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Journal of Animal Science logoLink to Journal of Animal Science
. 2022 Mar 11;100(6):skac075. doi: 10.1093/jas/skac075

The effect of reduced CP, synthetic amino acid supplemented diets on growth performance and nutrient excretion in wean to Finish swine

Caitlin E Vonderohe 1, Kayla M Mills 2, Shule Liu 3, Matthew D Asmus 4, Emily R Otto-Tice 5, Brian T Richert 6, Ji-Qin Ni 7, John Scott Radcliffe 8,✉
PMCID: PMC9175295  PMID: 35275195

Abstract

Mixed sex pigs (n = 720) were placed in 12 rooms (Purdue Swine Environmental Research Building) to measure the effect of reduced crude protein (CP), amino acid (AA)-supplemented diets on growth and the carcass. Pigs were blocked by body weight (BW) and gender and allotted to room and pen (10 mixed-sex pigs/pen). Pigs were fed a nine-phase, wean-finish program. Control pigs consumed corn-soybean meal-distiller’s dried grains with solubles (DDGS) diets containing no to minimal (Met) synthetic AA. The 2X diet was formulated to meet the seventh most-limiting AA, and balanced using synthetic AAs to meet all AA needs. The 1X diet was formulated to meet a CP value halfway between the control and 2X diet, and also balanced using synthetic AAs to meet all AA needs. Diets were formulated to identical net energy concentrations and balanced to meet standard ileal digestible NRC 2012 AA requirements. Pit vacuum samples were collected at the end of each growth phase for analyses of nitrogen, C and dry matter (DM). Pigs fed the Control and 1X diet grew faster (P < 0.005), had greater gain:feed (P < 0.001), and were heavier at market (P < 0.001) than animals fed the 2X diet. No consistent effects of diet were observed on average daily feed intake. Carcass data were analyzed for sex, diet and sex*diet effects. Reductions in dietary CP resulted in a linear reduction in ammonium nitrogen excretion per kg of BW gain in Nursery (P < 0.001) and Grow-Finish (P < 0.001) phases. Reductions in dietary CP, with synthetic AA supplementation resulted in a linear reduction in total nitrogen excreted per kg BW gain in the Grow-Finish phase (P < 0.001) and overall (P < 0.001). Total mineral excretion per kg gain was reduced in pigs fed 1X and 2X diets compared with control-fed pigs (P < 0.005). Reductions in dietary CP of ~3 and 5%-units from wean-finish result in reductions of total N excretion of 11.7 and 24.4%, respectively. Reduced performance and carcass characteristics observed in pigs fed the 2X diets indicates an inaccurate estimate of NRC 2012 AA requirements or ratios to lysine in a low CP diet.

Keywords: amino acids, environmental footprint, protein, swine

Introduction

In the natural world, the limited amount of fixed nitrogen sources have selected for very limited productivity, but high biodiversity in naturally occurring plant life (Erisman et al., 2013). When nitrogen leaches from fields after swine manure application, it can cause downstream acidification and eutrophication of bodies of water (Steinfeld and Wassenaar, 2007; Erisman et al., 2013). Excessive nitrogen can also result in downstream homogenization of plant populations because nitrogen can be phytotoxic in large doses and subsequently selects for nitrogen-tolerant species (Kenny and Hatfield, 2008; Erisman et al., 2013).

Inorganic nitrogen (as nitrate) can also discharge into drinking water resources after field application of manure. Excessive nitrates in drinking water can cause methemoglobinemia, abortion, and is associated with stomach cancer (Steinfeld, 2006). Human health risks, coupled with environmental damage associated with excessive nitrogen, has driven interest in strategies to reduce nitrogen excretion from swine.

Producers have successfully reduced nitrogen excretion from swine with dietary inclusion of synthetic amino acids (AA). Investigators have reported an 8.5% reduction in nitrogen excretion for every one percentage-unit reduction in dietary crude protein (CP) (Sutton and Richert, 2004). However, other investigators have noted a reduction in growth performance (Kerr and Easter, 1995) and energy retention with excessive dietary CP reduction (Jones et al., 2014). Therefore, the objective of this experiment was to determine the effect of using large quantitites of synthetic AA to balance diets to the seventh limiting AA on growth performance and manure characteristics in wean-to-finish swine.

Materials and Methods

All procedures were approved by the Purdue University Animal Care and Use Committee (PACUC# 1117000447).

Seven hundred twenty mixed sex pigs [Duroc X (York x Landrace)] were placed in 12 rooms at the Purdue Swine Environmental Research Building (SERB) to investigate the effects of feeding a reduced CP diet with supplemental synthetic AA on growth performance and environmental footprint. Each room contained 6 pens with 10 pigs per pen, and 2 manure pits (1.8 m deep) under sets of 3 pens, allowing for quantitative collection of manure. Pigs were blocked by source (Sow vs. Gilt farm), body weight (BW), and sex and randomly assigned to room and diet.

Diets

Each room was assigned one of three dietary treatments (4 rooms per diet). The control diet was formulated to meet the first limiting AA requirement and had no synthetic AA with the exception of methionine in nursery phases 1 to 3. The 2X diet was balanced to the 7th limiting AA, with synthetic AA used to meet the pigs’ requirement for the first 5 to 6 limiting AA. The 1X diet was formulated to have a CP concentration equidistant between the control and 2X diets. The result was that the 1X and 2X diets contained a stepwise reduction in CP from the control diet. During nursery phases 1-3, and then for nursery phase 4 to finisher 2, soy protein concentrate and soybean meal (SBM), respectively were reduced from the control diet as synthetic AA were increased in the 1X and 2X diets. Ractopamine (Paylean, Greenfield, IN) was added in finisher 2 diets, and therefore dietary CP could only be reduced to 16% in the 2X diet to meet Paylean feeding label requirements. Ractopamine was added to all the diets in the finisher 2 phase to maximize industry applicability of the study. Although this limited the degree to which CP was reduced in final finisher phase, the addition of ractopamine was in accordance with industry best practices at the time the study was conducted.

Diets (Tables 1 and 2) were formulated to meet or exceed all nutritional requirements (NRC, 2012), and were fed in nine dietary phases (four nursery phases, three grower phases, and two finisher phases). Nursery 1 and 2 were 7 d, Nursery 3 and 4 were 14 d, and the remaining dietary phases were 21 d. Diets were balanced to meet or exceed NRC (2012) standardized ileal digestible (SID) AA ratios to SID lysine. Net energy was kept constant across treatments and synthetic AA were added as needed, including lysine, methionine, threonine, tryptophan, isoleucine and valine (Ajinomoto, Tokyo, Japan)

Table 1.

