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Amino Acids in the Production of Chicken Egg and Muscle
Amino Acids in the Production of Chicken Egg and Muscle BERTHA MUNKS, ABNER ROBINSON, ELIOT F. BEACH, AND HAROLD H. WILLIAMS Research Laboratory, Children's Fund of Michigan, Detroit 2, Michigan (Received for publication, March 1, 1945)
A
LTHOUGH vegetable proteins can be produced more cheaply and efficiently, soybean protein being outstanding in this respect, in terms of agricultural resources eggs and chicken are second only to whole milk as economical sources of animal protein for human beings (Anonymous, 1944; Harding, 1944). The protein of eggs has long been regarded as superior in nutritive quality, and recent studies have demonstrated that the proportion of essential amino acids apparently is ideal (Harding, 1944; Sumner, 1938). During the development of the embryo there is adequate material to produce such diversified proteins as muscles, organs, immune bodies, hormones, blood, and cartilaginous and keratin proteins. As Sherman (1933) has pointed out, "the nature of the nutrients in eggs is of almost as much interest and importance as their amount. The fact that when an egg is kept at a proper temperature for about three weeks without the addition of anything from without, it produces a chick so well developed as to begin at once to walk and to eat the same food as the adult, suggests that the egg must contain substances which are very efficient as sources both of the energy and the materials for growth and development." This paper is concerned with the amounts and distribution of nine amino acids in the white, yolk and membrane
of chicken egg and similar values for the skeletal muscle of chicken. The lipid distribution in the egg and muscle tissues has already been reported (Kaucher, Galbraith, Button, and Williams, 1943). Inasmuch as the food requirement of young poultry encompasses the demands for egg production as well as for growth, such data are useful in determining the most efficient feed mixture. Analyses of the tissues produced indicate both the total and the relative amounts required. This is particularly true, in poultry nutrition, of the protein requirement in terms of the essential amino acids as was stressed in a recent review (Heuser, 1941). EXPERIMENTAL
One dozen grade B eggs was weighed, boiled for 15 minutes and reweighed. The coagulated whites and yolks were separated and prepared for analysis (Beach, Munks, and Robinson, 1943). Another dozen eggs was weighed, the raw white separated from the yolks and both weighed. The yolks and whites were recombined, mixed, and poured into centrifuge bottles, which were placed in a steam bath until the material coagulated. Membranes were peeled from the shells of eggs, washed with saline until the biuret reaction of the washings was negative, air dried, and then ground into powder. The analytical procedures applied to these materials have been re459
460
BERTHA MUNKS, ABNER ROBINSON, ELIOT F. BEACH, HAROLD H. WILLIAMS
ported (Beach, Munks, and Robinson, 1943). RESULTS
Approximately 12 percent of the total egg weight was shell. Of the edible portion, 65 percent was white and 35 percent yolk. The amounts of nine amino acids in the several egg fractions and in the muscle are given in Table 1. For all of the amino acids determined, with the exception of phenylalanine, threonine and
represent the amounts and proportions of these amino acids which must be made available to produce one egg. In Table 3, the amino acid pattern of the egg proteins is compared with those of the muscle tissues. The molecular proportionality takes into account the different molecular weights of the amino acids and permits a truer comparison than percentage composition data. It is evident that the relative amino acid pattern of egg protein is quite different than that of muscle
TABLE 1.—Amino acid content of chicken egg and muscle protein Egg (Edible Portion)
Arginine Histidine Lysine Phenylalanine Tyrosine Tryptophane Threonine Cystine Methionine
Whitef
Yolkf
Totalt
5.7 1.4 4.9 6.2 4.5 1.4 4.0 1.9 6.6#
6.8 1.5 5.7 4.4 4.7 1.4 3.5 2.2 3.0#
6.4 2.0 5.2 5.8 4.8 1.4 3.9 2.2 5.2#
(values in per cent of dry protein) Muscle**
Egg§ Membrane
Light
Dark
6.7 2.6 2.8 2.6 2.0 2.5 5.2 11.2 5.4#
6.9 2.3 8.4 3.8 4.2 1.3 4.7 0.8 3.4
7.1 2.3 8.4 4.6 4.3 1.2 4.6 0.9 3.6
* Fat-extracted dry weight corrected for ash and moisture, and nitrogen content calculated to 16 percent t Averages per egg from analyses of the whites and yolks (separately) of one dozen cooked eggs, j Averages per egg from analyses of mixed whites and yolks of one dozen eggs. Average total weight, (inch shell) uncooked, 58.1 gm.; average weight, yolk+white, 51.2 gm. (protein, 5.4 gm.) § Averages per egg from analyses of composite of membranes from several dozen eggs (protein, 0.12 gm.) ** Beach, Munks and Robinson, 1943. $ Calculated as total organic sulfur less cystine sulfur.
