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Ingredient Quality and Its Impact on Digestion and Absorption in Poultry12
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INGREDIENT QUALITY AND ITSIMPACT ON DIGESTION AND ABSORPTION IN POULTRY^^^ MICHAEL S. LILBURN Department ofAnimal Sciences, The Ohio State UniversiQ, Wooster, OH 44691 Phone: (216) 263-3992 FAX: (216) 263-3949
Primary Audience: Nutritionists
ENERGY SOURCES DIETARY FATS The source of feed grade fats, both from the perspective of origin ( i e . animal or plant) and processing (i.e. soapstock vs. restaurant grease), are the two largest determinants of overall feeding quality. Carver [l] reported that the absorption of lipid from diets containing 3% tallow was 80%, but this factor decreased to < 60% after hydrogenation. Absorption of hydrogenated tallow fatty acids further declined to approximately 40%. Ren-
1 Salaries and
I
ner and Hill [2] reported that the chain length of saturated fatty acids significantlyinfluenced utilization. In order of increasing chain length, C:12 lauric acid was absorbed significantly better (65%) than C:14 myristic acid (25%) or C:16 palmitic acid (5%). In a separate experiment, chicks did not absorb palmitic and stearic acids compared with 88% absorption for oleic acid (C 18:l). This finding indirectly supported the earlier observations [l]. The proportion of saturated and unsaturated fatty acids in an intact fat or mixture of fatty acids can also have a significant effect on overall lipid digestibility. Renner and Hill [3]
research support provided by State and Federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University. Manuscript NO. 22-96. 2 Presented at the 1995 Poultry Science Association Informal Poultry Nutrition Symposium: '!Advancements in Diet Modifcation and Digestion in Poultry. "
Symposium LILBURN reported that in hydrolyzed tallow, palmitic (30%) and stearic acids (22%) were only minimally absorbed compared with hydrolyzed lard (51%; 36%) and hydrolyzed soybean oil (84%; 78%). The concentration of unsaturated fatty acids in each of those sources was 50%, 62%, and76%, respectively. The absorption of palmitic and stearic acids from intact tallow and lard were nearly double that of their respective hydrolyzed fatty acids, whereas the difference between intact soybean oil and its hydrolyzed fatty acids were not as great. Within each fat source, the absorption of unsaturated fatty acids was not nearly as sensitive to the form of the lipid (i.e. intact vs. hydrolyzed). These findings are similar in scope to the results of Young [4]. More recently, Wiseman and Lessire [5] also found progressive increases in palmitic and stearic acid digestibility with increasing proportions of rape oil in a tallow:rape oil mixture. The synergistic effects of unsaturated fatty acids on saturated fat absorption also appear in the metabolizable energy (ME) values for individual fatty acids when compared with mixtures of different fats [4,6,7]. In some cases, the ME of a 5050 mixture of saturated and unsaturated fat sources is greater than the mean of the two fat sources alone [8]. The concentration of free fatty acids within any commercial fat source is a commonly used indicator of quality, even though some commercial sources have a high proportion of FFA (Le. acidulated soapstock). An important preliminary step in the digestion of lipids is the hydrolysis of intact triglycerides into free fatty acids and 2-monoglycerides. The monoglycerides enhance the overall solubility of mixed micelles, the form in which lipids are presented to the intestinal lining for absorption [9,10,11,12].The critical relationships between concentration and source of FFA and their effect on the ME of different commercial fats are thoroughly discussed [13, 14, 15, 161. CORN In most of the U.S., corn is either the cereal of choice or the basis for pricing other cereal grains. Within the past few years, there has been considerable interest in the nutritional quality of corn as affected by adverse growing conditions. Dry conditions are the norm in some parts of the country [17] as
79 compared with droughts (i.e. 1988), which are considered to be atypical. In either case, these types of conditionscan have a significant influence on the overall nutritivevalue of corn. The greatest change associated with dry growing conditions is an increase in crude protein [17, 181. The increases in crude protein are not accompanied by proportional increases in amino acid content, however, and commonly used amino acid prediction equations [191may overestimate the actual amino acid content [181. Another area which has been questioned over the past few years is the relationship between bushel weight of corn and energy content.A commonly cited paper [20] suggests that growing conditions which predispose corn to lower test weights at harvest will also result in lower metabolizable energy concentrations. Thevariabilityin the originaldata and the small declines in ME actually observed suggest that bushel weight and ME were not highly correlated and numerous reports since then corroborate this conclusion [21, 22, 23, 24,251.
