Gaseous emissions from group-housed gestating sows kept on deep litter and offered an ad libitum high-fibre diet

Agriculture, Ecosystems and Environment 132 (2009) 66–73

Contents lists available at ScienceDirect

Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee

Gaseous emissions from group-housed gestating sows kept on deep litter and offered an ad libitum high-fibre diet F.X. Philippe a, B. Canart a, M. Laitat b, J. Wavreille c, M. Vandenheede a, N. Bartiaux-Thill c, B. Nicks a, J.F. Cabaraux a,* a b c

Veterinary Ecology and Ethology Unit, Department of Animal Production, Baˆt. B43, Faculty of Veterinary Medicine, University of Lie`ge, 4000 Lie`ge, Belgium Department of Production Animals Clinic, Baˆt. B42, Faculty of Veterinary Medicine, University of Lie`ge, 4000 Lie`ge, Belgium Department of Animal Productions and Nutrition, Walloon Agricultural Research Centre, 5030 Gembloux, Belgium

A R T I C L E I N F O

A B S T R A C T

Article history: Received 27 November 2008 Received in revised form 16 February 2009 Accepted 25 February 2009 Available online 3 April 2009

Gaseous emissions from agriculture contribute to a number of environmental effects. Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are greenhouse gases taking part in the global problem of climate change. Ammonia (NH3) emissions are responsible of soil and water acidification and eutrophication and contribute also to indirect emissions of N2O. The objective of this study was to investigate the effects of a high-fibre diet offered ad libitum to gestating sows on gaseous emissions (NH3, N2O, CH4, CO2 and water vapour (H2O)). Four successive batches of 10 gestating sows were used for this trial. Each batch was divided into 2 homogeneous groups randomly allocated to a treatment: restricted conventional cereals based diet or high-fibre diet based on sugar beet pulp (42%). The groups were separately kept in two identical rooms equipped with a straw-bedded pen of 12.6 m2. For restricted sows, meals were provided once a day in individual feeding stalls available only during the feeding time. In both rooms, ventilation was automatically adapted to maintain a constant ambient temperature. The gas emissions were measured by infrared photoacoustic detection during 6 consecutive days at the 6th, 9th and 12th weeks of gestation. Sows performance (body weight gain, backfat thickness, number and weight of piglets) was not significantly different according to the diet. With sows offered high-fibre diet and compared to sows offered restricted diet, gaseous emissions were significantly greater for NH3 (9.64 g NH3-N d1 sow1 vs. 5.37 g NH3-N d1 sow1; P < 0.001), CH4 (17.20 g d1 sow1 vs. 15.21 g d1 sow1; P < 0.01), CO2 (3.00 kg d1 sow1 vs. 2.41 kg d1 sow1; P < 0.001) and H2O (4.71 kg d1 sow1 vs. 3.68 kg d1 sow1; P < 0.001) and significantly lower for N2O (0.97 g N2O-N d1 sow1 vs. 2.48 g N2O-N d1 sow1; P < 0.001) and CO2 equivalents (0.88 kg d1 sow1 vs. 1.55 kg d1 sow1; P < 0.001). In conclusion, the effects of high-fibre diet offered to gestating sows on deep litter on environment seem ambiguous with an increase of NH3 emissions but a decrease of N2O and CO2 equivalent emissions. ß 2009 Elsevier B.V. All rights reserved.

Keywords: Ammonia Deep litter Gestating sow Greenhouse gases High-fibre diet Sugar beet pulp

1. Introduction Usually, gestating sows are restrictedly fed to prevent excessive body weight gain and fat deposition (Noblet et al., 1990) that could lead to locomotive problems and peri-partum diseases (Dourmad et al., 1994). However, feed restriction causes sustained feeding motivation resulting in stereotypic behaviour and impairment of animal welfare (Broom, 1988; Terlouw et al., 1991). Several studies

* Corresponding author at: Veterinary Ecology and Ethology Unit, Department of Animal Production, Faculty of Veterinary Medicine, University of Lie`ge, Boulevard de Colonster, 20, Baˆt. B43, 4000 Lie`ge, Belgium. Tel.: +32 4 366 59 03; fax: +32 4 366 41 22. E-mail address: [email protected] (J.F. Cabaraux). 0167-8809/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2009.02.016

showed that providing high-fibre diet (HFD) to gestating sows may prevent occurrence of stereotypes by reducing feeding motivation without negative impacts on body weight and performance (Ramonet et al., 1999; Whittaker et al., 2000; Philippe et al., 2008). Sugar beet pulp (SBP) based diets are more effective on satiety and on reduction of voluntary feed intake than other fibre sources, probably in relation with their great water retention capacity (Brouns et al., 1995; Whittaker et al., 2000; van der PeetSchwering et al., 2004). So, HFD offered ad libitum is a suitable mean to combine animal welfare and performance but is linked to a greater feed cost but that could be compensated by a lower cost of the ad libitum feeding equipment (Steffens, 2005). Before recommending it, an environmental impact of this feeding system is important to be assessed, and particularly emissions of pollutant gases such as ammonia (NH3) and greenhouse gases (GHG). Indeed,

