GLOBAL WARMING
• Distribution of solar radiation entering the atmosphere
–
–
–
–
20% reflected by the atmosphere
20% absorbed by the atmosphere
51% is absorbed by the earth
9% is reflected by the earth and dust
• Distribution of emitted infrared radiation
– 17% escapes atmosphere
– 83% is held and re-emitted
• Maintains atmospheric temperature
• Increased concentrations of CO2, CH4 and other gases increase
amounts of infrared radiation that is trapped and re-emitted
– Increases atmospheric temperature
UNDERSTANDING GLOBAL WARMING
EVIDENCE FOR GLOBAL WARMING
• Since 1860
– CO2 concentration in atmosphere has increased by 24%
– CH4 concentration in atmosphere has doubled
– Mean global temperature has increased by 2oF
• 10 hottest days on record have occurred since 1980
ENVIRONMENTAL EFFECTS OF GLOBAL WARMING
• Average temperature will increase by 2 to 6oF in next century
• An increase in extreme weather events
– Droughts, floods etc.
– Concern for insurance industry
• Sea levels will increase .5 to 3 feet
– Threaten coastal resources, wetlands, and islands
– Saline water will pollute water supplies of coastal cities
• Increased range of diseases associated with tropical climates
– Malaria, dengue fever, and yellow fever will occur at higher latitudes
• Heat stress and death of humans and animals
– Particularly a concern in elderly
• Increases air conditioning needs
– Angus cattle?
• Rapidly reproducing species of weeds, rodents, insects, bacteria
and viruses may occur at higher latitudes
• Crop may be susceptible to new insect and disease problems
• Reduced forest health and changes in tree species
GASES ASSOCIATED WITH GLOBAL WARMING
Current Rate of Half
concentration increase life
____Gas____
(ppmV) (%/yr) _(yr)_
Carbon dioxide
360
.5
150
Methane
1.7
.7
7-10
Nitrous oxide
.31
.2
150
Fluorinated
hydrocarbons
Water vapor
-
% of US
GHG
Relative
GHF contribution GH effect
emissions __%__ ( /kg) (_/mole)
81
55-60
1
1
10
15-20
62
22
7
5
310 310
2
-
-
-
-
• Sources
– Carbon dioxide
• Hydrocarbon combustion
– Methane
• Livestock, manure, wastewater treatment, landfills and fuel production
– Nitrous oxide
• Hydrocarbon combustion, industrial processes, denitrification of
manure and soil N
– Fluorinated hydrocarbons
• Refrigeration, dry cleaning, chemical manufacturing
– Water vapor
• Increased temperature from other GHG
LIVESTOCK AGRICULTURE’S ROLE IN GREENHOUSE
GASES
• Nitrous oxide
– Difficult to determine amount
– Likely to be high in animals that excrete high concentrations
of Nitrogen
• N2O emissions are 10 times greater from fields with manure
application compared to unfertilized fields
• N2O emissions can be considerable from fields or pastures with
soil compaction under wet conditions
• Methane
Sources
Natural
Wetland
Oceans
Termites
Burning
Industrial
Gas and oil
Coal
Charcoal
Landfills
Waste water treatment
Agricultural
Rice
Livestock
Manure
Burning
CH4
million metric
tons/yr
% of
total
115
15
20
10
24.4
3.2
4.2
2.1
50
40
10
30
25
10.6
8.4
2.1
6.4
5.3
60
80
10-25
5
12.8
17.0
2.1
1.0
% of
anthropogenic
sources
16.1
12.8
3.2
9.6
8.0
19.3
25.8
3.2-7.7
1.6
• Implications
– Anthropogenic sources contribute 66% of all methane
emissions
– Livestock production and manure are the largest
anthropogenic sources
– Methane emissions from anthropogenic sources are increasing
1%/yr
• Methane emissions from livestock in Iowa
Cattle
Swine
Poultry
Sheep
Horse
Direct emissions Manure
--------------tons/year-----------352,000
14,900
22,400
102,000
NA
1,770
4,312
208
983
170
% of total
73.5
24.9
.4
.9
.2
GREENHOUSE GAS PRODUCTION IN LIVESTOCK
• Methane
– Produced by anerobic fermentation of carbohydrates in the
rumen, large intestine, or stored manure
– Represents a loss of 4 to 10% of the dietary energy in
ruminant animals
• Methane production
Starch
(In grains)
Cellulose
(In plant fiber)
Digested by bacterial enzymes
Glucose
(a simple sugar)
Metabolized by bacteria through
Glycolysis
NADH2
Pyruvate
(a 3-C intermediate)
In aerobic organisms
run through TCA
cycle producing
more NADH2 used
used for ATP
production in
electron transport
Acetic acid
In aerobic organisms
run through electron
transport to produce
ATP and H2O
In anerobic organisms
NADH2
Propionic acid
Butyric acid
(Volatile fatty acids)
CH4
(Belched gases by
eructation)
VOLATILE FATTY ACIDS
• In animals
– Absorbed through wall of the rumen in ruminants or large
intestine of ruminants and nonruminants
– Metabolized by the animal for energy
• Main source of energy for ruminants
– Provide 70% of the energy in ruminants
– Production of different VFAs and methane vary with diet
• In manure
– Volatile fatty acids contribute to manure odor
• Acetic acid and propionic acid smell like vinegar
• Butyric acid smells like rancid butter
FACTORS AFFECTING METHANE AND VFA
PRODUCTION IN THE RUMEN OF RUMINANTS
• Dietary factors
– High forage levels of diet
• Promotes cellulose digesting bacteria in rumen
• Increases production of acetic acid and methane
• Decreases production of propionic acid
– High grain levels of diet
• Promotes starch digesting bacteria in rumen
• Increases production of propionic acid
• Decreases production of acetic acid and methane
– Fine grinding or pelleting of forage
• Decreases the amount of time the cattle spend chewing
• Decreases saliva flow and secretion of the buffer, sodium
bicarbonate.
