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Effect of reduced crude protein on ammonia, methane, and chemical odorants emitted from pig houses
Livestock Science 169 (2014) 118–124
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Effect of reduced crude protein on ammonia, methane, and chemical odorants emitted from pig houses Michael J. Hansen a, Jan V. Nørgaard b,n, Anders Peter S. Adamsen a, Hanne D. Poulsen b a b
Department of Engineering, Aarhus University, Hangøvej 2, 8200-DK Aarhus N, Denmark Department of Animal Science, Aarhus University, Blichers Allé 20, 8830-DK Tjele, Denmark
a r t i c l e in f o
abstract
Article history: Received 5 March 2014 Received in revised form 27 August 2014 Accepted 31 August 2014
The aim of the present study was to investigate the effect of reduced crude protein level in finisher diets on ammonia, methane, and chemical odorants emitted from pig houses. Over a period of 44 days, pigs in two similar houses with 32 pigs (55–100 kg) in each were fed either a low-protein or a standard protein diet containing 136 or 159 g crude protein kg 1, respectively. The diets were formulated to be isoenergetic (8.1 MJ net energy kg 1 as fed) and were supplemented with indispensable amino acids to fulfill amino acid recommendations. A photoacoustic gas monitor was used to measure ammonia and methane during the whole experimental period, and Proton-TransferReaction Mass Spectrometry (PTR-MS) was used to measure chemical odorants during the last 11 days. The results demonstrated that the crude protein level could be reduced by supplementing indispensable amino acids without impairing growth, feed utilization, and meat percentage. Reduced crude protein level lowered the ammonia emission, whereas no significant effect was seen on the methane emission and the total odor activity value based on chemical odorants. In conclusion, reduced crude protein level is an effective method to reduce ammonia emitted from pig houses. However, more research is needed to investigate how optimization of the amino acids content can influence the emission of individual chemical odorants. Furthermore, PTR-MS was demonstrated to be a suitable method for estimating the effect of a given feeding strategy on the emission of chemical odorants. & 2014 Elsevier B.V. All rights reserved.
Keywords: Pigs Protein Ammonia Methane Odor PTR-MS.
1. Introduction Emission of ammonia and odor from modern intensive pig production and abatement technologies for reducing the environmental impact of pig production have gained increased focus during the last years. Emission of ammonia from pig production has a negative effect on the surrounding ecosystem due to deposition of nitrogen, and odor
n
Corresponding author. Tel.: þ45 87157816. E-mail address: [email protected] (J.V. Nørgaard).
http://dx.doi.org/10.1016/j.livsci.2014.08.017 1871-1413/& 2014 Elsevier B.V. All rights reserved.
causes nuisance to the people living in the vicinity of the production systems (Aneja et al., 2009). Several types of abatement technologies have been investigated, including air cleaning (e.g. biological air cleaning), slurry treatment (e.g. slurry acidification), and optimized feeding (e.g. reduced crude protein level). It has been demonstrated that both air cleaning (Melse and Ogink, 2005), slurry acidification (Kai et al., 2008), and optimized feeding (Hayes et al., 2004; Le et al., 2007b; Leek et al., 2007) can be used to reduce the emission of ammonia and to some extent odor. Air cleaning and slurry treatment systems are add-on technologies that require implementation in the ventilation
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or slurry system and with increased production costs. Optimization of the nutrients in the feed has the advantage that it does not require new investments, however, the challenge is to formulate a diet that gives the same production results (growth performance and carcass characteristics) with less nutritional input. The effect of reduced crude protein level on ammonia and odor emission has been investigated in several studies (Hayes et al., 2004; Le et al., 2009, 2008, 2007b; Leek et al., 2007) showing that reduced crude protein has a clear effect on ammonia emission, whereas the effect on odor is only significant when the crude protein level is reduced from a high level (21–22% crude protein) to a low level (13–16% crude protein) (Hayes et al., 2004; Leek et al., 2007). Most of the studies that have addressed the effect of reduced crude protein level on odor are based on dynamic olfactometry (CEN, 2003), where human panelists are used to estimate the odor concentration. Only a few studies have investigated the relation between crude protein level and emission of chemical odorants (Hobbs et al., 1998, 1996) and there is a lack in knowledge about how reduced crude protein level affects the individual chemical odorants measured in full-scale production facilities. In recent years, Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) has been applied for on-line measurements of chemical odorants from pig houses and in relation to abatement technologies (Feilberg et al., 2010; Hansen et al., 2012b; Liu et al., 2011). The PTR-MS has the advantage that it can measure most of the relevant chemical odorants found in air from pig houses, and furthermore, it can provide continuous data with high sensitivity and time resolution. The aim of the present study was to investigate how reduced crude protein affects the individual chemical odorants, ammonia and methane emitted from pig houses under realistic production conditions.
they were slaughtered after 44 days. The pigs were fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively (Table 1). The diets were formulated to be isoenergetic (8.1 MJ net energy kg 1 as fed) and to contain 7.4 g standardized ileal digestible (SID) lysine kg 1 as fed. The diets were optimized to supply SID indispensable amino acids in relation to SID lysine according to the Danish recommendations for pigs weighing 55–105 kg (Tybirk et al., 2012).
2. Materials and methods
2.3. Analytical methods
2.1. Pig houses
Ammonia in the exhaust air was measured during the whole experimental period, whereas chemical odorants were measured during the last 11 days of the experimental period. At the end of the experimental period, a representative sample of slurry (ca. 1 L) was collected from each pen. Temperature, relative humidity, and airflow rate in each pig house were recorded every two minutes (VengSystem A/S, Roslev, Denmark). Calibrated measuring fans were used to estimate the airflow rate (Reventa, Horstmar, Germany). The concentrations of ammonia, methane, and carbon dioxide were measured using a photoacoustic gas monitor INNOVA 1412 combined with a multipoint sampler INNOVA 1309 (LumaSense Technologies A/S, Ballerup, Denmark). The system with INNOVA 1412 and INNOVA 1309 was set up with one channel for the ventilation outlet in each pig house and one channel for the fresh air supply to the pig houses. Heated and insulated sample tubes of Teflon (outer diameter: 8 mm, inner diameter: 6 mm, Mikrolab A/S, Aarhus Denmark) for each channel were flushed continuously (ca. 7 L min 1) with a Capex L2 diaphragm Teflon pump (Charles Austen Pumps Ltd., Byfleet, UK). The sample line between the diaphragm pump and the
Two identical pig houses were used in the experiment. Each pig house contained two pens with space for 16 finishing pigs in each. The pens were designed with slatted floor in the entire area of the pen and two 60 cm deep slurry pits underneath each pen. The two slurry pits for each pen were placed on load cells (TEKFA A/S, Galten, Denmark) to record the weight of the slurry. The ventilation system in the pig houses was a negative pressure system with a diffuse ceiling inlet and one outlet mounted in the ceiling. The ventilation rate was controlled according to a set temperature at 20 1C (days 0–2), 19 1C (days 3–14), and 18.5 1C (days 15–44). The experiment took place at Aarhus University, Foulum, from April to May 2013, and the average outdoor temperature during this period was 13.074.5 1C. 2.2. Animals and diets Thirty-two cross-bred finishing pigs [Duroc (Danish Landrace Yorkshire)] with an initial body weight of ca. 55 kg were inserted in each pig house. The pigs were weighed at the beginning, after three weeks, and before