F.X. Philippe et al. / Agriculture, Ecosystems and Environment 132 (2009) 66–73

with fattening pigs in metabolism cages, providing HFD decreases NH3 emissions by reducing slurry pH and shifting nitrogen (N) excretion from urea to faecal proteins (Canh et al., 1997, 1998a,b; Lynch et al., 2007). At the opposite, enteric fermentations enhance methane (CH4) production (Le Goff et al., 2002; Aarnink and Verstegen, 2007). NH3-emissions contribute to soil and water acidification and eutrophication (Degre´ et al., 2001) and to indirect emissions of N2O (Intergovernmental Panel on Climate Change, 2006a). Furthermore, NH3 is well known as a toxic gas, irritating the respiratory tract at concentrations exceeding 15 ppm (Urbain, 1997; Banhazi et al., 2008). The most important GHG associated with livestock production are carbon dioxide (CO2), CH4 and nitrous oxide (N2O) (Pain, 1998; Degre´ et al., 2001; Nicks et al., 2004). N2O also contributes to the destruction of the ozone shield. CO2 contribution to the greenhouse effect is less important than that of CH4 and N2O, whose global warming potentials (GWP) over a 100-year period are, respectively, 21 and 310 times that of CO2 (Intergovernmental Panel on Climate Change, 2007). Moreover, one can estimate usually that CO2 production by livestock is compensated by CO2 consumption by photosynthesis of plants used as feed. However, experiments carried out with weaning and fattening pigs (Philippe et al., 2007a,b; Cabaraux et al., 2009) showed that CO2-emissions might differ only because of housing conditions while diet characteristics, feed intakes, animal performances and climate conditions were similar. Besides, CO2-production by animals and manure is an essential parameter for ventilation rate estimation using a mass balance method (Phillips et al., 1998; Pedersen et al., 1998). Water vapour (H2O) production may also be used for ventilation rate estimation (Pedersen et al., 1998). Further, determination of H2O emission is a key factor in specifying ventilation rates in order to avoid excessive indoor relative humidity in livestock buildings, especially with bedded systems (ICAE, 2002). Actually, few data are available about gaseous emissions from pigs on deep litter and still less with gestating sows offered a HFD. Therefore the aim of this study was to investigate the effects of HFD offered ad libitum to gestating sows kept on deep litter on gaseous emissions of NH3, N2O, CH4, CO2 and H2O. 2. Materials and methods The trials were carried out in experimental rooms located at the Faculty of Veterinary Medicine of Lie`ge University (Belgium). The ethical committee of our Institute approved the use and treatment of animals in this study. 2.1. Animals and feed Four successive batches of 10 Belgian Landrace gestating sows were used. They were divided into 2 homogeneous groups of 5 animals according to the parity, the body weight and the backfat thickness. Each group was randomly allocated to a treatment: restricted (R) or ad libitum (A) feeding regimes. Four weeks after service, the sows arrived in the experimental rooms and 15 days prior to giving birth, they moved to farrowing pens; the stay duration was thus 10 weeks for each batch. Each group was housed in a separated experimental room, fitted with a straw based litter pen. The R sows received a conventional gestation diet (8876 kJ net energy kg1) based on cereals (66% of wheat, wheat bran, barley and corn; Table 1). The amounts of daily feed were determined per batch as function of parity and backfat thickness. The feed was supplied once a day at 08:30 am and the sows were blocked in individual feeding stalls during the feeding time (1 h). The A sows had unrestricted access to a HFD (8034 kJ net energy kg1)

67

Table 1 Composition of diets (as-fed basis). Conventional diet, Restrictedly fed

Ingredient (%) Wheat Wheat bran Barley Corn Sugar beet pulp Chicory pulp Peas Rapeseed meal Palm kernel meal Sunflower meal Soybean pod and shell Citrus Sugar-beet molasses Mineral–vitamin complexa Pig fat Soybean oil Linseed oil L-Threonine Chemical composition (%) Moisture Crude protein Crude fat Crude ash Crude fibre Starch Sugar NSPb Acid Detergent Lignin Acid Detergent Fibre Neutral Detergent Fibre Net Energy (kJ kg1)

33.03 12.50 11.90 10.00 6.70 – 4.60 5.00 4.00 3.90 4.00 – – 2.44 1.73 – 0.20 –

10.4 13.2 4.4 5.1 8.2 37.4 3.4 26.1 2.4 11.5 21.8 8876

Sugar beet pulp based diet, Ad libitum fed

14.00 14.90 – – 42.37 7.00 – 7.00 – 8.00 – 3.00 1.50 1.19 – 0.90 0.10 0.04

10.6 12.9 2.7 6.0 13.6 13.5 6.5 47.8 2.6 18.8 37.0 8034

a Provided the following nutrients per 1 g of premix: lysine, 149.9 mg; thre´onine, 46.2 mg; methionine + cystine, 13.7 mg; vitamin A, 1200 IU; vitamin D3, 200 IU; vitamin E, 12.0 mg; riboflavin, 0.5 mg; niacinamide, 2.5 mg; pantothenic acid, 1.8 mg; choline, 60.6 mg; vitamin B12, 3 mg; folic acid, 0.3 mg; biotin, 0.05 mg; Cu, 1.5 mg; Mn, 5 mg; Fe, 15 mg; Zn, 10 mg; I, 0.2 mg; Se, 0.04 mg. b Non-starch polysaccharides, calculated as DM  (CP + crude fat + crude ash + starch + sugar).

based on SBP (42%). There was a drinker with ad libitum access in each pen. Individually, the sows were weighted and the backfat thickness was measured on P2-site by ultrasonography (Dourmad et al., 2001), at the beginning and at the end of the trial period. The feed and water intakes were recorded per group and per batch. Moreover, at birth, the number of piglets born alive and stillborn was also recorded. 2.2. Experimental rooms Two identical rooms with an area of 30.2 m2 and a volume of 103 m3 were arranged and equipped to house both one group of 5 gestating sows on a straw-based deep litter (Fig. 1). The room for R sows contained a straw-bedded pen of 12.6 m2 (2.5 m2 sow1) and 5 individual feeding stalls with front troughs and rear gates. These stalls were raised the height of 30 cm. These rear gates allowed preventing the access to the stalls outside of the feeding time. The room for A sows contained only a straw-bedded pen of 12.6 m2 (2.5 m2 sow1) with a one place feeding trough in the front side. In each pen, the whole wheat straw deep litter was realized with a 30 cm layer (150 kg) before the arrival of the animals. Thereafter, depending on the cleanliness of the litter and the sows, weighted supplementary amounts of straw were regularly provided in each pen. Between each batch, the pens were cleaned. The manures were weighted and sampled, and their dry matter,

F.X. Philippe et al. / Agriculture, Ecosystems and Environment 132 (2009) 66–73

68

Fig. 1. Plan of the experimental rooms.

