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Particle size and heat treatment of barley in diets for early-weaned piglets
Animal Feed Science and Technology 84 (2000) 13±21
Particle size and heat treatment of barley in diets for early-weaned piglets P. Medel, M. GarcõÂa, R. LaÂzaro, C. de Blas, G.G. Mateos* Departamento de ProduccioÂn Animal, ETSI AgroÂnomos, Universidad PoliteÂcnica de Madrid, 28040 Madrid, Spain Received 4 October 1999; received in revised form 18 January 2000; accepted 31 January 2000
Abstract One hundred and twenty male piglets weaned at 20 days and weighing 5.71.0 kg were used in a 28-day trial to evaluate the effect of dietary particle size and heat treatment of barley on performance and total tract apparent digestibility. There were four dietary treatments: coarsely ground barley (4.5 mm screen); ®nely ground barley (2.5 mm screen); micronized and then ®nely ground barley (2.5 mm screen); and ®nely ground (2.5 mm screen) and then expanded barley. All the diets contained 500 g of barley issued from the same batch/kg. There were six replicates of ®ve piglets per treatment. Total tract apparent digestibility of organic matter (OMD), energy (ED) and crude protein (CPD) were assessed from samples taken at 14 and 28 days from each replicate using chromic oxide as indigestible marker. No differences were found between results associated with screen sizes in the raw barley-based diets. Processing of barley caused an increase in starch gelatinization, a decrease in the proportion of large particles (>1.25 mm) and an increase in the proportion of ®ne particles (<0.16 mm; p<0.05), as compared with unprocessed barley. Piglets fed processed barley-based diets grew faster than piglets fed raw barley-based diets only in the ®rst 14 days of experiment (232 vs. 204 g per day; p0.04). Feed conversion was not modi®ed by barley processing. Processed barley-based diets showed higher values for OMD, ED and CPD than raw barley-based diets, but only the difference for OMD approached signi®cance (0.817 vs. 0.784; p0.07). It is concluded that processing of barley improved piglet performance in the ®rst 14 days post-weaning, and that no differences exist between processing techniques or grinding size of barley for any of the traits studied. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Barley; Expansion; Micronization; Piglet nutrition; Particle size
*
Corresponding author. Tel.: 34-915-497978; fax: 34-915-499763. E-mail address: [email protected] (G.G. Mateos) 0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 8 4 0 1 ( 0 0 ) 0 0 1 1 1 - 5
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1. Introduction Cereal grains are the major energy source in early-weaned piglet diets (Partridge and Gill, 1993). The digestive tract of piglets is immature at this age (Aumaitre et al., 1995), and is not entirely adapted to digest vegetable raw materials. The nutritive value of cereals for piglets can be improved by different methods, although information is limited and contradictory (Hutton and Armstrong, 1976; Lawrence, 1978; Partridge and Gill, 1993). Reducing particle size improves pellet quality and increases the surface of the ingredient available to the digestive enzymes. This can lead to an increase in feed ef®ciency of piglets fed barley-based diets. However, in most of the studies the positive response to a reduction in particle size was obtained with physical magnitudes of the grain greater than those used under practical conditions (Lawrence, 1970; Goodband and Hines, 1988). Otherwise, an excessive ®neness of particles increases the energy required for grinding, decreases milling production output (Wondra et al., 1995) and might induce gastric ulceration (Ayles et al., 1996). In addition, the effects of grinding size vary according to type of cereal (Healy et al., 1994) and might be more important for simple than for complex diets (Kim et al., 1995). Heat processing of barley has improved feed ef®ciency and piglet performance in previous works (Aumaitre, 1976; Medel et al., 1999). However, the extension and signi®cance of the effects vary among studies. For example, Vestergaard et al. (1990) found a positive response in performance when barley was cooked under pressure compared to raw barley, but no differences were observed when barley was extruded. In fact, Hongtrakul et al. (1998) found different responses to extrusion of maize in different trials, without any clear explanation. Type of processing affects degree of starch gelatinization, which is believed to in¯uence starch digestibility and growth performance (Lawrence, 1978). However, little effect of degree of gelatinization of the cereal portion of the diet on piglet performance has been observed previously (Hongtrakul et al., 1998; Medel et al., 1999). Therefore, a great deal of confusion exists concerning both the optimum particle size and the interest of heat processing and degree of starch gelatinization of barley in commercial piglet diets. The aim of the current study was to examine the effect of grinding raw barley through two screen sizes (2.5 vs. 4.0 mm) and of cereal processing by two techniques (micronization and expansion) on performance and total tract digestibility of early weaned piglet diets. 2. Materials and methods 2.1. Diets A single batch of winter barley was split into three fractions. The ®rst fraction was ground coarse (4.0 mm screen) or ®ne (2.5 mm screen) through a hammer mill. The second fraction was micronized (Microred 20, Micronizing Company, Framlingham, UK). Whole grains were macerated for 24 h until reaching 193 g/kg humidity and then passed through the micronizer. The temperature and humidity of the grains in the last section of the machine were 748C and 112 g/kg, respectively. Afterwards, the grains were
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Table 1 Determined chemical composition of raw and processed barley (g/kg, as feed basis) Barley
Nutrients (g/kg) Dry matter Crude protein Ash Starch Starch gelatinizationa Total NSP Total b-glucans Total xylans Soluble xylans a
Raw
Micronized
Expanded
884 99 21 520 0.186 15.2 3.5 6.0 0.4
879 100 19 510 0.301 15.6 3.6 6.4 0.32
895 104 30 512 0.311 14.0 3.1 5.5 0.39
As a proportion of total starch.