methionine, the egg yolk protein has concentrations equal to or higher than egg white. The membrane protein contains an exceptionally high concentration of cystine (11.2 percent), but has relatively low contents of lysine, phenylalanine and tyrosine. The concentration of the amino acids in the two types of muscle protein is practically the same. In contrast to egg protein, the muscle protein is notably higher in lysine and threonine and lower in phenylalanine and the sulfur-containing amino acids—cystine and methionine. Table 2 gives the average amounts of amino acids found per egg. The data
protein. To illustrate, for each two molecules of tryptophane in the whole egg there are three molecules of cystine and four of histidine, whereas in muscle there are. one molecule of cystine and five molecules of histidine for each two molecules of tryptophane. DISCUSSION
Only recently has it been feasible to study the amino acid requirements of the chicken, which appears to have relatively complicated nutritional requirements. The fowl is extremely sensitive to inadequate amounts of some dietary factors and until provision was made for
AMINO ACIDS IN PRODUCTION OF CHICKEN EGG AND MUSCLE
these it was not possible to feed highly purified diets in which sources of protein or amino acids could be specifically defined. The determination and provision of such factors, free of protein contaminants recently has made possible extensive studies on the amino acid requirements of the chicken, by several groups of investigators (Almquist, 1942). The chicken appears unable to synthesize arginine, histidine, lysine, tryptophane, methionine, leucine, isoleucine, phenylalanine, threonine and valine. These amino acids, therefore, must be supplied by the diet. Glycine and glutamic acid are essential for good growth but can be synthesized only to a limited TABLE 2.-—Average amino acid content of one chicken egg* {values in milligrams) Edible Portion
Arginine Histidine Lysine Phenylalanine Tyrosine Tryptophane Threonine Cystine Methionine
White
Yolk •
Total
Egg Membrane
169 42 145 184 133 42 119 56 196
168 37 141 108 116 34 86 54 74
344 108 280 312 258 75 210 118 280
8 3 3 3 2 3 6 14 6
* See footnotes to Table I.
extent. Tryosine and cystine are not essential in the diet if sufficient amounts of phenylalanine and methionine are present. However, tyrosine and cystine can spare parts of the requirements for phenylalanine and methionine, respec* Mol.wt. of phenylalanine: mol. wt. of tyrosine 165.09 : 181.09 x=237 237+315 = 552 t 2Xmol. wt. of methionine: mol. wt. of cystine 2X 149.15 : 240.23 x=?164 164+286=450
461
tively, and therefore can be considered to be only semi-dispensable (Almquist, 1942; Almquist, 1944). From the analyses reported in this paper it is possible to estimate the quantitative dietary requirements of certain amino acids for egg production and also for growth. The amino acids herein determined represent all but three (leucine, isoleucine and valine) of the indispensable amino acids required by the chicken. To produce one egg (Table 2) the hen requires in her diet the following minimums of amino acids: arginine, 352 mg.; histidine, 111 mg.; lysine, 283 mg.; tryptophane, 78 mg.; threonine, 216 mg.; phenylalanine, 315 mg., methionine, 286 mg.; tyrosine, 260 mg.; and cystine, 132 mg. If tyrosine was not present in the diet the requirement could be met by an addition 237mg. of phenylalanine* (total 552 mg.) and a diet in which cystine was not present would fill the need for that amino acid if it contained an additional 164 mg. of methionine f (total 450 mg.). It is evident that for very good egg production—200 eggs or more per year (Titus, 1939), considerable quantities of high quality protein must be provided for the laying hen. The usual practice has been to feed a diet containing 15 to 20 percent high quality protein, of which not less than 20 percent comes from such animal sources as liquid skim milk, liquid buttermilk, dried skim milk, dried buttermilk, meat scrap, or fish meal (Titus, 1939). These animal proteins are expensive ingredients of the poultry ration but are fed to insure sufficient in:: gms. of phenylalanine : gms. of tyrosine :: x : 260 :: gms. of methionine : gms. cystine :: x : 132
462
BERTHA MUNKS, ABNER ROBINSON, ELIOT F. BEACH, HAROLD H. WILLIAMS