PROTEIN SOURCES FEATHER MEAL Early studies suggested that dried, powdered feather meal, while high in crude protein, was deficient in essential amino acids [XI.Subsequent improvements in processing methods allowed for steam hydrolysis of feathers, improving the overall nutritional qualityof feather meal, although it is still only a supplemental ingredient [27, 28, 291. Sullivan and Stephenson [30] suggested that there was no relationship between processing method and the nutritional quality of feather meal, but Naber [31] reported that feather meals containing 70 to 80% pepsin-digestible protein were nutritionally superior to a sample with only 64% digestible protein. Subsequent studies confirmed the importance of processingon the overall quality of a particular feather meal [32,33, 341. Even with the best of processing conditions, however, feather meal still faces amino acid imbalance and digestibility problems [31, 34, 35, 36, 371. Lanthionine is a unique, amino acid containing sulfur formed during the course of feather meal processing [37]. Han and Parsons [38] reported that in a comparison of seven commercial samples, lanthionine concentration was significantly
JAPR INGREDIENT QUALITY
80 correlated negatively with other in vitro and in vivo assays. These authors also compared two concentrations of pepsin (0.2% and 0.002%) and found that the lower concentration was more definitive with respect to separating better from poorer quality feather meal samples. Johnston and Coon [39] had previously shown that lower levels of pepsin would increase the variation in digestibility estimates with different animal protein sources. SOYBEAN MEAL It has long been recognized that urease enzyme activity is positively correlated with trypsin inhibitor activity in soybean meal and
is an adequate measure of soybean meal underprocessing [40]. More recently, an assay which was originally described by Evans and St. John [41] has received considerable research interest relative to measuring the extent of soybean meal overprocessing. Solubility of soybean meal protein in 0.2% potassium hydroxide (KOH) has been shown to be an effective measure of soybean meal overprocessing [42, 43, 441. Araba and Dale [45] also suggested that protein solubility might also be used as another indicator of soybean meal underprocessing, but this conclusion was not supported by the data of AndersonHafermann [&].
CONCLUSIONS AND APPLICATIONS 1. The absorption of saturated fatty acids from intact animal fats is much greater than that of the hydrolyzed fatty acids from the same sources. 2. The published amino acid prediction equations [19] for corn may overestimate the actual amino acid concentrations if higher than normal protein levels are the result of an environmental stress (i.e., drought). 3. Urease activity measurement and potassium hydroxide (KOH) solubility (0.2%) are good estimates of under processing and overheating of commercial soybean meal, respectively.
REFERENCES AND NOTES 2. Renner, R and F.W. Hill, 1961a. Utilization of fatty acids by the chicken. J. Nutr. 74:25!9-264.
10. Senior, J., 1964. Intestinal absorption of fats. J. Lipid Res. 5495-521. 11. Garreti, RL and R J . Young, 1975. Effect of micelle formation on the absorption of neutral fat and fatty acids by the chicken. J. Nutr. 105:827-838.
3. Renner, R and F.W. Hill, 1961b. Factors affecting the absorbability of saturated fatty acids in the chick. J. Nutr. 74254-258.
12. Sklan, D., 1979.Digestion and absorption of lipids in chicks fed triglycerides or free fatty acids: Synthesis of monoglycerides in the intestine. Poultry Sci. 58:885-889.
4. Young, RJ., 1961.The energyvalue of fats and fatty acids for chicks. 1. Metabolizable energy. Poultry Sci. 4111225-1233.
13. Huyghebaert, G., G. De Munler, and G.De Groote, 1988.The metabolizable energy ( M E " ) of fats for broilers in relation to their chemical composition. Anim. Feed Sci. Tech. 20:45-58.
1. Carver, D.S., EE Rice, R E Gray, and P. Mone, 1955. The utilization of fats of different melting points added to broiler feed. Poultry S i . 3494-546.
