Livestock Science 109 (2007) 194 – 203
www.elsevier.com/locate/livsci
Nutrition, key factor to reduce environmental
load from pig production ☆
A.J.A. Aarnink ⁎, M.W.A. Verstegen
Animal Sciences Group, Wageningen UR, P.O. Box 65, 8200 AB Lelystad, Netherlands
Abstract
In different parts of Europe animal production is highly concentrated. Pig production generally is the main animal production
activity in these areas. Main concerns of these large numbers of pigs are the amount of surplus nutrients in excreta and gaseous
losses to the environment. Main nutrients of concern are N, P, and heavy metals and main gaseous losses of concern are ammonia,
odour, and methane. Although losses are inevitable to a certain extent, nutrition seems to be a key factor in reducing these losses.
Main nutritional strategies to reduce N and P excretions from pigs are: phase feeding (N, P), supplementation of limiting amino
acids to the diet (N), and addition of phytase to the diet (P). Nutritional strategies to reduce heavy metals excretions from pigs are:
finding alternative, natural, growth promoters that could replace Cu and Zn in the diet; using feedstuffs for the diet that are less
contaminated with Cd. Main strategies to reduce ammonia emissions are: 1) lowering crude protein intake in combination with
addition of limiting amino acids; 2) Shifting nitrogen excretion from urine to faeces by including fermentable carbohydrates in the
diet; 3) lowering pH of urine by adding acidifying salts to the diet; 4) lowering the pH of faeces by inclusion of fermentable
carbohydrates in the diet. These strategies proved to be independent from each other and effects are additive. By combining these
strategies a total reduction of ammonia emission in growing-finishing pigs of 70% could be reached. Strategies to reduce odour
emission are: 1) reducing protein fermentation by balancing available protein and fermentable carbohydrates in the large intestine;
2) Minimizing breakdown of absorbed sulphur amino acids. More studies are needed in this area of research, but results until now
are very promising. A clear relationship exists between fermentable carbohydrates in the diet and methane emissions. This
disadvantage should be considered when tackling ammonia emission by this strategy. It is concluded that there is a large potential
to reduce environmental load within pig dense areas by nutritional means.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Pigs; Nutrition; Environment; Minerals; Heavy metals; Ammonia; Odour; Methane
1. Introduction
☆
This paper is part of the special issue entitled “Digestive Physiology in
Pigs” guest edited by José Adalberto Fernández, Mette Skou Hedemann,
Bent Borg Jensen, Henry Jørgensen, Knud Erik Bach Knudsen and Helle
Nygaard Lærke.
⁎ Corresponding author. Tel.: +31 320 293589; fax: +31 320 238050.
E-mail address: [email protected] (A.J.A. Aarnink).
1871-1413/$ - see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.livsci.2007.01.112
In different parts of Europe animal production is
highly concentrated. Especially in these areas farms
have expanded and have become more specialized.
Concentration, expansion and specialization have economical advantages; however, there are also some
drawbacks. One of the main concerns is the heavy
environmental load caused by these large numbers of
animals. Pig production generally is the main animal
A.J.A. Aarnink, M.W.A. Verstegen / Livestock Science 109 (2007) 194–203
production activity in these areas. Environmental load
can be divided into mineral load to the soil and gaseous
load to the air. The mineral load is caused by the high
manure application level on the soil, caused by the
unbalance between manure production and manure
requirement in these areas. Main problems arise from
nitrogen, phosphorus, and heavy metals. Surplus
nitrogen leaches to ground and surface waters, causing
high nitrate levels in ground water. Runoff of especially
phosphorus leads to eutrofication of surface waters.
