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LIVESTOCK’S ROLE INTHE NITROGEN
CYCLE IN AGRICULTURAL SYSTEMS
ROLE OF PROTEIN NUTRITION IN N MANAGEMENT OF
LIVESTOCK
• Proteins are the basic unit of life
• Average composition of protein
%
Carbon
53
Hydrogen
7
Oxygen
23
Nitrogen
16
Possibly sulfur and phosphorus
1
PROTEIN STRUCTURE
• Primary structure
– Chains of amino acids linked by a peptide linkage
– Amino acids are organic acids having an amino group on
the alpha-carbon
O
H2N
C
OH
C
H
R
– The side chain ( R) is different for each amino acid and
determines the properties of the amino acid and protein
– There are 22 amino acids commonly found in proteins in
varying amounts
– Order of amino acids in any protein is specific and
associated with the function of that protein.
AMINO ACIDS FOUND IN PROTEINS
• Neutral amino acids (No
special group)
–
–
–
–
–
–
–
Glycine
Alanine
Serine
Valine
Leucine
Isoleucine
Threonine
• Acidic amino acids (Have an
extra COOH group)
– Aspartic acid
– Asparagine
– Glutamic acid
• Basic amino acid (Have an
extra NH2)
–
–
–
–
Lysine
Arginine
Histidine
Glutamine
• Sulfur-containing amino
acids (Contain S)
– Methionine
– Cysteine
– Cystine
• Aromatic amino acids
(Contain a benzene group)
– Phenylalanine
– Tysosine
– Tryptophan
• Imino acids (Heterocyclic
amino acids)
– Proline
– Hydroxyproline
PROTEIN ANALYSIS
• In applied nutrition, protein content of feeds is normally
determined as crude protein
• Crude protein
– Calculation
• CP% = N% x 6.25
• Limitations of CP determination
– Nitrogen in feeds may come from true protein or nonprotein
nitrogen sources
• True protein
– Only source of protein that can be used by nonruminant
(monogastric) animals
• Nonprotein nitrogen (NPN)
– NPN may be utilized to meet the protein needs of ruminant
animals
– Nonruminants can not utilize NPN
– Crude protein says nothing about the amino acid
composition of a feed
• Assume that amino acid composition for any particular feed is
constant
– Crude protein says nothing about the digestibility of the
protein
PROTEIN DIGESTION IN NONRUMINANTS
• Digestion
Stomach and intestinal enzymes
Protein
Amino acids
•Digestion is normally high, but variable
Protein digestion, %
(swine)
Corn
85
Soybean meal
84-87
Wheat
89
Wheat bran
75
Meat and bone meal
84
Poultry byproduct meal
77
•Digestibility may be reduced by excessive heating.
PROTEIN DIGESTION IN RUMINANTS
• Rumen
True protein
NPN
Undegraded
Recycled via
saliva
(20% of dietary N)
Degraded
CHOs
Small intestine
Metabolizable
protein
VFAs
Microbes
NH3
Microbial
protein
NH3
Liver
Urea
Kidney
Excreted
• Ruminal degradation of true protein
– By ruminal bacteria and protozoa
– Not totally desirable
• There is always some loss of NH3
– Reduces efficiency
– Increases N excretion
• Valuable to have protein escape ruminal degradation in animals
with high protein requirements
– Factors affecting ruminal protein degradation
• Protein source
% degraded in 24 hours
Fish meal
51
Corn (Grain or DDGS)
50
Cottonseed meal
78
Soybean meal
89
Alfalfa (and most other forages)
90
• Heat treatments
100 C for 4 hours
Soybean meal
Reduced protein degradation
• Tannins in feeds reduce protein degradation
– Example: Birdsfoot trefoil
• Factors affecting microbial protein production in the
rumen
– Ruminal NH3-N concentration
Microbial
protein
(% of Max)
Ruminal NH3-N
