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Evaluering af mulige tiltag til reduktion af landbrugets metanemissioner

2 Methane emissions from pig production

• 2.1 Introduction
• 2.2 Data material
• 2.3 Results and discussion
• 2.4 Conclusions
• 2.5 References

Henry Jørgensen, Danmarks JordbrugsForskning, Afd. for Husdyrsundhed, Velfærd og Ernæring

2.1 Introduction

Increased demand of high energy cereals for direct human use and increased availability of fibre rich ingredients from, for instance, the feed milling or starch extraction/fermentation industries have promoted an increased utilisation of fibre rich by-products in the pig feeds. The direct use of forage is also increasing. Other benefits, such as increased wellbeing of animals, improvement of the gut transit or reduction of stomach ulcers also favour an increased utilisation of fibre rich ingredients in pig feeds. An increased dietary fibre level in the diet is on the other hand associated with a reduced available energy content, so if the diet is not combined with high energy ingredients such as animal fat or vegetable oil, the amount of feed required per produced animal unit will increase.

The fermentation of carbohydrates in the pigs' digestive system specially the lower gut results predominantly in short chain fatty acids as acetic, propionic and butyric acid, gasses as carbon dioxide (CO₂), hydrogen (H2) and methane (CH₄), urea and heat. It should also be noted that, during the fermentation process, an important bacterial mass is produced. The short chain fatty acids can be utilised in the pigs' metabolism and can contribute with a significant part of its maintenance. From an energy point of view, only CH₄ and H2 are important as they represent a loss of energy. However, information on gas production by pigs is rather limited. From an environmental point of view CH₄ is especially interesting as it contributes to global warming. The CH₄ productions by pigs vary with their age or live weight and the type of diet they receive. Here the type and amount of dietary fibre is most important. In the present report some examples from experiment with pigs measuring methane production will be discussed. All experiments were carried out in the respiration chambers at Research Centre Foulum.

2.2 Data material

The respiration chambers were established at Foulum in 1990 and several experiments have been carried out on growing/finishing pigs from 30 – 120 kg live weight. Other experiments on sows in different stages as dry, pregnant and lactating including their piglets. To measure emissions from the piglets alone, experiments have been carried out with artificial sows.

The respiration chambers consist of climatic controlled airtight rooms, where the animals' energy metabolism can be measured. The measured parameters are heat production and the animals' consumption of oxygen and production of carbon dioxide, methane and hydrogen. The chambers work from the so called indirect principle, where the atmospheric air is ventilated through the cambers and the amount of air is measured together with the concentration of oxygen, carbon dioxide and methane in both ingoing and outgoing air (Jørgensen, 2001; Jørgensen et al., 1996). When the consumed amount of oxygen and produced amount of carbon dioxide and methane is known the heat production can be calculated (Christensen and Thorbek, 1987).

2.3 Results and discussion

In general the gastrointestinal tract of pigs develops with age towards increased capacity and ability to ferment the dietary fibre fraction of the diet. This is illustrated for growing pigs in Table 2.1. The results show an increase in methane production from 3.4 to 5.6 litres CH₄ per day. However, expressed relative to either digested energy or gross energy there is only a slight increase.

Table 2.1. Methane production by growing pigs.

DE, digested energy; DC, digestibility coefficient; GE, gross energy.

Sows are normally feed restricted in the dry and following pregnancy period (approximately 2 Feed Units (FUp) per day) in order not to gain excessive weight and following health problems around farrowing and lactation. The last 3-4 weeks during pregnancy, the feeding level is in general increased to 3 FUp per day. Table 2.2 shows results from an experiment with pregnant sows fed a standard diet or one of two fibre rich diets supplemented with either wheat bran or sugar beet pulp. Fibre from wheat bran is more resistant to fermentation than fibre from sugar beet pulp and as expected the amount of fibre fermented and the production of CH₄ is higher when sows are fed sugar beet pulp. A higher feeding level increases the methane production but relative to either digested energy or gross energy the production is lower.