take of the indispensable amino acids. With the knowledge of the amino acid requirements for egg production it will be possible, as knowledge of the amino acid composition of various inexpensive sources of vegetable proteins becomes available, to substitute proteins in the poultry ration and insure the most economical feeding of the required amino
peculiarly characterized by the increase in the protein content of its body. Since protean is the most valuable constituent of meat, it can readily be seen that the growth of animals—especially of cattle, swine, sheep, and poultry-—is the basis of meat production." From data available (Hawkins, and Titus, 1939) on the chemical composition
TABLE 3.—Molecular proportions of amino acids in proteins of chicken egg and muscle* {ratio with respect to tryptophane) Egg (Edible Portion)
Arginine Histidine Lysine Phenylalanine Tyrosine Tryptophane Threonine Cystine Methionine
White
Yolk
Total
Egg Membrane
9.6 2.6 9.8 11.0 7.3 2.0 9.9 2.3 13.0
11.5 2.8 11.5 7.8 7.6 2.0 8.6 2.7 5.9
10.5 3.8 10.5 10.3 7.8 2.0 9.6 2.7 10.2
6.3 2.8 3.1 2.6 1.8 2.0 7.1 7.6 5.9
Muscle Light
Dark
12.4 4.6 18.0 7.2 7.2 2.0 12.3 1.0 7.1
13.8 5.0 19.5 9.4 8.0 2.0 13.1 1.2 8.2
* See footnotes to Table I.
acids for the highest egg production efficiency. The analyses of muscle tissue indicate amino acid requirements for growth different from those for egg production (Table 3). The higher contents of arginine, histidine, lysine and threonine in chicken muscle, over those of the egg, indicate a relatively greater need for these amino acids during the period of muscle formation, or growth. The needs for glysine and cystine for feather formation are high during growth and thereafter for maintenance, since feather replacement is a continuing requirement. Hawkins and Titus (1939) have pointed out: "From the standpoint of animal nutrition, growth is essentially a storage of protein. It is true that other substances are stored simultaneously, and that water is stored in even greater quantity than is protein: nevertheless, the growth of an animal is
of the empty body of poultry and the analyses given herein, it is possible to estimate the amino acid requirements for a given growth weight of poultry. On the average, a chicken with an empty body weight of 1 kilogram (2.2 pounds) would be 20 percent protein, or 200 grams. A bird with an empty body weight of 2.5 kilograms (5.5 pounds) would be approximately 22 percent protein, or 550 grams. To produce 200 grams of body protein on the basis of the figures in Table 2 would require a minumum of 14 grams of arginine, 4.6 grams of histidine and 16.8 grams of lysine in the diet. Thus, to increase the empty weight of the chicken two and one-half times would require almost three times as much of these amino acids. The importance of such values lies in the fact that as the requirements for growth are defined in more precise terms,
AMINO ACIDS IN PRODUCTION or CHICKEN EGG AND MUSCLE
it is possible to feed animals more economically and efficiently. It has been shown that the greatest relative average efficiency of the utilization of feed for growth in chickens occurs when the total food consumed contains 20 to 21 percent protein (Titus, 1939). This varies with the biological value of the protein and would be less the higher the protein quality or the more efficient the protein in supplying the indispensable amino acids. Since protein is one of the most, if not the most, expensive components of the ration, it is of great economic importance to formulate rations from cheap vegetable proteins. This may be possible with knowledge of the amino acid requirements for growth and production and knowledge of the amino acid content of various protein sources. The function of the egg is the production of a new and viable organism, for which it contains the necessary materials. The relationship between the primary chemical constituents of the egg may have a different significance, therefore, than that between similar constituents of body tissues such as muscle and organs where functional capacity and purpose are interdependent. For example, the quantity of fat and protein in the chicken egg appears to be very constant (Cruickshank, 1941), whereas the fat content of a tissue like muscle may be quite variable (Kaucher, Galbraith, Button, and Williams, 1943). Furthermore, the amount of fat in the egg appears to be characteristic of the species, being highest for the egg of the chicken as compared to lower values for reptiles, frogs and fish (Needham, 1931). The protein to fat ratio of the chicken egg is approximately 1; other species lower in the evolutionary scale have more protein in proportion to fat in their eggs and protein to fat ratios of 2 to 10 or greater. A low protein to fat ratio in the egg, which