¯aked through rif¯ed rolls and ®nely ground (2.5 mm screen). The third fraction was ®nely ground (2.5 mm screen) and then expanded at 1208C and 30 bars during 5 s, by a single expander (KAHL O.E. 30.2, Hamburg, Germany). The chemical analyses of the three barley fractions are shown in Table 1. A complex diet based on barley (500 g/kg) was formulated, and four diets were mixed by substituting (w/w) the different samples of barley. The ingredient composition and the estimated nutrient value of the experimental diets, according to FEDNA (1999), is shown in Table 2. Analysed chemical composition of diets is presented in Table 3. Chromium oxide was included as an undigestible marker for determination of total tract apparent digestibility of organic matter (OMD), energy (ED) and crude protein (CPD). 2.2. Experimental procedure One hundred and twenty male cross-bred (LandraceLarge White) piglets from 30 litters (four piglets per litter) weaned at 20 days of age and weighing 5.71.0 kg, were used. Piglets were blocked by litter and then allotted in groups of ®ve per cage, with six pens per treatment. The animals were housed in 24 ¯at-deck pens (11 m) provided with individual feeder (5 spaces) and a nipple drinker, and had ad libitum access to feed throughout the trial. Average feed intake (AFI), daily gain (ADG) and feed conversion ratio (FCR) were recorded weekly. Diarrhoea incidence and mortality were recorded daily. On days 14 and 28 of the experiment, a pooled sample of faeces from at least four pigs per pen was taken by rectal massage, and frozen until chemical analyses. 2.3. Chemical analyses Feeds and faeces were dried (608C, 48 h), ground (1 mm screen) and analysed following the methods of the Association of Of®cial Analytical Chemist (1995) to determine moisture by the oven-drying method (930.15), ash (942.05) and crude protein by the Kjeldahl method (984.13). Gross energy was determined with an adiabatic bomb
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Table 2 Composition of diets and estimated nutrient value (g/kg, as fed basis) Ingredients (g/kg) Barley Sun¯ower oil Full fat soybean (extruded) Fish meal LT Dried whey Calcium carbonate DL-Metionine L-Lysine hydrochloride L-Threonine Citric acid Vitamin and mineral premixa Chromic oxide
500 12.3 151.3 105 200 5.8 1.3 1.7 1.1 15 3.5 3
Estimated nutrient valueb Metabolisable energy (MJ/kg) Net energy (MJ/kg) Crude protein (g/kg) Total lysine (g/kg) Neutral detergent ®bre (g/kg) Starch (g/kg) Calcium (g/kg) Available phosphorus (g/kg) Sodium (g/kg)
13.3 10.3 213.0 14.5 104.6 256.0 7.2 4.1 2.4
a
Mineral and vitamin premix supplied for 1 kg of complete diet: Vitamin A, 15.000 IU; Vitamin D3, 1.900 IU; Vitamin E, 30 IU; Vitamin K, 1.6 mg; Thiamine, 1.1 mg; Ribo¯avin, 5 mg; Pantothenic acid, 14 mg; Niacin, 25 mg; Pyridoxin, 2.5 mg; Biotin, 150 mg; Folic acid, 200 mg; Cyanocobalamin, 25 mg; Choline, 250 mg; Fe, 75 mg; Cu, 160 mg; Zn, 110 mg; Mn, 50 mg; Co, 100 mg; Se, 300 mg; I, 1 mg; Carbadox, 50 ppm. b According to FEDNA (1999) tables of composition of raw materials.
calorimeter (IKA-4000, Schott IbeÂrica, Spain). Chromium content of feed and faeces was analysed by atomic absorption (Smith-Hieftje 22, Thermo Jarrell Ash, MA, USA). Previously, samples were ashed (5508C) and then digested by boiling with a solution of 1.5 M HNO3 and KCl (3.81 g/l). The NSP and û-glucans of the barley samples were Table 3 Chemical composition of experimental diets (g/kg, as feed basis) Processing
Screen (mm) Dry matter (g/kg) Crude protein (g/kg) Ash (g/kg) Gross energy (MJ/kg) Digestible energya (MJ/kg) a
Barley Raw
Raw
Micronized
Expanded
4.0 901 207 81 16.60 12.80
2.5 900 208 84 16.52 12.65
2.5 882 212 81 16.26 12.83
2.5 896 212 81 16.67 13.28
Calculated using the digestibility parameters shown in Table 6.
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Ê man and Graham (1987), respectively. analysed by the method of Theander (1991) and A Barley xylans were analysed following the method of Saini and Henry (1989). Analysis of the particle distribution of the experimental feeds was determined in two representative samples by wet sieving. A 55 g dried sample was placed in 1100 ml of distilled water and 30 ml of a commercial detergent. The sample was left overnight at room temperature with continuous stirring and then emptied onto a sieve stack as described by GarcõÂa et al. (1999). Starch gelatinization, as a proportion of total starch, was determined by enzymatic hydrolysis as described by Medel et al. (1999). 2.4. Statistical analysis Data were analysed as a completely randomised block design with litter as block effect and type of diet as main effect by using the GLM procedure of SAS (1990). Initial body weight was used as a linear covariate. Pre-planned comparisons were used to determine the effect of particle size, processing and type of processing of barley by using the contrast method. The effects of age and its interaction with type of diet on digestive ef®ciency data were analysed using the repeated measures procedure of SAS (1990). 3. Results Particle size distribution of experimental diets is shown in Table 4. Coarsely ground raw barley-based diet produced a greater proportion of large particles (>0.63 mm) and a smaller proportion of small particles (<0.16 mm) than ®nely ground raw barley-based diet. Furthermore, processing of barley decreased the proportion of large particles (>1.25 mm), and increased that of ®ne particles (<0.16 mm), but type of processing did not affect particle size. Table 4 Particle size distribution of experimental dietsa Particle size distribution >2.5 mm 1.25± 2.5 mm Barley Raw Raw Micronized Expanded SEM (n2) Signi®cance of contrastb
a b
Screen (mm) 4.0 0.006 2.5 0 2.5 0 2.5 0 ± 1 0.001 2 ± 3 ±
0.105 0.065 0.020 0.020 0.005 0.002 0.0007 0.99
0.630± 0.315± 0.160± <0.160 mm 1.25 mm 0.630 mm 0.315 mm 0.076 0.050 0.050 0.056 0.005 0.01 0.44 0.18
0.066 0.065 0.075 0.072 0.005 0.93 0.20 0.59
0.066 0.075 0.070 0.082 0.005 0.25 0.90 0.14
0.681 0.745 0.783 0.770 0.009 0.005 0.04 0.13
Expressed as a proportion of total particles. 1 Ð 2.5 mm vs. 4.0 mm in raw barley; 2 Ð raw vs. processed barley; 3 Ð expanded vs. micronized barley.
