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Supplementation of carbohydrases or phytase individually or in combination to diets for weanling and growing-finishing pigs¹

O. A. Olukosi^*, J. S. Sands and O. Adeola^*,2

^* Department of Animal Sciences, Purdue University, West Lafayette, IN 47907-2054; and Danisco Animal Nutrition, Marlborough, Wiltshire, SN8 1XN, UK

	Abstract

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The overall objective of the studies reported here was to evaluate the growth and nutrient utilization responses of pigs to dietary supplementation of phytate- or nonstarch polysaccharide-degrading enzymes. In Exp. 1, growth performance and nutrient digestibility responses of forty-eight 10-kg pigs to dietary supplementation of phytase or a cocktail of xylanase, amylase, and protease (XAP) alone or in combination were evaluated. The growth response of one hundred fifty 23-kg pigs to dietary supplementation of phytase or xylanase individually or in combination was studied in Exp. 2 in a 6-wk growth trial, whereas Exp. 3 investigated the nutrient digestibility and nutrient retention responses of thirty 24-kg pigs to dietary supplementation of the same enzymes used in Exp. 2. In Exp. 1, the pigs were used in a 28-d feeding trial. They were blocked by BW and sex and allocated to 6 dietary treatments. The treatments were a positive control (PC) diet; a negative control (NC) diet marginally deficient in P and DE; NC with phytase added at 500 or 1,000 phytase units (FTU)/kg; NC with xylanase at 2,500 units (U)/kg, amylase at 400 U/kg, and protease at 4,000 U/kg; and NC with a combination of phytase added at 500 FTU/kg and XAP as above. In Exp. 2 and 3, the 5 dietary treatments were positive control (PC), negative control (NC), NC plus 500 FTU of phytase/kg, NC plus 4,000 U of xylanase/kg, and NC plus phytase and xylanase. In Exp. 1, low levels of nonphytate P and DE in the NC diet depressed (P < 0.05) ADG of the pigs by 16%, but phytase linearly increased (P < 0.05) ADG by up to 24% compared with NC. The cocktail of XAP alone had no effect on ADG of pigs, but the combination of XAP and phytase increased (P < 0.05) ADG by 17% compared with the NC treatment. There was a linear increase (P < 0.01) in Ca and P digestibility in response to phytase. In Exp. 2, ADG was 7% greater in PC than NC (P < 0.05); there were no effects of enzyme addition on any response. In Exp. 3, addition of phytase alone or in combination with xylanase improved (P < 0.05) P digestibility. Phosphorus excretion was greatest (P < 0.01) in the PC and lowest (P < 0.05) in the diet with the combination of phytase and xylanase. The combination of phytase and xylanase improved P retention (P < 0.01) above the NC diet to a level similar to the PC diet. In conclusion, a combination of phytase and carbohydrases improved ADG in 10-kg but not 23-kg pigs, but was efficient in improving P digestibility in pigs of all ages.

Key Words: carbohydrase • digestibility • growth • phytase • pig • retention

	INTRODUCTION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Phytic acid and soluble nonstarch polysaccharides (NSP) are some important antinutritive components in plant-based feedstuffs. Low-glucosinolate rapeseed (canola) has high protein but also resistant phytate (Aumaitre et al., 1989, Newkirk and Classen, 1998). Wheat middlings have intrinsic phytase activity (Han et al., 1997); however, wheat contains up to 6.5% pentosans (Wootton et al., 1995), which may increase digesta viscosity and reduce animal growth (Vinkx and Delcour, 1996). Phytase supplementation of P-deficient diets resulted in improved growth performance of pigs (Nasi, 1990; Cromwell et al., 1993; Han et al., 1997) and improved P and Ca utilization (Nasi, 1990; Adeola, 1995). Adding carbohydrases to a wheat-based diet fed to young pigs resulted in improved ADG and ADFI (Cadogan et al., 2003), increased total tract digestibility of DM and N (Mavromichalis et al., 2000), and improved energy digestibility in wheat-soybean meal (SBM) diet (Li et al., 1996). Feedstuffs are heterogeneous in composition; hence to derive maximum benefits from enzyme supplementation, the use of cocktail of enzymes with different activities that target the different chemical components might be more beneficial than using an enzyme with a single activity.