Composition of nursery diets

Ingredient, % Nursery 1 Nursery 2 Nursery 3 Nursery 4
CTL 1X 2X CTL 1X 2X CTL 1X 2X CON 1X 2Xn
Corn, yellow dent 27.95 31.53 35.16 34.07 37.90 41.79 39.53 43.59 47.74 46.13 56.32 66.92
Corn DDGS, 7% 10.00 10.00 10.00 15.00 15.00 15.00
Soybean meal, 47.5% CP 15.00 15.00 15.00 18.00 18.00 18.00 20 20 20 31.14 21.84 11.96
Soy protein concentrate 8.07 4.61 0.99 8.04 4.40 0.44 11.20 7.28 3.14
Soybean oil 4.72 4.35 3.93 4.91 4.49 4.04 2.50 2.07 1.59
Choice white grease 4.71 3.39 1.90
Plasma spray-dried 6.50 6.50 6.50 2.50 2.50 2.50
Se premix 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05
Blood meal spray-dried 1.00 1.00 1.00 1.00 1.00 1.00
Whey, dried 25.00 25.00 25.00 25.00 25.00 25.00 10.00 10.00 10.00
Fish meal, menhaden 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00
Lactose 5.00 5.00 5.00
Limestone 1.14 1.15 1.16 0.99 1.01 1.03 0.91 0.92 0.94 1.09 1.13 1.18
Monocalcium phosphate 21% 0.05 0.09 0.13 0 0.01 0.05 0.15 0.19 0.23 0.78 0.85 0.93
Trace Mineral Premix- pigs 0.18 0.18 0.18 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15
Vitamin Premix- Nursery 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25
Salt 0.25 0.25 0.25 0.25 0.25 0.25 0.46 0.47 0.47 0.35 0.35 0.35
Phytase 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10
Carbadox 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25
Zinc Oxide 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38
l-Lysine HCl 0.166 0.339 0.177 0.365 0.176 0.375 0.295 0.608
dl-Methionine 0.113 0.148 0.198 0.072 0.125 0.183 0.061 0.119 0.181 0.004 0.087
l-Threonine 0.074 0.001 0.095 0.07 0.016 0.151
l-Tryptophan 0.005 0.017 0.048 0.01 0.043 0.052
l-Isoleucine 0.01 0.0001 0.041
l-Valine 0.04 0.033 0.042 0.021
Calculated composition, %
Lysine 1.80 1.80 1.79 1.63 1.63 1.62 1.55 1.54 1.53 1.20 1.18 1.15
Threonine 1.21 1.13 1.11 1.10 1.01 1.00 1.07 0.97 0.94 0.86 0.73 0.71
Methionine 0.50 0.51 0.54 0.46 0.49 0.52 0.45 0.48 0.51 0.37 0.33 0.36
Met + Cysteine 1.02 1.00 0.99 0.90 0.90 0.90 0.83 0.83 0.83 0.74 0.65 0.63
Tryptophan 0.36 0.33 0.31 0.33 0.32 0.31 0.3 0.28 0.27 0.26 0.2 0.20
Isoleucine 1.11 1.01 0.94 1.09 0.97 0.86 1.08 0.96 0.83 0.95 0.78 0.62
Valine 1.39 1.28 1.18 1.28 1.17 1.08 1.3 1.19 1.1 1.09 0.92 0.77
Arginine 1.64 1.45 1.25 1.58 1.38 1.17 1.66 1.45 1.23 1.42 1.13 0.83
Histidine 0.75 0.70 0.64 0.70 0.64 0.58 0.64 0.58 0.52 0.6 0.51 0.41
Leucine 2.31 2.16 2.00 2.17 2.01 1.85 2.01 1.84 1.66 2.07 1.83 1.57
Phenylalanine 1.28 1.17 1.07 1.20 1.08 0.97 1.15 1.03 0.91 1.1 0.92 0.73
Tyrosine 2.22 2.04 1.85 2.07 1.87 1.67 2 1.79 1.58 1.95 1.63 1.28
Crude Protein 26.16 24.43 22.7 24.92 23.08 21.25 26.52 24.56 22.59 22.87 19.59 16.31
Phosphorus 0.66 0.65 0.64 0.63 0.63 0.6 0.64 0.63 0.62 0.63 0.61 0.58
Analyzed composition, %
Lysine 1.76 1.74 1.81 1.56 1.68 1.54 1.52 1.47 1.57 1.18 1.22 1.11
Threonine 1.15 1.07 1.09 0.97 0.97 0.87 0.99 0.89 0.88 0.82 0.75 0.64
Methionine 0.52 0.49 0.49 0.41 0.47 0.44 0.46 0.45 0.52 0.33 0.31 0.31
Met + Cysteine 0.96 0.91 0.88 0.77 0.83 0.73 0.82 0.76 0.84 0.65 0.61 0.56
Tryptophan 0.32 0.31 0.32 0.32 0.3 0.3 0.29 0.28 0.27 0.24 0.23 0.18
Isoleucine 1.03 0.96 0.88 0.97 0.97 0.77 1.09 0.97 0.89 0.9 0.8 0.59
Valine 1.42 1.32 1.27 1.24 1.22 1.04 1.25 1.11 1.08 1.06 0.93 0.74
Arginine 1.52 1.39 1.29 1.38 1.39 1.09 1.58 1.39 1.27 1.36 1.18 0.8
Histidine 0.71 0.67 0.61 0.65 0.65 0.53 0.67 0.6 0.56 0.59 0.52 0.39
Leucine 2.28 2.17 2.03 2.05 2.06 1.74 2.21 2.03 1.91 1.97 1.84 1.48
Phenylalanine 1.26 1.18 1.09 1.13 1.13 0.9 1.26 1.13 1.03 1.12 0.99 0.73
Tyrosine 2.05 1.91 1.81 1.81 1.82 1.46 2 0.69 1.65 1.8 1.59 1.18
Crude Protein 25.36 23.48 22.41 24.44 22.62 19.11 25.15 24.19 22.53 22.57 19.13 15.022
Phosphorus 0.68 0.64 0.68 0.68 0.65 0.62 0.69 0.68 0.63 0.68 0.69 0.65
Carbon 40.79 41.57 40.2 41.14 40.47 39.44 40.2 40.3 39.66 41.54 39.5 38.95
Dry Matter 78.53 79.15 79.41 79.15 77.25 80.33 81.75 79.62 80.89 82.07 82.21
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Table 2.

