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Interdepartmental Nutrition Program and Department of Animal Science, North Carolina State University, Raleigh, NC 27695;
* Universidade Federal do Rio Grande do Sul, Porto Alegre-RS, Brazil 91540; and
Milk Specialties Company, Dundee, IL 60118
3To whom correspondence should be addressed. E-mail: jack_odle{at}ncsu.edu.
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • soy protein • amino acid digestibility • milk replacer
The piglet has gained much popularity as a pediatric research model (1,2). Most infant formula companies routinely use piglets as a preclinical model of infant nutrition. Indeed, in 2003, the NIH National Center for Research Resources established a National Swine Research and Resource Center because of the dramatic increase in the use of pigs as models of human disease. In particular, the gastrointestinal tract of pigs is more similar to that of humans than other domestic and research animal species (1). Our research efforts have thus focused on defining better the nutrient needs of piglets both to improve their utility as a biomedical model and to advance production in agriculture.
Several alternative ingredients have been evaluated as complete or partial replacements for milk-based ingredients to reduce diet costs. In terms of protein, soybean meal, isolated soy protein (ISP)4 (3), hydrolyzed soy proteins (4), and wheat gluten (5) have been the more common alternatives. Overall, the use of vegetable proteins usually results in lower growth performance for young pigs (<14 d old). Poor performance has been explained by a temporary enzymatic limitation on digestion of vegetable nutrient sources and a transient intestinal hypersensitivity to soy proteins (glycinin and ß-conglycinin) in young pigs (6). However, McCracken et al. (7) observed that neither intact nor hydrolyzed soy proteins elicit intestinal inflammation in neonatal pigs. Similarly, Moughan et al. (8) reported no difference in digestive enzyme activity in piglets fed ISP or bovine milk protein–based diets. Therefore, the objective of this experiment was to evaluate the partial replacement of milk protein by a hydrolyzed vegetable protein mixture (HVPM) in liquid diets fed to piglets from 2 to 19 d of age.
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MATERIALS AND METHODS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Antibiotic-free diets were prepared by Milk Specialties as dry powdered formulas, differing primarily in source of protein. In the first replicate, 4 diets were utilized: 1) a positive control diet with whey as the only protein source (whey diet), 2) a hydrolyzed vegetable protein mixture (HVPM) replacing 31% of the whey protein (Lo HVPM diet), 3) a hydrolyzed vegetable protein mixture replacing 62% of the whey protein (Hi HVPM diet), and 4) a negative control diet with isolated soy protein (ISP) replacing 62% of the whey protein (ISP diet). The HVPM contained soy, wheat, and other proteins that were subjected to partial enzymatic hydrolysis. Because the growth performance of piglets fed the positive control (whey) diet was lower than those fed the test diets in the 1st replicate, a 5th diet was included in the 2nd replicate of the experiment. In that diet, 47% of the whey protein was replaced by casein (casein diet). The data from piglets fed the casein diet were used only as a reference for the positive control (whey) diet and were not included in the statistical analyses. Diets were formulated (Tables 1 and 2) to contain similar metabolizable energy (ME) contents and total lysine levels to exceed the NRC requirements for 3- to 5-kg piglets (10). Cobalt-EDTA was prepared as described by Uden et al. (11) and was added (0.1%) to the diets 36 h before the end of the experiment to serve as an inert digestibility marker. Diets were reconstituted (180 g/L) on a daily basis and kept refrigerated at 4°C until feeding. Fresh liquid diet was added to the bottles 4 times/d (at 0800, 1300, 1800, and 2300 h) to ensure that piglets had free access to fresh feed.
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Plasma and intestinal analyses. Plasma urea nitrogen (PUN) was assayed by the quantitative urease/Berthelot procedure (Sigma Diagnostics) based on published methods (13,14). Leucine aminopeptidase (LAP) activity was measured in mucosal homogenates as described by Goldbarg and Ruttenburg (15). The protein content of the homogenates was determined by the biuret method (16). The 3-cm small-intestine segments were processed for histomorphology as previously described (17); 6 villus height and width and crypt depth measurements were made on each sample, and villus surface area was calculated as follows: Area = (width x 3.14) x (2 x height + radius).
