J. Anim. Sci. 2002. 80:3222-3229
© 2002 American Society of Animal Science
Additivity and associative effects of metabolizable energy and amino acid digestibility of corn, soybean meal, and wheat red dog for White Pekin ducks1
D. Hong*,
D. Ragland
and
O. Adeola*,2
* Departments of Animal Sciences and
and
Veterinary Clinical Sciences, Purdue University, West Lafayette, IN 47907
2 Correspondence:
Phone: 765-494-4848; Fax: 765-494-9346; E-mail:
ladeola{at}purdue.edu.
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Abstract
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The additivity of true amino acid digestibility (TAAD) and true metabolizable energy (TME) values in corn, soybean meal, and wheat red dog for White Pekin ducks was investigated. Differences between observed values for the complete diets and values predicted from measurements of individual ingredients were used to test additivity. Eight ducks were each assigned to the following dietary treatments: corn, soybean meal (44% CP), wheat red dog (wheat by-product with less than 4% fiber), complete Diet 1 (corn-soybean meal), complete Diet 2 (corn-red dog-soybean meal), and dextrose. Dextrose-fed ducks were used to estimate endogenous losses. The nitrogen-corrected TME (TMEn) in corn, soybean meal, wheat red dog, and two complete diets were 3.411, 2.919, 2.502, 3.148, and 3.111 kcal/g, respectively. In general, the TME and TMEn values observed in the two complete diets were not different (P > 0.05) from predicted values and indicated that the TME and TMEn in corn, soybean meal, and wheat red dog were all additive. The mean TAAD of corn, soybean meal, wheat red dog, and the two complete diets were not different, and were 87.03, 88.15, 90.58, 85.83, and 87.02%, respectively. The differences in TAAD between observed and predicted values were significant (P < 0.05) only for arginine, lysine, and aspartate in complete Diet 1, and for arginine, histidine, lysine, and aspartate in complete Diet 2. These results indicated that TME and TMEn values for corn, soybean meal, and wheat red dog were all additive in the two complete diets, but digestibilities of some amino acids were not additive and demonstrated some associative effects.
Key Words: Amino Acids • Metabolizable Energy • Soyabean Oilmeal • Wheat Milling Residues
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Introduction
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Additivity of nutrients is a crucial consideration in the formulation of diets for poultry. It is assumed that the supply of nutrients in a complete diet is equal to the sum of the supply based on the digestibility values determined from the single ingredients. However, few studies have confirmed this assumption. There are some reports of associative (nonadditivity) effects in ruminant animals when they are fed a diet composed of forage or low quality roughage and a readily available energy source because of changes in pH value, VFA concentration, and microbial activity in the rumen (Thompson et al., 1991; Kienzle, 1994). Information regarding additivity from pig (Imbeah et al., 1988; Furuya and Kaji, 1991) and broiler (Angkanaporn et al., 1996) experiments showed that nutrients may not always be additive under certain circumstances. In our previous study (Hong et al., 2001), we investigated the possible nutrient additivity and associative effects for barley and canola meal with White Pekin ducks and observed that the ME values of barley and canola meal were additive in a complete diet but digestibilities of some amino acids were not additive. Therefore, in order to further improve the practical formulation of diets for ducks, studies with a wider variety of feedstuffs are warranted. Corn and soybean meal are two of the most common feed ingredients used to formulate diets for poultry in the United States. Wheat red dog, a low fiber by-product composed primarily of wheat offal is often used in duck diets in a variety of situations.
The objective of the present study was to determine the additivity and associative effects of the metabolizable energy and amino acid digestibility of corn, soybean meal, and wheat red dog for ducks.
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Materials and Methods
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Management of Ducks and Diets
Forty-eight 11-wk-old White Pekin male ducks with an average weight of 3.8 kg were sorted according to initial weights and assigned to five dietary treatment groups and one feed-deprived group such that average weights across the six groups were similar (eight ducks per group). The ducks were randomly assigned to individual cages (0.66 x 0.66 m) and housed in an environmentally controlled room maintained at 25°C. Fluorescent bulbs provided 24-h lighting. The eight ducks assigned to the feed-deprived group were fed dextrose for estimation of endogenous losses of amino acids, energy, and nitrogen (Sibbald, 1979). The experimental diets consisted of corn, soybean meal, and wheat red dog and two complete diets composed of corn and soybean meal, and corn, soybean meal, and wheat red dog (Table 1
).
Excreta Collection Equipment and Methodology
Traditional excreta collection methods, where trays are placed under cages, are not appropriate for ducks because they consume much greater quantities of water than chickens (Siregar and Farrell, 1980). As such, ducks often produce highly liquid excreta, which results in dry matter losses due to splatter from the contact of forcefully ejected excreta with collection trays. Therefore, the attachment of a collection apparatus to ducks was devised for collection of contaminant-free excreta to accurately estimate nutrient and energy output.
