Quantitative results for methane production of cattle in Germany

An extensive number of investigations on the energetic utilization efficiency of nutrients and feedstuffs by cattle were carried out in the former Oskar-Kellner-Institute (now the »Oskar Kellner« Research Unit of Nutritional Physiology at the Research Institute for the Biology of Farm Animals (FBN), Dummerstorf ). The amounts of methane (CH4) that they produced were compiled and stratified with regard to various performances, dietary nutrient composition and nutrition levels. With increasing food intake and performance, an increase of CH4 emission per animal was observed. However, with increasing performance, a strong decrease of CH4 production per unit of product was determined. Altogether, the 12.74 million cattle in Germany produce 1.04 million tons of CH4 per year. This represents 1.25 % of the CH4 production of the 1.3 thousand million (UK)/billion (US) cattle in the world or 0.22 % of the total emission on the earth. As a greenhouse gas, CH4 from cattle worldwide and from cattle in Germany account for 3.5 % and 0.04 % of global warming, respectively. In addition, opportunities for a further reduction of enteric CH4 release are discussed.


Introduction
Mitigation of methane (CH4) production by ruminants, and in particular cattle, has become a subject of public discussion and an important area of research because accumulation of this greenhouse gas contributes to global warming.(PELCHEN et al. 1998, SEELAND andMARTIN 1998).Exact and reproducible determinations of CH4 emissions form the basis for decreasing the uncertainty in greenhouse gas emission inventories and for the development of viable reduction strategies.Of note, exact measurements of enteric CH4 production have been carried out worldwide in only a few institutions because of the large technical effort that these entail.One of these facilities is the Oskar Kellner Institute, founded by NEHRING, which is now a research unit at the Research Institute for the Biology of Farm Animals (FBN) in Dummerstorf (Germany).Using respiration chambers, large data sets have been created including CO2 production (JENTSCH et al. 2009) and CH4 production over a time period of 32 years (JENTSCH et al. 2000 and2001).
Here, information obtained from these studies and data from more recent publications by JENTSCH et al. (2007) andVERMOREL et al. (2008) are used to calculate reasonable quantitative values for CH4 emissions from cattle in Germany.

Material and methods
For the evaluation, data from 337 respiration experiments each with 3-12 animals of various categories (oxen, young bulls, lactating and non-lactating cows, heifers) were used.The measurements were made in respiration chambers between 1957 to 1989 within the scope of investigations on energetic feed evaluation and energy requirement of farm animals (JENTSCH et al. 2000(JENTSCH et al. , 2001(JENTSCH et al. , 2003)).Using CH4 release data from these studies, regression equations were formed allowing calculation of CH4 formation from the level of feed intake or the nutrient composition of the diet (JENTSCH et al. 2007).
By means of the following equation, CH4 production can be predicted on the basis of the content of digestible nutrients in the diet.
where is m the CH4 energy (kJ), x1 the digestible crude protein (g), x2 the digestible crude fat (g), x3 the digestible starch and sugar (g), x4 the digestible N-free residues (g) (that is the digestible fraction of plant cell wall substances).Thus, for example, 1.32 kJ CH4 is formed per 1 g of digestible crude protein, with nutritional fats exerting a negative influence on CH4 formation and N-free residues accounting for the highest value at 2.78 kJ per g.
A calculation based on the relation between dry matter intake (DMI) per kg live weight and daily CH4 release leads to comparable results: where is y the CH4 energy (kJ), x the DMI (g feed/kg BW).
For the estimations presented, the daily CH4 production per animal was calculated using equation 2. The daily feed intake was adjusted to body weight and performance according to data published by PIATKOWSKI et al. (1990).The following conversion factors given by BROUWER (1965) and HOFFMANN and SCHIEMANN (1980) have been used to convert CH4 energy (kJ) to CH4 values in mass units (g, kg): 0.716 g/l; 39.57 kJ/l; 1g = 55 kJ.VERMOREL et al. (2008) used data from feeding trials to calculate the quantity of released CH4 based on equations from the literature estimating the digestible and metabolizable energy of the rations.Their results are compared with the data presented here.

