A comparison of the nutritional value of organic-acid preserved corn and heat-dried corn for pigs

Animal Feed Science and Technology 214 (2016) 95–103

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A comparison of the nutritional value of organic-acid preserved corn and heat-dried corn for pigs X. Xu a , H.L. Wang a , P. Li a , Z.K. Zeng a , Q.Y. Tian a , X.S. Piao a,∗ , E.Y.W. Kuang b a State Key Laboratory of Animal Nutrition, Ministry of Agriculture Feed Industry Centre, China Agricultural University, Beijing 100193, China b Kemira (Asia) Company Limited, Shanghai 200233, China

a r t i c l e

i n f o

Article history: Received 14 May 2015 Received in revised form 11 February 2016 Accepted 21 February 2016 Keywords: Amino acid digestibility Corn Energy content Organic-acid preservation Performance Piglets

a b s t r a c t Three experiments were conducted to compare the digestible (DE) and metabolizable energy (ME) content (Exp. 1), as well as the apparent (AID) and standardized (SID) ileal digestibility of amino acids (AA) (Exp. 2) in organic-acid preserved and heat-dried corn. In addition, the performance of weanling pigs fed diets containing the two corns was compared (Exp. 3). In Exp. 1, 12 growing barrows (28.5 ± 1.50 kg) were randomly allotted to 1 of 2 groups and fed diets containing 970 g/kg organic-acid treated or heat-dried corn to determine the DE and ME content of the two differently processed corns. The results indicated that the DE and ME of organic-acid treated corn were 16.6 and 16.3 MJ/kg, which was greater than the 16.4 and 15.9 MJ/kg, for the DE and ME of heat-dried corn (P < 0.05 and P < 0.01). In Exp. 2, 18 growing barrows (27.6 ± 4.38 kg), fitted with a T-cannula in the distal ileum, were allotted to be fed 1 of 3 semi-synthetic diets with 6 pigs per treatment. Two of the 3 diets were of similar composition to those used in Exp. 1 while the 3rd was a nitrogen-free diet that was used to measure basal endogenous losses of CP and AA. The results from Exp. 2 showed no significant difference in the AID or SID of CP and AA between the 2 corns. In Exp. 3, 60 piglets, weaned at 28 day (7.34 ± 1.243 kg), were randomly allotted to 1 of 2 complete diets with 5 pigs per pen and 6 pens per dietary treatment for 4 weeks. Piglets fed organicacid treated corn had 10.5% greater average daily gain (389 g/day) than pigs fed heat-dried corn (352 g/day; P < 0.05). Feeding organic-acid treated corn significantly increased average daily feed intake by 12.5% (604 vs. 539 g/day) compared with heat-dried corn (P < 0.05). In conclusion, the available energy content of organic-acid treated corn was greater than heat-dried corn, and organic-acid treated corn improved weanling pig performance. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Corn is widely used in swine feeds as an energy source and the quality of corn has been shown to affect pig performance (Linneen et al., 2008). However, molds in corn are becoming a serious problem (Williams et al., 2004). Corn production techniques have been rapidly improved aiming to utilize corn more efficiently. Drying is a natural and efficient process in

Abbreviations: ME, metabolizable energy; DE, digestible energy; ADFI, average daily feed intake; ADG, average daily gain; BW, body weight; AA, amino acid; CP, crude protein; AID, apparent ileal digestible; SID, standard ileal digestible. ∗ Corresponding author. Fax: +86 1062733688. E-mail address: piaoxsh@mafic.ac.cn (X.S. Piao). http://dx.doi.org/10.1016/j.anifeedsci.2016.02.016 0377-8401/© 2016 Elsevier B.V. All rights reserved.

