Effects of feed processing on the apparent ileal digestibility of amino acids in pig diets containing wheat bran or wheat middlings Jarmo Valaja Agricultural Research Centre ofFinland, Institute ofAnimal Production, FIN-31600 Jokioinen, Finland, e-mail: jarmo.valaja@mlt.fi Hilkka Siljander-Rasi Agricultural Research Centre ofFinland, Swine Research Station, FIN-05840 Hyvinkää, Finland Markku Mäkinen Agricultural Research Centre ofFinland, Institute ofAnimal Production, FIN-31600 Jokioinen, Finland The effecls of feed processing on the apparent ileal digestibility of amino acid and the utilisation of nitrogen (N) in diets containing wheat by-products were studied in five castrated male pigs (live weight 40-109 kg). A T-cannula was surgically fitted into the caecum of the pigs at a live weight of 27 kg using the steered ileo-caecal valve technique. The experiment was conducted with a 6 x 5 cyclic change-over design in which six diets were arranged 2x3 factorially. The corresponding factors were type of wheat by-product in the diets: wheat bran (152 g/kg) or wheat middlings (328 g/kg), and method of feed processing: steam pelleting, expanding or extrusion. The other die- tary feed ingredients were barley and soya bean meal. The feed-processing method or dietary wheat by-product had no effect on the apparent ileal digest- ibility of amino acids and crude protein. The pigs on diets containing wheat middlings tended to retain more N per intake (p<0.10) than did those on wheat bran diets. The wheat middlings diets also tended to have higher biological values than did the wheat bran diets (p<0.!0). Further, daily N retention tended to be better with expanding than with pelleting (p<0.10). The N retention differ- ences were mainly caused by the differences in N intakes of the treatments. In conclusion, feed processing at a moderate temperature or wheat by-product in the diets had no influence on the apparent ileal digestibility of amino acids. Key words: pelleting, expanding, extrusion, protein, swine, nitrogen utilisation, wheat by-product ©Agricultural and Food Science in Finland Manuscript received September 1996 557 Vol. 5 0 996): 557-565. AGRICULTURAL AND FOOD SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=dOlRYJzyocW12rWG.O4w3kCDGJmlPQdBsCgFpTQ.r4VBuHinl0ihQUbvcCY7usxQ74fRkpkyX0Jo9eoFN63ymPW2Dir5RaOd7F3zmPppzsrram1trhIZUbNRyRQwaEBog4nt_mbPs7B1eQD1kuXc9INSoS4VmHc-uvk8CVbPxM1lLI8Ps2rk__fQ8RvLh2M-paW9or4Yb5WGxvhSP7sv53r3nMbim0eO26O3m3XosMq6RFsWx01BtkLVsqtrCGUkgdwQOKs4mJ_hvg-edA5S-zjOSR-pVEhaBa9IL1VsgULFjIX8z91OCfJL-z1YZ_jqp2pU27YAKw-u1p82CWlKQVEbpGwrS82S_gVTFb8 Valaja, J. et al. Effects offeed processing on the apparent ileal digestibility ofamino acids ntroduction Pressurized hydrothermal feed processing meth- ods such as pelleting, expanding and extrusion are commonly used in the feed industry to im- prove the nutritive value and hygienic quality of feed ingredients or compounds. The process- ing treatments are claimed to rupture the cell- wall matrix and liberate intracellular nutrients available for endogenous enzymes. Improve- ments in protein and amino acid digestibility have usually been only minor or non-existent (Skochetal. 