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Effect of microbial phytase on energy availability, and lipid and protein deposition in growing swine^1,2

J. L. Shelton^*, L. L. Southern^*,3, T. D. Bidner^*, M. A. Persica^*, J. Braun, B. Cousins and F. McKnight

^* Department of Animal Sciences, Louisiana State University Agricultural Center Baton Rouge 70803-4210; and BASF AG, Ludwigshafen, Germany; and and BASF Corporation, Mount Olive, NJ

	Abstract

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Two experiments were conducted to determine the effect of phytase on energy availability in pigs. In Exp. 1, barrows (initial and final BW of 26 and 52 kg) were allotted to four treatments in a 2 x 2 factorial arrangement. Corn–soybean meal (C-SBM) diets were fed at two energy levels (2.9 and 3.2 x maintenance [M]) with and without the addition of 500 phytase units/kg of diet. The diets contained 115% of the requirement for Ca, available P (aP), and total lysine, and Ca and aP were decreased by 0.10% in diets with added phytase. Pigs were penned individually and fed daily at 0600 and 1700, and water was available constantly. Eight pigs were killed and ground to determine initial body composition. At the end of Exp. 1, all 48 pigs were killed for determination of carcass traits and protein and fat content by total-body electrical conductivity (TOBEC) analysis. Six pigs per treatment were ground for chemical composition. In Exp. 2, 64 barrows and gilts (initial and final BW of 23 and 47 kg) were allotted to two treatments (C-SBM with 10% defatted rice bran or that diet with reduced Ca and aP and 500 phytase units/kg of diet), with five replicate pens of barrows and three replicate pens of gilts (four pigs per pen). In Exp. 1, ADG was increased (P < 0.01) in pigs fed at 3.2 x M. Based on chemical analyses, fat deposition, kilograms of fat, retained energy (RE) in the carcass and in the carcass + viscera, fat deposition in the organs, and kilograms of protein in the carcass were increased (P < 0.10) in pigs fed the diets at 3.2 vs. 2.9 x M. Based on TOBEC analysis, fat deposition, percentage of fat increase, and RE were increased (P < 0.09) in pigs fed at 3.2 x M. Plasma urea N concentrations were increased in pigs fed at 3.2 x M with no added phytase but were not affected when phytase was added to the diet (phytase x energy, P < 0.06). Fasting plasma glucose measured on d 28, ultrasound longissimus muscle area (LMA), and 10th-rib fat depth were increased (P < 0.08) in pigs fed phytase, but many other response variables were numerically affected by phytase addition. In Exp. 2, phytase had no effect (P > 0.10) on ADG, ADFI, gain:feed, LMA, or 10th-rib fat depth. These results suggest that phytase had small, mostly nonsignificant effects on energy availability in diets for growing pigs; however, given that phytase increased most of the response variables measured, further research on its possible effects on energy availability seems warranted.

Key Words: Energy • Fat • Growth • Phytase • Pigs • Protein

	Introduction

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The addition of phytase to corn–soybean meal (C-SBM) diets for swine has been shown to increase the availability of Ca and P (Jongbloed et al., 1992; Radcliffe et al., 1995; Kemme et al., 1997). Phytase also has been shown to increase energy and AA availability in diets for nonruminants (Namkung and Leeson, 1999; Radcliffe et al., 1999; Ravindran et al. 1999), but there is much less data on AA and energy effects than on the Ca and P effects. Furthermore, most of this research has been done on poultry, not swine. Johnston (2000) reported that phytase increased GE digestibility in pigs fed a C-SBM diet. Williams (2001) reported that phytase increased starch digestibility in pigs fed C-SBM diets and plasma glucose concentration in pigs after a meal (Williams et al., 2001). However, not all of the data indicate that phytase affects AA and energy availability. Biehl and Baker (1997) reported no effect of phytase on true nitrogen-corrected ME in cecectomized roosters fed dehulled SBM.

Thus, the objective of these experiments was to determine the effect of phytase on energy utilization, and protein and fat deposition in growing pigs fed a C-SBM diet.

