Published January 20, 2015
Carbon footprint and ammonia emissions of California beef production systems1
K. R. Stackhouse-Lawson,* C. A. Rotz,† J. W. Oltjen,* and F. M. Mitloehner*2
*Department of Animal Science, University of California, Davis 95616; †USDA-ARS, Pasture Systems and Watershed
Management Research Unit, University Park, PA 16802
ABSTRACT: Beef production is a recognized source
of greenhouse gas (GHG) and ammonia (NH3) emissions; however, little information exists on the net
emissions from beef production systems. A partial life
cycle assessment (LCA) was conducted using the Integrated Farm System Model (IFSM) to estimate GHG
and NH3 emissions from representative beef production
systems in California. The IFSM is a process-level farm
model that simulates crop growth, feed production and
use, animal growth, and the return of manure nutrients
back to the land to predict the environmental impacts
and economics of production systems. Ammonia emissions are determined by summing the emissions from
animal housing facilities, manure storage, field applied
manure, and direct deposits of manure on pasture and
rangeland. All important sources and sinks of methane,
nitrous oxide, and carbon dioxide are predicted from primary and secondary emission sources. Primary sources
include enteric fermentation, manure, cropland used in
feed production, and fuel combustion. Secondary emissions occur during the production of resources used on
the farm, which include fuel, electricity, machinery, fertilizer, and purchased animals. The carbon footprint is
the net exchange of all GHG in carbon dioxide equivalent (CO2e) units per kg of HCW produced. Simulated
beef production systems included cow-calf, stocker, and
feedlot phases for the traditional British beef breeds and
calf ranch and feedlot phases for Holstein steers. An
evaluation of differing production management strategies resulted in ammonia emissions ranging from 98 ±
13 to 141 ± 27 g/kg HCW and carbon footprints of 10.7
± 1.4 to 22.6 ± 2.0 kg CO2e/kg HCW. Within the British
beef production cycle, the cow-calf phase was responsible for 69 to 72% of total GHG emissions with 17 to
27% from feedlot sources. Holstein steers that entered
the beef production system as a by-product of dairy
production had the lowest carbon footprint because the
emissions associated with their mothers were primarily
attributed to milk rather than meat production. For the
Holstein system, the feedlot phase was responsible for
91% of the total GHG emission, while the calf-ranch
phase was responsible for 7% with the remaining 2%
from transportation. This simulation study provides
baseline emissions data for California beef production
systems and indicates where mitigation strategies can be
most effective in reducing emissions.
Key words: ammonia, beef cattle, carbon footprint, farm model, greenhouse gas, simulation.
© 2012 American Society of Animal Science. All rights reserved.
INTRODUCTION
Anthropogenic greenhouse gas (GHG) and ammonia (NH3) emission reporting from livestock production
has increased in priority on political, social and eco-
1 The authors appreciate the assistance of Larry Forero and Josh
Davy UC Cooperative Extension advisors in Shasta and Tehama
County, as well as George and Chris McArthur and Henry Giacomini
Shasta county beef producers. Thanks also to anonymous feedlot owners and operators, and calf ranch owners and operators in California
who contributed to developing our simulated production systems.
2 Corresponding author: [email protected]
Received August 31, 2011.
Accepted August 19, 2012.
J. Anim. Sci. 2012.90:4641–4655
doi:10.2527/jas2011-4653
nomic agendas. However, reporting accurate GHG and
NH3 emissions is challenging due to the complexity of
animal production systems and the regional ecological
differences that drive biological processes.
Evaluation of gaseous emissions from animal production systems requires a whole system modeling
approach (Stewart et al., 2009). Greenhouse gas emissions and the associated carbon footprint are often determined through Life Cycle Assessment (LCA). An LCA
includes all primary emissions during the production
process and the secondary emissions that occur during
the production of resources used in the production process (Rotz et al., 2010). Quantification of these emissions can be assisted through simulation of the produc-
4641
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Stackhouse-Lawson et al.
tion processes using a tool such as the Integrated Farm
System Model (IFSM; USDA-ARS, 2011). This farm
scale simulation integrates the interacting processes of
pasture, rangeland and crop growth, crop harvest, feed
storage, grazing, feeding, animal production, and manure
handling to determine the long-term performance, environmental impact, and economics of production systems.
This approach can help avoid practices that may reduce
NH3 emissions while increasing GHG emissions and situations where emissions may be reduced at the expense of
productivity (Janzen et al., 2006).
The objective of this work was to use simulation
modeling combined with LCA to compare the cradleto-farm gate carbon footprint and NH3 emissions of the
major beef production systems in California. Production
phases included cow-calf, stocker, feedlot, Holstein calf
ranch, and Holstein feedlot phases. The calculation of
net emissions determined the relative contribution of
each phase to the overall emissions and carbon footprint
of the consumable product.
MATERIALS AND METHODS
Model description
Beef production systems were modeled according to
industry typical production practices using the IFSM (Rotz
et al., 2005; Rotz et al., 2011). The major processes of feed
production, animal performance, and manure production
and handling were simulated through time over 25 yr of
weather to estimate daily and long term emissions. This
software and additional information on the model are available through the internet (USDA-ARS, 2011).
A cradle-to-farm gate LCA is used in IFSM to integrate
emissions from primary and secondary GHG sources (Rotz
et al., 2010; Rotz et al., 2011). Primary emissions are gases
produced by the animal (enteric fermentation), emissions
from feces and urine, and emissions during the production
of feed. Secondary emissions are emitted during the production of resources used, which include machinery, fertilizer, fuel, electricity, and other important inputs used in
the production process. Primary and secondary emissions
are interlinked and dependent on the efficiency of the cattle
production system and the length of the animal’s productive life. A carbon footprint is determined by totaling the
net lifetime GHG emissions and dividing by lifetime production in kg of HCW.
A beef production system represents all phases necessary to produce a finished market beef animal. Beef
production systems vary depending on region and include 1) cow-calf and feedlot phases, 2) cow-calf, stocker, and feedlot phases, 3) cow-calf and stocker phases
(more unusual, only 1 to 2% of beef are finished on
grass), and 4) calf ranch and feedlot phases for Holstein
cattle. Greenhouse gas emissions were simulated for
each phase and totaled to obtain emissions per unit of
finished beef. To account for the loss of animals, emissions for the cow-calf and stocker phases were increased
to account for mortality in the subsequent phases. Emissions from replacement heifers, nursing calves, and bulls
are included in the cow-calf phase emissions.
The system boundaries are beyond the physical
form of each operational phase to include the production of feeds and other resources used to maintain the
herds (Figure 1). Emissions from the production of feed
crops are included in the carbon footprint whether the
feed is produced on the ranch or purchased from an outside farm. In the IFSM, all manure nutrients are assumed
to be used in feed-crop production unless a portion is
designated as exported from the farm. Manure from
California beef feedlots is most often exported for use
in organic vegetable operations; therefore, greenhouse
gas emissions are reported with and without inclusion of
emissions resulting from manure beyond the farm gate.
The 3 GHG gases emitted from beef cattle production are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Each has different global warming
potentials which quantify the capacity of the gas to trap
heat in the atmosphere. To standardize GHG emissions,
the International Panel on Climate Change (IPCC, 2001)
has established the global warming potential equivalence
index to convert GHG to CO2e units. In our model, the
conversion factors are 25 kg of CO2e/kg CH4 and 298
kg CO2e/kg N2O (IPCC, 2007).
Primary GHG emissions
Primary GHG emissions include all CO2, CH4, and
N2O produced during the production of feed, maintenance of animals, and handling of manure. Process level
simulation is used to predict animal and manure storage emissions; simpler relationships are used to estimate
emissions from less important sources (Rotz et al., 2010,
2011).