5. Wiseman, J. and M. Lessire, 1987. Interactions between fats of differin chemical content: A availability of fatty acids. k r . Poultry Sci. 2 8 : 6 7 7 4 y t
6. Artman, N.R, 1964. Interactions of fats and fatty acids as energy sources for the chick. Poultry Sci. 439941004.
7. KcteLs, E and G. De Groote, 1989. Effect of ratio of unsaturated to saturated fatty acids of the dietary lipid fraction on utilization and metabolizable energy of added fats in young chicks. Poultry Sci. 681506-1512. 8. Sibbald, I.R, SJ. Slinger, and G.C. Ashton, 1960. Factors affecting the metabolizable energy content of Doultrv feeds. 2. Variabilitv in the M.E. values attributed 'to samples of tallow a n i undegummed soybean oil. PoultIy Sci. 40:303-308. 9. Hofman, AF. and B. Borgstrom, 1962. Physicochemical state of lipids in intestinal content during their digestion and absorption. Fed. Proc. 21:43-50.
14. Wiseman, J. and F. Salvador, 1991.The influence of free fatty acid content and degree of saturation on the apparent metabolizable energyvalue of fats fed to broilers. Poultry S i . 7057S582.
15. Wiseman,J., F. Salvador, and J. Craigon, 1991. Prediction of the apparent metabolizable energy content of fats fed to broiler chickens. Poultry Sci. 701527-1533. 16. Thacker, P.A., G.L. Campbell, and Y. Xu, 1994. Composition and nutritive value of acidulated fatty acids, degummed canola oils, and tallow as energy sources for starting broiler chicks. Anim. Feed Sci.Tech. 4631-260. 17. Bdock, D.G., P.L. Raynor, and S. Savage, 1989. Variation of protein and fat concentrations among commercial corn hybrids grown in the Southeastern USA. J. Prod. Agric. 2:157-161. 18. Lilburn, M.S., E.M. Ngidi, N.E. Ward, and C.Llames, 1991. The influence of severe drought on
Symposium LILBURN
81
selected nutritional characteristics of commercial corn hybrids. Poultry Sci. 70:2329-2334.
33. Wessels, J.P.H., 1972.Astudyof the protein quality of different feather meals. Poultry Sci. 51537-541.
19. National Research Council, 1994. Nutrient Requirements of Poultry. 9th Rev. Edition. Natl. Acad. Press, Washington, DC.
34. Papadopoolos, M.C., A.R El Boushy, and E H . Ketelaars, 1985. Effect of different processing conditions on amino acid digestibility of feather meal determined by chicken assay. Poultry Sci. 64:1729-1741.
20. Leeson, S. and J.D. Summers, 1976. Effect of adverse growing conditions on corn maturity and feeding value for poultry. Poultry Sci. 55:588-593. 21. Libum, M.S. and N. Dale, 1989. Characterization of two samples of corn that vary in bushel weight. Poultry Sci. 68:857-860. 22. Leeson, S., A. Yersin, and L Voker, 1993. Nutritive value of the 1992 corn crop. J. Appl. Poultry Res. 2:208-213. 23. Reed, R , J.D. Latshaw, and M.S. Lilburn, 1993. The relationship between bushel weight, kernel weight, and nutrient content of commercial corn hybrids. Poultry Sci. 72(Suppl.): 127. 24. Dale, N., 1994. Relationship between bushel weight, metabolizable energy, and protein content of corn from an adverse growing season. J. Appl. Poultry Res. 3:83-86.
25. Hsu, L and J . L Sell, 1995. Nutritional value for growing turkeys of corn of light test weight. Poultry Sci. (in press). 26. Routh, J.I., 1942. Nutritional studies on powdered chicken feathers. J. Nutr. 24:39%404. 27. Wilder, O.H., P.C. Ostby, and B.R Gregory, 1955. The use of chicken feather meal in feeds. Poultry Sci. 34518-524. 28. Lillie, RJ., J . R Sizemore,and C.A Denton, 1956. Feather meal in chick nutrition. Poultry Sci. 35:316-318. 29. Naber, EC. and C.L Morgan, 1956. Feather meal and poultry meat scrap in chick starting rations. Poultry Sci. 35:888-895. 30. Sullivan, T.W. and EL Stephenson, 1957. Effect of processing methods on the utilization of hydrolyzed poultry feathers by growing chicks. Poultry Sci. 36361365. 31. Naber, EC., S.P. Touchbum, ED. Barnett, and C.L Morgan, 1961. Effect of processing methods and amino acid supplementation on dietary utilization of feather meal protein by chicks. PoultrySci.401234-1245.
32. Eggum, B.O., 1970. Evaluation of protein quality of feather meal under different treatments. Acta Agr. Scand. 20230-234.
