J. Anim. Sci. 2003. 81:2270-2278
© 2003 American Society of Animal Science
Nutritional evaluation of egg byproducts in diets for early-weaned pigs1
L. S. Schmidt,
C. M. Nyachoti2 and
B. A. Slominski
Department of Animal Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2
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Abstract
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A total of 272 Cotswold pigs (17 ± 1 d) were utilized in three experiments to evaluate the nutritive value of spray-dried egg proteins for early-weaned pigs. In all experiments, pigs were stratified by sex and initial BW and then assigned randomly to experimental diets. In Exp.1, four corn–soybean meal-based diets containing 7% of either spray-dried porcine plasma (SDPP), spray-dried technical albumen (SDTA), SDTA stored at 70°C for 3 d (SDTA-ht), or spray-dried whole egg (SDWE) were assigned to five pens each with four pigs for a 3-wk study period. Average daily gain, ADFI, and gain:feed ratio (G:F) were determined. At the end of wk 3, five pigs per treatment were killed to determine ileal AA and energy digestibilities, as well as Enterobacteriaceae counts. Compared with the SDPP diet, ADG and G:F were lower (P < 0.05) for SDTA-, SDTA-ht- and SDWE-containing diets. Apparent ileal digestibilities of cystine, histidine, isoleucine, methionine, and threonine in the SDPP diet were lower (P < 0.05) than in diets containing spray-dried egg products. Ileal digestible energy content did not differ (P > 0.05) in all diets (3.1 to 3.2 Mcal/kg). Enterobacteriaceae counts were lower in the SDTA-ht diet than in either the SDTA or SDWE diets (P < 0.05). In Exp. 2, the effect of substituting SDPP with varying levels of SDTA was investigated. Diets were randomly assigned to five pens (except for the 100% SDTA diet, which had four pens), each with four pigs. Average daily gain, ADFI, and G:F decreased linearly as the level of SDTA was increased in the diet (P < 0.05). Replacing SDPP with SDTA at 25 or 50% had no effect on pig performance (P > 0.10). In Exp. 3, phase I diets containing 0, 25, or 50% SDTA in place of SDPP (7% of the diet) were each assigned at random to eight pens each with four pigs for a 14-d period, after which all pigs were switched to a common phase II diet lacking both SDPP and SDTA for another 14 d. Average daily feed intake and ADG did not differ among all diets in phase I and II and overall (d 0 to 28). Pigs fed the diet containing 50% SDTA in phase I had lower (P < 0.05) G:F than those fed the SDPP diet. The results indicate that technical albumen can replace 25 to 50% of SDPP in early-weaned pig diets without compromising performance, and further suggest that heat-treated SDTA may affect intestinal microbial population in pigs.
Key Words: Antibacterial Activity • Egg Products • Lysozyme • Performance • Piglets • Weaning
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Introduction
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The use of complex nursery diets based on costly ingredients for early-weaned pigs offers a strong economic incentive to identify cheaper alternative ingredients (Dritz et al., 1996
). Spray-dried egg products generally contain a large proportion of egg albumen, which has an excellent amino acid profile with a relatively high level of methionine compared to spray-dried porcine plasma (Kats et al., 1994; Owen et al., 1995). However, efforts to utilize spray-dried egg products in diets for early-weaned pigs have yielded conflicting results. For instance, Zimmerman (1999) observed a linear decline in growth performance of weanling pigs as dietary level of egg products increased from 3 to 9%, but others could not demonstrate such an effect (Owen et al., 1993; James et al., 1999).
Eggs also contain several antimicrobial proteins, including lysozyme. Lysozyme, in its native conformation, preferentially cleaves the N-acetylmuramic acid and N-acetylglucosamine residues in gram-positive bacteria and has only a limited ability to affect gram-negative bacteria. However, structural modification through means such as thermal treatment has been shown to enhance the ability of lysozyme to reduce the survival rate of gram-negative bacteria in vitro (Ibrahim et al., 1996; Ibrahim, 1998; During et al., 1999). Storing spray-dried technical albumen (SDTA) at 70°C for 3 d was shown to lower the catalytic activity of native lysozyme (Schmidt, 2001), which may influence microbial populations in piglets fed SDTA-containing diets.
