TY - JOUR
AU - Powers, W.
AB - Abstract The objective of this study was to test the hypothesis that reducing dietary CP by 1.5% and supplementing crystalline AA (CAA) to meet the standardized ileal digestible (SID) AA requirements for growing and finishing pigs decreases air emissions of ammonia (NH3), nitrous oxide (N2O), and carbon dioxide (CO2) compared with an industry standard diet, without reducing growth performance. Seventy-two pigs were allocated to 12 rooms (6 pigs per room) and 2 diets (6 rooms per diet) formulated according to a 5-phase feeding program across the grow-finish period (107 d total). The diets consisted of a standard diet containing 18.5 to 12.2% CP or a reduced CP diet containing 17.5 to 11.0% CP + CAA over the course of the 5-phase feeding program. Gases (NH3, N2O, hydrogen sulfide, methane, nonmethane total hydrocarbon, and CO2) and ventilation rates were measured continuously from the rooms. Compared with standard diet, ADG and feed conversion of pigs fed reduced CP + CAA diets did not differ (2.7 kg gain/d and 0.37 kg gain/kg feed, respectively). Compared with standard diet, feeding reduced CP + CAA diets decreased (P < 0.01) NH3 emissions by 46% over the 107-d period (5.4 and 2.9 g · pig–1 · d–1, respectively). Change in NH3 emissions for each percentage unit reduction in dietary CP concentration corresponded with 47.9, 53.2, 26.8, 26.5, and 51.6% during Phases 1 through 5, respectively. Emissions of other gases did not differ between diets. Feeding reduced CP diets formulated based on SID AA requirements for grow-finisher swine is effective in reducing NH3 emissions from housing compared with recent industry formulations and does not impact growth performances. INTRODUCTION Feeding reduced CP diets with crystalline AA (CAA) supplementation reduces ammonia (NH3) emissions without negative impact on animal performance (Canh et al., 1997; Hayes et al., 2004). Powers et al. (2007) reported NH3 emissions reductions by 22 and 48% when pigs were fed reduced CP diets with 3 CAA (i.e., Lys, Thr, and Met) or 5 CAA (i.e., Lys, Thr, Trp, Met, and Ile), respectively, compared with a diet containing only supplemental crystalline L-Lys. These earlier studies however were based on the National Research Council (1998) true ileal digestible AA requirements. Very limited data exists on the impact of feeding reduced CP diets on emissions of other gases. One study reported 27.3 and 3.8% decrease in methane (CH4) and carbon dioxide (CO2) and (Atakora et al., 2003) and up to 16.5% in CO2 equivalents (CO2eq; Atakora et al., 2002). The literature does not report on the potential impact of reduced CP diets on emissions of nitrous oxide (N2O), the strongest greenhouse gas (GHG) that would originate from agricultural sources. Dietary N is a precursor to N2O emissions from manure, hence the potential benefits of feeding reduced CP diets on N2O emissions represents a knowledge gap. Furthermore, air emission data from pigs fed diets based on standardized ileal digestible (SID) AA requirements (National Research Council, 2012) are not available. We hypothesized that reducing CP by 1.5% and supplementing CAA to meet the SID AA requirements (National Research Council, 2012) for growing and finishing pigs decreases air emissions of NH3, N2O, and CO2 compared with an industry standard diet, without reducing growth performance. The objectives of the study were to measure air emissions and growth performance of pigs fed reduced CP and standard industry diets across the entire growing and finishing periods. MATERIALS AND METHODS Experimental Facility, Animals, and Management The experiment was conducted at the Animal Air Quality Research Facility (AAQRF) at Michigan State University following approval from the Institutional Animal Care and Use Committee (Protocol No. 06/12-109-00). At the beginning of the experiment, 72 crossbred barrows with an initial body weight of 21.6 kg were randomly allocated to 12 rooms (2.59 m wide × 3.97 m long × 2.14 m high) with 6 pigs in each room (Table 1). Pigs were confined in a raised-deck pen (1.5 m wide × 3.1 m long) with a plastic-coated woven wire floor. At the end of Phase 2, one pig was removed from each room to maintain floor-space allowance. Floor-space allowance was in line with commercial practice at 0.775 m2/pig and 0.930 m2/pig for Phases 1 and 2 and Phases 3 through 5, respectively. Each room was individually heated and cooled, using only fresh, outside air, and exhausting all of the air to the outside (no recycling). Room temperatures were adjusted weekly to remain within the thermoneutral comfort zone of the animals, based on the average pig BW within the room (Table 1). Room temperature was controlled using ventilation rate of a conditioned air plenum. Fluorescent lighting was programmed to turn on at 0600 h and turn off at 2000 h. All pigs in each room were weighed as a group weekly and at the start and end of each phase. Pigs were provided ad libitum access to feed and water. Swinging nipple waterers were located above the middle of the pens and a feeder was located at one end. Daily feed was added to feeders and recorded, and feeder height was adjusted on a regular basis to prevent feed wastage. Feeders were cleaned and the remaining feed mass was recorded weekly and at the start and end of each phase. Diet samples were collected daily and pooled at the end of each feeding phase for analyses. Table 1. Experimental animal and management1 Experimental conditions  Phase 1  Phase 2  Phase 3  Phase 4  Phase 5  Phase length, d  33  25  19  21  9  Starting/ending pig age, d  60–92  93–117  118–136  137–157  158–166  Pigs, No./room  6  6  5  5  5  Floor-space allowance, m2/pig  0.775  0.775  0.930  0.930  0.930  Starting average BW, kg  21  52  75  94  113  Average room temperature, °C  22.7  21.4  20.2  20.3  20.0  Average room relative humidity, %  58.8  55.7  55.5  40.6  34.8  Lighting schedules, h  0600–2000  Feed and water routine check, h  0500 and 1800  BW collection frequency  Weekly and at each phase start and end  Manure sampling  Semiweekly and at each phase end  Experimental conditions  Phase 1  Phase 2  Phase 3  Phase 4  Phase 5  Phase length, d  33  25  19  21  9  Starting/ending pig age, d  60–92  93–117  118–136  137–157  158–166  Pigs, No./room  6  6  5  5  5  Floor-space allowance, m2/pig  0.775  0.775  0.930  0.930  0.930  Starting average BW, kg  21  52  75  94  113  Average room temperature, °C  22.7  21.4  20.2  20.3  20.0  Average room relative humidity, %  58.8  55.7  55.5  40.6  34.8  Lighting schedules, h  0600–2000  Feed and water routine check, h  0500 and 1800  BW collection frequency  Weekly and at each phase start and end  Manure sampling  Semiweekly and at each phase end  1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 157 d; initial BW = 94 kg; Phase 5 from pig age 158 to 166 d; initial BW = 113 kg. View Large Table 1. Experimental animal and management1 Experimental conditions  Phase 1  Phase 2  Phase 3  Phase 4  Phase 5  Phase length, d  33  25  19  21  9  Starting/ending pig age, d  60–92  93–117  118–136  137–157  158–166  Pigs, No./room  6  6  5  5  5  Floor-space allowance, m2/pig  0.775  0.775  0.930  0.930  0.930  Starting average BW, kg  21  52  75  94  113  Average room temperature, °C  22.7  21.4  20.2  20.3  20.0  Average room relative humidity, %  58.8  55.7  55.5  40.6  34.8  Lighting schedules, h  0600–2000  Feed and water routine check, h  0500 and 1800  BW collection frequency  Weekly and at each phase start and end  Manure sampling  Semiweekly and at each phase end  Experimental conditions  Phase 1  Phase 2  Phase 3  Phase 4  Phase 5  Phase length, d  33  25  19  21  9  Starting/ending pig age, d  60–92  93–117  118–136  137–157  158–166  Pigs, No./room  6  6  5  5  5  Floor-space allowance, m2/pig  0.775  0.775  0.930  0.930  0.930  Starting average BW, kg  21  52  75  94  113  Average room temperature, °C  22.7  21.4  20.2  20.3  20.0  Average room relative humidity, %  58.8  55.7  55.5  40.6  34.8  Lighting schedules, h  0600–2000  Feed and water routine check, h  0500 and 1800  BW collection frequency  Weekly and at each phase start and end  Manure sampling  Semiweekly and at each phase end  1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 157 d; initial BW = 94 kg; Phase 5 from pig age 158 to 166 d; initial BW = 113 kg. View Large Galvanized steel manure collection pans (1.52 m wide × 3.05 m long × 0.2 m high) were placed underneath the flooring of each pen to collect urine, feces, and wasted feed and water. The manure pans were cleaned completely at the start of each phase. In addition, collection pans were partially cleaned semiweekly within each phase to prevent overflow of the pans. Before removal, manure was mixed thoroughly in the pan. Removed manure was weighed