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Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids
Feed Supplements: Ruminally Protected Amino Acids C G Schwab, University of New Hampshire, Durham, NH, USA ª 2011 Elsevier Ltd. All rights reserved.
Amino Acid Nutrition of Dairy Cattle Sources of Absorbed Amino Acids Absorbed amino acids are provided by ruminally synthesized microbial protein, rumen-undegradable feed protein (RUP), and, to a lesser extent, endogenous protein. Microbial protein refers to the constituent proteins of the bacteria, protozoa, and fungi that grow and multiply in the rumen. RUP is that portion of feed protein that escapes or resists ruminal degradation. Endogenous protein refers to protein originating in the body. Sources of endogenous protein include mucoproteins in saliva, sloughed epithelial cells (from the respiratory tract, mouth, esophagus, rumen, omasum, and abomasum), and enzyme secretions into the abomasum. The endogenous protein contribution to the duodenum includes free endogenous secretions and endogenous proteins incorporated into the microbial protein flow. Microbial protein typically supplies a majority of the amino acids required by the ruminant animal. However, RUP may supply more than 50% of the absorbed amino acids in high-producing dairy cows fed a high-concentrate diet that is balanced to meet requirements for rumendegradable protein and RUP. The quantity of amino acids provided by free endogenous protein secretions is small and appears to be correlated closely to intake of indigestible organic matter. It appears that about 10% of the total supply of absorbed amino acids is provided by endogenous protein.
Factors Affecting the Profile of Absorbed Amino Acids Two factors account for most of the variation in amino acid profiles of duodenal protein. These are the proportional contribution that RUP makes to total protein passage and the amino acid composition of that portion of total dietary protein predicted to be RUP. This would be expected because feed proteins vary in amino acid composition and usually differ from ruminally synthesized microbial protein (Table 1).
Limiting Amino Acids Limiting amino acids are essential amino acids in digested protein that are in shortest supply relative to body requirements for absorbed amino acids. Methionine,
lysine, and histidine have been identified most often as the most limiting amino acids for dairy cattle. The extent and sequence of their limitation is affected primarily by the amount of RUP in the diet and its amino acid composition. Methionine has been shown to be first limiting for growth and milk protein production when dairy cattle were fed high forage or soybean hull-based diets and intake of RUP was low. Methionine has also been identified as first limiting for growing cattle and lactating cows that were fed a variety of diets in which most of the supplemental RUP was provided by soybean protein, animal-derived proteins, or a combination of the two. In contrast, lysine has been identified as first limiting for growth and milk protein synthesis when maize and feeds of maize origin provided most or all of the RUP in the diet. Relative to concentrations in microbial protein, feeds of maize origin are low in lysine content and similar in methionine content, whereas soybean products and most animal-derived proteins are similar in lysine content and low in methionine content (Table 1). Methionine and lysine have been identified as colimiting amino acids for milk protein synthesis when cows were fed maize silage-based diets with little or no protein supplementation. Histidine has been identified as first limiting for milk protein production when dairy cows were fed grass silage/cereal (barley and oats)-based diets, with or without feather meal as the sole source of RUP supplementation. It should not be too surprising that these amino acids have all been shown to be first limiting. First, all have been identified as being among the most limiting amino acids in microbial protein. Methionine has been identified as first limiting and lysine as second limiting in microbial protein for nitrogen retention of both growing cattle and growing lambs. Histidine has been identified as possibly third limiting for sheep. Second, concentrations of methionine and lysine in most feed proteins are lower than those in microbial protein (Table 1). Thus, most feed proteins are not complementary to microbial protein and instead, when they are fed, will exacerbate rather than eliminate deficiencies of methionine and lysine in metabolizable protein. This also appears to be why methionine and lysine become more limiting (relative to the other essential amino acids) with increasing intakes of complementary sources of RUP.
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390 Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids Table 1 A comparison of the essential amino acid (EAA) profiles of body lean tissue and milk with that of ruminal bacteria and protozoa and some common feeds Arg
His
Ile
Leu
Lys
Met
Phe
Thr
Trp
Val
EAA
Item
(% of total EAA)
Animal products Lean tissuea Milkb
16.8 7.2
6.3 5.5
7.1 11.4
17.0 19.5
16.3 16.0
5.1 5.5
8.9 10.0
9.9 8.9
2.5 3.0
10.1 13.0
– –
Rumen microbes Bacteriac Protozoad
10.4 9.3
4.1 3.6
11.5 12.7
15.9 15.8
16.5 20.6
5.1 4.2
10.1 10.7
11.3 10.5
2.7 2.8
12.4 9.7
– –
Foragese,f Alfalfa hay Alfalfa silage Corn silage Grass hay Grass silage
12.5 10.9 6.2 11.7 9.4
4.7 4.7 5.7 4.9 5.1
10.3 11.1 10.6 10.0 10.9
17.9 17.9 27.2 18.8 18.8
12.4 12.1 7.9 10.5 10.1
3.8 3.8 4.8 3.9 3.7
11.6 11.7 12.1 11.8 13.4
10.6 10.7 10.1 10.9 10.2
3.6 2.7 1.4 3.7 3.3
12.7 14.1 14.1 13.6 15.0
41.2 35.6 31.6 33.1 32.6
Grainse Barley Corn Oats Sorghum Wheat
13.4 11.5 16.6 9.4 13.6
6.1 7.8 5.9 5.7 7.1
9.2 8.2 9.1 9.3 9.6
18.5 27.9 17.7 31.9 19.3
9.6 7.1 10.1 5.4 8.1
4.5 5.3 4.2 4.2 4.6
13.5 11.5 12.5 12.3 13.3
9.1 8.8 8.4 7.8 8.4
3.1 1.8 2.9 2.5 3.5
13.0 10.0 12.6 11.6 12.3
37.7 40.1 41.2 42.8 34.4
Plant proteinse Brewers’ grains Canola meal Corn DDG w/sol. Corn gluten meal Cottonseed meal Linseed meal Peanut meal Soybean meal Sunflower meal
14.7 16.5 10.7 7.1 26.0 20.9 27.6 16.2 20.8
5.1 6.6 6.6 4.7 6.6 4.8 6.0 6.1 6.2
9.8 9.0 9.8 9.1 7.3 11.0 8.1 10.1 9.9
20.0 15.9 25.4 37.2 13.8 14.5 15.9 17.2 15.2
10.4 13.2 5.9 3.7 9.7 8.7 8.3 13.9 8.0
4.3 4.4 4.8 5.2 3.7 4.2 2.9 3.2 5.6
11.7 9.5 12.9 14.1 12.5 11.1 12.1 11.6 11.0
9.1 10.4 9.1 7.5 7.6 8.9 6.7 8.7 8.7
2.5 3.4 2.3 1.2 2.8 3.7 2.4 2.8 2.9
12.1 11.1 12.4 10.3 10.0 12.3 9.8 10.2 11.7
39.2 42.6 37.8 45.2 42.6 42.2 40.1 45.3 42.2
7.8 16.2 13.1 19.5
1.3 2.7 6.4 5.3
2.2 11.4 9.2 7.7
22.7 19.9 16.2 17.2
15.9 6.0 17.2 14.5
2.1 1.8 6.3 3.9
12.1 11.6 9.0 9.4
7.7 11.1 9.4 9.1
2.8 1.7 2.4 1.6
15.4 17.6 10.8 11.8
56.4 42.7 44.5 35.7
5.0
4.5
12.1
21.2
17.6
3.3
7.0
14.1
3.5
11.7
42.2
Animal proteinse Blood meal Feather meal Fish meal Meat and bone meal Whey, dry
(% of CP)
a
Average values of empty, whole body carcasses as reported in three studies. Average values as reported in three studies. c The mean of average values from over 100 dietary treatments. d Average values from 15 literature reports. e Calculated from values presented in National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th revised edn. Washington, DC: National Academy Press. f Legume and grass hays and silages are mid-maturity. b
Third, lysine is more vulnerable to heat processing than the other essential amino acids. Overheating feed proteins can decrease lysine concentrations as well as decrease the digestibility of the remaining lysine more than that of total protein. Finally, concentrations of histidine are lower in grasses and legumes, oats, barley, and particularly feather meal, as compared to most other feeds (Table 1). This is probably why diets consisting solely of these feeds have been shown to be more limiting in histidine than in methionine or lysine.
