1. Dynamics of Protein Metabolism in the Ruminant

9. 2.2

10. 2.3

12. Analysis of Dietary Protein
Crude protein (CP %) = total N (%)  6.25
Factor is based on 16% N in protein.
True protein varies between 13 to 19% N.
Source %N in protein Conversion factor
oilseed proteins
cereal proteins
meat or fish
alfalfa
true microbial protein
Not all N in protein is present as true protein.
Crude protein provides a rough estimate of dietary protein concentration for two reasons. First it is based on concept that 16% of the weight of protein is N, but the N in true protein varies between 13 to 19%. Secondly, not all N in protein sources is present as true protein.

16. Classification of protein and nitrogen fractions in feedstuffs
Total
Borate
Buffer
Neutral
Detergent
Acid
Detergent
Sol A B1
Insol B2 B3 C
Sol A1 B1 B2
Insol B3 C
Sol A1 B1 B2 B3
Insol C
Solubility in borate-phosphate buffer, neutral detergent and acid detergent.
Fractions A and B1 are soluble in borate buffer. Precipitation of this fraction with tungstic acid allows the determination of the A fraction. Extraction with neutral detergent buffer isolates fractions A, B1 and B2 (soluble in ND) from B3 and C (insoluble in ND). Acid detergent partitions proteins into fractions C (insoluble in AD), and A and all the B’s (soluble in AD.

18. Crude Protein True protein (60 to 80%) Non-protein nitrogen Lignified
Essential amino acids
Arginine (Arg)
Histidine (His)
Isoleucine (Ile)
Leucine (Leu)
Lysine (Lys)
Methionine (Met)
Phenylalanine (Phe)
Threonine (Thr)
Tryptophan (Trp)
Valine (Val)
Non-essential
amino acids
Alanine (Ala)
Asparagine (Asn)
Aspartic acid (Asp)
Cysteine (Cys)
Glutamic acid (Glu)
Glutamine (Gln)
Glycine (Gly)
Proline (Pro)
Serine (Ser)
Tyrosine (Tyr)
Amides
Amines
Amino acids
Peptides
Nucleic acids
Nitrates
Ammonia
Urea
Crude protein is a useful measure for evaluating diets but it oversimplifies the very complex nitrogenous components of diets.
Although some feedstuffs particularly fresh forages and silages contain substantial amounts of organic NPN, from a practical point of view, NPN in formulated feeds refers to added materials, primarily urea.

19. Fraction A contains ammonia, nitrates, amino acids and peptides; ruminal degradation is assumed to be instantaneous and none reaches the small intestine. B1 consists of globulins and some albumins. Because ruminal degradation is 200 to 300 %/h, it is almost completely fermented in the rumen. B2 proteins contain most of the albumins and glutelins. Ruminal degradation is 5 to 15 %/h. B3 proteins are prolamins, extensin proteins (cell wall associated proteins) and heat denatured proteins that did not undergo the Maillard reaction. They are degraded in the rumen at 0.1 to 1.5 %/h. Fraction C proteins consist of Maillard reaction proteins (heat damaged protein) and nitrogen bound to lignin. They are not degraded in the rumen.

20. Calculations Log of % nutrient remaining Protein Fraction A, B1 B2
B3 C
Hours
Calculate slope (change per hour) of each line.
Slope = kd, has units of % of pool remaining that is lost per hour.

21. Terms for describing nitrogen components of feedstuffs
Degradable Intake Protein (DIP): dietary crude protein degraded in the rumen.
Undegraded intake protein (UIP): dietary crude protein that is not degraded in the rumen and escapes or bypasses the rumen to the intestine. It is largely true protein but also contains ADFIP.
Soluble protein (SolP): Contains non-protein nitrogen, amino acids and peptides. Soluble protein is degraded instantaneously in the rumen.
Protein requirements of the young growing ruminants and productive dairy cows often exceed the ruminal synthesis of microbial protein. Recognition of this requirement has resulted in the development of protein systems for beef and dairy cattle that distinguishes between dietary protein that is degraded in the rumen and dietary protein that escapes ruminal degradation.

22. Terms for describing nitrogen components of feedstuffs
Non-protein nitrogen (NPN): Includes amides, amines, amino acids, some peptides, nucleic acids, nitrates, urea, ammonia. Degraded instantaneously in the rumen.
Acid detergent fiber insoluble protein (ADFIP): Consists of heat damaged protein and nitrogen associated with lignin. Resists ruminal fermentation and is indigestible in the small intestine.

