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ANIMAL NUTRITION |
Department of Animal Production, Universidad Politécnica de Madrid, Ciudad Universitaria, 28040 Madrid, Spain
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: heat processing • nutrient digestibility • pig performance • rice • starch gelatinization
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). In fact, Mathews et al. (1999) showed that components in boiled rice inhibit secretion of electrolytes in the small intestine, reducing the magnitude of secretory diarrhea. Also, Mateos et al. (2006) showed that the inclusion of broken rice in the diet in substitution of corn increases nutrient digestibility and ADG with little effect on G:F ratio.
Heat processing (HP) of cereals gelatinizes the starch portion of the grain, which may result in improved nutrient utilization. But the information available on the beneficial effects of HP on apparent total tract digestibility (ATTD) of dietary components and pig growth is contradictory. Medel et al. (2002, 2004) showed that HP of cereals improves ATTD of nutrients in young pigs, but Van der Poel et al. (1990) did not show any effects of HP on digestibility. Moreover, no effects of increased starch gelatinization (SG) resulting from HP were observed on ATTD of dietary components (Zarkadas and Wiseman, 2002). These discrepancies might be explained, at least in part, because the type of cereal used and the conditions applied during HP varied among experiments. An excess of heat increases SG but might also increase the proportion of resistant starch (RS), reducing its digestibility (Sagum and Arcot, 2000). The hypothesis tested in this study was that feeding rice-based diets improves digestibility and ADG as compared with feeding corn-based diets and that degree of HP of rice would not further improve any digestive or performance trait. The current study investigated the influence of the main cereal of the diet, HP of rice, and the degree of SG of rice on digestibility of dietary components and productive performance of young pigs.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Experimental procedures followed the principles for care of animals in experimentation (Boletín Oficial del Estado, 2005). One hundred sixty crossbred (Pietrain xLarge White) x(Large White xLandrace) pigs, barrows, and gilts at the same proportion, weaned at 25 ± 2 d of age and 6.5 ±0.5 kg of BW, were obtained from a commercial farm (Proinserga S.A., Segovia, Spain) and transported 95 km to the experimental facilities. Upon arrival, pigs were ear-tagged, weighed, and penned in groups of 5 according to treatment and BW. Pigs were housed in flat-deck pens (1.1 x1.1 m) provided with individual feeders (5 spaces) and nipple water drinkers and were allowed free access to feed and water throughout the trial. Room temperature was maintained at 32 ±1°C for the first week and was reduced by approximately 2°C per week until reaching 26°C. During the experiment, pigs that showed symptoms of diarrhea, as assessed by veterinarian inspection, were treated with Excenel (0.4 mL/10 kg of BW every 24 h; Pharmacia and Upjohn, Puurs, Belgium) until the diarrhea ceased.
Experimental Design, Diets, and Feeding Program
The experimental design was completely randomized, with 8 pens (replicates) with 5 pigs/pen for each treatment. A batch of broken rice (Japonica variety; 80% Senia and 20% Tainato cultivars Oryza sativa L.) was obtained from a commercial supplier (Esasa, Cabezón de Pisuerga, Valladolid, Spain), sieved, cleaned, and divided into 3 portions. The first portion was ground through a hammer mill with a 2.5-mm screen and used as such (degree of SG of 11%). The second portion was steam-cooked (Amandus Kahl, Reinbek, Germany) for 60 min (105 ± 3°C) to obtain a moderate degree of SG (52%) and cooled, dried, and milled through a hammer mill (2.5-mm screen) before being included in the diet. The third portion was steam-cooked for 90 min at a temperature of 120 ±3°C and flaked through riffled rolls. The degree of SG of this portion was 76%. Corn (Zea mays L.) was obtained from the same commercial supplier as the rice and was cooked for 60 min at 117 ± 3°C and treated as the third portion of rice. The degree of SG obtained for corn was 84%. The chemical analyses of the experimental cereals are shown in Table 1.
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). All of the diets were formulated according to the ingredient composition of the Fundación Española para el Desarrollo de la Nutrición Animal (2003) and met or exceeded the nutrient requirements recommended by the National Research Council (1998). Celite (acid-washed diatomaceous earth, Ceca, Saint-Bautizile, France) was added at 0.6% to all diets as an additional AIA source. No growth promoters were included in the diets.