Ruminally Protected Amino Acids History of Development Interest in protecting free amino acids from ruminal degradation dates back to the 1960s and early 1970s, when it became apparent from abomasal, intestinal, and intravenous infusion trials that the profile of absorbed amino acids was not always optimum in ruminants. These trials indicated that the sulfur amino acids were clearly first limiting for wool growth and body weight gains of sheep and that methionine was a limiting amino
Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids
acid for growing cattle and lactating dairy cows. Thus, several laboratories began to devise procedures to protect methionine from ruminal degradation. Subsequent interest developed in protecting lysine when it was discovered to be a second limiting for growing lambs and either first or second limiting for growing cattle and lactating dairy cows. Many approaches have been evaluated to physically protect methionine and lysine from ruminal degradation. Initial attempts focused on protecting methionine with lipids, often in combination with inorganic materials and carbohydrates as stabilizers, softening agents, and fillers. For example, in the 1960s, Delmar Chemicals of Canada developed a product in which a core of DL-methionine, colloidal kaolin, and tristearin was wrapped in a continuous film of tristearin. The product contained 20% methionine. A few years later, Rumen Kjemi A/S of Oslo, Norway, introduced a somewhat more efficacious product (Ketionin) that had a higher intestinal release of the encapsulated methionine. The product contained 30% DL-methionine, 2% glucose, 4% stabilizer, antioxidant and flavoring agents, 6% CaCO3, and 58% tristearin and oleic acid. Several other lipid-protected methionine products have also been evaluated. The greatest challenge with using lipids as the primary encapsulating material is to identify a combination of materials and process that has both a high ruminal escape and intestinal release of the amino acid. The most effective approach has been to surface-coat amino acids with enzyme-resistant, pH-sensitive synthetic polymers that are insoluble in the more neutral pH environment of ruminal digesta but highly soluble in the acidic abomasum. This approach provides for a postruminal delivery system that is independent of enzyme function and, instead, relies on the pH differences between the rumen and the abomasum for ruminal protection and intestinal release. Polymerprotected amino acids have higher ruminal protection and intestinal release coefficients than other products. The patent rights for the use of pH-sensitive polymers for protecting nutrients from ruminal degradation is currently held by Adisseo Animal Nutrition, Antony, France. Another method that has been explored for increasing supplies of methionine and lysine to ruminants is the use of derivatives and analogues of these amino acids. Most of the derivatives and analogues that have been investigated for level of rumen protection are those of methionine. Amino acid derivatives are free amino acids to which a chemical blocking group has been added to the -amino group, or in which the acyl group has been modified. Some examples of derivatives that have been shown to have some resistance to ruminal degradation
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are isopropyl-DL-methionine, t-butyl-DL-methionine, N-stearoyl-DL-methionine, N-oleoyl-DL-methionine, capryl-caproylic-DL-methionine, and di-hydroxymethylL-lysine-Ca. There is evidence that the extent of ruminal escape is greater with shorter-chain alkyl esters than with longer-chain alkyl esters. Although these and other derivatives show promise, most have not been investigated adequately to determine the extent to which they will increase postruminal supplies of absorbable methionine. An amino acid analogue results from the substitution of the -amino group of an amino acid with a nonnitrogenous group. The most studied amino acid analogue is methionine hydroxy analogue (MHA; DL- -hydroxy- -mercaptobutyrate), more appropriately called 2-hydroxy-4-(methylthio)butanoic acid (HMB). Studies indicate that free HMB (1) is more resistant to ruminal degradation than free methionine, (2) is more absorbable from the rumen and omasum than methionine, and (3) is converted to methionine in most mammalian tissues. However, because of no measurable effects on blood methionine concentrations when fed to cows on methionine-adequate diets, or on the content of milk protein when fed to methionine-deficient cows, it appears that feeding HMB, in either the acid or salt form, has little or no replacement value for ruminally protected methionine. Research has shown that several esters of HMB enhance ruminal escape of HMB, at least in part, because of their apparent ability to be absorbed across the rumen wall. The isopropyl ester of HMB (HMBi) has been shown to have an excellent replacement value for absorbed methionine.
Examples of Commercial Protected Methionine Products Mepron M85 (Evonik-Degussa Corporation, Germany): This is an example of a surface-coated, carbohydrate-protected product. The small pellets have a diameter of 1.8 mm, a length of 3–4 mm, and an approximate density of 1.2 g cm 3. The pellets consist of a core of methionine and starch coated with several thin layers of ethylcellulose and stearic acid. The final product contains a minimum of 85% DL-methionine, and approximately 8.5% nonstructural carbohydrates, 3.5% neutral detergent fiber, 1.5% ash, 1.0% moisture, and 0.5% crude fat. The technology is a combination of coating materials and application that allows for a large payload of methionine. Because enzymatic digestion of the ethylcellulose is minimal, degradation of the product occurs primarily through physical action and abrasion. The result is a product that is slowly degraded in the rumen and slowly releases methionine into the intestine.
