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Nutrient and Energy Utilization in Enzyme-Supplemented Starter and Grower Diets for White Pekin Ducks¹

O. Adeola^2,*, D. J. Shafer and C. M. Nyachoti

^* Department of Animal Sciences, Purdue University, West Lafayette, IN 47907; Maple Leaf Farms, Syracuse, IN 46567; and Department of Animal Science, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada

² Corresponding author: ladeola{at}purdue.edu

	ABSTRACT

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The aim of this study was to determine the effect of enzyme supplementation on energy and nutrient utilization in White Pekin ducks fed starter and grower diets. In each of 2 experiments, 8 ducks were assigned to each starter or grower diet without or with enzyme supplementation at 1 g/kg of diet in a 2 x 2 factorial arrangement of treatments for a 120-h nutrient utilization assay. Starter and grower diets in experiment 1 contained 3.68 and 2.51% N, respectively, and 4.321 and 4.274 kcal/ g of gross energy, respectively. Corresponding values in experiment 2 were 2.93 and 2.89% and 3.994 and 3.930 kcal/g. The enzyme supplement was a cocktail containing 7,500 units of protease and 44 units of cellulase per gram. Endogenous energy losses were from 23 to 44 kcal in the 2 experiments, and endogenous amino acid (AA) losses ranged from 14 mg for Trp to 137 mg for Asp. In experiment 1, a lower energy output of ducks fed the grower diet, coupled with lower N output, resulted in greater (P < 0.05) diet AME_n for the grower than the starter diet. Apparent digestibilities of all AA were higher (P < 0.05) in the starter diet than in the grower diet regardless of enzyme supplementation, more so for the S-containing AA. Average true digestibility of all AA was 93.7 and 90.4% for the starter and grower diets, respectively. There was no effect of enzyme supplementation of diet on the true digestibility of AA except for Met. Average true digestibility of all AA for diets not supplemented or supplemented with enzyme were 91.3 and 92.8%, respectively. In experiment 2, energy utilization of the grower diet was higher (P < 0.05) than that of the starter diet. Lysine and Asp showed lower (P < 0.05) apparent digestibility in the grower than in the starter diet. Enzyme supplementation of starter or grower diets did not affect the apparent digestibility of AA, except for Met, whose digestibility was increased by 2.4 percentage points in an enzyme-supplemented diet (P < 0.05). Except for Trp, true digestibility of AA was not affected by diet type or enzyme supplementation. The results show that the enzyme cocktail evaluated improved AA and energy utilization in White Pekin ducks and that such an enzyme-related response is diet composition-dependent.

Key Words: duck • energy and nutrient utilization • enzyme supplementation • grower • starter

	INTRODUCTION

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The application of exogenous enzymes in poultry nutrition has been driven by accruing benefits in terms of improved dietary nutrient utilization and growth performance. Researchers have clearly demonstrated that supplementing poultry diets with appropriate enzyme activities increases energy and N retention in chickens (Bedford and Classen, 1992; Bedford, 1995; Ghazi et al., 2003). Furthermore, it has been shown that use of a combination of enzyme activities act synergistically thus providing better responses than single activities used individually (Morgan and Bedford, 1995; Meng et al., 2005).

To date, much of the research on enzyme application in poultry nutrition has involved chickens. However, considering that differences in energy and nutrient utilization exist between chickens and ducks (Muztar et al., 1977; Siregar and Farrell, 1980), it is possible that the response to dietary enzyme supplementation is different between chickens and ducks. There are only a few studies that have investigated the use of enzymes in duck nutrition (Hong et al., 2002a; Adeola and Bedford, 2004; Adeola et al., 2007). In the study of Adeola and Bedford, xylanase supplementation to a high-viscosity wheat improved energy, fat, N, and starch digestibilities in White Pekin ducks, but enzyme effect could not be demonstrated in a low-viscosity wheat. In the study of Hong et al. (2002a), supplementing an enzyme cocktail containing protease, amylase, and xylanase to starter and grower duck diets improved growth performance and utilization of N and amino acids (AA) but not that of energy. Results of these studies and those of others (Ghazi et al., 2003) clearly demonstrated that response to supplemental enzyme depends on several factors, including type and amount of enzyme activity used and diet composition. Thus, the objective of the current study was to investigate the effects of enzyme supplementation to 2 types of starter and grower diets on energy and nutrient utilization by White Pekin ducks. The enzyme supplement used was a cocktail containing protease and cellulase activities, with side activities of pentosanase, -galactosidase, and amylase.