Results and discussion
The DMI of dairy cows has been calculated for individual performance levels, for the dry period and for the maintenance energy requirement according to PIATKOWSKI et al. (1990).Thereafter, DMI increases with increasing annual milk yield from 22.3 (4 000 kg of milk) to 31.5 g/kg body weight (10 000 kg of milk) (Table 1).As shown in table 2, the calculated CH4 emission per cow increases according to the performance levels from 351 g/d at 4 000 kg milk to 424 g/d at 10 000 kg.According to equation (1), this surprisingly small elevation can be attributed to the high proportion of starch in the concentrate.This is also confirmed by the responses to low-concentrate rations fed during the dry period and at maintenance conditions (Table 2).Therefore, the annual CH4 emissions per cow range from 123.1 kg at 4 000 kg milk to 145.5 kg at 10 000 kg milk.However, the release of CH4 per kg of milk decreases by more than a half from 30.8 to 14.6 g.This leads, in turn, to a significant reduction of CH4 emissions in high yielding cows.This reduction is due to the fact that, for example, 50 cows with 8 000 kg milk produce the same amount of milk as 100 cows with 4 000 kg per year, but there will be no CH4 production derived from the maintenance needs for half of the cows.With an average milk yield of 6 849 kg (Arbeitsgemeinschaft Deutscher Rinderzüchter [ADR] 2008) per cow and year, 135 kg of CH4 are emitted.The corresponding annual CH4 emission of the 4 087 million dairy cows then amounts to 551 745 tons.
Under French production conditions VERMOREL et al. (2008) have calculated a mean annual CH4 production of 117.7 kg per cow with a milk yield of 6 300 kg/a ranging from 90-164 kg.Thus, despite the different methodological approaches our calculated mean annual CH4 production value agrees well, considering the performance differences.
In addition to dairy cows, another category of »other cows« that are not milked and are kept as suckler cows should be considered.Their milk is used directly by the calf and amounts to 2 000 kg per year.Assuming an average body weight of 650 kg and a daily feed consumption of 15.4 g/kg body weight, the annual CH4 production of these cows amounted to 98 kg.
The equation used for dairy cows to calculate the daily CH4 production is also valid for growing cattle.Hence, for the range of 200 to 400 kg body weight, 60.6 kg CH4 per animal are produced.
The CH4 release values for young fattening bulls as given in Table 4 were calculated with the same approach.In young fattening bulls, the annual CH4 emission was estimated to be 70.8 kg.VERMOREL et al. (2008) have reported values of 45.5 kg of CH4 for heifers and 49.4 kg for young fattening cattle of both sexes.Thus, the differences between French and German results in young animals are greater than for cows.This may be partly attributable to the lower body weight gain and the higher age of calving of up to 30 months in Germany and the use of heifers for fattening.
For calves of less than 12 months of age, a body weight of 200 kg and a feed intake of 4.5 kg had been assumed.Based on these data, CH4 production values of 24.2 g per kg DMI, of 109 g per day and of 39.8 kg per year were calculated.
For breeding bulls with a daily DMI of 9 kg CH4 release per kg DM, per day and per year was estimated to be 28.9 g, 260 g and 95 kg, respectively.
The CH4 production of all cattle in Germany (ADR 2008) can be differentiated by the various animal categories and is given in Table 5.Thus, the 12 737 000 head of cattle kept in Germany in 2007 produced per year 1 035 347 tons of CH4, of which 60 % can be attributed to dairy and suckler cows.
In conclusion the CH4 emissions of cattle kept in Germany represent about 1 million tons per year and have to be seen in the context of the global CH4 output into the atmosphere which amounts to an estimated 400-450 million tons.Main sources are the lowland marshes and wetlands, the burning of forests and grasslands, the strongly increasing numbers of termites in the harvested tropical forests, rice fields, coal mines, landfills, the oceans and finally the approximately 1.3 thousand million (UK)/billion (US) cattle worldwide.Their share has been calculated at 80-90 million tons, accounting for about one fifth of the total emissions.Thus, the cattle in Germany emit 1.25 % of the global CH4 produced by cattle or 0.22 % of the total emissions, including the above-mentioned sources, such as lowland marshes.Based on our current state of knowledge, the total annual release of CH4 as a greenhouse gas provides a share of 18.6 % to global warming.The share of the global cattle population of 1.3 thousand million (UK)/billion (US) is thus one fifth, i.e. 3.5 %, and the CH4 emissions of cattle in Germany amount to 0.04 %.
A high proportion of agricultural greenhouse-gas emissions are generated by dairy cattle enteric CH4 production.This contribution can be reduced primarily by increasing the performance and thus, the milk yield per animal.A further important economic effect should also be considered: 50 cows producing 8 000 kg of milk per year have the same milk output as 100 dairy cows with an annual performance of 4 000 kg milk.Thus, the CH4 emitted for the maintenance requirements of the smaller number of cows shows a reduction and, at the same time, the number of sheds and working expenses for milking decline.
The CH4 released by cattle is produced by ruminal methanogens during the microbial digestion of nonstarch polysaccharides (e.g.cellulose).This unique and valuable capacity of ruminants allows utilizing substrates indigestible to pigs, poultry and man, thereby lessen the competition for food resources.Therefore, it is not justified to assess cattle industry by its contribution to global warming only.Rather, in a comprehensive assessment with regard to global food security in terms of quantity and quality it is necessary to include fully all available food energy sources such as also the nonstarch biomass.

Table 5
Balance of CH4 emission of the various categories of cattle in Germany Bilanz der CH4-Emission der einzelnen Kategorien des Rinderbestandes in Deutschland