392 Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids
METHIOPLUS (Kemin Industries, Des Moines, IA, USA): Methioplus is produced by encapsulating DL-methionine with hydrogenated vegetable oils. The preparation method is described as microencapsulation by spray freezing using the patented MICROPEARLS process. The coating material and method of application are designed to provide a coating matrix that is able to resist rumen breakdown and release the ingredient in the intestine. The yellow microcapsules contain 55% DL-methionine. Met-Plus (Novus International, Inc., St. Louis, MO, USA): This is an example of a lipid-protected product. It is a matrix compound that contains 65% DL-methionine embedded in a mixture of calcium salts of long-chain fatty acids, lauric acid, and butylated hydroxytoluene (BHT); BHT is a preservative for the fatty acids. However, like other lipid-coated products, the technology relies on achieving a balance between ruminal protection and intestinal release so as to maximize the amount of methionine available for intestinal absorption while minimizing losses in the rumen and in feces. Smartamine M (Adisseo, Antony, France): This is an example of a lipid/pH-sensitive polymer-protected product. It is a surface-coated product that contains a minimum of 75% DL-methionine. The small 2-mm pellets consist of a core of DL-methionine and ethyl cellulose that is covered with a coat of stearic acid containing small droplets of poly(2-vinylpyridine-co-styrene). The copolymer contributes 3% by weight of the final product. The presence of the copolymer appears to alter the stereochemistry of the stearic acid such that the surface coating becomes enhanced in its resistant to ruminal degradation. The presence of the copolymer, because of its solubilization at low pH, also allows for rapid release of the methionine in the abomasum. MetaSmart (Adisseo, Antony, France): This is the HMBi. While technically an amino acid analogue, it is usually referred to as a protected methionine product because of its ability to provide significant amounts of absorbable HMB to the cow. The compound is formed by reacting Rhodimet AT88 (HMB) with isopropanol. The resulting HMBi provides for a limited degree of protection from ruminal degradation, but it provides a vehicle for a more rapid absorption across the ruminal and omasal walls. Commercial Sources of Methionine Analogues There are three commercial sources of free methionine analogues. These are Alimet (Novus International, Inc., St. Louis, MO, USA), Rhodimet AT88 (Adisseo, Antony, France), and MFP (Novus International, Inc., St. Louis, MO, USA). Alimet and Rhodimet AT88 are both liquid sources of HMB. Chemically, the compounds are the same. Both are used extensively as a substitute for
methionine in the poultry and swine industry. However, Novus International also has Alimet patented for use in dairy cows and recommends its use as a source of ruminally protected methionine. Adisseo considers the ruminal escape and ruminal absorption of Rhodimet AT88 to be too low to recommend its use as a source of ruminally protected methionine. Novus International also recommends the use of MFP, which is the Ca salt of HMB, and thus the dry source of HMB, as a source of ruminally protected methionine. Both companies recognize the potential benefits of feeding HMB on rumen function (e.g., increased fiber and protein digestion and increased bacterial protein synthesis and efficiency of synthesis) and animal performance (e.g., increased milk yield and butterfat content). Commercial Sources of Rumen-Protected Lysine AminoShure-L (Balchem Corporation, New Hampton, NY, USA): Launched in 2008, AminoShure-L was the first commercial source of rumen-protected lysine to become available in the United States. The product is formed by encapsulating L-lysine-HCl with multiple layers of foodgrade lipids. The spherical shaped tan to light brown granules contain 38% crude protein, a minimum of 36% lysine, 53% ether extract, and 9.0% chloride. MEGAMINE-L (Church & Dwight Co., Princeton, NJ, USA): Released in 2009, the final product contains 80% Megalac and 20% lysine-HCl. The product is formed by adding lysine-HCl to the Megalac production process. The resulting 0.32 cm pellets have a density of 1.05 and contain 68% fat, 16% lysine, 7% calcium, and 5% lipidsoluble materials. Ethoxyquin is added as a preservative. LYS-50 (Kemin Industries, Des Moines, IA, USA): LYS-50 is produced by the same MICROPEARLS process as described for Methioplus. The product typically contains 50% L-lysine-HCl. Efficacy of Products Responsible use of ruminally protected methionine and lysine products requires estimates of their ability to provide methionine and lysine for protein synthesis. Insofar as possible, estimates of ‘methionine and lysine bioavailability’ must be accurate and reliable under the conditions in which they are fed in production systems. Approaches
Unfortunately, there is no universally accepted, standardized procedure(s) for obtaining estimates of methionine and lysine bioavailability. These are needed to bring uniformity to estimates of amino acid bioavailability and to more accurately compare the efficacy of different products. Current approaches can be categorized as factorial
Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids
approaches, blood response approaches, and production response approaches. The factorial approach involves independent measurements of ruminal escape, intestinal disappearance (digestibility), and, in the case of free or protected forms of HMB, metabolic conversion to methionine. Animals with cannulae in the rumen, duodenum, and preferably also in the ileum are required. Estimates of ruminal escape and intestinal disappearance of amino acid from protected methionine and lysine products have been obtained using both the in situ nylon-bag procedure and the cannulated cow in vivo procedure. Use of the in situ procedure requires measurements of rate of passage of protected amino acid products from the rumen. Factorial approaches, particularly those involving in situ nylon-bag techniques, have been questioned as to their appropriateness for measuring the intestinal release of amino acids from a rumen-protected product that relies on abrasion and physical forces for its degradation. Moreover, the procedures do not account for the physiological aspects of digestion such as mastication and digesta passage. The in situ procedure is also not suitable for soluble or liquid products such as HMB and HMBi. Blood response approaches are an attractive alternative to factorial approaches because they are easier to conduct and they allow liquid and pulverulent products to be evaluated. Studies with cattle have shown that a linear relationship exists between increasing supplies of absorbable methionine and lysine and plasma methionine and lysine concentrations. Two variations of the approach have been used. The first is the dose–response approach. This approach involves determination of differences in the slope of measured blood amino acid concentrations between graded dietary doses of the product and graded intestinal doses of the infused amino acid. The second is the ‘area under the curve’ (AUC) approach. This approach involves the ruminal administration of a pulsed dose of equimolar amounts of different methionine or lysine sources and comparing the AUC of the plasma methionine and lysine response curves that result. To obtain estimates of methionine bioavailability for methionine products, Smartamine M is often used as the positive control treatment with the assumption that it has a methionine bioavailability value of 80%. A milk protein content response approach has also been used to obtain estimates of amino acid bioavailability. This approach involves determination of differences in slope of measured milk protein concentrations between graded dietary inclusion levels of the product and graded intestinal infusions of the free amino acid when cows are fed a basal diet deficient in the amino acid in question. As with the blood response approach, some of the studies that focused on obtaining estimates of methionine bioavailability for
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methionine products replaced intestinally infused methionine with Smartamine M as the positive control treatment with the assumption that Smartamine M has a methionine bioavailability value of 80%. Numerous studies with lactating cows indicate that content of milk protein is the most responsive criterion to small changes in concentrations of methionine and lysine in metabolizable protein. Using production responses such as milk yield, milk fat concentration, and milk component yields as criteria for comparing or evaluating products as sources of rumenprotected amino acids is not valid because of the effect that changes in rumen function can have on them. For example, several experiments have indicated increases in forage and fiber digestion, protein digestion, acetate-topropionate ratios, bacterial protein synthesis, efficiency of bacterial protein synthesis, and protozoan numbers as a result of feeding methionine hydoxy analogue. When these benefits are realized and one or more of the effects are limiting animal performance, it should not be surprising that increases in feed intake, milk yield, and milk fat concentration are observed.