23. Protein content of common feedstuffs
CP DIP UIP SolP NPN ADFIP
Feedstuff %DM %CP %CP %CP %SolP %CP
Alfalfa silage
Barley silage
Corn silage
Alfalfa hay
Timothy hay
Barley straw
Barley grain
Fermented feeds such as silages contain large amounts of soluble protein all of which is NPN. Hay proteins contain less soluble protein, but like the silages the protein is largely degradable in the rumen. Barley straw contains very little protein, much of which is lignified N and unavailable to the animal. Barley grain contains less soluble protein but the majority of the insoluble protein is readily degraded in the rumen. In feeds the unavailable N ranges from 3 to 15% of total N.

24. Protein content of protein supplements
CP DIP UIP SolP NPN ADFIP
Plant sources %DM %CP %CP %CP %SolP %CP
Canola meal
Soybean meal
Soypass*
Brewer’s grains
Corn distiller’s gr
Corn gluten meal
*Commercial product: LignoTech USA, Inc.
Protein supplements are defined as having a crude protein content of
> 20%.
Principle protein supplements of plant origin, such as canola meal and soybean meal, are derived from the meals after the oil has been extracted from the seeds. The majority of the protein in meals is degraded in the rumen. The degradablility of the protein in meals may be altered with the application of heat. Heat denatures the protein changing its solubility. SoyPass is a heat treated soybean meal with higher UIP than untreated soybean meal. The intestinal digestibility of the UIP is similar to untreated SBM. Increasing the UIP increases the bypass value of the protein.
Distillers grains and brewers grains are by-products of the distilleries and breweries. Corn gluten meal is a by-product of corn starch and corn syrup manufacture, it is the residue remaining after removal of the larger part of starch and germ, and separation of the bran. All are high in bypass protein.

25. Protein content of protein supplements
CP DIP UIP SolP NPN ADFIP
%DM %CP %CP %CP %SolP %CP
Animal sources
Blood meal
Feather meal
Fishmeal
Meat and bone
Non-protein nitrogen sources
Urea
All animal protein sources are high in crude protein with high bypass value. There are limits to the amount of these protein sources that can be included in the ration because they tend to be less palatable. In 1997, the USDA prohibited the feeding of ruminant products to ruminant animals and thus there is little feeding of meat and bone meal. This move was in response to BSE.

26. Ruminally Protected Protein
A nutrient(s) fed in such a form that provides an increase in the flow of that nutrient(s), unchanged, to the abomasum, yet is available to the animal in the intestine
Methods to decrease the rate and extent of ruminal degradation involved the use of heat, chemical agents, or combination of both

27. Heat Processing
Heat processing decrease rumen protein degradation by denaturation of proteins and by the formation of protein-CHO (Millard reactions) and protein cross-links. Commercial methods that rely solely on heat include: cooker-expeller, roasting, extrusion, pressure toasting, and micronization.
Heat processing reduced fraction A, increases fraction B, and C, and decreases in the fractional rates of degradation of the fraction B

28. Heat Processing cont.
Over heating also causes significant losses of lysine, cysine, and arginine.
Among those AA, lysine is the most sensitive to heat damage and undergoes both destruction and decreased availability

29. Chemistry of the Maillard reaction between reducing sugars and lysine residues during heat treatment of proteins
Heating is a common method of increasing the protein escape from the rumen. The mechanism of protection with heat treatment involves principally the Maillard reaction sequence between the -amino group of lysine residues and carbonyl compounds, usually reducing sugars such as glucose and fructose. The formation of the Shiff’s base is reversible but the modified Amadori compound and the polymers are nutritionally unavailable.

30. Heat Processing
Careful control of heating conditions is required to optimize the content of digestible RUP.
Under heating results in only small increase
in digestible RUP.
. Over heating reduces the intestinal digestibility of RUP through the formation of indigestible Millard products and protein complexes.

32. Chemical Treatment
Chemical treatment of feed proteins can be divided into three categories: 1) chemicals that combine with and introduce cross-links in proteins, (2) chemicals that alter protein structure by denaturation (e.g., acids, alkalis, and ethanol), and (3) chemicals that bind to proteins but with little or no alteration of protein structure (e.g., tannins).