	Materials and Methods

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The Louisiana State University (LSU) Agricultural Center Animal Care and Use Committee approved all methods used in these experiments.

Two experiments were conducted to determine the effect of microbial phytase supplementation in C-SBM diets on energy availability and protein and lipid deposition in growing swine.

Experiment 1

General. Forty-eight crossbred barrows from the LSU Agricultural Center Swine Farm with average initial and final BW of 26.4 and 52.0 kg, respectively, were used in this experiment. The pigs were individually penned in 1.1- x 3.7-m pens with solid concrete floors at the LSU Veterinary School Swine Facility, and they were allotted to four treatments in a 2 x 2 factorial arrangement. Corn–soybean meal diets were fed at two energy levels (2.9 and 3.2 x maintenance [M]) with and without the addition of 500 phytase units/kg of diet (Table 1). Maintenance intake was considered to be 106 kcal of ME/kg of BW^0.75 (NRC, 1998). Defatted rice bran (10%) was added to the diets to decrease the energy content. Natuphos 600 (BASF Corp., Mt. Olive, NJ) was included in the diet at 0.083%, which added 500 phytase units/kg of diet. Actual analysis of the diets for phytase indicated that the diets provided 535 phytase units/kg of diet. The diets were formulated with the NRC model to contain 115% of the Ca, available P (aP), and Lys requirement for 20-kg pigs gaining 300 g of lean tissue per day (NRC, 1998). All other AA met or exceeded the ratio to Lys calculated using the NRC model (NRC, 1998). The diets also contained an equal ME:Lys ratio. On d 21 of the experiment, the diets were reformulated to contain 115% of the Ca, aP, and Lys requirement for 35-kg pigs gaining 300 g of lean tissue per day (NRC, 1998). Otherwise the diets were as previously described. Analyzed AA and mineral contents of corn, SBM, and defatted rice bran were used to formulate diets (Table 2). The AA composition of corn, SBM, and rice bran was determined after acid hydrolysis (AOAC, 1990), whereas total sulfur AA content was determined after performic acid oxidation followed by acid hydrolysis (AOAC, 1990). Tryptophan content was determined after alkaline hydrolysis (AOAC, 1990). The mineral composition of the feed sources was determined by inductively coupled plasma emission spectroscopy (model Optima 3000, Perkin Elmer, Norwalk, CT 06859) after digestion in nitric acid and peroxide.

Pigs were given ad libitum access to water throughout the experiment.

Blood Analysis. On d 0 and 14 of the experiment, blood was taken from all pigs 2 h after initiation of feeding for determination of plasma urea N (PUN) levels. Blood also was collected on d 28 from all pigs at 0 and 30 min after initiation of feeding for determination of glucose concentrations. Blood was collected 30 min after initiation of feed based on the data of Williams et al. (2001). Blood was collected via the anterior vena cava and placed into 7-mL tubes containing 17.5 mg of sodium fluoride and 14.0 mg of potassium oxalate (Monoject, Sherwood Medical, St. Louis, MO). The samples were then centrifuged at 1,500 x g at 4°C for 30 min. After centrifugation, the plasma from each sample was collected and frozen until analysis. Plasma urea N concentrations were determined by the methods of Laborde et al. (1995). Glucose concentrations were determined by a spectrophotometric procedure (Sigma, 1989a).