A Comparison of Some Available Products Relying on the blood and milk protein content response approaches as being the most appropriate techniques for arriving at estimates of ‘methionine and lysine bioavailability’, a summary of available research indicates that Smartamine M clearly has the greatest efficacy as a source of absorbable methionine. The industry use of a methionine bioavailability value of 80% appears reasonable when the manufacturers recommendations for mixing with other supplements and rations are followed. The data are not as consistent for Mepron M85 and MetaSmart as they are for Smartamine M but it appears that the methionine bioavailability value for the two products is somewhere between 40 and 50%. It is the opinion of the author that there is not enough data to make similar claims of efficacy. Research indicates no measurable effects of Alimet or Rhodimet AT88 on blood methionine concentrations when fed to cows on methionine-adequate diets, or on content of milk protein when fed to methionine-deficient cows. Therefore, it appears that feeding HMB, in either the acid or salt form, has little or no replacement value for ruminally protected methionine. It appears quite certain that the methionine bioavailability of these two products is less than 5%. Pulse-dosing large amounts into the rumen has yielded apparent rumen escape values of 40–50%. However, adding incremental amounts of these products to methionine-deficient diets has not increased milk protein concentrations or blood methionine concentrations.
394 Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids
The rumen-protected lysine products have been introduced only recently and have not had the research scrutiny of most of the methionine supplements. However, because they are all lipid-encapsulated or lipid-protected products, and depend on both the mechanical and enzymatic aspects of digestion throughout the gastrointestinal tract for lysine release, it is unlikely in most cases that more than half of the protected lysine is available for absorption in the small intestine. The Benefits of Using Rumen-Protected Methionine and Lysine Products The use of these products is of significant help in achieving a more desirable profile of the most limiting amino acids in metabolizable protein. Clearly, their use allows the alleviation of methionine and lysine deficiencies without increasing the intake of RUP or changing the profile of the other essential amino acids in metabolizable protein. However, their use also allows for more selective use of protein supplements, without regard to their content of methionine and lysine, to more adequately meet desired levels of other limiting amino acids in metabolizable protein. The result is more efficient use of absorbed amino acids for protein synthesis, increased weight gains and higher levels of milk protein production, and reduced need for RUP in the diet. The use of rumen-protected methionine and lysine products has been limited. Reasons for this include (1) inadequate knowledge of amino acid requirements and the required concentrations of limiting amino acids in metabolizable protein, (2) lack of easy-to-use computer models that predict accurately their need, (3) issues of product efficacy and cost relative to anticipated benefits, and (4) lack of ease of incorporating desired concentrations into the diet. However, their use continues to increase as some of these issues have been resolved. The greatest increase in use has occurred where there has been a genuine desire to increase milk protein production while maintaining or decreasing the use of dietary protein.
Conclusions Identifying technologies for manufacturing high-quality ruminally protected amino acids has proven to be a challenging task. Currently, commercial products are limited to protected methionine and lysine. It is anticipated that derivatives and analogues of methionine, and modifications thereof, will be evaluated further as effective alternatives to protected methionine. The availability of an efficacious technology for increasing lysine supplies to dairy cattle would be desirable where high corn diets are
fed and high-lysine protein supplements such as blood meal and meat meal are not an option. The use of protected amino acids with established efficacy values, along with selective use of protein supplements, gives dairy producers the opportunity to balance diets for amino acids more adequately. The recent introduction of rumen-protected lysine products is welcomed because they allow for achieving higher concentrations of lysine in metabolizable protein than otherwise possible, particularly when high corn diets are fed and high-lysine protein supplements such as blood meal and meat meal are not an option. See also: Nutrients, Digestion and Absorption: Fermentation in the Rumen.
Further Reading Chalupa W (1975) Rumen bypass and protection of proteins and amino acids. Journal of Dairy Science 58: 1198–1218. Graulet B, Richard C, and Robert JC (2005) Methionine availability in plasma of dairy cows supplemented with methionine hydroxyl analog isopropyl ester. Journal of Dairy Science 88: 3640–3649. Greenwood RH and Titgemeyer EC (2000) Limiting amino acids for growing Holstein steers limit-fed soybean hull-based diets. Journal of Animal Science 78: 1997–2004. Kim CH, Kim TG, Choung JJ, and Chamberlain DG (2001) Effects of intravenous infusion of amino acids and glucose on the yield and concentration of milk protein in dairy cows. Journal of Dairy Research 68: 27–34. Koenig KM and Rode LM (2001) Ruminal degradability, intestinal disappearance, and plasma methionine response of rumenprotected methionine in dairy cows. Journal of Dairy Science 84: 1480–1487. Loerch SC and Oke BO (1989) Rumen protected amino acids in ruminant nutrition. In: Friedman M (ed.) Absorption and Utilization of Amino Acids, Vol. 3, pp. 187–200. Boca Raton, FL: CRC Press, Inc. National Research Council (1996) Nutrient Requirements of Beef Cattle, 7th revised edn. Washington, DC: National Academy Press. National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th revised edn. Washington, DC: National Academy Press. Robinson PH (1996) Rumen protected amino acids for dairy cattle: What is the future? Animal Feed Science and Technology 59: 81–86. Rulqin H, Guinard J, and Ve´rite´ R (1998) Variation of amino acid content in the small intestine digesta of cattle: Development of a prediction model. Livestock Production Science 53: 1–13. Rulquin H, Graulet B, Delaby L and Robert JC (2006) Effect of different forms of methionine on lactational performance of dairy cows. Journal of Dairy Science 89: 4387–4394. Rulquin H and Kowalczyk J (2003) Development of a method for measuring lysine and methionine bioavailability in rumen-protected products for cattle. Journal of Animal and Feed Sciences 12(3): 465–474. Rulquin H, Pisulewski PM, Ve´rite´ R, and Guinard J (1993) Milk production and composition as a function of postruminal lysine and methionine supply: A nutrient-response approach. Livestock Production Science 37: 69–90. Schwab CG (1995) Protected proteins and amino acids for ruminants. In: Wallace RJ and Chesson A (eds.) Biotechnology in Animal Feeds and Animal Feeding, pp. 115–141. New York: VCH Publishers Inc.; Weinheim, Federal Republic of Germany: VCH Verlagsgesellschaft.
Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids Schwab CG (1996) Rumen-protected amino acids for dairy cattle: Progress towards determining lysine and methionine requirements. Animal Feed Science and Technology 59: 87–101. St-Pierre NR and Sylvester JT (2005) Effects of 2-hydroxy-4-(methylthio) butanoic acid (HMB) and its isopropyl ester on milk production and composition by Holstein cows. Journal of Dairy Science 88: 2487–2497.
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Sudekum KH, Wolffram S, Ader P, and Robert JC (2004) Bioavailability of three ruminally protected methionine sources in cattle. Animal Feed Science and Technology 113: 17–25. Vyas D and Erdman RA (2009) Meta-analysis of milk protein yield responses to lysine and methionine supplementation. Journal of Dairy Science 92: 5011–5018.