1983,Fadel et al. 1988, Sauer et al. 1990, Herkelman et al. 1990, Laurinen et al. 1995). Processing has, however, increased the protein digestibility of certain feeds, e.g. beans, by inactivating antinutritional substances (Van der Poel et al. 1991). High temperature feed processing can also cause Maillard reactions, which depress the digestibility and utilisation of lysine in the feeds (Björk and Asp 1983). Wheat bran and wheat middlings are wheat milling by-products obtained from the milling process either separately or in combination. Wheat bran, derived mainly from partly ligni- fied pericarp and testa layers of the grain, con- tains high amounts of insoluble dietary fibre. Wheat middlings, however, consist of protein- rich aleurone layers and parts of endosperm, and contain more unlignified soluble dietary fibre (Bach Knudsen and Hansen 1991). Dietary in- clusion of fibre-rich wheat bran has decreased the feed retention time from mouth to anus and depressed the digestibility of nutrients includ- ing protein (Stanogias and Pearce 1985). The effects of the different feed-processing methods on the apparent ileal digestibility of amino acids have not been studied very widely (Herkelman et al. 1990, Van der Poel et al. 1990). Moreover, expanding is a fairly new processing method and no data are yet available on its ef- fects on the ileal digestibility of amino acids. The purpose of this study was to compare the effects of pelleting, expanding or extrusion on the apparent ileal digestibility of protein and amino acids in diets containing either wheatbran or wheat middlings. The total tract digestibility of protein and the utilisation of nitrogen were also studied. Material and methods Animals and experimental procedure The study was conducted on five castrated male pigs (Finnish Yorkshire) with an average live weight of 40.3 to 109.1 kg. A silicone T-cannula was surgically fitted into the caecum of the pigs at an average live weight of 27.3 kg with the steered ileo-caecal valve (SICV) technique (Mroz et al. 1994). This technique allows ileal digesta to be collected quantitatively via a valve- steering system. The animals were placed indi- vidually in pens of 1.43 m x 1.23 m with a slat- ted plastic floor and kept there throughout the study. During the 2-week post-operative period feed allowance was gradually increased to the experimental level. The experiment was conducted with a 6 x 5 cyclic change-over design in which six experi- mental treatments were arranged 2x3 factorial- ly. The corresponding factors were wheat by- product in the diet: wheat bran or wheat mid- dlings, and the methodof feed processing: steam pelleting, expanding or extrusion. The five 15- day experiment periods comprised preliminary feeding for 7 days followed by 5 days of total collection of faeces and urine (Table 1). Faeces were collected withplastic bags attached around the anus with glued adhesive tape and snap-fas- teners (Van Kleef et al. 1994). The plastic col- lection bags were replaced with new ones after the pigs had defecated. The faeces were collect- ed and weighed and frozen at -20°C. Ileal di- gesta was collected continuously during two 12 h periods between 06.00 and 18.00 h at an inter- val of 3 days into a plastic bag attached to the barrel of the cannula. The bags were changed at least hourly. The digesta was weighed and fro- zen immediately at -20°C. Urine was collected 558 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Table I. Scheme of experimental procedure. Day 1-7 Preminary feeding 8-12 Total collection of faeces and urine 13 Continuous collection of ileal digesta for 12 h (between 06.00 and 18.00h) 14 15 Continuous collection of ileal digesta for 12 h (between 06.00 and 18.00h) daily into 40 ml of 10N H 2 S04, sampled and frozen at -20°C. Experimental feeds and feeding Isoenergetic experimental feeds were formulat- ed to contain similar amounts of crude protein, lysine and neutral detergent fibre (NDF). The feeds, which consisted of barley, soya bean meal, vegetable oil and either wheat bran or wheat middlings (Table 2), were supplemented with minerals and vitamins and L lysine HCI and DL methionine to meet the requirements of grow- ing pigs (Tuori et al. 1995). The two feed mix- tures were either steam pelleted, expanded or extruded