Table 1 Feed composition of a low-protein and a standard protein diet for finishing pigs containing 136 and 159 g crude protein kg 1, respectively. Itema
Low-protein
Standard
Wheat Barley Soy bean meal, toasted, dehulled Calcium carbonate Mono calcium phosphate Salt Vitamin-mineral premixb Phytasec L-Lysine HCL L-Threonine DL-Methionine L-Tryptophan L-Valine
42.1 45.0 9.8 1.27 0.684 0.390 0.200 0.020 0.338 0.131 0.052 0.017 0.010
48.4 32.3 16.7 1.26 0.587 0.392 0.200 0.020 0.134 0.037 0.022 0 0
g 100 g 1 diet. Trouw Nutrition Denmark A/S. Content per g premix: 2500 IU vitamin A, 500 IU vitamin D3, 23.4 IU vitamin E, 0.6 mg vitamin K3, 0.6 mg vitamin B1, 1.2 mg vitamin B2, 3 mg D-panthotenic acid, 6.4 mg niacin, 0.060 mg biotin, 21.3 mg α-tocopherol, 0.006 vitamin B12, 0.6 mg vitamin B6, 50 mg Fe (Fe(II) sulfate), 41.3 mg Cu (Cu(II) sulfate), 50 mg Zn (Zn(II) oxide), 13.9 mg Mn (Mn(II) oxide), 0.076 mg KI, and 0.075 mg Se (Se-selenite). c Natuphos 5000, 5641 FTU/g, BASF, 2300 Copenhagen, DK. a
b
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multipoint sampler was flushed for 10 s, and the measurement chamber in the photoacoustic gas monitor was flushed for 20 s during each measurement cycle. The sample integration time was set at 5 s, and compensation for water vapor interference and cross interference between gasses (ammonia, carbon dioxide, methane, and nitrous oxide) was applied. The photoacoustic gas monitor INNOVA 1412 was calibrated by LumaSense Technologies A/S prior to the measurements. Gas detection tubes (Kitagawa, KawasakiCity, Japan) were used to check the concentrations measured by the photoacoustic gas monitor. The multipoint sampler was used to switch between the channels, and during each measurement, ten measurement cycles (ca. 12.7 min) were performed by the photoacoustic gas monitor on each channel. The data signal was stable after six to seven cycles and the last three measurement cycles were averaged and used to estimate the concentrations of ammonia, methane, and carbon dioxide. The concentrations of ammonia and methane measured in the fresh air supply to the pig house were subtracted from the concentrations measured in the air from the pig houses. For each channel a result was recorded approximately every 64 min and in total 23 measurements of ammonia, methane, and carbon dioxide concentrations were estimated each day during the experimental period. Chemical odorants were measured by a high sensitivity PTR-MS (Ionicon Analytik, Innsbruck, Austria). The chemical odorants included hydrogen sulfide, methanethiol, dimethyl sulfide, trimethylamine, acetic acid, butanoic acid, propanoic acid, 4-methylphenol, indole, and skatole and were chosen since they are considered to be some of the most important odorants or some of the odorants that are found in the highest concentrations in air from pig houses (Hansen et al., 2012a). The PTR-MS was operated with standard drift tube conditions: voltage at 600 V, a pressure between 2.1 and 2.2 mbar, and a temperature of 60 1C. The inlet temperature was 60 1C. Single ion monitoring was used, and the sensitivity was estimated based on rate constants for proton transfer, the estimated drift tube residence time, and the mass specific transmission factors as described by de Gouw and Warneke (2007). The rate constants for proton transfer were calculated using the method described by Su and Chesnavich (1982). The humidity dependency of hydrogen sulfide (m/z 35) was corrected according to the method described by Feilberg et al. (2010). In order to perform compound assignment air samples were collected on sorbent tubes for thermal desorption and a gas chromatograph with a mass spectrometer (TD-GC/MS) and in Tedlar bags for a gas chromatograph with a sulfur chemiluminescence detector (GC–SCD). The use of TD-GC/MS and GC–SCD for compound assignment in air from pig houses has previously been described in detail (Feilberg et al., 2010; Hansen et al., 2012b). Heated and insulated Teflon tubes (outer diameter: 3.2 mm, inner diameter: 1.6 mm, Mikrolab A/S, Aarhus Denmark) from the ventilation outlet in the pig houses were connected to a heated switch box with a five-way PEEK valve (Bio-Chem Valve Incorporated, Boonton, New Jersey, USA). The PTR-MS was connected to the five-way PEEK valve, and the software of the PTR-MS controlled the switching between channels. In between measurements on the pig houses, instrumental background was measured
using a Supelpure™ HC filter (Supelco, Bellefonte, Pennsylvania, USA). Each hour, the PTR-MS measured 48 measurements cycles (12 min) on each channel. The last 20 measurement cycles were averaged and used to estimate the concentrations of the chemical odorants. The instrumental background was subtracted from the concentrations measured in the air from the pig houses. For each channel a result was recorded every 60 min and in total 24 measurements of each chemical odorant were estimated each day during the last 11 days of the experimental period. Slurry samples were analyzed for total nitrogen using the Kjeldahl method (Tecator™ Digestion System, Foss, Hillerød, Denmark) and ammoniacal nitrogen photometrically using a commercial kit using the indophenol blue method (Spectroquant Test kit no. 1.00683.0001, Merck KGaA, Darmstadt, Germany). The pH-value of the slurry samples were measured by a pH-meter (Metrohm AG, Herisau, Switzerland). The dry matter content in slurry was determined after drying at 105 1C for 24 h. 2.4. Data analysis The odor activity value (OAV) was estimated based on odor threshold values (OTV) as reported by Nagata (2003). The OAV for each odorant was calculated as OAV¼concentration (nL L 1)/OTV (nL L 1) and the total OAV was estimated as the sum of the OAV for the individual chemical odorants. The results were analyzed using linear models in SAS (Littel et al., 2002). Data analysis regarding ammonia, methane, and chemical odorants was performed with each pig house as the experimental unit. The emissions of ammonia, methane and odorants were estimated based on the measured concentrations and the average of the air flow rate for each hour. One experimental period was performed and the daily emission of ammonia, methane and odorant per pig and the daily average of the total OAV were used as response variables in the statistical analysis. The statistical model for ammonia emission (g pig 1 day 1), methane emission (g pig 1 day 1), chemical odorants (mg pig 1 day 1), climatic conditions, and total OAV included diet as a fixed effect. The statistical model for bodyweight, average daily growth, feed utilization, and carcass parameters included diet as a fixed effect and initial bodyweight as a covariate. The level of significance was defined as a P-value below 0.05. 3. Results The performance of the pigs in terms of bodyweight, average daily growth, feed utilization, and carcass parameters is presented in Table 2. There was no significant difference between the standard protein diet and the lowprotein diet regarding the performance of the pigs neither during the first or second half, nor during the overall six week period. The climatic conditions in the two pig houses applied for the two diets are presented in Table 3. The ventilation rate was based on a set temperature controlled by the ventilation system, and there was no significant difference between the indoor temperature and the ventilation rate in the two pig houses. There were significant
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Table 2 Start and end weight, average daily growth, feed utilization, carcass weight, and meat percentage for finishing pigs fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively. Itema
Standard
SEMb
P-value
Bodyweight, kg Start weight 55.5 End weight 102.0
55.5 101.6
– 1.0
– 0.74
Average daily growth, g day 1 Weeks 1–3 1019 Weeks 4–6 1096 Weeks 1–6 1058
1048 1063 1047
27 26 22
0.45 0.37 0.74
Feed utilization, Weeks 1–3 Weeks 4–6 Weeks 1–6 Carcass Weight, kg Meat, % a b
Low-protein
g g1 0.40 0.40 0.40
0.42 0.40 0.41
0.01 0.01 0.01
0.46 0.99 0.83
78.0 60.9
77.8 60.8
0.7 0.3
0.77 0.69
n ¼32. SEM: standard error mean.