Heavy metals accumulate in the soil and will give
environmental problems in mid and long term, while
residence times, depending on element and property of
the soil, can vary from hundreds to thousands of years
(L'Herroux et al., 1997; Nicholson et al., 1999). The
gaseous load can be divided into ammonia, odour, and
methane. Uncontrolled ammonia deposition causes
nitrogen enrichment of poor nature soils and acidification of the soil, thereby affecting natural vegetation
(Fangmeier et al., 1994). Odour gives a problem when
pig farms are located close to residential areas. Odour is
more a nuisance problem than an environmental
pollutant. Methane is the most important non-CO2
greenhouse gas (Houghton et al., 1996). Around 20% of
global methane emission is estimated to come from
ruminants and animal wastes (Tamminga, 2003).
Methane has a high global warming potential, the
impact of one molecule of methane on global warming
is 20 times that of CO2 (IPCC, 1992).
By the EU Council different directives have been issued
to control environmental pollution. Every EU-country also
has its own legislation, but these should comply with the
EU directives. The majority of environmental legislations
are set by the EU. With respect to animal production and
environment mainly three directives are of importance:
1) integrated pollution prevention and control directive
(IPPC Directive 96/61/EC); 2) nitrate directive (Directive 91/676/EEC); 3) national emission ceilings directive
(NEC Directive 2001/81/EC). The aim of the IPPC directive is to reduce emissions to air, water and soil, and to
make efficient use of resources. This directive is focussing on large farms (N 2000 growing-finishing pigs;
N 750 sows; N 40 000 chickens). These farms should use
the best available techniques (BAT) to reduce environmental pollution. The nitrate directive aims to prevent
pollution of surface and groundwater by excess nutrients
(nitrogen) from agriculture. Nitrate levels in groundwater are set to a maximum of 50 mg/l and the yearly Napplication with manure should not exceed 170 kg/ha.
The NEC directive aims to control emission of SO2,
NOx, VOC's and NH3 by defining national emission
ceilings. States have to draw up programs to meet their
195
emission ceiling by 2010. In the Kyoto protocol the industrialised countries have agreed to reduce the emission
of greenhouse gases in the period between 2008–2012
by an average of 5%.
Although nutrient losses are inevitable (Tamminga,
2003), nutrition seems to be a key factor in reducing
environmental pollution. The objective of this paper is
to describe possibilities to manipulate emissions of environmental pollutants from pig production by nutritional
means.
2. Nutrition and mineral excretion
According to Jongbloed et al. (1999) the major
challenge in several countries is finding an acceptable
balance between the input and output of minerals per ha of
cultivated land. The main concerning minerals are N and
P. Nitrogen and phosphorus are required by pigs in a
significant amount, still most of N and P in the diet is
excreted again via faeces and urine. Van der PeetSchwering et al. (1999) estimated excretions of N, relative
to input by feed, varying on average from 38% for
weaners, 63% for growing-finishing pigs, and 75% for
sows. For P they estimated excretions, relative to the input
by feed, of on average 46% for weaners, 67% for
growing-finishing pigs, and 76% for sows.
Nitrogen excretion can be reduced by matching the
protein/amino acids content of the diet as close as possible
to the pigs' requirement. Protein levels are generally
higher than actually required. Safety margins in the protein
content of the diet are used to account for: 1) suboptimal
amino acid ratios; 2) variations in requirement between
animals with different genotypes; 3) variations in requirement caused by differences in age or production stadiums;
4) variations in the actual content and digestibility of
essential amino acids in the diet. Different studies show
that protein content of the diet could be reduced by 30–
40 g/kg without any effect on growth rate or feed efficiency, when limiting amino acids are supplemented to the
diet (Canh et al., 1998e; Dourmad et al., 1993; Lenis and
Schutte, 1990). According to Rademacher (2000) approximately 25% of the protein in a typical corn and soybean
diet can not be used, because of unbalanced amino acids.
These amino acids are broken down and the nitrogen is
excreted as urea in urine.