Body composition, amino acid, and Co analysis. Carcasses were ground twice through a fixed-die meat grinder. Subsamples of the final mixture were stored at –20°C until analysis for dry matter, ash, protein (nitrogen x 6.25), and fat (18). Amino acid and Co analyses of diets and ileal digesta were performed by a commercial laboratory (Experiment Station Chemical Labs), utilizing Association of Official Analytical Chemists methods (18). Only the ileal digesta samples from piglets fed the whey, Hi HVPM, ISP, and casein diets were subjected to amino acid analysis. Digestibility values for the Lo HVPM diet were assumed to be intermediate between those for the whey and Hi HVPM diets. Tryptophan concentrations were not determined. Apparent ileal digestibility of nutrients was calculated by comparing the ratio of nutrient to Co in the diet to the ratio in the ileal digesta (11).
Statistical analyses. Piglets were assigned to treatments according to a completely randomized design, without regard to gender or litter of origin. Two piglets were excluded from the trial because they developed severe diarrhea and had very low feed intake. The effects of dietary protein were assessed by ANOVA using the General Linear Model procedure of SAS (version 8.1, SAS Institute); treatment means were separated using Tukey’s test. For growth performance variables, initial body weight was included in the model as a covariable, and the reported values are the least-square (covariate-adjusted) means ± SEM. Differences were considered significant when P < 0.05.
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RESULTS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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22% more feed than those fed the whey diet (Fig. 1, P < 0.05). Piglets fed the casein diet consumed 283 ± 27 g/d. Collectively, the Hi HVPM diet increased efficiency (weight gain/feed intake) by 16%, compared to the whey diet (P < 0.05, data not shown).
Apparent ileal dry matter and amino acid digestibility and intake.
The diets did not differ in apparent ileal dry matter digestibility (Table 3). Apparent ileal digestibility of most amino acids was 7–10% greater for the whey diet than for the Hi HVPM or ISP diets. Nearly all essential amino acids were more digestible in the whey diet than in either the Hi HVPM or ISP diet. The casein diet dry matter digestibility was 89.7 ± 1.3% and amino acid digestibilities were 90.3 ± 1.3% and 87.1 ± 2.9% for essential and total amino acids, respectively. Daily intakes of apparent ileal digestible lysine (5.1 g/d), leucine (6.4 g/d), isoleucine (3.8 g/d), or valine (3.7 g/d) did not differ among the treatments (data not shown). However, piglets fed the whey diet had a lower intake of apparent ileal digestible methionine, histidine, and phenylalanine than piglets fed the Hi HVPM and ISP diets (Fig. 2, P < 0.01). Piglets fed the ISP diet had a lower intake of threonine, but the intake of arginine was 3-fold that of piglets fed the whey diet. Similarly, intake of apparent ileal digestible arginine by piglets fed Hi HVPM was 2-fold that of piglets fed the whey diet. Collectively, total essential amino acid intake was 20% greater for piglets fed the Hi HVPM and ISP diets than for piglets fed the whey diet (data not shown). The intakes of digestible nonessential amino acids (i.e., serine, glycine, glutamine, and tyrosine) also were greater for piglets fed the Hi HVPM and ISP diets than for those fed the whey diet (data not shown). The intake of total analyzed amino acids (not shown) was 25% greater for piglets fed the Hi HVPM and ISP diets than for those fed the whey diet. Piglets fed the casein diet had an intake of essential amino acids and total analyzed amino acids of 29.5 ± 2.9 and 59.4 ± 5.6 g/d, respectively.