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Table 5 Effect of dietary treatment on performance of piglets according to the period Period (day) 0±14 ADG Barley Raw Raw Micronized Expanded SEM (n6) Signi®cance of contrastd
Screen (mm) 4.0 2.5 2.5 2.5 1 2 3
14±28 a
208 204 225 238 10 0.80 0.02 0.39
b
AFI
208 210 224 232 11 0.92 0.21 0.61
c
FCR
1.00 1.04 1.00 0.98 0.04 0.48 0.28 0.76
0±28
ADG
AFI
484 470 482 502 21 0.62 0.47 0.50
684 671 701 713 27 0.69 0.22 0.72
FCR 1.42 1.43 1.46 1.42 0.05 0.81 0.69 0.43
ADG
AFI
FCR
346 337 353 370 13 0.62 0.13 0.38
446 440 463 473 18 0.79 0.14 0.66
1.29 1.31 1.31 1.28 0.03 0.67 0.81 0.41
a
Average daily gain (ADG, g). Average daily feed intake (AFI, g). c Feed conversion ratio (FCR, g feed intake/g weight gain). d 1 Ð 2.5 mm vs. 4.0 mm in raw barley; 2 Ðraw vs. processed barley; 3 Ð expanded vs. micronized barley. b
The in¯uence of the diet on performance of animals is shown in Table 5. Processing of barley resulted in a higher ADG in the ®rst 14 days of experiment (232 vs. 204 g per day, p0.02), but the effect disappeared thereafter (470 vs. 492 g per day from 14 to 28 days; Table 6 Effect of dietary treatment on the total tract apparent digestibility of dietary nutrientsa Total tract apparent digestibilityb coefficients
Source of variation
Organic matter
Energy
Protein
0.804 0.784 0.808 0.826 0.014
0.771 0.766 0.789 0.797 0.013
0.736 0.751 0.766 0.769 0.015
0.34 0.07 0.39
0.85 0.13 0.70
0.49 0.38 0.94
Days post-weaning (day) 14 28
0.803 0.807
0.778 0.783
0.759 0.752
SEM (n24) p
0.010 0.87
0.009 0.76
0.011 0.41
Barley Raw Raw Micronized Expanded SEM (n12)
Screen (mm) 4.0 2.5 2.5 2.5
Signi®cance of contrastc
1 2 3
a
Expressed as a proportion. Interaction between treatment and time was not signi®cant (p>0.05). c 1 Ð 2.5 mm vs. 4.0 mm in raw barley; 2 Ð raw vs. processed barley; 3 Ð expanded vs. micronized barley. b
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p>0.15). Feed ef®ciency and incidence of scours as measured by proportion of animals that needed antibiotic treatment were not affected by diet. Neither particle size nor type of processing affected any of the performance traits studied. The OMD, ED and CPD of the diets are shown in Table 6. Processing of barley tended to increase OMD (0.817 vs. 0.784; p0.07) and ED (0.793 vs. 0.766; p0.13), but neither grinding size nor type of processing affected nutrient digestibility. Digestive ef®ciency was similar among treatments at 14 or 28 days (p>0.15), and no interactions between age and type of diet were detected for any trait. 4. Discussion Grinding size did not affect signi®cantly piglet performance or apparent digestibility of nutrients. Previous results with piglets are confusing due to the wide range of screen sizes used, the type of cereal tested and the differences in complexity of the experimental diets. Reducing particle size is generally expected to improve performance and FCR because the surface area of the ingredients available to the digestive enzymes is increased. At this respect, Wu and Fuller (1974) found a positive response in ADG and FCR for the ®rst week after weaning (28±35 days of age) when the screen size used for maize grinding was decreased from 9.5 to 1.6 mm. However, they did not ®nd any difference when comparing samples prepared with screen sizes of 4 and 1.6 mm. Healy et al. (1994) reported that reducing the particle size of maize from 900 to 300 mm improved ADG and FCR for the ®rst two weeks after weaning (22±36 days of age), but not thereafter. However, reducing the particle size of hard or soft sorghum to the same extent as for maize, did not affect performance for any of the periods studied. An excessive ®neness of the feed induces gastric ulceration and impairs AFI and ADG of pigs (Hedde et al., 1985; Hale and Thompson, 1986; Ayles et al., 1996). Partridge and Gill (1993) suggested that the negative effect of an excessive ®neness of particle size is especially important with wheat, due to the tendency of this cereal to become sticky and pasty in the buccal cavity because of its high gluten content. The problem might be of less importance for barley because particles of 0.2 mm did not affect the performance of growing pigs (Chu et al., 1998). Goodband and Hines (1988) working with barley diets, did not observe any difference in piglet performance from 0 to 14 days, but a positive response of 5% in ADG and in FCR was found from 0 to 35 days when the screen size was reduced from 4.8 to 3.2 mm. On the other hand, Gipp et al. (1995) failed to ®nd differences in performance of 7.5 kg piglets with screen sizes of 6.35, 4.76 or 3.18 mm. Similarly, we did not observe any improvement on performance or digestibility of nutrients due to a reduction of screen size from 4 to 2.5 mm. In the current experiment processing of barley caused a 13% improvement in growth in the ®rst 14 days of the experiment, which agrees with previous results in piglets (Aumaitre, 1976; Medel et al., 1999). However, no differences were detected between 14 and 28 days. Studies conducted with piglets fed barley diets show that processing caused an increase in nutrient digestibility (Chu et al., 1998; Huang et al., 1998). In the current study, processed barley diets showed a 4% higher total tract apparent OMD than the control diet at 14 and 28 days, although this improvement was not associated with better
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P. Medel et al. / Animal Feed Science and Technology 84 (2000) 13±21