Other N losses that appear in the urine are amino
acids in ideal protein, but at a level that is above
requirement. N losses in urine also occur when energy in
the diet limit protein deposition, this means that protein
gain is in the energy dependent phase. Increasing the
digestibility of protein and amino acids can decrease N
excretion, as well, when at the same time the protein
196
A.J.A. Aarnink, M.W.A. Verstegen / Livestock Science 109 (2007) 194–203
level of the diet is reduced. In that respect it should be
emphasized that only an increase in ileal digestibility of
amino acids is relevant for the update of the protein
content (Moughan and Fuller, 2003). The increase can
be obtained by including feedstuffs with a higher
digestibility, by adding enzymes or by reducing components in the diet which causes endogenous losses. These
last components are called anti-nutritional factors and
they can decrease apparent N digestibility considerably
(Tamminga et al., 1995). In a few papers positive effects
of xylanase enzyme on ileal digestibility of protein and
amino acids were found (Barrera et al., 2004; Diebold
et al., 2004). However, others did not find an effect of
xylanase addition on protein and amino acid digestibility
(Gdala et al., 1997; Zijlstra et al., 2004).
Protein/amino acids requirement is different for the
different production stadiums of the pig. By introducing
more diets for the different stadiums a closer match can
be obtained between intake and requirement. A three
phase feeding program can reduce N excretion by 16%
when compared to a one phase feeding program for
growing-finishing pigs (Rademacher, 2000). Former
mentioned author estimated that for a 900 pig unit 11 ha
less land is required to apply the manure; 63 and 52 ha of
land for one phase and three phase feeding, respectively.
Phase feeding also can reduce P excretion, because
the required concentration of P per kg of feed decreases
with increasing live weight of the pig (Jongbloed and
Lenis, 1998). However, main reduction of P excretion
can be obtained by increasing P digestibility. In
feedstuffs of plant origin two third of total P is present
as phytic acid P, which is almost indigestible for pigs
(Jongbloed, 1987). According to Jongbloed and Lenis
(1998) phytase-supplemented feeds for growing-finishing pigs and pregnant sows need little or no supplementary P. Depending on P sources, pig category and
phytase dose, P-digestibility can increase varying from
8 to 30% units (Jongbloed et al., 2004; Van der PeetSchwering et al., 1999; Walz and Pallauf, 2003). In The
Netherlands phytase is already included in most of the
pig feed.
3. Nutrition and heavy metals
Main heavy metals of concern in pig manure are
copper, zinc, and cadmium. In The Netherlands concentrations in manure of growing-finishing pigs for Cu, Zn,
and Cd of 381, 619, and 0.31 mg/kg dm have been
measured (Anonymous, 1996). However, for Cu and Zn
these values are not up to date anymore, while in 2000
maximum supplementation values have been set for pig
diets (Anonymous, 1999); Table 1). These values are
lower than the limits set by EU legislation, which are for
all pig diets 175 and 250 mg/kg feed for Cu and Zn,
respectively. Within the UK for Zn supplementation a
veterinary prescription is required for pigs over 10 kg. For
Cu limits were set of 175 mg/kg dm for growers (b30 kg),
100 mg/kg dm for finishers (30–90 kg) and nil for sows
(N 90 kg) (Nicholson et al., 1999). In New Zealand the
average Cu content of pig feed is 125 mg/kg (Wang et al.,
2004). Cadmium is not supplemented to the diet, but gets
into the feed by using contaminated feedstuffs.
Most of the ingested Cu, Zn, and Cd by pigs is
excreted again in the manure (N90%). In The Netherlands for the year 2000 87%, 86%, and 57% of Cu, Zn,
and Cd input on arable land originated from manure
(Delahaye et al., 2003). Already a lot has been reached
to reduce Cu and Cd input on arable land. In The
Netherlands from 1980 to 2000 the yearly inputs of Cu
and Cd were reduced from 600 to 350 g/ha and from 6 to
1.5 g/ha, respectively; the load of Zn remained nearly
the same (1 kg/ha; Dach and Starmans, 2005). Still,
present inputs of heavy metals are too high and reducing
their contents in the diet should reduce concentrations in
the manure. Other, natural, growth promoters should
replace Cu and Zn in the diet. More research about
possible alternatives is necessary. By using less
contaminated feedstuffs Cd in the diet can be reduced.