Amino Acid Nutrition of Dairy Cattle Sources of Absorbed Amino Acids Absorbed amino acids are provided by ruminally synthesized microbial protein, rumen-undegradable feed protein (RUP), and, to a lesser extent, endogenous protein. Microbial protein refers to the constituent proteins of the bacteria, protozoa, and fungi that grow and multiply in the rumen. RUP is that portion of feed protein that escapes or resists ruminal degradation. Endogenous protein refers to protein originating in the body. Sources of endogenous protein include mucoproteins in saliva, sloughed epithelial cells (from the respiratory tract, mouth, esophagus, rumen, omasum, and abomasum), and enzyme secretions into the abomasum. The endogenous protein contribution to the duodenum includes free endogenous secretions and endogenous proteins incorporated into the microbial protein flow. Microbial protein typically supplies a majority of the amino acids required by the ruminant animal. However, RUP may supply more than 50% of the absorbed amino acids in high-producing dairy cows fed a high-concentrate diet that is balanced to meet requirements for rumendegradable protein and RUP. The quantity of amino acids provided by free endogenous protein secretions is small and appears to be correlated closely to intake of indigestible organic matter. It appears that about 10% of the total supply of absorbed amino acids is provided by endogenous protein.
Factors Affecting the Profile of Absorbed Amino Acids Two factors account for most of the variation in amino acid profiles of duodenal protein. These are the proportional contribution that RUP makes to total protein passage and the amino acid composition of that portion of total dietary protein predicted to be RUP. This would be expected because feed proteins vary in amino acid composition and usually differ from ruminally synthesized microbial protein (Table 1).
Limiting Amino Acids Limiting amino acids are essential amino acids in digested protein that are in shortest supply relative to body requirements for absorbed amino acids. Methionine,
lysine, and histidine have been identified most often as the most limiting amino acids for dairy cattle. The extent and sequence of their limitation is affected primarily by the amount of RUP in the diet and its amino acid composition. Methionine has been shown to be first limiting for growth and milk protein production when dairy cattle were fed high forage or soybean hull-based diets and intake of RUP was low. Methionine has also been identified as first limiting for growing cattle and lactating cows that were fed a variety of diets in which most of the supplemental RUP was provided by soybean protein, animal-derived proteins, or a combination of the two. In contrast, lysine has been identified as first limiting for growth and milk protein synthesis when maize and feeds of maize origin provided most or all of the RUP in the diet. Relative to concentrations in microbial protein, feeds of maize origin are low in lysine content and similar in methionine content, whereas soybean products and most animal-derived proteins are similar in lysine content and low in methionine content (Table 1). Methionine and lysine have been identified as colimiting amino acids for milk protein synthesis when cows were fed maize silage-based diets with little or no protein supplementation. Histidine has been identified as first limiting for milk protein production when dairy cows were fed grass silage/cereal (barley and oats)-based diets, with or without feather meal as the sole source of RUP supplementation. It should not be too surprising that these amino acids have all been shown to be first limiting. First, all have been identified as being among the most limiting amino acids in microbial protein. Methionine has been identified as first limiting and lysine as second limiting in microbial protein for nitrogen retention of both growing cattle and growing lambs. Histidine has been identified as possibly third limiting for sheep. Second, concentrations of methionine and lysine in most feed proteins are lower than those in microbial protein (Table 1). Thus, most feed proteins are not complementary to microbial protein and instead, when they are fed, will exacerbate rather than eliminate deficiencies of methionine and lysine in metabolizable protein. This also appears to be why methionine and lysine become more limiting (relative to the other essential amino acids) with increasing intakes of complementary sources of RUP.
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390 Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids Table 1 A comparison of the essential amino acid (EAA) profiles of body lean tissue and milk with that of ruminal bacteria and protozoa and some common feeds Arg
His
Ile
Leu
Lys
Met
Phe
Thr
Trp
Val
EAA
Item
(% of total EAA)
Animal products Lean tissuea Milkb
16.8 7.2
6.3 5.5
7.1 11.4
17.0 19.5
16.3 16.0
5.1 5.5
8.9 10.0
9.9 8.9
2.5 3.0
10.1 13.0
– –
Rumen microbes Bacteriac Protozoad
10.4 9.3
4.1 3.6
11.5 12.7
15.9 15.8
16.5 20.6
5.1 4.2
10.1 10.7
11.3 10.5
2.7 2.8
12.4 9.7
– –
Foragese,f Alfalfa hay Alfalfa silage Corn silage Grass hay Grass silage
12.5 10.9 6.2 11.7 9.4
4.7 4.7 5.7 4.9 5.1
10.3 11.1 10.6 10.0 10.9
17.9 17.9 27.2 18.8 18.8
12.4 12.1 7.9 10.5 10.1
3.8 3.8 4.8 3.9 3.7
11.6 11.7 12.1 11.8 13.4
10.6 10.7 10.1 10.9 10.2
3.6 2.7 1.4 3.7 3.3
12.7 14.1 14.1 13.6 15.0
41.2 35.6 31.6 33.1 32.6
Grainse Barley Corn Oats Sorghum Wheat
13.4 11.5 16.6 9.4 13.6
6.1 7.8 5.9 5.7 7.1
9.2 8.2 9.1 9.3 9.6
18.5 27.9 17.7 31.9 19.3
9.6 7.1 10.1 5.4 8.1
4.5 5.3 4.2 4.2 4.6
13.5 11.5 12.5 12.3 13.3
9.1 8.8 8.4 7.8 8.4
3.1 1.8 2.9 2.5 3.5
13.0 10.0 12.6 11.6 12.3
37.7 40.1 41.2 42.8 34.4
Plant proteinse Brewers’ grains Canola meal Corn DDG w/sol. Corn gluten meal Cottonseed meal Linseed meal Peanut meal Soybean meal Sunflower meal
14.7 16.5 10.7 7.1 26.0 20.9 27.6 16.2 20.8
5.1 6.6 6.6 4.7 6.6 4.8 6.0 6.1 6.2
9.8 9.0 9.8 9.1 7.3 11.0 8.1 10.1 9.9
20.0 15.9 25.4 37.2 13.8 14.5 15.9 17.2 15.2
10.4 13.2 5.9 3.7 9.7 8.7 8.3 13.9 8.0
4.3 4.4 4.8 5.2 3.7 4.2 2.9 3.2 5.6
11.7 9.5 12.9 14.1 12.5 11.1 12.1 11.6 11.0
9.1 10.4 9.1 7.5 7.6 8.9 6.7 8.7 8.7
2.5 3.4 2.3 1.2 2.8 3.7 2.4 2.8 2.9
12.1 11.1 12.4 10.3 10.0 12.3 9.8 10.2 11.7
39.2 42.6 37.8 45.2 42.6 42.2 40.1 45.3 42.2
7.8 16.2 13.1 19.5
1.3 2.7 6.4 5.3
2.2 11.4 9.2 7.7
22.7 19.9 16.2 17.2
15.9 6.0 17.2 14.5
2.1 1.8 6.3 3.9
12.1 11.6 9.0 9.4
7.7 11.1 9.4 9.1
2.8 1.7 2.4 1.6
15.4 17.6 10.8 11.8
56.4 42.7 44.5 35.7
5.0
4.5
12.1
21.2
17.6
3.3
7.0
14.1
3.5
11.7
42.2
Animal proteinse Blood meal Feather meal Fish meal Meat and bone meal Whey, dry
(% of CP)
a
Average values of empty, whole body carcasses as reported in three studies. Average values as reported in three studies. c The mean of average values from over 100 dietary treatments. d Average values from 15 literature reports. e Calculated from values presented in National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th revised edn. Washington, DC: National Academy Press. f Legume and grass hays and silages are mid-maturity. b
Third, lysine is more vulnerable to heat processing than the other essential amino acids. Overheating feed proteins can decrease lysine concentrations as well as decrease the digestibility of the remaining lysine more than that of total protein. Finally, concentrations of histidine are lower in grasses and legumes, oats, barley, and particularly feather meal, as compared to most other feeds (Table 1). This is probably why diets consisting solely of these feeds have been shown to be more limiting in histidine than in methionine or lysine.