Composition of grower-finisher diets

Ingredient, % Grower 1 Grower 2 Grower 3 Finisher 1 Finisher 2
CTL 1X 2X Control 1X 2X Control 1X 2X CTL 1X 2X Control 1X 2X
Corn, yellow dent 48.19 59.06 69.84 47.70 58.05 69.11 49.80 60.30 71.28 67.90 76.39 85.27 60.39 67.35 74.53
Soybean meal, 47.5% CP 28.09 18.32 8.29 25.92 16.37 6.16 23.92 14.34 4.07 21.62 13.85 5.53 29.54 23.16 16.47
Corn DDGS, 7% 18.00 18.00 18.00 20.00 20.00 20.00 20.00 20.00 20.00 5.00 5.00 5.00 5.00 5.00 5.00
Limestone 1.03 0.98 1.02 0.91 1.02 1.00 0.97 1.01 1.06 0.94 0.98 1.02 0.95 0.98 1.01
Monocalcium phosphate 21% 0.70 0.78 0.86 0.73 0.81 0.89 0.57 0.65 0.73 0.46 0.52 0.57 0.40 0.45 0.50
Salt 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.30 0.30 0.30 0.30 0.30 0.30
Choice white grease 2.99 1.55 0.04 3.93 2.60 1.00 3.92 2.55 1.00 3.38 2.27 1.00 2.90 1.99 1.00
Trace Mineral Premix 0.15 0.15 0.15 0.09 0.09 0.09 0.09 0.09 0.09 0.08 0.08 0.08 0.08 0.08 0.08
Vitamin Premix 0.25 0.25 0.25 0.15 0.15 0.15 0.15 0.15 0.15 0.13 0.13 0.13 0.13 0.13 0.13
Phytase 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10
Se premix 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.03 0.03 0.03 0.03 0.03 0.03
Lincomix (20 g Linco/lb) 0.10 0.10 0.10 0.04 0.04 0.04 0.04 0.04 0.04 0.03 0.03 0.03
Rabon Larvacide 0.04 0.04 0.04 0.04 0.04 0.04 0.05 0.05 0.05 0.05 0.05 0.05
Paylean, 2.25 g/lb 0.15 0.15 0.15
l-lysine HCl 0.309 0.627 0.303 0.627 0.304 0.63 0.246 0.51 0.202 0.414
DL-Methionine 0.065 0.063 0.063 0.065 0.012 0.07
l-Threonine 0.007 0.144 0.011 0.151 0.008 0.149 0.034 0.148 0.031 0.123
l-Tryptophan 0.004 0.058 0.02 0.076 0.022 0.078 0.008 0.053 0.032
l-Valine 0.033 0.076 0.075 0.078 0.035
l-Isoleucine 0.03 0 0.032 0.054 0.051
Calculated composition, %
Lysine 1.14 1.12 1.09 1.09 1.07 1.04 1.04 1.01 0.99 0.88 0.86 0.84 1.1 1.08 1.06
Threonine 0.83 0.69 0.67 0.81 0.68 0.66 0.78 0.64 0.62 0.65 0.56 0.54 0.77 0.7 0.69
Methionine 0.37 0.32 0.34 0.36 0.32 0.33 0.35 0.31 0.32 0.29 0.25 0.27 0.33 0.31 0.33
Met + Cysteine 0.73 0.63 0.59 0.72 0.62 0.58 0.69 0.6 0.55 0.59 0.51 0.49 0.68 0.63 0.61
Tryptophan 0.25 0.19 0.19 0.24 0.2 0.19 0.22 0.19 0.18 0.19 0.15 0.15 0.24 0.2 0.19
Isoleucine 0.92 0.74 0.58 0.89 0.72 0.56 0.86 0.68 0.54 0.71 0.56 0.46 0.86 0.74 0.61
Valine 1.06 0.89 0.73 1.04 0.86 0.75 1 0.83 0.71 0.82 0.68 0.6 0.97 0.85 0.76
Arginine 1.35 1.05 0.74 1.3 1 0.69 1.24 0.94 0.63 1.06 0.82 0.56 1.31 1.11 0.9
Histidine 0.59 0.49 0.39 0.57 0.48 0.37 0.55 0.45 0.35 0.47 0.39 0.3 0.55 0.48 0.42
Leucine 2.07 1.82 1.56 2.05 1.8 1.54 2 1.75 1.48 1.62 1.42 1.2 1.84 1.67 1.5
Phenylalanine 1.08 0.88 0.69 1.05 0.86 0.66 1.01 0.82 0.62 0.84 0.69 0.52 1 0.88 0.74
Tyrosine 1.9 1.56 1.21 1.86 1.52 1.16 1.79 1.45 1.09 1.46 1.19 0.89 1.75 1.52 1.29
Crude Protein 22.43 19 15.66 21.93 18.57 15.21 21.16 17.79 14.41 17.32 14.6 11.89 20.46 18.23 16
Phosphorus 0.62 0.6 0.58 0.63 0.6 0.58 0.58 0.56 0.54 0.48 0.46 0.44 0.5 0.48 0.47
Analyzed composition, %
Lysine 1.14 1.1 1.05 1.05 1.04 0.96 1.05 1.05 0.91 0.83 0.84 0.82 1.09 1.04 1.05
Threonine 0.8 0.69 0.63 0.75 0.65 0.59 0.76 0.65 0.58 0.58 0.52 0.49 0.73 0.64 0.65
Methionine 0.32 0.3 0.33 0.3 0.29 0.31 0.31 0.29 0.23 0.24 0.22 0.27 0.3 0.27 0.32
Met + Cysteine 0.32 0.29 0.25 0.3 0.28 0.25 0.3 0.28 0.21 0.24 0.22 0.18 0.29 0.26 0.26
Tryptophan 0.23 0.2 0.17 0.24 0.19 0.17 0.22 0.21 0.2 0.19 0.16 0.17 0.24 0.2 0.18
Isoleucine 0.86 0.74 0.56 0.81 0.68 0.54 0.87 0.73 0.52 0.66 0.56 0.45 0.87 0.73 0.65
Valine 1.01 0.89 0.7 0.96 0.83 0.71 1 0.86 0.7 0.76 0.64 0.54 0.97 0.82 0.76
Arginine 1.28 1.04 0.7 1.18 0.94 0.67 1.21 0.99 0.57 0.93 0.75 0.51 1.23 1 0.89
Histidine 0.56 0.49 0.38 0.54 0.47 0.37 0.54 0.46 0.32 0.41 0.35 0.27 0.51 0.44 0.39
Leucine 1.96 1.8 1.46 1.86 1.71 1.46 1.93 1.73 1.33 1.45 1.29 1.1 1.76 1.57 1.42
Phenylalanine 1.06 0.93 0.69 1.02 0.88 0.67 0.99 0.85 0.57 0.76 0.65 0.5 0.97 0.83 0.74
Tyrosine 1.71 1.48 1.08 1.64 1.4 1.07 1.62 1.37 0.95 1.21 1.02 0.8 1.55 1.31 1.2
Crude Protein 23.02 19.04 15.02 20.69 17.21 14.47 21.5 18.24 15.29 18.42 16.33 13.56 22.71 19.29 18.08
Phosphorus 0.7 0.72 0.66 0.69 0.67 0.92 0.88 0.62 0.78 0.47 0.76 0.3 0.47 0.48 0.49
Carbon 40.26 39.93 38.47 40.47 39.94 38.62 40.19 39.35 38.86 41.92 40 40.04 40.95 40.99 40.8
Dry matter 82.06 82.21 82.26 86.52 86.98 87.05 85.43 85.37 85.15 85.03 84.37 85.41 82.95 82.37 82.99
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Performance data collection

Pigs had ad libitum access to feed and water via two single space feeders and two nipple waterers and were housed at 0.84 m2/pig. Pigs and feeders were weighed at each diet change (d 0, 7, 14, 28, 42, 63, 84, 105, 126, and prior to market). Pigs in the heaviest replicates were marketed at d 139 and pigs on the light replicates were marketed on d 147 in an attempt to better mimic industry practices and have a similar BW across replicates.

Morbidity and mortality were recorded daily. When deemed necessary, pigs were administered injectable antibiotics and treatments were recorded. Animals of the same sex within a pen were tattooed with a common pen number so that carcass data could be collected from the packing plant (Tyson Foods Inc., Logansport, IN). Aerial gas concentrations were determined every 2 h from each room and coupled with continuous airflow rates to determine daily gas emissions from each room and have been reported previously (Liu et al., 2017).

Sample collection and analysis

Samples of feed were ground through a 1 mm screen using a Wiley mill (Thomas Scientific, Swedsboro, NJ) for subsequent analyses. Feed was analyzed for dry matter (DM), ash, total Kjeldahl nitrogen (TN), C and total P in the Purdue Animal Sciences Nutrition Laboratory and AA concentrations by the University of Missouri Experiment Station Laboratory.

Manure volume was calculated at each diet change by using manure depth measurements in each pit. Manure pit samples were collected at the end of the nursery, grower, and finisher phases using a vacuum sampler in a grid sampling pattern. Samples were homogenized and a sub-sample was frozen (–20 °C) for subsequent analyses. All feed and manure samples were analyzed in duplicate and required to be within 5% of each other to accept the values. In addition to the vacuum samples, at the end of the experiment, manure pits were emptied into a small Slurry Store, mixed, and a representative subsample was collected and frozen (–20 °C) for subsequent analyses. These manure slurry samples were analyzed for pH, DM, ash, TN, ammonium N (AmmN), C and P.

Carbon was measured on feed and slurry using a Flash EA 1112 Series Nitrogen-Carbon Analyzer (CE Elantech, Inc. Lakewood, NJ). Dry matter was measured following a 12 h drying period at 100 °C, and ashing occurred over 8 h at 600°C in a muffle furnace (Thermo Fisher Scientific, Inc. Waltham, MA). Total nitrogen and AmmN were measured using the micro-kjeldahl procedure (Bremner and Keeney, 1965). Manure pH was measured using an Orion 310 basic PerpHecT LogR pH meter (Thermo Fisher Scientific Inc. Waltham, MA). Phosphorus was measured colorimetrically in feed and feces following a nitric-percholoric acid digestion (Murphy and Riley, 1962).