Carbon Dioxide. The major sources of CO2 from
beef production systems are animal respiration and microbial respiration from land applied manure. Manure
storage is also a small contributor. Rangeland forages,
pastures grasses, and croplands assimilate CO2 from the
atmosphere through photosynthetic fixation during periods of forage and crop growth and emit CO2 through
plant and soil respiration and manure decomposition. On
an annual basis rangeland forages, pasture grasses, and
croplands are a net sink where plants assimilate more
CO2 than is emitted (Chianese et al., 2009a).
To predict CO2 emissions from feed production (for
rangeland, pasture, and crops), a carbon balance is determined that considers all flows in and out of the land dur-
Carbon footprint and ammonia emissions in beef
4643
Figure 1. Primary and secondary emission sources for partial life cycle assessment of the carbon footprint of the California beef production system.
ing the production of forage and feed for the herd (Rotz
et al., 2010). In the current study, the carbon balance also
includes carbon from animal and manure sources. These
sources are often ignored in GHG accounting (IPCC,
2001, 2007); however, when looking at the partial life
cycle from cradle to farm gate, it is important to consider all carbon emission sources and sinks. Respired
CO2, enteric CH4, and carbon converted to body mass
are integral parts of the carbon balance that begins with
photosynthetic fixation by plants. Plants are consumed
by the animals that release a portion of the carbon back
to the atmosphere and use carbon for growth and muscle
development. To predict the total C fixed through photosynthesis and emitted through autotrophic and heterotrophic respiration, we include the net C assimilated in
the feed consumed by the animals converted to CO2e.
Carbon dioxide emitted by the herd is predicted as
a function of DMI and BW of 6 possible animal groups
(Chianese et al., 2009a). The 6 animal groups are cows,
nursing calves, young heifers, yearling replacement
heifers, stocker cattle, and finishing cattle with animal
characteristics defined by breed (Rotz et al., 2005). Animals are fed to meet requirements for minimum forage,
energy, and protein using requirements based upon the
Cornell Net Carbohydrate and Protein System, level 1
(Fox et al., 2004). Animals on pasture can be fed an all
forage diet where grain supplementation is used only
in an emergency if cow BW loss reaches 0.9 kg/d or
stocker rate of BW gain drops to 10% of their desired
rate of BW gain due to poor forage quality (Rotz et al.,
2005). Carbon dioxide emitted from manure in drylot
corrals and on pasture and rangeland is determined using an empirical equation that incorporates effects of air
temperature and manure surface area (Chianese et al.,
2009b).
Operation of equipment releases CO2 when fossil
fuel is burned (Rotz et al., 2010). The conversion used to
determine CO2 from fossil fuel use is 2.64 kg of CO2/L
of diesel fuel consumed (Wang, 2007). Fuel use is predicted in IFSM through the simulation of equipment operations used in feed production and feed and manure
handling (Rotz et al., 2011). For the present study, a
pickup truck was added for general use in the cow-calf
and stocker phases as this is typical for the industry.
Methane. Enteric fermentation is the largest contributor of CH4 from beef cattle (USEPA, 2009). Manure storage and manure deposited on corral floors,
pastures, and rangelands also contribute, but to a lesser
extent (Chianese et al., 2009c). To predict enteric CH4, a
model is used where methane emissions are a nonlinear
function of metabolizable energy intake and the ratio of
starch over ADF content in the diet (Mills et al., 2003).
Total DMI for the animal group is the sum of the DMI
for maintenance and gain (Rotz et al., 2005). The DMI
for maintenance is the NEm requirement divided by the
NEm of the diet and the DMI required for BW gain is
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Stackhouse-Lawson et al.
the NE required to meet the ADG goal divided by the
NEg of the diet. Daily CH4 emissions are predicted for
the 6 possible beef animal types based on their diets.
The model responds with increased CH4 emissions from
high fiber diets and decreased CH4 emissions with diets
high in starch (Rotz et al., 2010, 2011). This relationship, developed for dairy cattle, provided the only suitable model for predicting enteric methane from cattle on
very high or all forage diets. For high concentrate diets,
predicted methane production was limited to a lower
value similar to the IPCC (2006a) emission factor for
feedlot cattle.
The cow-calf phase is maintained on rangeland or
pasture all year long. Methane is predicted from pasture
and rangeland using an average emission factor of 0.76
g of CH4/kg of feces DM (Chianese et al., 2009c). As
such, the manure CH4 emission from grazing cattle is
a function of daily manure excretion and the time spent
on the pasture or rangeland each day (Rotz et al., 2010).
Feedlot animals are housed in dirt-floored drylot
corrals where manure accumulates in a pack. To predict
CH4 emissions from this manure pack, an adaptation of
the tier 2 approach of the (IPCC, 2006a) is used, where
the methane emission rate is a linear function of ambient
outdoor temperature (Rotz et al., 2011). Stored manure
also contributes to CH4 emissions and is predicted as a
function of the total volatile solids in the storage and a
methane conversion factor modeled as a linear function
of ambient temperature (Rotz et al., 2011).
Nitrous Oxide. Cultivated croplands and pastures
are the largest source of N2O emissions due to the manure and fertilizer N inputs. Daily nitrous oxide emissions from croplands and pastureland are simulated as a
function of soil texture, moisture content, and N content
(Rotz et al., 2011).
Nitrous oxide is produced in lower amounts from
drylot corral manure packs. These emissions are predicted using the tier 2 approach from the IPCC (2006a)
using an emission factor of 0.02 kg of N2O-N/kg of N
excreted in the corral (Rotz et al., 2010). Nitrogen excreted is multiplied by the emission factor and the N to
N2O conversion factor of 1.57 to obtain predicted N2O
emission. Manure stored in stacks has an emission factor
of 0.005 kg N2O-N/kg of N stored (IPCC, 2006a).
Secondary GHG emissions
Secondary emission sources include the production of electricity, fuel, machinery, fertilizer, pesticide,
and purchased feed used in the maintenance of animals,
handling of manure, and production of feed (Rotz et al.,
2010). Emissions for the production of fuel and electricity are set using the emission factors of 0.374 kg of
CO2e/L of fuel and 0.73 kg of CO2e/kWh of electricity
(Wang, 2007). The amounts of fuel and electricity used
are determined through the simulation of production
processes by IFSM (Rotz et al., 2011).
Emissions associated with machinery include those
during manufacture along with those for maintenance
and repairs. The GHG emission factor for the production
of machinery is 3.54 kg of CO2e/kg of machinery mass
(Rotz et al., 2010). Machinery use and repairs are predicted through the simulation of machinery operations
(Rotz et al., 2011).
For our analysis, fertilizer, pesticide and seed use
only apply to off-farm feed production. Fertilizer use is
based upon the defined application rates and crop areas
(Rotz et al., 2011). Emission factors for nitrogen, phosphate, and potash production are 3.31, 1.03, and 0.87 kg
of CO2e/kg, respectively (Wang, 2007). Pesticide use is
based on typical requirements for producing each crop
(Penn State, 2011) and the land area used for that crop.
This emission is generally small and a set emission factor of 22 kg of CO2e/kg of pesticide active ingredient
is used (Wang, 2007). Emission from seed production
is also very small (0.3 kg of CO2e/kg of seed; Rotz et
al., 2011). User-assigned crop areas and typical seeding
rates for each crop are used to predict seed use.