	MATERIALS AND METHODS

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The procedures used in the surgical preparation of male ducks (drakes) for excreta collection in the current study were those previously described by Adeola et al. (1997). Briefly, each bird was surgically fitted with a retainer ring from a Playtex bottle set (Playtex Products, Dover, DE) 3 d before the start of the experiment. The plastic retainer lids from the nurser set were modified by drilling 12 holes, 2 mm in diameter, in the ring similar to the 12 points on a clock. Birds were restrained in a plexiglass box, and the feathers from a 5-cm zone adjacent to the vent were removed to expose the skin. The skin was then sanitized with a dilute solution of chlorhexidine diacetate. Four milliliters of 2% lidocaine hydrochloride were injected around the vent to desensitize the area (1 mL in each of 4 regions). The modified retainer ring was then secured to the skin using a continuous suture pattern. The plastic bottle of the nurser set was measured and cut to a length of 3 cm below the threads on the bottle. A Whirl-Pak bag (Fort Atkinson, WI) with a capacity of 480 mL was then taped to the exterior of the plastic bottle below the threads. Another Whirl-Pak bag with a capacity of 480 mL was then placed through the bore of the bottle and screwed into the modified retainer ring attached to the bird for excreta collection. The exterior bag served to protect the inner bag from accidental puncture.

Feeding and Excreta Collection Procedures
The current study utilized the same TME bioassay that has been used previously to evaluate the nutritive value of feedstuffs for ducks in our laboratory and was originally modified from the bioassay described by McNab and Blair (1988). The experimental protocol used in the present study has been outlined previously (Adeola et al., 1997). Birds were denied access to feed for 48 h before feeding the test diets, but each bird was force-fed dextrose solution (30 g/dL of water) at 24 and 30 h after feed was withdrawn. Thirty grams (30 g/dL of water) of each diet was force-fed to the 8 assigned ducks at 48 and 54 h after feed withdrawal, whereas those assigned to the feed-deprived group for estimation of endogenous losses were force-fed dextrose (30 g/dL of water). All ducks were fitted with their respective collection apparatus at the time of the first feeding of test diets. Collection bags were changed within the first 6 h after placement and every 12 h thereafter during the 54-h collection period. Collected excreta were immediately frozen until further processing for analyses. The Purdue University Animal Care and Use Committee approved all of the feeding, surgical, and collection protocols in the present study.

Ducks and Diets
The investigation consisted of 2 experiments designed to determine the nutrient and energy utilization responses of ducks to enzyme supplementation of 4 pelleted, commercial-type diets. In experiment 1, four diets consisting of starter and grower diets supplemented with an enzyme cocktail at 0 g or 1.0 g/kg in a 2 x 2 factorial arrangement of treatments. Experiment 2 also used 4 diets consisting of starter and grower diets (different from that used in experiment 1) supplemented with an enzyme cocktail at 0 g or 1.0 g/kg arranged in a 2 x 2 factorial. The enzyme cocktail, Vegpro, was supplied by Alltech Inc. (Nicholasville, KY) and contained 7,500 units of protease and 44 units of cellulase per gram plus side activities of pentosanase, -galactosidase, and amylase. The following ingredients supplied AA and energy in experiment 1: yellow corn, soybean meal, bakery meal, wheat by-products, Met hydroxyl analog, L-Lys.HCl, and animal-vegetable blend. In experiment 2, yellow corn, soybean meal, wheat, wheat middlings, Met hydroxyl analog, L-Lys.HCl, and animal-vegetable blend supplied AA and energy. The diets were pelleted but reground through a 1-mm screen before the addition of enzyme and feeding. The respective average BW (mean ± SD) and age of White Pekin ducks used in experiments 1 or 2 were 4.58 ± 0.375 or 4.16 ± 0.215 kg and 9 or 8 wk.

Analyses
Frozen excreta samples were transferred to aluminum pans and placed in an oven at 55°C for 96 h. Dried excreta and feed samples were ground through a 0.5-mm screen and thoroughly mixed before analyses. Samples of feed and excreta were oven-dried at 110°C for 24 h for DM determination. Nitrogen and energy content in feed and excreta were determined by the combustion method using the Leco model NS 2000 combustion analyzer (Leco Corp., St. Joseph, MI) and bomb calorimetry using Parr 1261 adiabatic calorimeter (Parr Instruments Co., Moline, IL), respectively. Amino acid analyses were conducted at the University of Missouri Experiment Station Chemical Laboratory (Columbia, MO). Samples for AA analysis were prepared using a 24-h hydrolysis in 6 N hydrochloric acid at 110°C under an atmosphere of N. For Met and Cys, performic acid oxidation was performed before acid hydrolysis. Samples for Trp analysis were hydrolyzed using barium hydroxide. Amino acids in hydrolysates were determined by HPLC (AOAC, 2000; 982.30E [a, b, c]).