Statistical analysis

Data were analyzed using the GLM procedure of SAS 9.4 (Cary, NC), with pen as the experimental unit for growth performance and carcass data, pit for manure data, and room for emission data. Linear and quadratic responses were compared using single degree of freedom contrasts for decreasing dietary CP concentration. Gas emissions were analyzed using the Mixed procedure in SAS with fixed effects of day and treatment. A P value ≤ 0.05 indicated a significant difference where P values between 0.05 < P ≤ 0.10 were considered a trend.

Results

Feed composition

Analyzed content of the feed was generally similar to calculated values (Tables 1 and 2). A stepwise reduction in CP was achieved in each dietary phase.

Average daily gain

Average daily gain (ADG; Table 3) was similar across treatments for the first 7 d post-weaning (P > 0.10). However, in the second week post-weaning, pigs fed the Control and 1X diets grew faster compared to pigs fed the 2X diet (P < 0.05). There were no differences in growth rate in the third nursery phase (P > 0.10), but in the fourth nursery phase, animals fed the 2X diet grew slower than pigs fed the 1X and Control diets (P < 0.05). Differences in growth rate in the second and fourth nursery phases drove an overall reduction in ADG for pigs fed the 2X diet compared with those fed the Control and 1X diets (P < 0.001) during the nursery period.

Table 3.

The effects of lowering dietary crude protein and adding synthetic amino acids on growth performance

Diet1 MSE P Linear P Quadratic P
Control 1X 2X
Pig BW, kg
 Day 0 6.2279 6.2049 6.1940 0.69083 0.9920 0.8655 0.9720
 Day 7 7.4290 7.5525 7.4520 0.7717 0.8407 0.9182 0.5635
 Day 14 9.9027 10.1917 9.8726 0.8781 0.3865 0.9059 0.1712
 Day 28 16.8821 17.3940 16.8208 1.1783 0.1891 0.8577 0.0704
 Day 42 26.4495a 26.7025a 25.1492b 1.7250 0.0059 0.0114 0.0405
 Day 63 43.8239a 42.6060a 40.7084b 2.4695 0.0002 <0.0001 0.5840
 Day 84 64.8898a 64.4769a 61.1584b 2.9240 <0.0001 <0.0001 0.0515
 Day 105 87.1706a 86.9978a 83.2905b 3.2197 <0.0001 <0.0001 0.0320
 Day 126 108.6599a 110.1645a 105.7972b 3.3309 0.0001 0.0042 0.0008
 Mkt 129.019a 129.032a 125.080b 3.9212 0.0008 0.0008 0.0527
ADG, kg
 Days 0–7 0.1715 0.1925 0.1797 0.0410 0.2123 0.4950 0.1050
 Days 7–14 0.3533b 0.3770a 0.3458b 0.0362 0.0111 0.4708 0.0036
 Days 14–28 0.4985 0.5144 0.4962 0.0322 0.1126 0.8117 0.0386
 Days 28–42 0.6833a 0.6648a 0.5928b 0.0507 0.0012 0.2416 <0.0001
 Days 42–63 0.8273a 0.7573b 0.7409b 0.0500 <0.0001 <0.0001 0.0359
 Days 63–84 1.0031b 1.0351a 0.9738c 0.0409 <0.0001 0.0258 <0.0001
 Days 84–105 1.0609 1.0724 1.0539 0.0599 0.5611 0.6838 0.3215
 Days 105–126 1.0233b 1.1031a 1.0717a 0.0682 0.0006 0.0168 0.0018
 Days 126–mkt2 1.2428a 1.1468b 1.1715b 0.1020 0.0052 0.0140 0.0182
 Nursery, Days 0–42 0.4814a 0.4880a 0.4513b 0.0296 0.0001 0.0008 0.0049
 Grower, Days 42–105 0.9638a 0.9570a 0.9229b 0.0337 0.0002 <0.0001 0.1087
 Finisher, Days 105–mkt 1.1188 1.1159 1.1157 0.0563 0.9804 0.7828 0.7771
 Overall, Days 0–mkt 0.8619a 0.8621a 0.8344b 0.0254 0.0003 0.0004 0.0361
ADFI, kg
 Days 0–7 0.1777 0.1970 0.1887 0.0283 0.0679 0.1804 0.0563
 Days 7–14 0.4173 0.4363 0.4107 0.0552 0.2558 0.6790 0.1110
 Days 14–28 0.7202b 0.7627a 0.6612c 0.0601 <0.0001 0.0012 <0.0001
 Days 28–42 1.0895ab 1.1062a 1.0470b 0.0866 0.0584 0.0945 0.0848
 Days 42–63 1.6792a 1.6016b 1.6490a 0.0977 0.0272 0.5607 0.0101
 Days 63–84 2.2954 2.3035 2.2992 0.1293 0.9689 0.6471 0.9807
 Days 84–105 2.8462 2.9022 2.8997 0.1934 0.4573 0.5642 0.7021
 Days 105–126 3.2424b 3.3673a 3.3357ab 0.1749 0.0448 0.0762 0.0747
 Days 126–mkt 3.1215 3.1348 3.1602 0.1694 0.7251 0.4319 0.8875
 Nursery, days 0–42 0.6797a 0.7057a 0.6704b 0.0446 0.0228 0.0124 0.0003
 Grower, days 42–105 2.2782 2.2673 2.2915 0.1101 0.7484 0.6774 0.5256
 Finisher, days 105–mkt 3.1964 3.2948 3.2548 0.1371 0.2426 0.1977 0.2769
 Overall, days 0–mkt 2.0487 2.0709 2.0618 0.0814 0.6383 0.5785 0.4445
Gain:feed
 Days 0–7 0.9562 0.9705 0.9538 0.1199 0.8742 0.6821 0.7530
 Days 7–14 0.8546 0.8669 0.8109 0.0896 0.0871 0.9214 0.7478
  Days 14–28 0.6980b 0.6892b 0.7701a 0.0647 <0.0001 0.0003 0.0073
  Days 28–42 0.6293a 0.6039a 0.5725b 0.0507 0.0012 0.0003 0.8120
  Days 42–63 0.4921a 0.4744b 0.4472c 0.0253 <0.0001 <0.0001 0.6234
  Days 63–84 0.4380b 0.4530a 0.4250c 0.0242 0.0012 0.0355 0.0006
  Days 84–105 0.3726 0.3710 0.3646 0.0248 0.4699 0.2486 0.6796
  Days 105–126 0.3162 0.3285 0.3225 0.0259 0.2662 0.4083 0.1612
  Days 126–mkt 0.3938a 0.3662b 0.3710b 0.0287 0.0046 0.0027 0.0192
 Nursery, day 0–42 0.6873 0.6731 0.6786 0.0314 0.2927 0.3387 0.2139
 Grower, day 42–105 0.4237a 0.4208a 0.4033b 0.0155 <0.0001 <0.0001 0.0286
 Finisher, day 105–mkt 0.3502 0.3440 0.3432 0.0203 0.4308 0.2102 0.5623
 Overall, day 0–mkt 0.4210a 0.4143a 0.4051b 0.0122 0.0001 0.0001 0.3238
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Values with different superscripts, within a row are different (P < 0.05)

Pigs fed the Control diet grew faster than those fed the 1X and 2X diets in the first grower phase (d105-market (mkt); P < 0.001). In the second grower phase, pigs fed the 1X diet grew the fastest, followed by Control-fed pigs, and then pigs fed the 2X diet (P < 0.001). There were no differences in ADG in the third grower phase (P > 0.10), but differences in growth rate in the early grower phases resulted in greater ADG for pigs fed the Control and 1X diet compared to 2X-fed pigs for the overall grower period (d 42–105; P < 0.001).