The objectives of the current study were to evaluate the nutritional value of SDTA with or without storage at 70°C for 3 d (SDTA-ht) and spray-dried whole egg (SDWE) in diets for early-weaned pigs. Enterobacteriaceae counts in ileal digesta were also determined.
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Materials and Methods
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Egg Products Evaluated
The egg products evaluated were obtained from Canadian Inovatech Inc. (Winnipeg, Manitoba, Canada). They included SDTA, SDTA-ht, and SDWE. Spray-dried technical albumen was stored at 70°C for 3 d to further pasteurize the product, increase protein digestibility through increased denaturation, and to enhance the antimicrobial activity of native lysozyme.
Experiment 1
The replacement value of egg products for spray-dried porcine plasma (SDPP) in diets for early-weaned pigs was assessed in a 21-d performance trial. Eighty Cotswold pigs averaging 5.8 ± 1.2 kg and weaned at 17 ± 1 d were blocked on the basis of sex and BW and then assigned randomly from within block to four dietary treatments as follows: 1) a corn–soybean meal control diet containing 7% SDPP; 2) control with SDTA substituted for SDPP; 3) control with 7% SDTA-ht in place of SDPP; and 4) control with 7% SDWE in place of SDPP. All diets were formulated to contain 22% CP, 1.5% total lysine, and 0.36% methionine, and met or exceeded NRC (1998) requirements for all other nutrients (Table 1). Chromic oxide was included in all diets as an indigestible marker. Each dietary treatment was assigned to five replicate pens per treatment and pigs had unlimited access to feed and water. Individual BW and pen feed disappearance were monitored weekly. Room temperature was initially set at 29.5°C and gradually reduced by 1.5°C/wk.
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Table 1. Ingredient composition and calculated composition of experimental diets used Experiment 1 (as-fed basis)
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At the end of the trial, one pig, selected at random from each pen, was held under halothane general anesthesia and then killed via cardiac puncture with sodium pentobarbital (50 mg/kg of BW) to facilitate collection of digesta from the last 30 cm of the small intestine in order to determine amino acid digestibilities and Enterobactericea counts. Digesta was collected immediately into sterile containers by flushing with cold physiological saline. Digesta samples were divided into two portions; one was used immediately to determine Enterobacteriaceae counts and the other kept frozen at -20°C until required for chemical analyses. All experimental procedures were reviewed and approved by the University of Manitoba Animal Care Committee, and pigs were cared for according to the guidelines of the Canadian Council on Animal Care (CCAC, 1993).
Experiments 2 and 3
Based on the results of Exp. 1, the use of SDTA in nursery diets was evaluated further in two performance trials that lasted 21 d (Exp. 2) or 28 d (Exp. 3). Each experiment used 96 Cotswold pigs weaned at 17 ± 1 d with an average initial BW of 5.6 ± 1.1 and 6.2 ± 1.0 kg for Exp. 2 and 3, respectively. Assignment of pigs to dietary treatments, monitoring of performance criteria, and management of room conditions were as described for Exp. 1.
In Exp. 2, five dietary treatments in which SDPP was replaced with SDTA at 0, 25, 50, 75, or 100% were each assigned to five replicate pens (except for the 100% SDTA diet, which had only four replicates due to space limitation) with four pigs per pen. Diets were formulated to 22% CP, 1.45% lysine, and a minimum of 0.36% methionine (Table 2). In Exp. 3, the effect of substituting SDPP with 25 or 50% SDTA in phase I nursery diets and its influence on subsequent piglet performance was assessed. Three diets formulated to contain 22% CP, 1.45% lysine, and a minimum of 0.36% methionine (Table 3) were assigned to eight replicate pens with four pigs per pen for a 14-d period postweaning (phase I). Pigs were then switched to a common phase II diet for another 14 d. The phase II diet was formulated to contain 1.25% lysine and 0.34% methionine (Table 3).