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many areas and it can prevent mold. In most areas, corn can be dried after harvest, but this technique requires a high energy input. Therefore, it will be beneficial if a better way to preserve corn can be identified. Many reports have shown that organic acids such as formic acid, propionic acid, formate and propionate sprayed onto corn can prevent mold and improve livestock performance (Young et al., 1970; Tsiloyiannis et al., 2001a, 2001b; Luan et al., 2013). Although the results of many experiments have indicated that organic acids used as a feed additive (i.e., directly incorporated into the feed) may benefit intestinal health (Dibner and Buttin 2002; Hansen et al., 2007; Garcia et al., 2007), it is not known if spraying organic acids onto corn during processing has the same effect. Therefore, this study was conducted to test the hypothesis that the DE and ME as well as the apparent ileal (AID) and standardized ileal (SID) digestibility of organicacid preserved corn is greater than heat-dried corn. The second hypothesis was that pigs fed diets containing organic-acid treated corn will have improved performance compared with pigs fed diets containing heat-dried corn. 2. Materials and methods 2.1. General The organic-acid treated and heat-dried corn were produced from the same source (moisture = 186 g/kg, before processing). One batch of the corn grain was processed by spraying organic-acids (composition: formic acid = 568 g/kg, propionic acid = 177 g/kg, ammonium salt = 52 g/kg, sodium salt = 28 g/kg, moisture = 175 g/kg; dosage rate 7 kg/t corn) onto the corn. The organic-acid was sprayed onto the corn after the corn was threshed. A second batch of the corn was dried by heating using a concurrent–countercurrent flow-type grain dryer (TDH300, Jinghua, Henan, China). The corn was dried with a concurrent flow hot air in three stages: (1) 140 ◦ C for 2 h, (2) 110 ◦ C for 1 h and (3) 70 ◦ C for 1 h followed by a countercurrent flow cooling period of 2 h. At the end of the drying process, the moisture content of the corn had dropped to 140 g/kg. During these steps, the grain temperature did not exceed 50 ◦ C thus avoiding a reduction in the quality of the corn (Huang et al., 2015). After treatments, both batches of corn were placed in the same store room (Ministry of Agriculture Feed Industry Centre, Beijing, China) under natural conditions for 7 months (the temperature and humidity of the room averaged 20 ◦ C and 50%). The chemical content and mycotoxin levels of the two corns are shown in Table 1. The protocols used in these experiments were approved by the China Agricultural University Institutional Animal Care and Use Committee (Beijing, China). All experiments were conducted at China Agriculture University Animal Experiment Base (Fengning, China). 2.2. Animals and experimental design All pigs were Duroc × Landrace × Large White crossbreds. In Exp. 1 and 2, the pigs were individually housed in 1.2 × 0.7 × 0.9 m3 stainless steel metabolism cages located in an environmentally controlled room (daily range from 20 to 24 ◦ C). In Exp. 3, 60 weanling pigs were housed in twelve 1.8 × 1.2 m2 with 5 pigs per pen. The pens had half solid and half slatted floors. 2.3. Exp. 1 Exp. 1 was conducted to determine the DE and ME of the two of corns. Twelve barrows (28.5 ± 1.50 kg) were assigned to 1 of 2 experimental treatments. The experimental diets consisted of 970 g/kg organic-acid treated or heat-dried corn supplemented with minerals and vitamins (Table 2). The diets were provided at a rate of 40 g/kg of BW determined at the initiation of the adaptation period. The daily feed allowance was divided into two equal sized meals fed at 08:00 and 16:00 h. Water was freely available from a low-pressure drinking nipple. The diets were provided in mash form. After an adaptation period of 7 days, a total collection of faeces and urine was conducted for 5 successive days following the methods described by Li et al. (2015). The feed intake of pigs was recorded daily. Feed refusals and spillage were collected daily and analyzed for DM. Faeces were collected immediately as they appeared in the metabolism crates and placed in plastic bags to be stored at −20 ◦ C. Urine was collected in a bucket placed under the metabolic crate. The buckets contained 10 mL of 6N HCl for every 1000 mL of urine. Every day, the total urine volume was measured and a 100 mL aliquot from every 1000 mL of urine was filtered through gauze and 50 mL of the mixed urine samples were transferred into a screw-capped tube and immediately stored at −20 ◦ C until needed for analysis. At the end of the collection period, faeces were thawed, pooled by pig, homogenized, sub-sampled, dried for 72 h in a 65 ◦ C drying oven and ground through a 1-mm screen. Likewise, all stored urine samples were mixed and homogenized for each pig. 2.3.1. Exp. 2 Exp. 2 was designed to determine the AID and SID of CP and AA in the 2 batches of corn. Eighteen barrows (27.6 ± 4.38 kg) were surgically fitted with a T-cannula in the distal ileum using procedures adapted from Stein et al. (1998). Before surgery, barrows were fasted for 24 h. The post-operative period was 14 d during which time a balanced diet was provided to allow ad libitum intake to the pigs. The barrows were assigned to 1 of 3 treatments. Two of the experimental diets were formulated to be similar to those used in Exp. 1 (Table 2). In addition, a nitrogen-free diet was used to estimate basal endogenous losses (IAAend ) of CP and AA. All diets contained 2.5 g/kg chromic oxide as an indigestible marker.