Pigs fed the 1X and 2X diets grew faster than control-fed pigs in the finisher 1 phase (d 105 to 126; P < 0.001), but this pattern reversed during finisher 2 (d 126 to 140), where Control-fed animals grew faster than both 1X- and 2X-fed pigs (P < 0.05). Therefore, there were no differences in ADG for the overall finisher phase (d105-mkt; P>0.100.9804).

For the entire wean-to-finish study, pigs fed the 2X diet grew 3.2% slower than pigs fed the Control or 1X diets (P < 0.001).

Body weight

There were not differences in mean BW observed at d 0, 7, 14 or 28 post weaning (P > 0.05). At 42 d postweaning, pigs fed the Control and 1X diets were heavier than pigs fed the 2X diets (P < 0.05). The 2X pigs were also lighter than 1X and Control pigs at d 63, 84, 105, 126, and were marketed approximately 4 kg lighter than pigs fed the 1X and Control diets (P < 0.05).

Average daily feed intake

Pigs fed the 1X diet tended to consume more feed (Table 3) during the first 7 d post-weaning than Control-fed pigs with pigs fed the 2X diet consuming an intermediate amount (P < 0.10). There was no difference in average daily feed intake (ADFI) during the second week post-weaning (P > 0.10). However, in the third nursery phase (days 14 to 28), pigs fed the 1X diet consumed the greatest quantity of feed, followed by Control-fed pigs and then pigs fed the 2X diet (P < 0.0001). This pattern tended to continue during the final nursery phase (days 28 to 42; P < 0.10). For the overall nursery period (days 0 to 42), pigs fed the Control and 1X diets consumed more feed than pigs fed the 2X diet (P < 0.05).

In the grower 1 phase, pigs fed the 2X and Control diets consumed more feed than pigs fed the 1X diet (P < 0.05). There were no differences in ADFI among treatments in the latter two grower phases (P > 0.10; P > 0.10) or for the overall grower period (days 42 to 105; P > 0.10).

During the first finisher phase (days 105 to 126), pigs fed the 1X diet consumed more feed than pigs fed the Control diet, with pigs fed the 2X diet consuming an intermediate amount (P < 0.05). However, no differences were observed in feed intake in the late finisher phase (P > 0.10), or for the overall finisher period (P > 0.10).

For the entire wean-to-finish period, no differences in ADFI were observed (P > 0.10) among dietary treatments.

Feed efficiency

There was no difference in feed conversion in the first two weeks post-weaning (Table 3; Week 1: P > 0.10; Week 2: P > 0.05). During the third nursery phase, pigs fed the 2X diet had a greater gain:feed (G:F) compared to Control- and 1X-fed pigs (P < 0.001). However, this reversed in the final nursery phase where we observed higher G:F for Control- and 1X-fed pigs compared to 2X-fed pigs (P < 0.05). As a result there was no difference in feed efficiency among treatments for the overall nursery period (P > 0.10).

In the early grower period, all three treatments were different in feed efficiency (G:F), with pigs fed the Control diet having the greatest G:F, followed by pigs-fed the 1X diet, and then pigs fed the 2X diet (P < 0.001). The top two switched rank during the second grower phase with pigs fed the 1X diet having the greatest G:F, followed by Control-fed pigs, and then pigs fed the 2X diet (P < 0.05). In the final grower phase no differences in feed conversion were observed among dietary treatments (P > 0.1). For the overall grower period (days 42 to 105), pigs fed the 1X and Control diets had greater G:F compared to pigs fed the 2X diet (P < 0.001).

There was no difference in G:F among diets in the early finisher phase (P > 0.10). However, in the late finisher, pigs fed the Control diets had a greater G:F compared to both 1X- and 2X-fed pigs (P < 0.05).

Overall, from wean to finish, pigs fed the Control and 1X diets had greater Gain:Feed compared to pigs fed the 2X diet (P < 0.001).

Pig health

Tracking pig health and therapeutic treatments throughout the study (Table 4), an overall decrease in frequency of unhealthy pigs fed the 2X diet compared to the Control fed pigs (P < 0.05) was observed. This resulted in fewer therapeutic treatments (injections) being administered during the grower period and overall to pigs fed the 2X diets compared to Control-fed pigs with the 1X-fed pigs being intermediate (P < 0.05).

Table 4.

The effects of lowering dietary crude protein and adding synthetic amino acids on the frequency of observed unhealthy pigs and of treatments.

Diet MSE P
Control 1X 2X
Frequency of unhealthy pigs
 Nursery Period 0.0224 0.0189 0.0177 0.0040 0.2734
 Grower Period 0.0116 0.0102 0.0095 0.0018 0.3100
 Finisher Period 0.0030 0.0052 0.0036 0.0031 0.6148
 Overall 0.0142a 0.0125ab 0.0115b 0.0015 0.0978
Frequency of treatment by injection
 Nursery Period 0.0357 0.0314 0.0281 0.0077 0.4177
 Grower Period 0.0195a 0.0142ab 0.0115b 0.0039 0.0515
 Finisher Period 0.0043 0.0076 0.0060 0.0044 0.5797
 Overall 0.0231a 0.0193ab 0.0165b 0.0034 0.0638
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Values with different superscripts, within a row are different (P < 0.05).

Carcass characteristics

There were no differences among treatments for carcass fat depth (P > 0.05; Table 5). Pigs fed the 2X diet had smaller loin depths (P < 0.05) compared to 1X- and Control-fed pigs and tended to have lower percent lean than pigs fed the 1X diet (P < 0.10). However, pigs fed the 2X diet held an advantage for base meat price compared to 1X-fed pigs (P < 0.05). Pigs fed the 1X diet had greater carcass yield (P < 0.05) than pigs fed the Control diet and greater carcass grade premium (P < 0.05) than pigs fed the 2X diet, but also had a larger sort loss (P < 0.05) than pigs fed the 2X diet. Pigs fed the 1X diet had heavier carcass weights (P < 0.05) than pigs fed the 2X diets with Control-fed pigs being intermediate. When all summed together, final carcass price per kg was not affected by dietary treatment (P > 0.12). When final carcass price was combined with average carcass weights, pigs fed the 1X diets had the greatest revenue per pig ($163.72), followed by the Control-fed pigs ($162.08), and lastly the 2X-fed pigs ($160.73).

Table 5.

The effects of lowering dietary crude protein and adding synthetic amino acids on carcass characteristics

