Transcript Slide 1

THE NITROGEN CYCLE
ANIMAL AGRICULTURE’S CONTRIBUTION TO
N LOADING OF THE ENVIRONMENT
• Gaseous emissions
Total agriculture
Animal agriculture
% of emissions in the US
NH3
N 2O
NO
80
50
6
47-73
25
1
• Contribution of different species to atmospheric
ammonia
• Contributions to total N in watersheds
• Origin of livestock odor
Odor compound
Large intestine
Carbohydrates
(Starch, cellulose)
Protein
Volatile fatty acids
(Acetic, Propionic, Butyric acids;
may be absorbed or excreted)
H2S and mercaptans
(Passed as gas)
Other amines, phenols, and
indoles (Absorbed from LI &
excreted in urine)
Manure
Carbohydrates
(Secondary
fermentation
Lactic acid
greater at:
Manure pH > 4.5;
High manure moisture;
High ambient temperatures)
Air
Volatile fatty acids and alcohols
Protein
Butyric acid
NH3, H2S, mercaptans, branched
chain VFAs (Isobutyric, Isovaleric),
Amines (Putrescine, Cadaverine),
Phenols (Phenol, p-Cresol),
Indoles (indole, Skatole)
CH 4
Emissions increased with increased temperature, moisture, humidity, agitation,
dust, pH, wind, surface exposure
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
• Ten amino acids that can’t be synthesized in adequate
quantities are called ‘essential amino acids’
– Required in diet on nonruminant animals
– Essential amino acids
Phenylalanine
Valine
Tryptophan
Threonine
Isoleucine
Methionine
Histidine
Arginine
Leucine
Lysine
• Other amino acids can be synthesized by animal cells
and are called ‘nonessential amino acids’
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 on 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
Total protein
NPN
Undegraded
Small intestine
Metabolizable
protein
Degraded
Recycled via
saliva
(20% of dietary N)
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
51
50
78
89
90
Fish meal
Corn
Cottonseed meal
Soybean meal
Alfalfa
• 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
THE PROTEIN REQUIREMENT
• Nonruminants
– Not a requirement for protein per se, but really a
requirement for the 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
DIETARY STRATEGIES TO REDUCE N LOADING OF
THE ENVIRONMENT BY NONRUMINANTS
• Reduce feed waste
– Animals can be sloppy eaters
– Amounts
• 5 – 6% of feed contributing 7.5% of the N in manure
– May be as high as 20%
– Strategies
• Feed pelleted feeds instead of mash
• Do not overfill feeders
• Properly position feeders
• Maximize the apparent digestibility of N
– Feed highly digestible protein sources
– Feed processing
• Grinding
• Pelleting, expanding, or extruding
– Enzyme addition (?)
• Precision feeding of protein
– Avoid feeding protein in excess of requirements
• Example (Feeding regimes for swine giving equal performance)
%CP in diets
Grower phase
17.8
17.8
16.2
Finisher phase
17.1
15.4
13.5
lb/pig
Manure N
6.3
5.8
4.9
Gaseous N
2.4
2.1
1.8
% reduction
Manure N
9
23
Gaseous N
12
25
• Advantages
– Reduces feed costs
– Reduces environmental N load
• Strategies
– Feed proteins for optimal gain, not necessarily maximum gain
– Minimize safety margins in dietary formulation
– Balance for available amino acids
• Strategy
– Utilize high quality protein sources or synthetic amino
acids to feed an ‘ideal’ protein
– An ideal protein has all of the essential amino acids in
amounts proportional to their requirements relative to
lysine
– Potential (200 lb swine)
14% CP
12% CP
Corn-soybean meal + lysine
_______
g/d
Retained N
Fecal N
Urinary N
Total N excreted
% reduction
26
7
34
41
-
_______
10% CP
+ lysine
threonine
tryptophan
methionine
26
7
25
32
22
– Amino acids currently economically produced
»
»
»
»
Lysine
Methionine
Threonine
Tryptophan
26
7
17
24
42
– Separate animals by sex and feeding phase