Calculations of AME values were performed as described previously (Sibbald, 1976). The AME, AME_n, TME, and TME_n were calculated using the following formulas: AME = (EI – EO)/FI; AME_n = AME – (8.22 x ANR/FI); TME = AME + (EEL/FI); TME_n = TME – (8.22 x ANR/FI) – (8.22 x ENL/FI), where EI = gross energy intake of the diet; EO = the gross energy output; FI = feed intake (g); ANR = apparent N retention calculated as the difference between N intake and N output; and EEL and ENL = endogenous energy (kcal) and N (g) loss, respectively, from the group of feed-deprived ducks. Because catabolic compounds in excreted N can contribute to fasting energy loss, excreted energy was corrected to zero N balance using a factor of 8.22 kcal/g (Hill and Anderson, 1958). Apparent AA digestibility (AAAD) was calculated from the intake of AA and the corresponding output in the excreta. Apparent AA digestibility = (AA intake – AA output)/AA intake. True AA digestibility = AAAD + (endogenous AA output/AA intake). Data were analyzed as a 2 x 2 factorial arrangement of treatments in a randomized block design using the GLM procedures of SAS (2006). The factors included diet type (starter or grower) and Vegpro (0 or 1 g/kg). Because there were no interactions of factors for the reported response criteria, interaction term was pooled with the error term. Statistical significance was determined at an level of 0.05.

	RESULTS

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The analyzed DM, N, gross energy, and AA contents of the base diets used in experiments 1 and 2 are presented in Table 1. The endogenous outputs of N, energy, and AA in fasted ducks are shown in Table 2. Fasted ducks in experiment 1 excreted 653 mg of N and 23 kcal of energy over the 54-h collection period. These amounts were lower than for fasted ducks in experiment 2, which excreted 1,824 mg of N and 44 kcal of energy during the same period of time (Table 2). Endogenous AA excretion in experiment 1 ranged from a low value of 13.9 mg of Trp to a high value of 109.6 mg of Leu among the indispensable AA. Corresponding low and high values for experiment 2 were 13.3 mg for Met and 83.3 mg for Leu. Among the dispensable AA, endogenous excretion of Glu and Asp made up the largest proportion at 181.3 and 137.3 mg, respectively, in experiment 1 and 115.4 and 95.3 mg, respectively, in experiment 2. Overall, fasted ducks excreted 1,325 mg of endogenous AA in experiment 1 compared with 1,025 mg in experiment 2, suggesting that a large proportion of the 1,824 mg of endogenous N excreted by duck in experiment 2 may be associated with uric acid N.

	DISCUSSION

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Because energy utilization is affected by age, species, and protein quality of a feed, ME values should be corrected for N retention that occurs during the assay period. Correction of the TME content to zero N balance for diets assayed in experiments 1 and 2 resulted in a reduction of from 7 to 10%. This range is in agreement with previous studies in ducks fed complete diets (as opposed to single ingredients) reported by Hong et al. (2002b) and in which there was a 9% reduction in TME after correction to zero N balance.

There are several studies that have examined the use of exogenous enzymes in poultry diets, and many of these have reported significant improvements in nutrient utilization and growth performance of birds fed enzyme-supplemented diets (Brenes et al., 1993; Hong et al., 2002a; Adeola and Bedford, 2004). The use of multienzyme blend has often been reported to be more effective than individual enzymes (Morgan and Bedford, 1995; Meng et al., 2005). Vegpro, the enzyme tested in the present study, is a commercially available cocktail containing protease, cellulase, pentosanase, -galactosidase, and amylase activities. It is designed for use mainly as a protease for improving nutrient utilization from high-protein ingredients. The enzyme cocktail contained side activities of pentosanase, -galactosidase, and amylase activities in addition to cellulase and protease activities and was expected to improve energy and N utilization by increasing the digestion of starch and nonstarch polysaccharides thus releasing entrapped nutrients (Morgan and Bedford, 1995). Amylase is a hydrolase that catalyzes the hydrolysis of O-glycosyl compounds. The findings of Brown (1996) indicated that digestion of the starch component of corn resistant to midgut digestion was completed in the hindgut, suggesting that amylase could improve the digestion of this fraction. Corn and soybean meal, the majority of the feed ingredients in poultry diets, usually contain 6 to 7% crude fiber and stachyose and raffinose, none of which are well digested by birds. These compounds can significantly increase the excretion of some endogenous AA, because they can adsorb peptides, AA, and digestive enzymes and increase pancreatic juices and mucin production in the lumen (Coon et al., 1990). The cellulase and -galactosidase activities in the enzyme cocktail used in the current study were expected to digest crude fiber, stachyose, and raffinose in the diets. Furthermore, Ritz et al. (1995) demonstrated that feed efficiency of turkeys fed amylase-supplemented diets was significantly increased over the control birds during the third week. In a previous broiler study, Charlton and Pugh (1995) reported that Vegpro increased TME_n for peas, beans, and soybean meal by 14.3, 9.2, and 4.1%, respectively. Similarly, Schutte and Pereira (1998) reported that Vegpro improved nutrient utilization and performance of broiler chicks, improvements that the authors attributed to improved protein digestion.