performance. The observed improvement of digestibility due to processing agrees with previous data (Medel et al., 1999), and is slightly higher than the values reported by Aumaitre (1976). Expansion and micronization produced similar degrees of starch gelatinization, nutrient digestibility and piglet performance, results that agree with data presented by Vestergaard et al. (1990) and Medel et al. (1999). The digestibility of nutrients was similar when assessed at 14 and 28 days after weaning. Van der Poel et al. (1989) reported higher OMD and CPD in piglets of 7.2 kg than in piglets of 5.8 kg. In the current study, the digestibility of diets was determined with heavier pigs (8.8 and 15.6 kg) which might explain the lack of response with age. In conclusion, decreasing particle size of barley within the range tested (4.0 vs. 2.5 mm) had no signi®cant effect on total tract apparent digestibility or performance of piglets. Heat processing only improved performance in the ®rst 14 days after weaning and no differences between micronization and expansion were detected for any of the traits studied. Based on this experiment, heat processing of barley in diets for early-weaned piglets is recommended. Acknowledgements This research was supported by CICYT project AGF96-1142. Thanks are due to A. Sanz and G. Fructuoso for their help in the management of the animals and to Y. Alegre for typing the manuscript. References Ê man, P., Graham, H., 1987. Analysis of total and insoluble mixed-linked (1±3), (1±4)-û-D-glucans in barley A and oats. J. Agric. Food Chem. 35, 704±709. Aumaitre, A., 1976. EÂvaluation de divers traitements technologiques des ceÂreÂales. Ann. Zootech. 25, 41±51. Aumaitre, A., Peiniau, J., Madec, F., 1995. Digestive adaptation after weaning and nutritional consequences in the piglet. Pig News Inf. 16, 73N±79N. Ayles, H.L., Friendship, R.M., Ball, R.O., 1996. Effect of dietary particle size on gastric ulcers, assessed by endoscopic examination, and relationship between ulcer severity and growth performance of individually fed pigs. Swine Health Prod. 5, 211±216. Association of Of®cial Analytical Chemist, 1995. Of®cial Methods of Analysis, 16th Edition. AOAC, Washington, DC. Chu, K.S., Kim, J.H., Chae, B.J., Chung, Y.K., Han, I.K., 1998. Effects of processed barley on growth performance and ileal digestibility of growing pigs. Asian-Australasian J. Anim. Sci. 11, 249±254. FEDNA, 1999. Normas FEDNA para la formulacioÂn de piensos compuestos. de Blas, C., Mateos, G.G., Rebollar, P.G. (Eds.), FEDNA, Madrid, Spain, 496 pp. GarcõÂa, J., CarabanÄo, R., de Blas, J.C., 1999. Effect of ®ber source on cell wall digestibility and rate of passage in rabbits. J. Anim. Sci. 77, 898±905. Gipp, W.F., Clark, C.K., Bryan, K.S., 1995. In¯uence of barley ®neness of grind on starter, grower and ®nisher swine performance. J. Anim. Sci. 73 (Suppl. 1), 179. Goodband, R.D., Hines, R.H., 1988. An evaluation of barley in starter diets for swine. J. Anim. Sci. 66, 3086± 3093. Hale, O.M., Thompson, L.M., 1986. In¯uence of particle size of wheat on performance of ®nishing swine. Nutr. Rep. Int. 33, 307±311.
P. Medel et al. / Animal Feed Science and Technology 84 (2000) 13±21
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Healy, B.J., Hancock, J.D., Kennedy, G.A., Bramel-Cox, P.J., Behnke, K.C., Hines, R.H., 1994. Optimum particle size of corn and hard and soft sorghum for nursery pigs. J. Anim. Sci. 72, 2227±2236. Hedde, R.D., Lindsey, T.O., Parish, R.C., Daniels, H.D., Morgenthien, E.A., Lewis, H.B., 1985. Effect of diet particle size and feeding of H2-receptor antagonists on gastric ulcers in swine. J. Anim. Sci. 61, 179±186. Hongtrakul, K., Goodband, R.D., Behnke, K.C., Nelssen, J.L., Tokach, M.D., BergstroÈm, J.R., Nessmith Jr., W.B., Kim, I.K., 1998. The effects of extrusion processing of carbohydrate sources on weanling pig performance. J. Anim. Sci. 76, 3034±3042. Huang, S.X., Sauer, W.C., Pickard, M., Li, S., Hardin, R.T., 1998. Effect of micronization on energy, starch and amino acid digestibility in hulless barley for young pigs. Can. J. Anim. Sci. 78, 81±87. Hutton, K, Armstrong D.G., 1976. Cereal processing. In: Swan, H., Lewis, D. (Eds.), Nutrition Conference for Feed Manufacturers. Butterworths, London, UK, pp. 47±63. Kim, I.H., Hancock, J.D., Hines, R.H., Rantanen, M.M., Burham, L.L., 1995. Effects of particle size (1000 and 500 mm in simple and complex diets for weanling pigs. J. Anim. Sci. 73 (Suppl. 1), 179. Lawrence, T.J.L., 1970. Some effects of including differently processed barley in the diet of the growing pig. Anim. Prod. 12, 139±150. Lawrence, T.J.L., 1978. Processing and preparation of cereals for pig diets. In: Haresign, W., Lewis, D. (Eds.), Recent Advances in Animal Nutrition. Butterworths, London, UK, pp. 83±98. Medel, P., Salado, S., Mateos, G.G., de Blas, C., 1999. Processed cereals in diets for early-weaned piglets. Anim. Feed Sci. Technol. 82, 145±156. Partridge, G.G., Gill, B.P., 1993. New approaches with pig weaner diets. In: Garnsworthy, P.C., Cole, D.J.A. (Eds.), Recent Advances in Animal Nutrition. Nottingham University Press, UK, pp. 221±248. Saini, H.S., Henry, R.J., 1989. Fractionation and evaluation of triticale pentosans. Comparison with wheat and rye. Cereal Chem. 66, 11±14. SAS, 1990. SAS1 User's Guide: Statistics. SAS Inst. Inc., Cary, NC. Theander, O., 1991. Chemical analysis of lignocellulose materials. Anim. Feed Sci. Technol. 32, 35±44. Van der Poel, A.F.B., Den Hartog, L.A., Van den Abeele, T.H., Boer, H., Van Zuilichem, D.J., 1989. Effect of infrared irradiation or extrusion processing of maize on its digestibility in piglets. Anim. Feed Sci. Technol. 26, 29±43. Vestergaard, E.M., Danielsen, V., Jacobsen, E.E., Rasmussen, V., 1990. Heat treated cereals for piglets. Beretning Fra Statens Husdyrbrugsforsog 674, 71. Wondra, K.J., Hancock, J.D., Behnke, K.C., Hines, R.H., Stark, C.R., 1995. Effects of particle size and pelleting on growth performance, nutrient digestibility, and stomach morphology in ®nishing pigs. J. Anim. Sci. 73, 757±763. Wu, J.F., Fuller, M.F., 1974. A note on the performance of young pigs given maize-based diets in different physical forms. Anim. Prod. 18, 317±320.