Ruminally Protected Amino Acids History of Development Interest in protecting free amino acids from ruminal degradation dates back to the 1960s and early 1970s, when it became apparent from abomasal, intestinal, and intravenous infusion trials that the profile of absorbed amino acids was not always optimum in ruminants. These trials indicated that the sulfur amino acids were clearly first limiting for wool growth and body weight gains of sheep and that methionine was a limiting amino
Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids
acid for growing cattle and lactating dairy cows. Thus, several laboratories began to devise procedures to protect methionine from ruminal degradation. Subsequent interest developed in protecting lysine when it was discovered to be a second limiting for growing lambs and either first or second limiting for growing cattle and lactating dairy cows. Many approaches have been evaluated to physically protect methionine and lysine from ruminal degradation. Initial attempts focused on protecting methionine with lipids, often in combination with inorganic materials and carbohydrates as stabilizers, softening agents, and fillers. For example, in the 1960s, Delmar Chemicals of Canada developed a product in which a core of DL-methionine, colloidal kaolin, and tristearin was wrapped in a continuous film of tristearin. The product contained 20% methionine. A few years later, Rumen Kjemi A/S of Oslo, Norway, introduced a somewhat more efficacious product (Ketionin) that had a higher intestinal release of the encapsulated methionine. The product contained 30% DL-methionine, 2% glucose, 4% stabilizer, antioxidant and flavoring agents, 6% CaCO3, and 58% tristearin and oleic acid. Several other lipid-protected methionine products have also been evaluated. The greatest challenge with using lipids as the primary encapsulating material is to identify a combination of materials and process that has both a high ruminal escape and intestinal release of the amino acid. The most effective approach has been to surface-coat amino acids with enzyme-resistant, pH-sensitive synthetic polymers that are insoluble in the more neutral pH environment of ruminal digesta but highly soluble in the acidic abomasum. This approach provides for a postruminal delivery system that is independent of enzyme function and, instead, relies on the pH differences between the rumen and the abomasum for ruminal protection and intestinal release. Polymerprotected amino acids have higher ruminal protection and intestinal release coefficients than other products. The patent rights for the use of pH-sensitive polymers for protecting nutrients from ruminal degradation is currently held by Adisseo Animal Nutrition, Antony, France. Another method that has been explored for increasing supplies of methionine and lysine to ruminants is the use of derivatives and analogues of these amino acids. Most of the derivatives and analogues that have been investigated for level of rumen protection are those of methionine. Amino acid derivatives are free amino acids to which a chemical blocking group has been added to the -amino group, or in which the acyl group has been modified. Some examples of derivatives that have been shown to have some resistance to ruminal degradation
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are isopropyl-DL-methionine, t-butyl-DL-methionine, N-stearoyl-DL-methionine, N-oleoyl-DL-methionine, capryl-caproylic-DL-methionine, and di-hydroxymethylL-lysine-Ca. There is evidence that the extent of ruminal escape is greater with shorter-chain alkyl esters than with longer-chain alkyl esters. Although these and other derivatives show promise, most have not been investigated adequately to determine the extent to which they will increase postruminal supplies of absorbable methionine. An amino acid analogue results from the substitution of the -amino group of an amino acid with a nonnitrogenous group. The most studied amino acid analogue is methionine hydroxy analogue (MHA; DL- -hydroxy- -mercaptobutyrate), more appropriately called 2-hydroxy-4-(methylthio)butanoic acid (HMB). Studies indicate that free HMB (1) is more resistant to ruminal degradation than free methionine, (2) is more absorbable from the rumen and omasum than methionine, and (3) is converted to methionine in most mammalian tissues. However, because of no measurable effects on blood methionine concentrations when fed to cows on methionine-adequate diets, or on the content of milk protein when fed to methionine-deficient cows, it appears that feeding HMB, in either the acid or salt form, has little or no replacement value for ruminally protected methionine. Research has shown that several esters of HMB enhance ruminal escape of HMB, at least in part, because of their apparent ability to be absorbed across the rumen wall. The isopropyl ester of HMB (HMBi) has been shown to have an excellent replacement value for absorbed methionine.
Examples of Commercial Protected Methionine Products Mepron M85 (Evonik-Degussa Corporation, Germany): This is an example of a surface-coated, carbohydrate-protected product. The small pellets have a diameter of 1.8 mm, a length of 3–4 mm, and an approximate density of 1.2 g cm 3. The pellets consist of a core of methionine and starch coated with several thin layers of ethylcellulose and stearic acid. The final product contains a minimum of 85% DL-methionine, and approximately 8.5% nonstructural carbohydrates, 3.5% neutral detergent fiber, 1.5% ash, 1.0% moisture, and 0.5% crude fat. The technology is a combination of coating materials and application that allows for a large payload of methionine. Because enzymatic digestion of the ethylcellulose is minimal, degradation of the product occurs primarily through physical action and abrasion. The result is a product that is slowly degraded in the rumen and slowly releases methionine into the intestine.