Table 2.2. Pregnant sows feed on 2 feeding levels.

LW, live weight; DE, digested energy; DC, digestibility coefficient; GE, gross energy.

A comparison of the ability of growing pigs and sows to digested and utilise various fibre rich feedstuffs are shown in Table 2.3. The sows' production of methane is as expected higher than for the growing pig even with equal inclusion level of fibre rich feedstuffs. The reason is the sows relatively greater capacity for fermentation and also that the sows are fed on a relatively lower level relative to body size. However, in the actual experiment for the most voluminous fibre feedstuffs neither the sows nor the growing pigs were able to consume more. The experiment also shows great variation in the fermentability of the different fibres. Fibre in seed residue is an example of fibres resistant to fermentation. Furthermore, there was variation among animals, some animals had low methane production independent of amount and fibre source. Fibre easily fermented are pea hulls, sugar beet pulp and potato pulp and in the experiment with sows the methane production can be as high as 2.7% of the gross energy. When comparing different fibre rich feedstuffs contributing to CH₄ emission it must be considered that the lower energy digestibility will imply that the pigs must consume a larger quantity to obtain the same production.

Table 2.3. Methane production by dry sows and growing pigs feed different fibre-rich by products.

LW, live weight; DE, digested energy; DC, digestibility coefficient; GE, gross energy.

Feeding of lactating sows require diet with a higher energy density, which means a diet with low fibre content, and in order to obtain higher energy density addition of fat is a normal practice. Table 2.4 shows lactating sows fed with low and high dietary fat. The total daily amount of produced methane is 12 – 17 litre/day. However, because of relative low fibre content and high feed intake methane energy expressed relative to gross energy is measured to 0.5 –0.7%. Increased amount of fat in a diet for ruminants is expected to decrease CH₄ production in the rumen. Pigs as non-ruminants have their main fermentation in the hindgut after digestion and absorption of the fatty acids. Most fat sources have a relative high digestibility (90%) (Jørgensen and Fernández, 2000) and consequently only limited amount of the fatty acids reach the hindgut. The present experiment used addition of animal fat with a high digestibility and there was not any effect on CH₄ production (Jørgensen et al., 1996). However, in other experiments with growing pigs fed with either rapeseed oil or fish oil, which have mostly long chain fatty acids, marginal reductions in the methane production have been found. The slightly higher methane production of the high fat diet shown in Table 2.4 could partly be explained by a higher content of soybean meal to supply equal amount of protein per net energy unit (Theil et al., 2004). Soybean meal is known to have an easily fermented fibre (Jørgensen, 1997). It remains to be tested if fat sources with medium chain fatty acids, i.e. coco-nut oil and palm oil which is known to depress methane production in ruminants (Machmüller et al., 2003), would have a beneficial effect in reducing methane production in pigs as well. In the experiment with the lactating sows the measurement was done on both sow and piglets. In an other experiment where the piglets were fed with a artificial mother the piglets had a methane production of approximately on 0.1% on the gross energy.

Table 2.4. Methane production by lactating sows feed low and high dietary fat (Theil et al. 2004).

LW, live weight; DE, digested energy; DC, digestibility coefficient; GE, gross energy.

Diets for growing pigs have changed over time. In order to reduce N-pollution to the environment, diets have been formulated more close to the pigs' requirement with regard to amino acid composition. This trend in diet composition is illustrated in Table 2.5 with diet no 5 and 6 (Sørensen and Fernández, 2003), where diet no 6 is supplemented with free amino acids. Both diets give the same growth potential, but diet no 6 has a reduced dietary protein content and because of a reduced content of especially soybean meal less fibre is fermented. A slightly lower production of methane can be expected. Based on the data shown there was a satisfactory correlation between the amount of fibre fermented and the CH₄ production both on growing pigs and sows. In both cases the methane production is below 0.6 % of gross energy as given in the report on emission from the Danish agriculture (Mikkelsen et al., 2004).