Therefore, the specific objectives of these experiments were to evaluate the efficacy of dietary supplementation of a cocktail of xylanase, amylase, and protease (XAP) or phytase used individually or in combination in diets marginally deficient in DE and P on the growth performance and apparent digestibility of nutrient in 10-kg pigs fed corn-SBM based diets; and efficacy of supplementation of phytase or xylanase used alone or combined on growth performance, nutrient digestibility, and nutrient and energy retention of growing-finishing pigs fed wheat-SBM diets.

	MATERIALS AND METHODS

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All animal experimentation procedures were approved by the Purdue Animal Care and Use Committee. All the pigs used in the 3 experiments were obtained from Purdue University Swine Research Unit.

Experiment 1

Forty-eight (24 barrows and 24 gilts) 10-kg crossbred (Hampshire x Duroc x Yorkshire x Landrace) pigs were used for the 28-d feeding and growth trials. The pigs were blocked by BW and sex and allocated to dietary treatments in a randomized complete block design. Each treatment had 8 replicates, with 4 replicates per sex. The pigs were in individual stainless-steel pens (0.76 x 0.89 m) equipped with water nozzles, stainless steel feeders, and plastic-coated, expanded metal floors, as described by Adeola et al. (1995). The pens were located in an environmentally controlled building maintained at 23 ± 2°C with a 12-h light (0700 to 1900):12-h dark cycle. Feed and water were provided for ad libitum. Growth performance data were collected weekly, and fecal collection was done in the last 3 d of wk 2 and 4 of the study to enable comparison of the effect of the phytase and XAP on digestibility at these 2 periods. Defecation was induced by rectal palpation, and the feces collected were immediately stored frozen at –20°C until analysis.

The treatments were (1) positive control (PC) diet, which met or exceeded the NRC (1998) requirements for DE and P; (2) negative control (NC) diet, which met 97% of the DE and 90% of the P requirements; (3) NC + phytase (Phyzyme XP phytase, Danisco Animal Nutrition, Marlborough, UK) added at 500 phytase units per kg of feed (as-fed basis); (4) NC + phytase added at 1,000 FTU/kg; (5) NC + a cocktail of XAP (Avizyme 1500, Danisco Animal Nutrition) added at 0.5 g/kg, which supplied, per kg of diet (as-fed basis), 2,500 units (U) of xylanase, 400 U of amylase, and 4,000 U of protease; and (6) NC + phytase added at 500 FTU/kg and XAP added at the rate indicated for treatment 5. One phytase unit (FTU) was defined as the quantity of enzyme required to liberate 1 µmol of inorganic P/min, at pH 5.5, from an excess of 15 µM sodium phytate at 37°C. One unit of xylanase was defined as the quantity of the enzyme that liberated 1 µmol of xylose equivalent per min; 1 U of amylase was defined as the amount of the enzyme catalyzing the hydrolysis of 1 µmol of glucosidic linkage per minute; and 1 protease U was defined as the quantity of the enzyme that solubilized 1 µg of azocasein per minute. Chromic oxide was added as an indigestible marker to enable determination of digestibility by the index method. The diets were fed as mash; the ingredient compositions of the experimental control diets used in all the experiments are shown in Table 1.

One hundred fifty 23-kg pigs (75 barrows and 75 gilts) of the same breed used in Exp. 1 were used for the 42-d growth trial. The pigs were blocked by BW and sex and allocated to 5 dietary treatments, such that the average BW of the pigs was similar across treatments. There were 6 replicate pens per diet, with 5 pigs per replicate pen. The diets (Table 1) were wheat-SBM-based, with wheat middlings and canola meal serving as additional sources of NSP. The dietary treatments were 1) PC diet, which met or exceeded NRC (1998) requirements for DE and P; 2) NC diet that met 97% of the DE and 83% of the P requirements; 3) NC + phytase added at 500 FTU/kg of diet (as-fed basis); 4) NC + xylanase added at 4,000 U/kg of feed (as-fed basis); and 5) NC + phytase added at 500 FTU/kg and xylanase added at 4,000 U/kg. The pigs were fed the diets as mash for 42 d; data on ADG and ADFI were taken every 2 wk.