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Table 1 Analysed nutrient content of heat-dried corn and organic-acid preserved corn (g/kg of dry matter).a

Dry matter Gross energy (MJ/kg) Crude protein Calcium Total phosphorus Ash Ether extract Neutral detergent fiber Acid detergent fiber Glucose Fructose Sucrose Starch Resistant starch Formic acid Propionic acid Essential amino acids Arginine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine Nonessential amino acids Alanine Aspartic acid Cystine Glutamic acid Glycine Proline Serine Tyrosine a

Heat-dried corn

Organic-acid preserved corn

885.0 18.1 88.7 0.24 2.4 13.2 40.4 134.0 29.0 5.7 4.5 0.6 676.0 87.5 – –

873.0 18.1 89.4 0.23 2.6 12.9 40.7 148.0 31.5 8.5 9.8 0.9 650.0 56.3 3.8 1.5

3.5 2.6 2.8 11.8 2.6 2.0 8.4 3.3 0.7 4.5

3.8 2.6 2.9 12.1 2.6 1.9 8.7 3.3 0.6 4.6

0.62 0.55 0.28 1.49 0.34 0.73 0.40 0.21

0.63 0.57 0.27 1.54 0.34 0.77 0.41 0.22

All analysis were conducted in duplicate.

The feeding and management of pigs was similar to Exp. 1. The 7-days experiment consisted of a 5-days acclimation period followed by a 2-days (10 h/day) collection of ileal digesta as described by Stein et al. (2006). A plastic bag was attached to the cannula barrel using a cable tie to collect digesta. Bags were removed whenever they were filled with digesta and immediately stored at −20 ◦ C to prevent the bacterial degradation of AA in the digesta. At the end of the experiment, the ileal samples were thawed, mixed within animal and diet, and a sub-sample was collected and lyophilized in a vacuum-freeze dryer (Tofflon Freezing Drying Systems, Minhang District, Shanghai, China), ground through a 1-mm screen, and thoroughly mixed before chemical analysis. 2.3.2. Exp. 3 Exp. 3 was conducted to evaluate the nutritional value of the two batches of corn. Sixty piglets (7.34 ± 1.243 kg BW), weaned d 28 postpartum, were used to evaluate the effects of organic-acid treated and heat-dried corn on performance and diarrhea incidence. The experiment was a completely randomized design with 2 dietary treatments and 6 replicate pens containing 5 piglets. Pigs were weighed and allotted by sex, ancestry, and weight. There were 3 pens of barrows and 3 pens of gilts per treatment. Two diets were formulated according to the nutrient requirements suggested by NRC (1998) for nursery pigs. The diets contained 2.5 g/kg of Cr2 O3 as an indigestible marker. The ingredient composition of the experimental diets is shown in Table 2. Ambient temperature within the room was approximately 30 ◦ C immediately after weanling and was adjusted to approximately 26 ◦ C by the end of the experiment. Pigs had free access to feed and water throughout the experiment. Diets were all provided in mash form. Piglets with clinical signs of diarrhea (fecal consistency = 4) and simultaneous dehydration, fever, growth check, and apathy were treated daily (during a 3-days period) with 1 mL (intramuscular injection) of Enrofloxacin per animal. During the experimental period, 3 piglets fed the heat-dried corn and 1 piglet fed the organic-acid treated corn were treated with Enrofloxacin for 3 days. In addition, 4 piglets fed the heat-dried corn and 4 piglets fed the organic-acid treated corn were treated with Enrofloxacin for 1 day. Pigs and feeders were weighed at 0750 h on day 0 and 28 to calculate average daily gain (ADG), average daily feed intake (ADFI), and gain to feed ratio (G:F). Fresh fecal grab samples were collected on day 25–27, pooled by pen, and stored at