and mass recorded. A homogenous subsample was collected each time during manure cleaning and stored at –20°C. All subsamples were thawed and combined into a composite phase sample for compositional analyses. Diets Ingredient and nutrient composition of experimental diets are presented in Table 2. Diets were formulated based on SID AA requirements National Research Council (2012) over a 5- phase feeding program (Growing Phases 1 and 2, and Finishing Phases 1, 2, and 3, the latter from here on referred to as Phases 3, 4, and 5). Half of 12 rooms were randomly selected to receive 1 of 2 diets (standard CP diet or reduced CP diet), resulting in 6 replicates (rooms) per treatment. Diets within phases were formulated to be isocaloric on a SID Lys/ME basis. Across all 5 phases, all standard diets were formulated to meet SID AA requirement using supplemental crystalline L-Lys · HCl and L-Thr, and also sulfur AA for Growing Phases 1 (L-Met + L-Cys) and 2 (L-Met). Within each phase, a reduced CP diet was formulated by lowering the total CP concentration of the standard diet by 8.3% units in Phases 1 and 2, and by 9, 11, and 13% units in Phases 3, 4, and 5, respectively. Hence, for the reduced CP diets, additional L-Met + L-Cys were supplemented across all phases, L-Trp was supplemented for Phase 1 only, and L-Ile and L-Val were supplemented for Phase 5. Within phases, standard and reduced CP diets were formulated to contain the same concentration of standardized total tract digestible (STTD) P. Diets were analyzed for N, Ca, P, and AA concentrations (Table 2) before feeding of each phase. The analyzed N and calculated (N × 6.25) were very close with less than 1.5% difference, except for Phase 1 reduced CP diet with a difference of 4.5%, which is within an acceptable limit of 5%. For Phase 1 standard and reduced CP diets, a formulation error in inclusion rates of limestone and monocalcium phosphate resulted in greater P than Ca concentration (calculated and analyzed). However, the calculated concentration of P on a STTD basis was well within acceptable range of dietary intake, with a Ca:STTD P of 0.64:0.46. Table 2. Ingredient and nutrient composition of standard CP and reduced CP diets (dry matter basis)   Phase1 1  Phase 2  Phase 3  Phase 4  Phase 5  Ingredient  Standard  Reduced  Standard  Reduced  Standard  Reduced  Standard  Reduced  Standard  Reduced  Corn, yellow dent  66.88  70.91  69.20  72.91  71.08  74.56  72.89  76.74  74.53  78.93  Soybean meal, dehull, sol. extr  24.51  20.20  20.39  16.47  16.29  12.41  12.18  7.83  8.10  3.31  Wheat middlings  5.00  5.00  7.50  7.50  10.00  10.00  12.50  12.50  15.00  15.00  Limestone  0.80  0.81  1.16  1.18  1.05  1.08  1.08  1.08  1.02  1.05  Calcium phosphate (monocalcium)  1.51  1.54  0.50  0.55  0.43  0.48  0.27  0.34  0.25  0.29  Soybean oil  0.50  0.50  0.51  0.45  0.43  0.55  0.33  0.52  0.28  0.27  Sodium chloride  0.30  0.30  0.30  0.30  0.30  0.30  0.30  0.30  0.30  0.30  Trace vitamin mix2  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  Trace mineral mix3  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  L-Lysine·HCl  0.22  0.36  0.20  0.32  0.19  0.31  0.21  0.35  0.26  0.41  L-Threonine  0.04  0.10  0.03  0.08  0.03  0.09  0.04  0.10  0.06  0.13  DL-Methionine  0.02  0.04  0.01  0.03  –  0.01  –  0.01  –  0.01  L-Cysteine  0.02  0.03  –  0.01  –  0.01  –  0.01  –  0.01  L-Tryptophan  –  0.01  –  –  –  –  –  –  –  –  L-Isoleucine  –  –  –  –  –  –  –  –  –  0.04  L-Valine  –  –  –  –  –  –  –  –  –  0.02  Analyzed composition, %DM unless otherwise noted      CP  18.46  17.48  16.51  15.55  15.16  13.90  13.99  12.34  12.23  10.97      DM  88.1  87.8  89  88.9  88.8  88.5  88.2  88.3  88.3  88.3      Ca  0.79  0.89  0.73  0.76  0.66  0.70  0.69  0.65  0.36  0.51      P  0.90  0.93  0.59  0.56  0.57  0.57  0.57  0.58  0.31  0.46      Amino acid                              Lysine  1.12  1.15  1.00  1.04  0.87  0.87  0.78  0.86  0.77  0.72          Methionine  0.30  0.28  0.30  0.30  0.23  0.24  0.22  0.21  0.19  0.19          Tryptophan  0.22  0.24  0.20  0.19  0.19  0.17  0.15  0.16  0.16  0.16          Threonine  0.68  0.70  0.63  0.65  0.55  0.52  0.52  0.54  0.50  0.48          Isoleucine  0.73  0.67  0.69  0.64  0.59  0.56  0.55  0.46  0.45  0.38          Leucine  1.56  1.48  1.49  1.41  1.39  1.31  1.29  1.15  1.17  1.05          Valine  0.79  0.73  0.78  0.71  0.72  0.68  0.62  0.55  0.63  0.55  Formulated composition, %DM unless otherwise noted      CP, total  18.24  16.72  16.83  15.43  15.41  14.01  14.02  12.46  12.66  11.00      CP, SID4  15.47  14.14  14.20  12.98  12.93  11.71  11.68  10.33  10.48  9.04      Amino acid, SID                              Arg  1.06  0.93  0.96  0.84  0.86  0.74  0.75  0.63  0.65  0.51          His  0.43  0.39  0.40  0.36  0.37  0.33  0.33  0.29  0.30  0.25          Ile  0.64  0.57  0.58  0.51  0.51  0.45  0.45  0.38  0.39  0.34          Leu  1.38  1.28  1.29  1.20  1.19  1.10  1.10  0.99  1.00  0.89          Lys  0.97  0.97  0.86  0.86  0.76  0.76  0.68  0.69  0.63  0.63          Met  0.28  0.28  0.25  0.25  0.22  0.22  0.21  0.20  0.19  0.18          Total sulfur  0.55  0.55  0.49  0.49  0.45  0.44  0.42  0.40  0.39  0.37          Phe  0.77  0.69  0.70  0.63  0.63  0.56  0.57  0.49  0.50  0.41          Total aromatic  1.26  1.13  1.15  1.03  1.03  0.91  0.92  0.78  0.80  0.66          Thr  0.59  0.59  0.53  0.53  0.48  0.48  0.44  0.44  0.41  0.41          Trp  0.19  0.17  0.17  0.15  0.15  0.13  0.13  0.12  0.11  0.11          Val  0.71  0.64  0.65  0.59  0.60  0.53  0.54  0.46  0.48  0.42      ME, Kcal/kg  3,281  3,286  3,298  3,298  3,293  3,301  3,286  3,300  3,280  3,286      SID Lysine/ME  2.95  2.96  2.61  2.61  2.31  2.30  2.08  2.08  1.93  1.93      Fermentable fiber  11.61  10.82  11.17  10.46  10.71  9.99  10.24  9.43  9.77  8.89      Ca, total  0.64  0.64  0.59  0.59  0.53  0.54  0.50  0.50  0.47  0.47      P, total  0.72  0.71  0.51  0.50  0.49  0.48  0.46  0.45  0.45  0.44      P, STTD5  0.46  0.45  0.27  0.27  0.25  0.25  0.23  0.23  0.22  0.22    Phase1 1  Phase 2  Phase 3  Phase 4  Phase 5  Ingredient  Standard  Reduced  Standard  Reduced  Standard  Reduced  Standard  Reduced  Standard  Reduced  Corn, yellow dent  66.88  70.91  69.20  72.91  71.08  74.56  72.89  76.74  74.53  78.93  Soybean meal, dehull, sol. extr  24.51  20.20  20.39  16.47  16.29  12.41  12.18  7.83  8.10  3.31  Wheat middlings  5.00  5.00  7.50  7.50  10.00  10.00  12.50  12.50  15.00  15.00  Limestone  0.80  0.81  1.16  1.18  1.05  1.08  1.08  1.08  1.02  1.05  Calcium phosphate (monocalcium)  1.51  1.54  0.50  0.55  0.43  0.48  0.27  0.34  0.25  0.29  Soybean oil  0.50  0.50  0.51  0.45  0.43  0.55  0.33  0.52  0.28  0.27  Sodium chloride  0.30  0.30  0.30  0.30  0.30  0.30  0.30  0.30  0.30  0.30  Trace vitamin mix2  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  Trace mineral mix3  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  L-Lysine·HCl  0.22  0.36  0.20  0.32  0.19  0.31  0.21  0.35  0.26  0.41  L-Threonine  0.04  0.10  0.03  0.08  0.03  0.09  0.04  0.10  0.06  0.13  DL-Methionine  0.02  0.04  0.01  0.03  –  0.01  –  0.01  –  0.01  L-Cysteine  0.02  0.03  –  0.01  –  0.01  –  0.01  –  0.01  L-Tryptophan  –  0.01  –  –  –  –  –  –  –  –  L-Isoleucine  –  –  –  –  –  –  –  –  –  0.04  L-Valine  –  –  –  –  –  –  –  –  –  0.02  Analyzed composition, %DM unless otherwise noted      CP  18.46  17.48  16.51  15.55  15.16  13.90  13.99  12.34  12.23  10.97      DM  88.1  87.8  89  88.9  88.8  88.5  88.2  88.3  88.3  88.3      Ca  0.79  0.89  0.73  0.76  0.66  0.70  0.69  0.65  0.36  0.51      P  0.90  0.93  0.59  0.56  0.57  0.57  0.57  0.58  0.31  0.46      Amino acid                              Lysine  1.12  1.15  1.00  1.04  0.87  0.87  0.78  0.86  0.77  0.72          Methionine  0.30  0.28  0.30  0.30  0.23  0.24  0.22  0.21  0.19  0.19          Tryptophan  0.22  0.24  0.20  0.19  0.19  0.17  0.15  0.16  0.16  0.16          Threonine  0.68  0.70  0.63  0.65  0.55  0.52  0.52  0.54  0.50  0.48          Isoleucine  0.73  0.67  0.69  0.64  0.59  0.56  0.55  0.46  0.45  0.38          Leucine  1.56  1.48  1.49  1.41  1.39  1.31  1.29  1.15  1.17  1.05          Valine  0.79  0.73  0.78  0.71  0.72  0.68  0.62  0.55  0.63  0.55  Formulated composition, %DM unless otherwise noted      CP, total  18.24  16.72  16.83  15.43  15.41  14.01  14.02  12.46  12.66  11.00      CP, SID4  15.47  14.14  14.20  12.98  12.93  11.71  11.68  10.33  10.48  9.04      Amino acid, SID                              Arg  1.06  0.93  0.96  0.84  0.86  0.74  0.75  0.63  0.65  0.51          His  0.43  0.39  0.40  0.36  0.37  0.33  0.33  0.29  0.30  0.25          Ile  0.64  0.57  0.58  0.51  0.51  0.45  0.45  0.38  0.39  0.34          Leu  1.38  1.28  1.29  1.20  1.19  1.10  1.10  0.99  