Table 3 Average climatic conditions in pig houses in an experiment with finishing pigs (55–100 kg) fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively. a
Item
Low-protein
Standard
SEM
Temperature, 1C Relative humidity, % Ventilation rate, m3 h 1 Carbon dioxide, mL L 1
21.0 51.9 2255 1249
21.1 48.6 2063 1137
0.2 1.0 94 24
a b
n ¼44. SEM: standard error mean.
b
121
differences between the relative humidity and the carbon dioxide concentration for the two pig houses. The daily ammonia emission (g pig 1 day 1) is presented in Fig. 1, and it shows a clear distinction between the low and standard protein diets. There was a significant (P¼0.0002) difference between the ammonia emission for the two diets. The average ammonia emission was 6.0 g day 1 pig 1 for the low-protein diet and 7.8 g day 1 pig 1 for the standard protein diet. The total ammonia emission during the 44 day experimental period was 23% lower for the low-protein diet (263 g pig 1) compared to the standard protein diet (342 g pig 1). The emission of ammoniacal nitrogen relative to the ingested amount of nitrogen was 14% lower for the low-protein diet (4.3%) compared to the standard diet (5.0%). Slurry characteristics measured at the end of the experimental period are presented in Table 4. In general total nitrogen in slurry, ammoniacal nitrogen in slurry and pH were lower for the low-protein diet. The methane emission (g pig 1 day 1) is shown in Fig. 2 and demonstrates that the methane emission was increasing during the experimental period, but there was no significant (P¼0.21) difference between the two diets. The total methane emission during the 44 day experimental period was 181 g pig 1 for the lowprotein diet and 157 g pig 1 for the standard protein diet.
Table 4 Ingested nitrogen, total nitrogen, ammoniacal nitrogen, dry matter and pH measured in slurry at the end of an experiment with finishing pigs (55–100 kg) fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively. Itema
Low-protein Standard
P-value
Pen
1
0.63 0.02 0.15 0.002
2.58 Ingested nitrogen, kg pig 1 Total nitrogen in slurry, kg pig 1 0.92 Ammoniacal nitrogen in slurry, kg pig 1 0.71 Dry matter, % 10.3 pH in slurry 6.94 a
2
1
2
2.45 0.77 0.65 9.1 6.75
2.97 1.02 0.92 5.8 7.48
2.69 1.13 0.97 9.2 7.35
One slurry sample was collected from each pen.
Fig. 1. Ammonia emission from two houses with finishing pigs (55–100 kg) fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively.
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Fig. 2. Methane emission from two houses with finishing pigs (55–100 kg) fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively.
Table 5 Average emissions of chemical odorants (mg pig 1 day 1) and total odor activity value (OAV) in an experiment with finishing pigs (55–100 kg) fed a lowprotein diet or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively. Values in brackets are average of OAV for the individual chemical odorants. Itema d
Hydrogen sulfide m/z 35 Methanethiol m/z 49 Dimethyl sulfide m/z 63 Trimethylamine m/z 60 Acetic acid m/z 61 þ43 Propanoic acid m/z 75 þ57 Butanoic acid m/z 89þ71 4-methylphenol m/z 109 Indole m/z 118 Skatole m/z 132 Total OAV
OTVb
Low-protein
Standard
SEMc
P-value
0.41 0.07 3.0 0.032 6.0 5.7 0.19 0.054 0.30 0.0056
140 (118) 21 (86) 28 (1.7) 25 (154) 2581 (66) 759 (17) 558 (303) 118 (207) 4.5 (1.5) 2.0 (31) 986
143 (133) 16 (72) 24 (1.6) 29 (195) 2334 (66) 675 (17) 472 (281) 111 (215) 4.0 (1.5) 1.3 (23) 1005
6 2 2 1 110 28 21 7 0.3 0.3 31
0.73 0.08 0.12 0.03 0.13 0.05 0.008 0.53 0.30 0.11 0.68
a
n¼ 11. OTV: odor threshold values (nL L 1) reported by Nagata (2003). c SEM: standard error mean. d m/z: mass-to-charge ratio. b
Average emissions of ten chemical odorants (mg pig 1 day 1) in the ventilation air from the pig houses and the OAV estimated based on OTV are shown in Table 5. The emissions of propanoic acid and butanoic acid were significantly higher for the low-protein diet whereas the emission of trimethylamine was significantly lower. The emissions of the other chemical odorants were not significant different between the two diets. No significant difference was found between the total OAV for the two diets (Fig. 3). The estimated OAV for the individual chemical odorants demonstrate that the compounds that contributed the most to OAV were hydrogen sulfide, methanethiol, trimethylamine, butanoic acid, and 4-methylphenol (Table 5). 4. Discussion The main focus in the present study was the effect of reduced crude protein level on ammonia, methane, and
chemical odorants emitted from pig houses. However, if low-protein diets should be an alternative to other types of abatement technologies, it is important that the performance of the pigs in terms of growth, feed utilization, and carcass quality is unaffected compared to a standard protein diet for finishing pigs. In the present study, the average daily growth, feed utilization, and carcass meat percentage were not affected by feeding a low-protein diet (13.6% crude protein) compared to a standard protein diet (15.9% crude protein). The results are in line with previous studies (Ball et al., 2013; Canh et al., 1998) and confirm that low-protein diets supplemented with crystalline amino acids to provide sufficient concentrations of the indispensable amino acids can be fed to finishing pigs without impairing growth performance. Although there were significant differences in relative humidity and carbon dioxide concentration for the two pig houses, the climatic conditions were within the same
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Fig. 3. Odor activity value in air from two houses with finishing pigs (55–100 kg) fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively.
range and may only have a limited influence on the emission of ammonia, methane, and chemical odorants. The results demonstrate that the low-protein diet had a significantly lower ammonia emission compared to the standard protein diet. The slurry characteristic was measured at the end of the experimental period and demonstrated a lower total nitrogen and ammoniacal nitrogen content and pH-value in the slurry for the low-protein diet. These results confirm previous studies where it has been demonstrated that lowering the crude protein level results in lower nitrogen content in slurry, lower pH value in slurry and as a result, lower ammonia emission (Hayes et al., 2004; Le et al., 2009, 2007b; Leek et al., 2007). In the present study, the ammonia emission was 23% lower in the low-protein diet compared to the standard protein diet equivalent to 10% for every 10 g kg 1 reduction in dietary crude protein content. Previous studies that have demonstrated that 10 g kg 1 reduction in dietary crude protein content results in 8–13% reduction in ammonia emission (Canh et al., 1998; Hayes et al., 2004; Le et al., 2009, 2007b; Leek et al., 2007). The low-protein diet did not have an effect on the methane emission which is in accordance with previous studies (Le et al., 2009). This does not mean, however, that methane emissions cannot be affected by the level of dietary crude protein, because practical diets based on fiber-rich protein sources such as rape seed meal or sun flower cake often will result in increased protein concentrations along with increased fermentable fiber concentrations which are known to stimulate methane emission from pigs (Jørgensen et al., 2011). The effect of a low-protein diet on odor was evaluated based on the emission of ten chemical odorants and the estimated OAV using the odor threshold values (OTV) as reported by Nagata (2003). The chemical odorants included sulfur compounds, trimethylamine, carboxylic acids, 4-methylphenol, indole, and skatole. In general, there were higher emissions of most odorants for the low-protein diet except for trimethylamine where the emission was lower. In particular, the emissions of carboxylic acids were higher for the low-protein diet and this could be explained by the lower
pH-value in slurry. The lower emission of the nitrogen containing odorant trimethylamine for the low-protein diet could be explained by the lower nitrogen excretion in slurry for this diet. Despite the higher emission of most odorants for the low-protein diet there was no significant effect on the total OAV. In general, the compounds contributing the most to the OAV for both diets were hydrogen sulfide, methanethiol, trimethylamine, butanoic acid, and 4-methylphenol which are in accordance with other studies addressing chemical odorants in pig house air (Feilberg et al., 2010; Liu et al., 2011). Previous studies have demonstrated an effect of reduced crude protein level on odor measured by dynamic olfactometry (Hayes et al., 2004; Leek et al., 2007). In these studies, the crude protein level was reduced from a high level (21–22%) to a low level (13–16%) by decreasing the content of soya bean meal and supplementing with the same amount of indispensable crystalline amino acids. It is very likely that the pigs in the studies by Hayes et al. (2004) and Leek et al. (2007) were supplied with protein above the requirements in the high protein diets. A protein supply above the requirements of the pigs will cause a higher excretion of undigested protein and urinary nitrogen and sulfate to the slurry thus providing more substrates for production and emission of chemical odorants (Le et al., 2007a). In the studies by Le et al. (2009) and Hansen et al. (2007), the crude protein level was only reduced from 15–16% to 12–14% and optimized according to the requirements of the pigs, and in these studies, no effect was seen on odor measured by dynamic olfactometry. In the present study with a similar range in protein (15.9–13.6%), the diets were optimized according to the minimum requirements of all indispensible amino acids. Consequently, low-protein diets optimized according to the amino acid requirements of the pigs may result in differences in the emission of some chemical odorants, but the effect on the total OAV is insignificant. Particular indispensable amino acids are precursors of some of the important chemical odorants with low OTV (e.g. methionine: sulfur compounds and tryptophan: phenols and indoles) and more research is needed to investigate how these amino acids can be optimized to give an effect on odor from pig houses.