organic matter and N-contents, analysed by the Kjeldahl method, were determined. Each room was ventilated with an exhaust fan (Fancom, Panningen, The Netherlands) and the ventilation rate was adapted automatically to maintain a constant ambient temperature by means of regulator FCTA (Fancom, Panningen, The Netherlands). Fresh air entered through an opening of 0.34 m2 which was connected to the service corridor of the building; the outside air was thereby preheated before entering the experimental rooms. The air temperatures of the experimental rooms, the corridor and the outside were measured automatically every hour. The ventilation rates were measured continuously and the hourly means were recorded with an Exavent apparatus (Fancom, Panningen, The Netherlands) with accuracy of 35 m3 h1, i.e. 1% of the maximum ventilation rate of the fan. 2.3. Gas emissions measurement The concentrations of gases in the experimental rooms and in the corridor supplying fresh air were measured by infrared photoacoustic detection with a Photoacoustic Multi-gas Monitor - INNOVA 1312 (LumaSense Technologies A/S, Ballerup, Denmark) equipped and calibrated for simultaneous measurement of NH3, N2O, CH4, CO2 and H2O. The lower levels of detection were 0.2 ppm for NH3, 0.03 ppm for N2O, 0.1 ppm for CH4 and 3.4 ppm for CO2, with an accuracy rate of 95%. The air in the experimental rooms was sampled just upstream of the exhaust fan and that one of the corridor, at 1 m from the air inlet. For each batch, the concentrations were measured 3 times (weeks 6, 9 and 12 of gestation) and for 6 consecutive days. The Multi-gas monitor was programmed by conducting a cycle of 3 measurements every hour, once every 20 min, the air being sampled successively in the 2 experimental rooms and the corridor. For each gas, the emissions (Egas) were calculated on an hourly basis and expressed in mg h1 using the following formula: Egas ¼ D  ðCi  CeÞ with D, the hourly mass flow (kg air h1); Ci and Ce, the concentrations of gas in the air of the room and corridor respectively (mg kg1 air). The mean emissions per day and per sow were calculated for each series of measurements. The GWP of the GHG, N2O and CH4 together, was expressed in CO2 equivalents (CO2eq) using the following equation: 1

CO2 eqðkg d

sow1 Þ ¼ 21 ECH4 þ 310EN2 O

with ECH4 and EN2 O being the emissions of CH4 and N2O (kg d1 sow1) respectively, and taking into account that the warming potentials of CH4 and N2O over a 100-year period are,

respectively, 21 and 310 times that of CO2 (Intergovernmental Panel on Climate Change, 2007). For EN2 O , indirect emissions from atmospheric deposition of N from NH3 on soils and water surfaces have been added to the direct emissions. The indirect emissions were calculated considering an emission of 0.01 kg N2O-N kg1 emitted NH3-N (Intergovernmental Panel on Climate Change, 2006b). Intergovernmental Panel on Climate Change (2006b) excluded CO2 emissions from this estimation because he estimated that CO2 production by livestock is compensated by CO2 consumption by photosynthesis of plants used as feed. 2.4. Nitrogen balance Nitrogen balance (g N day1 sow1) was calculated for each diet with inputs corresponding to N-straw and N-feed intakes and outputs corresponding to N-retention by sows, N content of manure and N from gaseous emissions of NH3, N2O and dinitrogen (N2). Straw protein content is 38.6 g kg1 (Sauvant et al., 2004). Nretention was estimated as a part of N-feed. According to Philippe et al. (2008), N-retention coefficient is similar despite different fibrous content. The coefficient of 15% was used and obtained by combining several data from literature (Dourmad et al., 1999; Fernandez et al., 1999; van der Peet-Schwering et al., 1999; Dourmad et al., 2001, 2008; Philippe et al., 2008). Nitrogen from N2 was estimated by the following equation: N2 -N ¼ ðN-straw þ N-feedÞ  ðN-retained þ N-manure þ NH3 -N þ N2 O-NÞ: 2.5. Statistical analyses For performance data recorded per sow, the differences between groups offered 2 different diets (R vs. A) were tested using analysis of variance with 2 criteria (proc GLM) (SAS, 2005): diet (1 df), batches (3 df) and interaction between diet and batches. For intake data, manure characteristics and N balance, recorded per pen, the differences were tested in the same way but with only diet (1 df) as criterion (proc GLM) (SAS, 2005). For room temperatures, ventilation rates and gas emissions, the combined data from the 4 batches were tested in the form of a mixed model for repeated measurements with 2 criteria (proc MIXED) (SAS, 2005): diet (1 df) and week of measurement (2 df), interaction between diet and week of measurement, with 144 (24 h  6 d) successive measurements per week. Residuals were normally distributed, with a null expectation (proc UNIVARIATE) (SAS, 2005). Correlation between successive measurements was modelled using a type 1-autoregressive structure.

F.X. Philippe et al. / Agriculture, Ecosystems and Environment 132 (2009) 66–73 Table 2 Air temperatures and ventilation rates of experimental rooms, service corridor and outside. Batches 1a Temperatures (˚C) R A Service corridor Outside

20.7  1.1 20.8  1.3 18.5  1.6 12.9  4.9

2a

3a

4a

Table 3 Animal performance as influenced by the diet -restricted conventional diet (R) or ad libitum high-fibre diet (A)- in gestating sows (mean  standard deviation between the 4 batches). R

1–4b

16.3  1.7 16.5  1.6 14.1  2.3 4.0  4.0

18.0  3.1 18.5  2.9 16.4  3.6 13.4  5.4

19.4  1.1 19.5  1.1 17.3  1.3 16.0  1.4

18.6  1.9 18.8  1.8 16.6  1.9 11.6  5.2

Ventilation rates (m3 h1 sow1) R 298  41 166  90 A 257  34 146  19

229  76 214  90

360  79 310  76

263  84 232  69

R: room with sows offered restricted conventional diet; A: room with sows offered ad libitum high-fibre diet. a Mean  standard deviation between mean values of the 3 periods of measurements. b Mean  standard deviation between the 4 batches.

3. Results 3.1. Climatic characteristics of the rooms The data about the air temperatures and the ventilation rates are shown in Table 2. The differences between experimental rooms were not statistically significant (P > 0.05). The average temperatures of the air were 18.7 8C in the experimental rooms, 16.6 8C in the service corridor and 11.6 8C outside. The mean ventilation rate was 248 m3 h1 per sow. The lower temperatures in experimental rooms during the second batch are due to cooler temperature of the outside and incoming air. Nevertheless, despite large variations of the outside temperatures between batches (4.0  4.0–16.0  1.4 8C), the temperatures in the experimental rooms stayed stable with a standard deviation between batches around 2 8C. This was due to the automatic adaptation of the ventilation rates to the inside temperatures. The slightly higher ventilation rates in the room with the R groups are explained by the lower thermal leakage of the walls, linked to the positioning of the rooms in the building. 3.2. Animal performance The average staying duration of batches was 70  5 d. The performance is presented in Table 3. There were no significant differences between groups for animal performance excepted for feed intakes (P < 0.05) and non-starch polysaccharides intakes (P < 0.001) which were both greater in the A group. The mean initial and final body weights were respectively 202 and 256 kg with an average daily gain of 727 g d1. The mean initial and final backfat thicknesses were respectively 14.6 and 21.0 mm. The net energy intakes were not significantly different between the 2 groups. On average, each sow gave birth to 13.2 piglets of which 11.8 were alive.