34. Chemical Treatment cont.
For a variety of reasons, often including less than desired levels of effectiveness, use of chemical agents as the sole treatment for increasing the RUP content of feed proteins has not received commercial acceptance.
A more effective approach involving “chemical” agents has been to combine chemical and heat treatments.
An example of this approach is the addition of lignosulfonate, a byproduct of the wool pulp industry that contains a variety of sugars (mainly xylose), to oilseed meals before heat treatment.

36. Chemical Treatment cont.
The combined treatments enhance non-enzymatic browning (Millard reactions) because of the enhanced availability of sugar aldehydes that can react with protein.

37. Characterization of Protein Sources
Common protein supplements that are high in RUP are:
Fish meal
Meat and bone meal (MBM)
Feather meal (FtM)
Blood meal (BM)
Corn gluten meal (CGM)
Distillers dried grains (DDG)
DDG with solubles (DDGS)
Brewers dried grains (BDG)
Brewers wet grains (BWG)

47. Nitrogen transactions in the rumen
Sources of nitrogen in the rumen
Dietary crude protein (true protein and NPN).
Recycled microbial protein (bacteria and protozoa).
Endogenous N (urea, abraded epithelial cells, salivary proteins).
Crude protein (soluble and insoluble) is useful to describe the diet but when it comes to describing protein metabolism in the rumen, N transactions, which include all forms of N, must be considered.
Factors affecting the extent of ruminal degradation of fermentable particulate proteins will depend on the structural characteristics of proteins, the number of hydrolysable sites, time of residence in the rumen, rate of solubilization, enzymatic concentration and pH.
All interconversions of N in the rumen occur by the action of microorganisms.

48. Degradation of nitrogenous compounds by ruminal microorganisms
Bacteria
30 to 50% of the bacteria are proteolytic.
Most species have some activity with the exception of the main cellulolytic bacteria (Fibrobacter succinogenes, Ruminococcus flavefacians, R. albus).
Major proteolytic bacteria: Ruminobacter amylophilus, Butyrivibrio Fibrisolvens and Prevotella ruminicola.
P. ruminicola is the most numerous proteolytic bacteria (> 60% of ruminal bacteria) with strains that occur on both roughage and mixed roughage-concentrate diets.

49. Bacteria cont’d Protozoa Fungi
R. amylophilus is the most active proteolytic bacteria. Important on starch-based diets.
Breakdown of both soluble and insoluble protein in the rumen.
Protozoa
Minor involvement in soluble protein breakdown.
Engulf and hydrolyze particulate proteins and bacteria.
Predatory activity of protozoa against rumen bacteria contributes to bacterial protein degradation and turnover in the rumen.
Fungi
Minor role in protein degradation.

50. PROTEIN OLIGOPEPTIDES DIPEPTIDES AMINO ACIDS AMMONIA Dipeptidyl
D. ruminantium, B. fibrisolvens, E. caudatum
Clostridium spp, E. simplex, E. budayi
E. caudatum ecaudatum, E. ruminantium, E. maggii
Fusobacterium spp., E. medium
L. multipara O. caudatus, P. ruminicola
P. multivesiculatum, R. amylophilus, S. ruminantium
O. joyonii, N. frontalis, S. bovis, P. communis
OLIGOPEPTIDES
Dipeptidyl
peptidase
S. bovis, R. amylophilus, P. ruminicola
DIPEPTIDES
D. ruminantium, E. caudatum
F. succinogenes, M. elsdenii, P. ruminicola
Isotricha spp., L. multipara, S. ruminantium
Dipeptidase
Protein degradation in the rumen
Hydrolysis of protein by rumen microorganisms releases oligopeptides (4 to 9 AA), which are broken down to smaller peptides and finally to amino acids. Peptide breakdown in the rumen is a two-step process, dipeptidyl peptidases releases dipeptides (and tripeptides) from oligopeptides, followed by dipeptidases which cleave the resulting dipeptides into amino acids. The only common bacterial species that possesses high dipeptidyl peptidase is P. ruminicola. Ciliate protozoa also have high peptidase activity. Amino acid degradation is rapid yielding carbon skeletons and ammonia.
AMINO ACIDS
C. aminophilum, C. sticklandii
P. anerobius, B. fibrisolvens, P. ruminicola
M. elsdenii, S. ruminantium, E. caudatum
Isotricha spp.
AMMONIA