Ultrasound and Carcass Evaluation. At the beginning of the experiment, eight pigs with an average BW of 27.7 kg were slaughtered by exsanguination following electrical stunning at the LSU Agricultural Center Meats Laboratory for determination of initial body composition and initial organ weights and composition. Ultrasound backfat and longissimus muscle area (LMA) measurements were determined on d 35 of the experiment. These measurements were made by a single technician using a real-time ultrasound (Aloka 500, 12.5-cm and 3.5-MHz probe, Corometrics Medical Systems, Wallingford, CT). On each of d 35 and 42 of the experiment, six pigs per treatment were slaughtered. Hair, hoof coverings, and tails were removed from the carcass, but the heads remained on the carcass. Carcass measurements and values from total-body electrical conductivity (TOBEC; model MQI-27: Meat Quality Inc., Springfield, IL) analysis (for calculation of total protein and fat content in the carcass) were obtained from the left side of all carcasses after cooling at 2°C for 20 h. The linear carcass measurements included dressing percentage, LMA, average backfat, 10th-rib fat depth, and carcass length. Longissimus muscle area was determined by tracing the longissimus muscle surface area at the 10th-rib. Tenth-rib fat depth was determined by measuring the fat thickness at the 10th-rib, three-quarters of the lateral length of the longissimus muscle, perpendicular to the outer skin surface. Average backfat was determined by averaging the backfat thickness at the first and last rib and last lumbar vertebra.

Three pigs per treatment from each of the slaughter groups were used for determination of body composition by grinding and chemical analyses on d 35 and 42 of the experiment. Separate slaughter days were necessary because not all 48 pigs could be processed in 1 d. Organs (stomach, small intestine, large intestine, heart, lungs, liver and gallbladder, kidneys, spleen, and pancreas) were collected, individually weighed, and frozen together for further analysis. The stomach and intestines were cleaned before weighing. Total blood for the 24 pigs used for determination of body composition was collected, weighed, and a 10-mL sample was taken. The blood was then centrifuged and frozen as previously described for further analysis of plasma protein concentration (Sigma, 1989b). The response variables derived from the chemical body composition data included the weight, percentage, and daily accretion rate of protein, fat, and ash in the carcass and viscera, retained energy (RE) in the carcass and viscera, heat production (HP), net energy for production (NE_p), NE_m, viscera weights, viscera weights as a percentage of final BW, and viscera energy expenditure.

On the day after taking carcass measurements, the left sides of the 24 carcasses were transferred to the LSU Muscle Foods Laboratory, partially frozen by placing them in a -40°C freezer for 8 h, and ground once through a 1.91-cm plate and twice through a 0.79-cm plate using a Weiler grinder (model 878, Weiler and Co., Inc., Whitewater, WI). The ground samples were sealed and frozen for later analyses. On the day after grinding the carcasses, the organs were combined and ground through a 0.32-cm plate using a Butcher Boy grinder (model TCA 32, Lasar Mfg. Co., Inc., Los Angeles, CA), mixed in a single-phase induction motor mixer (serial No. 4173W 3, Howell Electronic Motors Co., Howell, MI), sealed, and frozen for later analyses. All samples were homogenized at speed 3 (Brinkman homogenizer model PT 10/35, Brinkman Instrument, Westbury, NY) into a paste before analysis.

Prediction equations for the determination of protein and fat using readings from TOBEC were obtained from the 24 pigs whose body composition was determined by grinding and subsequent analysis. The equations were developed using similar methodology to that of Higbie et al. (2002). The equations used carcass TOBEC readings (phase maximum average, PMA) and linear carcass measurements. The prediction equation to estimate kilograms of DM in pork carcasses was as follows:

where R² = 0.96 and root mean square error (RMSE) = 0.20. The prediction equation to estimate kilograms of protein was as follows:

where R² = 0.91 and RMSE = 0.12. The prediction equation to estimate kilograms of fat was as follows:

where R² = 0.85 and RMSE = 0.22. Percentages of DM, protein, and fat using TOBEC prediction equations were determined by the following equations:

To determine total BW at grinding, the following equation was used:

Protein and fat deposition were determined by the following equation:

Initial protein and fat content were based on actual analysis of the eight pigs slaughtered at the beginning of the experiment. The percentage of protein or fat increase was determined by the following equation:

The DM, CP, fat, and ash content were determined on the left side of the carcass and on the organ fraction. Crude protein was determined using a Bran Luebbe auto analyzer 3 digital colorimeter (serial No. 9521423, Buffalo Grove, IL). Fat was determined using a CEM (model AVC-80, Matthews, NC) with a solvent recovery system (model AEF-81, CEM). Dry matter was determined by weighing a 5.0-g sample and placing it into a drying oven at 100°C for 24 h. Ash was determined by placing the samples into an oven and ashing for 12 h at 550°C.