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Table 2. Ingredient composition and calculated composition of experimental diets used Experiment 2 (as-fed basis)
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Table 3. Ingredient composition and calculated composition of experimental diets used Experiment 3 (as-fed basis)
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Sample Preparation and Chemical Analysis
All analyses were performed in duplicate. For Enterobacteriaceae counts, a portion of the digesta was serially diluted in saline (0.85%), plated in triplicate on violet red bile agar (Becton Dickinson, Cockeysville, MD) using a pour plate-overlay technique, and incubated at 35°C for 24 h. Results are expressed as cfu/g of digesta (DM basis). Digesta samples were freeze-dried, and along with diet samples, ground to pass through a 1-mm screen and thoroughly mixed before analyses. Samples were dried in a convection oven at 105°C for 16 h for DM determination, and CP (N x 6.25) content was determined using nitrogen analyzer (NS 2000, Leco Corp., St. Joseph, MI). Chromic oxide content was determined using atomic absorption spectroscopy as described by Williams et al. (1962). A 100-mg sample was weighed for acid hydrolysis according to AOAC (1984) and as modified by Mills et al. (1989) for AA analysis. Briefly, samples were digested in 4 mL of 6 N HCl in vacuo for 24 h at 110°C, neutralized with 4 mL of 25% (wt/vol) NaOH, and allowed to cool to room temperature. The mixture was then made to 50-mL volume with sodium citrate buffer (pH 2.2) and analyzed using an LKB 4151 Alpha analyzer (LKB Biochrom, Cambridge, U.K.). Samples for methionine and cystine analyses were oxidized with formic acid prior to acid hydrolysis. Tryptophan was not determined.
Calculations and Statistical Analyses
Calculations of apparent ileal amino acid digestibilities were performed as described previously (Nyachoti et al., 1997). Data were subjected to ANOVA using the GLM procedures of SAS (SAS Inst., Inc., Cary, NC). Single-df contrasts were performed to assess the effect of egg byproducts, whereas linear, cubic, and quadratic contrasts were performed to assess the effect of increasing levels of dietary SDTA. For the digestibility data, diet, pig, and body weight (covariable) were included as sources of variation. When a significant F-value for treatment (P < 0.05) was observed in the analysis of variance, treatment means were compared using Duncan’s multiple-range test (Duncan, 1955).
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Results
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Experiment 1
The amino acid compositions of SDPP, SDTA, and the experimental diets are shown in Table 4. Analyzed lysine content was lower than formulated for all diets, whereas methionine content was slightly lower and higher in the SDPP diet and in diets containing spray-dried egg products, respectively. Initial and final BW, ADFI, ADG, and gain:feed ratio (G:F) are presented in Table 5. Replacing SDPP in the pig starter diet with egg products had no effect (P > 0.05) on ADFI (Table 5). Pigs fed the SDPP control diet had higher (P < 0.01) ADG than those fed diets containing spray-dried egg byproducts (Table 5). There were no differences in ADG among pigs fed diets containing the egg-by products (P > 0.05). Compared with the SDPP-control diet, G:F was poorer (P < 0.05) in pigs fed diets containing spray-dried egg byproducts. Feeding diets containing SDTA-ht or SDWE resulted in poorer (P < 0.05) G:F compared with feeding the SDPP control diet. The G:F was progressively reduced as the dietary level of SDTA increased up to a 75% inclusion rate, although this reduction was not significant (P > 0.05) (Table 6).