51. Properties of ammonia producing bacteria
High Numbers
Low Activity
Butyrivibrio fibrisolvens
Megasphaera elsdenii
Prevotella ruminicola
Selenomonas ruminantium
Streptococcus bovis
> 109 per ml
10 to 20 nmol NH3 min-1
(mg protein)
Low Numbers
High Activity
Clostridium aminophilum
Clostridium sticklandii
Peptostreptococcus anaerobius
107 per ml
300 nmol NH3 min-1
(mg protein)
Bacteria with amino acid deaminating capability fall into two groups: numerically abundant bacteria with low deaminiative activity, and few species with exceptionally high deaminative activity. The bacteria with high activity are atypical in that they ferment amino acids as their major source of energy and N. Ciliate protozoa also play a significant role in deamination of amino acids.

52. Breakdown of NPN in the rumen
Major sources of NPN include: dietary NPN, and recycled urea.
Extremely rapid and releases ammonia.
Major end product of protein degradation in
the rumen
Ammonia

53. Influence of diet on proteolysis
Concentrate
Increase in total microbial population, including several of the more active protein degrading bacteria which are also amylolytic (Prevotella rumincola, Ruminobacter amylophilus and Streptococcus bovis).
Fresh forage
Increase in the proportion of proteolytic bacteria relative to total microbial population.
Increased proteolytic activity is associated with feeding high proportions of cereals in the diet and fresh forage. Proteolytic activity of the rumen fluid, the numbers of proteolytic bacteria, and the predominant proteolytic species are all diet dependent but are related more to energy level and fermentability rather than level and type of protein.

54. Microbial protein synthesis in the rumen
End products of proteolysis (ammonia, peptides, amino acids) are sources of N for the synthesis of microbial protein. Maximization of microbial protein synthesis requires a continuous supply of fermentable carbohydrates, ammonia, peptides, amino acids and other nutrients. A shortage of any of these can limit protein synthesis.

55. Factors Influencing Microbial Protein Synthesis
Ammonia
Most important source of N for bacterial protein synthesis.
50 to 80% of bacterial N is derived from ammonia.
Bacteria hydrolyzing structural carbohydrates utilize ammonia as N source.
Several mechanisms for the uptake of ammonia:
high affinity, low Km (ammonia concentration) enzyme system
glutamate synthetase - glutamate synthase (GS-GOGAT)
lower affinity, higher Km system
NADP-glutamate dehydrogenase (NADP-GDH), NAD-GDH and alanine dehydrogenase.
Minimum level of ammonia is necessary for maximum growth and efficiency (5 mg/100 ml of rumen fluid).
The high affinity enzyme system of ammonia assimilation is found under conditions of low ammonia concentration but is not significant under conditions of high ammonia concentration. The rumen concentrations in vivo would seldom be low.

56. Peptides and amino acids
20 to 50% of ruminal microbial N is derived from this pool.
Supplying preformed peptides and amino acids spares the cost associated with synthesizing amino acids.
Rapidly fermenting organisms, bacteria hydrolyzing non-structural carbohydrates (starch, pectin, sugars), utilize peptides, amino acids and ammonia.
Availability of peptides improves microbial growth.

57. Synchronization of protein and carbohydrate degradation
Microbial protein synthesis is maximized when the release of N from protein occurs with the release of energy from the degradation of carbohydrates.
Fractional Outflow Rates
Increasing the rate of passage removes the more mature organisms, reducing the median age of the microbes.
Reduces the amount of energy expended on maintenance so more energy can be used for growth.
As the rate of passage from the rumen increases there is greater opportunity for bacteria to pass out of the rumen.

58. Efficiency of Microbial Growth14 12 10 8
BCP/100 gm TDN 6 pH
Rate of passage 4 2 55 70
Diet % of TDN (DOM)

59. Effect of dilution rate on YATP.
This figure indicates that with increasing dilution rates a greater proportion of the energy derived from glucose is being used for net culture growth.
Effect of dilution rate on YATP.

60. Reduces the amount of intraruminal N recycling (microbial protein turnover).
This figure shows the relationship between dilution rate from the rumen and magnitude of microbial turnover at three different lysis rates: 0.1 (), 0.01 () and 0.001().