4. Nutrition and ammonia emission
Ammonia in pig manure mainly originate from the
breakdown of urea in urine. Only a small part comes
from the breakdown of protein in the faeces (Aarnink
et al., 1993). The rate at which urea is converted to
ammonia depends on the urease activity. In pure urine
no urease is present, so conversion only starts when
urine mixes with faeces or when it contacts soiled floors.
In a clean pen the main part of ammonia emits from the
manure pit (Aarnink et al., 1997). In soiled pens,
however, also a lot of ammonia emits from the floor
(Banhazi, 2005). In water solutions like manure
ammonia is easily ionized. The release of ammonia
from the manure is a slow process governed by factors
as ammonia concentration, pH, temperature, air velocity, and emitting surface area. In Fig. 1 the emission of
Table 1
Maximum supplementation values in mg/kg feed for copper and zinc
to pig diets in The Netherlands (Anonymous, 1999)
Feed
Cu
Zn
Piglet
Growing-finishing
Sows
160
15
20
100
60
65
A.J.A. Aarnink, M.W.A. Verstegen / Livestock Science 109 (2007) 194–203
197
Fig. 1. Nitrogen chain in growing-finishing pigs (Aarnink, 1997).
ammonia in the nitrogen chain of fattening pigs is given.
This figure shows that almost half of the nitrogen
excreted by urine and faeces can emit during storage of
the manure inside the pig house and during surface
application of the manure.
There are a few options to tackle ammonia emissions
by nutritional means:
1. Reducing nitrogen excretion by lowering crude
protein intake;
2. Shifting nitrogen excretion from urea in urine to
protein in faeces;
3. Lowering the pH of manure by:
a. lowering the pH of faeces;
b. lowering the pH of urine.
4.1. Lowering crude protein intake
The urea excretion in the urine can be reduced by
improving the nitrogen utilisation in pig feed. Aarnink
et al. (1993) estimated by model calculations a 9%
reduction of ammonium nitrogen content in manure
when dietary crude protein is reduced by 10 g/kg. This
was confirmed by Sutton et al. (1998), who found
reductions in ammonium nitrogen and total nitrogen
concentrations in manure of 28% when the crude protein
content in the diet was reduced from 130 to 100 g/kg and
supplemented with limiting amino acids. Assuming
other parameters to be the same a similar reduction in
ammonia emission can be expected as the reduction in
ammonia concentration (Elzing and Kroodsma, 1993).
This was confirmed in a research of Canh et al. (1998e).
They compared three levels of protein content in the diet
(165, 145, and 125 g/kg). On average, for every 10 g/kg
reduction in crude protein content of the diet they found
a 10% lower ammonium content of the manure and a 10
to 12.5% lower ammonia emission. The somewhat
higher reduction of ammonia emission compared to the
reduction in ammonium content could be explained by
the fact that the pH of the manure was lowered as well,
when dietary crude protein level decreased. Latimier
and Dourmad (1993) also found similarity in the relative
reduction in nitrogen excretion and ammonia emission.
Kay and Lee (1997) found reductions in ammonia
emission of 58% in growing pigs and of 46% in
finishing pigs when the crude protein content of the diets
were reduced by 60 and 65 g/kg, respectively. It should
be remarked that in earlier studies water intake was often
restricted. At ad libitum water intake a decreased protein
content of the diet reduces voluntary water intake
(Fremaut and De Schrijver, 1991). This will cause the
manure to be more concentrated, and therefore the
difference in ammonium concentration may be less
pronounced when water is available ad libitum compared to the restricted situation.
