To illustrate use of the model, a series of simulations
was done to compare production strategies for 4
representative farms in central Pennsylvania and 2 in
southern California. The first of the simulated Pennsylvania
farms was relatively small, with 60 cows plus their
replacements. Moderate-sized Holsteins were used, with
a mature cow weight of 650 kg. Annual milk production
was 8,500 kg/cow, with 3.5% fat and 3.1% protein concentrations.
Cows were housed in a tie stall barn, with
heifers housed in a bedded pack barn. Manure from the
tie stall barn was hauled and applied to fields each day,
where the manure was handled in a semisolid form with
daily use of 2.5 kg/cow of straw bedding. All animals
were fed high-forage diets, with similar amounts of forage
coming from corn silage, alfalfa silage, and alfalfa
hay. The annual lactating cow replacement rate was
35%, with calves born randomly throughout the year.
A major emission for this production system was
CH4 generated by the animals and the bedded pack
manure in the heifer facility (Table 2). Of this total,
76% came from enteric fermentation. Nitrous oxide
emissions were relatively small, but considering their
large effect on global warming, these small levels had
an effect on overall GHG emissions. About half of the
total GHG emission for the production system came
from CO2 emitted by the animals and manure in their
housing facilities. This emission source was more than
offset by the assimilation of CO2 in feed production,
so overall the farm was a net sink for CO2. Emissions
through the combustion of fuel were relatively small
compared with other sources. The total from secondary
sources was greater, making up 20% of the net total
of all sources and sinks. This general trend among the
various sources and sinks was similar across all production
systems (Table 2). The net GHG emission or
C footprint for this production system was 0.69 kg of
CO2e/kg of ECM.
To illustrate use of the model, a series of simulationswas done to compare production strategies for 4representative farms in central Pennsylvania and 2 insouthern California. The first of the simulated Pennsylvaniafarms was relatively small, with 60 cows plus theirreplacements. Moderate-sized Holsteins were used, witha mature cow weight of 650 kg. Annual milk productionwas 8,500 kg/cow, with 3.5% fat and 3.1% protein concentrations.Cows were housed in a tie stall barn, withheifers housed in a bedded pack barn. Manure from thetie stall barn was hauled and applied to fields each day,where the manure was handled in a semisolid form withdaily use of 2.5 kg/cow of straw bedding. All animalswere fed high-forage diets, with similar amounts of foragecoming from corn silage, alfalfa silage, and alfalfahay. The annual lactating cow replacement rate was35%, with calves born randomly throughout the year.A major emission for this production system wasCH4 generated by the animals and the bedded packmanure in the heifer facility (Table 2). Of this total,76% came from enteric fermentation. Nitrous oxideemissions were relatively small, but considering theirlarge effect on global warming, these small levels hadan effect on overall GHG emissions. About half of thetotal GHG emission for the production system camefrom CO2 emitted by the animals and manure in theirhousing facilities. This emission source was more thanoffset by the assimilation of CO2 in feed production,
so overall the farm was a net sink for CO2. Emissions
through the combustion of fuel were relatively small
compared with other sources. The total from secondary
sources was greater, making up 20% of the net total
of all sources and sinks. This general trend among the
various sources and sinks was similar across all production
systems (Table 2). The net GHG emission or
C footprint for this production system was 0.69 kg of
CO2e/kg of ECM.
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