Carcass characteristics
Diet Fat depth, mm
MSE P-value
Sex CTRL 1X 2X Diet Sex Diet*Sex
B 0.9025 0.8775 0.8941 22.64 0.0826 0.6539 <0.0001 0.5748
G 0.7241 0.7383 0.7658 18.86 Linear Quadratic
20.66 20.52 21.08 0.5055 0.5258
Loin depth, mm
Diet MSE P-value
Sex CTRL 1X 2X Diet Sex Diet*Sex
B 2.9583 2.9508 2.8750 74.37 0.0979 0.0124 0.2426 0.6930
G 2.9583 2.9975 2.9100 75.06 Linear Quadratic
75.13a 75.54a 73.46b 0.0203 0.0507
Percent lean
Diet MSE P-value
Sex CTRL 1X 2X Diet Sex Diet*Sex
B 55.100 55.233 54.825 55.052 0.7118 .0628 <0.0001 0.9315
G 56.141 56.316 55.758 56.072 Linear Quadratic
55.620ab 55.775a 55.219b 0.1140 0.0779
Base meat price
Diet MSE P-value
Sex CTRL 1X 2X Diet Sex Diet*Sex
B 70.181 70.082 71.431 70.565 1.5118 0.0461 0.0061 0.4573
G 71.753 71.067 71.905 71.575 Linear Quadratic
70.967ab 70.575b 71.668a 0.1129 0.05035
Yield, %
Diet MSE P-value
Sex CTRL 1X 2X Diet Sex Diet*Sex
B 74.845 76.102 75.322 75.423 1.6443 0.0072 0.4871 0.8359
G 74.820 76.644 75.619 75.694 Linear Quadratic
74.83b 76.37a 75.47ab 0.1836 0.0041
Premium grade, %
Diet MSE P-value
Sex CTRL 1X 2X Diet Sex Diet*Sex
B 6.6975 6.8841 6.1325 6.5714 0.8800 0.0236 0.1536 0.5918
G 6.6983 7.2958 6.6183 6.8708 Linear Quadratic
6.697ab 7.090a 6.375b 0.2088 0.0144
Sort loss
Diet MSE P-value
Sex CTRL 1X 2X Diet Sex Diet*Sex
B 1.5750 2.1450 1.1041 1.6081 0.9765 .0254 0.0019 0.6621
G 0.8508 1.1350 0.6066 0.8642 Linear Quadratic
1.212ab 1.640a 0.855b 0.2092 0.0156
Carcass value per 100 wt
Diet MSE P-value
Sex CTRL 1X 2X Diet Sex Diet*Sex
B 75.304 74.821 76.460 75.528 3.28486 0.1882 0.0002 0.7178
G 77.608 77.228 77.917 77.582 Linear Quadratic
76.452 76.025 77.188 0.2512 0.1533
Actual weight
Diet MSE P-value
Sex CTRL 1X 2X Diet Sex Diet*Sex
B 217.00 215.67 209.08 213.91 9.2723 0.0330 0.0737 0.1782
G 207.25 215.167 207.416 209.94 Linear Quadratic
212.12ab 215.417a 208.25b 0.1524 0.0274
Diet
Sex CTRL 1X 2X
B 12 12 12 36
G 12 12 12 36
24 24 24
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Values with different superscripts, within a row are different (P < 0.05).

Manure

Overall there was not a significant reduction in manure volume excreted per kg gain by 2X-fed pigs compared to Control- and 1X-fed pigs (Table 6; Linear P > 0.10). There was no difference observed among treatments in DM excreted per kg gain (P > 0.10) or P excretion per kg gain (P > 0.10). Pigs fed the Control diet excreted a greater quantity of ash per kg of gain compared to both 1X- and 2X-fed pigs (P < 0.05). Manure pH tended (P < 0.10) to be reduced linearly from Control- to 2X-fed pigs. Pigs fed the 2X diet excreted less AmmN compared to Control-fed pigs, with the 1X-fed pigs excreting an intermediate quantity per kg of gain (P < 0.05). Reducing dietary CP by ~3 (1X) and 5 (2X) percentage units resulted in an 11.7 and 24.4 % reduction in total nitrogen excretion, respectively (P < 0.001).

Table 6.

The effects of lowering dietary crude protein and adding synthetic amino acids on nutrient excretion

Diet MSE P Values
Control 1X 2X Diet Lin Quad
Nursery wet volume (L) 7.01 6.82 6.81 1.7083 0.9683 0.8235 0.9087
Nursery dry matter (g) 400.29 438.35 404.64 78.9056 0.5806 0.9130 0.3054
Nursery ash (g) 70.62 71.33 67.32 8.3065 0.5958 0.4362 0.5184
Nursery total P (g) 7.19 7.14 9.12 4.3463 0.5916 0.3857 0.5949
Nursery AmmN (g) 19.09a 15.91b 12.25c 1.9641 <0.0001 <0.0001 0.7803
Nursery total N (g) 35.68 31.56 29.19 6.0123 0.1168 0.0428 0.7401
G/F Wet volume (L) 7.85 7.43 6.82 1.2183 0.2557 0.1044 0.8583
GF Dry matter (g) 264.78ab 254.54b 301.33a 37.1976 0.0488 0.0627 0.0912
G/F ash (g) 82.86a 78.30ab 73.93b 5.5908 0.0157 0.0044 0.9691
G/F total P (g) 9.85 9.83 8.84 1.2669 0.2169 0.1144 0.6993
G.F AmmN (g) 39.62a 31.64b 22.22c 2.0132 <0.0001 <0.0001 0.4192
G/F total N (g) 40.75a 32.81b 24.79c 3.3085 <0.0001 <0.0001 0.9784
Overall wet volume (L) 7.70 7.32 6.80 1.1523 0.3107 0.1324 0.8835
Total dry matter (g) 368.69 308.90 350.37 76.6574 0.2994 0.6375 0.1421
Total ash (g) 87.172a 79.35b 73.57b 7.2894 0.0046 0.0012 0.7485
Overall Total P (g) 5.61 5.42 4.94 0.8212 0.2610 0.1282 0.3866
Overall AmmN (g) 32.26a 27.81ab 23.20b 4.5014 0.0025 0.0006 0.9674
Overall total N (g) 38.40a 33.89b 29.01c 4.1894 0.0009 0.0002 0.9199
Manure vol. (L/kg ADG) 7.70 7.32 6.80 1.1523 0.3107 0.1324 0.8835
Dry matter (g/kg ADG) 368.69 308.90 350.37 76.6574 0.2994 0.6375 0.1421
Ash (g/kg ADG) 87.172a 79.35b 73.57b 7.2894 0.0046 0.0012 0.7485
P (g/kg ADG) 5.61 5.42 4.94 0.8212 0.2610 0.1282 0.3866
AmmN (g/kg ADG) 32.26a 27.81ab 23.20b 4.5014 0.0025 0.0006 0.9674
Total N (g/kg ADG) 38.40a 33.89b 29.01c 4.1894 0.0009 0.0002 0.9199
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Values with different superscripts, within a row are different (P < 0.05).

Emissions

Daily and cumulative CO2, N2O, H2S, and methane (CH4) emissions (Tables 7 and 8) were similar across dietary treatments for all growth periods and overall (P > 0.05). The only exception was, in the first week post-weaning, pigs fed the 1X and 2X diets emitted less daily N2O than pigs fed the control diet (P < 0.05).

Table 7.

The effect of lowering dietary crude protein and adding synthetic amino acids on cumulative gas emission per animal unit