Experiment 3

Thirty 24-kg barrows of the same breed as used in Exp. 1 were used for nutrient digestibility and retention trial. The barrows were allocated to the same 5 dietary treatments used in Exp. 2, and initial BW was approximately equal in all the treatments. The barrows were housed in stainless-steel metabolism crates measuring 0.83 x 0.71 m that allowed for total but separate collection of feces and urine following the procedure of Adeola and Bajjalieh (1997). Briefly, after the barrows were put in the crates, they were fasted for 24 h but given free access to water. They were then fed the experimental diets on d 2 of the adjustment period of the experiment. The barrows were fed to a total maximum feed allotment of 5% of their BW. The feed allotment was reduced if necessary according to the ADFI of the pigs, but the daily feed allotment was never reduced below 3% of the BW; this ensured that feed wastage was kept to a minimum during the trial. The 5-d adjustment period to the experimental diets and crates was followed by 5 d of feeding the experimental diets. Pigs had ad libitum access to water and were fed 2 equal amounts of feed daily at 0600 and 1600 in mash form. To minimize ammonia loss from urine, 10 mL of 30% formaldehyde solution was added to the bucket for urine collection every morning. Feed leftovers were collected each day to determine ADFI.

Chemical Analyses

Dried fecal, orts, and feed samples were ground to pass through 0.5-mm screen using a mill grinder (Retsch ZM 100, Retsch GmbH, Haan, Germany). Urine samples were thawed and thoroughly mixed, after which 2 subsamples of 800 mL each were filtered 3 times using glass wool and then dried in forced-air oven; the dried urine was stored at –20°C before analysis. For DM determination, samples were dried at 100°C in a drying oven (Precision Scientific Co., Chicago, IL) for 24 h. Gross energy was determined with a bomb calorimeter (Parr 1261 bomb calorimeter, Parr Instruments Co., Moline, IL) using benzoic acid as the calibration standard. Nitrogen was determined by the combustion method (Leco FP analyzer Model 602600, Leco Corp., St. Joseph, MI) using EDTA as the calibration standard. Samples were digested in concentrated nitric acid and 70% perchloric acid to solubilize Ca and P. The concentration of P in the supernatant was measured using a kit (kit #670, Sigma Diagnostics Inc., St. Louis, MO) as described by Onyango et al. (2004). The Ca content of the supernatant was determined using flame atomic absorption spectrometry (FS 240 AA, Varian Inc., Palo Alto, CA).

Calculations

Apparent total tract digestibility (AND) was calculated using the formula

where AND is expressed as a percentage, N_out is the nutrient output, and N_int is the nutrient intake. Daily nutrient retention was calculated, keeping in mind that the experimental diets were fed for 5 d, using the relation

where N_ret is the nutrient retention per day, N_fec is the nutrient voided in feces, N_uri is the nutrient voided in the urine, and

where N_conc is the concentration of the nutrient in the diets.

Statistical Analysis

Data on growth performance (in Exp. 1 and 2), nutrient digestibility (in Exp. 1 and 3), and retention (in Exp. 3) were analyzed using the GLM procedure (SAS Inst. Inc., Cary, NC). In Exp. 1, in which digestibility data were collected at 2 periods (wk 2 and 4) of the study, the effects of the period and dietary treatments on nutrient digestibility were examined. Because there were no period x diet interactions, the interaction term was removed, and the data were reanalyzed. The main effect means of period and diets were presented. Means were separated using orthogonal polynomial contrasts to examine linear or quadratic effects of phytase. Specific orthogonal contrasts were also used to compare PC or enzyme supplementation with the NC. Differences were regarded as significant at P < 0.05.