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5. Conclusions It can be concluded that feeding finishing pigs low crude protein diets supplemented with indispensable amino acids according to the requirements of the pigs is an effective method to lower the ammonia emission from pig houses without impairing growth performance and carcass characteristics whereas no effect was seen on the methane emission. Reduced crude protein had no effect on the total odor activity value (OAV), but more research is needed to investigate if the content of amino acids can be further optimized to lower odor from pig houses. Furthermore, it was demonstrated that proton-transfer-reaction mass spectrometry (PTR-MS) is a suitable method to investigate the effect of a given feeding strategy on the emission of chemical odorants from pig houses. Conflict of interest All authors do not have any actual or potential conflict of interest including any financial, personal or other relationships with other people or organizations within three years of beginning the submitted work that could inappropriately influence, or be perceived to influence, their work.
Acknowledgments The study was partly funded by European Community's Seventh Framework Programme (FP7/2007–2013) under the grant agreement no. 266018, the Danish Pig Levy Fund, and Aarhus University. References Aneja, V.P., Schlesinger, W.H., Erisman, J.W., 2009. Effects of agriculture upon the air quality and climate: research, policy, and regulations. Environ. Sci. Technol. 43, 4234–4240. Ball, M.E.E., Magowan, E., McCracken, K.J., Beattie, V.E., Bradford, R., Gordon, E.J., Robinson, M.J., Smyth, S., Henry, W., 2013. The effect of level of crude protein and available lysine on finishing pig performance, nitrogen balance and nutrient digestibility. Asian Australas. J. Anim. Sci. 26, 564–572. Canh, T.T., Aarnink, A.J.A., Schutte, J.B., Sutton, A., Langhout, D.J., Verstegen, M.W.A., 1998. Dietary protein affects nitrogen excretion and ammonia emission from slurry of growing-finishing pigs. Livest. Prod. Sci. 56, 181–191. de Gouw, J., Warneke, C., 2007. Measurements of volatile organic compounds in the earth's atmosphere using proton-transferreaction mass spectrometry. Mass Spectrom. Rev. 26, 223–257. CEN, 2003. Air quality – determination of odour concentration by dynamic ofactometry. EN 13725. European Committee for Standardization, Brussels, Belgium.
Feilberg, A., Liu, D., Adamsen, A.P.S., Hansen, M.J., Jonassen, K.E.N., 2010. Odorant emissions from intensive pig production measured by online proton-transfer-reaction mass spectrometry. Environ. Sci. Technol. 47, 5894–5900. Hansen, C.F., Sorensen, G., Lyngbye, M., 2007. Reduced diet crude protein level, benzoic acid and inulin reduced ammonia, but failed to influence odour emission from finishing pigs. Livest. Sci. 109, 228–231. Hansen, M.J., Adamsen, A.P.S., Pedersen, P., Feilberg, A., 2012a. Prediction of odor from pig production based on chemical odorants. J. Environ. Qual. 41, 436–443. Hansen, M.J., Liu, D., Guldberg, L.B., Feilberg, A., 2012b. Application of proton-transfer-reaction mass spectrometry to the assessment of odorant removal in a biological air cleaner for pig production. J. Agric. Food Chem. 60, 2599–2606. Hayes, E.T., Leek, A.B.G., Curran, T.P., Dodd, V.A., Carton, O.T., Beattie, V.E., O'Doherty, J.V., 2004. The influence of diet crude protein level on odour and ammonia emissions from finishing pig houses. Bioresour. Technol. 91, 309–315. Hobbs, P.J., Misselbrook, T.H., Pain, B.F., 1998. Emission rates of odorous compounds from pig slurries. J. Sci. Food Agric. 77, 341–348. Hobbs, P.J., Pain, B.F., Kay, R.M., Lee, P.A., 1996. Reduction of odorous compounds in fresh pig slurry by dietary control of crude protein. J. Sci. Food Agric. 71, 508–514. Jørgensen, H., Theil, P.K., Knudsen, K.E.B., 2011. Enteric Methane Emission from Pigs. In: Carayannis, E.G. (Ed.), Planet Earth 2011 - Global Warming Challenges and Opportunities for Policy and Practice, InTech Europe, Rijeka, Croatia, pp. 605–623. Kai, P., Pedersen, P., Jensen, J.E., Hansen, M.N., Sommer, S.G., 2008. A whole-farm assessment of the efficacy of slurry acidification in reducing ammonia emissions. Eur. J. Agron. 28, 148–154. Le, P.D., Aarnink, A.J.A., Jongbloed, A.W., 2009. Odour and ammonia emission from pig manure as affected by dietary crude protein level. Livest. Sci. 121, 267–274. Le, P.D., Aarnink, A.J.A., Jongbloed, A.W., Peet Schwering, C.M.C., Ogink, N.W.M., Verstegen, M.W.A., 2007a. Effects of crystalline amino acid supplementation to the diet on odor from pig manure. J. Anim. Sci. 85, 791–801. Le, P.D., Aarnink, A.J.A., Jongbloed, A.W., van der Peet-Schwering, C., Ogink, N.W.M., Verstegen, M.W.A., 2008. Interactive effects of dietary crude protein and fermentable carbohydrate levels on odour from pig manure. Livest. Sci. 114, 48–61. Le, R.D., Aarnink, A.J.A., Jongbloed, A.W., van der Peet-Schwering, C., Ogink, N.W.M., Verstegen, M.W.A., 2007b. Effects of dietary crude protein level on odour from pig manure. Animal 1, 734–744. Leek, A.B.G., Hayes, E.T., Curran, T.P., Callan, J.J., Beattie, V.E., Dodd, V.A., O’Doherty, J.V., 2007. The influence of manure composition on emissions of odour and ammonia from finishing pigs fed different concentrations of dietary crude protein. Bioresour. Technol. 98, 3431–3439. Littel, R.C., Stroup, W.W., Freund, R.J., 2002. SAS for Linear Models, 4th edition SAS Institute, Cary, NC. Liu, D., Feilberg, A., Adamsen, A.P.S., Jonassen, K.E.N., 2011. The effect of slurry treatment including ozonation on odorant reduction measured by in-situ PTR-MS. Atmos. Environ. 45, 3786–3793. Melse, R.W., Ogink, N.W.M., 2005. Air scrubbing techniques for ammonia and odor reduction at livestock operations: review of on-farm research in the Netherlands. Trans. ASAE 48, 2303–2313. Nagata, Y., 2003. Measurement of odor threshold by triangle odor bag method, Odor measurement review, Ministry of the Environment Goverment of Japan 118–127. Su, T., Chesnavich, W.J., 1982. Parametrization of the ion-polar molecule collision rate constant by trajectory calculations. J.Chem. Phys. 76, 5183–5185. Tybirk, P., Sloth, N.M., Jørgensen, L., 2012. Nutrient requirement standards, 17th edition Pig research Centre, Copenhagen, Denmark.