Diet SE P
Control 1X 2X
NH3(g/AU)
 7 to 14 302.36 251.51 245.99 938.05 0.9989
 7 to 28 1,360.10 1,093.88 862.77 938.05 0.9321
 7 to 42 2,610.48 1,870.53 1,393.08 938.05 0.6515
 7 to 63 4,689.79 3,043.06 2,101.07 938.05 0.1502
 7 to 84 6,405.34a 4,156.01ab 2,691.19b 938.05 0.0234
 7 to 105 7,675.14a 5,168.32ab 3,255.19b 938.05 0.0057
 7 to 126 8,759.33a 5,920.58b 3,711.57b 938.05 0.0014
 7 to 140 9,620.70a 6,437.73b 4,058.76b 938.05 0.0004
 7 to 147 9,311.67a 5,995.66b 4,056.06b 1,078.82 0.0038
CO2 (kg/AU)
 7 to 14 179.73 190.89 180.92 69.02 0.9921
 7 to 28 452.38 507.49 445.62 69.02 0.7859
 7 to 42 644.28 698.50 636.92 69.02 0.7893
 7 to 63 874.80 923.22 880.71 69.02 0.864
 7 to 84 1,094.35 1,144.94 115.21 69.02 0.8734
 7 to 105 1,277.33 1,339.09 1,313.73 69.02 0.8173
 7 to 126 1,431.60 1,497.22 1,480.46 69.02 0.7842
 7 to 140 1,529.92 1,596.74 1,585.47 69.02 0.7653
 7 to 147 1,567.13 1,600.84 1,623.50 75.82 0.8696
N2O (mg/AU)
 7 to 14 18,011 11,519 14,141 9,002.10 0.8769
 7 to 28 47,704 38,595 37,326 9,002.10 0.6750
 7 to 42 66,248 54,767 54,340 9,002.10 0.5722
 7 to 63 85,701 72,846 73,555 9,002.10 0.5283
 7 to 84 99,493 86,729 88,816 9,002.10 0.5636
 7 to 105 111,181 99,198 101,659 9,002.10 0.6123
 7 to 126 121,831 110,147 113,472 9,002.10 0.6413
 7 to 140 128,658 117,096 121,176 9,002.10 0.6560
 7 to 147 130,083 117,750 122,278 9,499.10 0.6515
H2S (g/AU)
 7 to 14 4.43 7.40 4.57 77.13 0.9995
 7 to 28 23.36 27.89 28.03 77.13 0.9988
 7 to 42 46.91 59.64 63.96 77.13 0.9869
 7 to 63 113.53 156.20 195.19 77.13 0.7564
 7 to 84 208.38 256.89 369.30 77.13 0.2097
 7 to 105 340.31 404.28 554.74 77.13 0.1386
v7 to 126 482.99 538.18 691.86 77.13 0.1477
 7 to 140 542.58 594.25 747.42 77.13 0.1566
 7 to 147 544.53 488.43 739.25 95.14 0.1551
CH4(g/AU)
 63 to 84 3,694.07 5,153.01 4,222.78 1,565.48 0.8017
 63 to 105 6,809.66 9,845.81 7,678.43 1,565.48 0.3806
 63 to 126 9,586.62 13,316.00 11,508.00 1,565.48 0.2576
 63 to 140 11,129.00 15,379.00 14,279.00 1,565.48 0.1549
 63 to 147 11,772.00 15,620.00 16,320.00 1,745.38 0.1572
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Values with different superscripts, within a row are different (P < 0.05).

Table 8.

The effect of lowering dietary crude protein and adding synthetic amino acids on average daily gas emission per animal unit.

Diet SE P
Control 1X 2X
NH3(g/AU*d)
 7 to 14 37.7947 31.4391 30.7483 11.745 0.9989
 14 to28 75.5529 60.1691 44.056 11.745 0.9321
 28 to 42 89.6702a 55.4752b 37.8793b 11.745 0.6515
 42 to63 98.7767a 55.8345b 33.7137b 11.745 0.1502
 63 to 84 81.6927a 52.9978ab 28.1012b 11.745 0.0234
 84 to105 60.4668 48.2051 26.857 11.745 0.0057
 105 to 126 51.6286 35.8223 21.7323 11.745 0.0014
 126 to 140 61.526 36.9393 24.7669 11.745 0.0004
 140 to 147 46.1848a 32.7844ab 20.1072b 13.755 0.0038
CO2(kg/AU*d)
 7 to 14 22.4663 23.8614 22.6152 1.3093 0.9921
 14 to28 19.4748 22.6143 18.907 1.3093 0.7859
 28 to 42 13.7070 13.6436 13.6646 1.3093 0.7893
 42 to63 10.9773 10.7008 11.6088 1.3093 0.8640
 63 to 84 10.4551 10.5582 11.1669 1.3093 0.8734
 84 to105 8.7131 9.2452 9.4531 1.3093 0.8173
 105 to 126 7.3462 7.5299 7.9395 1.3093 0.7842
 126 to 140 7.0229 7.1088 7.5009 1.3093 0.7653
 140 to 147 5.1141 5.3319 6.153 1.7869 0.8696
N2O (mg/AU*d)
 7 to 14 2251.33a 1439.84b 1767.57b 170.82 0.8769
 14 to28 2120.92 1934.01 1656.10 170.82 0.6750
 28 to 42 1324.58 1155.15 1215.33 170.82 0.5722
 42 to63 926.34 860.91 915.00 170.82 0.5283
 63 to 84 656.76 661.08 726.71 170.82 0.5636
 84 to105 556.59 593.8 611.55 170.82 0.6123
 105 to 126 507.14 521.38 562.54 170.82 0.6413
 126 to 140 487.66 496.32 550.29 170.82 0.6560
 140 to 147 382.76 371.67 449.54 231.77 0.6515
H2S (g/AU*d)
 7 to 14 0.5547 0.9252 0.5719 0.9839 0.9995
 14 to28 1.3521 1.4638 1.6758 0.9839 0.9988
 28 to 42 1.6821 2.2683 2.5664 0.9839 0.9869
 42 to63 3.1720 4.5976 6.2488 0.9839 0.7564
 63 to 84 4.5169 4.7948 9.5766 0.9839 0.2097
 84 to105 6.2820 7.0185 7.5446 0.9839 0.1386
 105 to 126 6.7945 6.3862 6.5296 0.9839 0.1477
 126 to 140 4.2564 4.0052 3.9687 0.9839 0.1566
 140 to 147 3.5629 3.2426 4.3974 1.2008 0.1551
CH4(g/AU*d)
 63 to 84 167.26 234.48 192.52 28.7387 0.8017
 84 to 105 148.36 223.47 164.55 28.7387 0.3806
 105 to 126 132.24 165.26 182.35 28.7387 0.2576
 126 to 140 110.16 147.32 197.97 28.7387 0.1549
 140 to 147 110.97 115.17 208.79 32.9955 0.1572
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Values with different superscripts, within a row are different (P < 0.05)

There were no differences in daily NH3 emissions (Table 7) across treatments (P > 0.05) until the fourth nursery phase where pigs fed the 1X and 2X diets produced less NH3 per day than pigs fed the Control diet (P < 0.05). The same pattern of emission continued in the first grower phase, with the Control-fed pigs producing more NH3 than both the 1X- and 2X-fed pigs (P < 0.001). In the second grower phase, pigs fed the 2X diet emitted a smaller quantity of NH3 per day than the pigs fed the Control diet, with the 1X-fed pigs being intermediate (P < 0.05). There were no differences in daily NH3 emissions in the third grower phase (P > 0.10) and first finisher phase (P > 0.10). In the second finisher phase there was a tendency for pigs fed the 1X and 2X diets to produce less NH3 than Control fed pigs until d 140 (P < 0.100.0867) and from days 140 to 147 pigs fed the 2X diet produced less NH3 than those fed the Control diet, with pigs fed the 1X diet producing an intermediate amount (P < 0.05).

Cumulatively, no differences in NH3 emissions (Table 8) were observed (P > 0.05) until the end of the second grower phase (d 84), where pigs fed the Control diet emitted a greater mass of NH3 per animal unit than 2X-fed pigs, with 1X-fed pigs being intermediate (P < 0.05). Pigs fed the 2X diet continued to produce less cumulative NH3 than Control-fed pigs, with 1X-fed pigs being intermediate, in the third grower phase (P=0.0057). By the end of the first finisher phase (d 126), Control-fed pigs produced a greater cumulative amount of NH3 per AU than both the 1X- and 2X-fed pigs (P < 0.05). This pattern of emission persisted until all pigs were marketed (P < 0.05), where the 2X pigs produced 56% less total NH3 than pigs fed the Control diet. This means that for every 1%-unit reduction in CP (from the Control to 2X diet) we observed approximately a 1 kg reduction of NH3 produced per animal unit.