1.00  0.89          Lys  0.97  0.97  0.86  0.86  0.76  0.76  0.68  0.69  0.63  0.63          Met  0.28  0.28  0.25  0.25  0.22  0.22  0.21  0.20  0.19  0.18          Total sulfur  0.55  0.55  0.49  0.49  0.45  0.44  0.42  0.40  0.39  0.37          Phe  0.77  0.69  0.70  0.63  0.63  0.56  0.57  0.49  0.50  0.41          Total aromatic  1.26  1.13  1.15  1.03  1.03  0.91  0.92  0.78  0.80  0.66          Thr  0.59  0.59  0.53  0.53  0.48  0.48  0.44  0.44  0.41  0.41          Trp  0.19  0.17  0.17  0.15  0.15  0.13  0.13  0.12  0.11  0.11          Val  0.71  0.64  0.65  0.59  0.60  0.53  0.54  0.46  0.48  0.42      ME, Kcal/kg  3,281  3,286  3,298  3,298  3,293  3,301  3,286  3,300  3,280  3,286      SID Lysine/ME  2.95  2.96  2.61  2.61  2.31  2.30  2.08  2.08  1.93  1.93      Fermentable fiber  11.61  10.82  11.17  10.46  10.71  9.99  10.24  9.43  9.77  8.89      Ca, total  0.64  0.64  0.59  0.59  0.53  0.54  0.50  0.50  0.47  0.47      P, total  0.72  0.71  0.51  0.50  0.49  0.48  0.46  0.45  0.45  0.44      P, STTD5  0.46  0.45  0.27  0.27  0.25  0.25  0.23  0.23  0.22  0.22  1Phase 1 from pig age 60 d to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 d to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 d to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 d to 157 d; initial BW = 94 kg; Phase 5 from pig age 158 d to 166 d; initial BW = 113 kg. 2The vitamin mix provided the following (per kg of diet): vitamin A, 1,133.98 IU; vitamin D3, 204.12 IU; vitamin E, 4.99 IU; niacin, 4.08 mg; pantothenic acid, 3.18 mg; vitamin K, 0.53 mg; riboflavin, 0.68 mg; vitamin B12, 4.54 mg. 3The trace mineral mix provided the following (per kg of diet): Cu from copper sulfate, 8.34 mg; Fe from ferrous sulfate, 83.75 mg; Zn from zinc sulfate, 100.06 mg; Mn from 50% manganese oxide and 50% manganese sulfate, 33.34 mg; I from calcium iodate, 0.86 mg; and Se from sodium selenite, 0.3 mg. 4SID, standardized ileal digestible. 5Standardized total tract digestible. View Large Table 2. Ingredient and nutrient composition of standard CP and reduced CP diets (dry matter basis)   Phase1 1  Phase 2  Phase 3  Phase 4  Phase 5  Ingredient  Standard  Reduced  Standard  Reduced  Standard  Reduced  Standard  Reduced  Standard  Reduced  Corn, yellow dent  66.88  70.91  69.20  72.91  71.08  74.56  72.89  76.74  74.53  78.93  Soybean meal, dehull, sol. extr  24.51  20.20  20.39  16.47  16.29  12.41  12.18  7.83  8.10  3.31  Wheat middlings  5.00  5.00  7.50  7.50  10.00  10.00  12.50  12.50  15.00  15.00  Limestone  0.80  0.81  1.16  1.18  1.05  1.08  1.08  1.08  1.02  1.05  Calcium phosphate (monocalcium)  1.51  1.54  0.50  0.55  0.43  0.48  0.27  0.34  0.25  0.29  Soybean oil  0.50  0.50  0.51  0.45  0.43  0.55  0.33  0.52  0.28  0.27  Sodium chloride  0.30  0.30  0.30  0.30  0.30  0.30  0.30  0.30  0.30  0.30  Trace vitamin mix2  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  Trace mineral mix3  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  L-Lysine·HCl  0.22  0.36  0.20  0.32  0.19  0.31  0.21  0.35  0.26  0.41  L-Threonine  0.04  0.10  0.03  0.08  0.03  0.09  0.04  0.10  0.06  0.13  DL-Methionine  0.02  0.04  0.01  0.03  –  0.01  –  0.01  –  0.01  L-Cysteine  0.02  0.03  –  0.01  –  0.01  –  0.01  –  0.01  L-Tryptophan  –  0.01  –  –  –  –  –  –  –  –  L-Isoleucine  –  –  –  –  –  –  –  –  –  0.04  L-Valine  –  –  –  –  –  –  –  –  –  0.02  Analyzed composition, %DM unless otherwise noted      CP  18.46  17.48  16.51  15.55  15.16  13.90  13.99  12.34  12.23  10.97      DM  88.1  87.8  89  88.9  88.8  88.5  88.2  88.3  88.3  88.3      Ca  0.79  0.89  0.73  0.76  0.66  0.70  0.69  0.65  0.36  0.51      P  0.90  0.93  0.59  0.56  0.57  0.57  0.57  0.58  0.31  0.46      Amino acid                              Lysine  1.12  1.15  1.00  1.04  0.87  0.87  0.78  0.86  0.77  0.72          Methionine  0.30  0.28  0.30  0.30  0.23  0.24  0.22  0.21  0.19  0.19          Tryptophan  0.22  0.24  0.20  0.19  0.19  0.17  0.15  0.16  0.16  0.16          Threonine  0.68  0.70  0.63  0.65  0.55  0.52  0.52  0.54  0.50  0.48          Isoleucine  0.73  0.67  0.69  0.64  0.59  0.56  0.55  0.46  0.45  0.38          Leucine  1.56  1.48  1.49  1.41  1.39  1.31  1.29  1.15  1.17  1.05          Valine  0.79  0.73  0.78  0.71  0.72  0.68  0.62  0.55  0.63  0.55  Formulated composition, %DM unless otherwise noted      CP, total  18.24  16.72  16.83  15.43  15.41  14.01  14.02  12.46  12.66  11.00      CP, SID4  15.47  14.14  14.20  12.98  12.93  11.71  11.68  10.33  10.48  9.04      Amino acid, SID                              Arg  1.06  0.93  0.96  0.84  0.86  0.74  0.75  0.63  0.65  0.51          His  0.43  0.39  0.40  0.36  0.37  0.33  0.33  0.29  0.30  0.25          Ile  0.64  0.57  0.58  0.51  0.51  0.45  0.45  0.38  0.39  0.34          Leu  1.38  1.28  1.29  1.20  1.19  1.10  1.10  0.99  1.00  0.89          Lys  0.97  0.97  0.86  0.86  0.76  0.76  0.68  0.69  0.63  0.63          Met  0.28  0.28  0.25  0.25  0.22  0.22  0.21  0.20  0.19  0.18          Total sulfur  0.55  0.55  0.49  0.49  0.45  0.44  0.42  0.40  0.39  0.37          Phe  0.77  0.69  0.70  0.63  0.63  0.56  0.57  0.49  0.50  0.41          Total aromatic  1.26  1.13  1.15  1.03  1.03  0.91  0.92  0.78  0.80  0.66          Thr  0.59  0.59  0.53  0.53  0.48  0.48  0.44  0.44  0.41  0.41          Trp  0.19  0.17  0.17  0.15  0.15  0.13  0.13  0.12  0.11  0.11          Val  0.71  0.64  0.65  0.59  0.60  0.53  0.54  0.46  0.48  0.42      ME, Kcal/kg  3,281  3,286  3,298  3,298  3,293  3,301  3,286  3,300  3,280  3,286      SID Lysine/ME  2.95  2.96  2.61  2.61  2.31  2.30  2.08  2.08  1.93  1.93      Fermentable fiber  11.61  10.82  11.17  10.46  10.71  9.99  10.24  9.43  9.77  8.89      Ca, total  0.64  0.64  0.59  0.59  0.53  0.54  0.50  0.50  0.47  0.47      P, total  0.72  0.71  0.51  0.50  0.49  0.48  0.46  0.45  0.45  0.44      P, STTD5  0.46  0.45  0.27  0.27  0.25  0.25  0.23  0.23  0.22  0.22    Phase1 1  Phase 2  Phase 3  Phase 4  Phase 5  Ingredient  Standard  Reduced  Standard  Reduced  Standard  Reduced  Standard  Reduced  Standard  Reduced  Corn, yellow dent  66.88  70.91  69.20  72.91  71.08  74.56  72.89  76.74  74.53  78.93  Soybean meal, dehull, sol. extr  24.51  20.20  20.39  16.47  16.29  12.41  12.18  7.83  8.10  3.31  Wheat middlings  5.00  5.00  7.50  7.50  10.00  10.00  12.50  12.50  15.00  15.00  Limestone  0.80  0.81  1.16  1.18  1.05  1.08  1.08  1.08  1.02  1.05  Calcium phosphate (monocalcium)  1.51  1.54  0.50  0.55  0.43  0.48  0.27  0.34  0.25  0.29  Soybean oil  0.50  0.50  0.51  0.45  0.43  0.55  0.33  0.52  0.28  0.27  Sodium chloride  0.30  0.30  0.30  0.30  0.30  0.30  0.30  0.30  0.30  0.30  Trace vitamin mix2  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  Trace mineral mix3  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  0.10  L-Lysine·HCl  0.22  0.36  0.20  0.32  0.19  0.31  0.21  0.35  0.26  0.41  L-Threonine  0.04  0.10  0.03  0.08  0.03  0.09  0.04  0.10  0.06  0.13  DL-Methionine  0.02  0.04  0.01  0.03  –  0.01  –  0.01  –  0.01  L-Cysteine  0.02  0.03  –  0.01  –  0.01  –  0.01  –  0.01  L-Tryptophan  –  0.01  –  –  –  –  –  –  –  –  L-Isoleucine  –  –  –  –  –  –  –  –  –  0.04  L-Valine  –  –  –  –  –  –  –  –  –  0.02  Analyzed composition, %DM unless otherwise noted      CP  18.46  17.48  16.51  15.55  15.16  13.90  13.99  12.34  12.23  10.97      DM  88.1  87.8  89  88.9  88.8  88.5  88.2  88.3  88.3  88.3      Ca  0.79  0.89  0.73  0.76  0.66  0.70  0.69  0.65  0.36  0.51      P  0.90  0.93  0.59  0.56  0.57  0.57  0.57  0.58  0.31  0.46      Amino acid                              Lysine  1.12  1.15  1.00  1.04  0.87  0.87  0.78  0.86  0.77  0.72          Methionine  0.30  0.28  0.30  0.30  0.23  0.24  0.22  0.21  0.19  0.19          Tryptophan  0.22  0.24  0.20  0.19  0.19  0.17  0.15  0.16  0.16  0.16          Threonine  0.68  0.70  0.63  0.65  0.55  0.52  0.52  0.54  0.50  0.48          Isoleucine  0.73  0.67  0.69  0.64  0.59  0.56  0.55  0.46  0.45  0.38          Leucine  1.56  1.48  1.49  1.41  1.39  1.31  1.29  1.15  1.17  1.05          Valine  0.79  0.73  0.78  0.71  0.72  0.68  0.62  0.55  0.63  0.55  Formulated composition, %DM unless otherwise noted      CP, total  18.24  16.72  16.83  15.43  15.41  14.01  14.02  12.46  12.66  11.00      CP, SID4  15.47  14.14  14.20  12.98  12.93  11.71  11.68  10.33  10.48  9.04      Amino acid, SID                              Arg  1.06  0.93  0.96  0.84  0.86  0.74  0.75  0.63  0.65  0.51          His  0.43  0.39  0.40  0.36  0.37  0.33  0.33  0.29  0.30  0.25          Ile  0.64  0.57  0.58  0.51  0.51  0.45  0.45  0.38  0.39  0.34          Leu  1.38  1.28  1.29  1.20  1.19  1.10  1.10  0.99  1.00  0.89          Lys  0.97  0.97  0.86  0.86  0.76  0.76  0.68  0.69  0.63  0.63          Met  0.28  0.28  0.25  0.25  0.22  