Retained energy was calculated using three methods. Retained energy was calculated as energy retained in protein and in fat from TOBEC prediction equations and also from actual carcass analysis using values of 5.66 and 9.46 Mcal/kg for protein and fat, respectively (Ewan, 2001). Furthermore, GE was determined on samples of carcass and viscera of the initial and final pigs by a bomb calorimeter (model 1341 Plain Jacket Calorimeter, Parr Instrument Co., Moline, IL). Retained energy was calculated using the following equation:

Net energy for production was calculated using the following equation:

Net energy for M was estimated by the following equation (Just, 1982):

Total HP was estimated by the following equation (Noblet et al., 1994):

Organ energy expenditures were calculated based on total HP of each pig. The portal-drained viscera (gastrointestinal tract, spleen, and pancreas), liver, heart, lungs, and kidneys were estimated to represent 22.5, 22.5, 10.0, 2.5, and 12.0% of total HP, respectively (Barcroft, 1947; Bard, 1961; Wade and Bishop, 1962; Forster, 1964; Milnor, 1968; Neutze et al., 1968; Smith and Baldwin, 1974; Canas et al., 1982; Thomson et al., 1995; Yen, 1997). Organ energy expenditure per gram of organ was calculated as (energy expenditure of the organ/organ weight in grams) for pigs fed the C-SBM diet at 3.2x M. Organ energy expenditures for all pigs were then calculated as previously described by Knowles et al. (1998):

Statistical Analysis. Data were analyzed by ANOVA procedures appropriate for a completely randomized design using the GLM procedures of SAS (SAS Inst., Inc., Cary, NC). The statistical model included treatment. For the growth, blood, and carcass measurement data, initial BW was used as a covariate. Day-0 PUN concentration was used as a covariate for d-14 PUN concentration. Contrast statements were included to examine phytase, energy, and phytase x energy effects as a 2 x 2 factorial arrangement of treatments. The pig was the experimental unit for all data.

Experiment 2

General. Sixty-four crossbred barrows and gilts from the LSU Agricultural Center Swine Farm with an initial and final BW of 23.3 and 47.4 kg were used in this experiment. They were allotted to two treatments in a randomized complete block design on the basis of weight and ancestry. There were eight replications (five replications of barrows and three replications of gilts) per treatment and four pigs per replication. The two dietary treatments (Table 3) were: 1) C-SBM control and 2) C-SBM with reduced Ca and aP with 500 phytase units/kg of diet. Defatted rice bran (10%) was included in the diets to decrease the ME content. Natuphos 1200 (BASF Corp.) was analyzed to contain 1,530 phytase units/kg. It was added to the diet at 0.033% to provide 500 phytase units/kg of diet. Actual analysis of the diet indicated that the diet contained 475 phytase units/kg diet. The diets were formulated to contain 1.02% Lys, 0.65% Ca, and 0.25% aP (Ca and aP were reduced by 0.10% in the diet with added phytase). All other AA met or exceeded the ratio to Lys calculated using the NRC model (NRC, 1998). All pigs were weighed on d 14 and at termination of the experiment (d 28) to determine ADG, ADFI, and gain:feed. Pigs were allowed ad libitum access to feed and water throughout the experiment.

Tenth-rib fat depth difference was determined by the following equation:

Statistical Analysis. Data were ANOVA procedures appropriate for a completely randomized block design using the GLM procedures of SAS (SAS Inst., Inc., Cary, NC). The statistical model included treatment, replication, and sex. There were no treatment x sex interactions so this term was removed from the model. The pen of pigs was the experimental unit for all data.

	Results

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Experiment 1

Growth Performance and Blood Metabolites. Daily gain was increased (P < 0.01) in pigs fed at 3.2 x M compared with pigs fed at 2.9 x M, but gain:feed was not affected (P > 0.10) by diet (Table 4). Pigs fed the diets at 3.2 x M had an increased (P < 0.09) PUN, but phytase addition eliminated the increase in PUN (phytase x energy, P < 0.06). Pigs fed the diets with added phytase had an increase (P < 0.08) in fasting plasma glucose.