392 Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids
METHIOPLUS (Kemin Industries, Des Moines, IA, USA): Methioplus is produced by encapsulating DL-methionine with hydrogenated vegetable oils. The preparation method is described as microencapsulation by spray freezing using the patented MICROPEARLS process. The coating material and method of application are designed to provide a coating matrix that is able to resist rumen breakdown and release the ingredient in the intestine. The yellow microcapsules contain 55% DL-methionine. Met-Plus (Novus International, Inc., St. Louis, MO, USA): This is an example of a lipid-protected product. It is a matrix compound that contains 65% DL-methionine embedded in a mixture of calcium salts of long-chain fatty acids, lauric acid, and butylated hydroxytoluene (BHT); BHT is a preservative for the fatty acids. However, like other lipid-coated products, the technology relies on achieving a balance between ruminal protection and intestinal release so as to maximize the amount of methionine available for intestinal absorption while minimizing losses in the rumen and in feces. Smartamine M (Adisseo, Antony, France): This is an example of a lipid/pH-sensitive polymer-protected product. It is a surface-coated product that contains a minimum of 75% DL-methionine. The small 2-mm pellets consist of a core of DL-methionine and ethyl cellulose that is covered with a coat of stearic acid containing small droplets of poly(2-vinylpyridine-co-styrene). The copolymer contributes 3% by weight of the final product. The presence of the copolymer appears to alter the stereochemistry of the stearic acid such that the surface coating becomes enhanced in its resistant to ruminal degradation. The presence of the copolymer, because of its solubilization at low pH, also allows for rapid release of the methionine in the abomasum. MetaSmart (Adisseo, Antony, France): This is the HMBi. While technically an amino acid analogue, it is usually referred to as a protected methionine product because of its ability to provide significant amounts of absorbable HMB to the cow. The compound is formed by reacting Rhodimet AT88 (HMB) with isopropanol. The resulting HMBi provides for a limited degree of protection from ruminal degradation, but it provides a vehicle for a more rapid absorption across the ruminal and omasal walls. Commercial Sources of Methionine Analogues There are three commercial sources of free methionine analogues. These are Alimet (Novus International, Inc., St. Louis, MO, USA), Rhodimet AT88 (Adisseo, Antony, France), and MFP (Novus International, Inc., St. Louis, MO, USA). Alimet and Rhodimet AT88 are both liquid sources of HMB. Chemically, the compounds are the same. Both are used extensively as a substitute for
methionine in the poultry and swine industry. However, Novus International also has Alimet patented for use in dairy cows and recommends its use as a source of ruminally protected methionine. Adisseo considers the ruminal escape and ruminal absorption of Rhodimet AT88 to be too low to recommend its use as a source of ruminally protected methionine. Novus International also recommends the use of MFP, which is the Ca salt of HMB, and thus the dry source of HMB, as a source of ruminally protected methionine. Both companies recognize the potential benefits of feeding HMB on rumen function (e.g., increased fiber and protein digestion and increased bacterial protein synthesis and efficiency of synthesis) and animal performance (e.g., increased milk yield and butterfat content). Commercial Sources of Rumen-Protected Lysine AminoShure-L (Balchem Corporation, New Hampton, NY, USA): Launched in 2008, AminoShure-L was the first commercial source of rumen-protected lysine to become available in the United States. The product is formed by encapsulating L-lysine-HCl with multiple layers of foodgrade lipids. The spherical shaped tan to light brown granules contain 38% crude protein, a minimum of 36% lysine, 53% ether extract, and 9.0% chloride. MEGAMINE-L (Church & Dwight Co., Princeton, NJ, USA): Released in 2009, the final product contains 80% Megalac and 20% lysine-HCl. The product is formed by adding lysine-HCl to the Megalac production process. The resulting 0.32 cm pellets have a density of 1.05 and contain 68% fat, 16% lysine, 7% calcium, and 5% lipidsoluble materials. Ethoxyquin is added as a preservative. LYS-50 (Kemin Industries, Des Moines, IA, USA): LYS-50 is produced by the same MICROPEARLS process as described for Methioplus. The product typically contains 50% L-lysine-HCl. Efficacy of Products Responsible use of ruminally protected methionine and lysine products requires estimates of their ability to provide methionine and lysine for protein synthesis. Insofar as possible, estimates of ‘methionine and lysine bioavailability’ must be accurate and reliable under the conditions in which they are fed in production systems. Approaches
Unfortunately, there is no universally accepted, standardized procedure(s) for obtaining estimates of methionine and lysine bioavailability. These are needed to bring uniformity to estimates of amino acid bioavailability and to more accurately compare the efficacy of different products. Current approaches can be categorized as factorial
Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids
approaches, blood response approaches, and production response approaches. The factorial approach involves independent measurements of ruminal escape, intestinal disappearance (digestibility), and, in the case of free or protected forms of HMB, metabolic conversion to methionine. Animals with cannulae in the rumen, duodenum, and preferably also in the ileum are required. Estimates of ruminal escape and intestinal disappearance of amino acid from protected methionine and lysine products have been obtained using both the in situ nylon-bag procedure and the cannulated cow in vivo procedure. Use of the in situ procedure requires measurements of rate of passage of protected amino acid products from the rumen. Factorial approaches, particularly those involving in situ nylon-bag techniques, have been questioned as to their appropriateness for measuring the intestinal release of amino acids from a rumen-protected product that relies on abrasion and physical forces for its degradation. Moreover, the procedures do not account for the physiological aspects of digestion such as mastication and digesta passage. The in situ procedure is also not suitable for soluble or liquid products such as HMB and HMBi. Blood response approaches are an attractive alternative to factorial approaches because they are easier to conduct and they allow liquid and pulverulent products to be evaluated. Studies with cattle have shown that a linear relationship exists between increasing supplies of absorbable methionine and lysine and plasma methionine and lysine concentrations. Two variations of the approach have been used. The first is the dose–response approach. This approach involves determination of differences in the slope of measured blood amino acid concentrations between graded dietary doses of the product and graded intestinal doses of the infused amino acid. The second is the ‘area under the curve’ (AUC) approach. This approach involves the ruminal administration of a pulsed dose of equimolar amounts of different methionine or lysine sources and comparing the AUC of the plasma methionine and lysine response curves that result. To obtain estimates of methionine bioavailability for methionine products, Smartamine M is often used as the positive control treatment with the assumption that it has a methionine bioavailability value of 80%. A milk protein content response approach has also been used to obtain estimates of amino acid bioavailability. This approach involves determination of differences in slope of measured milk protein concentrations between graded dietary inclusion levels of the product and graded intestinal infusions of the free amino acid when cows are fed a basal diet deficient in the amino acid in question. As with the blood response approach, some of the studies that focused on obtaining estimates of methionine bioavailability for
393
methionine products replaced intestinally infused methionine with Smartamine M as the positive control treatment with the assumption that Smartamine M has a methionine bioavailability value of 80%. Numerous studies with lactating cows indicate that content of milk protein is the most responsive criterion to small changes in concentrations of methionine and lysine in metabolizable protein. Using production responses such as milk yield, milk fat concentration, and milk component yields as criteria for comparing or evaluating products as sources of rumenprotected amino acids is not valid because of the effect that changes in rumen function can have on them. For example, several experiments have indicated increases in forage and fiber digestion, protein digestion, acetate-topropionate ratios, bacterial protein synthesis, efficiency of bacterial protein synthesis, and protozoan numbers as a result of feeding methionine hydoxy analogue. When these benefits are realized and one or more of the effects are limiting animal performance, it should not be surprising that increases in feed intake, milk yield, and milk fat concentration are observed.
