3 Life Cycle Inventory
This study uses the “Tier 2” approach described in the IPCC Guidelines to calculate
methane emissions from enteric fermentation [16]. Thereby, the methane emissions
from enteric fermentation of a dairy cow during its lifetime are calculated from the
gross energy intake (GE), the methane conversion rate (Ym) and the energy content
of methane (55.56 MJ/kg). Based on the IPCC standard, the methane conversion
rate (Ym) was assumed to be 6%, the value for dairy cows in developing countries.
Further details of modelling are described for each measure individually.
Different breeds (A)
The four major dairy breeds in South Africa are Holstein, Jersey, Guernsey and
Ayrshire [3]. This study analysed the environmental impact of raw milk from
Ayrshire and Holstein breeds.
A production mix of the five farms where data was collected (see Chapter
“Sustainability Performance Evaluation for Selecting the Best Recycling Pathway
During Its Design Phase”) with an equal share from each farm was modelled. Three
farms keep only Holstein cows and two farms keep both Holstein and Ayrshire cows.
The number of dairy cows per farm varied between 260 and 1345. Data on feed
quantities were collected from each farm. Silage maize and grain maize in concentrated feed was modelled based on kg input and published inventories [8]. The
quantity of hay, pasture grass and kikuyu silage was included based on the production
area on each farm. Ryegrass was irrigated on all farms, whereas kikuyu grass was
cultivated under rainfed conditions. For silage and grain maize, the share of irrigation
was based on the average share in South Africa from 2006 to 2013 [17].
Addressing enteric fermentation (B)
Enteric fermentation was responsible for about 20% of the worldwide greenhouse
gas emissions from agriculture, forestry and other land use (AFOLU) from 2000 to
2010, of which cattle contributed the largest share (75%). The enteric emissions
increased most in Africa during this period (by 2.4% per year) [1].
Due to the importance of bovine enteric methane emissions, research has been
carried out to determine means of reduction. Feed supplements have been found to
achieve a significant reduction in methane emissions from enteric fermentation. The
effect of administering the methane inhibitor 3-nitrooxypropanol (3NOP) was
analysed during a 12-week experiment in Pennsylvania (US): 48 Holstein cows
were fed 60–80 mg of 3NOP per kg dry feed [18]. The feed consisted mainly of
maize silage (42.2%) and alfalfa haylage (18%). The rumen methane emissions
were measured five times during this period. An average reduction of 30% in rumen
methane emissions was observed for the cows that were fed with 3NOP, while the
milk yield was not affected.
To estimate the effect of the methane inhibitor 3NOP on the environmental impact
on South African milk, 3NOP supplementation was modelled for one farm with
118
R. Keller et al.
This study uses the “Tier 2” approach described in the IPCC Guidelines to calculate
methane emissions from enteric fermentation [16]. Thereby, the methane emissions
from enteric fermentation of a dairy cow during its lifetime are calculated from the
gross energy intake (GE), the methane conversion rate (Ym) and the energy content
of methane (55.56 MJ/kg). Based on the IPCC standard, the methane conversion
rate (Ym) was assumed to be 6%, the value for dairy cows in developing countries.
Further details of modelling are described for each measure individually.
Different breeds (A)
The four major dairy breeds in South Africa are Holstein, Jersey, Guernsey and
Ayrshire [3]. This study analysed the environmental impact of raw milk from
Ayrshire and Holstein breeds.
A production mix of the five farms where data was collected (see Chapter
“Sustainability Performance Evaluation for Selecting the Best Recycling Pathway
During Its Design Phase”) with an equal share from each farm was modelled. Three
farms keep only Holstein cows and two farms keep both Holstein and Ayrshire cows.
The number of dairy cows per farm varied between 260 and 1345. Data on feed
quantities were collected from each farm. Silage maize and grain maize in concentrated feed was modelled based on kg input and published inventories [8]. The
quantity of hay, pasture grass and kikuyu silage was included based on the production
area on each farm. Ryegrass was irrigated on all farms, whereas kikuyu grass was
cultivated under rainfed conditions. For silage and grain maize, the share of irrigation
was based on the average share in South Africa from 2006 to 2013 [17].
Addressing enteric fermentation (B)
Enteric fermentation was responsible for about 20% of the worldwide greenhouse
gas emissions from agriculture, forestry and other land use (AFOLU) from 2000 to
2010, of which cattle contributed the largest share (75%). The enteric emissions
increased most in Africa during this period (by 2.4% per year) [1].
Due to the importance of bovine enteric methane emissions, research has been
carried out to determine means of reduction. Feed supplements have been found to
achieve a significant reduction in methane emissions from enteric fermentation. The
effect of administering the methane inhibitor 3-nitrooxypropanol (3NOP) was
analysed during a 12-week experiment in Pennsylvania (US): 48 Holstein cows
were fed 60–80 mg of 3NOP per kg dry feed [18]. The feed consisted mainly of
maize silage (42.2%) and alfalfa haylage (18%). The rumen methane emissions
were measured five times during this period. An average reduction of 30% in rumen
methane emissions was observed for the cows that were fed with 3NOP, while the
milk yield was not affected.
To estimate the effect of the methane inhibitor 3NOP on the environmental impact
on South African milk, 3NOP supplementation was modelled for one farm with
118
R. Keller et al.