4.2. Shifting nitrogen excretion from urea in urine to
protein in faeces
The breakdown of protein in manure is a slow
process. At a manure temperature of 18 °C it takes
70 days before 43% of protein has been broken down
(Spoelstra, 1979). In contrast the breakdown of urea to
ammonia and carbon dioxide is a fast process that covers
only hours. By bacterial fermentation in the large
intestine nitrogen from dietary protein is incorporated
into bacterial protein (Bakker et al., 1998). Furthermore,
urea excreted from the blood into the large intestine can
be incorporated in bacterial protein. Bakker et al. (1996)
found a net appearance of nitrogen in the large intestine,
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reducing nitrogen excretion in the urine, but similar
nitrogen retention when raw potato starch was added to
the diet. Kreuzer and Machmüller (1993) found that
addition of 10 to 22% NSP in pig's diet reduced urinary
nitrogen excretion from 20 to 28%. When increasing
NSP content of the diet from 14 to 31%, Canh et al.
(1997) found a decrease in the urinary nitrogen to faecal
nitrogen ratio from 3.8 to 1.2, while apparent nitrogen
digestibility decreased from 85 to 75%. Combining
different studies Jongbloed (2001) found the relationship between NSP content of the diet and the urinaryN/faecal-N ratio as shown in Fig. 2. Enzyme supplementation (glucanase and xylanase) reduced the effect of
NSP on urinary nitrogen to faecal nitrogen ratio and pH,
thereby increasing ammonia emission at the high protein
level (220 g/kg; O'Connell et al., 2006). However, these
authors found no increase in ammonia emission when
enzymes were supplemented at the low protein level
(160 g/kg).
It should be remarked that increasing the level of
NSP in the diet also has negative impacts. At higher
NSP levels nutrient digestibility decreases and increases
waste production (Moeser and Van Kempen, 2002),
which is undesirable in animal dense areas.
4.3. Lowering the pH of faeces
With bacterial fermentation in the large intestine also
volatile fatty acids (VFA) are formed. These VFA lowers
the pH of faeces and of manure. Different experiments
were performed by Canh et al. (1997, 1998c,d). With
larger proportions of NSP in the diet of pigs, they not only
found a shift in excretion ratio between urine and faeces,
but a lower pH of faeces and manure, as well. In their
study they mixed faeces from growing pigs fed different
levels of NSP with standard urine. Thus the effects could
be totally ascribed to the faeces and not to urine. They
found a decrease of manure pH with 0.12 units and a
reduction of ammonia emission by 5.1% for every 100 g/d
extra intake of NSP (range NSP intake: 200–700 g/d;
mean feed intake: 1.35 kg/d). Also, after a storage period
of 16 days, VFA content of the manure increased with
increasing NSP content of the diet. The most profound
effect on pH of manure was found when sugar beet pulp
silage (SBPS) was included in the diet of growing pigs.
Levels of 0, 5, 10, and 15% SBPS gave NSP levels in DM
of 27.5, 30.5, 34.0, and 36.5%, respectively. These levels
had no effect on the ammonium content of the manure.
However, the pH was significantly lowered by 1.5 units
and ammonia emission by 40% when 15% SBPS was
included in the diet, compared to the control diet without
SBPS.
4.4. Lowering the pH of urine
The manure pH can also be lowered by lowering the
pH of urine. The urinary pH will alter when the electrolyte
balance of the diet changes (Patience et al., 1987). Mroz
et al. (1996) and Canh et al. (1998b) studied the effects of
level and source of acidifying calcium salts on the pH of
urine and manure and on ammonia emission from manure
of growing-finishing pigs in a laboratory setting. Replacing CaCO3 by CaSO4, CaCl2, or Ca-benzoate significantly reduced the pH of urine and manure and the
ammonia emission from the manure. By replacing 6 g of
calcium in the form of CaCO3 by Ca-benzoate urinary and
manure pH was lowered from 6.8 to 5.3 and from 8.0 to
6.4, respectively. In that case ammonia emission was
reduced by almost 60%. For Ca-sulphate and Ca-chloride
effects were lower (approximately 35% reduction of
ammonia emission), although the pH's of the urine were
similar. This is mainly caused by the fact that benzoic acid
is broken down to hippuric acid, which is then excreted in
urine. The buffering capacity of hippuric acid causes the
pH of the mixture of urine and faeces to increase less than
with the sulphate and chloride treatments. Kim et al.