35. Moran, ET., Jr., J.D. Summers, and SJ. Slinger, 1966. Keratin as a source of protein for the growing chick. 1.Amino acid imbalance as the cause for inferior performance of feather meal and the implication of disulfide bonding in raw feathers as the reason for poor digestibility. Poultry Sci. 45:1257-1266. 36. MacAlpine, R and CG. Payne, 1977. Hydrolyzed feather protein asa source of amino acids for broilers. Br. Poultry Sci. 18265-273. 37. Baker, D.H., RC. Blitenthal, K.P. Boebel, G.L. Czamecki, LL. Southern, and G.M. Willis, 1981. Protein-amino acid evaluation of steam-processed feather meal. Poultry Sci. 60:1865-1872. 38. Han, Y. and C.M. Parsons, 1991. Protein and amino acid quality of feather meals. Poultry Sci. 70312822. 39. Johnston, J. and C.N. Coon, 1979. The use of vaqing levels of pepsin for pepsin digestion studies with animal protein. Poultry Sci. 58:1271-1273.
40.Balloun, S., 1980. Soybean Meal in Poultry Nutrition. Amer. soybean Assn., St. Louis, MO. 41. Evans, RJ. and J.LSt. John, 1945. Estimation of the relative nutritive value of vegetable proteins by two chemical methods. J. Nutr. 30:209-215. 42. Araba, M. and N.M. Dale, 1990a. Evaluation of protein solubility as an indicator of overprocessing soybean meal. Poultry Sci. 6976433. 43. Parsons, C.M., K. Hashimoto, K.J. Wedekind, and D.H. Baker, 1991. Soybean protein solubility in potassium hydroxide: An in vitro test of in vivo protein quality. J. Anim. Sci. 69:2918-2924. 44. Femandeq S.R, Y. Zhang, and C.M. Parsons, 1993. Determination of protein solubility in oilseed meals using coomassie blue dye binding. Poultry Sci. 72:19251930.
45. Araba, M. and N.M. Dale, 1990b. Evaluation of protein solubility as an indicator or underprocessing of soybean meal. PoultIy Sci. 691749-1752. 46. Anderson-Hafermann, J.C., Y. Zhang, C.M. Parsons, and T. Hymowitz, 1992. Effect of heating on nutritional quality of conventional and kunitz trypsin inhibitor-free soybeans. Poultry Sci. 71:170&1709.
INGREDIENT QUALITY AND ITSIMPACT ON DIGESTION AND ABSORPTION IN POULTRY^^^ MICHAEL S. LILBURN Department ofAnimal Sciences, The Ohio State UniversiQ, Wooster, OH 44691 Phone: (216) 263-3992 FAX: (216) 263-3949
Primary Audience: Nutritionists
ENERGY SOURCES DIETARY FATS The source of feed grade fats, both from the perspective of origin ( i e . animal or plant) and processing (i.e. soapstock vs. restaurant grease), are the two largest determinants of overall feeding quality. Carver [l] reported that the absorption of lipid from diets containing 3% tallow was 80%, but this factor decreased to < 60% after hydrogenation. Absorption of hydrogenated tallow fatty acids further declined to approximately 40%. Ren-
1 Salaries and
I
ner and Hill [2] reported that the chain length of saturated fatty acids significantlyinfluenced utilization. In order of increasing chain length, C:12 lauric acid was absorbed significantly better (65%) than C:14 myristic acid (25%) or C:16 palmitic acid (5%). In a separate experiment, chicks did not absorb palmitic and stearic acids compared with 88% absorption for oleic acid (C 18:l). This finding indirectly supported the earlier observations [l]. The proportion of saturated and unsaturated fatty acids in an intact fat or mixture of fatty acids can also have a significant effect on overall lipid digestibility. Renner and Hill [3]
research support provided by State and Federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University. Manuscript NO. 22-96. 2 Presented at the 1995 Poultry Science Association Informal Poultry Nutrition Symposium: '!Advancements in Diet Modifcation and Digestion in Poultry. "
Symposium LILBURN reported that in hydrolyzed tallow, palmitic (30%) and stearic acids (22%) were only minimally absorbed compared with hydrolyzed lard (51%; 36%) and hydrolyzed soybean oil (84%; 78%). The concentration of unsaturated fatty acids in each of those sources was 50%, 62%, and76%, respectively. The absorption of palmitic and stearic acids from intact tallow and lard were nearly double that of their respective hydrolyzed fatty acids, whereas the difference between intact soybean oil and its hydrolyzed fatty acids were not as great. Within each fat source, the absorption of unsaturated fatty acids was not nearly as sensitive to the form of the lipid (i.e. intact vs. hydrolyzed). These findings are similar in scope to the results of Young [4]. More recently, Wiseman and Lessire [5] also found progressive increases in palmitic and stearic acid digestibility with increasing proportions of rape oil in a tallow:rape oil mixture. The synergistic effects of unsaturated fatty acids on saturated fat absorption also appear in the metabolizable