	RESULTS

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Experiment 1

Growth performance of pigs receiving phytase or XAP individually or in combination in Exp. 1 is shown in Table 2. Pigs on PC diet gained 19% more (P < 0.05) than those on the NC diet, whereas ADG was linearly improved by 24% with phytase supplementation (P < 0.05). Feed intake and G:F were not affected by any dietary treatment. Whereas XAP alone did not affect any of the growth performance response, the combination of phytase at 500 FTU/kg and XAP improved (P < 0.05) ADG by 20% compared with pigs on the NC diet.

The diets used for Exp. 2 and 3 were analyzed for phytase and xylanase activity, the control diets had 601 FTU/kg and 112 U/kg of phytase and xylanase activities, respectively. The diet with supplemental phytase had analyzed activity of 1,226 FTU/kg; the diet with xylanase had analyzed activity of 2,505 U/kg, whereas the diet with combination of phytase and xylanase had 968 FTU/kg and 2,363 U/kg of phytase and xylanase activities, respectively. The result showed that there was considerable background phytase activity in the diets; however, xylanase activity was lower than the intended activity of 4,000 U/kg.

Table 4 shows the result of growth performance of 23-kg pigs receiving xylanase or phytase individually or in combination. Average daily gain was 6% lower (P < 0.05) in NC compared with PC treatment. There were no effects of phytase or xylanase individually or in combination on any of the growth performance responses. The pigs that received the PC diet were 2.3 kg heavier than those that received the NC diet at the end of 6 wk of the study. There were no effect of any of the treatments on ADFI and G:F.

Table 5 shows the apparent total tract digestibility of nutrients in 24-kg pigs receiving wheat-SBM diet. The dietary treatments had no effects on N and energy digestibility. Phosphorus digestibility was improved (P < 0.05) above the NC diet by the use of phytase alone or in combination with xylanase. Calcium digestibility was lower (P < 0.05) in PC compared with NC, but there were no effects of any of the enzymes on Ca digestibility. Digestible energy content of the diets was greater (P < 0.01) in PC compared with NC diet, but DE was not affected by phytase or xylanase individually or in combination.

	DISCUSSION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

One possibility for differences observed in Exp. 1 and 2 of the current study with regard to the effect of carbohydrases on performance of pigs could be the difference in the enzymes used. In Exp. 1, the enzyme used had xylanase, amylase, and protease activities, whereas the enzyme used in Exp. 2 only had xylanase activity. The combined activities of xylanase, amylase, and protease likely had greater effect on improving the nutritive value of the diets than xylanase activity alone. For example, in a poult study, yla et al. (1996) found that to obtain complete dephosphorylation (removal of phosphate groups from phytic acid in this instance) of corn-SBM diet, it was necessary to use an enzyme cocktail rather than an enzyme that had only 1 activity. An enzyme cocktail that contained phytase, pectinase, acid phosphatase, and protease activities was more effective than phytase alone at promoting the performance of the turkey poults.

Another possibility for the differences observed in response to the enzymes used in Exp. 1 and 2 could be due to differences in feedstuffs fed. In Exp. 1, the diets were corn-based with wheat middlings and canola meal making up 220 g/kg of the diet. In Exp. 2, the diets were wheat-based; wheat, wheat middlings, and canola meal made up 871 g/kg of the diets. There were no analyses for level of xylans in the diets used in the current experiments, but based on book values for xylose contents of wheat, wheat-middlings, and canola meal (Knudsen, 1997), the NC diets in Exp. 1 and 2 had 3.81 and 9.80 g of xylose per kg of diet (as-fed basis), respectively; hence it was expected that the effect of xylanase would have been more apparent in Exp. 2 than in Exp. 1. Dornez et al. (2006) pointed out the implication in animal feeding of the presence of endoxylanase in the outer layer of wheat because it may be responsible for part of the degradation of arabinoxylans observed during digestion. It is noted in Exp. 3 that digestibility was high in NC and was similar to digestibility observed in PC for DM and energy. It is likely that the intrinsic endoxylanase activity of wheat (Cleemput et al., 1997) is responsible for this high digestibility, making it less likely to observe a response to supplemented xylanase.