Number of sows Parity Initial body weight (kg) Final body weight (kg) Body weight gain (kg) Average daily gain (g d1) Feed intake (kg d1) N intake (g d1 sow1) Net energy intake (MJ d1 sow1) NSPa intake (g d1 sow1)

7.6  1.9 2.5  0.53

Table 5 presents the overall means of gas emissions and Fig. 2 shows the evolution of the gas emissions from the beginning to the

20 4.2  1.3 201.3  5.4 257.1  16.8 53.8  14.4 735.0  243.5 3.28b  0.31 67.6  6.4 26.32  2.48 1566d  148 8.7  2.3 2.6  0.47

Initial backfat thickness (mm) Final backfat thickness (mm) Backfat thickness gain (mm)

14.5  2.4 20.7  2.2 6.2  2.0

14.7  2.0 21.3  0.7 6.6  2.2

Number of born piglets Alive Stillborn Total

11.0  1.1 1.8  1.2 12.7  0.9

12.6  1.3 1.1  0.5 13.7  1.3

Within a row, values without a common superscript letter (a,b; c,d) differ at P < 0.05 and P < 0.001 respectively. a Non-starch polysaccharides.

end of the gestating period. The room with A sows produced per day significantly and proportionately 80% more NH3 (P < 0.001), 61% less N2O (P < 0.001), 13% more CH4 (P < 0.01), 43% less CO2eq (P < 0.001), 24% more CO2 (P < 0.001) and 28% more H2O (P < 0.001) than room with R sows. 3.5. Nitrogen balance Feed provides nearby 90% of N-inputs while N-straw is less important (Table 6). Whatever the diet, N-manure represents the main part of N-outputs but in greater proportion for A sows than R sows (67% vs. 45% of N-outputs). This higher N-manure is associated to lower N2 emissions (6% vs. 31% of N-outputs). 4. Discussion While feed intakes were higher for A sows (nearly 10%), net energy intakes were similar in the 2 groups. It shows that ad libitum-fed sows with a SBP-based diet can regulate their Table 4 Manure characteristics as influenced by the diet -restricted conventional diet (R) or ad libitum high-fibre diet (A)- in gestating sows (mean  standard deviation between the 4 batches). R 1

3.4. Gas emissions

A

20 4.4  1.3 202.9  5.3 255.4  8.0 52.5  8.6 719.5  160.0 2.99a  0.26 63.2  5.4 26.57  2.28 782c  67

Water intake per sow l d1 l kg1 ingested feed

3.3. Amounts and composition of manure The amount of supplied straw was alike for each group (1.33 kg d1 sow1) (Table 4). Although not significant, the collected manure was 20% greater in the A pen (P = 0.11). The dry matter and organic matter contents and the pH of the manure did not differ between groups and were respectively 30%, 24% and 8.28. The manure of A sows contained more total N than that one of R sows either expressed by kg manure (+32%, P = 0.08) or per day and per sow (+55%, P < 0.01).

69

1

Supplied straw (kg d sow ) Collected manure (kg d1 sow1) Manure–straw ratio Manure composition Dry matter (%) Organic matter (%) pH Total nitrogen g N kg1 manure g N d1 sow1 Ammonium nitrogen g N-NH4 kg1 manure g N-NH4 d1 sow1

A 1.33  0.22 3.93  0.96 2.93  0.50

1.34  0.23 4.75  1.27 3.51  0.63

28.78  4.98 24.13  4.36 8.24  0.13

30.67  2.49 25.14  2.40 8.31  0.01

8.49  1.36 32.44a  4.88

11.25  2.54 51.12b  7.04

1.73  0.80 6.46  2.90

3.06  1.68 14.19  8.34

Within a row, values without a common superscript letter (a,b) differ at P < 0.01.

F.X. Philippe et al. / Agriculture, Ecosystems and Environment 132 (2009) 66–73

70

Table 5 Gas emission factors (mean  standard deviation between the 4 batches) from gestating sows kept on deep litter and offered a restricted conventional diet (R) or ad libitum diet (A). Sow1 day1

Place1 year1

LU1 day1

Significance

NH3 (g N) R 5.37  1.15 A 9.64  3.71

1960  420 3519  1354

11.72  2.51 21.03  8.09

***

N2O (g N) R 2.48  1.12 A 0.96  0.22

905  409 350  80

5.41  2.44 2.09  0.48

***

5552  2949 6278  1825

33.19  17.63 37.52  10.91

**

566  190 321  77

3.38  1.13 1.92  0.46

***

CH4 (g) R A

15.21  8.08 17.20  5.00

CO2eq (kg) R 1.55  0.52 A 0.88  0.21 CO2 (kg) R A

2.41  0.26 3.00  0.26

880  95 1095  95

5.26  0.57 6.54  0.57

***

H2O (kg) R A

3.68  0.51 4.71  1.04

1343  186 1719  380

8.03  1.11 10.27  2.27

***

LU: livestock unit, equal to 500 kg body weight. ** P <0.01. *** P < 0.001.