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Table 2 The ingredient composition of diets based on heat-dried corn or organic-acid corn used in the 3 experiments (g/kg as fed). Ingredients

Exp.1 Heat-dried corn

Heat-dried corn 970.0 – Organic-acid preserved corn – Cornstarch – Dehulled soybean meal Fish meal – Whey powder – Soybean oil – – Sucrose – Acetate cellulosea – Plasma protein powder 16.3 Dicalcium phosphate 5.7 Limestone – Chromic oxide 3.0 Salt – Potassium carbonate Magnesium oxide – – l-Lysine HCl, 78% dl-Methionine hydroxyl analogue, 84% l-Threonine – l-Tryptophan – b – Zinc oxide Vitamin and mineral 5.0 premixc,d,e Chemical composition (g/kg DM) Dry matter (g/kg) 893 76.6 Crude protein (g/kg) 19.4 Crude fiber (g/kg) Neutral detergent fiber (g/kg) 110 Acid detergent fiber (g/kg) 25.1 17.5 Ash (g/kg) 15.5 Gross energy (MJ/kg) Starch (g/kg) 580 75.1 Resistant starch (g/kg) Glucose (g/kg) Fructose (g/kg) Sucrose (g/kg)

Exp.2

Exp.3

N-free Organic-acid preserved corn

Heat-dried corn

Heat-dried Organic-acid preserved corn corn

Organic-acid preserved corn

– 970.0 – – – – – – – – 16.3 5.7 – 3.0 – – – –

– – 756.5 – – – 30.0 150.0 20.0 – 29.0 – 2.5 3.0 3.0 1.0 – –

966.5 – – – – – – – – – 15.0 8.0 2.5 3.0 – – – –

– 966.5 – – – – – – – – 15.0 8.0 2.5 3.0 – – – –

626.6 – – 212.3 20.0 50.0 21.6 – – 30.0 9.6 8.2 2.5 3.0 – – 0.7 1.4

– 626.6 – 212.3 20.0 50.0 21.6 – – 30.0 9.6 8.2 2.5 3.0 – – 0.7 1.4

– – – 5.0

– – – 5.0

– – – 5.0

– – – 5.0

1.2 0.4 2.5 10.0

1.2 0.4 2.5 10.0

895 76.4 1.91 108 25.8 17.9 15.5 577

890 75.4 1.93 124 27.5 17.2 15.3 568 46.6

896 186 43.2 210 61.1 19.4 18.6 448 58.3 17.3 4.1 5.3

890 184 44.1 214 63.2 19.7 18.6 445 35.6 19.4 7.8 8.1

889 75.7 19.3 125 27.6 17.7 15.4 571 47.6

74.5

a

Produced by Sinopharm Chemical Reagent Company Limited. Zinc oxide was added in the diets in the first week and the last three weeks the zinc oxide was replaced by corn. c Premix in Exp.1 supplied per kg diet: retinyl acetate, 11 000 IU; cholecalciferol, 1500 IU; DL-␣-tocopheryl acetate, 44.1 IU; menadione sodium bisulfite complex, 4 mg; riboflavin, 5.22 mg; d-calcium-pantothenate, 20 mg; niacin, 26 mg; vitamin B12 , 0.01 mg; Mn (MnSO4 ·H2 O), 35 mg; Fe (FeSO4 ·H2 O), 100 mg; Zn (ZnSO4 ·7H2 O), 90 mg; Cu (CuSO4 ·5H2 O), 16.5 mg; I (CaI2 ), 0.3 mg; Se (Na2 SeO3 ), 0.3 mg. d Premix in Exp.2 supplied per kg diet: retinyl acetate, 11 000 IU; cholecalciferol, 1500 IU; DL-␣-tocopheryl acetate, 44.1 IU; menadione sodium bisulfite complex, 4 mg; riboflavin, 5.22 mg; d-calcium-pantothenate, 20 mg; niacin, 26 mg; vitamin B12 , 0.01 mg; Mn (MnSO4 ·H2 O), 35 mg; Fe (FeSO4 ·H2 O), 100 mg; Zn (ZnSO4 ·7H2 O), 90 mg; Cu (CuSO4 ·5H2 O), 16.5 mg; I (CaI2 ), 0.3 mg; Se (Na2 SeO3 ), 0.3 mg. e Premix in Exp.3 supplied per kg diet: retinyl acetate, 5512 IU; cholecalciferol, 2200 IU; DL-␣-tocopheryl acetate, 30 IU; menadione sodium bisulfite complex, 4 mg; riboflavin, 5.22 mg; d-calcium-pantothenate, 20 mg; niacin, 26 mg; vitamin B12 , 0.01 mg; Mn (MnSO4 ·H2 O), 40 mg; Fe (FeSO4 ·H2 O), 75 mg; Zn (ZnSO4 ·7H2 O), 75 mg; Cu (CuSO4 ·5H2 O), 100 mg; I (CaI2 ), 0.3 mg; Se (Na2 SeO3 ), 0.3 mg. b