Emission factors were developed for the major feeds
imported into the production systems. Steam flaked corn
makes up 80 to 85% of the concentrate diet fed to feedlot
cattle in California. The corn, typically transported from
the Midwest, is processed with steam during flaking. A
representative corn farm was simulated using IFSM with
climatic data from Iowa to determine a typical GHG
emission of 0.25 kg CO2e/kg DM of corn produced. We
assumed a round trip distance traveled and the resulting fuel use to transport grain from Iowa to California
was 5,800 km and 2,300 L, respectively. Fuel use was
multiplied by the fuel emission factors above and divided by the mass of corn DM transported to obtain a
carbon footprint of 0.32 kg CO2e/kg DM. For the steam
processing, we assumed gas use was 12.8 m3/t DM of
corn (L. McKinney, Kansas State University, KS, personal communication), which gave a footprint for steam
processing of 0.03 kg CO2e/kg DM. The total carbon
footprint or secondary emission assigned to steam flaked
corn used in California was 0.6 kg CO2e/kg DM.
Another major feed used in beef production is hay.
Representative farm simulations with IFSM were again
used to obtain a typical emission associated with alfalfa
or stock quality hay production of 0.2 kg CO2e/kg DM.
Considering that the transport was from within or near
California, an emission associated with transport of 0.2
kg CO2e/kg DM was assigned giving a total emission of
0.4 kg CO2e/kg DM.
Other feeds included milk replacer for the Holstein
calf ranch and cotton seed, fat and minerals primarily
Carbon footprint and ammonia emissions in beef
for the finishing operations. No information was found
on the GHG emissions associated with the production of
milk replacer. A value of 12.5 kg CO2e/kg of milk powder was estimated based upon the production and drying
of powdered milk (Ramirez et al., 2006). For all other
feeds, a secondary emission value of 1.0 kg CO2e/kg
DM was used. Considering the relatively small amounts
of these other feeds fed, error in the estimation of this
value had little effect on the overall carbon footprint of
California beef production systems.
Ammonia emissions
Cattle are not efficient users of protein N, and excess
protein N is excreted primarily in urine as urea. Following excretion, ammonia emission from a manure surface
involves 5 important processes: urea hydrolysis, dissociation, diffusion, aqueous-gas partitioning, and mass
transport away from the manure surface to the atmosphere (Rotz et al., 2011). The 4 important NH3 sources
are housing facilities, manure storage, field applied manure, and direct deposits on pasture or rangeland. Linking the models for each of the emission processes predicts the emission rates from each of the major farm or
ranch NH3 sources.
Fecal and urine excretions in a feedlot form a thin
layer of manure across the soil surface where the emission processes transform the N and control the NH3
emission rate (Rotz et al., 2011). Because the manure remains on this surface for many days, most of the ammoniacal N is transformed and volatilized. When manure is
scraped from the feedlot surface and stacked for storage
or composting, remaining organic N slowly decomposes
to form ammoniacal N. Daily emission rate is predicted
as a function of the exposed surface area, ammoniacal N
concentration, temperature, air velocity, and surface pH
(Rotz et al., 2011).
Ammonia emission from pasture and rangeland is
also predicted considering the dissociation, diffusion,
aqueous-gas partitioning, and mass transport processes.
Daily emissions are a function of the amount and form of
N applied, ambient temperature, and precipitation (Rotz
et al., 2011). Excreted N is determined by the diet and
the portion of time each animal group spends on pasture
or rangeland. Remaining N is available for fertilization
of the growing forage.
Production Systems
California beef production. Beef cattle production
in California is unique, when compared to beef production systems in other regions of the United States. California’s predominant rangeland is mediterranean where
forage growth is supported by rains in the winter and
4645
early spring. The state also has intermountain ranges
where forage growth occurs during the late spring and
early summer. Therefore, cattle graze the lower elevation forage during the winter months and are then transported to the intermountain ranges during the summer
months, or are moved onto irrigated pasture during the
late summer. California is also unique in that it is home
to approximately 2 million dairy cows, 20% of the nation’s entire herd. Bull calves from the dairy sector enter
the beef supply chain and make up a large portion of the
feedlot cattle in the state. Additionally, California grows
relatively little of the grain crops used in finishing cattle
rations, and the cost of transport of these crops from the
Midwestern US is high.
California beef cattle production typically consists
of a 3-phase system: 1) cow-calf, 2) stocker, and 3) feedlot. Each phase is often owned and operated independent
of the other phases. The producers in the cow-calf phase
maintain a breeding herd of cows, replacement heifers,
and bulls. Cows are usually maintained extensively on
rangelands or pasture, where they give birth to calves
that are sold at weaning (typically around 205 d of age).
The producers of cattle in the stocker phase purchase
the weaned calf and add additional BW through grazing extensive rangelands. The animal exits the stocker
phase and is sold into the feedlot at approximately 350
kg BW. Feedlots maintain large numbers of cattle and
utilize high energy feed sources to increase BW gain and
decrease time spent on feed. Cattle leave the feedlot to
enter the food chain at approximately 550 kg and about
17 mo of age.
Holstein steers are managed with a 2-phase system: 1) calf ranch and 2) feedlot. At birth the bull calves
are purchased by a calf ranch that specializes in rearing calves. The calves exit the calf ranch at 4 mo of age
when they are sold to the feedlot. They remain in the
feedlot until they weigh approximately 550 kg and are
15 mo of age.
Simulated ranches and farms. Representative farms
or ranches were simulated for each phase of beef cattle
production. Our production systems were defined through
consultation from beef researchers, UC Cooperative Extension advisors, and beef cattle producers. All simulations
were conducted for a 20 to 25 yr period using recent historical weather for their location.
The cow-calf phase was simulated in Tehama County, representative of Mediterranean climate rangeland
and typical of many cow-calf operations in California.
The herd was comprised of 600 Black Angus cows, 20
Black Angus bulls, 90 replacement heifers (15% replacement rate), and 574 September born nursing calves
(considering 4% twins and 8% mortality). The average
lifespan of the cows was 8 yr with a calving interval of
365 d, thus each cow was expected to have 6 calves dur-
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Stackhouse-Lawson et al.
ing her life. Cull cow production was included by adding 125 kg SBW to the amount of animal mass produced
per finished steer when calculating the footprint for the
full system (Tables 4 and 5).
Cattle were produced on 2671 ha of rangeland and
pasture with a medium sandy loam soil typical of this
region (Table 1). Land use was determined based on a
stocking rate of 4.5 ha/cow, which represented an average between extensive winter and spring rangeland and
irrigated spring and summer pasture. Rangeland forage
consisted of annual and perennial grassland (Table 1).
Cattle were fed primarily through grazing, but during
times of poor forage growth, they were supplemented
with poured protein supplement blocks (referred to as a
protein tub) and stock quality hay. Nursing calves were
creep fed a grain supplement and weaned at 210 d of
age weighing 280 kg. All feed other than grassland was
purchased and brought onto the ranch. One pickup truck
was used that consumed 4,450 L/yr of fuel in the activities of the operation. Dry hay was stored inside a shed
and a machine shed was on site.