consumption to recommended levels. As a consequence, no differences between the animal performance occurred, in agreement with previous results (Paboeuf et al., 2000; Guillemet et al., 2007). Impact of SBP on feeding motivation is principally thanks to great water retention capacity, physical bulk, higher eating time and delayed gastric emptying (Martin and Edwards, 1994; Ramonet et al., 1999, 2000a; Guerin et al., 2001; Rijnen et al., 2003). The voluntary intakes in the A group (about 3.3 kg d1 sow1) were lower than values cited in the literature with about 4.1 kg d1 for diets based on 45% (van der Peet-Schwering et al., 2004), 50% (Brouns et al., 1995) or 60% SBP (Whittaker et al., 2000). But, in addition to SBP properties, several other factors may influence feed intakes, like energy density of the diet (Dourmad, 1991). The collected manure (kg d1 sow1) and manure N content (g kg1 manure) were greater in the group with A sows in comparison with the group with R sows. Although not significant, these differences could be partially explained by higher feed, N, NSP and water intakes and lower digestibility of organic matter, and more particularly for the N (Le Goff et al., 2002; Masse et al., 2003; Serena et al., 2007). A difference between the manure pH was expected but not observed. Indeed, Canh et al. (1998a,b) observed a decrease of faeces pH from growing-finishing pigs offered SBP based diet with, as a consequence, a decrease of the slurry pH. These changes were explained by the increase of volatile fatty acids content in faeces, which are produced by microbial fermentations, these fermentations being enhanced by the presence of fibres in the diet. These observations on pH were not confirmed in the present trial where faeces and urine were collected as accumulated manure and not as slurry. It may be that the manure hides some differences existing at faeces and urine levels. Furthermore, NH3 emissions in the pen with A sows were greater than in the pen with R sows, which is in opposition with the finding of some authors who observed a decrease in NH3 emissions from slurry of growing-finishing pigs offered SBP based diet (Kreuzer et al., 1998; Canh et al., 1998a,b). This decrease was attributed to a lower slurry pH and the shift of a part of excreted N from urine (as urea, a very volatile form of N) to faeces (as protein form, a more stable form of N) (Canh et al., 1997). In the

Fig. 2. Gas emissions per day and per sow (mean  standard deviation between the 4 batches) from deep litter pens with gestating sows offered a restricted conventional diet (R) or an ad libitum high-fibre diet (A) according to the gestation week (white, grey and black bars for weeks 6, 9 and 12 respectively) Significance between week of measurement: NS: P > 0.05; *P < 0.05; **P < 0.01; ***P < 0.001).

F.X. Philippe et al. / Agriculture, Ecosystems and Environment 132 (2009) 66–73 Table 6 Nitrogen balance (g N day1 sow1) for gestating sows offered a restricted conventional diet (R) or ad libitum diet (A) (mean  standard deviation between the 4 batches). R N-inputs N-straw (estimated) N-feed N-outputs N-retention (estimated) N-manure NH3-N N2O-N N2-N (estimated)

A

8.2  1.3 (12%) 63.3  5.5 (88%) 9.5  0.8 32.4a  4.9 5.4c  1.2 2.5e  1.1 21.8a  4.1

(13%) (45%) (8%) (3%) (31%)

8.3  1.4 (11%) 67.7  6.4 (89%) 10.1  1.0 51.1b  7.0 9.6d  3.7 1.0f  0.2 4.3b  4.9

(13%) (67%) (13%) (1%) (6%)

Within a row, values without a common superscript letter (a,b; c,d; e,f) differ at P < 0.01, P = 0.07 and P < 0.05 respectively.

experiments of Canh et al. (1997, 1998a,b), the NH3 emissions were measured in laboratory conditions after mixing faeces and urine from fattening pigs, singly collected in metabolic cages. Thus, experimental conditions differ highly from current essay performed under field conditions with grouped sows kept on straw deep litter. Moreover, straw bedding may constitute a potential source of dietary fibre and consequently may reduce diet difference between groups. Besides, deep litters seem to emit more NH3 than slurry, as observed by Philippe et al. (2007a) and Cabaraux et al. (2009) with fattening and weaned pigs respectively. The manure characteristics may also explained difference in NH3emissions. Despite that the difference was not statistically significant, the higher ammonium-content of manure from A sows may contribute to higher NH3-emissions. Few data are available about N2O emissions by sows. The European Pollution Emission Register (2003) presents emissions factors varying from 1 to 5 g N2O d1 per sow. In the present trial, observed data were within the range but with significant greater values with R sows. The formation of N2O occurs during incomplete nitrification/denitrification processes that normally convert NH3 into N2 (Groenestein and Van Faassen, 1996). Nitrification needs aerobic conditions whereas denitrification needs anaerobic conditions. Nitrous oxide is mainly synthesized during denitrification, in case of presence of oxygen or low availability of degradable carbohydrates or both (Poth and Focht, 1985). During nitrification, N2O can also be synthesized where there is a lack of oxygen or a nitrite accumulation or both (Groenestein and Van Faassen, 1996; Veeken et al., 2002). In deep litters, both aerobic and anaerobic sites are present but heterogeneous conditions make N2O formation variable and explain variations observed by several authors (Hassouna et al., 2005; Philippe et al., 2007a,b). In the present trial, more N2O and, according to the N-balance, more N2 were emitted from room with R sows. Thus it seems that nitrification/denitrification process was in progress in the litter of R sows but failed to achieve full conversion of all the substrate into N2 with more N2O emitted as by-product. Therefore, favouring emissions of non-pollutant N2 may be unproductive if suboptimal conditions lead to higher N2O emissions with large warming potential. Methane originates both from digestive tract of animal and from manure. Enteric production is function of fibres intake, as measured in metabolic cages by several authors (Kirchgessner et al., 1991; Le Goff et al., 2002; Ramonet et al., 2000b). Le Goff et al. (2002) observed increasing enteric CH4 from 4 to 8 g d1 by increasing NDF-intake from 210 g to 435 g d1. The botanical origin and the solubility and fermentation properties of the fibres influence also the CH4 enteric production (Noblet et al., 2003). Production from manure comes from anaerobic degradation of