• Allows rumen pH to decrease
• Decreases growth of cellulolytic bacteria
• Decreases production of acetic acid and methane
• Increases production of propionic acid
– Increasing forage maturity
•
•
•
•
•
•
Causes more chewing
Increases saliva flow and secretion of buffer, sodium bicarbonate
Increases rumen pH
Increases growth of cellulolytic bacteria
Increases production of acetic acid and methane
Decreases production of propionic acid
– Feeding fats containing unsaturated fatty acids
• An unsaturated fatty acid is a fatty acid that has one or more
double bonds in the chain
• The rumen bacteria use hydrogens to saturate (replace double
bonds with hydrogens) unsaturated fatty acids
• Example
H
H
H C C C C COOH
H H H H
Unsaturated fatty acid
H+
H H H H
H C C C C COOH
H H H H
Saturated fatty acid
• Results
– Decreased acetic acid and methane production
– Increased propionic acid production
• Important to feed no more than 5% fat to ruminants
– Feeding ionophores
• Antibiotics that include
– Monensin, sold as Rumensin
– Lasalocid, sold as Bovatec
• Increase propionic acid production
• Decrease acetic acid and methane production
• Production factors
– Rate of gain
• Regardless of diet, ruminants produce methane each day at a
maintenance level
– Every day the cattle or sheep is on the farm, they produce more
methane
• The faster an animal grows or the more milk is produced, the
lower the amount of methane produced per unit of meat or milk
produced
N2O PRODUCTION
• N2O is produced during denitrification of NO3
– Occurs under anerobic conditions
• Wet, compacted soils
• Anerobic lagoons
– Amount associated with livestock production is directly
related to amounts of N excreted.
FACTORS AFFECTING N2O PRODUCTION
• Diet
– Nonruminants
• Amounts of protein fed
– Increased protein = increased N excretion
• Amino acid balance
– Poor amino acid balance = increased N excretion
– Ruminants
• Amounts of protein fed
– Increased protein = increased N excretion
• Ratio of degraded to undegraded protein in the rumen
– Increased protein degraded in rumen = increased N excretion
• Ratio of degradable protein to digestible carbohydrate in the
rumen
– High proportion of degradable protein to digestible carbohydrate =
increased N excretion
» Digestible carbohydrate is needed to convert degraded NH3 into
microbial protein
• Amino acid balance
– Poor amino acid balance = increased N excretion
• Manure handling
– Storage losses
• Anerobic Lagoons > Slurries > Compost
STRATEGIES TO REDUCE GHG EMISSIONS
ASSOCIATED WITH LIVESTOCK PRODUCTION
• Production system manipulation
– Limit management approaches that just maintain ruminant
animals with little production
• Example - Backgrounding cattle
– Maximize reproductive efficiency
– Maximize disease control and herd health
• Dietary manipulation
– Nonruminants
• Manage diet to minimize N excretion and waste
– Review N section
» Do not feed excess protein
» Balance for amino acids
» Use crystalline amino acids to create the ‘ideal’ protein
» Use phase feeding with 4 or more phases
» Use split sex feeding
» Limit feed waste
» Promote lean growth through genetic manipulation or feed
additives:
Ractopamine
– Ruminants
• Maximize the proportion of grain in the diet
– Effects
» Reduces CH4 production
» Increases incorporation of NH3 into microbial protein
Reduces urinary N
» Increases rate of gain
Reduces lb GHG/lb gain
– Maximum proportions of grain
» Beef feedlot – 90%
» Lactating dairy cows – 50%
» Consequences of excess grain feeding
Beef feedlot - Acidosis, Liver abscesses
Dairy cows – Low milk fat, Displaced abomasum, Laminitis
– Limitation of strategy
» Amount of CO2 released during production of N-fertilizer used to
produce grain
• Processing feeds
– Grinding and pelleting
» Reduces CH4 by 20%
– Steam-flaking
» Reduces CH4 by 40%
• Feed ionophores