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Table 4. Amino acid composition (%) of spray dried porcine plasma, spray-dried technical albumen, and diets used in Experiment 1
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Table 5. Performance and bacterial counts in ileal digesta of early-weaned pigs’ fed diets containing spray-dried porcine plasma (SDPP), spray-dried technical albumen (SDTA), SDTA stored in a hot room (70°C) for 3 d (SDTA-ht), and spray-dried whole egg (SDWE) for 21 d in Experiment 1
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Table 6. Apparent ileal digestibility of selected amino acids of diets based on spray-dried porcine plasma (SDPP), spray-dried technical albumen (SDTA), SDTA stored in a hot room (70°C) for 3 d (SDTA-ht) and spray-dried whole egg (SDWE) fed to early-weaned pigs in Experiment 1
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Apparent Ileal Amino Acid Digestibilities
The apparent ileal digestibilities of amino acids are shown in Table 6
. Among the essential amino acids, only apparent ileal arginine, phenylalanine, leucine, and lysine were similar (P > 0.05) among the diets containing SDPP, SDTA, SDTA-ht, and SDWE. The apparent ileal digestibilities of all other essential amino acids were higher (P < 0.05) in diets containing technical-grade egg products than in the SDPP control diet. Overall, indispensable amino acid digestibilities in the diets containing technical-grade egg products ranged from76 to 97% compared with 70 to 85% in the SDPP control diet (Table 6). Of the dispensable amino acids, apparent ileal digestibility of glutamic acid was higher (P < 0.05) in the SDPP control diet compared with the diets containing spray-dried egg products. Cystine, glycine, and tyrosine apparent digestibilities were higher (P < 0.05) in diets containing spray-dried egg products than in the SDPP control diet (Table 6). Apparent ileal digestible energy was similar (P > 0.10) among dietary treatments and averaged (mean ± SE) 3.12 ± 0.27, 3.06 ± 0.22, 3.22 ± 0.27, and 3.20 ± 0.18 (Mcal/kg) for control, SDTA-, SDTA-ht-, and SDWE-containing diets, respectively.
Antibacterial Activity
Relative to piglets fed the SDPP control diet, Enterobacteriaceae counts in piglets fed diets containing SDTA or SDTA-ht were not different (P > 0.05, Table 5). However, there were significant differences (P < 0.05) in ileal Enterobacteriaceae counts among the three dietary treatments containing technical-grade egg products. Piglets fed the diet containing SDTA-ht had the lowest (P < 0.05) counts (mean ± SE) at 6.6 ± 0.2 cfu (log10 cfu) whereas those fed the SDWE-containing diets had the highest counts (7.3 ± 0.1); those on SDTA-containing diet had an intermediate count (7.1 ± 0.3). Piglets fed the control had 7.0 ± 0.1 cfu.
Experiment 2
Initial and final BW, ADFI, ADG, and G:F are shown in Table 7. As the proportion of SDTA was increased at the expense of SDPP to 75 or 100%, ADFI decreased linearly (P < 0.002, Table 7). Pigs fed the 0:100 (SDPP:SDTA) diet had the poorest (P < 0.05) ADFI compared with all other treatments, followed by those fed the 25:75 diet, where ADFI was lower (P < 0.05) than that of pigs fed diets containing 50% or less SDTA. There were no differences in ADFI between the control and diets containing 50% or less SDTA (P > 0.05, Table 7). Replacing SDPP with 50% or less SDTA in starter diets had no effect (P > 0.05) on ADG. However, as the dietary proportion of SDTA was increased to 75 or 100%, ADG was reduced significantly (P < 0.01). The G:F was not different (P > 0.05) among pigs fed the SDPP control diet and those fed the diets containing 25 or 50% SDTA. Increasing the proportion of SDTA to 100% reduced (P < 0.05) G:F compared with SDPP control or diets containing 50% or less SDTA.
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Table 7. Performance of early-weaned pigs fed diets containing various levels of spray-dried technical albumen (SDTA) substituted for spray-dried porcine plasma (SDPP) for 21 d in Experiment 2
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Experiment 3
The initial and final BW averaged 6.5 and 18.1 kg, respectively, across treatments (Table 8). The ADFI and ADG were not different (P > 0.05) among treatments in phase I, II, and overall (d 0 to 28) (Table 8). As the dietary content of SDTA was increased to 50% during phase I, G:F was reduced (P < 0.05) compared with the control, but the difference between 25% and 50% was not significant (P > 0.05). Gain to feed ratio was not affected by dietary treatment in phase II or overall (d 0 to 28) (Table 8).
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Table 8. Performance of early-weaned pigs fed phase I diets containing various levels of spray-dried technical albumen (SDTA) substituted for spray-dried porcine plasma (SDPP) in Experiment 3
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Discussion
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Egg-breaking facilities produce substantial quantities of egg byproducts each year that are unsuitable for human consumption but which could potentially be utilized in diets for early-weaned pigs. Because eggs are a source of good-quality protein, byproducts of the egg-breaking industry could be used effectively as a feed ingredient in nursery diets. The current study evaluated technical-grade egg products, namely SDTA and SDWE as potential ingredients in diets for early-weaned pigs, using a diet with SDPP as a standard. Storing SDTA at 70°C for 3 d was expected to further destabilize the protein, making it more digestible and reducing the catalytic activity of native lysozyme, thus optimizing its antibacterial properties (Ibrahim et al., 1996). In earlier studies, the catalytic activity of lysozyme in STDA was shown to decline from 360 to 192 u/mg following a 3-d storage period at 70°C (Schmidt, 2001). Furthermore, the company providing the product routinely uses these conditions to further pasteurize the product.