71

organic matter (Hellmann et al., 1997) and is mainly performed by mesophilic bacteria (25–40 8C) with an optimal pH of 7.0–7.2. The synthesis takes place mainly in the waste areas and is strongly influenced by its properties like litter aeration and dry matter content (Misselbrook et al., 2000). In the present experiment, CH4 emissions from A sows were 2 g d1 greater than these ones from R sows and could be explained by a greater enteric production of the sows offered HFD. Carbon dioxide from piggeries has two origins: mainly animal respiration but also manure. CO2 exhalation is estimated to about 2.8 kg d1 per sow, according to CIGR equations based on body weight (International Commission of Agricultural Engineering, 2002). This production is also function of metabolism and activity. Several studies concluded that HFD-fed sows were less active than conventional diet-fed sows (Bergeron et al., 2000; Paboeuf et al., 2000; van der Peet-Schwering et al., 2003; de Leeuw et al., 2005). This is associated with an increase of lying time related to reduction of feeding motivation and improved welfare. In this study, video recording of animal activity (unpublished data) showed that A sows could be considered as more active because of higher time feeding (twice as much than restricted-fed sows). Therefore, greater CO2 productions from room with A sows could be expected and was observed. Releases from manure have also two sources: hydrolysis of urea leading to NH3 and CO2 and anaerobic degradation of organic components (Aarnink et al., 1995; Ni et al., 1999). With R sows, production from manure seems to be neglected while with A sows, production could be estimated to about 0.2 kg. Some studies already showed negligible releases from manure (Anderson et al., 1987; Van‘t Klooster and Heitlager, 1994). Other studies with fattening pigs estimated emissions from slurry or litter between 0.2 and 0.5 kg CO2 per pig and per day (Ni et al., 1999; Jeppsson, 2000; Philippe et al., 2007a). Availability of degradable organic matter, temperature and oxygenation level in the litter may influence releases from manure (Aarnink et al., 1995; Ni et al., 1999). Due to the higher warming potential over a 100-year period of N2O compared to CH4 (310 vs. 21 times that of CO2) (Intergovernmental Panel on Climate Change, 2007), the CO2eq emissions were significantly lower with the A sows (43%) than with the R sows. Indeed, with the A sows, even if the CH4 and NH3 (used for the calculation of the indirect emissions of N2O) emissions were higher (+13% and +80% respectively), the differences in N2O emissions were more relevant (61%). Furthermore, the CO2 emissions were higher (+24%) with the A sows but not used for the CO2eq calculation (Intergovernmental Panel on Climate Change, 2006b). Like CH4 and CO2, H2O emissions have two origins: animals and manure. Evaporation by animals is function of body weight, heat production and ambient temperature (International Commission of Agricultural Engineering, 2002). With bedded systems, H2O emissions are enhanced by the high temperature met in litter due to fermentations (Nicks et al., 2004; Philippe et al., 2007a,b). By contrast, emissions from slatted floor systems are negligible (Philippe et al., 2007b). In the current experiment, the room with A sows emitted about 1 kg H2O more than the room with R sows what could be explained by the water intakes of A sows who drank about 1 l water more than the R sows. 5. Conclusion Feeding an ad libitum fibrous diet (42% SBP) to group-housed gestating sows kept on straw deep litter did not modify performance at short term. However, despite a good brand image for the consumer and a welfare improvement for the sows, environmental impacts of this system seem to be ambiguous. Compared with a conventional restrictedly fed diet, it is related to

72

F.X. Philippe et al. / Agriculture, Ecosystems and Environment 132 (2009) 66–73

more NH3 emissions, which, mainly, contribute to the acidification of soils and waters and eutrophication. About greenhouse gases, there is an increase of CO2 and CH4-emissions but a reduction of N2O-emissions. Considering global warming potential of each gas, this leads to a reduction of CO2eq emissions. Acknowledgment The research was financially supported by the Agriculture General Directorate of the Ministry of the Walloon Region of Belgium. References Aarnink, A.J.A., Verstegen, M.W.A., 2007. Nutrition, key factor to reduce environmental load from pig production. Livest. Sci. 109, 194–203. Aarnink, A.J.A., Keen, A., Metz, J.H.M., Speelman, L., Verstegen, M.W.A., 1995. Ammonia emission patterns during growing periods of pigs housed on partially slatted floors. J. Agric. Eng. Res. 62, 105–116. Anderson, G.A., Smith, R.J., Bundy, D.S., Hammond, E.G., 1987. Model to predict gaseous contaminants in swine confinement buildings. J. Agric. Eng. Res. 37, 235–253. Banhazi, T.M., Seedorf, J., Rutley, D.L., Pitchford, W.S., 2008. Identification of risk factors for sub-optimal housing conditions in Australian piggeries: Part 1 Study justification and design. J. Agric. Saf. Health 14, 5–20. Bergeron, R., Bolduc, J., Ramonet, Y., Meunier-Salau¨n, M.C., Robert, S., 2000. Feeding motivation and stereotypies in pregnant sows fed increasing levels of fibre and/ or food. Appl. Anim. Behav. Sci. 70, 27–40. Broom, D., 1988. Sow welfare indicators. Vet. Rec. 123, 235–1235. Brouns, F., Edwards, S.A., English, P.R., 1995. Influence of fibrous feed ingredients on voluntary intake of dry sows. Anim. Feed Sci. Technol. 54, 301–313. Cabaraux, J.F., Philippe, F.X., Laitat, M., Canart, B., Vandenheede, M., Nicks, B., 2009. Gaseous emissions from weaned pigs raised on different floor systems. Agric. Ecosyst. Environ. 130, 86–92. Canh, T.T., Verstegen, M.W.A., Aarnink, A.J.A., Schrama, J.W., 1997. Influence of dietary factors on nitrogen partitioning and composition of urine and feces of fattening pigs. J. Anim. Sci. 75, 700–706. Canh, T.T., Aarnink, A.J.A., Verstegen, M.W.A., Schrama, J.W., 1998a. Influence of dietary factors on the ph and ammonia emission of slurry from growingfinishing pigs. J. Anim. Sci. 76, 1123–1130. Canh, T.T., Sutton, A.L., Aarnink, A.J.A., Verstegen, M.W.A., Schrama, J.W., Bakker, G.C., 1998b. Dietary carbohydrates alter the fecal composition and ph and the ammonia emission from slurry of growing pigs. J. Anim. Sci. 76, 1887–1895. de Leeuw, J.A., Jongbloed, A.W., Spoolder, H.A.M., Verstegen, M.W.A., 2005. Effects of hindgut fermentation of non-starch polysaccharides on the stability of blood glucose and insulin levels and physical activity in empty sows. Livest. Prod. Sci. 96, 165–174. Degre´, A., Verhe`ve, D., Debouche, C., 2001. Emissions gazeuses en e´levage porcin et modes de re´duction: revue bibliographique. Biotechnol. Agron. Soc. Environ. 5, 135–143. Dourmad, J.Y., 1991. Effect of feeding level in the gilt during pregnancy on voluntary feed-intake during lactation and changes in body-composition during gestation and lactation. Livest. Prod. Sci. 27, 309–319. Dourmad, J.Y., Etienne, M., Prunier, A., Noblet, J., 1994. The effect of energy and protein-intake of sows on their longevity—a review. Livest. Prod. Sci. 40, 87–97. Dourmad, J.Y., Guingand, N., Latimier, P., Seve, B., 1999. Nitrogen and phosphorus consumption, utilisation and losses in pig production: France. Livest. Prod. Sci. 58, 199–211. Dourmad, J.Y., Etienne, M., Noblet, J., 2001. Measuring backfat depth in sows to optimize feeding strategy. INRA Prod. Anim. 14, 41–50. Dourmad, J.Y., Etienne, M., Valancogne, A., Dubois, S., van Milgen, J., Noblet, J., 2008. InraPorc: a model and decision support tool for the nutrition of sows. Anim. Feed Sci. Tech. 143, 372–386. European Pollutant Emission Register, 2003. Supporting document on determination of emissions from pig and poultry farms. http://eper.eea.europa.eu/eper/ guidance.asp. Accessed October 31, 2008. Fernandez, J.A., Poulsen, H.D., Boisen, S., Rom, H.B., 1999. Nitrogen and phosphorus consumption, utilisation and losses in pig production: Denmark. Livest. Prod. Sci. 58, 225–242. Groenestein, C.M., Van Faassen, H.G., 1996. Volatilization of ammonia, nitrous oxide and nitric oxide in deep-litter systems for fattening pigs. J. Agric. Eng. Res. 65, 269–274. Guerin, S., Ramonet, Y., Le Cloarec, J., Meunier-Salau¨n, M.C., Bourguet, P., Malbert, C.H., 2001. Changes in intragastric meal distribution are better predictors of gastric emptying rate in conscious pigs than are meal viscosity or dietary fibre concentration. Br. J. Nutr. 85, 343–350. Guillemet, R., Hamard, A., Quesnel, H., Pe`re, M.C., Etienne, M., Dourmad, J.Y., Meunier-Salau¨n, M.C., 2007. Dietary fibre for gestating sows: effects on parturition progress, behaviour, litter and sow performance. Animal 1, 872–880. Hassouna, M., Robin, P., Texier, C., Ramonet, Y., 2005. NH3, N2O, CH4 emissions from pig-on-litter systems. In: INRA (Ed.), Proceedings of the International Workshop on Green Pork Production. Paris, France, 1–3 February, pp. 121–122.

