Overview of Sweden’s current Tier 2 approach
The cattle industry in Sweden has, as in other developed countries, undergone large changes in structure and intensity in recent years. Numbers of dairy farms and animals have decreased, but the total production of milk has remained stable due to increasing milk production per cow. Today most farmers produce the forage for cattle feeding themselves but concentrates are often bought from feed companies. Changes have also occurred in feed evaluation and diet formulation methods.
Enteric fermentation emissions from dairy and non-dairy cattle, sheep and horses, and manure management methane emissions from non-dairy cattle are key categories in the national inventory. Sweden has used a country-specific Tier 2 approach for enteric fermentation from dairy and other cattle since the late 1990s. The approach used was updated in 2016. A Tier 1 approach is used for other livestock types (Table 1).
Table 1: Overview of Tiers used for livestock methane emissions in Sweden’s national GHG inventory
|Livestock types||Tier used for enteric fermentation (CH4)||Year adopted*||Tier used for manure management (CH4)||Year adopted*|
|Pigs||T1||-||T2||1990s (later discontinued)|
*Year refers to the year of NC submission
Livestock characterization: Table 2 shows how livestock are categorized for estimation of different emission sources. Livestock population data comes from the Farm Register administered by the Swedish Board of Agriculture and Statistics Sweden. The register collects population data in mid-June of each year and this is taken to be the annual average. The Farm Register does not include data on the distribution of calves older and younger than 6 months. The inventory therefore assumes that 60% are younger than 6 months and the rest are over 6 months old.
Table 2. Livestock subgroups used in Sweden’s inventory
|Categories according to IPCC Guidelines||Sub-categories Enteric Fermentation||Sub-categories Methane from manure management||Sub-categories N2O from manure management||Sub-categories N2O from grazing animals|
|Dairy Cattle||Dairy cows||Dairy cows||Dairy cows||Dairy cows|
|Non-Dairy Cattle||Beef cows||Beef cows||Beef cows||Beef cows|
|Other cattle||Growing animals (12-24 months)||Growing animals (12-24 months)||Growing animals (12-24 months)|
|Calves > 6 months||Calves > 6 months||Calves > 6 months|
|Calves < 6 months||Calves < 6 months||Calves < 6 months|
Source: NIR 2003
Sweden’s approach for enteric fermentation estimates has developed over time.
(1) 1990s and early 2000’s
In the 1990s and early 2000s, Sweden’s inventory used a country-specific methodology to estimate feed energy requirements and emission factors for cattle. The main difference with the IPCC model is that the Swedish model used metabolisable energy as opposed to gross energy intake. Furthermore, the energy loss through methane emissions is calculated as a fraction of digestible energy. This fraction is determined by total feed intake and digestibility of the feed, and therefore varies with diet, whereas the IPCC expresses feed energy content as a constant fraction of gross energy in feed.
The energy requirements for maintenance, growth, lactation and pregnancy are estimated in terms of metabolisable energy (MJ/day). This is then converted to digestible energy using an expression from Lindgren (1980):
Metabolisable energy (% of digestible energy) = 83,2 + 2,53*L 0,045 * G 0,184* Rp,
where L is the total feed intake expressed as a multiple of maintenance energy, G is the share (%) of roughage in the feed and Rp is the crude protein concentration (%) of the feed. Digestible energy is then used to calculate the methane conversion rate as:
Methane conversion rate (% methane in digestible energy) = 15,7 0,030 * SK 1,4 * L,
where SK is the digestibility of the feed (% of gross energy) and L is the total feed intake expressed as a multiple of maintenance energy. The emission factor can be calculated as:
Emission factor (kg CH4/head and year) = (DE * Ym 55,65) * 365
where DE is the digestible energy (MJ/head and day) and Ym is the methane conversion rate (% of digestible energy). For dairy cows the calculation is performed for a lactation period of 305 days and a non-lactating period of 60 days, which are summed to give the annual CH4 emission per animal.
To implement this methodology, milk yield data was used together with national feed tables to estimate the key parameters describing diet composition and quality. Data on milk yields came from the trade organisation Swedish Milk, as reported by their supplier farmers who use a production evaluation tool to optimize production. This database covers about 80% of dairy farmers. Farmers not linked to Swedish Milk are assumed to have a lower productivity because the main reason for keeping cows is not commercial production. Milk yield data were then used together with the national feed tables that underlie the production evaluation tool to estimate diet components and diet quality.