5 mg%
12%
Crude protein in diet, %
– Rate of ammonia release
Urea
[NH3]
Treshold
Biuret
2
Time after feeding, hours
– Energy level of the diet
• Energy and C-skeletons needed by rumen bacteria to produce
microbial protein from ruminal NH3
• Protein digestion in the abomasum and small intestine
– Similar to nonruminants
– Proteins are digested to amino acids
OVERVIEW OF AMINO ACID
UTILIZATION AFTER DIGESTION
Body Protein
Non-protein
Derivatives
Dietary
Protein
Cellular Amino
Acids
Glucose
Ammonia
TCA cycle
CO2 + Energy
Urea or Uric acid
Fatty acids
AMINO ACID METABOLISM
• Protein synthesis
– Mechanism
• Protein synthesis controlled by DNA in the nucleus of
cells
• DNA is divided into subunits of 3 bases specific for each
amino acid
• Messenger RNA is produced from DNA
• Messenger RNA migrates to ribosomes where it acts as
the template for protein
• To be used in protein synthesis, amino acids are bound
to transfer RNA (specific)
• Transfer RNA travels along the messenger RNA to place
amino acid in chain
• If an given amino acid is not present, synthesis of this
protein stops and no more amino acids will be used
– Hormonal control
Growth hormone
Thyroxine
Amino acid
Increase IGF (Liver)
Growth hormone
Testosterone
Insulin
Transport
Amino acid
Muscle
DNA synthesis
X
Synthesis
Increase IGF (Muscle)
Protein
Estrogen
Testosterone
Degradation
• Transamination
– Transfer of an amino group from one amino acid to
another carbon chain (called a keto acid) to
construct a new amino acid
• Alpha amino acid1 + keto acid2
keto acid1 +
alpha amino acid2
– Importance
• A method of synthesizing some specific amino
acids from intermediates of carbohydrate
metabolism or vis versa
• These amino acids are called ‘nonessential’
because they are not needed in the diet
• Deamination
– Releases amino group from excess amino acids
– Mechanism
NH2
R
C
O
COOH + O
R C COOH + NH3
(C skeleton)
H
– Uses of C skeleton
• Energy metabolism
• Glucose synthesis
• New amino acids
– Removal of NH3
O
• Mammals
– Synthesis of urea
– Detoxifies NH3
H2N
C
NH2
• Poultry
– Synthesis of uric acid; excreted with feces
O
H
N
C
H
N
C
C
O
C
C
N
H
N
H
O
THE PROTEIN REQUIREMENT
• Nonruminants
– Not a requirement for protein per se, but really a
requirement for 10 essential amino acids
– Essential amino acids in the diet
• For growth of pigs
–
–
–
–
–
–
–
–
–
–
Phenylalanine
Valine
Tryptophan
Threonine
Isoleucine
Methionine
Histidine
Arginine
Lysine
Leucine
• Additional amino acids for poultry
– Arginine
– Glycine
• Cystine can replace ½ of the methionine
• Tyrosine can replace 1/3 of the phenyalanine
– Balance of amino acids in a diet is as important as the
amounts of individual amino acids
• Amino acids can only be used to the extent of the least abundant
amino acid relative to the animal’s requirement
– Remainder of amino acids will be deaminated and N will be
excreted as:
» Urea in mammals
» Uric acid in poultry
» Ammonia in fish
• An excess of one amino acid may cause a deficiency of another
amino acid
Excess leucine
Deficiencies of valine and isoleucine
• The term “protein quality” refers to the amino acid balance of a
protein relative to an animal’s requirement for each of the essential
amino acids
– A “high quality protein” called an “ideal protein” has the essential
amino acids present in proportions equal to an animal’s
requirements.