The surgical collection method was described previously by Adeola et al. (1997). In summary, approximately 3 d before the start of the experiment, each duck was surgically fitted with modified plastic retainer lids from a Playtex nurser bottle set (Playtex Products, Dover, DE). The ducks were placed in a restraint box, and feathers around the vent were removed. Four milliliters of 2% lidocaine hydrochloride (Phoenix Pharmaceutical, Inc., St. Joseph, MO) were injected around the vent to desensitize the area (1 mL in each of four regions). A continuous suture was applied to secure the retainer ring to the skin of the ducks. The plastic bottle of the nurser set was measured and cut to a length of 3 cm below the threads on the bottle and Whirl-Pak bags (NASCO, Ft. Atkinson, WI) inserted into the bore of the bottle, so that the edges of the bags hung over the threads of the bottle. The bottle and Whirl-Pak bag were then screwed onto the modified retainer ring attached to the duck and the collection apparatus was completed.
Feeding Techniques and Experimental Procedures
The ME assay used in the present experiment followed the standard techniques devised by Sibbald (1976) and the modifications suggested by McNab and Blair (1988). The modified true metabolizable energy (TME) bioassay improved the precision of Sibbald’s method by extending the collection time from 24 to 48 h and decreased the stress on the birds used for the determination of endogenous losses by administering dextrose instead of no feed at all. In using the assay for ducks, it became necessary to modify the techniques again, because many ducks were observed to regurgitate a generous portion of the test ingredient when 50 g was tube-fed at one time. We found that it was necessary to feed the test ingredients in two equal portions, 6 h apart, and to extend excreta collection time from a total of 48 to 54 h.
The experimental protocol is summarized in Table 2. Each experiment lasted 102 h with an initial 48-h feed-deprived period and a 54-h excreta collection period. All ducks were fitted with their respective collection apparatus at the time of the first feeding of experimental diets. The Whirl-Pak bags containing excreta were changed within the first 6 h after placement and every 12 h thereafter during the 54-h collection period. All of the feeding and surgical collection protocols in the present study were approved by the Purdue University Animal Care and Use Committee.
Chemical Analysis
All excreta samples were frozen immediately after collection. At the completion of the experiment, all samples were transferred to aluminum pans and placed in a forced-air oven for 96 h. A temperature of 55°C was chosen to minimize the volatilization of fatty acids. After drying, excreta samples were ground through a 0.5-mm screen prior to analysis. Dry matter was determined by drying the samples at 110°C for 24 h. Nitrogen determination was by the combustion method with the LECO model FP-2000 Nitrogen Analyzer (LECO, St. Joseph, MI). The energy contents of the feedstuffs and excreta samples were determined by bomb calorimetry with benzoic acid as a standard (Parr, Moline, IL). Amino acid compositions were determined at the University of Missouri Chemistry Laboratory (AOAC, 1995).
Calculations and Statistical Analysis
The TME contents of the feedstuffs were calculated using methods described by Sibbald (1976). The TME and nitrogen-corrected TME (TMEn) in kcal/g were calculated as follows:
where EI is gross energy intake (kcal); EO is gross energy output (kcal); FI is the intake of the feedstuffs (50 g); ANR is apparent nitrogen retention (g); FEL is fasting energy loss (kcal) from the feed-deprived ducks, and FNL is fasting nitrogen loss (g). Nitrogen retained in tissues can be catabolized to yield energy-containing excretory compounds that contribute to fasting energy loss. Therefore, the gross energy excreted was corrected to zero-nitrogen balance using a factor of 8.22 kcal/g (Hill and Anderson, 1958). The true amino acid digestibility (TAAD) was calculated as [(AA intake - AA output)/AA intake] + (endogenous AA output/AA intake).
Additivity was tested by comparing the differences between observed digestibility coefficients of the complete diet and predicted values from measurements determined with individual ingredients (corn, wheat red dog, and soybean meal). Analysis of variance using the General Linear Model (GLM) procedure of SAS (SAS Inst., Inc., Cary, NC) was performed as a randomized complete block design. Treatment mean differences were tested with the least significant difference procedure (Steel and Torrie, 1980).
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Results and Discussion
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The crude protein, nitrogen, and amino acid contents of the ingredients and the complete diets used in the study are shown in Table 3. The crude protein and amino acid composition of corn, soybean meal, and wheat red dog were similar to those listed by NRC (1994). The two complete diets were formulated to contain 16% crude protein.