−18 ◦ C until analysis to determine nutrient digestibility. Fecal consistency and the incidence of post-weanling diarrhea were determined each day for 28 days after weanling as described previously (Heo et al., 2008). Briefly, faeces were assessed using a subjective score on a four-point scale ranging from 1 to 4, and a fecal consistency of either 3 or 4 was considered as diarrhea. 2.4. Chemical analysis The corn, diets, faeces, and digesta samples were analyzed for Kjeldahl N (Thiex et al., 2002) and ether extract (Thiex et al., 2003). Dry matter (DM) (AOAC Method 930.15), starch (AOAC Method 948.02), ash (AOAC Method 942.05), calcium (AOAC Method 927.02) and phosphorus (AOAC Method 965.17) were determined using the methods of the Association of Official Analytical Chemists (AOAC, 2000). Resistant starch was determined using the methods of the Association of Official Analytical Chemists (AOAC Method 2002.02). Neutral detergent fiber (NDF) and acid detergent fiber (ADF) concentrations were determined using the methods of Van Soest et al. (1991). GE was determined with an oxygen bomb calorimeter (Parr Instruments, Moline, IL). The corn samples were analyzed for aflatoxins (AFB1, AFB2, AFG1 and AFG2), deoxynivalenol (DON)

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and zearalenone (ZEN) by the methods published by Peter and Bernhard (2006). Soluble sugar (glucose, fructose, and sucrose) concentrations in corns and diets were analyzed using High Performance Liquid Chromatography (HPLC). Before analysis for AA, the two corns, diets, and ileal digesta samples were hydrolyzed with 6N HCl for 24 h at 110 ◦ C (AOAC Method 999.13) and analyzed for AA using an Amino Acid Analyzer (Hitachi L-8900, Tokyo, Japan). Methionine and cystine were determined as methionine sulfone and cysteic acid after cold performic acid oxidation overnight and hydrolyzed with 7.5N HCl for 24 h at 110 ◦ C (AOAC Method 994.12) using an Amino Acid Analyzer (Hitachi L-8800, Tokyo, Japan). Tryptophan was determined after LiOH hydrolysis for 22 h at 110 ◦ C (AOAC Method 998.15) using High Performance Liquid Chromatography (Agilent 1200 Series, Santa Clara, CA). The chromium concentration of the diets, faeces, and digesta samples were measured (AOAC Method 993.23) after nitric acid-perchloric acid wet ash sample preparation. All analyses were conducted in duplicate. 2.5. Calculations In Exp. 1, the DE and ME values in the two corns were calculated according to the direct method (Adeola, 2001). The formula to calculate DE and ME are shown below: The DE of the diet=

(GE in feed intake − GE in faeces) feed intake

The ME of the diet=

(GE in feed intake − GE in faeces − GE in urine) feed intake

The correction for DE content (ME) of the corn =

The DE (ME) of the diet 0.97

(0.97 is the percentage of energy-contributing ingredient in the diet). In Exp. 2, the AID for each AA in the diets containing corn was calculated using the equations described by Stein et al. (2007):