» It says nothing about the concentration of protein in the diet
– A ration with a “high quality protein” may be composed from two
or more feeds if they complement each other’s deficiencies
20 kg pig
Corn
Soybean meal
Corn/soybean meal mix
Amino acid requirements of pigs (% of protein)
Leucine Lysine S-containing AAs Tryptophan
3.8
4.4
2.8
.7
12.5
2.3
3.0
1.1
7.4
6.3
2.6
1.3
11.5
4.4
2.7
1.2
– An “ideal” protein can be synthesized by adding individual amino
acids to a diet
• Ruminant protein requirements
– Ruminants have no essential amino acid requirements in their
diets
• The rumen microbes can synthesize all of the amino acids
– Ruminants require
• Degradable N up to 12% crude protein in the diet dry matter
– To meet the N needs of the rumen bacteria
• Undegraded protein above 12% crude protein
FACTORS AFFECTING PROTEIN REQUIREMENTS
• Growth
– Young, growing animals deposit more protein, but have lower
feed intakes than larger animals
Swine, kg
1-5
5-10
10-20
20-35
35-60
CP reqt. %
27
20
18
16
14
• Sex
– Males deposit more protein at a given weight than females
300 kg large frame gaining 1 kg/d
Bulls
Steers
Heifers
gm protein/day
807
804
735
• Production of milk, eggs, or wool
METHODS TO MINIMIZE NITROGEN
EXCRETION BY LIVESTOCK
• Nonruminants
– Do not overfeed
protein
• Separate sexes
• Phase feed
– Balance amino acids
• Use individual amino
acids
• Ruminants
– Do not overfeed
protein
• Phase feed
– Properly balance
rumen undegraded and
degraded proteins
• Undegraded proteins
– Young cattle and dairy
cows in early lactation
• Degraded proteins
– All other cattle
– Feed high energy diet
with degraded proteins
– Growth promotants
and BST
MANURE HANDLING AND STORAGE TO
MINIMIZE N LOADING OF THE ENVIRONMENT
• Reason to store manure
– Preserve and contain manure nutrients until it can be
spread onto the land at a time compatible with climate and
cropping system
• Goals
– Maintain excreted N in non-volatile organic forms
• Undigested protein
• Microbial N
• Urea
– Minimize volatilization of NH3
•
•
•
Minimizes PM2.5
Minimizes N deposition in terrestial and aquatic ecosystems
Reduces manure odors
– If N is volatilized, it should be in the form of N2
– Prevent losses of N into surface and ground water sources
• Provide adequate storage until it can be safely spread
N TRANSFORMATIONS IN LIVESTOCK
PRODUCTION AND MANURE STORAGE
FACILITIES
Manure N
Anerobic microbial
degradation (slow)
C skeletons
H 2S
VOCs
Fecal N
(20-40% of N)
Microbial N
NH4+
Urine N
(60-80% of N)
Microbial
O
urease (rapid)
H2N C NH2 + H+ + H2O
2NH4+
Slow
aerobic Anerobic
NH3
pH (volatile)
2HCO3• In poultry
•Urinary N is secreted as uric acid with the feces
NO2
N2
FACTORS AFFECTING NH3 LOSS FROM
LIVESTOCK HOUSING AND MANURE
STORAGE FACILITIES
• NH3 volatilization increased by:
– Increasing manure pH
• Increased by increased HCO3 and NH3
(Gay and Knowlton, 2005)
– Increased difference in NH3 concentration between air at
manure surface and ambient air
Ambient air
Manure surface
NH3
NH3 NH3 NH3
NH3 NH3 NH3
NH3 NH3 NH3
– Increased surface area
– Increased air velocity at surface
– Increased ambient temperature
• Increases urease activity
• Increases NH3 mass transfer coefficient
• Increases ventilation from confinement buildings
– Decreased ambient temperatures increase NH3 concentrations in
confinement buidings
– Increased moisture
N LOSSES FROM DIFFERENT MANURE
HANDLING AND STORAGE SYSTEMS
Daily scrape and haul from barn
Open lot
Pile (Cattle/Swine)
Pile (Poultry)
Compost
Deep pit (Poultry)
Litter
Pit under floor (Swine)
Tank above ground top loaded
Tank above ground bottom loaded
Tank above ground with cover
Holding basin
Anerobic lagoon w/ no cover
Constructed wetlands
N loss, %
20-35
40-70
10-40
5-15
20- 50
25-50
25-50
15-30
20-35
5-10
2-30
20-40
70-80
15
N retention, %
65-80
30-60
60-90
85-95
50-80
50-75
50-75
70-85
65-80
90-95
70-98
60-80
15-30
85