61. Intraruminal nitrogen recycling
Turnover of bacteria and protozoa.
30 to 55% of bacterial N
75 to 90% of protozoal N
Causes of microbial N recycling
Engulfment and subsequent digestion of bacterial cells by protozoa
Lysis due to autolytic enzymes, bacteriocins, or other soluble compounds in response to nutrient deprivation or interspecies competition
Activity of bacteriophages and mycoplasmas.
It is generally accepted that protozoal predation has the greatest impact on bacterial N recycling. However, even in the absence of protozoa, a considerable amount of N is recycled between the rumen ammonia pool and microbes both indicating that many of the microorganisms secrete N or die and are fermented in the rumen.

62. Ammonia accumulation in the rumen
Ammonia concentration exceeds the capacity of the ruminal bacteria to utilize it.
Absorbed across the ruminal wall into the blood where it is transported to the liver and metabolized to urea.
Urea is filtered by the kidney and excreted in urine as waste N.
In addition to poor N retention, the synthesis of urea from ammonia also has an energetic cost (12 kcal/g N) to the animal.
One of the principle disadvantages of using urea as a source of NPN is that it is broken down too rapidly, resulting in ammonia overflow and inefficient N retention.

69. Urea recycling
Blood urea originates from the endogenous metabolism of tissue protein, the deamination of excess absorbed amino acids and the absorption of ruminal ammonia.
Recycled to the rumen primarily through the rumen wall and to a lesser extent via saliva (approx 15% of urea recycled to the rumen is via saliva)
Facultative microorganisms located on the rumen epithelium wall have urease activity
Due to the location of the ureolytic microorganisms on the rumen epithelium these microorganisms are important in the hydrolysis of urea transferred across the rumen wall. These microorganisms move into rumen fluid when the epithelial cells they are attached to move into the rumen contents and are largely responsible for the urease activity in rumen fluid. The organisms in the fluid are important in hydrolyzing dietary and salivary urea.
At low ruminal ammonia concentrations, there is an influx of urea to the rumen to maintain optimum levels of ammonia. Consequently, although N supply by the diet may be subject to great variation over a diurnal period, the diffusion process acts to stabilize ammonia concentrations in the rumen.

70. Factors involved in increasing the permeability of the rumen wall to urea
The rate of diffusion of urea from the blood to the rumen is increased by increasing the level of nutrition. Increasing amounts of VFA promote proliferation of the epithelium lining the rumen wall and stimulate cell proliferation.

71. Composition of microbial protein reaching the intestine
Hay Hay and Conc
sheep sheep sheep sheep2
N in rumen digesta, g
Fungi
Protozoa
Bacteria
N in rumen digesta, % of total microbial N
Fungi
Protozoa
Bacteria
N in duodenal digesta, g
Fungi
Protozoa
Bacteria
N in duodenal digesta, % of total microbial N flow
Fungi
Protozoa
Bacteria
The majority of microbial protein flowing from the rumen to the intestine is of bacterial origin. Bacterial protein contibutes from 70 to 95% of the microbial protein, protozoa from 5 to 30% and fungi less than 5%.

72. Undegraded dietary protein
Protein that escapes microbial degradation passes to the lower digestive tract where it will be largely degraded. Only the very refractive N component such as N bound to lignin or products of the Maillard reaction will not be degraded.
Benefit to the animal of supplying UIP will depend on the provision of essential amino acids that are required in excess of what is supplied by microbial protein.
The undegraded fraction of dietary protein is of considerable interest because it can be manipulated by dietary treatment (heat) and by the use of specialized ingredients high in UIP.

73. Protein digestion in the abomasum
HCl
Protein
Denatured protein
disruption of non-covalent bonds
uncoiling of protein
HCl
Pepsinogen
(inactive)
Pepsin
(hydrolysis bonds at
carboxylic end of
aromatic AA and Leu)
The abomasum functions like the acid-secreting stomach in monogastric animals and humans. Hydrochloric acid (HCl) denatures the protein by disrupting the non-covalent bonds causing the protein to unfold. This is important for increasing the access of various proteases (enzymes that hydrolyze protein) to peptide bonds. Proteases are secreted in an inactive form (zymogen or proenzyme). HCl activates the proenzyme pepsinogen to pepsin by cleavage of a small peptide. Pepsin hydrolyzses peptide bonds at the carboxylic end of aromatic amino acids and Leu to yield smaller polypeptides.
Pepsin
Small polypeptides
few amino acid
Denatured
protein
pH 1.6 to 3.2