The difference in the effect of the combination of carbohydrases and phytase on growth performance of pigs in Exp. 1 and 2 of the current study might also be age related. The pigs used were 10- and 23-kg in Exp. 1 and 2, respectively. Graham et al. (1988) observed that 20-kg pigs responded more to ß-glucanase supplementation than finishing pigs weighing 60 to 95 kg. Older pigs may respond less to supplementation of NSP-degrading enzymes than younger pigs due to increased population and activity of microbes that are able to break down the NSP portion of the feed, especially in the terminal portion of the gastrointestinal tract of older pigs. Lending support to this view is the observation by Castillo et al. (2006), who did not detect xylanase activity in early weaned pigs receiving plant extract in their diet. In contrast, Inborr et al. (1999) reported 6 and 20 U/g of DM of xylanase activity in the stomach and ileum, respectively, of 38-kg pigs (1 unit was defined as the amount of enzyme needed to release 1 µmol of xylose in 1 min); the xylanase activity was suggested to be due to microbial activity in response to a previous meal of wheat bran.

Diebold et al. (2004) reported that the effects of xylanase on ileal and total tract nutrient and energy digestibility became less apparent as the pigs they used matured. Jensen et al. (1997) noted that the activities of trypsin, chymotrypsin, and amylase at 28 d were less than one-half of the activities at 56 d. Furthermore, Graham et al. (1986) and Lindemann et al. (1986) noted that older pigs have a more mature gastrointestinal tract with a microbial population quite different from that of younger pigs and hence are able to utilize cereal components better than younger pigs. Li et al. (1996) observed effect of age of pigs on the response of pigs to supplementation of ß-glucanase to a hull-less barley-based diet. Graham et al. (1988) also noted the effect of age on the efficacy of ß-glucanase because the same enzyme did not show improvement in nutrient digestibility in 40-kg pigs. These observations indicate the possibilities that nutrient availability from the feed-stuffs is low or that the pigs at the age used in this study were able to derive enough DE, Ca, and P, which were the limiting nutrients, from their diets even without the use of the phytase or XAP.

In Exp. 1, N, Ca, and P digestibility was greater in pigs at wk 4 than wk 2 of the study. Digestibility was about 7 percentage points greater in wk 4 than wk 2 for Ca and P, and about 3 percentage points greater for N. The observation of greater digestibility in wk 4 may indicate that the older pigs were able to obtain more nutrients from their diets without the aid of the enzymes. This may also indicate that the enzymes were more beneficial to the animals at younger age than when they were older.

In Exp. 1, supplemental phytase produced improvement in growth performance of the 10-kg pigs. Several studies have shown improvement in growth performance of pigs after the use of phytase (Nasi, 1990; Cromwell et al., 1993; Adeola et al., 1998). On the other hand, in Exp. 2 where phytase was added at the rate of 500 FTU/kg, there were no effects of the enzyme on growth performance of the 23-kg pigs. The diets used in the 2 studies were both formulated to be marginally deficient in total and nonphytate P so that the response to phytase should have been apparent. The differences in response to phytase could also be due to diet or age differences or a combination of these 2 factors. Three possible sources of phytase to animals during digestion are the enzyme from feedstuffs, from microbial population within the intestinal tract, and possible presence of intestinal phytase. The wheat-based diet used in Exp. 2 may have had high intrinsic phytase activity as the result of analysis for phytase activity in the control diets show, and as has been observed by others (Han et al., 1997; Godoy et al., 2005). The high background phytase activity in the wheat and wheat middlings used in the diets fed in Exp. 2 may have reduced the effect of added phytase. In fact, P digestibility in NC in Exp. 3 was almost twice the digestibility in Exp. 1, which may be indicative of high intrinsic phytase activity in wheat and wheat middlings used in the diet.