Ultrasound and Carcass Evaluation. Initial carcass composition and organ weights from the eight pigs slaughtered at the beginning of the experiment are shown in Table 5. Carcass composition of the pigs on treatment using actual chemical analysis is shown in Table 6. Fat percentage in the carcass, kilograms of fat in the carcass, fat deposition in the carcass, fat deposition in the carcass + viscera, RE in the carcass and carcass + viscera (determined by protein and fat analysis), and HP were increased (P < 0.05) in pigs fed at 3.2 x M compared with pigs fed at 2.9 x M. Fat deposition in the viscera, kilograms of protein in the carcass, and RE (determined by GE analysis) also were increased (P < 0.10) in pigs fed at 3.2 x M relative to those fed at 2.9 x M.

Experiment 2

In Exp. 2, diet did not affect (P > 0.10) ADG, ADFI, gain:feed, initial or final LMA, initial or final 10th-rib fat depth, and LMA or 10th-rib fat depth difference (Table 9).

	Discussion

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In Exp. 1, PUN levels were increased in pigs fed the higher energy level but not in pigs fed phytase. This response indicates that phytase may have more of an effect on PUN levels in pigs fed closer to ad libitum intake. Fasting plasma glucose levels were increased in pigs fed phytase in Exp. 1, which agrees with the results of Williams et al. (2001). However, there was no effect of phytase on glucose levels 30 min after initiation of feeding, which does not agree with Williams et al. (2001). Williams et al. (2001) reported that plasma glucose peaked in blood 30 min after initiation of feeding; however, it may have peaked at a different time in the present study, which may explain the difference in results. The increase in fasting glucose concentration by phytase may be explained by the positive effect of phytase on carbohydrate digestion and absorption (Williams et al., 2001); however, we would have expected more of a response 30 min after the initiation of feeding. Phytate may influence starch digestibility through interaction with amylase enzyme, proteins associated with starch, Ca (which catalyzes amylase activity), or with starch itself (Deshpande and Cheryan, 1984; Thompson and Yoon, 1984).

O’Quinn et al. (1997) reported no effect in finishing pigs on 10th-rib fat depth, last-rib backfat thickness, LMA, or dressing percentage when phytase was added at 500 phytase units/kg of diet to sorghum–SBM-based diets. However, Johnston (2000) reported an increase in 10th-rib fat depth in growing-finishing pigs fed C-SBM diets with the addition of phytase, indicating a possible increase in energy availability. Data from Exp. 1 showed no differences in dressing percentages, actual LMA, or ultrasound 10th-rib fat depth in pigs fed phytase. In Exp. 1, actual 10th-rib fat depth and ultrasound LMA were increased in pigs fed phytase, but in Exp. 2, ultrasound 10th-rib fat depth and LMA were not affected in pigs fed phytase. In the study by O’Quinn et al. (1997) and our Exp. 2, pigs were allowed ad libitum access to feed, but in Exp. 1, pigs were limit fed at 2.9 or 3.2 x M. The difference in the data of our Exp. 1 and the data of O’Quinn et al. (1997) may be due to the different levels of energy restriction.

Protein and fat deposition in the carcass were increased in pigs fed the higher energy level. Assuming that only energy is limiting in the diet, protein deposition increases linearly with energy intake (de Lange et al., 2001). Campbell et al. (1983) and Bikker et al. (1995) also reported an increase in protein and fat deposition in pigs fed an increased energy level. Retained energy also was increased in pigs fed the higher energy level, which was to be expected because of the increase in protein and fat deposition. The data from TOBEC prediction equations mimicked the data from grinding the pigs, in that protein and fat deposition and RE were increased when pigs were fed the higher energy level.