0.22  0.21  0.20  0.19  0.18          Total sulfur  0.55  0.55  0.49  0.49  0.45  0.44  0.42  0.40  0.39  0.37          Phe  0.77  0.69  0.70  0.63  0.63  0.56  0.57  0.49  0.50  0.41          Total aromatic  1.26  1.13  1.15  1.03  1.03  0.91  0.92  0.78  0.80  0.66          Thr  0.59  0.59  0.53  0.53  0.48  0.48  0.44  0.44  0.41  0.41          Trp  0.19  0.17  0.17  0.15  0.15  0.13  0.13  0.12  0.11  0.11          Val  0.71  0.64  0.65  0.59  0.60  0.53  0.54  0.46  0.48  0.42      ME, Kcal/kg  3,281  3,286  3,298  3,298  3,293  3,301  3,286  3,300  3,280  3,286      SID Lysine/ME  2.95  2.96  2.61  2.61  2.31  2.30  2.08  2.08  1.93  1.93      Fermentable fiber  11.61  10.82  11.17  10.46  10.71  9.99  10.24  9.43  9.77  8.89      Ca, total  0.64  0.64  0.59  0.59  0.53  0.54  0.50  0.50  0.47  0.47      P, total  0.72  0.71  0.51  0.50  0.49  0.48  0.46  0.45  0.45  0.44      P, STTD5  0.46  0.45  0.27  0.27  0.25  0.25  0.23  0.23  0.22  0.22  1Phase 1 from pig age 60 d to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 d to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 d to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 d to 157 d; initial BW = 94 kg; Phase 5 from pig age 158 d to 166 d; initial BW = 113 kg. 2The vitamin mix provided the following (per kg of diet): vitamin A, 1,133.98 IU; vitamin D3, 204.12 IU; vitamin E, 4.99 IU; niacin, 4.08 mg; pantothenic acid, 3.18 mg; vitamin K, 0.53 mg; riboflavin, 0.68 mg; vitamin B12, 4.54 mg. 3The trace mineral mix provided the following (per kg of diet): Cu from copper sulfate, 8.34 mg; Fe from ferrous sulfate, 83.75 mg; Zn from zinc sulfate, 100.06 mg; Mn from 50% manganese oxide and 50% manganese sulfate, 33.34 mg; I from calcium iodate, 0.86 mg; and Se from sodium selenite, 0.3 mg. 4SID, standardized ileal digestible. 5Standardized total tract digestible. View Large Gaseous Concentrations and Ventilation Measurements Gaseous concentration monitoring of each room and background air occurred in a sequential manner through software control (LabVIEW, National Instruments Corp., Austin, TX). Each of the 12 rooms was sampled for 15 min, whereby the sampling line was purged for the first 10 min and data were saved for 5 min. Ammonia was measured using a chemiluminescence NH3 analyzer (Model 17C, Thermo Fisher, Franklin, MA; detection limit of 0.001 mg/kg), which is a combination NH3 converter and NO-NO2–NOx analyzer. Hydrogen sulfide (H2S) was analyzed using a pulsed fluorescence SO2–H2S analyzer (TEI Model 450i, Thermo Fisher, Franklin, MA; detection limit of 0.003 mg/kg). Nonmethane total hydrocarbon (NMTHC) and CH4 were measured using a 55i CH4–NMTHC analyzer (Thermo Fisher, Franklin, MA; CH4: range = 0 to 100 mg/kg; detection limit = 0.05 mg/kg; NMTHC: range = 0 to 10 mg/kg; detection limit = 0.02 mg/kg). Nitrous oxide was measured using an Innova 1412 photoacoustic analyzer (Lumasense Technologies, Ballerup, Denmark; range = 0 to 50,000 mg/kg; detection limit = 0.03 mg/kg at 50,000 mg/kg range). Carbon dioxide was measured using an X-Stream infrared analyzer (Emerson Electric Co., St Louis, MO; 5.1 mg/kg detection limit at 1,000 mg/kg range). Airflow rates into each room were continuously measured using 15.24-cm orifice plates in the incoming ductwork of each room. Differential pressure transducers (Setra Model 239, Boxborough, MA) measured the pressure drop across orifice plates. Using calibration curves, airflow estimates were determined and automatically recorded every 30 sec. The temperature of each room was programmed based on the room temperature setting. Temperature and humidity of each room, measured using a CS500 Temperature and relative humidity probe (Campbell Scientific, Inc.; Logan, UT), were continuously monitored and recorded. In the event that the temperature fell outside of the specified range, an alarm system placed a series of phone calls to alert laboratory personnel. Gas emission rates were calculated as the product of ventilation rates and concentration differences between exhaust and background air. Chemical Analyses Feed and manure N concentrations were determined using the total Kjeldahl method (Method 928.08, AOAC, 2000). Feed AA content was analyzed by the University of Missouri Agriculture Experiment Station Laboratory using HPLC methods (Method 982.30, AOAC, 2006). Feed energy and mineral content (Ca, P, Mg, K, Na, S, Cu, Zn, Fe, Mn, Mo) were analyzed using bomb calorimetry and microwave digestion followed by Inductively Coupled Plasma Mass Spectrometry, respectively (Dairy One Inc.; Ithaca, NY). Manure P and K contents were analyzed using a Foss NIR System Model 6500 with Win ISI II v1.5 (Method 941.04, AOAC, 1984; Method 2001.11, AOAC, 2005; Dairy One Inc.; Ithaca, NY). Manure NH4+–N content was measured by distillation (AOAC, 2000, Method 928.08; Dairy One Inc.; Ithaca, NY). Global Warming Potentials Global warming potential (GWP) is a simple and commonly used estimator of the warming effects of different long-lived GHGs, and it is expressed in terms of emissions of CO2. Because GWP is always expressed relative to CO2, the GWP of CO2 is 1. Methane has a GWP of 24 over a 100-yr period, meaning that the emission of 1 unit of CH4 is the same as the emission of 24 units of CO2 over a 100-yr period. Nitrous oxide has a GWP of 298 over a 100-yr period (Bernstein et al., 2008). Statistical Analyses The PROC Mixed procedure of SAS v. 9.2 (SAS Inst. Inc., Cary, NC) was used to analyze the data. The effect of dietary treatments (reduced CP vs. standard CP) and different feeding phases (1 to 5) on gas emissions were treated as fixed factors in the mixed model. Pig groups, allocated to different rooms randomly at the start of the Phase 1, were treated as a random factor. Room was nested within dietary treatments. In addition, the same group of pigs was measured multiple times (from Phase 1 through Phase 5), therefore a repeated-measures analysis was applied to the phase factor. The repeated-measures analysis in this particular experimental design allowed for the use of fewer groups of pigs compared with the use of independent groups for each phase and a better control of individual group differences. In this study, phase was included in the model because we were interested in assessing whether there is a differential impact of dietary CP reduction for different phases of growth. Furthermore, a reduced CP feeding program is likely to be applied across all phases of growth. Pigs were assigned to the same treatment throughout the study to reduce the likelihood that phase carryover effects overwhelmed a treatment effect. The compound symmetry structure, which assumes the same covariance between any two measurements and the same variance of each measurement, was applied. The Kenward-Roger procedure was applied for calculating the denominator degrees of freedom. Tukey adjustment was used for multiple comparisons. Significant differences among least squares means were declared at P < 0.05. RESULTS AND DISCUSSION Pig Performance Phase corresponded to pig weight and age as follows: Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 157 d; initial BW = 94 kg; Phase 5 from pig age 158 to 166 d; initial BW = 113 kg. The ADG (1.013 kg · d–1 · pig–1), ADFI (2.714 kg · d–1 · pig–1), and feed efficiency (0.366 kg gain/kg feed) did not differ between standard and reduced CP diets (Table 3). Pigs had greater ADG during Phase 2 and they consumed more feed as they aged. Pigs had highest feed efficiency during Phases 1 and 2, and as they reached market body weight (120 kg), feed efficiency decreased (Table 3). Pig performance measures were similar to other studies (Carr et al., 2005; Powers et al., 2007). In this study, the reduced CP diets were adequately supplemented with all limiting AA and did not limit pig growth. Table 3. Least squares means for body weight gain, feed intake, and feed conversion of pigs fed a standard or reduced CP diet   ADG, kg · d–1 · pig–1  ADFI, kg · d–1 · pig–1  G:F, kg gain/kg feed  Main effects  Diet            Standard CP diet  1.0  2.7  0.36      Reduced CP diet  1.0  2.7  0.37      SE  0.02  0.04  <0.01  Phase1            1  0.95b  1.82e  0.52a      2  1.13a  2.34d  0.48a      3  1.04ab  2.99c  0.34b      4  1.01b  3.14b  0.32b      5  0.95b  3.28a  0.28c      SE  0.04  0.04  <0.01  Type 3 Tests of fixed effects (P-values)      Diet  0.68  0.86  0.69      Phase  0.01  <0.01  <0.01      Diet × Phase  0.39  0.42  0.37    ADG, kg · d–1 · pig–1  ADFI, kg · d–1 · pig–1  G:F, kg gain/kg feed  Main effects  Diet            Standard CP diet  1.0  2.7  0.36      Reduced CP diet  1.0  2.7  0.37      SE  0.02  0.04  <0.01  Phase1            1  0.95b  1.82e  0.52a      2  1.13a  2.34d  0.48a      3  1.04ab  2.99c  0.34b      4  1.01b  3.14b  0.32b      5  0.95b  3.28a  0.28c      SE  0.04  0.04  <0.01  Type 3 Tests of fixed effects (P-values)      Diet  0.68  0.86  0.69      Phase  0.01  <0.01  <0.01      Diet × Phase  0.39  0.42  0.37  a–dMeans within a column differ at P < 0.05. 