The ranch for the stocker phase was simulated in
Shasta County, representative of intermountain climate
rangeland, and typical of many stocker operations in
California. The herd of 1,000 Black Angus stocker cattle
was implanted with a growth hormone on arrival. Cattle
were maintained on 4047 ha of rangeland based on typical stocking rates of about 4.0 ha/animal. Cattle were
transported from the cow-calf phase in Gerber to McArthur, California in May (after weaning) and removed
from the rangeland in September. Rangeland forage
consisted of annual and perennial grassland produced
on a medium sandy loam soil (Table 1). Cattle were fed
primarily through grazing. During times of poor forage
Table 1. Characteristics of simulated beef production systems in California
Item
Cow-calf
Land and weather
Weather data location
Simulation, yr
Total land, ha
Owned, ha
Rented, ha
Soil type
Farm topography, % slope
Soil phosphorous, mg/kg
Crops
Initial sward DM, kg/ha
Initial sward composition
,cool-season grass:forb
Forage yield adjustment, %
Fertilizer, % manure
Grazing area summer,
spring, and fall, ha
Grazed forage
yield adjustment, %
Animal Management
Labor, min/animal-d
Number of animals,
Replacement heifers
Breed
Calving month
Weaning age, d
Days on feed
Mortality, %
Diet
Supplemental feed
Animal housing
1Finishing
Gerber, CA
25
2,671
890
1,781
Medium sandy loam
15 to 25
30 to 50
Perennial grassland
392
60:40
Stocker
McArthur, CA
25
4047
4047
Medium sandy loam
> 25
30 to 50
Perennial grassland
392
60:40
90
100
1,781
90
100
4,047
70
70
0.4
600
90
Angus
September
210
365
6.0
Grazing forage
Hay, protein tubs,
grain for calves
None
0.1
1,000
Angus
September
210
182
2.0
Grazing forage
Hay, protein tubs
None
Angus feedlot
Holstein calves
Holstein feedlot
Kettleman City, CA
25
17.8
17.8
Kettleman City, CA
25
17.8
17.8
Meloland, CA
19
17.8
17.8
Deep sandy loam
0 to 3
50 to 100
Deep sandy loam
0 to 3
50 to 100
0.1
5,000
Angus
September
210
121 and 212
1.6 and 2.8
High grain
finishing diet1
Cottonseed
Open lot
2
15,000
Holstein
All year
60
120
6.5
Milk and starter grain
(d 1-60), high grain1
(d 60-120)
Cottonseed
Deep sandy loam
0 to 3
50 to 100
0.1
5,000
Holstein
September
60
331
4.4
High grain
finishing diet1
Triplet hutches
diet varies but is approximately 75% steam flaked corn, 20% hay, and 3% cottonseed on DM basis with added fat and minerals.
Cottonseed
Open lot
Carbon footprint and ammonia emissions in beef
growth, they were supplemented with protein tubs and
stock quality hay purchased and brought onto the ranch.
Dry hay was stored inside a shed. One pickup truck was
used consuming 2,300 L/yr of fuel in the activities of the
stocker operation. Considering 2% mortality, 980 animals were sold to the finishing phase.
Two simulations were performed for the Angus
feedlot phase of the beef life cycle with cattle entering
the feedlot from 1) a stocker system at 379 kg or 2) a
cow-calf system at 280 kg (Table 2). Both simulations
for the feedlot phase were simulated in Kern County,
representative of mediterranean climate and typical of
the predominant beef feedlot operations in California.
The herd of 5,000 Black Angus cattle was implanted
with a growth hormone on arrival. Mortality was 1.6%
for simulation 1 and 3.2% for simulation 2. They were
housed on 17.8 ha of land. Cattle were transported from
McArthur (stocker phase, for simulation 1) or Gerber
(cow-calf phase, simulation 2) to Kettleman City, California in September.
Cattle were fed a high concentrate finishing diet of
approximately 75% (DM) steam flaked corn, 20% alfalfa hay, 3% cottonseed, fat, and mineral with an ionophore feed additive. All feed was purchased and brought
onto the feedlot. Finished BW was set at 571 kg with
HCW determined as 62% of FSBW. Cattle were housed
in a drylot corral and manure was collected by scraping.
Simulations were conducted to show the impacts of all
manure being exported from the production system (typical of California) compared to a scenario in which all
manure remains within the production system. Machinery included a tractor, one large feed mixer, one medium
box spreader, and 2 medium skid-steer loaders. Dry hay
was stored inside a shed, concentrate feeds were stored
in a commodity shed, and equipment was stored in a ma-
Table 2. Predicted performance for various beef production systems simulated with IFSM
Measure
Angus
cow 1
Angus
feedlot
(w/o
Angus
Angus stocker Holstein Holstein
calf Stocker feedlot phase)
calf
feedlot
DOF 2
365
212
182
121
212
121
334
BW, kg
Initial
40
283
379
280
42
139
Final
625
280
384
571
571
127
573
ADG, kg/d
1.1
0.5
1.4
1.4
0.7
1.3
8.0
DMI, kg/d 8.9
2.7
6.6
10.0
9.4
2.6 3
G:F
0.41
0.08
0.14
0.15
0.27
0.16
1Heifers calve at 2 yr of age.
2Days on feed.
3Dry matter intake is calculated for the period after calves are weaned and
housed in group pens on a high grain feedlot diet.
4647
chine shed.
The calf-ranch phase of the Holstein beef life cycle was simulated in Kern County, representative of a
mediterranean climate, and typical of many calf-ranch
operations in California (Table 1). The herd consisted
of 15,000 Holstein bull calves housed in triplicate calf
hutches on 17.8 ha of land. After birth, the calves were
transported 200 km to the calf ranch. Their carbon footprint leaving the dairy farm was determined to be 112
kg CO2e per calf through simulation of dairy production
systems using an economic allocation procedure (Rotz
et al., 2010).
Calves were fed replacement milk and starter grain
from d 1 to 60 and a high concentrate diet from d 60
to 120, which included cottonseed as a protein source.
Energy used to mix replacement milk and clean feeding equipment was included as a secondary emission in
the overall GHG calculation. Calves were weaned at 60
d of age with a mortality of 6.5%. Initial and final BW
was set at 42 and 127 kg, respectively. All feed was purchased and brought onto the ranch. Machinery included
2 tractors, 2 small feed mixers, 1 medium box spreader,
and 2 medium skid-steer loaders. Replacement milk was
stored inside a shed, other feeds were stored in a commodity shed, and equipment was stored in a machine
shed.
The Holstein feedlot phase was simulated in Imperial County, representative of desert climate, and typical
of predominant Holstein feedlot operations in California. The herd consisted of 5,000 Holstein steers. Animals were implanted with a growth hormone on arrival,
and mortality was 4.4%. Cattle were maintained on 17.8
ha of land for 331 d. Finished BW was set at 573 kg
and HCW was calculated as 59% of FSBW. Cattle were
transported from Kern County (calf-ranch phase) to Imperial county. All other assumptions were similar to the
Angus feedlot simulation.
Transportation of animals
Transportation of animals was not included in IFSM,
so separate calculations were applied to determine emissions associated with this component. The round trip
distance for transportation in the Angus production system that included the stocker phase was estimated at
2,350 km; without the stocker phase the distance was
2,150 km. For the Holstein system, the round trip distance was 550 km. Fuel use was estimated based upon a
typical truck load (50 animals) and fuel efficiency (2.5
km/liter). Greenhouse gas emissions were calculated by
multiplying the fuel use per animal transported by the
emission factors for fuel production and combustion.
This emission was increased an additional 40% to account for embodied CO2e in the manufacture and main-
4648
Stackhouse-Lawson et al.
tenance of the truck (Rotz et al., 2010).
Model uncertainty
All farm-level emission estimates have an uncertainty associated with their prediction. Net farm emission
uncertainty is determined by defining the uncertainties
of each component contributing to net GHG emissions.
Proper statistical quantification of biological system uncertainties requires large data sets that are not available.
Therefore, the IPCC (2006b) has used expert opinion to
estimate the uncertainty of emission factors used in predicting GHG emissions, and this provides the best basis
for estimating the uncertainty in predicting farm emissions. They report that their Tier 2 methodologies for CH4
emission from enteric fermentation and manure handling
have an uncertainty of ±20%, and state that this uncertainty can be reduced by applying their methodologies to
well defined conditions (IPCC, 2006a). Since our model
predicts emissions for a herd with a specific animal type
and feed composition, an uncertainty of ±10% is used to
predict enteric methane emission along with ±20% for
manure emissions (Chianese et al., 2009c). Similar to the
IPCC (2006a), an uncertainty of ±50% is used for N2O
emission from field and manure surfaces (Chianese et al.,
2009d). For fuel combustion and secondary emissions, an
uncertainty of 20% is used. This assumes that our transport distances for animals and feed generally represent
the average for production in California. No data exist
on the uncertainty in predicting NH3 emissions of farm
components, but preliminary evaluation of this emission
component indicates that predictions are within ±20% for
pasture, manure storage and feedlot surfaces (Rotz, unpublished data). The uncertainties of the emissions from
all farm components of each production phase are combined to give the overall uncertainty as the square root of
the sums of squares of each emission component times its
uncertainty (IPCC, 2006b).