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7% less protein and 23% more fat, compared to piglets fed the Hi HVPM or ISP diets (Table 4). Carcasses from piglets fed the casein diet were 70.3 ± 0.9% water, 13.6 ± 0.1% protein, 12.7 ± 0.9% fat, and 2.3 ± 0.03% ash. The accretion rates (g/d) of water and protein were 37 and 42% greater, respectively, in piglets fed the Hi HVPM, Lo HVPM and ISP diets compared to piglets fed the whey diet. Ash deposition rates were higher in piglets fed the Hi HVPM and ISP diets than in piglets fed the whey diet, whereas rates in piglets fed the Lo HVPM diet were intermediate. The nutrient accretion rates for piglets fed the casein diet were 204 ± 29 g/d of water, 42 ± 6 g/d of protein, 50 ± 8 g/d of fat, and 6.3 ± 1 g/d of ash.
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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130% greater than the rate observed in sow-reared piglets (17) and up to 180% greater than that reported in other artificial piglet-rearing studies (21).
The poorest performance was exhibited by piglets fed the whey diet. There is an apparent contradiction between this result and the widely held idea that newborn piglets have unique nutritional needs that include high-quality sources of nutrients, especially proteins, with milk-based proteins being considered of very high quality (22); however, this applies to animals in transition onto dry feed, and extrapolation to liquid-fed piglets should be done with caution. Newport (23) observed no effect on piglet performance from 2 to 28 d of age with partial replacement of dried skim milk by a mixture of ISP and dried whey when soy protein provided 37% of dietary protein. However, very poor growth was observed when soy protein provided 74% of dietary protein, with only 4 of 21 piglets surviving. This mortality was related to severe diarrhea. Jones et al. (24) reported that piglet performance was not affected when 25% of dried skim milk was replaced by soy flour as the protein source in a liquid diet fed to piglets from 21 to 36 d of age. Mateo and Veum (3) reported a decline of 50% in growth rates of piglets fed an ISP-based diet compared with piglets fed a dried skim milk– or casein-based diet from 1 to 15 d of age, but piglet performance did not differ from 15 to 29 d of age. McCracken et al. (7) reported an intermediate growth rate for piglets fed a hydrolyzed soy protein–based diet (109 g/d) compared with a casein/whey (121 g/d) and an intact soy protein–based diet (85 g/d) from 7 to 17 d of age. From these studies, it seems clear that the response to inclusion of a vegetable protein source depends on the percentage of inclusion, how it is processed, and the age of the piglets. Indeed, improved efficiency of utilization of vegetable proteins has been attributed to an adaptation of the digestive enzyme system of the piglets to the protein sources that occurs with age (25). Nonetheless, we found no literature showing better performance for any vegetable protein compared with milk-protein-based diets fed to such young pigs as we report in this experiment.
As expected, the apparent ileal digestibility of amino acids was greater for the whey diet. Apparent ileal digestibility of lysine was 85.55, 78.87, and 77.15% for the whey, Hi HVPM, and ISP diets, respectively. Overall, our data showed that the apparent ileal digestibility of essential amino acids and total analyzed amino acids was 8% lower for the Hi HVPM diet and 10% lower for the ISP diet, compared with the whey diet. Mavromichalis et al. (26) reported values of true ileal digestibility of sow’s milk as follows: lysine, 88%; methionine, 99%; threonine, 84%; leucine, 91%; histidine, 100%; valine, 87%; and arginine, 90%. All of these values are greater than those found in our research, even in the milk-based diets. However, our data were not adjusted for endogenous amino acid contamination; thus, this comparison is crude.
Despite the better apparent ileal amino acid digestibility observed for the whey diet, the daily intake of apparent ileal digestible amino acids was greater for most of the amino acids in piglets fed the Hi HVPM and ISP diets, and this is congruent with the superior growth performance observed in piglets consuming these diets. Although there was no difference for lysine intake, piglets fed the vegetable protein–containing diets consumed 114–205% more arginine, 69% more phenylalanine, 39% more methionine, and 46% more histidine than the whey-fed piglets (Fig. 2). Essential and total amino acid intakes were 20 and 28% lower, respectively, for the whey diet.