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Livestock Science journal homepage: www.elsevier.com/locate/livsci
Effect of reduced crude protein on ammonia, methane, and chemical odorants emitted from pig houses Michael J. Hansen a, Jan V. Nørgaard b,n, Anders Peter S. Adamsen a, Hanne D. Poulsen b a b
Department of Engineering, Aarhus University, Hangøvej 2, 8200-DK Aarhus N, Denmark Department of Animal Science, Aarhus University, Blichers Allé 20, 8830-DK Tjele, Denmark
a r t i c l e in f o
abstract
Article history: Received 5 March 2014 Received in revised form 27 August 2014 Accepted 31 August 2014
The aim of the present study was to investigate the effect of reduced crude protein level in finisher diets on ammonia, methane, and chemical odorants emitted from pig houses. Over a period of 44 days, pigs in two similar houses with 32 pigs (55–100 kg) in each were fed either a low-protein or a standard protein diet containing 136 or 159 g crude protein kg 1, respectively. The diets were formulated to be isoenergetic (8.1 MJ net energy kg 1 as fed) and were supplemented with indispensable amino acids to fulfill amino acid recommendations. A photoacoustic gas monitor was used to measure ammonia and methane during the whole experimental period, and Proton-TransferReaction Mass Spectrometry (PTR-MS) was used to measure chemical odorants during the last 11 days. The results demonstrated that the crude protein level could be reduced by supplementing indispensable amino acids without impairing growth, feed utilization, and meat percentage. Reduced crude protein level lowered the ammonia emission, whereas no significant effect was seen on the methane emission and the total odor activity value based on chemical odorants. In conclusion, reduced crude protein level is an effective method to reduce ammonia emitted from pig houses. However, more research is needed to investigate how optimization of the amino acids content can influence the emission of individual chemical odorants. Furthermore, PTR-MS was demonstrated to be a suitable method for estimating the effect of a given feeding strategy on the emission of chemical odorants. & 2014 Elsevier B.V. All rights reserved.
Keywords: Pigs Protein Ammonia Methane Odor PTR-MS.
1. Introduction Emission of ammonia and odor from modern intensive pig production and abatement technologies for reducing the environmental impact of pig production have gained increased focus during the last years. Emission of ammonia from pig production has a negative effect on the surrounding ecosystem due to deposition of nitrogen, and odor
n
Corresponding author. Tel.: þ45 87157816. E-mail address: [email protected] (J.V. Nørgaard).
http://dx.doi.org/10.1016/j.livsci.2014.08.017 1871-1413/& 2014 Elsevier B.V. All rights reserved.
causes nuisance to the people living in the vicinity of the production systems (Aneja et al., 2009). Several types of abatement technologies have been investigated, including air cleaning (e.g. biological air cleaning), slurry treatment (e.g. slurry acidification), and optimized feeding (e.g. reduced crude protein level). It has been demonstrated that both air cleaning (Melse and Ogink, 2005), slurry acidification (Kai et al., 2008), and optimized feeding (Hayes et al., 2004; Le et al., 2007b; Leek et al., 2007) can be used to reduce the emission of ammonia and to some extent odor. Air cleaning and slurry treatment systems are add-on technologies that require implementation in the ventilation
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or slurry system and with increased production costs. Optimization of the nutrients in the feed has the advantage that it does not require new investments, however, the challenge is to formulate a diet that gives the same production results (growth performance and carcass characteristics) with less nutritional input. The effect of reduced crude protein level on ammonia and odor emission has been investigated in several studies (Hayes et al., 2004; Le et al., 2009, 2008, 2007b; Leek et al., 2007) showing that reduced crude protein has a clear effect on ammonia emission, whereas the effect on odor is only significant when the crude protein level is reduced from a high level (21–22% crude protein) to a low level (13–16% crude protein) (Hayes et al., 2004; Leek et al., 2007). Most of the studies that have addressed the effect of reduced crude protein level on odor are based on dynamic olfactometry (CEN, 2003), where human panelists are used to estimate the odor concentration. Only a few studies have investigated the relation between crude protein level and emission of chemical odorants (Hobbs et al., 1998, 1996) and there is a lack in knowledge about how reduced crude protein level affects the individual chemical odorants measured in full-scale production facilities. In recent years, Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) has been applied for on-line measurements of chemical odorants from pig houses and in relation to abatement technologies (Feilberg et al., 2010; Hansen et al., 2012b; Liu et al., 2011). The PTR-MS has the advantage that it can measure most of the relevant chemical odorants found in air from pig houses, and furthermore, it can provide continuous data with high sensitivity and time resolution. The aim of the present study was to investigate how reduced crude protein affects the individual chemical odorants, ammonia and methane emitted from pig houses under realistic production conditions.
they were slaughtered after 44 days. The pigs were fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively (Table 1). The diets were formulated to be isoenergetic (8.1 MJ net energy kg 1 as fed) and to contain 7.4 g standardized ileal digestible (SID) lysine kg 1 as fed. The diets were optimized to supply SID indispensable amino acids in relation to SID lysine according to the Danish recommendations for pigs weighing 55–105 kg (Tybirk et al., 2012).
2. Materials and methods
2.3. Analytical methods
2.1. Pig houses
Ammonia in the exhaust air was measured during the whole experimental period, whereas chemical odorants were measured during the last 11 days of the experimental period. At the end of the experimental period, a representative sample of slurry (ca. 1 L) was collected from each pen. Temperature, relative humidity, and airflow rate in each pig house were recorded every two minutes (VengSystem A/S, Roslev, Denmark). Calibrated measuring fans were used to estimate the airflow rate (Reventa, Horstmar, Germany). The concentrations of ammonia, methane, and carbon dioxide were measured using a photoacoustic gas monitor INNOVA 1412 combined with a multipoint sampler INNOVA 1309 (LumaSense Technologies A/S, Ballerup, Denmark). The system with INNOVA 1412 and INNOVA 1309 was set up with one channel for the ventilation outlet in each pig house and one channel for the fresh air supply to the pig houses. Heated and insulated sample tubes of Teflon (outer diameter: 8 mm, inner diameter: 6 mm, Mikrolab A/S, Aarhus Denmark) for each channel were flushed continuously (ca. 7 L min 1) with a Capex L2 diaphragm Teflon pump (Charles Austen Pumps Ltd., Byfleet, UK). The sample line between the diaphragm pump and the
Two identical pig houses were used in the experiment. Each pig house contained two pens with space for 16 finishing pigs in each. The pens were designed with slatted floor in the entire area of the pen and two 60 cm deep slurry pits underneath each pen. The two slurry pits for each pen were placed on load cells (TEKFA A/S, Galten, Denmark) to record the weight of the slurry. The ventilation system in the pig houses was a negative pressure system with a diffuse ceiling inlet and one outlet mounted in the ceiling. The ventilation rate was controlled according to a set temperature at 20 1C (days 0–2), 19 1C (days 3–14), and 18.5 1C (days 15–44). The experiment took place at Aarhus University, Foulum, from April to May 2013, and the average outdoor temperature during this period was 13.074.5 1C. 2.2. Animals and diets Thirty-two cross-bred finishing pigs [Duroc (Danish Landrace Yorkshire)] with an initial body weight of ca. 55 kg were inserted in each pig house. The pigs were weighed at the beginning, after three weeks, and before