The rapid assay was devised for the determination of TME (Sibbald, 1976) and apparent metabolizable energy (AME) (Farrell, 1978), which are mathematically related to each other. However, because the former is corrected for metabolic fecal and endogenous urinary losses and are not affected by the level of feed intake (Sibbald, 1976), the TME values should be an improvement over AME. The endogenous output of nitrogen, energy, and amino acids are presented in Table 4. The fasting energy loss (37.01 kcal) during the 54-h collection period was in agreement with that of previous studies (Adeola et al., 1997), but the endogenous nitrogen loss was higher than previously reported. The endogenous amino acid outputs in the present study were in agreement with those reported by Ragland et al. (1999). Studies by Siriwan et al. (1994) demonstrated a relatively high content of threonine and serine in the endogenous secretion of chickens and pigs fed a protein-free diet because the muco-protein and pancreatic secretion of the small intestine are rich in threonine and serine in addition to proline. However, the observation was not evident in the present study with feed-deprived ducks.
The true metabolizable energy and amino acid digestibilities are shown in Table 5. The TME values were highest for corn, intermediate for the two complete diets and wheat red dog, and lowest for soybean meal (P < 0.05). The values of the two complete diets were not different. Correction of TME to zero-nitrogen balance for the five diets resulted in 7 to 10% reduction, which were the same in our previous study with ducks (Hong et al., 2001), and was higher than the 2 to 4% reduction in cockerels (McNab and Blair, 1988) and the 2 to 5% reduction in other studies with ducks (Adeola et al., 1997). Nitrogen-corrected TME is not affected by the physiological state of the bird; therefore, it is the most useful estimation of bioavailable energy under low feed intake conditions (Wolynetz and Sibbald, 1984). The TME and TMEn values of corn were in agreement with previous determinations in ducks (Adeola et al., 1997; King et al., 1997; Ragland et al., 1997). However, the TME value of corn was lower than observations by Sibbald (1976) for roosters. After nitrogen correction, the TMEn value of corn paralleled those listed by NRC (1994). For example, the TMEn value listed in the NRC (1994) in cockerel assays is 3.470 kcal/g, while our results for ducks was 3.411 kcal/g. When compared with that listed in the NRC (1994) for 48% CP soybean meal, the TMEn value of soybean meal was not different (2.502 vs 2.485 kcal/g). These suggest that the energy in corn and soybean meal were metabolized with similar efficiency in ducks and chickens. There is limited information about the metabolizable energy of wheat red dog in ducks. The TME and TMEn values observed in the current study are 3.125 and 2.919 kcal/g, respectively.
The basic method of the TME assay can be applied successfully to the measurement of amino acid digestibility because the energy input level does not influence amino acid excretion (Sibbald, 1979). The ducks used in the current study were not cecectomized because our previous study (Ragland et al., 1999) showed that there is no difference between cecectomized and noncecectomized ducks in TAAD for these ingredients. The mean TAAD value of soybean meal (90.58%) was highest among the five dietary treatments. The complete diet that consisted of corn and soybean meal had the lowest mean TAAD value (85.83%). The true digestibility values of many amino acids were similar for corn and wheat red dog (P > 0.05), except that digestibility of tryptophan and alanine in corn were higher. Poor apparent digestibilities of lysine and threonine in corn were also reported by Green et al. (1987) in cockerels and by Imbeah et al. (1988) in pigs because of their slow rate of absorption and high concentration in endogenous secretion. Lysine in cereals is mainly deposited in the poorly digested aleurone layer and little is found in the digestible prolamine fraction.
The TAAD values for soybean meal in the present study were close to the results of Angkaporn et al. (1996) in broilers, but lower than those of Likuski and Dorrell (1978) and Cave (1988) in roosters. Such species differences could be accounted for by the different collection periods and statistical methods. For example, the collection period after force-feeding was 24 h in the experiment of Likuski and Dorrell (1978), but 54 h in the present study for ducks. Cave (1988) used regression methods to determine endogenous amino acid losses, which generally were higher than those obtained from feed-deprived birds. When further compared with the NRC (1994) for roosters, the true digestibilities of amino acids for soybean meal were in good agreement. However, the results for corn were inconsistent. Most of the TAAD for corn were about 3 to 8 percentage units lower than the coefficients listed by NRC (1994), except methionine and threonine were similar and tryptophan and histidine were higher than those listed in the NRC (1994). Early studies adopting the 24-h collection for determination of the TAAD values in corn with roosters resulted in higher TAAD values than those listed by NRC (1994). The TAAD values of corn in the present study were also lower than those observed by Parsons (1992) with roosters. The number of studies conducted to determine the TAAD of wheat red dog in poultry are sparse. Mean TAAD value for wheat red dog (88.15%) was in agreement with a previous study by Ragland et al. (1999) in ducks (87.52%).