Particle size and heat treatment of barley in diets for early-weaned piglets P. Medel, M. GarcõÂa, R. LaÂzaro, C. de Blas, G.G. Mateos* Departamento de ProduccioÂn Animal, ETSI AgroÂnomos, Universidad PoliteÂcnica de Madrid, 28040 Madrid, Spain Received 4 October 1999; received in revised form 18 January 2000; accepted 31 January 2000
Abstract One hundred and twenty male piglets weaned at 20 days and weighing 5.71.0 kg were used in a 28-day trial to evaluate the effect of dietary particle size and heat treatment of barley on performance and total tract apparent digestibility. There were four dietary treatments: coarsely ground barley (4.5 mm screen); ®nely ground barley (2.5 mm screen); micronized and then ®nely ground barley (2.5 mm screen); and ®nely ground (2.5 mm screen) and then expanded barley. All the diets contained 500 g of barley issued from the same batch/kg. There were six replicates of ®ve piglets per treatment. Total tract apparent digestibility of organic matter (OMD), energy (ED) and crude protein (CPD) were assessed from samples taken at 14 and 28 days from each replicate using chromic oxide as indigestible marker. No differences were found between results associated with screen sizes in the raw barley-based diets. Processing of barley caused an increase in starch gelatinization, a decrease in the proportion of large particles (>1.25 mm) and an increase in the proportion of ®ne particles (<0.16 mm; p<0.05), as compared with unprocessed barley. Piglets fed processed barley-based diets grew faster than piglets fed raw barley-based diets only in the ®rst 14 days of experiment (232 vs. 204 g per day; p0.04). Feed conversion was not modi®ed by barley processing. Processed barley-based diets showed higher values for OMD, ED and CPD than raw barley-based diets, but only the difference for OMD approached signi®cance (0.817 vs. 0.784; p0.07). It is concluded that processing of barley improved piglet performance in the ®rst 14 days post-weaning, and that no differences exist between processing techniques or grinding size of barley for any of the traits studied. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Barley; Expansion; Micronization; Piglet nutrition; Particle size
*
Corresponding author. Tel.: 34-915-497978; fax: 34-915-499763. E-mail address: [email protected] (G.G. Mateos) 0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 8 4 0 1 ( 0 0 ) 0 0 1 1 1 - 5
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1. Introduction Cereal grains are the major energy source in early-weaned piglet diets (Partridge and Gill, 1993). The digestive tract of piglets is immature at this age (Aumaitre et al., 1995), and is not entirely adapted to digest vegetable raw materials. The nutritive value of cereals for piglets can be improved by different methods, although information is limited and contradictory (Hutton and Armstrong, 1976; Lawrence, 1978; Partridge and Gill, 1993). Reducing particle size improves pellet quality and increases the surface of the ingredient available to the digestive enzymes. This can lead to an increase in feed ef®ciency of piglets fed barley-based diets. However, in most of the studies the positive response to a reduction in particle size was obtained with physical magnitudes of the grain greater than those used under practical conditions (Lawrence, 1970; Goodband and Hines, 1988). Otherwise, an excessive ®neness of particles increases the energy required for grinding, decreases milling production output (Wondra et al., 1995) and might induce gastric ulceration (Ayles et al., 1996). In addition, the effects of grinding size vary according to type of cereal (Healy et al., 1994) and might be more important for simple than for complex diets (Kim et al., 1995). Heat processing of barley has improved feed ef®ciency and piglet performance in previous works (Aumaitre, 1976; Medel et al., 1999). However, the extension and signi®cance of the effects vary among studies. For example, Vestergaard et al. (1990) found a positive response in performance when barley was cooked under pressure compared to raw barley, but no differences were observed when barley was extruded. In fact, Hongtrakul et al. (1998) found different responses to extrusion of maize in different trials, without any clear explanation. Type of processing affects degree of starch gelatinization, which is believed to in¯uence starch digestibility and growth performance (Lawrence, 1978). However, little effect of degree of gelatinization of the cereal portion of the diet on piglet performance has been observed previously (Hongtrakul et al., 1998; Medel et al., 1999). Therefore, a great deal of confusion exists concerning both the optimum particle size and the interest of heat processing and degree of starch gelatinization of barley in commercial piglet diets. The aim of the current study was to examine the effect of grinding raw barley through two screen sizes (2.5 vs. 4.0 mm) and of cereal processing by two techniques (micronization and expansion) on performance and total tract digestibility of early weaned piglet diets. 2. Materials and methods 2.1. Diets A single batch of winter barley was split into three fractions. The ®rst fraction was ground coarse (4.0 mm screen) or ®ne (2.5 mm screen) through a hammer mill. The second fraction was micronized (Microred 20, Micronizing Company, Framlingham, UK). Whole grains were macerated for 24 h until reaching 193 g/kg humidity and then passed through the micronizer. The temperature and humidity of the grains in the last section of the machine were 748C and 112 g/kg, respectively. Afterwards, the grains were
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Table 1 Determined chemical composition of raw and processed barley (g/kg, as feed basis) Barley
Nutrients (g/kg) Dry matter Crude protein Ash Starch Starch gelatinizationa Total NSP Total b-glucans Total xylans Soluble xylans a
Raw
Micronized
Expanded
884 99 21 520 0.186 15.2 3.5 6.0 0.4
879 100 19 510 0.301 15.6 3.6 6.4 0.32
895 104 30 512 0.311 14.0 3.1 5.5 0.39
As a proportion of total starch.