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Individual pig BW were recorded on d 25 (beginning of the experiment) and on d 39 and 53. Feed was supplied ad libitum, and feed intake was recorded by pen. From these data ADFI, ADG, and G:F were calculated by period and for the entire experiment. Diarrhea incidence (DI) was estimated by pen as the number of days in which pigs showed clinical signs of diarrhea symptoms as a proportion of total number of days on trial. At 29, 39, and 53 d of age, representative fecal samples (300 g) were collected by rectal massage from at least 4 pigs from each pen, pooled by pen, frozen (–20°C), and stored. Before analysis, fecal samples were thawed overnight, homogenized, dried (60°C for 72 h), and ground (1-mm screen). Ingredients, feeds, and feces were analyzed for moisture by the oven-drying method (930.15), ash by muffle furnace (942.05), and ether extract by Soxhlet fat analysis (920.39) as described by the AOAC (2000). Crude protein was determined with a Leco FP-528 N analyzer (Leco Corp., St. Joseph, MI), and the GE was determined with an adiabatic bomb calorimeter (Parr 1356, Parr Instrument Co., Moline, IL). Acid insoluble ash of feeds and feces was determined by the method described by Vogtmann et al. (1975).
Starch content was measured in cereals and feeds according to the method of Karkalas (1985) with some modifications. Briefly, 150 mg per sample was weighed, divided into 3 fractions (replicates A, B, and C), and introduced into screw-cap culture tubes (25 x150 mm). The contents of each of the 3 replicates were mixed with 9 mL of 0.2 M sodium acetate (buffer A, pH 4.5), and 50 µL of heat-stable 
-amylase (Termamyl, Sigma Chemical Co., St. Louis, MO) was added to the B and C replicate tubes exclusively and softly mixed. Replicate A was used as a reagent blank. The tubes were tightly capped and maintained in a silicone bath at 103°C for 30 min to solubilize all the starch and sugars. Subsequently, tubes were removed from the silicon bath and cooled in an 18°C water bath (Tecator 1024 shaking water bath, Mount Holly, NJ) for 1 min. Excess surface water was eliminated, and the tube caps were carefully removed. Contents of tubes B and C were treated with 1 mL of amyloglucosidase buffer A solution (Boehringer Mannheim, Baden-Württemberg, Germany), and 1 mL of additional buffer A was added to tube A. The 3 replicates were incubated in a water bath (55°C, 2 h), cooled, and dried as described before, and the content of each tube was filtered. The solution obtained was used to determine glucose content by the glucose hexokinase assay NADPH reduction method (Boehringer Mannheim). Absorbance was measured at 340 nm, and total starch was calculated as determined glucose x0.9. The gelatinized starch was determined by enzymatic hydrolysis as described by Medel et al. (1999), and the RS was determined by using the Megazyme assay kit (Megazyme International Ireland Ltd., Wicklow, Ireland). The results were expressed as a proportion of total starch.
The particle size distribution (data not shown) and the mean particle size (MPS) of the experimental cereals and diets (Tables 1
and 3, respectively) were determined by the method proposed by the American Society of Agricultural Engineers (1995) using a filtra 200 (Filtra, S.A., Barcelona, Spain) provided with 5 sieves, ranging from 160 to 1,250 µm.
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Data were analyzed as a completely randomized design with type of diet as main effect using the GLM procedure (SAS Inst. Inc., Cary, NC). Orthogonal contrasts were performed to test differences between 1) cooked and flaked corn diet and the mean of the 3 rice-containing diets, 2) raw rice diet and the mean of the 2 HP rice diets, and 3) cooked rice diet and cooked and flaked rice diet. The experimental unit was the pen. Performance parameters were adjusted by including initial live BW as a covariate in the model. Data on DI were arcsin-transformed to normalize the variance. For digestibility data, age was considered as a repeated measure, because the same pigs were used at the 3 ages. The model included age as well as the interaction between diet and the linear and the quadratic effects of age. The MIXED procedure of SAS was used. The interaction between diet and the quadratic effect of age was not significant for any of the digestibility traits studied and was therefore not presented.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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The analyzed chemical composition of cereals and diets did not differ from expected values (Tables 1 and 3, respectively). Starch gelatinization of the cooked and flaked corn as a proportion of total starch was 84%. The SG of rice increased with HP from 11% for raw rice to 52% for cooked rice and 76% for cooked and flaked rice. Resistant starch content was greater for cooked corn than for cooked rice (2.21 vs. 1.70%). Heat processing of rice under moderate conditions decreased RS content from 1.83 to 1.45%. However, an increase in the severity of the process to increase degree of SG from 52 to 76% increased RS content to 1.95% (cooked-flaked rice). The MPS ranged from 405 µm for the cooked and flaked rice to 533 µm for the cooked and flaked corn. The MPS was greater for the corn- than for the rice-based diets (560 vs. 479 µm) and decreased with HP of the rice (510 vs. 499 vs. 428 µm for the raw, cooked, and cooked and rolled rice, respectively).