In general, replacing SDPP with technical-grade egg byproducts supported poorer piglet performance compared with the control diet containing 7% SDPP (Table 5). This was the case despite the fact that apparent ileal amino acid digestibilities and ileal digestible energy were similar or better in diets containing technical-grade egg products than in the SDPP control diet (Table 6). This observation agrees closely with that of James et al. (1999), who found that piglets fed nursery diets containing egg proteins had poorer growth performance compared with those fed SDPP control diets. Although not determined in the current study, it has been suggested that trypsin inhibitors present in egg proteins might be responsible for the poor performance of piglets fed diets containing egg proteins in place of SDPP. According to Van Nevel et al. (2000), whole egg products can inhibit 40 mg of trypsin/g of feed, but a 5% inclusion level in diets of early-weaned pigs might not contain sufficient levels of trypsin-inhibiting activity (TIA) to impact growth performance. Since SDTA contains a greater proportion of egg albumen, which contains the trypsin-inhibiting ovomucoid (Burley and Vadehra, 1989), and because SDTA was included at 7% in the present study, it can be speculated that the TIA in SDTA diets used in the current study was higher. However, since the apparent ileal amino acid digestibilities were similar or higher in diets containing egg products, it is unlikely that TIA were the cause of the poor piglet performance. Instead, the slight differences in the analyzed amino acid content (Table 4), in particular for lysine and threonine, may have contributed to the observed performance differences.
Piglet performance was reduced linearly as the dietary level of SDTA was increased (Table 7). This response pattern was similar to that reported by Zimmerman (1999), in which ADFI, ADG, and G:F were reduced linearly as the level of egg products was increased from 3 to 9% at the expense of SDPP. Although not supported by the current data or that of Zimmerman (1999), diets containing both SDPP and SDTA could be expected to support better piglet performance than diets containing either of the two ingredients alone. This is because SDTA, being high in methionine, could complement the methionine levels in SDPP, which is known to be low in this essential amino acid (Kats et al., 1994a; Owen et al., 1995). However, based on the results of the current study, replacing 25 to 50% of SDPP with SDTA does not appear to compromise piglet performance (Tables 7 and 8). These levels, which translate to 1.75 to 3.5% of the diet, agree closely with the 3 to 3.5% suggested as the levels at which egg proteins can replace SDPP in nursery diets without compromising performance (Owen et al., 1993).
Excluding SDPP and SDTA from phase II starter diets did not affect ADFI, ADG, or G:F over a 14-d period. Kats et al. (1994a) and James et al. (1999) reported reduced G:F in piglets fed phase II diets in which SDPP was removed compared with those that were fed phase I diets containing no SDPP. In the present study, G:F was 5.9% higher in piglets fed the diet containing 25% SDTA in phase I compared with those fed the SDPP control diet. This response could be attributed to the fact that removing SDPP from phase II diets may have taken away its protective effects, thus stimulating a high immunological response, which in turn compromised performance. The magnitude of such a response could, however, depend on nursery environment (Coffey and Cromwell, 1995) and herd health status (Bergstrom et al., 1997).
It was expected that thermal denaturation of SDTA through hot room (70°C for 3 d) storage, by reducing the catalytic activity of lysozyme, would increase its antimicrobial activity, thus promoting better gut health, higher nutrient utilization and, in turn, supporting better piglet performance. Also, this was expected to reduce the antinutritive effects of trypsin inhibitors or avidin and to enhance protein utilization. However, the pigs fed diets containing SDTA-ht tended to have poorer growth performance than those fed the diet containing 7% unheated SDTA (Table 5). Heat treatment may have led to the formation of Maillard reaction products, including carbohydrate– or lipid–protein conjugates, which may not be reflected in amino acid digestibility measurements (Friedman, 1996), but nonetheless, affect growth performance. Maillard reaction products have been shown to act as enzyme inhibitors (including pepsin, trypsin, carboxypeptidase A, and aminopeptidase N), mutagens, and nephrotoxins (Pitotti et al., 1994; Friedman, 1996).