The differences between observed ME values and predicted values from measurement determined with individual ingredients (corn, soybean meal, and wheat red dog) are shown in Table 6. Predicted values were calculated from the digestibility values determined with the individual ingredients and their relative proportions in the complete diets. For complete Diet 1, the respective TME and TMEn values observed were 0.072 and 0.059 kcal/g higher than predicted values. Corresponding values for complete Diet 2 were 0.081 and 0.055 kcal/g. These differences between observed and predicted values were not significant (P > 0.05), which indicated that the TME and TMEn of corn, soybean meal, and wheat red dog were all additive and did not have any significant associative effects in ducks. The nitrogen correction can result in less difference between observed and predicted metabolizable energy values. Recent studies indicated that the nonstarch polysaccharides of wheat have antinutritive properties, which may depress the ME value, starch digestibility, and nitrogen retention in chickens. Mollah and Annison (1981) reported that there was a synergistic effect in the dietary ME when wheat cultivars having an abnormally low AME value were combined with either corn or oat hulls for broilers. Because the hemicellulose from corn and oat hulls is more digestible than that from wheat, their presence in the intestinal tract may favor an optimal microflora for the digestion of starch, thereby improving the ME. However, this was not observed in the present study with wheat red dog (wheat by-product with less than 4% fiber) for ducks.
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Table 6. Differences between observed and predicted true metabolizable energy (TME) (kcal/g) and amino acid digestibility values (%) for complete dietsa
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The differences between the observed and predicted TAAD values for the two complete diets are also presented in Table 6
. The observed and predicted true digestibilities of most dispensable amino acids were similar (P > 0.05) in the two complete diets with the exception of aspartate. For indispensable amino acids, only digestibilities of arginine and lysine in complete Diet 1 and arginine, histidine, and lysine in complete Diet 2 were significantly different (P < 0.05). The differences between observed and predicted TAAD ranged from -5.87 (serine) to 6.99 (lysine) in complete Diet 1 and -8.89 (cysteine) to 9.82 (lysine) in complete Diet 2. The results of the present study indicated that there were some associative effects on TAAD for ducks fed a corn-soybean meal-wheat red dog-based diet. Several factors in the complete diets that not only affect the amino acid digestibility, but also influence the endogenous amino acid losses may account for the observation.
Corn and soybean meal 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 amino acids because they can adsorb peptides, amino acids, and digestive enzymes and increase pancreatic juices and mucin production in the lumen (Coon et al., 1990). The study of de Lange et al. (1989) demonstrated that purified pectin affect endogenous losses much larger than that of purified cellulose in pigs fed protein-free diets and indicated that different kinds of fibers have different effects on endogenous nitrogen losses.
Wheat red dog often contains high non-starch polysaccharides (pentosans), which consist of a (1–4)-ß-xylan chain with arabinose units substituted at the 2 and 3 positions of the xylose and arabinoxylan. Nonstarch polysaccharides can decrease the apparent amino acid digestibility through two ways. First, it can directly complex with digestive enzymes and reduce their activity or indirectly increase the bulk and viscosity of the intestinal contents and inhibit the rate of diffusion of substrates and enzymes (Angkanaporn et al., 1994). Second, the presence of pentosans accelerates the proliferation of microflora and the secretion of peptide hormone in the digestive tract and also increases endogenous amino acid output (Low, 1989).
Although heating soybean meal can denature the hemagglutinin and trypsin inhibitor to improve their nutritive values, overprocessing by autoclaving can result in nonenzymatic Maillard reactions between lysine and oligosaccharides and reduce the availability of lysine (Parsons, 1992).
It should be noted that dietary crude protein level might affect the amino acid digestibility values of ingredients. The study conducted by Fan et al. (1994) demonstrated that apparent ileal digestibility values of amino acids in feedstuffs are quadratically affected by their respective dietary levels. Thus, the different dietary protein levels of the five diets in the present experiment appeared to have an effect on the additivity of amino acids for ducks. Although many studies indicate that arginine can antagonize the utilization of lysine via a selective system, this may have exerted very little effect on the amino acid addititity in the present study.
In balance studies, there are three major methods most often used to measure digestibility—the direct method, the difference method, and the regression method. Fan and Sauer (1995) indicated that the direct method might not be suitable for the determination of digestibility values of feedstuffs with low-protein and poor palatability, such as barley and so on. However, the direct method was appropriate for the determination of energy and nutrient digestibilities in corn and soybean meal.
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Implications
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The study provided important information on the energy and amino acid utilization of corn, soybean meal, and wheat red dog by White Pekin ducks and indicated that the true metabolizable energy and nitrogen-corrected true metabolizable energy values of the three ingredients were all additive. However, the digestibilities of some amino acids were not additive and demonstrated some associative effects.
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Footnotes
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1 The financial support Maple Leaf Farms, Inc., Syracuse, Indiana, is thankfully acknowledged. The authors wish to thank Pat Jaynes and Jason Sands for their assistance. Journal paper No. 16667 of the Purdue University Agricultural Research Programs. 
Received for publication October 31, 2001.
Accepted for publication July 11, 2002.
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Abstract
Introduction