(3) 2017 onwards
In 2016, the Swedish Environmental Protection Agency commissioned a review of the inventory methodology for cattle enteric fermentation emissions by an expert at the Swedish University of Agricultural Sciences (Bertilsson, 2016). This revision considered that most feed farmers and advisers were by now using a specific software for cattle diet formulation, NorFor (http://www.norfor.info/; Volden, 2011). NorFor uses a net energy system rather than a metabolizable energy system, and its internal equations were developed on the basis of feed trials carried out over many years throughout Scandinavia. NorFor in fact automatically calculates enteric methane production from data input by farmers. For dairy cows, it uses an equation published by Nielsen et al. (2015):
CH4 (MJ/cow/day) = 1.39*DMI -0.091*FA
DMI = Dry Matter Intake, per cow and day
FA = Fatty Acids (g/kg DM in total feeds)
In the NorFor package GE is calculated according to Volden (2011). For the energy content in feed, a value of 18.4 MJ/kg DM is taken for grain-based concentrate, and 20.0 MJ/ kg DM for grass silage. The final value used depends on the proportions of concentrate and silage in the diet. For dairy cattle, feed consumption estimates are based on the recommendations in metabolisable energy as given in the national feed tables. The nutritional values of forages are according to data collected in the NorFor programme.
The live weight of cows is assumed to be 650 kg, based on research herds in the country. Average milk production is calculated from milk delivered to the dairies and on-farm consumption, i.e. total milk output divided by the number of dairy cows. Data on actual feeding practices are not widely available, so the inventory used the standard diets contained in web-based advisory packages that are widely used by farmers, as well as published surveys and others concerning feeding of cattle.
The values calculated (e.g. 141 kg CH4 head/year) were compared with values reported in nearby countries, such as Norway and Denmark.
Table 3. Data sources used in estimation of dairy cattle methane emissions
|Number of dairy cows||Federation of Swedish farmers|
|Milk delivered to Swedish dairies||The Swedish Board of Agriculture|
|On farm consumption (5.6%)||Federation of Swedish farmers|
|Total milk production including home consumption||Calculated|
|Fat,%||Federation of Swedish farmers|
|Protein, %||Federation of Swedish farmers|
|Total energy requirements, MJ ME for maintenance, milk production and pregnancy, |
Per cow and day
|National feed tables|
|Silage, MJ ME/kg DM||National feed tables|
|Concentrate, MJ ME/kg DM||Expert judgement|
|Silage fatty acids (FA), g/kg DM||NorFor|
|Concentrate FA, g/kg DM||NorFor|
|Forage proportion, %DM||Expert judgement|
|MJ ME/kg total feeds in diet||Calculated|
|FA, g/kg DM total feeds||Calculated|
|Dry Matter Intake (total), kg DM/cow/day||Calculated|
Source: Sweden NIR 2017
In the late 1990s, the IPCC Tier 2 methodology was applied to methane manure management emissions from cattle and pigs. The maximum methane production potential (Bo) and methane conversion factor (MCF) used IPCC default values, except for MCF for liquid manure, where a value of 10 % was adopted as it was considered to be more appropriate for Swedish conditions with its cold climate and because the slurry containers usually have a surface cover.
Data on manure production from cattle and pigs came from the Swedish Board of Agriculture, which had carried out large-scale experiments that determined the amount of manure produced per animal. The same value is used every year, except for dairy cattle, where manure production was assumed to be related to milk production, so the trend in manure production is extrapolated based on the trend in milk production.
Data on waste management systems derived from nationally representative surveys of fertilizer and animal manure used conducted by Statistics Sweden every two years. For intervening years, interpolated values are used.
(1) Lindgren 1980, Murphy 1992, Bertilsson 2001
(2) Spörndly 1999
Bertilsson J. 2016. Updating Swedish emission factors for cattle to be used for calculations of greenhouse gases. Report 292. Department of Animal Nutrition and Management. Swedish University of Agricultural Sciences
Lindgren E. 1980. Skattning av energiförluster i metan och urin hos idisslare (Estimates of energy losses in methane and urine for ruminant animals). Swedish University of Agricultural Sci-ences, Dept of livestock physiology, Report 47.
Murphy M. 1992. Växthusgasutsläpp från husdjur (Greenhouse gas emissions from livestock). Swedish Environmental Protection Agency. Report 4144.
Nielsen NI, Volden H, Åkerlind M, Brask M, Hellwing ALF, Stolen T, Bertilsson J. 2013. A prediction equation for enteric methane emission from dairy cows for use in NorFor, Acta Agriculturae Scandinavica, Section A — Animal Science, 63(3): 126-130, DOI: 10.1080/09064702.2013.851275.
Spörndly R. (ed). 2003. Fodertabeller för idisslare 2003 (Feed tables for ruminant animals). Swedish University of Agricultural Sciences. Department of Animal Nutrition and Management. Report 257
Volden H. (Ed.). 2011. Norfor –the Nordic feed evaluation system. EAAP publication No. 130. Wageningen Academic Publishers, Wageningen, the Netherlands.