Model evaluation of predicted animal emissions
To evaluate this new application of IFSM, predicted
animal emissions were compared to measured data obtained through experiments conducted by Stackhouse
et al. (2011). In these experiments, CH4, N2O, and CO2
emissions were recorded from 5 different animal types using a whole animal respiration chamber (Table 3). The 5
animal types were: finished Angus and Holstein feedlot
steers with BW of 540 and 530 kg, respectively, growing
Angus and Holstein feedlot steers with BW of 350 and
337 kg, and Holstein calves with a BW of 150 kg.
For further evaluation of the enteric emission model
as applied to beef cattle, simulated emissions were compared to those measured in a number of published stud-
Table 3. The IFSM evaluation comparing predicted
emissions from different animal types at different BW to
emissions measured in a whole animal respiration chamber study by (Stackhouse et al., 2011)
Calorimetric
emissions,
kg/animal/d
Breed,
BW, kg
CH4
N 2O
Angus, 540
Angus, 350
Holstein, 530
Holstein, 337
Holstein, 150
0.100
0.068
0.100
0.076
0.048
0.0004
0.0005
0.0004
0.0004
0.0003
Simulated
emissions,
kg/animal/d
Measured
DMI,1,2
CO2 kg/d
CH4
7.89 11.18 0.094
6.88
7.44 0.076
7.11 11.32 0.101
6.42
7.54 0.079
5.41
3.19 0.040
Simulated
DMI,
kg/d
N2O CO2
0.0005 8.22 10.40
0.0003 5.72
7.84
0.0004 8.17 10.57
0.0003 5.67
8.07
0.0002 2.42
3.87
1Dry matter intake from the measured animals were taken from the day before
the animals entered the chamber.
2Diet was similar across all animal types and was a high concentrate grain diet.
ies. These studies included cows, heifers and steers on
pasture or an all forage diet and heifers and steers fed
a high concentrate diet. For the high concentrate diets,
studies were selected that used diets similar to that used
in our simulation where about 90% of the diet was concentrate with corn normally being the primary concentrate fed. For each comparison, animals of the reported
type and size were simulated over 25 yr with the appropriate diet, and the predicted mean emission was compared to that reported in the experimental study.
RESULTS
Model evaluation
Emissions predicted by IFSM were similar to those
measured in whole animal respiration chambers according to BW and animal type (Table 3). Simulated CH4
emissions were within 1 to 11% of measured values
across the 5 animal groups showing good agreement.
Nitrous oxide emissions were very low for both simulated and measured data, and simulated emissions averaged 15% less than those measured. Differences between measured and simulated CO2 emissions were
greater with simulated values varying from 55% lower
to 21% greater than those measured. The greatest difference was for small Holstein animals where the model
under predicted measured emissions. Measured CO2
emissions were not greatly different across large differences in animal BW, which implies that the model more
accurately represented typical animal CO2 emissions as
a function of animal size.
When compared to emissions measured in other studies, simulated enteric methane emissions were generally
similar to those measured across a wide range in feed intake (Table 4). In 7 of the 13 comparisons for animals
on pasture or all forage diets, simulated emissions were
4649
Carbon footprint and ammonia emissions in beef
Table 4. A comparison of measured and simulated enteric methane emissions from various beef animals on all forage
and high concentrate diets
DMI, kg/d
Experimental study
Grazing cattle, all forage diet
Harper et al., 1999
McCaughey et al., 1999
Jones et al., 2011
Pavo-Zuckerman et al., 1999
DeRamus et al., 2003
Pinares-Patino et al., 2003
McGinn et al., 2011
DeRamus et al., 2003
Pavo-Zuckerman et al., 1999
McCaughey et al., 1997
Boadi et al., 2002
Laubach et al., 2008
Finish cattle, high concentrate diet
Harper et al., 1999
Beauchemin and McGinn, 2005
Boadi et al., 2004
Nkrumah et al., 2006
Cooprider et al., 2011
Emission rate, g/ d
Measurement method
Animal type
Body mass, kg
Measured
Simulated
Measured
Simulated
Micrometeorological
mass difference
SF6 tracer gas
Fourier transform infrared
spectrophotometer
SF6 tracer gas
SF6 tracer gas
SF6 tracer gas
Point source dispersion
SF6 tracer gas
SF6 tracer gas
SF6 tracer gas
SF6 tracer gas
Micrometeorological
mass difference
Bred heifers
436
8.3
8.2
230
240
First calf heifers
Dry cows
Lact. cows
Cows
Cows
Cows
Heifers
Heifers
Steers
Steers
Steers
Steers
511
496
515
514
551 to 631
723 to 800
271
295 to 400
333
398
345
325
9.7 to 11.4
10.2 to 10.7
13.1 to 14.0
9.7 to 12.0
5.0
7.8 to 9.9
13.2 to 14.9
11.1
-
9.6
10.2
11.0
7.6 to 10.6
8.1 to 11.1
9.9 to 12.0
4.6
7.5 to 9.6
7.1
8.2
7.7
6.1
262 to 304
130
230
168 to 240
120 to 255
204 to 273
141
125 to 176
140 to 201
173 to 219
228
161
299
293
307
217 to 290
204 to 275
264 to 331
158
175 to 240
210
236
229
209
436
9.1
9.1
70
82
452
300 to 570
508
600
6.8
8.8 to 12.4
9.6 to 11.6
9.9
6.8
8.7 to 10.4
10.1
9.9
62
50 to 112
90 to 123
136 to 1481
62
83 to 98
91
90
Micrometeorological
mass difference
Environmental chamber
SF6 tracer gas
Calorimetric chamber
Enclosed pens
Bred heifers
Heifers
Steers
Steers
Steers
1Reported model predicted enteric emissions based upon the animals and feeding strategy used. Measured data included emissions from accumulated manure.
similar to those measured or the ranges in simulated data
overlapped the measured ranges. In most cases though,
the model tended to over-predict methane emission with
values about 20% greater than the reported measured
values. In a few of the experimental studies, DMI were
exceptionally high or the CH4 emission was low in relation to dry matter intake. For all other studies, the CH4
emission was within the range of 17 to 28 g CH4/kg of dry
matter intake. For the simulated data, most values were
in the range of 23 to 31 g CH4/kg DMI. Given the uncertainty in measuring dry matter intakes and CH4 emissions
from grazing animals, the model was found to adequately
represent this emission source.
For feedlot animals on high concentrate diets, simulated emissions compared well with reported measured
values (Table 4). For both measured and simulated data,
the enteric emission was around 9 g CH4/kg of dry matter intake. The one exception was the study by Cooprider
et al. (2011) where the reported data was not measured
but predicted using mechanistic models of rumen function. Over all studies, the comparisons supported that
the model adequately represented enteric emissions over
a wide range in animal types and diets.
Simulated production systems
Average simulated performance results, including initial and final BW, ADG, DMI and G:F for each phase is
shown in Table 2. The Angus calf performance parameters
were simulated to represent an average of the annual calf
crop from the cow-calf operation. The stocker operation
performance results were simulated to start with the weaning BW of the calf from the cow-calf phase. The Angus
feedlot was simulated so that the initial BW in the feedlot
was the final BW in the stocker phase. An Angus feedlot
without a stocker phase was a production system where the
weaned calf was transferred directly to the feedlot for an 8
mo finishing period. Days on feed (DOF) reflect the time
animals spend in each phase. The predicted ADG, DMI,
and G:F were the average over the DOF.