– Compounds
» Monensin, sold as Rumensin
Do not feed to sheep
» Lasalocid, sold as Bovatec
– Reduces CH4 by 28%
• Addition of fats to ruminant diets
– Reduces CH4 by 33%
– Can’t feed more than 5% of the diet
» Greater amounts adversely affect fiber digestion and
feed intake
• Forages should be grazed or harvested when immature
– Effects
» Immature forages are more digestible and have less
fiber than mature forages
Reduces CH4
– Implications
» Use rotational grazing
Reduces CH4 by 22 to 50% compared to continuous
grazing
» Incorporate legume forage species in pastures
Reduces CH4 by 25% compared to grass
• Utilization of production-enhancing agents
– Types
» Beef cattle
Steroid implants (Trenbolone acetate, Estradiol)
Ractopamine
» Dairy cattle
Bovine somatotropin
– Effects
» Increases incorporation of amino acids into animal protein
Reduce N excretion
» Reduces GHG/lb product by increasing production
Reduces CH4/lb product by 4%
• Manage protein nutrition to minimize N excretion
– Review N strategies
– Strategies
» Reduce CP of diet
Reducing CP concentration of dairy cow from 17.5 to 12.5% CP:
Reduce N2O by 78%
» Lower the Rumen Degradable Protein:Undegradable protein ratio
» Increase energy concentration of the diet
» Use crystalline amino acids to balance amino acids of lactating
dairy cows
• Manipulation through manure handling and storage
– Effects of manure storage method
Anerobic
lagoon
CH4
Total GHG
Dominant gas
Slurry
Stockpiled
earthen pond Deep litter Compost
Relative emissions
10
8
6
1
Very high
4
2-3
1
CH4
CH4
CH4 & N2O
N2 O
– Effects related to:
• C:N ratio of the manure
Separated Farm yard
manure without
bedding
C:N
10
CH4 (g/cow/7 weeks)
26
N2O (mg/cow/7 weeks)
866
GHG (CO2 equiv./cow/7 wk)
878
• O2 exposure
– Reduces CH4
• Surface area
– Increased surface area increases gas release
– Covers reduce gas release
Deep litter
manure with
bedding
20
3
42
82
– Methane capture and use
• Requirements
– Anerobic, air-tight structure
– pH control
» pH 6.8 – 7.0
– High temperature
» 95oF
– Can not have a high concentration of NH3
– Expense
» $400 - $500/animal for large dairies (<3700 cows)
» $1200/animal for small dairies (<500 cows)
• Production
Swine
Gas yield, cubic ft/lb solids
12
Energy production, BTU/hr/animal 103
Animals needed to heat a
1500 ft2 house
535
Dairy
7.7
568
Beef
15
775
Poultry
8.8
5.25
99
72
10714
• Manipulation through manure application
– Frequent application of manure
• Prevents anerobic decay
• Traps C in soil organic matter or released to atmosphere as
CO2
– Timing of manure application
• Avoid application in later winter and early spring
– Plant growth is slow
» Little uptake of NO3
– Soils are water-logged
» Anerobic conditions promote denitrification of NO3 to
N2O
– Method of application
• Injection of manure reduces all N emissions by 90%
• Band application of surface produces more N2O than uniform
surface application
• Manipulation of GHG through carbon sequestration
– Plants sequester C, reducing atmospheric CO2
– Amounts of C sequestered
Crop
Pasture
Range
Hay land
Grain
Trees
tons C/acre
1.0
.12
.5
2.0
3.7
– Potential
• U.S. grazing lands = 524 million acres
• C sequestered
= 60 million tons
= 1.6 x all C emissions from all agriculture
– C sequestered may be increased by:
• Incorporation of legume forage species in pastures
– .18 - .27 ton/acre/year
• Improved grazing management (Weed control, alternate water sites)
– .05 - .13 ton/acre/year
• Rotational grazing
– 25% increase
– Producers may economically benefit from increased C
sequestration by selling C credits to industries producing
Greenhouse Gases
• 1 C credit = 1 ton C sequestered beyond a base value before
improved management
= 3.67 tons CO2 removed from the atmosphere
• Credits sold through markets
– Chicago Climate Exchange
• To date, few trades because of voluntary market