Hellmann, B., Zelles, L., Palojarvi, A., Bai, Q.Y., 1997. Emission of climate-relevant trace gases and succession of microbial communities during open-window composting. Appl. Environ. Microb. 63, 1011–1018. Intergovernmental Panel on Climate Change, 2006a. 2006 IPCC Guidelines for national greenhouse gas inventories. In: Eggleston, H.S., Buendia, L., Miwa, K., Ngara, T., Tanabe, K. (Eds.), Volume 1: General Guidance and Reporting. Prepared by the National Greenhouse Gas Inventories Programme. Institute for Global Environmental Strategies, Hayama, Japan. Intergovernmental Panel on Climate Change, 2006b. 2006 IPCC Guidelines for National Greenhouse Gas Inventories. In: Eggleston, H.S., Buendia, L., Miwa, K., Ngara, T., Tanabe, K. (Eds.), Volume 4: Agriculture, Forestry and Other Land Use. Prepared by the National Greenhouse Gas Inventories Programme. Institute for Global Environmental Strategies, Hayama, Japan. Intergovernmental Panel on Climate Change, 2007. In: Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M., Miller, H.L. (Eds.), Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. International Commission of Agricultural Engineering, 2002. Fourth Report of Working Group on Climatization of Animal Houses. Heat and Moisture Production at Animal and House Levels. Danish Institute of Agricultural Sciences, Horsens, Denmark. Jeppsson, K.H., 2000. Carbon dioxide emission and water evaporation from deep litter systems. J. Agric. Eng. Res. 77, 429–440. Kreuzer, M., Machmuller, A., Gerdemann, M.M., Hanneken, H., Wittmann, M., 1998. Reduction of gaseous nitrogen loss from pig manure using feeds rich in easilyfermentable non-starch polysaccharides. Anim. Feed Sci. Technol. 73, 1–19. Kirchgessner, M., Kreuzer, M., Muller, H.L., Windisch, W., 1991. Release of methane and of carbon-dioxide by the pig. Agribiol. Res. 44, 103–113. Le Goff, G., Le Groumellec, L., Van Milgen, J., Dubois, S., Noblet, J., 2002. Digestibility and metabolic utilisation of dietary energy in adult sows: influence of addition and origin of dietary fibre. Br. J. Nutr. 87, 325–335. Lynch, P.B., Bertholot, S., Verlait, F., Lawlor, P.G., 2007. Measuring changes in physical size and predicting weight of sows during gestation. Animal 1, 1335–1343. Martin, J.E., Edwards, S.A., 1994. Feeding behaviour of outdoor sows—the effects of diet quantity and type. Appl. Anim. Behav. Sci. 41, 63–74. Masse, D.I., Croteau, F., Masse, L., Bergeron, R., Bolduc, J., Ramonet, Y., MeunierSalau¨n, M.C., Robert, S., 2003. Effect of dietary fiber incorporation on the characteristics of pregnant sows slurry. Can. Biosyst. Eng. 45 (6), 12 7-6. Misselbrook, T.H., Van der Weerden, T.J., Pain, B.F., Jarvis, S.C., Chambers, B.J., Smith, K.A., Phillips, V.R., Demmers, T.G.M., 2000. Ammonia emission factors for UK agriculture. Atmos. Environ. 34, 871–880. Ni, J.K., Vinckier, C., Hendriks, J., Coenegrachts, J., 1999. Production of carbon dioxide in a fattening pig house under field conditions. II. Release from manure. Atmos. Envrion. 33, 3697–3703. Nicks, B., Laitat, M., Farnir, F., Vandenheede, M., Desiron, A., Verhaeghe, C., Canart, B., 2004. Gaseous emissions from deep-litter pens with straw or sawdust for fattening pigs. Anim. Sci. 78, 99–107. Noblet, J., Dourmad, J.Y., Etienne, M., 1990. Energy utilization in pregnant and lactating sows: modeling of energy requirements. J. Anim. Sci. 68, 562–572. Noblet, J., Bontems, V., Tran, G., 2003. Estimation of the energy value of compound feeds for pigs. INRA Prod. Anim. 16, 197–210. Paboeuf, F., Ramonet, Y., Corlouer, A., Dourmad, J.Y., Cariolet, R., Meunier-Salau¨n, M.C., 2000. Impact de l’incorporation de fibres dans un re´gime de gestation sur les performances zootechniques et le comportement des truies. Journees de la Recherche Porcine en France 32, 105–113. Pain, B., 1998. Gaseous pollutants from organic waste use in agriculture. In: Martinez, J., Maudet, M.N. (Eds.), Proceedings of the 8th International Conference of the FAO ESCORENA Network on Recycling of Agricultural, Municipal and Industrial Residues in Agriculture. Cemagref, Rennes, pp. 233–246. Pedersen, S., Takai, H., Johnsen, J.O., Metz, J.H.M., Koerkamp, P., Uenk, G.H., Phillips, V.R., Holden, M.R., Sneath, R.W., Short, J.L., White, R.P., Hartung, J., Seedorf, J., Schroder, M., Linkert, K.H., Wathes, C.M., 1998. A comparison of three balance methods for calculating ventilation rates in livestock buildings. J. Agric. Eng. Res. 70, 25–37. Philippe, F.X., Laitat, M., Canart, B., Vandenheede, M., Nicks, B., 2007a. Comparison of ammonia and greenhouse gas emissions during the fattening of pigs, kept either on fully slatted floor or on deep litter. Livest. Sci. 111, 144–152. Philippe, F.X., Laitat, M., Canart, B., Vandenheede, M., Nicks, B., 2007b. Gaseous emissions during the fattening of pigs kept either on fully slatted floors or on straw flow. Animal 1, 1515–1523. Philippe, F.X., Remience, V., Dourmad, J.Y., Cabaraux, J.F., Vandenheede, M., Nicks, B., 2008. Les fibres dans l’alimentation des truies gestantes. INRA Prod. Anim. 21, 277–290. Phillips, V.R., Holden, M.R., Sneath, R.W., Short, J.L., White, R.P., Hartung, J., Seedorf, J., Schroder, M., Linkert, K.H., Pedersen, S., Takai, H., Johnsen, J.O., Koerkamp, P., Uenk, G.H., Scholtens, R., Metz, J.H.M., Wathes, C.M., 1998. The development of robust methods for measuring concentrations and emission rates of gaseous and particulate air pollutants in livestock buildings. J. Agric. Eng. Res. 70, 11–24. Poth, M., Focht, D.D., 1985. N-15 kinetic-analysis of N2O production by nitrosomonas-europaea—an examination of nitrifier denitrification. Appl. Environ. Microbiol. 49, 1134–1141. Ramonet, Y., Meunier-Salau¨n, M.C., Dourmad, J.Y., 1999. High-fiber diets in pregnant sows: digestive utilization and effects on the behavior of the animals. J. Anim. Sci. 77, 591–599.