Greenhouse gas emissions and carbon footprints
for the Angus and Holstein beef production systems are
presented in Tables 5, 6, and 7. Emissions associated
with the cow-calf phase included those from the cows,
calves, replacements heifers, and bulls for 365 d, while
the stocker and feedlot phases only accounted for the
emissions from the single animal for the time the animal
was in that particular phase. The cow-calf phase of the
beef production system contributed the largest portion
4650
Stackhouse-Lawson et al.
Table 5. Greenhouse gas emissions and carbon footprint
for Angus beef production in California
Greenhouse gas emission per animal1
Production component
Cow calf
Methane
Nitrous oxide
Net biogenic carbon dioxide3
Combustion carbon dioxide
Secondary emissions
Total4
Stocker
Methane
Nitrous oxide
Net biogenic carbon dioxide
Combustion carbon dioxide
Secondary emissions
Total5
Finish
Methane
Nitrous oxide
Net biogenic carbon dioxide
Combustion carbon dioxide
Secondary emissions
Total6
Animal transport (full system)7
Total production system8
Farm gate carbon footprint9
kg CO2e/kg SBW
kg CO2e/kg HCW11
Gas,
CO2e,2
kg/ganimal/d kg/animal
Table 6. Greenhouse gas emissions and carbon footprint
for Angus beef production from weaning directly into
the feedlot (without stocker phase) in California
Greenhouse gas emission per animal1
Without
biogenic CO2,
kg/animal
Production component
0.525
0.009
−2.45
0.093
0.98
4,793
1,014
−896
34
356
5,301
4,793
1,014
−
34
356
6,197
0.218
0.005
−1.077
0.033
0.291
992
260
−196
6
53
1,115
992
260
−
6
53
1,311
0.095
0.016
−7.40
0.116
6.02
287
563
-896
14
697
713
65
7,392
10.6 ± 1.010
287
563
−
14
729
1,593
65
9,416
13.5 ± 1.2
17.7 ± 1.6
22.6 ± 2.0
1Expressed per animal exported to the next phase (i.e., for the cow calf
this is the number of calves produced, stockers are the number of stockers
produced and finished are the number of animals finished). The total for each
phase is adjusted by the mortality of the succeeding phases to obtain the total
for the production system per finished animal.
2Converted using global warming indexes of 25 units of carbon dioxide
equivalent (CO2e) per unit of methane and 298 units of CO2e per unit of
nitrous oxide.
3Net exchange of CO with the atmosphere including, assimilation in crop
2
and animal growth, respiration emission from animals and manure and assimilated CO2 converted to CH4.
4Includes the cows, calves, replacement heifers, and bulls for 365 d.
5Based on a 182 d feeding period.
6Based on a 121 d feeding period.
7Includes emissions from fuel combustion and that associated with production of the fuel and truck.
8Total GHG in CO e for the entire production systems adjusted per fin2
ished animal.
9Shrunk body weight (SBW) includes cull cows and bulls sold (125 kg
SBW per finished animal).
10The uncertainty in full system predictions is determined from the estimated uncertainties of each system component.
11Hot carcass weight (HCW) determined as 62% of SBW for the steer and
50% SBW for the cow.
(68%) of GHG to the Angus beef system that included
the stocker phase. When the stocker phase is used it con-
Cow calf
Methane
Nitrous oxide
Net biogenic carbon dioxide3
Combustion carbon dioxide
Secondary emissions
Total 4
Finish
Methane
Nitrous oxide
Net biogenic carbon dioxide
Combustion carbon dioxide
Secondary emissions
Total 5
Animal transport (full system)6
Total production system
Farm gate carbon footprint
kg CO2e/kg SBW8
kg CO2e/kg HCW9
Gas,
CO2e,2
kg/animal/d kg/animal
0.525
0.009
−2.45
0.093
0.98
0.103
0.009
−7.099
0.108
6.108
4,793
1,014
−896
34
356
5,301
547
517
−1,505
23
1,295
877
57
6,410
9.2 ± 0.97
15.4 ± 1.5
Without
biogenic CO2,
kg/animal
4,793
1,014
−
34
356
6,197
547
517
−
23
1,295
2,382
57
8,841
12.7 ± 1.2
21.2 ± 2.0
1Expressed
per animal exported to the next phase, i.e. for the cow calf
this is the number of calves produced, stockers are the number of stockers
produced and finished are the number of animals finished. The total for each
phase is adjusted by the mortality of the succeeding phases to obtain the total
for the production system per finished animal.
2Converted using global warming indexes of 25 units of carbon dioxide
equivalent (CO2e) per unit of methane and 298 units of CO2e per unit of
nitrous oxide.
3Net exchange of CO with the atmosphere including, assimilation in crop
2
and animal growth, respiration emission from animals and manure and assimilated CO2 converted to CH4.
4Includes the cows, calves, replacement heifers, and bulls for 365 d.
5Based on a 212 d feeding period.
6Includes emissions from fuel combustion and that associated with production of the fuel and truck.
7The uncertainty in full system predictions is determined from the estimated uncertainties of each system component.
8Shrunk body weight (SBW) includes cull cows and bulls sold (125 kg
SBW per finished animal).
9Hot carcass weight (HCW) determined as 62% of SBW for the steer and
50% SBW for the cow.
tributes the least (14%) of the 3 phases to total GHGs,
while the feedlot phase contributed 17%. Transportation
of cattle within the system contributed less than 1% of
the total GHG emission. For the Angus beef production
system that excluded the stocker phase, the cow-calf
phase was again the largest contributor (72%) of total
system GHG emission. The feedlot phase was responsible for 27% of total GHG. Following the standard procedure of excluding biogenic CO2, the carbon footprint
of the simulated Angus beef production system was 13.5
Carbon footprint and ammonia emissions in beef
Table 7. Greenhouse gas emissions and carbon footprint
for Holstein beef production in California
Greenhouse gas emission per animal1
Production component
Calf Ranch
Methane
Nitrous oxide
Net biogenic carbon dioxide3
Combustion carbon dioxide
Secondary emissions4
Total 5
Feedlot
Methane
Nitrous oxide
Net biogenic carbon dioxide
Combustion carbon dioxide
Secondary emissions
Total 6
Animal transport (full system)7
Total production system
Farm gate carbon footprint
kg/CO2e kg SBW9
kg/CO2e kg HCW10
Without
Gas,
CO2e,2 biogenic CO2,
kg/animal/d kg/animal
kg/animal
0.070
0
0.860
0.030
0.930
105
0
104
4
113
326
105
0
−
4
113
222
0.087
0.004
−6.14
0.098
6.84
822
573
−2,175
33
1,867
1,120
73
1,534
2.7 ± 0.48
822
573
−
33
1,866
3,295
73
3,601
6.3 ± 0.9
4.5 ± 0.6
10.7 ± 1.4
1Expressed
per animal exported to the next phase (i.e., for the cow calf
this is the number of calves produced, stockers are the number of stockers
produced and finished are the number of animals finished). The total for each
phase is adjusted by the mortality of the succeeding phases to obtain the total
for the production system per finished animal.
2Converted using global warming indexes of 25 units of carbon dioxide
equivalent (CO2e) per unit of methane and 298 units of CO2e per unit of
nitrous oxide.
3Net exchange of CO with the atmosphere including, assimilation in crop
2
growth and respiration emission from animals and manure.
4Includes 112 kg of CO e from the production of the calf in the dairy in2
dustry.
5Based on a 121 day feeding period.
6Based on a 334 day feeding period.
7Includes emissions from fuel combustion and that associated with production of the fuel and truck.