Table 1 Feed composition of a low-protein and a standard protein diet for finishing pigs containing 136 and 159 g crude protein kg 1, respectively. Itema
Low-protein
Standard
Wheat Barley Soy bean meal, toasted, dehulled Calcium carbonate Mono calcium phosphate Salt Vitamin-mineral premixb Phytasec L-Lysine HCL L-Threonine DL-Methionine L-Tryptophan L-Valine
42.1 45.0 9.8 1.27 0.684 0.390 0.200 0.020 0.338 0.131 0.052 0.017 0.010
48.4 32.3 16.7 1.26 0.587 0.392 0.200 0.020 0.134 0.037 0.022 0 0
g 100 g 1 diet. Trouw Nutrition Denmark A/S. Content per g premix: 2500 IU vitamin A, 500 IU vitamin D3, 23.4 IU vitamin E, 0.6 mg vitamin K3, 0.6 mg vitamin B1, 1.2 mg vitamin B2, 3 mg D-panthotenic acid, 6.4 mg niacin, 0.060 mg biotin, 21.3 mg α-tocopherol, 0.006 vitamin B12, 0.6 mg vitamin B6, 50 mg Fe (Fe(II) sulfate), 41.3 mg Cu (Cu(II) sulfate), 50 mg Zn (Zn(II) oxide), 13.9 mg Mn (Mn(II) oxide), 0.076 mg KI, and 0.075 mg Se (Se-selenite). c Natuphos 5000, 5641 FTU/g, BASF, 2300 Copenhagen, DK. a
b
120
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multipoint sampler was flushed for 10 s, and the measurement chamber in the photoacoustic gas monitor was flushed for 20 s during each measurement cycle. The sample integration time was set at 5 s, and compensation for water vapor interference and cross interference between gasses (ammonia, carbon dioxide, methane, and nitrous oxide) was applied. The photoacoustic gas monitor INNOVA 1412 was calibrated by LumaSense Technologies A/S prior to the measurements. Gas detection tubes (Kitagawa, KawasakiCity, Japan) were used to check the concentrations measured by the photoacoustic gas monitor. The multipoint sampler was used to switch between the channels, and during each measurement, ten measurement cycles (ca. 12.7 min) were performed by the photoacoustic gas monitor on each channel. The data signal was stable after six to seven cycles and the last three measurement cycles were averaged and used to estimate the concentrations of ammonia, methane, and carbon dioxide. The concentrations of ammonia and methane measured in the fresh air supply to the pig house were subtracted from the concentrations measured in the air from the pig houses. For each channel a result was recorded approximately every 64 min and in total 23 measurements of ammonia, methane, and carbon dioxide concentrations were estimated each day during the experimental period. Chemical odorants were measured by a high sensitivity PTR-MS (Ionicon Analytik, Innsbruck, Austria). The chemical odorants included hydrogen sulfide, methanethiol, dimethyl sulfide, trimethylamine, acetic acid, butanoic acid, propanoic acid, 4-methylphenol, indole, and skatole and were chosen since they are considered to be some of the most important odorants or some of the odorants that are found in the highest concentrations in air from pig houses (Hansen et al., 2012a). The PTR-MS was operated with standard drift tube conditions: voltage at 600 V, a pressure between 2.1 and 2.2 mbar, and a temperature of 60 1C. The inlet temperature was 60 1C. Single ion monitoring was used, and the sensitivity was estimated based on rate constants for proton transfer, the estimated drift tube residence time, and the mass specific transmission factors as described by de Gouw and Warneke (2007). The rate constants for proton transfer were calculated using the method described by Su and Chesnavich (1982). The humidity dependency of hydrogen sulfide (m/z 35) was corrected according to the method described by Feilberg et al. (2010). In order to perform compound assignment air samples were collected on sorbent tubes for thermal desorption and a gas chromatograph with a mass spectrometer (TD-GC/MS) and in Tedlar bags for a gas chromatograph with a sulfur chemiluminescence detector (GC–SCD). The use of TD-GC/MS and GC–SCD for compound assignment in air from pig houses has previously been described in detail (Feilberg et al., 2010; Hansen et al., 2012b). Heated and insulated Teflon tubes (outer diameter: 3.2 mm, inner diameter: 1.6 mm, Mikrolab A/S, Aarhus Denmark) from the ventilation outlet in the pig houses were connected to a heated switch box with a five-way PEEK valve (Bio-Chem Valve Incorporated, Boonton, New Jersey, USA). The PTR-MS was connected to the five-way PEEK valve, and the software of the PTR-MS controlled the switching between channels. In between measurements on the pig houses, instrumental background was measured
using a Supelpure™ HC filter (Supelco, Bellefonte, Pennsylvania, USA). Each hour, the PTR-MS measured 48 measurements cycles (12 min) on each channel. The last 20 measurement cycles were averaged and used to estimate the concentrations of the chemical odorants. The instrumental background was subtracted from the concentrations measured in the air from the pig houses. For each channel a result was recorded every 60 min and in total 24 measurements of each chemical odorant were estimated each day during the last 11 days of the experimental period. Slurry samples were analyzed for total nitrogen using the Kjeldahl method (Tecator™ Digestion System, Foss, Hillerød, Denmark) and ammoniacal nitrogen photometrically using a commercial kit using the indophenol blue method (Spectroquant Test kit no. 1.00683.0001, Merck KGaA, Darmstadt, Germany). The pH-value of the slurry samples were measured by a pH-meter (Metrohm AG, Herisau, Switzerland). The dry matter content in slurry was determined after drying at 105 1C for 24 h. 2.4. Data analysis The odor activity value (OAV) was estimated based on odor threshold values (OTV) as reported by Nagata (2003). The OAV for each odorant was calculated as OAV¼concentration (nL L 1)/OTV (nL L 1) and the total OAV was estimated as the sum of the OAV for the individual chemical odorants. The results were analyzed using linear models in SAS (Littel et al., 2002). Data analysis regarding ammonia, methane, and chemical odorants was performed with each pig house as the experimental unit. The emissions of ammonia, methane and odorants were estimated based on the measured concentrations and the average of the air flow rate for each hour. One experimental period was performed and the daily emission of ammonia, methane and odorant per pig and the daily average of the total OAV were used as response variables in the statistical analysis. The statistical model for ammonia emission (g pig 1 day 1), methane emission (g pig 1 day 1), chemical odorants (mg pig 1 day 1), climatic conditions, and total OAV included diet as a fixed effect. The statistical model for bodyweight, average daily growth, feed utilization, and carcass parameters included diet as a fixed effect and initial bodyweight as a covariate. The level of significance was defined as a P-value below 0.05. 3. Results The performance of the pigs in terms of bodyweight, average daily growth, feed utilization, and carcass parameters is presented in Table 2. There was no significant difference between the standard protein diet and the lowprotein diet regarding the performance of the pigs neither during the first or second half, nor during the overall six week period. The climatic conditions in the two pig houses applied for the two diets are presented in Table 3. The ventilation rate was based on a set temperature controlled by the ventilation system, and there was no significant difference between the indoor temperature and the ventilation rate in the two pig houses. There were significant
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Table 2 Start and end weight, average daily growth, feed utilization, carcass weight, and meat percentage for finishing pigs fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively. Itema
Standard
SEMb
P-value
Bodyweight, kg Start weight 55.5 End weight 102.0
55.5 101.6
– 1.0
– 0.74
Average daily growth, g day 1 Weeks 1–3 1019 Weeks 4–6 1096 Weeks 1–6 1058
1048 1063 1047
27 26 22
0.45 0.37 0.74
Feed utilization, Weeks 1–3 Weeks 4–6 Weeks 1–6 Carcass Weight, kg Meat, % a b
Low-protein
g g1 0.40 0.40 0.40
0.42 0.40 0.41
0.01 0.01 0.01
0.46 0.99 0.83
78.0 60.9
77.8 60.8
0.7 0.3
0.77 0.69
n ¼32. SEM: standard error mean.