In the dry and pregnancy period up to a few weeks before farrowing sows are feed restricted in order to avoid problem with overeating. ThR_refore it is of interest to feed high fibre diets. Table 2.5 shows two typical diets, no 11 with relative low dietary fibre content and the other no 12 with high fibre content. The diets were chosen as representative for sow diets with low (normal) dietary fibre content and high dietary fibre content. The fibre from sugar beet pulp is easily fermented and is also known to have positive effect on the sows' behaviour. The production of methane of both diets is above the value of 0.6 % as indicated for sows by Mikkelsen et al. (2004).

Table 2.5. Examples on trend in diets for growing pigs and dry sows (Data from Sørensen & Fernandez, 2003).

1Calculated from amount of fermented fibre (equations based on data in Table 1, 2, 3 and 4 for growing pigs and sows, respectively).
DC, digestibility coefficient; GE, gross energy.

2.4 Conclusions

Production of methane by piglets is low and is measured to be around 0.1% of the gross energy. Growing pigs' fed with low fibre content in the diet or a standard diet have a methane production from 0.2 to 0.5% of the gross energy. When feeding higher dietary fibre content the methane production can depending on fibre type and content contribute up to 1% of the gross energy. The trend in diet for growing pigs seems over the years to be a reduced protein content and thereby a slight reduction in fermentable fibre and CH₄. Dry and pregnant sows fed on maintenance have a methane production from 0.6 to 2.7 % of the gross energy depending on feeding level and fibre type. The methane production by lactating sows was measured to approximately to 0.6 % of the gross energy. In all the experiments the methane production by sows have been found to exceed 0.6 %.

This report only shows some examples of the Danish experiments, where measurements of methane have been included. In none of the experiments measurement of methane the main objective. Thus there have not been carried out systematic experiments to look at variation in methane production or using various fat sources or other means to possibly reduce methane emission from pigs. A more comprehensive review of all the available data and possible relation from chemical analysis or in vitro analysis to the measured in vivo measurements is warranted.

2.5 References

Christensen, K. & Thorbek, G. 1987. Methane excretion in the growing pig. Br. J. Nutr. 57, 355-361.

Jørgensen, H. 1997. Energy utilization of diets with different sources of dietary fibre in growing pigs. In: K. J. McCracken, E. F. Unsworth, and A. R. G. Wylie (Eds.) Energy Metabolism of Farm Animals. pp. 367-370. CAB International, University Press, Cambridge.

Jørgensen, H. 2001. Energimålinger ved hjælp af respirationskamre. JordbrugsForskning 5, 6-7.

Jørgensen, H., Jensen, S.K. & Eggum, B.O. 1996. The influence of rapeseed oil on digestibility, energy metabolism and tissue fatty acid composition in pigs. Acta Agric. Scand., Sect. A, Anim. Sci 46, 65-75.

Jørgensen, H., Zhao, X.Q. & Eggum, B.O. 1996. The influence of dietary fibre and environmental temperature on the development of the gastrointestinal tract, digestibility, degree of fermentation in the hind-gut and energy metabolism in pigs. Br. J. Nutr. 75, 365-378.

Machmüller, A., Soliva, C.R. & Kreuzer, M. 2003. Methane-suppressing effect of myristic acid in sheep as affected by dietary calcium and forage proportion. Br. J. Nutr. 90, 529-540.

Mikkelsen, M. H., Gyldenkærne, S., Poulsen, H.D., Olesen, J.E. & Sommer, S.G.. 2002. Opgørelse og beregningsmetode for landbrugets emissioner af ammoniak og drivhusgasser – i perioden 1985 - 2002. Arbejdsrapport fra DMU nr. 204.

Sørensen, P. & Fernández, J.A.. 2003. Dietary effects on the composition of pig slurry and on the plant utilization of pig slurry nitrogen. J. Agric. Sci. 140, 343-355.

Theil, P. K., Jørgensen, H. & Jakobsen, K. 2004. Energy and protein metabolism in lactating sows fed two levels of dietary fat. Livest. Prod. Sci. 89, 265-276.

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Version 1.0 Juli 2005, © Miljøstyrelsen.