(2004) found also a lower urine pH and ammonia
emission by replacing di-calcium-phosphate and calcium
carbonate by phosphoric acid and calcium sulphate.
4.5. Combined nutritional measures and ammonia
emission
Fig. 2. Relationship between NSP content of the diet and the urine-N/
faecal-N ratio (Jongbloed, 2001).
In a study of Bakker and Smits (2002) it was
determined whether the effects of the former mentioned
nutritional factors on ammonia emission are additive, with
no interaction between them. Different diets were
investigated based on combinations of 3 protein levels
(142, 161, 180 g/kg), 3 levels of acidifying salt (2.2, 6.9,
A.J.A. Aarnink, M.W.A. Verstegen / Livestock Science 109 (2007) 194–203
11.6 g/kg SO4− 2) and 3 levels of digestible fermentable
carbohydrates (62, 83, 104 g/kg). The diets were given to
pigs on balance cages and ammonia emission was
determined in an in-vitro set up, as described by Canh
et al. (1998a). The results showed no interaction between
the different nutritional factors. It was shown that
ammonia emission was linearly related to the levels of
protein, CaSO4, and fermentable carbohydrates in the
diet. The effects could be described with the following
model:
AE ¼ −5:747ð0:656Þ þ 0:056ð0:0038Þ⁎P
−0:050ð0:0091Þ⁎AS−0:010ð0:0013Þ⁎DFC
Where: AE = ammonia emission (g); P = protein (g/kg);
AS = acidifying salt (SO42−, g/kg); DFC = digestible fermentable carbohydrates (g/kg).
Reduction of the protein content from 180 to 142 g/
kg resulted in an ammonia emission reduction of 63%.
When increasing the sulphate concentration from 2.2 to
11.6 g/kg, in the form of CaSO4, ammonia emission was
lowered by 25%. When the digestible fermentable
carbohydrate concentration in the diet was increased
from 83 to 104 g/kg ammonia emission was lowered by
6%.
On basis of the first experiment 3 diets were selected
and the ‘in-vitro’ results of these diets were validated in
a real pig house. The following diets were tested: diet 1
with a high level of protein and low levels of CaSO4 and
digestible fermentable carbohydrates; diet 2 with
medium levels of these components and diet 3 with a
low level of protein and high levels of CaSO4 and
digestible fermentable carbohydrates. In the ‘in-vivo’
experiment the results of the ‘in-vitro’ experiment were
confirmed. Diet 2 with medium levels of protein, CaSO4
and DFC reduced ammonia emission by 44% when
compared to diet 1 with a high level of protein and low
levels of CaSO4 and DFC. Diet 3 with a low level of
protein and high levels of CaSO4 and DFC resulted in a
reduction of ammonia emission of 69% when compared
to diet 1.
5. Nutrition and odour emission
A great number of volatile compounds have been
identified in the air of pig confinement units. Largely the
same constituents have been identified in anaerobicallystored wastes. This confirms the general assumption that
malodours which are emitted from piggeries mainly
originate from the manure (Spoelstra, 1980). More than a
hundred odourous compounds have been identified in the
air of pig houses (Hartung and Phillips, 1994; O'Neill and
199
Phillips, 1992). According to Le et al. (2005) odours from
pig waste can be subdivided into four chemical groups:
sulphurous compounds, VFA, phenols and indoles, and
ammonia and volatile amines. Hobbs et al. (1995) found
odour from manure with high total solids being dominated
by sulphides, while acetic acid and phenols predominated
odours from slurry with low total solids. Merkel et al.