AID = 1 −

 AAd   Crf  ×

AAf

Crd

in this equation, AAd is the concentration of AA in the ileal digesta (g/kg of DM), AAf is the concentration of AA in the diets (g/kg of DM), Crf represents chromium concentration in the diet (g/kg of DM), and Crd represents chromium concentration in the digesta (g/kg of DM). The AID for CP was also calculated using this equation where the concentrations of AA were replaced by the concentration of the CP in the digesta and diets. The basal endogenous loss of each AA (IAAend , g/kg of DMI) at the distal ileum was determined based on the outflow obtained when pigs were fed the N-free diet using the equation of Stein et al. (2007): IAAend = AAd

 Crf  Crd

in this equation, AAd is the concentration of each AA in the ileal digesta collected from pigs fed the N-free diet. The endogenous outflow of CP was determined using the same equation where AAd was replaced by the concentration of the CP in the digesta. By correcting the AID of each AA that was calculated for each sample for the IAAend , the SID of each AA was calculated using the equation of Stein et al. (2007): SID = AID +

 IAA

end



AAdiet

In Exp. 3, the nutrient digestibility was determined by the indicator method. The formula was as follows: ATTD(%) = 1 −

(DC × FN) × 100% (FC × DN)

where ATTD is the apparent total tract nutrient digestibility, DC is the concentration of Cr2 O3 in diets (%), FN is the concentration of a nutrient in faeces (%), FC is the concentration of Cr2 O3 in faeces (%), and DN is the concentration of a nutrient in the diet (%). The diarrhoea incidence was estimated by pen as the proportion of days in which pigs showed clinical signs of diarrhoea with respect to the total number of days on test as described by Mateos et al. (2007). 3.1. Statistical analysis Data for Exp. 1 and 2 were analyzed as a randomized complete block design using the ANOVA procedure of SAS (SAS (SAS Institute, Cary, NC). Data for Exp. 3 were analyzed using the MIXED procedure of SAS (SAS Institute, Cary, NC). For pig performance data, the pen served as the experimental unit. The initial model included treatment, sex and the interaction

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Table 3 DE, ME and ATTD of GE of heat-dried corn and organic-acid preserved corn (MJ/kg, DM basis, Exp.1). Item

Heat-dried corn

Organic-acid preserved corn

SEM

P-value

DE ME ATTD of GE

16.36 15.90 0.904

16.64 16.28 0.920

0.06 0.04 0.005

<0.05 <0.01 <0.05

Table 4 Apparent ileal digestibility (AID) and standardized ileal digestibility (SID) of CP and AA of heat-dried corn and organic-acid preserved corn (g/kg DM basis, Exp. 2). Item

Heat-dried corn Organic-acid preserved corn SEM P-value

Apparent ileal digestibility (AID) Crude protein 725 Essential amino acids Arginine 813 786 Histidine 734 Isoleucine 856 Leucine 624 Lysine Methionine 827 835 Phenylalanine 646 Threonine 818 Tryptophan 742 Valine Nonessential amino acids 750 Alanine 727 Aspartic acid 739 Cystine 780 Glutamic acid 508 Glycine 723 Proline Serine 748 880 Tyrosine