• Separate sex feeding
– Protein requirements
» Intact males>Castrated males>Females
• Phase feeding
– As animal grows, protein requirement decreases as a
percentage of diet
– Potential of phase feeding (Swine)
Diet CP, %
N excretion, lb/pig/day
Reduction
Feeding system
Single feed Two feeds Three feeds
17 (55-220 lb) 17 (55-120 lb) 17 (55-110 lb)
15 (120-230 lb)15 (110-165 lb)
12 (165-230 lb)
.07
.064
.059
8.6
15.8
– Typical number of phases
» Swine 3-4
» Broilers 4
» Turkeys 6
– Limited by feed storage and handling
• Enhance lean growth (Swine)
– Mechanism
• Increases incorporation of amino acids into protein
• Reduces the effects of the maintenance requirement
– Strategies
• Genetically lean pigs
• Feed Ractopamine
– Sold as Paylean for pigs
– Used at 18 g/T for 150 to 240 lb (5 weeks)
» Effect decreases after 4 weeks
» Can’t be used longer than 90 days
– Mechanism
» Shifts energy from fat deposition to muscle growth in
ham, loin, belly and shoulder
– Effects
» Increases feed efficiency – 12%
» Increases daily gain – 10%
» Increases lean gain – 25- 37%
» Decreases N excretion by 11 to 34%
– Greatest improvement in genetically lean pigs
STRATEGIES TO REDUCE N EXCRETION BY
RUMINANTS
• Increase microbial protein production in the rumen
– Maximize feed intake
– Supply adequate, but not excess degradable protein
– Feed highly digestible grains
• Grain species
• Grain variety
• Grain processing
– Feed forages with high digestibility
• Balance supply of rumen degradable protein and
undegraded protein
– Supplemental protein source dependent on forage protein
degradability and energy level
• Ruminal degradability of protein
Ruminal degradability of protein, %
Forages
Alfalfa
Cool season grasses
Corn silage
Grains and protein supplements
Dry corn
High moisture corn
Soybean meal
Expeller soybean meal (Soyplus)
Corn gluten meal
Dry corn gluten feed
Dried distillers grains
Urea
90
90
60
50
55-60
65
40
25
70
50
100
• With proper balance of RDP and RUP, dietary N can be reduced by
10 to 15% and N excretion can be reduced by 20%
– Optimal balance of degradable and undegradable protein is
dependent on the animals’ body weights (growing-finishing
cattle) or stage of lactation (dairy cows)
• In young, light-weight cattle or dairy cows in early lactation,
metabolizable protein requirements exceed the amounts of
microbial protein produced
– Therefore, feed a supplement that is high in undegraded
protein
• In feedlot cattle near finish or dairy cows in late lactation,
microbial protein is adequate for metabolizable protein
needs
– Therefore, no supplemental protein needed if degradable N
needs are met.
• Implications
– Phase feed
– Example
Yearlings fed for 132 days
Diets balance for metabolizable protein and RDP requirements
Control diet
Phase feeding
13.6 % CP
12.7% CP
___________
__10.1% CP
Lb/steer
N intake
72.8
59.4
N retained in carcass
7.9
7.9
N excreted
64.9
51.5
% of excreted N volatilized
70.9
60.7
as NH3
• Balance diets for essential amino acids by
supplementing amino acids that are protected from
ruminal degradation
– Ruminal degradation of some amino acids are protected by
binding with minerals or poorly degraded proteins
– Protected amino acids currently economically viable
• Lysine
• Methionine
– Only economically viable for lactating dairy cows
– Reduces N excretion by 13 to 20%
• Utilize technologies to enhance incorporation of N into meat or milk
– Products
• Implants
– Trenbolone acetate (TBA) and/or Estradiol or Zeranol
• Feed additive
– Ractopamine (sold for cattle as Optiflex)
• Injection
– Bovine somatotropin (sold for daily cattle as Posilac)
– Effects
• Increase N incorporation in meat or milk by 15 to 20%