1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 to 166 d; initial BW = 113 kg. View Large Table 3. Least squares means for body weight gain, feed intake, and feed conversion of pigs fed a standard or reduced CP diet   ADG, kg · d–1 · pig–1  ADFI, kg · d–1 · pig–1  G:F, kg gain/kg feed  Main effects  Diet            Standard CP diet  1.0  2.7  0.36      Reduced CP diet  1.0  2.7  0.37      SE  0.02  0.04  <0.01  Phase1            1  0.95b  1.82e  0.52a      2  1.13a  2.34d  0.48a      3  1.04ab  2.99c  0.34b      4  1.01b  3.14b  0.32b      5  0.95b  3.28a  0.28c      SE  0.04  0.04  <0.01  Type 3 Tests of fixed effects (P-values)      Diet  0.68  0.86  0.69      Phase  0.01  <0.01  <0.01      Diet × Phase  0.39  0.42  0.37    ADG, kg · d–1 · pig–1  ADFI, kg · d–1 · pig–1  G:F, kg gain/kg feed  Main effects  Diet            Standard CP diet  1.0  2.7  0.36      Reduced CP diet  1.0  2.7  0.37      SE  0.02  0.04  <0.01  Phase1            1  0.95b  1.82e  0.52a      2  1.13a  2.34d  0.48a      3  1.04ab  2.99c  0.34b      4  1.01b  3.14b  0.32b      5  0.95b  3.28a  0.28c      SE  0.04  0.04  <0.01  Type 3 Tests of fixed effects (P-values)      Diet  0.68  0.86  0.69      Phase  0.01  <0.01  <0.01      Diet × Phase  0.39  0.42  0.37  a–dMeans within a column differ at P < 0.05. 1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 to 166 d; initial BW = 113 kg. View Large Manure Composition Daily manure excretion per pig (kg · d–1 · pig–1), total solid (%), manure N (%), manure NH4+–N (%), manure P (%), and manure K (%) are shown in Table 4. Manure excretion rate or total solids concentration across feeding phases did not differ between standard and reduced CP diets. Manure excretion (kg · d–1 · pig–1) during Phases 1 to 3 may reflect greater wasting of water as evidenced by <5% solids content of manure during those phases. It is important to note, however, that during Phases 1 through 3, nutrient content was greater than the mean pooled across phases and treatments, while mass of manure and solids excreted daily was below the overall mean. The reverse is true for Phases 4 and 5. The stored manure N (%, dry basis) did not differ among pig groups as a result of feeding the reduced CP diets compared with feeding standard diets; however, feeding reduced CP diets resulted in decreased manure NH4+–content, which agreed with the observation of Sutton et al. (1999). The findings of the current study reflect N remaining after storage ranging from 9 to 33 d, during which time NH3 volatilization had occurred. Manure P content was not affected by diet; however, pigs offered the standard CP diet excreted manure with greater K content. As pigs grew, the manure N and K decreased (P < 0.01 and P < 0.01; respectively; Table 4). Table 4. Least squares means of excretion characteristics of manure from grow-finish pigs fed either a standard CP diet or a reduced CP diet over 5 feeding phases   Manure excretion rate, kg · d–1 · pig–1  Total solids, %  Manure N, % DM  Manure NH4+–N, % DM  Manure P, % DM  Manure K, % DM  Main effect means      Diet                  Standard CP diet  7.9  4.1  9.25  5.61  2.69  5.11      Reduced CP diet  7.9  4.4  8.77  4.57  2.62  4.47      SE  0.6  0.4  0.27  0.28  0.09  0.15  Phase1                  1  8.08bc  1.65e  12.0a  5.62b  4.56a  7.37a      2  9.79a  2.95d  9.05b  5.74a  2.04c  5.00b      3  8.28b  3.73c  9.15c  5.97a  2.42b  4.86b      4  7.06cd  5.72b  7.88d  4.53c  2.20bc  3.75c      5  6.39d  7.16a  6.97d  3.55d  2.03c  2.98d      SE  0.51  0.36  0.27  0.28  0.11  0.21  Type 3 tests of fixed effects (P-value)      Diet  0.98  0.56  0.24  0.02  0.59  0.01      Phase  <0.01  <0.01  <0.01  <0.01  <0.01  <0.01      Diet × Phase  0.62  0.29  0.43  0.54  0.36  0.52    Manure excretion rate, kg · d–1 · pig–1  Total solids, %  Manure N, % DM  Manure NH4+–N, % DM  Manure P, % DM  Manure K, % DM  Main effect means      Diet                  Standard CP diet  7.9  4.1  9.25  5.61  2.69  5.11      Reduced CP diet  7.9  4.4  8.77  4.57  2.62  4.47      SE  0.6  0.4  0.27  0.28  0.09  0.15  Phase1                  1  8.08bc  1.65e  12.0a  5.62b  4.56a  7.37a      2  9.79a  2.95d  9.05b  5.74a  2.04c  5.00b      3  8.28b  3.73c  9.15c  5.97a  2.42b  4.86b      4  7.06cd  5.72b  7.88d  4.53c  2.20bc  3.75c      5  6.39d  7.16a  6.97d  3.55d  2.03c  2.98d      SE  0.51  0.36  0.27  0.28  0.11  0.21  Type 3 tests of fixed effects (P-value)      Diet  0.98  0.56  0.24  0.02  0.59  0.01      Phase  <0.01  <0.01  <0.01  <0.01  <0.01  <0.01      Diet × Phase  0.62  0.29  0.43  0.54  0.36  0.52  a–dMeans within a column differ at P < 0.05. 1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 to 166 d; initial BW = 113 kg. View Large Table 4. Least squares means of excretion characteristics of manure from grow-finish pigs fed either a standard CP diet or a reduced CP diet over 5 feeding phases   Manure excretion rate, kg · d–1 · pig–1  Total solids, %  Manure N, % DM  Manure NH4+–N, % DM  Manure P, % DM  Manure K, % DM  Main effect means      Diet                  Standard CP diet  7.9  4.1  9.25  5.61  2.69  5.11      Reduced CP diet  7.9  4.4  8.77  4.57  2.62  4.47      SE  0.6  0.4  0.27  0.28  0.09  0.15  Phase1                  1  8.08bc  1.65e  12.0a  5.62b  4.56a  7.37a      2  9.79a  2.95d  9.05b  5.74a  2.04c  5.00b      3  8.28b  3.73c  9.15c  5.97a  2.42b  4.86b      4  7.06cd  5.72b  7.88d  4.53c  2.20bc  3.75c      5  6.39d  7.16a  6.97d  3.55d  2.03c  2.98d      SE  0.51  0.36  0.27  0.28  0.11  0.21  Type 3 tests of fixed effects (P-value)      Diet  0.98  0.56  0.24  0.02  0.59  0.01      Phase  <0.01  <0.01  <0.01  <0.01  <0.01  <0.01      Diet × Phase  0.62  0.29  0.43  0.54  0.36  0.52    Manure excretion rate, kg · d–1 · pig–1  Total solids, %  Manure N, % DM  Manure NH4+–N, % DM  Manure P, % DM  Manure K, % DM  Main effect means      Diet                  Standard CP diet  7.9  4.1  9.25  5.61  2.69  5.11      Reduced CP diet  7.9  4.4  8.77  4.57  2.62  4.47      SE  0.6  0.4  0.27  0.28  0.09  0.15  Phase1                  1  8.08bc  1.65e  12.0a  5.62b  4.56a  7.37a      2  9.79a  2.95d  9.05b  5.74a  2.04c  5.00b      3  8.28b  3.73c  9.15c  5.97a  2.42b  4.86b      4  7.06cd  5.72b  7.88d  4.53c  2.20bc  3.75c      5  6.39d  7.16a  6.97d  3.55d  2.03c  2.98d      SE  0.51  0.36  0.27  0.28  0.11  0.21  Type 3 tests of fixed effects (P-value)      Diet  0.98  0.56  0.24  0.02  0.59  0.01      Phase  <0.01  <0.01  <0.01  <0.01  <0.01  <0.01      Diet × Phase  0.62  0.29  0.43  0.54  0.36  0.52  a–dMeans within a column differ at P < 0.05. 1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 to 166 d; initial BW = 113 kg. View Large Air Quality Over the course of the 107-d experimental period, air entering the rooms had an average temperature of 18.5°C, relative humidity of 80%, and background gas concentrations as follows: NH3, 0.28 mg/kg; N2O, 0.46 mg/kg; CO2, 513 mg/kg; O2, 21%; H2S, 0.01 mg/kg; CH4, 2.51 mg/kg, and NMTHC, 0.03 mg/kg. Mean room ventilation rates and temperatures for each feeding phase are shown in Fig. 1. Temperature setpoints in rooms decreased as pig body weight increased so as to remain in the recommended thermal conditions for growing-finishing swine (National Pork Board, 2003). Figure 1. View largeDownload slide (A) Room ventilation rates and (B) temperature during different feeding phases when grow-finish pigs were fed standard CP diets or reduced CP diets. Note: the bottom and top of each box are the 25th (Q1) and 75th (Q3) percentiles, the line near the middle of the box is the 50th percentile (median), and the diamond is the mean; the whiskers represent the lowest datum with 1.5 interquartile range (IQR = Q3–Q1) of the lower quartile and the highest datum with 1.5 IQR of the upper quartile; data points (small circles) that are not included between the whiskers are potential outliers). Figure 1. View largeDownload slide (A) Room ventilation rates and (B) temperature during different feeding phases when grow-finish pigs were fed standard CP diets or reduced CP diets. Note: the bottom and top of each box are the 25th (Q1) and 75th (Q3) percentiles, the line near the middle of the box is the 50th percentile (median), and the diamond is the mean; the whiskers represent the lowest datum with 1.5 interquartile range (IQR = Q3–Q1) of the lower quartile and the highest datum with 1.5 IQR of the upper quartile; data points (small circles) that are not included between the whiskers are potential outliers). NH3 and N2O Emissions Emissions of NH3 and N2O are presented in Tables 5 and 6, respectively. Reduced CP diets