Heat-dried corn Organic-acid preserved corn SEM P-value

738

12.12 >0.05

Standardized ileal digestibility (SID) 914 927

14.35 >0.05

804 796 728 841 658 836 846 642 817 753

29.35 15.86 24.05 10.88 24.32 7.24 12.76 25.41 19.68 16.32

>0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05

893 847 795 781 743 864 889 796 897 804

885 856 787 768 775 874 906 791 898 813

27.24 12.66 27.32 10.11 20.69 9.31 14.74 22.88 20.12 15.36

>0.05 >0.05 >0.05 >0.05 >.05 >0.05 >0.05 >0.05 >0.05 >0.05

738 754 742 787 532 720 764 871

24.24 16.13 16.95 15.36 21.89 27.11 15.87 29.02

>0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05

831 824 836 843 819 826 848 914

814 853 836 850 840 828 861 908

21.32 14.21 18.96 18.14 21.86 26.21 17.99 29.02

>0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05

between treatment and sex as main effects and replicate as random effects. However, no interactions were significant so the interaction term was removed from the model. In addition, the results of this analysis indicated that no sex-effects were significant and therefore only the main effect of treatment was included in the final model. Results were considered significant at P ≤ 0.05 and a trend at P ≤ 0.10. 4. Results 4.1. Chemical composition and mycotoxin content of the corn samples The chemical composition of the two corns is shown in Table 1. This demonstrated that the two processes had little effect on the chemical composition of corn. However, the soluble sugars and resistant starch concentration varies between the two processed corns. The glucose, fructose and sucrose concentrations in organic-acid treated and heat-dried corn were 8.5 vs. 5.7, 9.8 vs. 4.5 and 0.9 vs. 0.6 g/kg. The resistant starch concentrations were 87.5 g/kg in heat-dried corn and 56.3 g/kg in organic-acid treated corn. On a DM basis, the level of deoxynivalenol was 0.15 and 0.28 mg/kg in heat-dried corn and organic-acid treated corn, respectively. No other mycotoxins were detected in the two corn samples. 4.2. Energy digestibility On a DM basis, the DE of organic-acid treated corn was 16.64 MJ/kg, which was higher than the 16.36 MJ/kg of heat-dried corn (P < 0.05). The ME of organic-acid treated corn was 16.28 MJ/kg which was greater (P < 0.01) than the 15.90 MJ/kg of heat-dried corn. The ATTD of GE in organic-acid treated corn and heat-dried corn were 0.920 and 0.904 (P < 0.05), respectively (Table 3). 4.3. Amino acid digestibility The AID and SID of CP and AA are shown in Table 4. The AID and SID did not differ between organic-acid treated corn and heat-dried corn.

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Table 5 The effects of feeding a complete diet based on heat-dried corn or organic-acid preserved corn on piglet performance, incidence of diarrhea and the apparent digestibility of nutrients (Exp. 3). Heat-dried.corn.

Organic-acid preserved corn.

SEM.

P-value.

7.35. 17.19. 352 537 0.64

7.3. 18.2. 389 604 0.65

0.13. 0.15. 8.87 15.2 0.03

>0.05. <0.05 <0.05 <0.05 >0.05

82.2 81.9 71.0 83.6 67.7 37.9 36.6 54.2

81.1 81.0 70.9 84.7 66.9 39.1 39.1 58.9

1.02 1.13 2.52 0.94 1.22 1.79 1.86 2.53

>0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05 >0.05

a

Performance Initial body weight (kg) Final body weight (kg) Average daily gain (g)b Average daily feed intake (g)b Gain: Feedb Apparent digestibility of nutrients (%)a Dry matter Gross energy Crude protein Organic matter Ether extract Total ash Total phosphorus Calcium a

N = 6. The P-value and SEM of average daily gain, average daily feed intake and gain: feed for sex factor were P > 0.05, 8.87; P > 0.05, 15.2 and P > 0.05, 0.03, respectively. b

4.4. Performance trial 4.4.1. Pig performance The piglets fed organic-acid treated corn had greater ADG than the pigs fed heat-dried corn (389 vs 352 g/day; P < 0.05). The ADFI of pigs fed organic-acid treated corn was also greater compared with pigs fed heat-dried corn (604 vs. 539 g/day; P < 0.05). No piglets died during the experiment period. The diarrhea index in piglets did not differ between pigs fed heat-dried corn (1.59 ± 0.33) and organic-acid treated corn (1.52 ± 0.19; P > 0.05). 4.4.2. Nutrient digestibility The ATTD of nutrients in the complete diets is shown in Table 5. There were no differences in the ATTD of GE, DM, or nutrients between the 2 sources of corn. 5. Discussion 5.1. Chemical composition of corn There was little difference in the chemical composition of the two corns except for the concentrations of organic acids, soluble sugars and resistant starch. The concentration of resistant starch in heat-dried corn was higher compared with organic-acid treated corn which may decrease the digestibility of starch in pigs. The chemical composition of the 2 sources of corn was in agreement with that of NRC (2012). The mycotoxin levels in the corns were both considered to be at safe levels, which are defined as less than 1 mg kg−1 deoxynivalenol, 1 mg kg−1 zearalenone, and 200 ␮g kg−1 aflatoxins (Thaler and Reese, 2010). These results are in agreement with previous published reports (Jones et al., 1970). Therefore, compared with the traditional heat-dried preservation method, organic-acid may be used to preserve corn with lower level of resistant starch and no change in mycotoxin levels. 5.2. Energy concentration and energy digestibility Bayley et al. (1974) reported that propionic acid preserved corn contained more DE than dried corn and our results are in agreement with this determination. Bayley et al. (1974) reported that the ␣-linked polysaccharide concentration in the digesta of heat-dried corn was greater than that of organic-acid treated corn, which indicated that the ␣-linked polysaccharides had been incompletely digested. It appears that heat damage during the drying process resulted in ␣-linked glucose polymers which are not absorbed in the small intestine. The concentration of resistant starch in the heat-dried corn was higher compared with organic-acid treated corn which may explain the lower digestibility of ␣-linked polysaccharides. Organic acids may also increase gluconeogenesis. Formic acid and propionic acid may be converted to pyruvic acid which is a precursor of glucose. 5.3. Digestibility of crude protein and amino acids Little research has been conducted to determine the digestibility of AA in organic-acid treated corn. The average AID and SID for CP and most AA observed in this experiment are in agreement with NRC (2012) values. The SID for CP and Lys in