8The uncertainty in full system predictions is determined from the estimated uncertainties of each system component.
9Total GHG in CO e for the entire production systems adjusted per fin2
ished animal.
10Hot carcass weight (HCW) determined as 59% of SBW.
± 1.2 kg CO2e/kg SBW or 22.6 ± 2.0 kg CO2e/kg HCW
(Table 5). For the Angus beef production system without
the stocker phase the carbon footprint was 12.7 ± 1.2 kg
CO2e/kg SBW or 21.2 ± 2.0 kg CO2e/kg HCW (Table
6).
For the Holstein beef production system (Table 7),
the majority of the emissions from the cow were accounted for in dairy production, rather than beef production.
The calf entered the system with 112 kg of CO2e, which
accounted for the environmental cost of calf production
while a part of the dairy production system. In the Hol-
4651
stein beef system, the largest contribution (91%) of GHG
emission was from the feedlot. The calf-ranch contributed
7% of the total system GHG, and transport contributed
2%. The carbon footprint for the Holstein system was 6.3
± 0.9 kg CO2e/kg SBW or 10.7 ± 1.4 CO2e/kg HCW (Table 7). Including biogenic CO2 essentially provides a system expansion approach for allocating exported manure
C from the feedlot phase to other production systems that
utilize feedlot manure. This removes the manure C from
this phase of our simulated beef production system and
places it in the carbon footprint of the production system
using the manure.
Biogenic CO2 represents the net exchange of CO2
with the atmosphere including, assimilation in crop and
animal growth, respiration emission from animals, plants,
soil and manure, and assimilated CO2 that is converted
and emitted as CH4. Although standard LCA procedures
ignore these sources, including them provides a more accurate assessment of the farm gate footprint when large
amounts of carbon are exchanged with other production
systems or subsequent parts of the beef production system. Including biogenic CO2 essentially provides a system-expansion approach for allocating exported manure
C from the feedlot manure. This removes the manure C
from this phase of our simulated beef production system
and places it in the C footprint of the production system
using the manure. For the Angus beef system without the
stocker phase, including biogenic CO2 reduced the footprint by 27% (Table 6). For the Holstein beef system, the
carbon footprint was decreased by 58% by including biogenic CO2 (Table 7).
The handling of manure was the major factor contributing to the difference between including and excluding biogenic CO2. California feedlots sell the majority
of their manure to other farms as fertilizer. Therefore,
the reported carbon footprint values were calculated
with 100% of the manure from feedlots exported. This
assumed that the manure C became associated with the
carbon footprint of another production system. To further evaluate this effect, we included additional simulations where all manure remained in the beef production
systems. This implies that all manure goes back to land
used to produce feed for beef animals. Carbon footprints
were 19.5±1.7, 18.3±1.7, and 9.6±1.3 kg CO2e/kg HCW
for the Angus beef system including the stocker phase,
the Angus beef system without stockers, and the Holstein beef production system, respectively (Figure 2).
This was a 10 to 14% decrease in the footprint compared to not considering biogenic CO2. The remaining
difference includes CO2 assimilated in the C content of
the animal and that assimilated in the C released as CH4.
Simulated NH3 emissions from the full production
systems varied from 41.0 ± 5.4 to 49.8 ± 7.2 kg per finished animal (98 ± 13 to 141 ± 27 g/kg HCW) with the
4652
Stackhouse-Lawson et al.
Table 8. Carbon footprint and ammonia emissions of
each phase of beef production in California expressed
per unit of finished HCW
Production system
Conventional Angus
Cow-calf
Stocker
Feedlot
Feedlot, without
stocker phase
Animal transport,
full system
Total, with
stocker phase
Total, without
stocker phase
Holstein
Calf ranch
Feedlot
Animal transport,
full system
Total
Farm gate
carbon footprint,
kg CO2e/kg HCW1
15.4
3.2
3.8
5.7
Ammonia emission
kg/animal
19.6
3.5
17.9
30.2
g/kg HCW
47
8
43
73
0.2
22.6 ± 2.02
41.0 ± 5.4
98 ± 13
21.3 ± 2.0
49.8 ± 7.2
120 ± 17
0.7
9.8
0.2
10.7 ± 1.4
2.0
45.7
47.7 ± 9.0
6
135
141 ± 27
1Refer
to tables 4-6 for calculations of CO2e and HCW.
uncertainty in full system predictions is determined from the estimated uncertainties of each system component.
2The
lowest emission from the Angus system that included
the stocker phase (Table 8). In the Angus beef production system, total NH3 emission increased by 21% when
a stocker phase was not used as compared to that when
the stocker phase was included (Table 8). In the Angus
beef system that included the stocker phase, the cow-calf
phase emitted 48% of the total. The feedlot phase emitted 44% with 8% from the stocker phase. In the Angus
beef system that excluded the stocker phase, the largest
contributor was the feedlot phase emitting 61%, while
the cow-calf was only responsible for 39% of the total
NH3 emission. In the Holstein beef production system,
the feedlot phase emitted 96% of the total, while the calf
ranch emitted 4%.
DISCUSSION
In the United States, CH4 from enteric fermentation
in ruminant livestock species accounts for approximately
70% of GHG from livestock contributing 139 Tg CO2e/
yr (USEPA, 2009). Beef cattle are the largest contributor
of enteric CH4 producing nearly 72% of ruminant species (USEPA, 2009). This large contribution is due to
the beef cattle population of approximately 90 million
animals. The beef cattle industry spans the continental
United States and is comprised of various management
systems and farm and ranch sizes making the industry
diverse and complex. The complexity of this diverse industry further complicates GHG emission reporting and
suggests that individual life cycle evaluations of specific regional beef production should be conducted to
determine the true environmental impact of beef cattle.
Beef cattle production in California differs greatly from
production in the Midwestern states and thus must be
studied independently to better understand the environmental impact of the California cattle industry.
Often, reports that attempt to quantify GHG contributions from animal agriculture differ by region or scope
and therefore conclude with dissimilar results. In 2006,
the United Nations Food and Agriculture Organization
(UN FAO) published a report titled “Livestock’s Long
Shadow” estimating that livestock are responsible for approximately 7,100 Tg CO2e/yr or 18% of the world’s anthropogenic GHGs, which is a larger portion than all transportation (Steinfeld et al., 2006). In contrast, the USEPA
estimates that agriculture contributes 413.1 Tg CO2e/yr
or 5.8% of anthropogenic GHGs, and of that, livestock
are responsible for 198 Tg CO2e/yr or 3.4% (USEPA et
al., 2009; Pitesky et al., 2009). Although both reports use
holistic LCA tools, the conclusions are different due to the
regional inputs used. Therefore, it is important to evaluate the environmental impact of livestock systems within
their specific geographical region of production.
Using input parameters characteristic of California beef production, our LCA estimated that the carbon
footprint of Angus beef production systems range from
12.7 to 13.5 kg CO2e/kg SBW or 21.2 to 22.6 kg CO2e/
kg HCW. Our results are similar to the results from an
LCA conducted on a simulated U.S. herd in 2003, with
a reported carbon footprint ranging from 11.0 to 13.0
kg CO2e/kg SBW (Johnson et al., 2003). An LCA conducted on a simulated Midwestern herd reported results
slightly higher at 14.8 kg CO2e/SBW (Pelletier et al.,
2010), and this LCA did not include resource use and the
secondary emissions associated with the production and
maintenance of farm and ranch inputs. In comparison
to a simulated Alberta beef herd with a carbon footprint
of 22 kg CO2e/kg HCW (Beauchemin et al., 2010), our
estimated footprint is also similar. Casey and Holden
(2005) reported similar annual carbon footprints for an
Irish suckler-beef production system at 13.0 kg CO2e/kg
SBW; however, with a 2-yr grass fed fattening period
per animal the carbon footprint would likely double. An
LCA conducted in Japan concluded that the carbon footprint was 36.4 kg CO2e/kg HCW (Ogino et al., 2007)
which is much greater than our reported carbon footprints. This large difference is expected because 40% of
the feed for the Japanese beef system is shipped from the
U.S. The relatively small differences in carbon footprint
estimates from different reports are due to differences in
assumptions, approaches, and algorithms used as well
Carbon footprint and ammonia emissions in beef
as difference in climate and management. Often direct
LCA comparison is difficult for these reasons.