Discussion

Performance data shows a consistent, significant reduction in ADG, in pigs fed the 2X diet, which had a two-fold reduction in CP with the greatest proportion of synthetic AA compared to the control (which contained no synthetic AA supplementation) or 1X diets (intermediated level of CP and AA inclusion). Other authors (Kerr and Easter, 1995; Yin and Tan, 2010; Jones et al., 2014) have noted reductions in performance, carcass characteristics, and energy retention in extremely low CP, AA-supplemented diets. We hypothesize that this may be due to AA imbalances resulting from inconsistency in AA content and availability in feed ingredients, potentially improper AA ratios for the seventh to the tenth limiting AA, and inefficiencies in absorption (Otto et al., 2003; Maxwell et al., 2016; Apple et al., 2017).

Soybean meal is the grain protein source of choice in livestock feed because it has a relatively consistent and well-studied AA composition (Karr-Lilienthal et al., 2005). In this study, as dietary CP was reduced, the concentration of SBM included in the diet was also lower. As SBM was reduced, a greater proportion of dietary CP came from ingredients such as corn and corn dried distillers grains with soluble (DDGS). Corn DDGS have been reported to have highly variable AA concentrations and availabilities (Stein et al., 2006).

The analyzed values of AA content largely corresponded with calculated values. However, in some cases analyzed values were less than calculated values, especially in the 2X diet in the grower period. The 2X diet analyzed AA concentrations were consistently less than calculated values which corresponded to a decline in average daily gain in 2X-fed pigs compared to the control animals. A similar situation was observed in nursery 4, grower 1 and grower 2. In both finisher phases, we observed differences in ADG, but no consistent, significant differences in analyzed versus calculated AA content. The observed differences in analyzed versus calculated values were small, but may explain some of the performance patterns observed in pigs fed the 2X diet. This highlights the variability of AA content in feed ingredients, particularly DDGS, as a significant issue with precision diet formulation in diets balanced to the 5-7th limiting AA (Stein et al., 2006). It is also important to note that the analysis reflects total AA concentrations in the diet, not the digestibility of these AA, therefore it is also plausible that AA were present in the feed ingredients, but not accessible to the animal.

Human and rodent studies have reported that proteins are absorbed more efficiently as small peptides than as AA (Adibi, 2003; Otto et al., 2003). We did not determine the digestibility of AA in this study, so it is entirely possible that the animals fed the 1X diet had an advantage over the animals fed the 2X diet because they had a combination of small peptides and synthetics to absorb and deposit as muscle.

It is also possible that the growth performance reduction observed in pigs fed the 2X-diets may be due to a dietary imbalance of the lesser--limiting AA. Changes in availability and differences in analyzed values could have created an imbalance, particularly at the seventh or eighth limiting AA, that led to the growth deficit in 2X-fed pigs. For example, Maxwell et al. (2016), noted that when dispensable synthetic AA (histidine) were added to low CP diets of grow/finish swine, growth performance was maintained compared to a higher CP control, therefore it is possible that we could have improved growth performance of 2X-fed pigs by feeding synthetic histidine. It is also possible that the 2X reduction in CP resulted in an imbalance in non-essential AA. Although the pig can synthesize non-essential AA, the rate of synthesis and availability of precursors could limit the amount of these AA in the body, limiting growth (Hou and Wu, 2017). These results demonstrate that the NRC (2012) requirements may need to be reevaluated as reduced-CP diets become normalized in the swine industry.

The reduced growth performance in conjunction with reduced clinically sick pigs fed the 2X diet. We also noted reduced frequency of individual medical treatments in 2X-fed pigs compared to control animals. The reduction of dietary CP has been proposed as a health management tool in young animals by Kil and Stein (2010). Crude protein raises the pH of the stomach which facilitates pathogen survival and dissemination to the rest of the gastrointestinal tract (Kil and Stein, 2010). Other authors (Nyachoti et al., 2006) hypothesize that low CP, AA supplemented diets benefit the health of animals because the high digestibility of the synthetic AA reduces the production of toxic metabolites by microbial digestion of protein in the distal small intestine.

We calculated an approximately 8.5% reduction in nitrogen excretion per %-unit reduction in dietary CP (Sutton and Richert, 2004). On average, CP was reduced 2.7% and 5.4%-units, respectively for pigs fed the 1X and 2X diets compared to the control. We observed an 11.74% and 24.45% reduction in TN excretion in manure produced by pigs fed the 1X and 2X diets, respectively. This resulted in approximately a 4.5% reduction in TN excretion per %-unit reduction in dietary CP. This reduction is lower than expected but may be reflective of the fact that the last several diets had higher CP because the animals were fed ractopamine. It is also important to note that the aforementioned 8.5% estimate reflects the expected nitrogen reduction on fresh manure, but in this study, TN was measured on stored manure. Ammonium volatilizes to ammonia during manure storage (Erisman et al, 2013), therefore the increased ammonia measured in control-fed rooms could be from the volatilization of nitrogen in manure.

Ractopamine (Paylean, Greenfield, IN) is a well-studied β-andrenergic agonist commonly included in finishing diets of swine to improve late-stage growth performance (Watkins, 1990), and it was included in the Finisher II diets in this particular study to maximize the immediate-industry applicability of the collected data. There has been limited discourse on the impact of ractopamine use in reduced-CP diets, however regulations require that it is used with at least a 16% CP diet. Apple et al. (2017) suggest that this regulatory estimate may be arbitrary, but noted a similar reduction in growth performance with reductions in dietary CP, as were noted in this study, with the inclusion of Ractopamine. This suggests that further work should be done to tease out specific essential and non-essential AA requirements for animals fed ractopamine in conjunction with low CP diets. In conclusion, feeding high levels of synthetic AA to balance diets to the seventh limiting AA has a positive effect on reducing nitrogen excretion, may have positive health effects but can decrease growth performance. The reductions in growth performance may be reflective of inaccurate estimates of AA requirements and AA content of commonly used feed ingredients reported in the 2012 NRC Similar negative effects on energy retention (Jones et al., 2014), carcass characteristics and growth (Kerr and Easter, 1995; Yin and Tan, 2010) have been reported. It is possible that the observed reductions in performance are due to variability in the availability of essential and non-essential AA in feed ingredients or an imbalance in less-limiting essential AA.

Acknowledgments

This research is part of the USDA NIFA-AFRI program "Climate Change Mitigation and Adaptation in Agriculture” (Program code:A3141), and is supported by Agriculture and Food Research Initiative Competitive Grant no. 2011-68002-30208 from the USDA National Institute of Food and Agriculture. The authors wish to thank Ajinomoto for supplying synthetic amino acids.

Glossary

Abbreviations

AA

amino acid

ADFI

average daily feed intake

ADG

average daily gain

AmmN

ammonium nitrogen

AU

animal unit

BW

body weight

CP

crude protein

DDGS

dried distillers grains with soluble

DM

dry matter

Mkt

market

SBM

soybean meal

SERB

Purdue Swine Environmental Research Building

SID

standard ileal digestiability

TN

total nitrogen

Contributor Information

Caitlin E Vonderohe, USDA-ARS Children’s Nutrition Research Center, Pediatrics, Gastroenterology and Nutrition, Baylor College of Medicine, Houston, TX 77030, USA.

Kayla M Mills, USDA-ARS Beltsville Ag Research Center, Beltsville, MD 20705, USA.

Shule Liu, Clear Center, Department of Animal Science, University of California–Davis, Davis, CA 95616, USA.

Matthew D Asmus, Department of Animal Science, Purdue University, West Lafayette, IN 47907, USA.

Emily R Otto-Tice, Land O’Lakes, Inc., Arden Hills, MN 55126, USA.

Brian T Richert, Department of Animal Science, Purdue University, West Lafayette, IN 47907, USA.

Ji-Qin Ni, Department of Ag and Biological Engineering, Purdue University, West Lafayette, IN 47907, USA.

John Scott Radcliffe, Department of Animal Science, Purdue University, West Lafayette, IN 47907, USA.

Conflict of Interest Statement

The authors declare no real or perceived conflicts of interest.

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