These differences in amino acid intake were reflected in both carcass composition and tissue accretion rates. Piglets fed the whey diet deposited 32–48% less protein than other piglets; however, the lower growth rates of piglets fed the whey diet were compensated by the greater percentage of carcass fat in these piglets, resulting in no net difference in fat deposition rates. Disregarding treatment effects, piglet carcasses were fatter (13.4% fat) and had a lower protein percentage (13.5% protein) in this experiment compared with data reported by Oliver et al. (27) who studied piglets of similar age (11.6% fat and 15.6% protein). Total lysine per unit of metabolized energy in our diets was 1.03 g/MJ, which is slightly below NRC (10) recommendations for piglets from 3 to 5 kg (1.08 g/MJ) and much lower than that used by Oliver et al. (27) (1.48 g/MJ). This might explain the different body composition between the 2 experiments. However the lysine:ME ratio among the diets used in this experiment did not change significantly: 0.84, 0.84, and 0.79 g apparent ileal digestible lysine/MJ ME for the whey, Hi HVPM, and ISP diets, respectively. Thus, the differences among treatments are much more likely related to an imbalance of some amino acids (other than lysine) rather than the source of protein per se. An amino acid imbalance may result when diets contain a complement of amino acids well in excess of the limiting amino acid. A reduction in feed intake is common in most of these situations (10). Manufactured milk replacers can be especially subject to this imbalance because amino acid requirements are not yet well established for very young pigs consuming liquid diets. For example, one of the amino acids that had the highest variation among the experimental diets and higher difference in daily intake was arginine. The total arginine level in sow’s milk is 1.37% (26), 65% of the lysine level in the milk, whereas the NRC (10) suggests an arginine level of 40% of total lysine for 3- to 5-kg piglets. The level of total arginine in the experimental diets was 30, 55, and 78% of total lysine for the whey, Hi HVPM, and ISP diets, respectively. Consistent with our results, Kim et al. (21) recently reported a linear increase in piglet growth when arginine was supplemented incrementally (up to 0.4%) into a whey-based milk replacer.
Soybean meal was reported to induce a transient intestinal hypersensitivity in early-weaned piglets. Li et al. (6) reported that piglets fed a diet containing soy protein had depressed weight gain, lower villus height, and greater crypt depth from 3 to 4 wk of age compared with piglets fed milk protein–based diets. Dreau et al. (28) investigated the development of local and systemic immune responses to antigenic or nonantigenic (no immunoreactive glycinin or ß-conglycinin) proteins in early weaned piglets. Piglets fed nonantigenic soy proteins had greater villus height, villus perimeter, villus area, and villus height:crypt depth ratio. On the other hand, McCracken et al. (7) tested liquid diets based on intact or hydrolyzed soy proteins against a whey/casein–based diet in neonatal pigs and concluded that the lack of substantial dietary effects on intestinal variables demonstrates that neither hydrolyzed nor intact soy proteins result in significant intestinal inflammation when fed to neonatal pigs. In the present study, piglets fed the ISP diet had lower intestinal morphology measures than piglets fed the Lo HVPM diet (Table 5), but the effects were apparently insufficient to have a negative effect on the piglets’ growth (Fig. 1; Table 4).
Despite lower amino acid digestibility, both the HVPM and ISP were shown to be excellent alternatives to milk proteins used in liquid diet formulations for neonatal pigs. Even if the comparison with a milk protein–based diet was prejudiced by the low performance of our positive control, the growth performance data from the alternative protein sources were proven to be very similar to those found in current literature for piglets of same age. Data from this study also underscore that a good amino acid balance may be more important than the source of protein per se. Clearly, additional work is warranted to better define the nutritional (amino acid) requirements of very young liquid-fed piglets. In particular, these data suggest that arginine may be limiting in milk-based proteins. In conclusion, there is a valuable niche for alternative vegetable proteins in liquid diets for very young piglets. Exploitation of this fact will help to make liquid feeding technology more economically attractive to the swine industry.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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2 Supported in part by the North Carolina Agricultural Research Service and by a Coordenação de Aperfeiçoamento de Pessoal de Nível Superior educational fellowship to A.R.E.