A Comparison of Some Available Products Relying on the blood and milk protein content response approaches as being the most appropriate techniques for arriving at estimates of ‘methionine and lysine bioavailability’, a summary of available research indicates that Smartamine M clearly has the greatest efficacy as a source of absorbable methionine. The industry use of a methionine bioavailability value of 80% appears reasonable when the manufacturers recommendations for mixing with other supplements and rations are followed. The data are not as consistent for Mepron M85 and MetaSmart as they are for Smartamine M but it appears that the methionine bioavailability value for the two products is somewhere between 40 and 50%. It is the opinion of the author that there is not enough data to make similar claims of efficacy. Research indicates no measurable effects of Alimet or Rhodimet AT88 on blood methionine concentrations when fed to cows on methionine-adequate diets, or on content of milk protein when fed to methionine-deficient cows. Therefore, it appears that feeding HMB, in either the acid or salt form, has little or no replacement value for ruminally protected methionine. It appears quite certain that the methionine bioavailability of these two products is less than 5%. Pulse-dosing large amounts into the rumen has yielded apparent rumen escape values of 40–50%. However, adding incremental amounts of these products to methionine-deficient diets has not increased milk protein concentrations or blood methionine concentrations.
394 Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids
The rumen-protected lysine products have been introduced only recently and have not had the research scrutiny of most of the methionine supplements. However, because they are all lipid-encapsulated or lipid-protected products, and depend on both the mechanical and enzymatic aspects of digestion throughout the gastrointestinal tract for lysine release, it is unlikely in most cases that more than half of the protected lysine is available for absorption in the small intestine. The Benefits of Using Rumen-Protected Methionine and Lysine Products The use of these products is of significant help in achieving a more desirable profile of the most limiting amino acids in metabolizable protein. Clearly, their use allows the alleviation of methionine and lysine deficiencies without increasing the intake of RUP or changing the profile of the other essential amino acids in metabolizable protein. However, their use also allows for more selective use of protein supplements, without regard to their content of methionine and lysine, to more adequately meet desired levels of other limiting amino acids in metabolizable protein. The result is more efficient use of absorbed amino acids for protein synthesis, increased weight gains and higher levels of milk protein production, and reduced need for RUP in the diet. The use of rumen-protected methionine and lysine products has been limited. Reasons for this include (1) inadequate knowledge of amino acid requirements and the required concentrations of limiting amino acids in metabolizable protein, (2) lack of easy-to-use computer models that predict accurately their need, (3) issues of product efficacy and cost relative to anticipated benefits, and (4) lack of ease of incorporating desired concentrations into the diet. However, their use continues to increase as some of these issues have been resolved. The greatest increase in use has occurred where there has been a genuine desire to increase milk protein production while maintaining or decreasing the use of dietary protein.
Conclusions Identifying technologies for manufacturing high-quality ruminally protected amino acids has proven to be a challenging task. Currently, commercial products are limited to protected methionine and lysine. It is anticipated that derivatives and analogues of methionine, and modifications thereof, will be evaluated further as effective alternatives to protected methionine. The availability of an efficacious technology for increasing lysine supplies to dairy cattle would be desirable where high corn diets are
fed and high-lysine protein supplements such as blood meal and meat meal are not an option. The use of protected amino acids with established efficacy values, along with selective use of protein supplements, gives dairy producers the opportunity to balance diets for amino acids more adequately. The recent introduction of rumen-protected lysine products is welcomed because they allow for achieving higher concentrations of lysine in metabolizable protein than otherwise possible, particularly when high corn diets are fed and high-lysine protein supplements such as blood meal and meat meal are not an option. See also: Nutrients, Digestion and Absorption: Fermentation in the Rumen.
Further Reading Chalupa W (1975) Rumen bypass and protection of proteins and amino acids. Journal of Dairy Science 58: 1198–1218. Graulet B, Richard C, and Robert JC (2005) Methionine availability in plasma of dairy cows supplemented with methionine hydroxyl analog isopropyl ester. Journal of Dairy Science 88: 3640–3649. Greenwood RH and Titgemeyer EC (2000) Limiting amino acids for growing Holstein steers limit-fed soybean hull-based diets. Journal of Animal Science 78: 1997–2004. Kim CH, Kim TG, Choung JJ, and Chamberlain DG (2001) Effects of intravenous infusion of amino acids and glucose on the yield and concentration of milk protein in dairy cows. Journal of Dairy Research 68: 27–34. Koenig KM and Rode LM (2001) Ruminal degradability, intestinal disappearance, and plasma methionine response of rumenprotected methionine in dairy cows. Journal of Dairy Science 84: 1480–1487. Loerch SC and Oke BO (1989) Rumen protected amino acids in ruminant nutrition. In: Friedman M (ed.) Absorption and Utilization of Amino Acids, Vol. 3, pp. 187–200. Boca Raton, FL: CRC Press, Inc. National Research Council (1996) Nutrient Requirements of Beef Cattle, 7th revised edn. Washington, DC: National Academy Press. National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th revised edn. Washington, DC: National Academy Press. Robinson PH (1996) Rumen protected amino acids for dairy cattle: What is the future? Animal Feed Science and Technology 59: 81–86. Rulqin H, Guinard J, and Ve´rite´ R (1998) Variation of amino acid content in the small intestine digesta of cattle: Development of a prediction model. Livestock Production Science 53: 1–13. Rulquin H, Graulet B, Delaby L and Robert JC (2006) Effect of different forms of methionine on lactational performance of dairy cows. Journal of Dairy Science 89: 4387–4394. Rulquin H and Kowalczyk J (2003) Development of a method for measuring lysine and methionine bioavailability in rumen-protected products for cattle. Journal of Animal and Feed Sciences 12(3): 465–474. Rulquin H, Pisulewski PM, Ve´rite´ R, and Guinard J (1993) Milk production and composition as a function of postruminal lysine and methionine supply: A nutrient-response approach. Livestock Production Science 37: 69–90. Schwab CG (1995) Protected proteins and amino acids for ruminants. In: Wallace RJ and Chesson A (eds.) Biotechnology in Animal Feeds and Animal Feeding, pp. 115–141. New York: VCH Publishers Inc.; Weinheim, Federal Republic of Germany: VCH Verlagsgesellschaft.
Feed Ingredients | Feed Supplements: Ruminally Protected Amino Acids Schwab CG (1996) Rumen-protected amino acids for dairy cattle: Progress towards determining lysine and methionine requirements. Animal Feed Science and Technology 59: 87–101. St-Pierre NR and Sylvester JT (2005) Effects of 2-hydroxy-4-(methylthio) butanoic acid (HMB) and its isopropyl ester on milk production and composition by Holstein cows. Journal of Dairy Science 88: 2487–2497.
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Sudekum KH, Wolffram S, Ader P, and Robert JC (2004) Bioavailability of three ruminally protected methionine sources in cattle. Animal Feed Science and Technology 113: 17–25. Vyas D and Erdman RA (2009) Meta-analysis of milk protein yield responses to lysine and methionine supplementation. Journal of Dairy Science 92: 5011–5018.