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both sources of corn are in agreement with previous published data (Liu et al., 2014). The fact that the Lys concentration, as a percentage of CP, was approximately equal to 0.03 indicates little heat damage to the protein, which explains the high SID value of CP and AA (Kim et al., 2012). Therefore, treatment with organic-acid does not reduce the SID of CP and AA. 5.4. Effects of organic-acid treated corn on the performance of weanling pigs The observation that organic-acid treated corn improved weanling pig performance is in agreement with previous published data (Jones et al., 1970). The increased ADG for pigs fed organic-acid treated corn is likely caused by the increased ADFI. The higher concentration of soluble sugars in organic-acid treated corn compared with heat-dried corn may increase the sweetness which could improve the feed intake of piglets fed organic-acid treated corn. This is in agreement with previous reports which demonstrated that heat processing could lead sugar to Maillard reactions resulting in a decreased sugar level (Ana et al., 2012; Tanaka et al., 1998). In addition, some papers showed the heat process could damage the structure of starch which resulted in an increased stickyness in the mouth (Xu et al., 2015). The diarrhea index was at a healthy level for pigs fed diets containing both sources of corn. This is consistent with the mycotoxin concentration in the corn. Zinc oxide was added to both diets in the first week post-weaning at a dose of 2500 mg/kg, which may improve the gut health. As a consequence, the low diarrhea index and the fact that mortality was zero may be a result of the use of zinc oxide (Hahn and Baker, 1993; Hill et al., 2001; Li et al., 2015; Carlson et al., 2004). In Exp.1, a significant difference was observed for the ATTD for energy of the two corns while no difference in the ATTD of energy was observed in Exp. 3. Any differences between the two experiments are likely caused by the level of feed intake and the inclusion level of corn in the two experiments. In Exp.1, the diets were provided at a rate of 40 g/kg of BW determined at the initiation of the adaptation period to ensure the diets were completely consumed. However, in Exp. 3, the piglets had free access to feed. In addition, the diets contained 970 g/kg corn in Exp.1 while the diets of Exp.3 contained 627 g/kg corn. So the level of other ingredients may have influenced energy digestibility. Some studies have showed that dietary acidification with organic acids significantly decreased gastric pH (Bolduan et al., 1988; Risley et al., 1991; Gabert and Sauer, 1995) which can promote digestive enzymes secretion. In our research, although there was no difference in nutrient digestibility, the total digested nutrients were increased as feed intake increased which could explain the effect of organic acids. 6. Conclusions Our results indicate that treatment of corn with organic acid enhanced the DE and ME content of corn but had no effect on the AID and SID of CP and AA in pigs. The performance of weanling piglets fed diets containing organic-acid treated corn was improved compared with piglets fed diets containing heat-dried corn most probably due to the higher feed intake for pigs fed the organic-acid treated corn Therefore, treatment of high moisture corn with organic acids may be an attractive alternative to the traditional heat treatment of corn. Conflict of interest This work has no conflict of interest. Acknowledgments This study was completed at China Agricultural University Animal Experiment Base (Fengning, China). The authors thank Phil Thacker, Jianjun Zang, Long Pan and Xiaokang Ma for their input to this study. This study was made possible by a grant from the Kemira (Asia) Co., Inc., Shanghai (China) and the National Natural Science Foundation (No. 31372316). 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