decreased NH3 emissions compared with standard CP diet across all phases (P < 0.01; Table 5). For both dietary treatments, the emission rates increased (P < 0.05) from Phase 1 through Phase 3, then leveled off or decreased during Phases 4 and 5. The interactions between phase and treatment were significant (P < 0.05) indicating dietary effects were phase dependent. Although feeding the reduced CP diet resulted in lower NH3 concentrations (mg/kg) and emissions (mg/d), neither NH3 concentrations nor emissions as a function of per animal count (g · d–1 · pig–1) or N intake (g NH3/kg of N consumed) was influenced by diet during Phase 1. During Phases 2 through 5, feeding the reduced CP diet resulted in lower NH3 emissions (P < 0.05). The greater NH3 volatilization (P < 0.01) in rooms where the standard CP diets were fed likely explains the lack of difference in stored manure N content between diets. Table 5. Least squares means of ammonia emissions from grow-finish pigs fed either a standard CP diet or a reduced CP diet over 5 feeding phases1,2   Standard CP diet, Phase  Reduced CP diet, Phase  Type 3 tests of fixed effects  Parameter  1  2  3  4  5  1  2  3  4  5  Diet  Phase  Diet × Phase  Concentration, mg/kg  0.56  1.38a  2.71a  2.72a  2.45a  0.39  0.94b  1.83b  1.60b  1.33b  <0.01  <0.01  <0.01  Emissions, g · d–1 · pig–1  1.05  2.61a  8.28a  8.09a  6.82a  0.55  1.36b  5.39b  4.45b  2.60b  <0.01  <0.01  <0.01  Emissions, g · d–1 · AU–1  1.32a  17.10a  42.10a  33.50a  25.00a  6.99b  9.19b  27.90b  18.70b  9.72b  <0.01  <0.01  <0.01  Emissions, g NH3/kg of N consumed  19.6  41.9  116.5a  116.0a  106.0a  10.8  23.7  79.6b  71.6b  45.3b  <0.01  <0.01  <0.01    Standard CP diet, Phase  Reduced CP diet, Phase  Type 3 tests of fixed effects  Parameter  1  2  3  4  5  1  2  3  4  5  Diet  Phase  Diet × Phase  Concentration, mg/kg  0.56  1.38a  2.71a  2.72a  2.45a  0.39  0.94b  1.83b  1.60b  1.33b  <0.01  <0.01  <0.01  Emissions, g · d–1 · pig–1  1.05  2.61a  8.28a  8.09a  6.82a  0.55  1.36b  5.39b  4.45b  2.60b  <0.01  <0.01  <0.01  Emissions, g · d–1 · AU–1  1.32a  17.10a  42.10a  33.50a  25.00a  6.99b  9.19b  27.90b  18.70b  9.72b  <0.01  <0.01  <0.01  Emissions, g NH3/kg of N consumed  19.6  41.9  116.5a  116.0a  106.0a  10.8  23.7  79.6b  71.6b  45.3b  <0.01  <0.01  <0.01  a–bMeans within a row and feeding phase differ at P < 0.05 (e.g., standard CP diet in Phase 2 compared with reduced CP diet in Phase 2 is significantly different). 1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 to 166 d; initial BW = 113 kg. 2AU = animal unit, equivalent to 454 kg BW. View Large Table 5. Least squares means of ammonia emissions from grow-finish pigs fed either a standard CP diet or a reduced CP diet over 5 feeding phases1,2   Standard CP diet, Phase  Reduced CP diet, Phase  Type 3 tests of fixed effects  Parameter  1  2  3  4  5  1  2  3  4  5  Diet  Phase  Diet × Phase  Concentration, mg/kg  0.56  1.38a  2.71a  2.72a  2.45a  0.39  0.94b  1.83b  1.60b  1.33b  <0.01  <0.01  <0.01  Emissions, g · d–1 · pig–1  1.05  2.61a  8.28a  8.09a  6.82a  0.55  1.36b  5.39b  4.45b  2.60b  <0.01  <0.01  <0.01  Emissions, g · d–1 · AU–1  1.32a  17.10a  42.10a  33.50a  25.00a  6.99b  9.19b  27.90b  18.70b  9.72b  <0.01  <0.01  <0.01  Emissions, g NH3/kg of N consumed  19.6  41.9  116.5a  116.0a  106.0a  10.8  23.7  79.6b  71.6b  45.3b  <0.01  <0.01  <0.01    Standard CP diet, Phase  Reduced CP diet, Phase  Type 3 tests of fixed effects  Parameter  1  2  3  4  5  1  2  3  4  5  Diet  Phase  Diet × Phase  Concentration, mg/kg  0.56  1.38a  2.71a  2.72a  2.45a  0.39  0.94b  1.83b  1.60b  1.33b  <0.01  <0.01  <0.01  Emissions, g · d–1 · pig–1  1.05  2.61a  8.28a  8.09a  6.82a  0.55  1.36b  5.39b  4.45b  2.60b  <0.01  <0.01  <0.01  Emissions, g · d–1 · AU–1  1.32a  17.10a  42.10a  33.50a  25.00a  6.99b  9.19b  27.90b  18.70b  9.72b  <0.01  <0.01  <0.01  Emissions, g NH3/kg of N consumed  19.6  41.9  116.5a  116.0a  106.0a  10.8  23.7  79.6b  71.6b  45.3b  <0.01  <0.01  <0.01  a–bMeans within a row and feeding phase differ at P < 0.05 (e.g., standard CP diet in Phase 2 compared with reduced CP diet in Phase 2 is significantly different). 1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 to 166 d; initial BW = 113 kg. 2AU = animal unit, equivalent to 454 kg BW. View Large Table 6. Least squares means of nitrous oxide emissions from grow-finish pigs fed either a standard CP diet or a reduced CP diet over 5 feeding phases1,2   Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Emissions, g N2O/kg of N consumed  Main effect  Diet              Standard CP diet  0.47  0.08  0.34  1.14      Reduced CP diet  0.47  0.06  0.22  0.98      SE  <0.01  <0.01  0.03  0.08  Phase1              1  0.32e  0.01cd  0.10c  0.14cd      2  0.45d  –0.02d  –0.11d  –0.28d      3  0.53b  0.02c  0.12c  0.35c      4  0.50c  0.21a  0.85a  3.13a      5  0.56a  0.12b  0.44b  1.96b      SE  0.002  0.011  0.06  0.18  Type 3 tests of fixed effects (P-value)      Diet  0.55  0.02  0.01  0.15      Phase  <0.01  <0.01  <0.01  < 0.01      Diet × Phase  0.93  0.87  0.36  0.60    Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Emissions, g N2O/kg of N consumed  Main effect  Diet              Standard CP diet  0.47  0.08  0.34  1.14      Reduced CP diet  0.47  0.06  0.22  0.98      SE  <0.01  <0.01  0.03  0.08  Phase1              1  0.32e  0.01cd  0.10c  0.14cd      2  0.45d  –0.02d  –0.11d  –0.28d      3  0.53b  0.02c  0.12c  0.35c      4  0.50c  0.21a  0.85a  3.13a      5  0.56a  0.12b  0.44b  1.96b      SE  0.002  0.011  0.06  0.18  Type 3 tests of fixed effects (P-value)      Diet  0.55  0.02  0.01  0.15      Phase  <0.01  <0.01  <0.01  < 0.01      Diet × Phase  0.93  0.87  0.36  0.60  a–dMeans within a column variable differ at P < 0.05. 1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 to 166 d; initial BW = 113 kg. 2AU = animal unit, equivalent to 454 kg BW. View Large Table 6. Least squares means of nitrous oxide emissions from grow-finish pigs fed either a standard CP diet or a reduced CP diet over 5 feeding phases1,2   Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Emissions, g N2O/kg of N consumed  Main effect  Diet              Standard CP diet  0.47  0.08  0.34  1.14      Reduced CP diet  0.47  0.06  0.22  0.98      SE  <0.01  <0.01  0.03  0.08  Phase1              1  0.32e  0.01cd  0.10c  0.14cd      2  0.45d  –0.02d  –0.11d  –0.28d      3  0.53b  0.02c  0.12c  0.35c      4  0.50c  0.21a  0.85a  3.13a      5  0.56a  0.12b  0.44b  1.96b      SE  0.002  0.011  0.06  0.18  Type 3 tests of fixed effects (P-value)      Diet  0.55  0.02  0.01  0.15      Phase  <0.01  <0.01  <0.01  < 0.01      Diet × Phase  0.93  0.87  0.36  0.60    Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Emissions, g N2O/kg of N consumed  Main effect  Diet              Standard CP diet  0.47  0.08  0.34  1.14      Reduced CP diet  0.47  0.06  0.22  0.98      SE  <0.01  <0.01  0.03  0.08  Phase1              1  0.32e  0.01cd  0.10c  0.14cd      2  0.45d  –0.02d  –0.11d  –0.28d      3  0.53b  0.02c  0.12c  0.35c      4  0.50c  0.21a  0.85a  3.13a      5  0.56a  0.12b  0.44b  1.96b      SE  0.002  0.011  0.06  0.18  Type 3 tests of fixed effects (P-value)      Diet  0.55  0.02  0.01  0.15      Phase  <0.01  <0.01  <0.01  < 0.01      Diet × Phase  0.93  0.87  0.36  0.60  a–dMeans within a column variable differ at P < 0.05. 1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 to 166 d; initial BW = 113 kg. 2AU = animal unit, equivalent to 454 kg BW. View Large Other studies (Canh et al., 1998;Sutton et al., 1999;Otto et al., 2003; Panetta et al., 2006; Powers et al., 2007) demonstrated that reducing CP reduces NH3 emissions from manure. The current study and that of Powers et al. (2007) are, however, the only work reporting specifically on NH3 emissions from housing over the course of the grow-finish period. In addition, previous work, including that of Powers et al. (2007), were based on earlier AA requirements for grow-finisher swine and on either total or apparent ileal digestible AA basis (National Research Council, 1998). Recent industry standard diets have already implemented the use of crystalline L-Lys and L-Thr in grower-finisher diets; nonetheless, our study demonstrated that further reduction by only 1.5% in CP produced remarkable abatement in NH3 emissions in any given phase, from 25 to >50%. Because previous studies considered emissions from manure only, and did not generate emission values for treatment comparison, the impact of diet formulation on emission factors across studies cannot be made. Panetta et al. (2006) and Powers et al. (2007) are an exception. For pigs of BW similar to those in Phase 2 of the present study, Panetta et al. (2006) reported NH3 concentrations in room exhaust air that ranged from 2.66 mg/kg (diet