Intestinal phytase is implicated in intrinsic phytate hydrolysis ability of monogastric animals including man, chickens, and rats (Bitar and Reinhold, 1972). Although the level of the enzyme in pigs is much lower than for rats or chickens, there is evidence that it is present nonetheless (Hu et al., 1996; Schlemmer et al., 2001). The pigs used in Exp. 2 and 3 being older than those used in Experiment 1 probably had higher capacity for phytate hydrolysis. Adeola and King (2006) observed an increase in total jejunal alkaline phosphatase as pigs grew older. Alkaline phosphatase is different from phytase in some respects; however, Williams et al. (1985) suggested that intestinal alkaline phosphatase has hydrolytic actions against phytate and therefore an increase in alkaline phosphatase activity may suggest an increase in capacity for phytate hydrolysis.

Starch and other nutrients in cereals are located in the endosperm and the aleurone layer. During feed processing, the endosperm is broken and hence is exposed to the hydrolysis action of digestive enzymes. However, the aleurone layer has a resistant cell wall layer and is usually not affected by milling action during feed processing. The intact cell wall will reduce the contact between the digestive enzymes and their substrates, and consequently, the aleurone layer more or less shields nutrients and other minerals from the action of digestive enzymes. Graham et al. (1988), using an enzyme preparation that could degrade ß-glucan and arabinoxylan portions of wheat pollard and barley, reported improvement in digestibility of all nutrients in 20-kg pigs and concluded that the enzymes could make it possible to use greater proportion of these feedstuffs in feeding pigs. The authors observed that the enzyme preparation increased the breakdown of NSP in the terminal ileum of the pigs, thus improving digestibility; the increased solubility contributed to improved performance. Improved digestion observed when xylanase is used could be due to the release of nutrients from the endosperm after cell wall removal. Omogbenigun et al. (2004) showed that ileal nutrient digestibility of NSP was greater when enzymes containing cellulase, galactanase, mannanase, and pectinase activities were used in a diet compared with diets that did not have all the 4 enzyme activities.

Diebold et al. (2004) reported that xylanase supplementation of a wheat-based diet fed to weanling pigs did not have any effect on total tract nutrient digestibility. In the current studies, neither xylanase nor XAP improved N digestibility. However, XAP improved total tract P digestibility in 10-kg pigs, whereas xylanase did not produce similar effect in 23-kg pigs. The mechanism by which NSP-degrading enzymes may improve P digestibility is different from the mode of action of phytase. Simon (1998) suggested that the modes of action possibly include partial hydrolysis of soluble and insoluble NSP, decrease in digesta viscosity, and rupturing of NSP-containing cell wall, which will make the contents available for digestion. Frølich (1990) pointed out that in wheat, the aleurone layer encloses phytic acid and soluble NSP reducing contact between the substrates and digestive enzymes. Parkkonen et al. (1997) using in-vitro digestion technique reported that xylanase increased the permeability of the aleurone cell wall layer, which is the site of phytic acid storage. It is possible that XAP by improving aleurone layer permeability enhances the access of phytase to phytic acid, hence improving P digestibility and retention. Hence glycosidases that are able to break down the NSP fraction can facilitate the contact between phytase and phytate. Additionally, some soluble fiber-bound P may be released in the presence of glycosidases, and this may explain how XAP alone is able to increase P digestibility.

In conclusion, combination of xylanase, amylase, protease, and phytase improved performance of 10-kg pigs, whereas combination of xylanase and phytase did not produce this effect in 23-kg pigs. In 10-kg pigs, phytase improved P and Ca digestibility and XAP improved DE and P digestibility, whereas the combination of the 2 enzymes improved DE, P, and Ca digestibility. Phytase alone or combined with xylanase improved P digestibility in 23-kg pigs, but xylanase alone did not improve digestibility of any nutrient. Combination of phytase and xylanase improved daily retention of energy and P.

	Footnotes

 
¹ Journal paper No 2006-18050 of the Purdue University Agricultural Research Programs. The authors thank the staff of Purdue University Swine Research Unit for care of experimental animals and Pat Jaynes for able technical assistance.

² Corresponding author: ladeola{at}purdue.edu

Received for publication October 27, 2006. Accepted for publication March 6, 2007.

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