¯aked through rif¯ed rolls and ®nely ground (2.5 mm screen). The third fraction was ®nely ground (2.5 mm screen) and then expanded at 1208C and 30 bars during 5 s, by a single expander (KAHL O.E. 30.2, Hamburg, Germany). The chemical analyses of the three barley fractions are shown in Table 1. A complex diet based on barley (500 g/kg) was formulated, and four diets were mixed by substituting (w/w) the different samples of barley. The ingredient composition and the estimated nutrient value of the experimental diets, according to FEDNA (1999), is shown in Table 2. Analysed chemical composition of diets is presented in Table 3. Chromium oxide was included as an undigestible marker for determination of total tract apparent digestibility of organic matter (OMD), energy (ED) and crude protein (CPD). 2.2. Experimental procedure One hundred and twenty male cross-bred (LandraceLarge White) piglets from 30 litters (four piglets per litter) weaned at 20 days of age and weighing 5.71.0 kg, were used. Piglets were blocked by litter and then allotted in groups of ®ve per cage, with six pens per treatment. The animals were housed in 24 ¯at-deck pens (11 m) provided with individual feeder (5 spaces) and a nipple drinker, and had ad libitum access to feed throughout the trial. Average feed intake (AFI), daily gain (ADG) and feed conversion ratio (FCR) were recorded weekly. Diarrhoea incidence and mortality were recorded daily. On days 14 and 28 of the experiment, a pooled sample of faeces from at least four pigs per pen was taken by rectal massage, and frozen until chemical analyses. 2.3. Chemical analyses Feeds and faeces were dried (608C, 48 h), ground (1 mm screen) and analysed following the methods of the Association of Of®cial Analytical Chemist (1995) to determine moisture by the oven-drying method (930.15), ash (942.05) and crude protein by the Kjeldahl method (984.13). Gross energy was determined with an adiabatic bomb
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Table 2 Composition of diets and estimated nutrient value (g/kg, as fed basis) Ingredients (g/kg) Barley Sun¯ower oil Full fat soybean (extruded) Fish meal LT Dried whey Calcium carbonate DL-Metionine L-Lysine hydrochloride L-Threonine Citric acid Vitamin and mineral premixa Chromic oxide
500 12.3 151.3 105 200 5.8 1.3 1.7 1.1 15 3.5 3
Estimated nutrient valueb Metabolisable energy (MJ/kg) Net energy (MJ/kg) Crude protein (g/kg) Total lysine (g/kg) Neutral detergent ®bre (g/kg) Starch (g/kg) Calcium (g/kg) Available phosphorus (g/kg) Sodium (g/kg)
13.3 10.3 213.0 14.5 104.6 256.0 7.2 4.1 2.4
a
Mineral and vitamin premix supplied for 1 kg of complete diet: Vitamin A, 15.000 IU; Vitamin D3, 1.900 IU; Vitamin E, 30 IU; Vitamin K, 1.6 mg; Thiamine, 1.1 mg; Ribo¯avin, 5 mg; Pantothenic acid, 14 mg; Niacin, 25 mg; Pyridoxin, 2.5 mg; Biotin, 150 mg; Folic acid, 200 mg; Cyanocobalamin, 25 mg; Choline, 250 mg; Fe, 75 mg; Cu, 160 mg; Zn, 110 mg; Mn, 50 mg; Co, 100 mg; Se, 300 mg; I, 1 mg; Carbadox, 50 ppm. b According to FEDNA (1999) tables of composition of raw materials.
calorimeter (IKA-4000, Schott IbeÂrica, Spain). Chromium content of feed and faeces was analysed by atomic absorption (Smith-Hieftje 22, Thermo Jarrell Ash, MA, USA). Previously, samples were ashed (5508C) and then digested by boiling with a solution of 1.5 M HNO3 and KCl (3.81 g/l). The NSP and û-glucans of the barley samples were Table 3 Chemical composition of experimental diets (g/kg, as feed basis) Processing
Screen (mm) Dry matter (g/kg) Crude protein (g/kg) Ash (g/kg) Gross energy (MJ/kg) Digestible energya (MJ/kg) a
Barley Raw
Raw
Micronized
Expanded
4.0 901 207 81 16.60 12.80
2.5 900 208 84 16.52 12.65
2.5 882 212 81 16.26 12.83
2.5 896 212 81 16.67 13.28
Calculated using the digestibility parameters shown in Table 6.
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Ê man and Graham (1987), respectively. analysed by the method of Theander (1991) and A Barley xylans were analysed following the method of Saini and Henry (1989). Analysis of the particle distribution of the experimental feeds was determined in two representative samples by wet sieving. A 55 g dried sample was placed in 1100 ml of distilled water and 30 ml of a commercial detergent. The sample was left overnight at room temperature with continuous stirring and then emptied onto a sieve stack as described by GarcõÂa et al. (1999). Starch gelatinization, as a proportion of total starch, was determined by enzymatic hydrolysis as described by Medel et al. (1999). 2.4. Statistical analysis Data were analysed as a completely randomised block design with litter as block effect and type of diet as main effect by using the GLM procedure of SAS (1990). Initial body weight was used as a linear covariate. Pre-planned comparisons were used to determine the effect of particle size, processing and type of processing of barley by using the contrast method. The effects of age and its interaction with type of diet on digestive ef®ciency data were analysed using the repeated measures procedure of SAS (1990). 3. Results Particle size distribution of experimental diets is shown in Table 4. Coarsely ground raw barley-based diet produced a greater proportion of large particles (>0.63 mm) and a smaller proportion of small particles (<0.16 mm) than ®nely ground raw barley-based diet. Furthermore, processing of barley decreased the proportion of large particles (>1.25 mm), and increased that of ®ne particles (<0.16 mm), but type of processing did not affect particle size. Table 4 Particle size distribution of experimental dietsa Particle size distribution >2.5 mm 1.25± 2.5 mm Barley Raw Raw Micronized Expanded SEM (n2) Signi®cance of contrastb
a b
Screen (mm) 4.0 0.006 2.5 0 2.5 0 2.5 0 ± 1 0.001 2 ± 3 ±
0.105 0.065 0.020 0.020 0.005 0.002 0.0007 0.99
0.630± 0.315± 0.160± <0.160 mm 1.25 mm 0.630 mm 0.315 mm 0.076 0.050 0.050 0.056 0.005 0.01 0.44 0.18
0.066 0.065 0.075 0.072 0.005 0.93 0.20 0.59
0.066 0.075 0.070 0.082 0.005 0.25 0.90 0.14
0.681 0.745 0.783 0.770 0.009 0.005 0.04 0.13
Expressed as a proportion of total particles. 1 Ð 2.5 mm vs. 4.0 mm in raw barley; 2 Ð raw vs. processed barley; 3 Ð expanded vs. micronized barley.