However, in the present study, Vegpro had no effect on DM, N, and energy utilization in White Pekin ducks fed starter or grower diets. Because the concentration of N in the starter diet was higher than in the grower diet in experiment 1, ducks consumed and retained more N in absolute amounts than when fed the grower diet. However, when expressed as a percentage of N intake, there were no differences in the amount of N retained, thus suggesting that the enzyme tested had no effect on the efficiency of N utilization in ducks fed starter or grower diets. The present data showing no effect of enzyme supplementation on nutrient utilization in White Pekin ducks is in agreement with the results of Hong et al. (2002a), in which a grower diet was supplemented with an enzyme cocktail containing (per g) 4,000 units of amylase, 12,000 units of protease, and 1,600 units of xylanase. Early studies showed that dietary supplementation with amylase did not improve the performance and digestibility of chickens (Fry et al., 1958). Results of experiment 1 in the current research, however, are in contrast with the recent findings of Adeola and Bedford (2004) indicating improvements in apparent N retention and TME and TME_n in ducks fed xylanase-supplemented high-viscosity wheat. This might be due to the fact that in the current study complete diets were used as opposed to the single ingredient used in that study.

The study of Hong et al. (2002a) showed improvements in N retention and apparent ileal AA digestibility and apparent AA retention in White Pekin ducks fed an enzyme-supplemented grower diet. In a study with broilers, Meng et al. (2005) reported increased AME_n, apparent ileal starch and protein digestibility, and total tract non-starch polysaccharide digestibility in a wheat-soybean meal-canola meal-pea-based diet supplemented with a multicarbohydrase blend. The study of Zanella et al. (1999) demonstrated that the supplementation of low-energy broiler diets with an enzyme mixture containing amylase, protease, and xylanase improved digestibility of nutrients and bird performance. However, in the present study, enzyme supplementation did not influence N utilization. Nonetheless, it is important to note that enzyme supplementation numerically improved apparent N retention as a percentage of N intake by 8 and 5% in experiments 1 and 2, respectively. In a study with young ducks, Jamroz et al. (1998) reported that enzyme supplementation increased N utilization by 4.8 to 6.5%. Because the energy input does not influence AA excretion, the basic methodology of the TME assay can be applied to the measurement of AA digestibility (Sibbald, 1979). In experiment 1, enzyme supplementation improved the apparent digestibility of Arg, Leu, Met, Phe, Trp, Asp, Cys, and Tyr. This observation is consistent with the results of Hong et al. (2002a) indicating that enzyme supplementation to a grower diet improved apparent AA retention in White Pekin ducks. The observed improvements in apparent digestibility of AA with exogenous enzymes may reflect reduced endogenous AA losses resulting from an enzyme-facilitated denaturation of the antinutritional factors. Except for Met, there was no effect of enzyme supplementation in experiment 2 on AA digestibility. The lack of an enzyme effect on AA utilization may be explained by the fact that AA intake may have exceeded requirements.

In conclusion, nutrient and energy utilization in starter were better than in grower diets, and an enzyme cocktail (Vegpro) containing protease, amylase, and cellulase activities did not influence DM or N utilization in White Pekin ducks fed starter and grower diets. However, the enzyme improved apparent digestibility of AA, particularly Met, although this was not consistent across experiments.

	ACKNOWLEDGMENTS

 
We gratefully acknowledge the staff of Purdue University Poultry Research Unit and Brian Ford (Purdue University Small-Animal Housing Facility) for the management of experimental animals, Maple Leaf Farms (Syracuse, IN) for generous donation of ducks and feed, Charles Thomas (The Adeola Lab at Purdue University) for excellent technical assistance, and Alltech Inc. (Nicholasville, KY) for financial support.

	FOOTNOTES

 
¹ Journal paper number 2007-18108 of the Purdue University Agricultural Research Program.

Received for publication April 13, 2007. Accepted for publication October 31, 2007.

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