Table 3 Average climatic conditions in pig houses in an experiment with finishing pigs (55–100 kg) fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively. a
Item
Low-protein
Standard
SEM
Temperature, 1C Relative humidity, % Ventilation rate, m3 h 1 Carbon dioxide, mL L 1
21.0 51.9 2255 1249
21.1 48.6 2063 1137
0.2 1.0 94 24
a b
n ¼44. SEM: standard error mean.
b
121
differences between the relative humidity and the carbon dioxide concentration for the two pig houses. The daily ammonia emission (g pig 1 day 1) is presented in Fig. 1, and it shows a clear distinction between the low and standard protein diets. There was a significant (P¼0.0002) difference between the ammonia emission for the two diets. The average ammonia emission was 6.0 g day 1 pig 1 for the low-protein diet and 7.8 g day 1 pig 1 for the standard protein diet. The total ammonia emission during the 44 day experimental period was 23% lower for the low-protein diet (263 g pig 1) compared to the standard protein diet (342 g pig 1). The emission of ammoniacal nitrogen relative to the ingested amount of nitrogen was 14% lower for the low-protein diet (4.3%) compared to the standard diet (5.0%). Slurry characteristics measured at the end of the experimental period are presented in Table 4. In general total nitrogen in slurry, ammoniacal nitrogen in slurry and pH were lower for the low-protein diet. The methane emission (g pig 1 day 1) is shown in Fig. 2 and demonstrates that the methane emission was increasing during the experimental period, but there was no significant (P¼0.21) difference between the two diets. The total methane emission during the 44 day experimental period was 181 g pig 1 for the lowprotein diet and 157 g pig 1 for the standard protein diet.
Table 4 Ingested nitrogen, total nitrogen, ammoniacal nitrogen, dry matter and pH measured in slurry at the end of an experiment with finishing pigs (55–100 kg) fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively. Itema
Low-protein Standard
P-value
Pen
1
0.63 0.02 0.15 0.002
2.58 Ingested nitrogen, kg pig 1 Total nitrogen in slurry, kg pig 1 0.92 Ammoniacal nitrogen in slurry, kg pig 1 0.71 Dry matter, % 10.3 pH in slurry 6.94 a
2
1
2
2.45 0.77 0.65 9.1 6.75
2.97 1.02 0.92 5.8 7.48
2.69 1.13 0.97 9.2 7.35
One slurry sample was collected from each pen.
Fig. 1. Ammonia emission from two houses with finishing pigs (55–100 kg) fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively.
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Fig. 2. Methane emission from two houses with finishing pigs (55–100 kg) fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively.
Table 5 Average emissions of chemical odorants (mg pig 1 day 1) and total odor activity value (OAV) in an experiment with finishing pigs (55–100 kg) fed a lowprotein diet or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively. Values in brackets are average of OAV for the individual chemical odorants. Itema d
Hydrogen sulfide m/z 35 Methanethiol m/z 49 Dimethyl sulfide m/z 63 Trimethylamine m/z 60 Acetic acid m/z 61 þ43 Propanoic acid m/z 75 þ57 Butanoic acid m/z 89þ71 4-methylphenol m/z 109 Indole m/z 118 Skatole m/z 132 Total OAV
OTVb
Low-protein
Standard
SEMc
P-value
0.41 0.07 3.0 0.032 6.0 5.7 0.19 0.054 0.30 0.0056
140 (118) 21 (86) 28 (1.7) 25 (154) 2581 (66) 759 (17) 558 (303) 118 (207) 4.5 (1.5) 2.0 (31) 986
143 (133) 16 (72) 24 (1.6) 29 (195) 2334 (66) 675 (17) 472 (281) 111 (215) 4.0 (1.5) 1.3 (23) 1005
6 2 2 1 110 28 21 7 0.3 0.3 31
0.73 0.08 0.12 0.03 0.13 0.05 0.008 0.53 0.30 0.11 0.68
a
n¼ 11. OTV: odor threshold values (nL L 1) reported by Nagata (2003). c SEM: standard error mean. d m/z: mass-to-charge ratio. b
Average emissions of ten chemical odorants (mg pig 1 day 1) in the ventilation air from the pig houses and the OAV estimated based on OTV are shown in Table 5. The emissions of propanoic acid and butanoic acid were significantly higher for the low-protein diet whereas the emission of trimethylamine was significantly lower. The emissions of the other chemical odorants were not significant different between the two diets. No significant difference was found between the total OAV for the two diets (Fig. 3). The estimated OAV for the individual chemical odorants demonstrate that the compounds that contributed the most to OAV were hydrogen sulfide, methanethiol, trimethylamine, butanoic acid, and 4-methylphenol (Table 5). 4. Discussion The main focus in the present study was the effect of reduced crude protein level on ammonia, methane, and
chemical odorants emitted from pig houses. However, if low-protein diets should be an alternative to other types of abatement technologies, it is important that the performance of the pigs in terms of growth, feed utilization, and carcass quality is unaffected compared to a standard protein diet for finishing pigs. In the present study, the average daily growth, feed utilization, and carcass meat percentage were not affected by feeding a low-protein diet (13.6% crude protein) compared to a standard protein diet (15.9% crude protein). The results are in line with previous studies (Ball et al., 2013; Canh et al., 1998) and confirm that low-protein diets supplemented with crystalline amino acids to provide sufficient concentrations of the indispensable amino acids can be fed to finishing pigs without impairing growth performance. Although there were significant differences in relative humidity and carbon dioxide concentration for the two pig houses, the climatic conditions were within the same
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Fig. 3. Odor activity value in air from two houses with finishing pigs (55–100 kg) fed a low-protein or a standard protein diet containing 136 and 159 g crude protein kg 1, respectively.
range and may only have a limited influence on the emission of ammonia, methane, and chemical odorants. The results demonstrate that the low-protein diet had a significantly lower ammonia emission compared to the standard protein diet. The slurry characteristic was measured at the end of the experimental period and demonstrated a lower total nitrogen and ammoniacal nitrogen content and pH-value in the slurry for the low-protein diet. These results confirm previous studies where it has been demonstrated that lowering the crude protein level results in lower nitrogen content in slurry, lower pH value in slurry and as a result, lower ammonia emission (Hayes et al., 2004; Le et al., 2009, 2007b; Leek et al., 2007). In the present study, the ammonia emission was 23% lower in the low-protein diet compared to the standard protein diet equivalent to 10% for every 10 g kg 1 reduction in dietary crude protein content. Previous studies that have demonstrated that 10 g kg 1 reduction in dietary crude protein content results in 8–13% reduction in ammonia emission (Canh et al., 1998; Hayes et al., 2004; Le et al., 2009, 2007b; Leek et al., 2007). The low-protein diet did not have an effect on the methane emission which is in accordance with previous studies (Le et al., 2009). This does not mean, however, that methane emissions cannot be affected by the level of dietary crude protein, because practical diets based on fiber-rich protein sources such as rape seed meal or sun flower cake often will result in increased protein concentrations along with increased fermentable fiber concentrations which are known to stimulate methane emission from pigs (Jørgensen et al., 2011). The effect of a low-protein diet on odor was evaluated based on the emission of ten chemical odorants and the estimated OAV using the odor threshold values (OTV) as reported by Nagata (2003). The chemical odorants included sulfur compounds, trimethylamine, carboxylic acids, 4-methylphenol, indole, and skatole. In general, there were higher emissions of most odorants for the low-protein diet except for trimethylamine where the emission was lower. In particular, the emissions of carboxylic acids were higher for the low-protein diet and this could be explained by the lower
pH-value in slurry. The lower emission of the nitrogen containing odorant trimethylamine for the low-protein diet could be explained by the lower nitrogen excretion in slurry for this diet. Despite the higher emission of most odorants for the low-protein diet there was no significant effect on the total OAV. In general, the compounds contributing the most to the OAV for both diets were hydrogen sulfide, methanethiol, trimethylamine, butanoic acid, and 4-methylphenol which are in accordance with other studies addressing chemical odorants in pig house air (Feilberg et al., 2010; Liu et al., 2011). Previous studies have demonstrated an effect of reduced crude protein level on odor measured by dynamic olfactometry (Hayes et al., 2004; Leek et al., 2007). In these studies, the crude protein level was reduced from a high level (21–22%) to a low level (13–16%) by decreasing the content of soya bean meal and supplementing with the same amount of indispensable crystalline amino acids. It is very likely that the pigs in the studies by Hayes et al. (2004) and Leek et al. (2007) were supplied with protein above the requirements in the high protein diets. A protein supply above the requirements of the pigs will cause a higher excretion of undigested protein and urinary nitrogen and sulfate to the slurry thus providing more substrates for production and emission of chemical odorants (Le et al., 2007a). In the studies by Le et al. (2009) and Hansen et al. (2007), the crude protein level was only reduced from 15–16% to 12–14% and optimized according to the requirements of the pigs, and in these studies, no effect was seen on odor measured by dynamic olfactometry. In the present study with a similar range in protein (15.9–13.6%), the diets were optimized according to the minimum requirements of all indispensible amino acids. Consequently, low-protein diets optimized according to the amino acid requirements of the pigs may result in differences in the emission of some chemical odorants, but the effect on the total OAV is insignificant. Particular indispensable amino acids are precursors of some of the important chemical odorants with low OTV (e.g. methionine: sulfur compounds and tryptophan: phenols and indoles) and more research is needed to investigate how these amino acids can be optimized to give an effect on odor from pig houses.