(1969) and O'Neill and Phillips (1992) indicated that
sulphur containing compounds largely contribute to the
noxious odour from livestock buildings. Quantitatively
VFA are the most important groups of odour, of which
acetic acid is representing approximately 60% of total
VFA (Canh et al., 1997; Spoelstra, 1979).
Odourous compounds are formed by the slow
process of anaerobic digestion of organic substances
excreted with faeces and from the fast process of
enzymatic hydrolysis of some urinary compounds. In
Table 2 an overview is given of the products that are
formed by the microbial activity in manure from the
main components of urine and faeces.
From their review paper Le et al. (2005) concluded
that dietary composition and odour production and
emission have a cause-and-effect relationship and that
altering the sources and levels of crude protein and
fermentable carbohydrates can be a promising approach
to reduce odour nuisance. In a study Le et al. (submitted
for publication) compared three levels of crude protein
(120, 150, and 180 g/kg) and measured the effect on
odour concentration by olfactometry. Manure from 6
individual animals per treatment were collected in
separate manure pits. Odour concentration was determined in air directly collected above the manure of each
pit. Results showed a significant reduction in odour
Table 2
Overview of the volatile products formed by microbial activity in
manure from the main components in urine and faecesa
Urine
Faeces
Component
Conversion product in manure
Urea
Glucuronides
Hippuric acid
Sulphate
Protein
Ammonia
Glucuronic acid
Benzoic acid
Hydrogen sulphide
Volatile fatty acids
Phenols
Indole
Skatole
Ammonia
Amines
Mercaptans
Volatile fatty acids
Alcohols
Aldehydes
Carbohydrates
a
After Spoelstra (1979).
200
A.J.A. Aarnink, M.W.A. Verstegen / Livestock Science 109 (2007) 194–203
concentration of 77%, from 31 888 to 7259 odour units
per m3 of air (OUE/m3; CEN standard 13 725, 2003),
when dietary crude protein was reduced from 180 to
120 g/kg. Phenol, 4-ethyl phenol, indole, 3-methyl
indole, carbon disulphide, and methyl sulphide were
significantly reduced, as well. Protein content did not
affect concentrations in the manure of cresols. From this
study it was concluded that feeding a diet that better
meets the protein requirement of the pigs reduces odour
concentration and odour emission from pig manure. A
better fit to the animal's requirements can be achieved
by reducing the crude protein content of the diet and
supplementing the diet with essential amino acids.
Hayers et al. (2003) found a reduction of odour emission
of 31 and 33% by decreasing crude protein content from
190 to 160 and 130 g/kg, respectively. Also in the study
of Le et al. (submitted for publication) the reduction of
odour concentration and emission was higher in the
reduction step from 180 to 150 g/kg (60%) than from
150 to 120 g/kg. Obrock et al. (1997) found no
difference in odour concentration between treatments
of 130 and 90 g/kg crude protein. It seems that at low
protein concentrations odour production does not
change a lot. It might be that at low protein concentrations protein in the large intestine becomes the limiting
factor in biomass formation. This might cause surplus of
carbohydrates being converted to intermediate and
odourous compounds, e.g. VFA.
In another study of Le et al. (in press) the effect of
supplementation of certain amino acids to the diet on
odour concentration of air from the manure was
investigated. Treatments were: 1) basal diet with 150 g/
kg crude protein (No-AA); 2) basal diet with addition of
three times the requirement of sulphur containing amino
acids (S-AA); 3) basal diet with two times the
requirement of amino acids tryptophan, phenylalanine,
and tyrosine (T-AA). The results showed a dramatic
increase of odour concentrations by almost a factor 10 of
the S-AA diet compared to the No-AA diet (13 224 and
111 302 OUE/m3, respectively). No effect of T-AA on
odour concentration, however, was found. It seems that
surplus of sulphur amino acids are converted to
glucuronides and sulphates. After excretion these glucuronides are converted to odourous sulphur compounds
and sulphates are reduced to hydrogen sulphide (Spoelstra, 1979). Clark et al. (2005) also found increased peak
emissions of H2S from pig manure when increasing
sulphur amino acids in the diet.