energy (ME) values for individual fatty acids when compared with mixtures of different fats [4,6,7]. In some cases, the ME of a 5050 mixture of saturated and unsaturated fat sources is greater than the mean of the two fat sources alone [8]. The concentration of free fatty acids within any commercial fat source is a commonly used indicator of quality, even though some commercial sources have a high proportion of FFA (Le. acidulated soapstock). An important preliminary step in the digestion of lipids is the hydrolysis of intact triglycerides into free fatty acids and 2-monoglycerides. The monoglycerides enhance the overall solubility of mixed micelles, the form in which lipids are presented to the intestinal lining for absorption [9,10,11,12].The critical relationships between concentration and source of FFA and their effect on the ME of different commercial fats are thoroughly discussed [13, 14, 15, 161. CORN In most of the U.S., corn is either the cereal of choice or the basis for pricing other cereal grains. Within the past few years, there has been considerable interest in the nutritional quality of corn as affected by adverse growing conditions. Dry conditions are the norm in some parts of the country [17] as
79 compared with droughts (i.e. 1988), which are considered to be atypical. In either case, these types of conditionscan have a significant influence on the overall nutritivevalue of corn. The greatest change associated with dry growing conditions is an increase in crude protein [17, 181. The increases in crude protein are not accompanied by proportional increases in amino acid content, however, and commonly used amino acid prediction equations [191may overestimate the actual amino acid content [181. Another area which has been questioned over the past few years is the relationship between bushel weight of corn and energy content.A commonly cited paper [20] suggests that growing conditions which predispose corn to lower test weights at harvest will also result in lower metabolizable energy concentrations. Thevariabilityin the originaldata and the small declines in ME actually observed suggest that bushel weight and ME were not highly correlated and numerous reports since then corroborate this conclusion [21, 22, 23, 24,251.
PROTEIN SOURCES FEATHER MEAL Early studies suggested that dried, powdered feather meal, while high in crude protein, was deficient in essential amino acids [XI.Subsequent improvements in processing methods allowed for steam hydrolysis of feathers, improving the overall nutritional qualityof feather meal, although it is still only a supplemental ingredient [27, 28, 291. Sullivan and Stephenson [30] suggested that there was no relationship between processing method and the nutritional quality of feather meal, but Naber [31] reported that feather meals containing 70 to 80% pepsin-digestible protein were nutritionally superior to a sample with only 64% digestible protein. Subsequent studies confirmed the importance of processingon the overall quality of a particular feather meal [32,33, 341. Even with the best of processing conditions, however, feather meal still faces amino acid imbalance and digestibility problems [31, 34, 35, 36, 371. Lanthionine is a unique, amino acid containing sulfur formed during the course of feather meal processing [37]. Han and Parsons [38] reported that in a comparison of seven commercial samples, lanthionine concentration was significantly
JAPR INGREDIENT QUALITY
80 correlated negatively with other in vitro and in vivo assays. These authors also compared two concentrations of pepsin (0.2% and 0.002%) and found that the lower concentration was more definitive with respect to separating better from poorer quality feather meal samples. Johnston and Coon [39] had previously shown that lower levels of pepsin would increase the variation in digestibility estimates with different animal protein sources. SOYBEAN MEAL It has long been recognized that urease enzyme activity is positively correlated with trypsin inhibitor activity in soybean meal and
is an adequate measure of soybean meal underprocessing [40]. More recently, an assay which was originally described by Evans and St. John [41] has received considerable research interest relative to measuring the extent of soybean meal overprocessing. Solubility of soybean meal protein in 0.2% potassium hydroxide (KOH) has been shown to be an effective measure of soybean meal overprocessing [42, 43, 441. Araba and Dale [45] also suggested that protein solubility might also be used as another indicator of soybean meal underprocessing, but this conclusion was not supported by the data of AndersonHafermann [&].