4 Abbreviations used: Hi HVPM, high hydrolyzed vegetable protein mixture; HVPM, hydrolyzed vegetable protein mixture; ISP, isolated soy protein; LAP, leucine aminopeptidase; Lo HVPM, low hydrolyzed vegetable protein mixture; ME, metabolizable energy; PUN, plasma urea nitrogen.
Manuscript received 21 February 2005. Initial review completed 11 March 2005. Revision accepted 14 June 2005.
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LITERATURE CITED |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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1. Moughan, P. J., Birtles, M. J., Cranwell, P. D., Smith, W. C. & Pedraza, M. (1992) The piglet as a model animal for studying aspects of digestion and absorption in milk-fed human infants. Simopoulos, A. P. eds. Nutritional Triggers for Health and in Disease vol. 67:40-113 Karger Basel, Switzerland.
2. Tumbleson, M. E. & Schook, L. B. (1996) The piglet as a model animal for studying aspects of digestion and absorption in milk-fed human infants. Advances in Swine in Biomedical Research Plenum Press New York, NY.
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4. Zijlstra, R. T., Mies, A. M., McCracken, B. A., Odle, J., Gaskins, H. R., Lien, E. L. & Donovan, S. M. (1996) Short-term metabolic responses do not differ between neonatal piglets fed formulas containing hydrolyzed or intact soy proteins. J. Nutr. 126:913-923.
5. Chae, B. J., Han, I. K., Kim, J. H., Yang, C. J., Hancock, J. D., Kim, I. H. & Anderson, D. A. (1999) Effects of dietary protein sources on ileal digestibility and growth performance for early-weaned pigs. Livest. Prod. Sci. 58:45-54.
6. Li, D. F., Nelssen, J. L., Reddy, P. G., Blecha, F., Hancock, J. D., Allee, G. L., Goodband, R. D. & Klemm, R. D. (1990) Transient hypersensitivity to soybean meal in the early-weaned pig. J. Anim. Sci. 68:1790-1799.[Abstract]
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18. Association of Official Analytical Chemists (1997) Comparison of triglycerides and phospholipids as supplemental sources of dietary long-chain polyunsaturated fatty acids in piglets. Official Methods of Analysis 15th ed. AOAC Gaithersburg, MD.
19. Zijlstra, R. T., Whang, K. Y., Easter, R. A. & Odle, J. (1996) Effect of feeding a milk replacer to early-weaned pigs on growth, body composition, and small intestinal morphology, compared with suckled littermates. J. Anim. Sci. 74:2948-2959.[Abstract]
20. Kim, J. H., Heo, K. N., Odle, J., Han, K. & Harrell, R. J. (2001) Liquid diets accelerate the growth of early-weaned pigs and the effects are maintained to market weight. J. Anim. Sci. 79:427-434.
21. Kim, S. W., McPherson, R. L. & Wu, G. (2004) Dietary arginine supplementation enhances the growth of milk-fed young pigs. J. Nutr. 134:625-630.
22. Hansen, J. A., Nelssen, J. L., Goodband, R. D. & Weeden, T. L. (1993) Evaluation of animal protein supplements in diets of early-weaned pigs. J. Anim. Sci. 71:1853-1862.[Abstract]
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24. Jones, E. E., Coalson, J. A. & Lecce, J. G. (1977) Soy flour as a source of protein for baby pigs. J. Anim. Sci. 45:1073-1078.
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27. Oliver, W. T., Mathews, S. A., Phillips, O., Jones, E. E., Odle, J. & Harrell, R. J. (2002) Efficacy of partially hydrolyzed corn syrup solids as a replacement for lactose in manufactured liquid diets for neonatal pigs. J. Anim. Sci. 80:143-153.
28. Dreau, D., Lalles, J. P., Philouze-Rome, V., Toullec, R. & Salmon, H. (1994) Local and systemic immune responses to soybean protein ingestion in early-weaned pigs. J. Anim. Sci. 72:2090-2098.[Abstract]
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