containing supplemental L-Lys) to 1.05 mg/kg (diet containing L-Lys, DL-Met, L-Thr, L-Trp). These values compare with observed concentrations of 1.38 mg/kg (standard CP diet) and 0.94 mg/kg (reduced CP diet) in the present study. Using National Research Council 1998 nutritional guidelines, Powers et al. (2007) showed that what was a common commercial diet at that time resulted in 88.0 g/1,000 kg BW mean daily NH3 emissions. Powers et al. (2007) reported average daily mean NH3 emissions of 46.0 g/1,000 kg BW over the grow-finish period when diets containing 5 supplemental CAA were fed. Our similar 5 AA diet in this current study, which is based on National Research Council (2012), yielded very similar calculated mean grow-finish NH3 emission value of 47.6 g/1,000 kg BW. Our reduced diet yielded 29.0 g/1,000 kg BW, clearly demonstrating the additional benefits to further reductions in diet CP if availability of CAA is not limited and CAA prices are cost effective. No diet effect was observed for N2O emissions expressed as a function of pig count and animal unit (AU, equivalent to 454 kg BW; P > 0.05; Table 6). A strong phase effect was observed for emissions, with increasing emissions from Phase 1 to 4 followed by decreased emissions during Phase 5. This is due in part to the exhaust air from rooms having similar N2O concentrations as air entering the rooms during Phases 1 through 3, which resulted in very low (even negative) emission rates. The interactions between phase and treatment for concentration and emissions were not significant. Among possible N emissions (NH3, N2O, NO, NO2, and N2), NO and NO2 emissions were negligible in our study, and N2 gas was not measured. As the second most important N-containing gas, N2O was <1% of total N-NH3 + N-N2O emitted during Phases 1 through 3, and represented approximately 4% of total N-NH3 + N-N2O during Phases 4 and 5. H2S Concentration and Emissions Reduced H2S concentrations were observed in rooms where pigs were fed the reduced CP diets (P = 0.05; Table 7), but emissions did not differ between treatments (g · d–1 · pig–1, P = 0.06; g · d–1 · AU–1, P = 0.10). The interaction between phase and treatment was not significant for concentration or emissions variables (P > 0.05, Table 7). Phase effects were observed for both concentrations and emissions (P < 0.01, Table 7). The emissions (g · d–1 · AU–1) peaked during Phase 1 and then decreased with advancing pig age. Similar results were also observed in the study of Li et al. (2011). The rationale for this might be that a pig's digestive capacity gradually increases with maturity, as does stomach volume and gastric secretions (Manners, 1976). Table 7. Least squares means of hydrogen sulfide emissions from grow-finish pigs fed either a standard CP diet or a reduced CP diet over 5 feeding phases1,2   Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Main effect  Diet            Standard CP diet  0.016  0.062  0.413      Reduced CP diet  0.013  0.048  0.331      SE  <0.001  0.005  0.032  Phase        1  0.025a  0.064ab  0.808a      2  0.015b  0.041b  0.272b      3  0.015b  0.085a  0.435b      4  0.016b  0.081a  0.338b      5  0.002c  0.003c  0.009b      SE  0.001  0.007  0.054  Type 3 tests of fixed effects (P-value)      Diet  0.05  0.06  0.10      Phase  <0.01  <0.01  <0.01      Diet × Phase  0.21  0.13  0.56    Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Main effect  Diet            Standard CP diet  0.016  0.062  0.413      Reduced CP diet  0.013  0.048  0.331      SE  <0.001  0.005  0.032  Phase        1  0.025a  0.064ab  0.808a      2  0.015b  0.041b  0.272b      3  0.015b  0.085a  0.435b      4  0.016b  0.081a  0.338b      5  0.002c  0.003c  0.009b      SE  0.001  0.007  0.054  Type 3 tests of fixed effects (P-value)      Diet  0.05  0.06  0.10      Phase  <0.01  <0.01  <0.01      Diet × Phase  0.21  0.13  0.56  a–dSignificant differences within a column variable differ at P < 0.05. 1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 to 166 d; initial BW = 113 kg. 2AU = animal unit is equivalent to 454 kg BW. View Large Table 7. Least squares means of hydrogen sulfide emissions from grow-finish pigs fed either a standard CP diet or a reduced CP diet over 5 feeding phases1,2   Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Main effect  Diet            Standard CP diet  0.016  0.062  0.413      Reduced CP diet  0.013  0.048  0.331      SE  <0.001  0.005  0.032  Phase        1  0.025a  0.064ab  0.808a      2  0.015b  0.041b  0.272b      3  0.015b  0.085a  0.435b      4  0.016b  0.081a  0.338b      5  0.002c  0.003c  0.009b      SE  0.001  0.007  0.054  Type 3 tests of fixed effects (P-value)      Diet  0.05  0.06  0.10      Phase  <0.01  <0.01  <0.01      Diet × Phase  0.21  0.13  0.56    Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Main effect  Diet            Standard CP diet  0.016  0.062  0.413      Reduced CP diet  0.013  0.048  0.331      SE  <0.001  0.005  0.032  Phase        1  0.025a  0.064ab  0.808a      2  0.015b  0.041b  0.272b      3  0.015b  0.085a  0.435b      4  0.016b  0.081a  0.338b      5  0.002c  0.003c  0.009b      SE  0.001  0.007  0.054  Type 3 tests of fixed effects (P-value)      Diet  0.05  0.06  0.10      Phase  <0.01  <0.01  <0.01      Diet × Phase  0.21  0.13  0.56  a–dSignificant differences within a column variable differ at P < 0.05. 1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 to 166 d; initial BW = 113 kg. 2AU = animal unit is equivalent to 454 kg BW. View Large Methane and NMTHC Emissions No diet effect was observed for CH4 or NMTHC (Table 8). The CH4 emissions were greater during the finish phases (Phases 3 through 5) than grower phases (Phases 1 and 2). The NMTHC emissions showed a different trend from CH4 in that highest emissions (g · d–1 · AU–1) were observed during Phase 1. Our results disagree with those of Li et al. (2011) who observed increasing NMTHC emissions as pigs matured. The interactions between phase and treatment for concentration and emissions were not significant for either CH4 or NMTHC. Table 8. Least squares means of methane and nonmethane total hydrocarbon (NMTHC) emissions from grow-finish pigs fed either a standard CP diet or a reduced CP diet over 5 feeding phases1,2   Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Main effect  CH4  NMTHC  CH4  NMTHC  CH4  NMTHC  Diet                  Standard CP diet  3.67  0.05  3.17  0.04  15.57  0.28      Reduced CP diet  3.72  0.05  3.31  0.05  16.39  0.33      SE  0.04  <0.01  0.16  <0.01  0.84  0.03  Phase                  1  2.55d  0.05b  0.66d  0.05b  8.31e  0.61a      2  3.47c  0.03c  1.66c  0.03b  11.00d  0.22c      3  3.89b  0.03c  4.79a  0.08a  24.61a  0.42b      4  4.14b  0.03c  4.94a  0.03b  20.64b  0.12c      5  4.42a  0.08a  4.15b  0.05b  15.36c  0.17c      SE  0.06  <0.01  0.18  <0.01  0.83  0.04  Type 3 Tests of Fixed Effects (P-value)      Diet  0.41  0.17  0.55  0.28  0.50  0.20      Phase  <0.01  <0.01  <0.01  <0.01  <0.01  <0.01      Diet × Phase  0.34  0.71  0.46  0.93  0.33  0.94    Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Main effect  CH4  NMTHC  CH4  NMTHC  CH4  NMTHC  Diet                  Standard CP diet  3.67  0.05  3.17  0.04  15.57  0.28      Reduced CP diet  3.72  0.05  3.31  0.05  16.39  0.33      SE  0.04  <0.01  0.16  <0.01  0.84  0.03  Phase                  1  2.55d  0.05b  0.66d  0.05b  8.31e  0.61a      2  3.47c  0.03c  1.66c  0.03b  11.00d  0.22c      3  3.89b  0.03c  4.79a  0.08a  24.61a  0.42b      4  4.14b  0.03c  4.94a  0.03b  20.64b  0.12c      5  4.42a  0.08a  4.15b  0.05b  15.36c  0.17c      SE  0.06  <0.01  0.18  <0.01  0.83  0.04  Type 3 Tests of Fixed Effects (P-value)      Diet  0.41  0.17  0.55  0.28  0.50  0.20      Phase  <0.01  <0.01  <0.01  <0.01  <0.01  <0.01      Diet × Phase  0.34  0.71  0.46  0.93  0.33  0.94  a–dMeans within a column variable differ at P < 0.05. 