CONCLUSIONS AND APPLICATIONS 1. The absorption of saturated fatty acids from intact animal fats is much greater than that of the hydrolyzed fatty acids from the same sources. 2. The published amino acid prediction equations [19] for corn may overestimate the actual amino acid concentrations if higher than normal protein levels are the result of an environmental stress (i.e., drought). 3. Urease activity measurement and potassium hydroxide (KOH) solubility (0.2%) are good estimates of under processing and overheating of commercial soybean meal, respectively.
REFERENCES AND NOTES 2. Renner, R and F.W. Hill, 1961a. Utilization of fatty acids by the chicken. J. Nutr. 74:25!9-264.
10. Senior, J., 1964. Intestinal absorption of fats. J. Lipid Res. 5495-521. 11. Garreti, RL and R J . Young, 1975. Effect of micelle formation on the absorption of neutral fat and fatty acids by the chicken. J. Nutr. 105:827-838.
3. Renner, R and F.W. Hill, 1961b. Factors affecting the absorbability of saturated fatty acids in the chick. J. Nutr. 74254-258.
12. Sklan, D., 1979.Digestion and absorption of lipids in chicks fed triglycerides or free fatty acids: Synthesis of monoglycerides in the intestine. Poultry Sci. 58:885-889.
4. Young, RJ., 1961.The energyvalue of fats and fatty acids for chicks. 1. Metabolizable energy. Poultry Sci. 4111225-1233.
13. Huyghebaert, G., G. De Munler, and G.De Groote, 1988.The metabolizable energy ( M E " ) of fats for broilers in relation to their chemical composition. Anim. Feed Sci. Tech. 20:45-58.
1. Carver, D.S., EE Rice, R E Gray, and P. Mone, 1955. The utilization of fats of different melting points added to broiler feed. Poultry S i . 3494-546.
5. Wiseman, J. and M. Lessire, 1987. Interactions between fats of differin chemical content: A availability of fatty acids. k r . Poultry Sci. 2 8 : 6 7 7 4 y t
6. Artman, N.R, 1964. Interactions of fats and fatty acids as energy sources for the chick. Poultry Sci. 439941004.
7. KcteLs, E and G. De Groote, 1989. Effect of ratio of unsaturated to saturated fatty acids of the dietary lipid fraction on utilization and metabolizable energy of added fats in young chicks. Poultry Sci. 681506-1512. 8. Sibbald, I.R, SJ. Slinger, and G.C. Ashton, 1960. Factors affecting the metabolizable energy content of Doultrv feeds. 2. Variabilitv in the M.E. values attributed 'to samples of tallow a n i undegummed soybean oil. PoultIy Sci. 40:303-308. 9. Hofman, AF. and B. Borgstrom, 1962. Physicochemical state of lipids in intestinal content during their digestion and absorption. Fed. Proc. 21:43-50.
14. Wiseman, J. and F. Salvador, 1991.The influence of free fatty acid content and degree of saturation on the apparent metabolizable energyvalue of fats fed to broilers. Poultry S i . 7057S582.
15. Wiseman,J., F. Salvador, and J. Craigon, 1991. Prediction of the apparent metabolizable energy content of fats fed to broiler chickens. Poultry Sci. 701527-1533. 16. Thacker, P.A., G.L. Campbell, and Y. Xu, 1994. Composition and nutritive value of acidulated fatty acids, degummed canola oils, and tallow as energy sources for starting broiler chicks. Anim. Feed Sci.Tech. 4631-260. 17. Bdock, D.G., P.L. Raynor, and S. Savage, 1989. Variation of protein and fat concentrations among commercial corn hybrids grown in the Southeastern USA. J. Prod. Agric. 2:157-161. 18. Lilburn, M.S., E.M. Ngidi, N.E. Ward, and C.Llames, 1991. The influence of severe drought on
Symposium LILBURN
81
selected nutritional characteristics of commercial corn hybrids. Poultry Sci. 70:2329-2334.
33. Wessels, J.P.H., 1972.Astudyof the protein quality of different feather meals. Poultry Sci. 51537-541.
19. National Research Council, 1994. Nutrient Requirements of Poultry. 9th Rev. Edition. Natl. Acad. Press, Washington, DC.
34. Papadopoolos, M.C., A.R El Boushy, and E H . Ketelaars, 1985. Effect of different processing conditions on amino acid digestibility of feather meal determined by chicken assay. Poultry Sci. 64:1729-1741.