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Table 5 Effect of dietary treatment on performance of piglets according to the period Period (day) 0±14 ADG Barley Raw Raw Micronized Expanded SEM (n6) Signi®cance of contrastd
Screen (mm) 4.0 2.5 2.5 2.5 1 2 3
14±28 a
208 204 225 238 10 0.80 0.02 0.39
b
AFI
208 210 224 232 11 0.92 0.21 0.61
c
FCR
1.00 1.04 1.00 0.98 0.04 0.48 0.28 0.76
0±28
ADG
AFI
484 470 482 502 21 0.62 0.47 0.50
684 671 701 713 27 0.69 0.22 0.72
FCR 1.42 1.43 1.46 1.42 0.05 0.81 0.69 0.43
ADG
AFI
FCR
346 337 353 370 13 0.62 0.13 0.38
446 440 463 473 18 0.79 0.14 0.66
1.29 1.31 1.31 1.28 0.03 0.67 0.81 0.41
a
Average daily gain (ADG, g). Average daily feed intake (AFI, g). c Feed conversion ratio (FCR, g feed intake/g weight gain). d 1 Ð 2.5 mm vs. 4.0 mm in raw barley; 2 Ðraw vs. processed barley; 3 Ð expanded vs. micronized barley. b
The in¯uence of the diet on performance of animals is shown in Table 5. Processing of barley resulted in a higher ADG in the ®rst 14 days of experiment (232 vs. 204 g per day, p0.02), but the effect disappeared thereafter (470 vs. 492 g per day from 14 to 28 days; Table 6 Effect of dietary treatment on the total tract apparent digestibility of dietary nutrientsa Total tract apparent digestibilityb coefficients
Source of variation
Organic matter
Energy
Protein
0.804 0.784 0.808 0.826 0.014
0.771 0.766 0.789 0.797 0.013
0.736 0.751 0.766 0.769 0.015
0.34 0.07 0.39
0.85 0.13 0.70
0.49 0.38 0.94
Days post-weaning (day) 14 28
0.803 0.807
0.778 0.783
0.759 0.752
SEM (n24) p
0.010 0.87
0.009 0.76
0.011 0.41
Barley Raw Raw Micronized Expanded SEM (n12)
Screen (mm) 4.0 2.5 2.5 2.5
Signi®cance of contrastc
1 2 3
a
Expressed as a proportion. Interaction between treatment and time was not signi®cant (p>0.05). c 1 Ð 2.5 mm vs. 4.0 mm in raw barley; 2 Ð raw vs. processed barley; 3 Ð expanded vs. micronized barley. b
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p>0.15). Feed ef®ciency and incidence of scours as measured by proportion of animals that needed antibiotic treatment were not affected by diet. Neither particle size nor type of processing affected any of the performance traits studied. The OMD, ED and CPD of the diets are shown in Table 6. Processing of barley tended to increase OMD (0.817 vs. 0.784; p0.07) and ED (0.793 vs. 0.766; p0.13), but neither grinding size nor type of processing affected nutrient digestibility. Digestive ef®ciency was similar among treatments at 14 or 28 days (p>0.15), and no interactions between age and type of diet were detected for any trait. 4. Discussion Grinding size did not affect signi®cantly piglet performance or apparent digestibility of nutrients. Previous results with piglets are confusing due to the wide range of screen sizes used, the type of cereal tested and the differences in complexity of the experimental diets. Reducing particle size is generally expected to improve performance and FCR because the surface area of the ingredients available to the digestive enzymes is increased. At this respect, Wu and Fuller (1974) found a positive response in ADG and FCR for the ®rst week after weaning (28±35 days of age) when the screen size used for maize grinding was decreased from 9.5 to 1.6 mm. However, they did not ®nd any difference when comparing samples prepared with screen sizes of 4 and 1.6 mm. Healy et al. (1994) reported that reducing the particle size of maize from 900 to 300 mm improved ADG and FCR for the ®rst two weeks after weaning (22±36 days of age), but not thereafter. However, reducing the particle size of hard or soft sorghum to the same extent as for maize, did not affect performance for any of the periods studied. An excessive ®neness of the feed induces gastric ulceration and impairs AFI and ADG of pigs (Hedde et al., 1985; Hale and Thompson, 1986; Ayles et al., 1996). Partridge and Gill (1993) suggested that the negative effect of an excessive ®neness of particle size is especially important with wheat, due to the tendency of this cereal to become sticky and pasty in the buccal cavity because of its high gluten content. The problem might be of less importance for barley because particles of 0.2 mm did not affect the performance of growing pigs (Chu et al., 1998). Goodband and Hines (1988) working with barley diets, did not observe any difference in piglet performance from 0 to 14 days, but a positive response of 5% in ADG and in FCR was found from 0 to 35 days when the screen size was reduced from 4.8 to 3.2 mm. On the other hand, Gipp et al. (1995) failed to ®nd differences in performance of 7.5 kg piglets with screen sizes of 6.35, 4.76 or 3.18 mm. Similarly, we did not observe any improvement on performance or digestibility of nutrients due to a reduction of screen size from 4 to 2.5 mm. In the current experiment processing of barley caused a 13% improvement in growth in the ®rst 14 days of the experiment, which agrees with previous results in piglets (Aumaitre, 1976; Medel et al., 1999). However, no differences were detected between 14 and 28 days. Studies conducted with piglets fed barley diets show that processing caused an increase in nutrient digestibility (Chu et al., 1998; Huang et al., 1998). In the current study, processed barley diets showed a 4% higher total tract apparent OMD than the control diet at 14 and 28 days, although this improvement was not associated with better
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P. Medel et al. / Animal Feed Science and Technology 84 (2000) 13±21