The additional energy present in egg products (due to high fat content) was taken into account when formulating the diets, which may explain why there were no differences in apparent ileal digestible energy content of diets containing spray-dried egg products compared with the control diet containing 7% SDPP. However, as discussed previously, piglets fed diets containing spray-dried egg products had poorer growth rates compared with the control. This may have been due to the poor availability of fatty acids in SDTA or SDWE to the growing pig (Owen et al., 1993).
With the current desire to minimize or eliminate the use of in-feed antibiotics as growth promoters, identifying products that could be used as alternatives will be of great significance to the swine industry. Egg products have received a lot of attention in this regard, particularly due to their immunoglobulin content. However, because avian immunoglobulins may not withstand pelleting temperatures, their practical benefits may be limited. Egg products also contain lysozyme, a naturally occurring protein that can cleave the N-acetylmuramic acid and N-acetylglucosamine residues in the peptidoglycan of gram-positive bacteria. The antimicrobial activity of lysozyme has recently received considerable attention (Ibrahim et al., 1996). It has been shown that lysozyme denatured through thermal treatment exhibits a novel antimicrobial activity against gram-negative bacteria (Ibrahim et al., 1996; Ibrahim, 1998; During et al., 1999). The results of the current study, which show that Enterobacteriaceae counts in the ileal digesta of piglets fed the SDTA-ht diet were significantly reduced (P < 0.05; Table 5) compared with the untreated SDTA, suggest that the thermal treatment employed may have induced the novel antimicobial activity of lysozyme in SDTA by reducing its catalytic activity, as shown by Schmidt (2001). Since piglet performance was not improved when SDTA-ht was fed, despite the fact the reduction in Enterobacteriaceae counts coupled with the fact that amino acid digestibilities were similar or higher in this diet compared with control, it may be that counts present in all piglets were not high enough to affect performance.
Pigs fed the SDWE diet had the highest Enterobacteriaceae counts compared with those fed the other diets (Table 5). The higher fat level in SDWE vs. SDTA (25.6 vs. 15.4%) might have negated any antimicrobial benefits of lysozyme in SDWE by inhibiting gram-positive bacteria and allowing the proliferation of gram-negative bacteria (Sprong et al., 1999), which would explain the significantly higher Enterobacteriaceae counts seen in ileal digesta of pigs fed the SDWE diet compared with all other diets (Table 5). The current study indicates a potential for SDTA-ht to reduce Enterobacteriaceae levels; however, further research is needed to elucidate the factor(s) responsible and their mode of action. Finally, Enterobacteriaceae counts in the diet containing 7% SDTA were similar to those seen in the control diet containing 7% SDPP. Since the benefits of SDPP in nursery pig diets are partly attributable to its prevention against enterotoxigenic Escherichia coli infection, which contribute to the etiology of postweaning diarrhea (Hampson, 1994), the current observation suggests that SDTA might offer similar benefits, but this will have to be proven first.
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Implications
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The current study indicates that spray-dried technical albumen can be incorporated into diets for early-weaned pigs at 25 to 50% in place of spray-dried porcine plasma without compromising performance. Thermal treatment of spray-dried technical albumen seemed to enhance its antimicrobial activity, thereby offering a potential alternative to in-feed antibiotics in pork production. However, further research will be required before these novel antimicrobial effects can be fully exploited in nursery pig nutrition and management.
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Footnotes
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1 The authors gratefully acknowledge the financial support received from Agri-Food Research Development Initiative (ARDI), Canadian Bio-Systems Inc., and Canadian Inovatec Inc. 
2 Correspondence— phone: (204) 474-7323; fax: (204) 474-7628; E-mail: martin_nyachoti{at}umanitoba.ca.
Received for publication November 27, 2002.
Accepted for publication May 8, 2003.
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Abstract
Introduction