20. Leeson, S. and J.D. Summers, 1976. Effect of adverse growing conditions on corn maturity and feeding value for poultry. Poultry Sci. 55:588-593. 21. Libum, M.S. and N. Dale, 1989. Characterization of two samples of corn that vary in bushel weight. Poultry Sci. 68:857-860. 22. Leeson, S., A. Yersin, and L Voker, 1993. Nutritive value of the 1992 corn crop. J. Appl. Poultry Res. 2:208-213. 23. Reed, R , J.D. Latshaw, and M.S. Lilburn, 1993. The relationship between bushel weight, kernel weight, and nutrient content of commercial corn hybrids. Poultry Sci. 72(Suppl.): 127. 24. Dale, N., 1994. Relationship between bushel weight, metabolizable energy, and protein content of corn from an adverse growing season. J. Appl. Poultry Res. 3:83-86.
25. Hsu, L and J . L Sell, 1995. Nutritional value for growing turkeys of corn of light test weight. Poultry Sci. (in press). 26. Routh, J.I., 1942. Nutritional studies on powdered chicken feathers. J. Nutr. 24:39%404. 27. Wilder, O.H., P.C. Ostby, and B.R Gregory, 1955. The use of chicken feather meal in feeds. Poultry Sci. 34518-524. 28. Lillie, RJ., J . R Sizemore,and C.A Denton, 1956. Feather meal in chick nutrition. Poultry Sci. 35:316-318. 29. Naber, EC. and C.L Morgan, 1956. Feather meal and poultry meat scrap in chick starting rations. Poultry Sci. 35:888-895. 30. Sullivan, T.W. and EL Stephenson, 1957. Effect of processing methods on the utilization of hydrolyzed poultry feathers by growing chicks. Poultry Sci. 36361365. 31. Naber, EC., S.P. Touchbum, ED. Barnett, and C.L Morgan, 1961. Effect of processing methods and amino acid supplementation on dietary utilization of feather meal protein by chicks. PoultrySci.401234-1245.
32. Eggum, B.O., 1970. Evaluation of protein quality of feather meal under different treatments. Acta Agr. Scand. 20230-234.
35. Moran, ET., Jr., J.D. Summers, and SJ. Slinger, 1966. Keratin as a source of protein for the growing chick. 1.Amino acid imbalance as the cause for inferior performance of feather meal and the implication of disulfide bonding in raw feathers as the reason for poor digestibility. Poultry Sci. 45:1257-1266. 36. MacAlpine, R and CG. Payne, 1977. Hydrolyzed feather protein asa source of amino acids for broilers. Br. Poultry Sci. 18265-273. 37. Baker, D.H., RC. Blitenthal, K.P. Boebel, G.L. Czamecki, LL. Southern, and G.M. Willis, 1981. Protein-amino acid evaluation of steam-processed feather meal. Poultry Sci. 60:1865-1872. 38. Han, Y. and C.M. Parsons, 1991. Protein and amino acid quality of feather meals. Poultry Sci. 70312822. 39. Johnston, J. and C.N. Coon, 1979. The use of vaqing levels of pepsin for pepsin digestion studies with animal protein. Poultry Sci. 58:1271-1273.
40.Balloun, S., 1980. Soybean Meal in Poultry Nutrition. Amer. soybean Assn., St. Louis, MO. 41. Evans, RJ. and J.LSt. John, 1945. Estimation of the relative nutritive value of vegetable proteins by two chemical methods. J. Nutr. 30:209-215. 42. Araba, M. and N.M. Dale, 1990a. Evaluation of protein solubility as an indicator of overprocessing soybean meal. Poultry Sci. 6976433. 43. Parsons, C.M., K. Hashimoto, K.J. Wedekind, and D.H. Baker, 1991. Soybean protein solubility in potassium hydroxide: An in vitro test of in vivo protein quality. J. Anim. Sci. 69:2918-2924. 44. Femandeq S.R, Y. Zhang, and C.M. Parsons, 1993. Determination of protein solubility in oilseed meals using coomassie blue dye binding. Poultry Sci. 72:19251930.
45. Araba, M. and N.M. Dale, 1990b. Evaluation of protein solubility as an indicator or underprocessing of soybean meal. PoultIy Sci. 691749-1752. 46. Anderson-Hafermann, J.C., Y. Zhang, C.M. Parsons, and T. Hymowitz, 1992. Effect of heating on nutritional quality of conventional and kunitz trypsin inhibitor-free soybeans. Poultry Sci. 71:170&1709.