Digestibility Data
The ATTD of all dietary components (P <0.01) increased with age (Table 4). The substitution of corn by rice resulted in a marked improvement in ATTD of all dietary components (P <0.01) except for CP. Heat processing of rice improved ATTD of dietary components at d 29, but no beneficial effects were observed at d 39 or 53 of age. Increasing the degree of processing of rice by cooking and flaking reduced ATTD of GE (P< 0.05) and tended to decrease ATTD of DM and CP (P <0.10) at 29 d of age, but no effects were observed after this age.
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Performance Data
From d 25 to 39 of age, pigs fed rice had greater ADFI (481 vs. 391 g; P <0.01) and ADG (357 vs. 277 g; P <0.01) and tended to have greater G:F (0.746 vs. 0.704 g/g; P <0.10) than pigs fed HP corn (Table 5). From d 39 to 53 of age, no differences were observed for ADFI for rice and corn diets, but pigs fed rice grew faster (576 and tended to have greater G:F (0.654 vs. 0.629 g/g; P <0.10) than pigs fed corn. For the overall experiment, pigs fed rice consumed more feed (678 vs. 618 g; P <0.01), grew faster (466 vs. 407 g; P <0.01), and tended to have greater G:F (0.685 vs. 0.662 g/g; P <0.10) than pigs fed corn. No differences in productive traits due to HP of rice or degree of SG of rice were observed.
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). Heat processing of rice and degree of SG of rice did not affect DI. The only difference observed was from 39 to 53 d of age, in which pigs fed rice with a degree of SG of 76% had greater DI than pigs fed rice with a degree of SG of 52% (5.1 vs. 0.6%; P <0.05). |
DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Kim et al., 2005). Rice feeding also increased ATTD of all dietary components, an observation that is in agreement with previous research (Piao et al., 2002; Li et al., 2006; Mateos et al., 2006). The difference in nutrient digestibility between rice and corn might be related to differences in the composition of the 2 grains. Rice grain is characterized by its high starch content and low level of nonstarch polysaccharide (Choct, 2002). Also, starch encapsulation is lower for rice than for corn (Slaughter et al., 2001; Svihus et al., 2005), and rice has smaller size of starch granules (3 to 8 vs. 2 to 30 µm; Tester et al., 2004), lower amylose content (5 to 12 vs. 10 to 20%), and less lipid-amylose complexes (0.1 vs. 0.9 to 1.3%; Vandeputte and Delcour, 2004) than corn. Therefore, rice starch is expected to be more available to enzyme action than cornstarch.
Heat processing of rice increased SG and ATTD of dietary components at 29 d of age, but no differences were detected after this age. Studies have related the improvements observed in ATTD of starch and other dietary components in pigs fed HP cereals to increases in the degree of SG (Mercier and Feillet, 1975; Piao et al., 1999). In the current experiment, an increase in SG from 11% (raw rice) to 52% (cooked rice) resulted in an increase in nutrient utilization. However, when more severe HP conditions were applied to increase the degree of SG from 52 to 76%, no further improvements in digestibility of nutrients were observed. Our results are in agreement with Hongtrakul et al. (1998) that did not find any clear effect of HP of and degree of SG of rice and corn on pig performance. Similarly, no influence of degree of SG on productive performance of piglet has been reported with corn and barley diets (Medel et al., 1999), wheat and corn diets (Lawlor et al., 2003), and with rice diets (Mateos et al., 2007).
Corn is less digestible than rice, and therefore cooking of the cereal might be more beneficial for corn than for rice. In fact, it has been shown that an excess of heat increased the formation of RS or damaged starch in rice compared with corn during gelatinization (Eggum et al., 1993; Vasanthan and Bhatthy, 1998; Haralampu, 2000). An increase in RS hinders the accessibility of -amylase to nutrients (Englyst and Cummings, 1992), reducing its digestibility. On the other hand, HP of rice under mild conditions might improve utilization of rice, because under these circumstances, no formation of RS or Maillard reaction occurs. In the current study, moderate HP of rice increased SG from 11 to 52% and decreased the RS content slightly (from 1.83 vs. 1.45%), whereas severe HP of rice increased SG from 52 to 76% but also RS content from 1.45 to 1.95%. De Schrijver et al. (1999) demonstrated in rats that an increase in RS reduced ileal starch digestibility and increased the proliferation of colonic microorganisms. Also, Asp (1986) and Hakansson et al. (1987) showed that excess heat increased the formation of complex Maillard-type reactions between reduced sugars and amino groups reducing the availability of dietary protein. Therefore, severe HP of rice might be detrimental to nutrient digestibility and pig growth.