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5. Conclusions It can be concluded that feeding finishing pigs low crude protein diets supplemented with indispensable amino acids according to the requirements of the pigs is an effective method to lower the ammonia emission from pig houses without impairing growth performance and carcass characteristics whereas no effect was seen on the methane emission. Reduced crude protein had no effect on the total odor activity value (OAV), but more research is needed to investigate if the content of amino acids can be further optimized to lower odor from pig houses. Furthermore, it was demonstrated that proton-transfer-reaction mass spectrometry (PTR-MS) is a suitable method to investigate the effect of a given feeding strategy on the emission of chemical odorants from pig houses. Conflict of interest All authors do not have any actual or potential conflict of interest including any financial, personal or other relationships with other people or organizations within three years of beginning the submitted work that could inappropriately influence, or be perceived to influence, their work.
Acknowledgments The study was partly funded by European Community's Seventh Framework Programme (FP7/2007–2013) under the grant agreement no. 266018, the Danish Pig Levy Fund, and Aarhus University. References Aneja, V.P., Schlesinger, W.H., Erisman, J.W., 2009. Effects of agriculture upon the air quality and climate: research, policy, and regulations. Environ. Sci. Technol. 43, 4234–4240. Ball, M.E.E., Magowan, E., McCracken, K.J., Beattie, V.E., Bradford, R., Gordon, E.J., Robinson, M.J., Smyth, S., Henry, W., 2013. The effect of level of crude protein and available lysine on finishing pig performance, nitrogen balance and nutrient digestibility. Asian Australas. J. Anim. Sci. 26, 564–572. Canh, T.T., Aarnink, A.J.A., Schutte, J.B., Sutton, A., Langhout, D.J., Verstegen, M.W.A., 1998. Dietary protein affects nitrogen excretion and ammonia emission from slurry of growing-finishing pigs. Livest. Prod. Sci. 56, 181–191. de Gouw, J., Warneke, C., 2007. Measurements of volatile organic compounds in the earth's atmosphere using proton-transferreaction mass spectrometry. Mass Spectrom. Rev. 26, 223–257. CEN, 2003. Air quality – determination of odour concentration by dynamic ofactometry. EN 13725. European Committee for Standardization, Brussels, Belgium.
Feilberg, A., Liu, D., Adamsen, A.P.S., Hansen, M.J., Jonassen, K.E.N., 2010. Odorant emissions from intensive pig production measured by online proton-transfer-reaction mass spectrometry. Environ. Sci. Technol. 47, 5894–5900. Hansen, C.F., Sorensen, G., Lyngbye, M., 2007. Reduced diet crude protein level, benzoic acid and inulin reduced ammonia, but failed to influence odour emission from finishing pigs. Livest. Sci. 109, 228–231. Hansen, M.J., Adamsen, A.P.S., Pedersen, P., Feilberg, A., 2012a. Prediction of odor from pig production based on chemical odorants. J. Environ. Qual. 41, 436–443. Hansen, M.J., Liu, D., Guldberg, L.B., Feilberg, A., 2012b. Application of proton-transfer-reaction mass spectrometry to the assessment of odorant removal in a biological air cleaner for pig production. J. Agric. Food Chem. 60, 2599–2606. Hayes, E.T., Leek, A.B.G., Curran, T.P., Dodd, V.A., Carton, O.T., Beattie, V.E., O'Doherty, J.V., 2004. The influence of diet crude protein level on odour and ammonia emissions from finishing pig houses. Bioresour. Technol. 91, 309–315. Hobbs, P.J., Misselbrook, T.H., Pain, B.F., 1998. Emission rates of odorous compounds from pig slurries. J. Sci. Food Agric. 77, 341–348. Hobbs, P.J., Pain, B.F., Kay, R.M., Lee, P.A., 1996. Reduction of odorous compounds in fresh pig slurry by dietary control of crude protein. J. Sci. Food Agric. 71, 508–514. Jørgensen, H., Theil, P.K., Knudsen, K.E.B., 2011. Enteric Methane Emission from Pigs. In: Carayannis, E.G. (Ed.), Planet Earth 2011 - Global Warming Challenges and Opportunities for Policy and Practice, InTech Europe, Rijeka, Croatia, pp. 605–623. Kai, P., Pedersen, P., Jensen, J.E., Hansen, M.N., Sommer, S.G., 2008. A whole-farm assessment of the efficacy of slurry acidification in reducing ammonia emissions. Eur. J. Agron. 28, 148–154. Le, P.D., Aarnink, A.J.A., Jongbloed, A.W., 2009. Odour and ammonia emission from pig manure as affected by dietary crude protein level. Livest. Sci. 121, 267–274. Le, P.D., Aarnink, A.J.A., Jongbloed, A.W., Peet Schwering, C.M.C., Ogink, N.W.M., Verstegen, M.W.A., 2007a. Effects of crystalline amino acid supplementation to the diet on odor from pig manure. J. Anim. Sci. 85, 791–801. Le, P.D., Aarnink, A.J.A., Jongbloed, A.W., van der Peet-Schwering, C., Ogink, N.W.M., Verstegen, M.W.A., 2008. Interactive effects of dietary crude protein and fermentable carbohydrate levels on odour from pig manure. Livest. Sci. 114, 48–61. Le, R.D., Aarnink, A.J.A., Jongbloed, A.W., van der Peet-Schwering, C., Ogink, N.W.M., Verstegen, M.W.A., 2007b. Effects of dietary crude protein level on odour from pig manure. Animal 1, 734–744. Leek, A.B.G., Hayes, E.T., Curran, T.P., Callan, J.J., Beattie, V.E., Dodd, V.A., O’Doherty, J.V., 2007. The influence of manure composition on emissions of odour and ammonia from finishing pigs fed different concentrations of dietary crude protein. Bioresour. Technol. 98, 3431–3439. Littel, R.C., Stroup, W.W., Freund, R.J., 2002. SAS for Linear Models, 4th edition SAS Institute, Cary, NC. Liu, D., Feilberg, A., Adamsen, A.P.S., Jonassen, K.E.N., 2011. The effect of slurry treatment including ozonation on odorant reduction measured by in-situ PTR-MS. Atmos. Environ. 45, 3786–3793. Melse, R.W., Ogink, N.W.M., 2005. Air scrubbing techniques for ammonia and odor reduction at livestock operations: review of on-farm research in the Netherlands. Trans. ASAE 48, 2303–2313. Nagata, Y., 2003. Measurement of odor threshold by triangle odor bag method, Odor measurement review, Ministry of the Environment Goverment of Japan 118–127. Su, T., Chesnavich, W.J., 1982. Parametrization of the ion-polar molecule collision rate constant by trajectory calculations. J.Chem. Phys. 76, 5183–5185. Tybirk, P., Sloth, N.M., Jørgensen, L., 2012. Nutrient requirement standards, 17th edition Pig research Centre, Copenhagen, Denmark.