to form the six experimental feeds. The feeds were steam pelleted using 1.2% steam at a temperature of +62°C. Before expansion with the annular gap expander (Amandus Kahl Nachf. GmbH), the feeds were preconditioned for 25 min at +B5°C with 1.2% addition of water. The temperatures during expansion were +lOO- - and the pressure was 10 bar. During the extrusion phase with a twin-screw extruder (Clextral S.A.), the barrel temperature was + 150°C and the mass temperature before die was + 120°C. In the course of processing, moisture was added in the form of water and steam (9- 13%) and the pressure was 40 bar. The pigs were fed twice daily, at 06.00 and 18.00.The daily feeding scale was 2.7 times the assumed maintenance energy requirement (0.5 MJ ME/kg W 0 75; from 24.6 to 38.4 MJ ME/ day). The daily ratio was adjusted in each peri- od according to the body weight. During the feeding, water was added to the diets in a ratio of 1.5:1 and was also freely available from low- pressure drinking nipples. Chromium (Cr), yt- terbium (Yb) and cobalt (Co) were used as indi- gestible markers for the determination of nutri- ent digestibilities. Cr-mordanted straw (73 g Cr/kg DM) was added to the dietsat a level of2 g/kg feed (Udén et al. 1980). Yb-acetate and a lithum- Co-EDTA complex were dissolved in water and sprayed onto the surface of the barley in a batch- mixer. The barley was dried and ground and fed to the pigs at a level of 50 g/kg feed. Analytical procedure The feed, faeces and ileal digesta samples were freeze-dried and ground through 1-mm mash before analysis. Feeds, ileal digesta samples and faeces were analysed with the standard methods (AOAC 1984). Ether extract was determined af- ter acid hydrolysis. The NDF content of the feeds was analysed with the method of Robertson and van Soest (1981). The amino acids in feeds and ileal digesta samples were determined with a Beckman 6300 amino acid analyser after 23 h hydrolysis with 6.0 N HCI. Methionine and cys- tine were determined after oxidation to methio- nine sulphone and cysteic acid. Cr, Yb and Co were analysed by atomic absorption spectrome- try. All analyses were performed in duplicate except that of markers. Total tract digestibility values were calcu- lated from the total collection offaeces. Ileal di- gestibility values were calculated from the Cr ratio of feeds and ileal digesta because the fae- cal recovery rate of Cr was the closest to 100% (faecal recovery rate: Cr 95.3% (SE 2.49), Yb 114.9% (SE 3.31), Co 65.8% (SE 1.79)). The data were subjected to analysis of variance us- ing the GLM procedure of SAS (1985). The model was: y«kT v- + Pi + a , + d k +e ijki where y..k| is the dependent variable; pis the overall mean; p. is the effect of the period; a: is 559 Vol. 5 (1996): 557-565. AGRICULTURAL AND FOOD SCIENCE IN FINLAND Valaja, J. et al. Effects offeed processing on the apparent ileal digestibility ofamino acids Table 2. Dietary ingredients (g/kg) and chemical composition of diets (g/kg DM). Diet 12 3 4 5 6 Wheat by-product WB WM WB WM WB WM Processing P P EXP EXP EX EX Barley 633 523 633 523 633 523 Soya bean meal 152 96 152 96 152 96 Wheat bran 152 - 152 - 152 Wheat middlings - 328 - 328 - 328 Vegetable oil 30 20 30 20 30 20 L-lysine HCI 2 2.5 2 2.5 2 2.5 DL methionine 0.6 0.5 0.6 0.5 0.6 0.5 Minerals and vitamins 30.3 30.3 30.3 30.3 30.3 30.3 Analysed composition Dry matter, g/kg 897.0 897.1 892.9 888.8 943.5 946.2 Organic matter 940.5 943.7 948.7 948.0 948.8 948.9 Ash 59.5 56.3 51.3 52.0 51.2 51.1 Crude protein 181.8 157.3 187.1 183.1 182.2 176.4 Ether extract 69.8 62.1 70.5 67.0 74.3 65.4 Crude fibre 57.4 63.9 55.3 61.3 58.6 55.7 NDF 222.2 260.6 205.6 248.0 228.8 250.0 N-free extracts 631.6 660.4 635.8 636.6 633.7 651.5 