Rice feeding increased ADFI and ADG and tended to improve G:F of pigs. These results agree with previous research (Mateos et al., 2007). The reasons for the beneficial effects of rice on pig growth are not well understood. The increase in ADFI might be explained, in part, by the increased glycemic response observed in pigs fed rice (Vicente et al., 2006). Cereals that elicit relatively high glucose and insulin responses postprandially may lead to increased hunger, feed intake, and BW gain. In fact, Appleton et al. (2004) observed that cats fed a rice diet ad libitum consumed more energy and gained more BW than cats fed a corn- or a sorghum-based diet.
In the current experiment, HP of rice did not affect pig performance. Li et al. (2004) observed that extrusion of brown rice did not affect ADG of pigs and, in fact, decreased G:F (an effect that was attributed to the reduction in essential AA concentration observed). Medel et al. (2004) showed that pig growth was improved with HP of barley but not with HP of corn, suggesting that the response to HP depends on the cereal tested.
The incidence of diarrhea was greater for pigs fed rice than for pigs fed corn. However, the greater DI observed in pigs fed rice did not cause any detrimental effect on performance, probably because the treatments affected otherwise healthy pigs. In fact, the diarrhea ceased easily after antibiotic treatment, and no mortality was recorded during the trial. Our findings disagree with Pluske et al. (1996, 1998), who observed a lower incidence of diarrhea in pigs infected experimentally with Serpulina hyodysenteriae when they were fed rice-vs. wheat-based diets. Accordingly, it has been demonstrated that components in boiled rice inhibit the secretion of electrolytes in the small intestine and hence reduce the magnitude of secretory diarrhea due to infection by pathogens such as Escherichia coli (MacLeod et al., 1995; Mathews et al., 1999). The reasons for the discrepancy on the effects of rice feeding on DI are not known, but in the present experiment, pigs were not experimentally infected and were selected from a farm free of major diseases including hemolytic E. coli, S. hyodysenteriae, and other enteric pathogens. Therefore, no beneficial effects of rice feeding should be expected because of improved control of these diseases. Pigs fed rice consumed 23% more feed than pigs fed corn, and therefore more dietary nutrients were available in large intestine for bacterial growth. Hampson (1987) reported that pigs eating less feed after weaning were less likely to develop postweaning colibacillosis than pigs that consumed more feed. Also, in our experiment, the diets based on rice had smaller MPS than the diet based on corn, and a reduction in MPS increases the incidence of enteric disease. In the current study, the crude fiber content of the rice diets was 1.37%, an amount that might be below requirements for healthy development of the gastrointestinal tract of pigs (Hedemann et al., 2006; Mateos et al., 2007). The low dietary fiber content and the small MPS of the rice diets coupled with the greater feed intake observed in pigs fed rice might have increased the amount of nutrients that escaped digestion in the small intestine and reached the large intestine, predisposing pigs to diarrhea (Pluske and Hampson, 2005). Mateos et al. (2006) observed that the inclusion of moderate levels of oat hulls in diets based on rice low in fiber tended to reduce the incidence of diarrhea and improve productive performance of pigs.
From 39 to 53 d of age, pigs fed the diet based on rice with 76% of SG had greater DI than pigs fed the diet based on rice with 52% of SG (5.1 vs. 0.6%; P <0.05). The smaller MPS of the diet based on rice with 76% of SG together with the lower ATTD observed for this diet might be responsible, in part, for the increase in DI observed.
In conclusion, feeding rice instead of corn increased nutrient digestibility and pig growth. The application of a moderate amount of heat to rice improves nutrient utilization but had little effect on performance traits. A further increase in the severity of HP to increase the degree of SG to levels required by the industry for cooked wheat and corn does not further improve performance and may compromise digestibility of certain nutrients of rice at early ages.
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Footnotes |
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2 We thank J. R. Astillero, A. Caídas, and M. S. Gomez-Conde (Department of Animal Science, UP Madrid) for their assistance and expertise and to Esasa (Valladolid, Spain) for supplying the ingredients used in the experiment.
3 Corresponding author: gonzalo.gmateos{at}upm.es
Received for publication October 19, 2006. Accepted for publication September 10, 2007.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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-amylase on native and gelatinised starches. Biochem. Biophys. Acta 1525:29–36.[Medline]This article has been cited by other articles:
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