The carbon footprint for the California Holstein beef
production system was 6.3 kg CO2/kg SBW and 10.7 kg
CO2/kg HCW. In comparison to the Angus beef production system, the Holstein system contributes 50 to 63%
less GHG. This is because the breeding stock is not part
of the Holstein beef system, but rather a part of the dairy
production system. Therefore, emissions from the cow
are primarily accounted for in the carbon footprint of milk
rather than beef. The carbon footprint reported by Rotz et
al. (2010) for 2 California dairy herds ranged from 0.47
to 0.57 kg CO2e/kg energy corrected milk (ECM). It is
important that emissions are not double accounted from
separate and yet interlinked animal production systems,
such as dairy and Holstein beef production. In contrast
to the Angus beef production system, the feedlot phase
is responsible for the majority of GHG emitted from the
Holstein beef production system.
Our LCA results suggest that within the California
Angus beef production system, the cow-calf phase contributes 68 to 72% of total GHG emissions. The stocker
phase contributes 14% and the Angus feedlot is responsible for 17 to 27% of total GHG depending on management strategy. Our simulations suggest that the cowcalf phase contributes somewhat less of the total GHG
emissions compared with the work of Beauchemin et al.
(2010) who reported that the Canadian cow-calf system
was responsible for 80% of total GHG emissions. Johnson et al. (2003) reported that the cow-calf phase contributed 75% of the total GHG emission. Although there
are minor differences, these studies all confirm that the
cow calf phase is the major contributor to the overall
carbon footprint of traditional beef production.
The cow-calf phase differs from the stocker and feedlot phases because of the maintenance of the large number
of breeding stock required to produce the calves. Additionally, replacement heifers are maintained for 2 yr before producing their first calf. The cow-calf phase in California is also maintained on rangeland or pasture where
the high roughage diet increases CH4 production through
enteric fermentation. As such, the large majority of GHG
contribution from the beef production system is from the
beef cows. Little research has pursued viable GHG mitigation strategies for the cow-calf sector of the industry;
however, emission reductions in this sector would likely
have a greater impact on total GHG emission than mitigation strategies for the stocker or feedlot phases.
In contrast to general perception, the feedlot phase
contributes a relatively small amount of GHG to the beef
production system (17 to 27%). This is due to the shorter
duration of time that the cattle spend in the feedlot and to
the high grain diet that is fed, which reduces enteric CH4
production. Overall, the contribution of GHG emissions
4653
from the feedlot is primarily dependent on management
of manure and the time duration that cattle spend in the
feedlot.
Including a stocker phase in the California beef
production system increases GHG emissions by 6%.
Johnson et al. (2003) reported similar result with the
stocker phase increasing total GHG emissions by 4%.
The increased GHG emission from the stocker phase is
the result of grazing rangeland forage, which increases CH4 emissions from enteric fermentation compared
with feedlot diets. Additionally, during the stocker period, cattle have reduced ADG than animals that enter
the feedlot directly after weaning. Thus, they may be
harvested at a later age, producing more enteric CH4 and
manure during their lifetime. However, grazing animals
as stocker cattle reduces NH3 emissions from the beef
production system by 18%, and this strategy may reduce
production costs by requiring less high-priced corn for
feed (Stackhouse-Lawson et al., 2012).
To date, no other studies have determined NH3 emissions from the entire beef production system, so our full
system predictions cannot be compared with other data.
The majority of measured NH3 field emission data is reported from feedlots in desert climates. Measured NH3
emissions from Texas feedlots report daily emissions
ranging from 85 to 150 g/animal (Flesch et al., 2007;
Todd et al., 2008; Rhoades et al., 2010). Our simulated
Angus feedlot NH3 emissions are reported for the entire
time the animal remained in the feedlot and increased
with DOF ranging from 17.9 to 30.2 kg/animal and 43
to 73 g/kg HCW, depending if the stocker phase was
used. Simulated Holstein feedlot NH3 emissions were
47.7 kg/animal and 141 g/kg HCW. Thus, the average
daily emissions from the simulated California feedlots
were 148, 142, and 137 g/animal for the Angus feedlot
system with and without the stocker phases and the Holstein feedlot, respectively. Our simulated results are well
within measured NH3 emission ranges for beef feedlots.
Differences can be expected due to climate differences
between southern California and the Texas panhandle.
Also, our simulation gives average values over many
years of weather; whereas, the measured values represent shorter periods of time.
Accurate representation of CO2 is challenging when
conducting a partial LCA that stops at the farm-gate. For
this type of LCA, the full C balance including consumption or use of the products is not included. This effectively
shifts a portion of the carbon footprint from the consumer
or user to the producer. To obtain a complete farm gate
assessment, biogenic CO2 sources and sinks should be
included. Biogenic CO2 represents the net exchange of
CO2 with the atmosphere including, assimilation in crop
and animal growth, respiration emission from animals,
plants, soil and manure, and assimilated CO2 that is
4654
Stackhouse-Lawson et al.
converted and emitted as CH4. Including biogenic CO2
reduces the carbon footprint of the simulated California
Angus beef production system by 22 and 27% with and
without the stocker phases, respectively. For the Holstein
beef production system, the carbon footprint is decreased
by 58% by including biogenic CO2. Including biogenic
CO2, along with a complete carbon balance, ensures that
mitigation of GHG will be applied at points within the
production system that give the greatest benefit.
The effect of shifting the consumer’s portion of the
total footprint onto the producer is relatively small since
only minor amounts of C are assimilated in the meat.
In California beef systems though, the assumption on
manure use can have a substantial effect on the difference between including and excluding biogenic CO2.
California feedlots sell the majority of their manure to
other farms as fertilizer. However, unless biogenic CO2
is accounted for in the system or manure is treated as a
co-product in the LCA, the effect of exporting manure
for use in another farming system is ignored, and the C
assimilated in the manure remains as a component of
the beef production system. Since this C is assumed to
ultimately end up as CO2 in the atmosphere, the CO2
emission remains in the footprint of beef production. In
California, the manure C that is used for crop production
unrelated to livestock production should become associated with the carbon footprint of that production system.
This assumption on the end use of the manure results
in a 10 to 14% decrease in the carbon footprint of beef
production.
Our LCA demonstrates that the majority of GHG
emissions from the California beef production system
emanate from the cow-calf phase. Therefore, the cowcalf phase may deserve increased attention in the de-
Figure 2. Simulated carbon footprints of California beef production
systems with and without considering biogenic CO2 and without considering
the export of feedlot manure carbon from the production system. Standard
practice is to exclude biogenic sources of CO2 and when biogenic CO2 is
not considered, the export of manure has no impact on the carbon footprint.
Does not include manure in the system; when biogenic CO2 is not considered
manure has no impact on the production system.
velopment of effective mitigation strategies that most
significantly reduce GHG emissions without compromising productivity. Ammonia emissions are highest in
the cow-calf and feedlot phases and increase with DOF.
If the reduction of NH3 emissions becomes necessary,
the most opportune target is the feedlot through changes
in diet and manure handling. This regional level LCA
provides CA beef producers with a carbon footprint
bench mark unique to their management techniques and
specific climatic region.
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