilization and uptake by the mammary gland, allowing realistic efficiency values for amino acids. Nutritional hierarchical frameworks have been built for other species (Simpson et al., 2009).
Basically, this involves modeling the interactions between nutrients. In the cow, an amino acid might be required for the synthesis of glucose or the synthesis of protein. The priority depends on the other nutrients available at any given moment in time.
Putting amino acids to use
Ration formulation platforms allow nutritionists to formulate rations to meet amino acid needs. Some are limited to formulating for just lysine and methionine, while others allow for formulating for the other essential amino acids too. Some allow for formulating on the gram requirements, others for the ideal protein concept and some for both options.
Regardless, the following steps should be followed:
* The first step is to define the animals for which the ration is intended. This helps establish specific requirements for each feeding situation.
* Then, obtain proper feed analyses to match the ingredient sources with the animals' needs. Defined management practices help assess dry matter intake.
The actual formulation process starts with good carbohydrate and lipid balances, ensuring that the minerals and vitamins are correct. All are prerequisites to amino acid balancing.
One approach is to formulate a ration without constraining any amino acids. Save these rations, because they will serve as the base for ingredients and price.
* Next, formulate for lysine, and save the rations with the change in cost (which can go up or down depending on space, bypass protein sources and fermentable carbohydrate or energy needs).
* Finally, balance for optimal levels of both lysine and methionine, and save this ration; this will be the incremental cost that needs to be achieved and exceeded in milk and/or component improvements. Users must decide if they are most comfortable with a factorial approach or a ratio approach. Gram requirements need to be met in either case.
If other essential amino acids are limiting, supplementing with lysine or methionine will not result in any improvement in performance. Evidence strongly suggests that amino acids such as arginine, histidine or branched-chain amino acids can become limiting and will likely vary with the ingredients on hand.
Despite the limitations and hurdles to amino acid balancing that have been outlined in these two articles, the increased knowledge of dairy cow biology and the incorporation of that biology into nutritional modeling programs have advanced significantly over the years.
As a result, the concepts and techniques of amino acid balancing are beneficial and offer significant production and economic benefit versus ignoring the opportunities presented by these technologies.
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De Boer, G., J.J. Murphy and J.J. Kennelly. 1987. Mobile nylon bag for estimating intestinal availability of rumen undegradable protein. J. Dairy Sci. 70:977-982.
Frydrych, Z. 1992. Intestinal digestibility of rumen undegraded protein of various feeds as estimated by the mobile bag technique. Anim. Feed Sci. Tech. 37:161-172.
Huntington, G.B., and R.L. Prior. 1985. Net absorption of amino acids by portal-drained viscera and hind half of beef cattle fed a high concentrate diet. J. Anim. Sci. 60:l491-1499.
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