Just recently a study was finished to investigate the
interactive effect between protein content and fermentable
carbohydrates in the diet (Le et al., unpublished results).
This study showed a clear interactive effect between the
crude protein content of the diet and fermentable
carbohydrates on odour concentration. It seems that an
optimum balance between available fermentable protein
and fermentable carbohydrates in the large intestine of
pigs is a main factor in odour production in pigs. Shortage
of protein or shortage of fermentable carbohydrates will
both result in formation of odourous compounds. At
optimal levels, fermentable protein is used as the nitrogen
source and fermentable carbohydrates as the energy
source for biomass production.
6. Nutrition and methane emission
Methane mainly originates from bacterial fermentation
of carbohydrates under anaerobic conditions. In livestock
methane mainly originate from fermentation in the rumen
of ruminants (Monteny et al., 2001; Tamminga and
Verstegen, 1992). A small part is also coming from
fermentation in the colon of pigs. In pigs, however, a
bigger part seems to come from the manure during storage
(Monteny et al., 2001). Monteny et al. (2001) showed that
the methane emissions measured from animal houses,
expressed per kg live weight, did not differ much between
cattle and pigs.
There seems to be a close relationship between fermentable carbohydrates in the diet and methane production.
Kirchgessner et al. (1991) found the following relationship between bacterial fermentable substrate (BFS) and
methane emission: CH4 (g/d) = 2.85+ 13.0 BFS (kg/d);
when BFS N 80 g/kg dm. Increasing fermentable carbohydrate level in the diet to lower the pH of faeces and
manure and consequently ammonia emission, therefore
will at the same time increase methane production. Although methane production from pigs is relatively small
compared to ruminants, this strategy to reduce ammonia
emission seems therefore less preferable. PH itself also
influences methane production. Kim et al. (2004) found a
reduction of methane emission with 14% when ileal pH
was reduced with one unit by addition of acidogenic Ca
and P sources to pig diets.
7. Conclusions
• Main environmental problems related to intensive pig
production systems are: 1) overloading of arable land
with N, P, and heavy metals (mainly Cu, Zn, and Cd);
2) uncontrolled gaseous emissions of ammonia, odour,
and methane.
• Main nutritional strategies to reduce N and P
excretions from pigs are: phase feeding (N, P),
supplementation of limiting amino acids to the diet
(N), and addition of phytase to the diet (P).
A.J.A. Aarnink, M.W.A. Verstegen / Livestock Science 109 (2007) 194–203
• Main nutritional strategies to reduce ammonia emissions from pig production are: 1) lowering crude
protein intake in combination with supplementation of
limiting amino acids; 2) shifting nitrogen excretion
from urine to faeces by including fermentable
carbohydrates in the diet; 3) lowering pH of urine by
adding acidifying salts to the diet; 4) lowering the pH
of faeces by inclusion of fermentable carbohydrates in
the diet.
• Nutritional strategies to reduce heavy metals excretions from pigs are: finding alternative, natural, growth
promoters that could replace Cu and Zn in the diet;
using feedstuffs for the diet that are less contaminated
with Cd.
• Nutritional strategies to reduce ammonia emissions
from pig production proved to be independent from
each other and effects are additive. By combining
different strategies a total reduction of ammonia
emission in growing-finishing pigs of 70% could be
reached.
• Main nutritional strategies to reduce odour emission
from pig production are: 1) reducing protein fermentation by balancing available protein and fermentable
carbohydrates in the large intestine; 2) minimizing
breakdown of absorbed sulphur amino acids.
• More research is needed on the relationship between
nutrition and odour emission from pig production
facilities, but it seems to have a great potential.
• Methane emission from pig production increases at
increasing levels of fermentable carbohydrates in the
diet. This disadvantage should be considered when
tackling ammonia emission by this strategy.
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