1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 to 166 d; initial BW = 113 kg. 2AU = animal unit is equivalent to 454 kg BW. View Large Table 8. Least squares means of methane and nonmethane total hydrocarbon (NMTHC) emissions from grow-finish pigs fed either a standard CP diet or a reduced CP diet over 5 feeding phases1,2   Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Main effect  CH4  NMTHC  CH4  NMTHC  CH4  NMTHC  Diet                  Standard CP diet  3.67  0.05  3.17  0.04  15.57  0.28      Reduced CP diet  3.72  0.05  3.31  0.05  16.39  0.33      SE  0.04  <0.01  0.16  <0.01  0.84  0.03  Phase                  1  2.55d  0.05b  0.66d  0.05b  8.31e  0.61a      2  3.47c  0.03c  1.66c  0.03b  11.00d  0.22c      3  3.89b  0.03c  4.79a  0.08a  24.61a  0.42b      4  4.14b  0.03c  4.94a  0.03b  20.64b  0.12c      5  4.42a  0.08a  4.15b  0.05b  15.36c  0.17c      SE  0.06  <0.01  0.18  <0.01  0.83  0.04  Type 3 Tests of Fixed Effects (P-value)      Diet  0.41  0.17  0.55  0.28  0.50  0.20      Phase  <0.01  <0.01  <0.01  <0.01  <0.01  <0.01      Diet × Phase  0.34  0.71  0.46  0.93  0.33  0.94    Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Main effect  CH4  NMTHC  CH4  NMTHC  CH4  NMTHC  Diet                  Standard CP diet  3.67  0.05  3.17  0.04  15.57  0.28      Reduced CP diet  3.72  0.05  3.31  0.05  16.39  0.33      SE  0.04  <0.01  0.16  <0.01  0.84  0.03  Phase                  1  2.55d  0.05b  0.66d  0.05b  8.31e  0.61a      2  3.47c  0.03c  1.66c  0.03b  11.00d  0.22c      3  3.89b  0.03c  4.79a  0.08a  24.61a  0.42b      4  4.14b  0.03c  4.94a  0.03b  20.64b  0.12c      5  4.42a  0.08a  4.15b  0.05b  15.36c  0.17c      SE  0.06  <0.01  0.18  <0.01  0.83  0.04  Type 3 Tests of Fixed Effects (P-value)      Diet  0.41  0.17  0.55  0.28  0.50  0.20      Phase  <0.01  <0.01  <0.01  <0.01  <0.01  <0.01      Diet × Phase  0.34  0.71  0.46  0.93  0.33  0.94  a–dMeans within a column variable differ at P < 0.05. 1Phase 1 from pig age 60 to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 to 166 d; initial BW = 113 kg. 2AU = animal unit is equivalent to 454 kg BW. View Large CO2 Emissions and Calculated CO2eq A diet effect was not observed for CO2 or CO2eq concentrations or emissions (P > 0.05, Table 9). Similarly, interaction between phase and treatment was not significant for any variable. However, a phase effect was observed because CO2 emissions increased from 537.4 g · d–1 · pig–1 during Phase 1 to approximately 2,000 g · d–1 · pig–1 during Phases 3 through 5 (P < 0.01). The CO2 emissions based on AU (g · d–1 · AU–1) showed slightly different pattern compared with emissions based on pig count (g · d–1 · pig–1) in that the highest emission rates were observed during Phase 3. Table 9. Least squares means of CO2 and CO2 equivalent (CO2eq) concentrations and emissions from grow-finish pigs fed either a standard CP diet or a reduced CP diet over 5 feeding phases1,2   Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Main effect  CO2  CO2  CO2eq  CO2  CO2eq  Diet                Standard CP diet  713.4  1,461  1,563  7,531  8,022      Reduced CP diet  706.9  1,397  1,498  7,285  7,760      SE  5.4  34  34  159  163  Phase                1  585.5e  537d  556d  6,774d  7,010d      2  646.8d  746c  782c  4,940e  5,181e      3  690.0c  1,886b  2,013b  9,681a  10,333a      4  751.8b  2,037a  2,222a  8,488b  9,258b      5  876.8a  1,941ab  2,080b  7,159c  7,672c      SE  6.4  32  32  137  141  Type 3 tests of fixed effects (P-value)      Diet  0.42  0.21  0.20  0.30  0.27      Phase  <0.01  <0.01  <0.01  <0.01  <0.01      Diet × Phase  0.997  0.76  0.84  0.49  0.36    Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Main effect  CO2  CO2  CO2eq  CO2  CO2eq  Diet                Standard CP diet  713.4  1,461  1,563  7,531  8,022      Reduced CP diet  706.9  1,397  1,498  7,285  7,760      SE  5.4  34  34  159  163  Phase                1  585.5e  537d  556d  6,774d  7,010d      2  646.8d  746c  782c  4,940e  5,181e      3  690.0c  1,886b  2,013b  9,681a  10,333a      4  751.8b  2,037a  2,222a  8,488b  9,258b      5  876.8a  1,941ab  2,080b  7,159c  7,672c      SE  6.4  32  32  137  141  Type 3 tests of fixed effects (P-value)      Diet  0.42  0.21  0.20  0.30  0.27      Phase  <0.01  <0.01  <0.01  <0.01  <0.01      Diet × Phase  0.997  0.76  0.84  0.49  0.36  a–dMeans within a column variable differ at P < 0.05. 1Phase 1 from pig age 60 d to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 d to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 d to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 d to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 d to 166 d; initial BW = 113 kg. 2AU = animal unit, equivalent to 454 kg BW. View Large Table 9. Least squares means of CO2 and CO2 equivalent (CO2eq) concentrations and emissions from grow-finish pigs fed either a standard CP diet or a reduced CP diet over 5 feeding phases1,2   Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Main effect  CO2  CO2  CO2eq  CO2  CO2eq  Diet                Standard CP diet  713.4  1,461  1,563  7,531  8,022      Reduced CP diet  706.9  1,397  1,498  7,285  7,760      SE  5.4  34  34  159  163  Phase                1  585.5e  537d  556d  6,774d  7,010d      2  646.8d  746c  782c  4,940e  5,181e      3  690.0c  1,886b  2,013b  9,681a  10,333a      4  751.8b  2,037a  2,222a  8,488b  9,258b      5  876.8a  1,941ab  2,080b  7,159c  7,672c      SE  6.4  32  32  137  141  Type 3 tests of fixed effects (P-value)      Diet  0.42  0.21  0.20  0.30  0.27      Phase  <0.01  <0.01  <0.01  <0.01  <0.01      Diet × Phase  0.997  0.76  0.84  0.49  0.36    Concentration, mg/kg  Emissions, g · d–1 · pig–1  Emissions, g · d–1 · AU–1  Main effect  CO2  CO2  CO2eq  CO2  CO2eq  Diet                Standard CP diet  713.4  1,461  1,563  7,531  8,022      Reduced CP diet  706.9  1,397  1,498  7,285  7,760      SE  5.4  34  34  159  163  Phase                1  585.5e  537d  556d  6,774d  7,010d      2  646.8d  746c  782c  4,940e  5,181e      3  690.0c  1,886b  2,013b  9,681a  10,333a      4  751.8b  2,037a  2,222a  8,488b  9,258b      5  876.8a  1,941ab  2,080b  7,159c  7,672c      SE  6.4  32  32  137  141  Type 3 tests of fixed effects (P-value)      Diet  0.42  0.21  0.20  0.30  0.27      Phase  <0.01  <0.01  <0.01  <0.01  <0.01      Diet × Phase  0.997  0.76  0.84  0.49  0.36  a–dMeans within a column variable differ at P < 0.05. 1Phase 1 from pig age 60 d to 92 d; initial BW = 21 kg; Phase 2 from pig age 93 d to 117 d; initial BW = 52 kg; Phase 3 from pig age 118 d to 136 d; initial BW = 75 kg; Phase 4 from pig age 137 d to 158 d; initial BW = 94 kg; Phase 5 from pig age 159 d to 166 d; initial BW = 113 kg. 2AU = animal unit, equivalent to 454 kg BW. View Large When calculating the CO2eq emissions, because N2O and CH4 emissions are low from swine housing, CO2 was the most dominant GHGs, accounting for >90% of total CO2eq. Given the feeding strategy employed in this study (reduced diet CP), coupled with low emissions of N2O and CH4 from housing, it is not unexpected that no differences in CO2eq emissions were observed in the housing system. The potential for diet effects on CO2eq emissions lies in the manure management part of the livestock system, particularly N2O emissions that result following land application of manures containing different N content. In this study, the manure N content did not differ as a result of dietary treatments fed to the pigs suggesting that no difference in a feed-through-field CO2eq balance would be observed. Conclusion These findings illustrate that feeding reduced CP diets that are formulated based on National Research Council 2012 recommendations provides an effective tool for reducing NH3 emissions from swine housing compared with recent industry formulations. Previous work based on earlier nutritional guidelines (i.e., National Research Council, 1998) demonstrated large reductions in emissions as a result of reducing diet CP. As nutritional guidelines may continue to reduce CP and formulate based on SID AA basis (National Research Council, 2012), it could be expected that further reductions in diet CP would produce a diminishing returns effect on emissions. This study revealed that reductions remain large under present nutritional guidelines. The change in NH3 emissions for each percentage unit reduction of diet CP content that resulted from feeding the reduced CP diets compared with the standard CP diets corresponded to 47.9, 53.2, 26.8, 26.5, and 51.6% during Phases 1 through 5, respectively. With proper formulation, there are no negative impacts on pig performance. Reducing CP did not impact other gases (H2S, N2O, CH4, NMTHC, and CO2) emissions. This study considered emissions implications during swine housing only. Once manure is moved to long-term storage and applied to fields, diet effects on the volatilization of gases may be different from that observed during housing. Therefore, system emissions must be considered using a feed-through-field approach. LITERATURE CITED AOAC 1984. Official Methods of Analysis. 14th ed. Official Method 941.04. Assoc. Off. Anal. Chem., Arlington, VA. AOAC 2000. Official Methods of Analysis. 16th ed. Official Method 928.08. Assoc. Off. Anal. Chem., Arlington, VA. AOAC 2005. 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TI - Feeding reduced crude protein diets with crystalline amino acids supplementation reduce air gas emissions from housing
JF - Journal of Animal Science
DO - 10.2527/jas.2014-7746
DA - 2015-02-01
UR - https://www.deepdyve.com/lp/oxford-university-press/feeding-reduced-crude-protein-diets-with-crystalline-amino-acids-4eu0GF0R3A
SP - 721
EP - 730
VL - 93
IS - 2
DP - DeepDyve
ER -