performance. The observed improvement of digestibility due to processing agrees with previous data (Medel et al., 1999), and is slightly higher than the values reported by Aumaitre (1976). Expansion and micronization produced similar degrees of starch gelatinization, nutrient digestibility and piglet performance, results that agree with data presented by Vestergaard et al. (1990) and Medel et al. (1999). The digestibility of nutrients was similar when assessed at 14 and 28 days after weaning. Van der Poel et al. (1989) reported higher OMD and CPD in piglets of 7.2 kg than in piglets of 5.8 kg. In the current study, the digestibility of diets was determined with heavier pigs (8.8 and 15.6 kg) which might explain the lack of response with age. In conclusion, decreasing particle size of barley within the range tested (4.0 vs. 2.5 mm) had no signi®cant effect on total tract apparent digestibility or performance of piglets. Heat processing only improved performance in the ®rst 14 days after weaning and no differences between micronization and expansion were detected for any of the traits studied. Based on this experiment, heat processing of barley in diets for early-weaned piglets is recommended. Acknowledgements This research was supported by CICYT project AGF96-1142. Thanks are due to A. Sanz and G. Fructuoso for their help in the management of the animals and to Y. Alegre for typing the manuscript. References Ê man, P., Graham, H., 1987. Analysis of total and insoluble mixed-linked (1±3), (1±4)-û-D-glucans in barley A and oats. J. Agric. Food Chem. 35, 704±709. Aumaitre, A., 1976. EÂvaluation de divers traitements technologiques des ceÂreÂales. Ann. Zootech. 25, 41±51. Aumaitre, A., Peiniau, J., Madec, F., 1995. Digestive adaptation after weaning and nutritional consequences in the piglet. Pig News Inf. 16, 73N±79N. Ayles, H.L., Friendship, R.M., Ball, R.O., 1996. Effect of dietary particle size on gastric ulcers, assessed by endoscopic examination, and relationship between ulcer severity and growth performance of individually fed pigs. Swine Health Prod. 5, 211±216. Association of Of®cial Analytical Chemist, 1995. Of®cial Methods of Analysis, 16th Edition. AOAC, Washington, DC. Chu, K.S., Kim, J.H., Chae, B.J., Chung, Y.K., Han, I.K., 1998. Effects of processed barley on growth performance and ileal digestibility of growing pigs. Asian-Australasian J. Anim. Sci. 11, 249±254. FEDNA, 1999. Normas FEDNA para la formulacioÂn de piensos compuestos. de Blas, C., Mateos, G.G., Rebollar, P.G. (Eds.), FEDNA, Madrid, Spain, 496 pp. GarcõÂa, J., CarabanÄo, R., de Blas, J.C., 1999. Effect of ®ber source on cell wall digestibility and rate of passage in rabbits. J. Anim. Sci. 77, 898±905. Gipp, W.F., Clark, C.K., Bryan, K.S., 1995. In¯uence of barley ®neness of grind on starter, grower and ®nisher swine performance. J. Anim. Sci. 73 (Suppl. 1), 179. Goodband, R.D., Hines, R.H., 1988. An evaluation of barley in starter diets for swine. J. Anim. Sci. 66, 3086± 3093. Hale, O.M., Thompson, L.M., 1986. In¯uence of particle size of wheat on performance of ®nishing swine. Nutr. Rep. Int. 33, 307±311.
P. Medel et al. / Animal Feed Science and Technology 84 (2000) 13±21
21
Healy, B.J., Hancock, J.D., Kennedy, G.A., Bramel-Cox, P.J., Behnke, K.C., Hines, R.H., 1994. Optimum particle size of corn and hard and soft sorghum for nursery pigs. J. Anim. Sci. 72, 2227±2236. Hedde, R.D., Lindsey, T.O., Parish, R.C., Daniels, H.D., Morgenthien, E.A., Lewis, H.B., 1985. Effect of diet particle size and feeding of H2-receptor antagonists on gastric ulcers in swine. J. Anim. Sci. 61, 179±186. Hongtrakul, K., Goodband, R.D., Behnke, K.C., Nelssen, J.L., Tokach, M.D., BergstroÈm, J.R., Nessmith Jr., W.B., Kim, I.K., 1998. The effects of extrusion processing of carbohydrate sources on weanling pig performance. J. Anim. Sci. 76, 3034±3042. Huang, S.X., Sauer, W.C., Pickard, M., Li, S., Hardin, R.T., 1998. Effect of micronization on energy, starch and amino acid digestibility in hulless barley for young pigs. Can. J. Anim. Sci. 78, 81±87. Hutton, K, Armstrong D.G., 1976. Cereal processing. In: Swan, H., Lewis, D. (Eds.), Nutrition Conference for Feed Manufacturers. Butterworths, London, UK, pp. 47±63. Kim, I.H., Hancock, J.D., Hines, R.H., Rantanen, M.M., Burham, L.L., 1995. Effects of particle size (1000 and 500 mm in simple and complex diets for weanling pigs. J. Anim. Sci. 73 (Suppl. 1), 179. Lawrence, T.J.L., 1970. Some effects of including differently processed barley in the diet of the growing pig. Anim. Prod. 12, 139±150. Lawrence, T.J.L., 1978. Processing and preparation of cereals for pig diets. In: Haresign, W., Lewis, D. (Eds.), Recent Advances in Animal Nutrition. Butterworths, London, UK, pp. 83±98. Medel, P., Salado, S., Mateos, G.G., de Blas, C., 1999. Processed cereals in diets for early-weaned piglets. Anim. Feed Sci. Technol. 82, 145±156. Partridge, G.G., Gill, B.P., 1993. New approaches with pig weaner diets. In: Garnsworthy, P.C., Cole, D.J.A. (Eds.), Recent Advances in Animal Nutrition. Nottingham University Press, UK, pp. 221±248. Saini, H.S., Henry, R.J., 1989. Fractionation and evaluation of triticale pentosans. Comparison with wheat and rye. Cereal Chem. 66, 11±14. SAS, 1990. SAS1 User's Guide: Statistics. SAS Inst. Inc., Cary, NC. Theander, O., 1991. Chemical analysis of lignocellulose materials. Anim. Feed Sci. Technol. 32, 35±44. Van der Poel, A.F.B., Den Hartog, L.A., Van den Abeele, T.H., Boer, H., Van Zuilichem, D.J., 1989. Effect of infrared irradiation or extrusion processing of maize on its digestibility in piglets. Anim. Feed Sci. Technol. 26, 29±43. Vestergaard, E.M., Danielsen, V., Jacobsen, E.E., Rasmussen, V., 1990. Heat treated cereals for piglets. Beretning Fra Statens Husdyrbrugsforsog 674, 71. Wondra, K.J., Hancock, J.D., Behnke, K.C., Hines, R.H., Stark, C.R., 1995. Effects of particle size and pelleting on growth performance, nutrient digestibility, and stomach morphology in ®nishing pigs. J. Anim. Sci. 73, 757±763. Wu, J.F., Fuller, M.F., 1974. A note on the performance of young pigs given maize-based diets in different physical forms. Anim. Prod. 18, 317±320.