The protein percentage in the carcass from chemical or TOBEC analyses was not affected in pigs fed phytase, but there tended to be an increase in protein and fat deposition in the carcass and viscera in pigs fed phytase. In a comparative slaughter experiment, Ketaren et al. (1993) reported that phytase increased protein deposition in 20-kg pigs given ad libitum access to diets composed of SBM and sucrose. As in our Exp. 1, Ketaren et al. (1993) reported numerical increases in fat and energy deposition. Furthermore, they reported that efficiency of both protein and energy retention was increased by the addition of phytase. O’Quinn et al. (1997) reported no effect on CP or percentage fat or lean in pigs fed increasing levels of phytase. However, in their experiment, the pigs were allowed ad libitum access to feed, whereas the pigs in our experiment were limit fed.

Organ weight and organ energy expenditures also were determined in our experiment. Spleen weight was increased when pigs were fed at 3.2 x M with no added phytase. However, energy level did not affect spleen weight as a percentage of final BW. Energy level also increased pancreas, stomach, and liver + gallbladder weight. Liver + gallbladder weight was decreased in pigs fed phytase. This response was due to the weight of the liver + gallbladder in the pigs fed at 3.2 x M with no added phytase. Viveros et al. (2002) reported a decreased liver weight, expressed as grams per 100 g of BW, in broiler chicks fed diets with low nonphytate P levels and supplemented with phytase.

Energy expenditure in the liver + gallbladder was increased in pigs fed at 3.2 x M with no added phytase. Furthermore, spleen, stomach, and intestine weights were all numerically decreased when phytase was added to the diets of pigs fed at 3.2 x M. The organ data suggest that phytase may affect the NE_m of pigs. For example, the liver accounts for approximately 22.5% (Smith and Baldwin, 1974) of total HP in pigs; thus, reducing liver weight will reduce NE_m.

Phytase supplementation significantly affected only a few of the response variables in Exp. 1. However, when looking at growth performance, actual linear carcass measurements, protein and fat deposition (actual chemical analysis and TOBEC, and RE [actual chemical analysis and TOBEC]), phytase supplementation numerically increased 19 of 24 response variables when pigs were fed at either energy level. Similarly, in Exp. 2 four of the five response variables measured were numerically increased by phytase. When the experiments are combined, 23 out of 29 response variables were numerically increased when phytase was added to the diet. Early reports by Rojas and Scott (1969) and Miles and Nelson (1974) reported increased apparent ME yields for chicks fed diets with supplemental phytase. Similarly, Ravindran et al. (2000) reported that phytase increased apparent ME in diets for chicks. Data on the effects of phytase on energy availability in pigs are more limited. Johnston (2000) reported an increase in apparent ileal GE digestibility in 50-kg pigs, but O’Quinn et al. (1997) reported no increase in ileal GE digestibility in 50- to 80-kg pigs. However, total-tract digestibility of GE was not affected in the studies by O’Quinn et al. (1997) or Johnston (2000). In the experiments by O’Quinn et al. (1997) and Johnston (2000), the pigs used were older than the pigs used in our experiments. Also, the diet compositions were different in the experiments. The experiment by O’Quinn et al. (1997) used sorghum–SBM diets, but our experiments and the one by Johnston (2000) used C-SBM diets. As mentioned above, Ketaren et al. (1993) reported a numerical increase in energy deposition in 20-kg pigs fed diets with added phytase, which agrees with our results in Exp. 1.

	Implications

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These experiments indicate that growth, protein deposition, fat deposition, and retained energy are increased when energy level is increased in the diet for growing swine. Furthermore, because phytase numerically increased the majority of the response variables measured, more research is needed to determine the effect of phytase on energy availability for swine.

	Footnotes

 
¹ Approved for publication by the director of the Louisiana Agric. Exp. Stn. as manuscript No. 02-18-0634.

² The authors are thankful to F. M. LeMieux, J. Carothers, A. Guzik, R. L. Payne, B. Watson, C. Airhart, and S. B. Williams for assistance with data collection and laboratory analyses.

³ Correspondence—phone: 225-578-3449; fax: 225-578-3604; E-mail: lsouthern{at}agctr.lsu.edu.

Received for publication October 18, 2002. Accepted for publication May 2, 2003.

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