Essential amino acids Arginine 10.4 8.9 10.9 8.9 10.9 10.0 Histidine 4.2 3.6 4.4 4.2 4.3 4.0 Isoleucine 6.2 4.9 6.5 6.0 6.7 5.9 Leucine 11.8 9.6 12.2 11.4 12.7 11.1 Lysine 9.4 8.6 9.8 9.5 10.4 9.2 Methionine 3.3 3.0 3.2 3.1 3.6 3.4 Phenylalanine 8.1 6.8 8.6 7.9 8.7 7.5 Threonine 6.1 5.0 6.2 5.9 6.6 5.9 Valine 7,7 6.5 7.8 7.6 8.2 7.3 Non-essential amino acids Alanine 7.8 6.8 7.8 7.8 7.9 7.5 Aspargicacid 14.4 10.9 15.2 13.9 15.2 13.5 Cystine 3.1 3.1 3.3 3.1 3.2 3.1 Glutamic acid 34.8 30.4 37.3 34.5 36.3 34.3 Glycine 8.1 6.9 7.8 7.6 8.1 7.5 Serine 7.9 6.5 8.3 7.7 8.5 7.5 Tyrosine 4.6 3.7 4.8 4.4 5.0 4.2 WB=wheat bran, WM=wheat middlings, P=pelleted, EXP=expanded, EX=extruded and NDF=neutral detergent fibre. the effect of the animal; dk is the effect of the diet; and e jjk| is a normally distributed random variable. Five orthogonal contrasts were formed to test the following effects: Cl: wheat bran di- ets vs wheat middlings diets; C2: extruder processing vs pelleting and expanding; C3; pel- leting vs expanding; C4: interaction Cl*C2; and C5: interaction Cl*C3. RGSUILS One animal did not recover from the surgical operation and had to be excluded from the ex- periment. Also, one observation was lacking from the total tract digestibility data because of diet refusals caused by mild fever, and six ob- 560 Table 3. Effect of feed processing on total tract digestibility of crude protein and apparent ileal digestibility of crudeprotein and amino acids in diets containing wheat bran or wheat middlings (LS means). Diet 1 2 3 4 5 6 SEM2 Statistical significance of effect Wheat by-product WB WM WB WM WB WM Cl 1 C 2 C 3 C 4 C5 Processing P P EXP EXP EX EX n 3 4 2 3 4 2 4 Total tract digestibility Dry matter 83.0 80.3 83.1 81.5 82.5 83.0 0.33 ** * ns ** ns Crude protein 84.5 83.0 83.9 83.4 84.4 84.0 0.50 ns ns ns ns ns Ileal digestibility Dry matter 69.0 66.4 69.9 67.0 67.1 66.2 1.21 ns ns ns ns ns Crude protein 75.0 76.6 76.0 76.0 77.3 75.5 1.22 ns ns ns ns ns Essential amino acids Arginine 84.1 85.1 83.8 82.9 85.5 82.8 1.05 ns ns ns ns ns Histidine 80.9 81.9 82.4 81.2 81.7 80.5 0.89 ns ns ns ns ns Isoleucine 77.2 78.8 78.2 77.7 81.1 78.6 1.13 ns ns ns ns ns Leucine 79.0 81.5 79.9 79.7 82.8 79.9 0.94 ns ns ns o ns Lysine 77.6 84.2 78.2 78.4 82.6 79.8 1.32 ns ns ns o ns Methionine 83.7 87.2 81.9 81.7 85.0 84.2 1.17 ns ns o ns ns Phenylalanine 80.3 82.3 81.5 80.8 83.2 81.6 0.96 ns ns ns ns ns Threonine 72.7 73.3 73.3 72.8 76.4 73.2 1.26 ns ns ns ns ns Valine 75.9 77.8 75.7 76.0 77.8 75.3 1.21 ns ns ns ns ns Non-essential amino acids Alanine 72.7 76.1 72.2 73.9 74.5 72.4 1.35 ns ns ns ns ns Aspartic acid 72.8 75.8 75.8 74.9 78.4 75.3 1.48 ns ns ns ns ns Cystine 77.3 81.8 74.4 74.3 71.8 73.7 3.39 ns ns ns ns ns Glutamic acid 85.8 87.9 86.8 85.7 88.1 87.3 0.89 ns ns ns ns ns Glycine 72.1 69.1 73.4 71.0 70.2 68.9 2.06 ns ns ns ns ns Serine 76.5 78.2 78.7 78.2 80.7 77.4 1.16 ns ns ns ns ns Tyrosine 79.4 80.6 80.0 79.3 81.4 78.8 0.94 ns ns ns ns ns WB=wheat bran, WM=wheat middlings, P=pelleted, EXP=expanded, EX=extruded. 1. Contrasts: Cl: wheat bran diets vs wheat middlings diets (1,3 and 5 vs 2, 4 and 6); C2: extruded diets vs pelleted and expanded diets (5 and 6 vs I, 2, 3 and 4); C3; pelleted diets vs expanded diets (I and 2 vs 3 and 4); C4:interaction Cl*C2; and Cs:interaction Cl*C3. 2. For ileal digestibility, the SEM of diet I and 6 is table value multiplied by 1.10, the SEM of diet 3 table value multiplied by 1.31 and the SEM of diet 2 and 5 table value multiplied by 1.87.For total tract digestibility the SEM of diets 1,3,4and 5 is table value multiplied by 1.17, and the SEM of diet 2 is table value multiplied by 1.44. 3. n for total tract digestibility, see Table 3. Significance: ns=non-significant, o=p