74. Secretion and activation of pancreatic and intestinal proteolytic enzymes
Polypeptides
Short peptides AA
Intestinal
endocrine cell
CCK and Secretin
Cholecystokinin (CCK)
Pancreatic
acinar cell
Intestinal
mucosal cell
Enterokinase
Polypeptides, short peptides and amino acids signal to the intestinal endocrine cell to secrete into the blood the hormones cholecystokinin (CCK) and secretin. These hormones signal the pancreatic and intestinal cells to secrete proteases into the lumen of the intestinal tract. The proteases are secreted in an inactive form and require hydrolysis of a small peptide to become active.
Trypsinogen
Trypsin
Chymotrypsinogen
Proelastase
Procarboxypeptidase
Chymotrypsin
Elastase
Carboxypeptidase

75. Sites of hydrolysis of proteolytic enzymes
Pancreas
Trypsin Dibasic AA (Arg, Lys),
C-terminal end
Chymotrypsin Aromatic C terminal peptides
Elastase Neutral C terminal peptides
Carboxypeptidase C-terminal end
Intestine
Enteropeptidase N-terminal end

76. Digestion in the small intestine
Pancreatic and intestinal
proteases
Amino acids
Dipeptides
Tripeptides
Polypeptides
Oligopeptides
Intestinal di- and tripeptidases
(cell membrane and cytosol)
Dipeptides
Tripeptides
Amino
acids

77. Protein absorption Small intestine Major site of absorption
Amino acids absorbed in the ileum
Dipeptides and tripeptides absorbed in the jejunum
Active transport (energy dependent)
9 carrier systems for amino acids
specific for certain amino acids

78. Protein metabolism Intestinal cell Liver
Glu, Asp, Gln metabolized by intestinal cell
provides 40% of energy requirements
Liver
protein synthesis
synthesis of non-essential amino acids
C-skeletons catabolized for energy and the amine group metabolized to urea

79. Nitrogen metabolism in the large intestine
N supplied to the lower tract comes from the recycling of urea and other endogenous protein (sloughed epithelial cells, enzymes and glycoproteins of mucus).
Energy substrates come from the residual fermentable fibre, the glycocalyx of rumen microorganisms, starch and other polysaccharides that have resisted rumen and enteric digestion.
As the amount of fermentable energy from the diet reaching the lower tract increases, microbial synthesis increases and fecal N excretion increases.

80. Routes of nitrogen excretion
Urine (urea)
Endogenous urinary N from the catabolism of tissue proteins
Absorption and metabolism of excess ruminal ammonia.
Catabolism of excess absorbed amino acids
Feces
Microbial N synthesized in and passed from the large intestine.
Sloughed cells and secretions of the GI tract.
Undigested unabsorbed dietary protein.

81. Feed Rumen Small intestine Large intestine Undegradable in rumen
NPN
Indigestible
Digestible
Peptides
amino
acids
Plasma urea
NH3
Rumen
Energy
Microbial N
Tissues
Maintenance
Growth
Conceptus
Lactation
Wool
NH3
Peptides
amino
acids
Small intestine
Endog N
Energy
NH3
Large intestine
Microbial N
Endog N
Urine
Feces

82. Meeting the protein requirements of ruminant animals
Degradable intake protein in the rumen for ruminal microorganisms to maximize digestibility of the diet and feed intake.
Absorbable essential amino acids at the intestine from the digestion of microbial protein produced in the rumen and dietary intake protein that escapes rumen fermentation.

87. Defaunation (protozoal removal)
Removal of protozoal predation of bacteria.
Increases substrates (starch) available for fermentation and growth by bacteria.
Increases amount of bacterial protein synthesized in the rumen.
Increases the flow of microbial protein from the rumen.
Reduction in ammonia concentration.
Because protozoa have such an impact on the amount of bacterial nitrogen recycled in the rumen, thereby reducing the amount of microbial N flowing from the rumen, there is a great interest in reducing or eliminating protozoa.

88. Chemistry of the Maillard reaction between reducing sugars and lysine residues during heat treatment of proteins
Heating is a common method of increasing the protein escape from the rumen. The mechanism of protection with heat treatment involves principally the Maillard reaction sequence between the -amino group of lysine residues and carbonyl compounds, usually reducing sugars such as glucose and fructose. The formation of the Shiff’s base is reversible but the modified Amadori compound and the polymers are nutritionally unavailable.