F.X. Philippe et al. / Agriculture, Ecosystems and Environment 132 (2009) 66–73 Ramonet, Y., Robert, S., Aumaitre, A., Dourmad, J.Y., Meunier-Salau¨n, M.C., 2000a. Influence of the nature of dietary fibre on digestive utilization, some metabolite and hormone profiles and the behaviour of pregnant sows. Anim. Sci. 70, 275–286. Ramonet, Y., van Milgen, J., Dourmad, J.Y., Dubois, S., Meunier-Salau¨n, M.C., Noblet, J., 2000b. The effect of dietary fibre on energy utilisation and partitioning of heat production over pregnancy in sows. Br. J. Nutr. 84, 85–94. Rijnen, M.M.J.A., Verstegen, M.W.A., Heetkamp, M.J.W., Haaksma, J., Schrama, J.W., 2003. Effects of dietary fermentable carbohydrates on behavior and heat production in group-housed sows. J. Anim. Sci. 81, 182–190. SAS, 2005. SAS/STAT User’s Guide, Version, 9.1. SAS Institute Inc., Cary, North Caroline, USA. Sauvant, D., Perez, J.M., Tran, G., 2004. Tables of Composition and Nutritional Value of Feed Materials: Pigs, Poultry, Cattle, Sheep, Goats, Rabbits Horses and Fish, 2nd ed. INRA Editions, Paris, France. Serena, A., Hedemann, M.S., Knudsen, K.E.B., 2007. Feeding high fibre diets changes luminal environment and morphology in the intestine of sows. Livest. Sci. 109, 115–117. Steffens, R., 2005. Gesundheit und leistung von sauen nach unterschiedlicher fu¨tterung in der tra¨chtigkeit (u¨bliches alleinfutter restriktiv im vergleich zu trockenschnitzelreichem mischfutter ad libitum). DVM thesis. Tiera¨rztliche Hochschule, Hannover, Germany. Terlouw, E.M.C., Lawrence, A.B., Illius, A.W., 1991. Influences of feeding level and physical restriction on development of stereotypies in sows. Anim. Behav. 42, 981–991.

73

Urbain, B., 1997. Toxicite´ de l’ammoniac pour l’appareil respiratoire du porc. PhD Thesis. University of Lie`ge, Belgium. van der Peet-Schwering, C.M.C., Jongbloed, A.W., Aarnink, A.J.A., 1999. Nitrogen and phosphorus consumption, utilisation and losses in pig production: The Netherlands. Livest. Prod. Sci. 58, 213–224. van der Peet-Schwering, C.M.C., Spoolder, H.A.M., Kemp, B., Binnendijk, G.P., den Hartog, L.A., Verstegen, M.W.A., 2003. Development of stereotypic behaviour in sows fed a starch diet or a non-starch polysaccharide diet during gestation and lactation over two parities. Appl. Anim. Behav. Sci. 83, 81–97. van der Peet-Schwering, C.M.C., Kemp, B., Plagge, J.G., Vereijken, P.F.G., den Hartog, L.A., Spoolder, H.A.M., Verstegen, M.W.A., 2004. Performance and individual feed intake characteristics of group-housed sows fed a nonstarch polysaccharides diet ad libitum during gestation over three parities. J. Anim. Sci. 82, 1246– 1257. Van‘t Klooster, C.E., Heitlager, B.P., 1994. Determination of minimum ventilation rate in pig houses with natural ventilation based on carbon dioxide balance. J. Agric. Eng. Res. 57, 279–287. Veeken, A., de Wilde, V., Hamelers, B., 2002. Passively aerated composting of straw-rich pig manure: effect of compost bed porosity. Compost Sci. Util. 10, 114–128. Whittaker, X., Edwards, S.A., Spoolder, H.A.M., Corning, S., Lawrence, A.B., 2000. The performance of group-housed sows offered a high fibre diet ad libitum. Anim. Sci. 70, 85–93.