463
reflects a high fat content, appears to have been successfully accomplished only by the birds, although the reptiles show an approximation to this achievement, which may indicate a particular character associated with terrestrial eggs (Needham, 1931). As has been suggested (Needham, 1931), the small egg, such as that of the fishes, starts its development rapidly and in a matter of hours gives rise to a free-swimming larva, capable of independent existence, with digestive and nervous systems already formed. But from this time on development proceeds very slowly because, containing only scanty supplies of nourishment within itself, much of its energies must be devoted to hunting for and digesting food. In contrast, the large egg of the chicken shows very little development in the first few days, but in the later stages it develops more rapidly and attains adult form in much shorter time because the chick embryo has an abundant food supply within the egg, and having no occasion to spend its time searching for food, can devote its total energies to further development. The importance of the high fat content of the chicken egg is further borne out by a comparison of the sources of energy used by the developing embryos of different species. For example, it has been shown that the main source of energy in the chicken egg combusted during em-> bryonic development is fat. However, other embryos do not use fat to the sameextent. The developing chick embryo utilizes, in terms of total material burnt, about 3 percent carbohydrate, 6 percent protein and 91 percent fat, whereas the frog embryo utilizes 7 percent carbohydrate, 71 percent protein, and 22 percent fat (Needham, 1931). This difference appears to be associated with the difference between terrestrial and aquatic forms
464
BERTHA MTJNKS, ABNER ROBINSON, ELIOT F. BEACH, HAROLD H. WILLIAMS
and leads to the generalization that "aquatic embryos use a great deal of protein during their ontogeny, but terrestrial ones are sparing of it" (Needham, 1931). It appears to be very significant that as animals became more complicated and adaptable to varied surroundings, that is, higher in the taxonomic scale, they loaded their eggs to a greater extent with fat and, the chicken being an outstanding example of complexity and adaptability in evolutionary evolvement among egg producers, has been most successful in doing this. It appears likely, therefore, that most of the fatty materials of the egg used for energy by the developing chick embryo arise from the neutral fat or "nonessential" lipid portion. In the case of the egg, however, this fraction should probably not be designated by the latter term as has been done in the case of the lipids of muscles or other body tissues (Kaucher, Galbraith, Button, and Williams, 1943). For, although the ultimate disposal of the neutral fat fraction may be similar in the egg to that of muscle, that is, as a source of energy, unlike the cellular lipids (phospholipid, cholesterol and cerebroside) which are a relatively constant fraction characteristic of a tissue, the neutral fat fraction of muscle or other body tissues is variable depending on the nutritive state of the animal, whereas in the egg it is relatively constant in quantity and thus may be considered of equal biological significance to the cellular type lipids. Thus, it seems that most of the amino acids in the egg are utilized as structural material, being incorporated directly into
the newly-formed, diversified tissue proteins of the chick, and not wasted in supplying the energy demands of the developing embryo. REFERENCES
Almquist, H. J., 1942. The amino acid requirements and protein metabolism of the avian organism. Federation Proceedings 1: 269-273. Almquist, H. J., and C. R. Grau, 1944. The amino acid requirements of the chick. J. Nutrition 28: 325-331. Anonymous, 1944. Relations between feed, livestock, and food. Nutrition Rev. 2: 51-54. Beach, Eliot F., Bertha Munk's and Abner Robinson, 1943. The amino acid composition of animal tissue protein. J. Biol. Chem. 148:431-439. Block, Richard J., 1944. Nutritional opportunities with amino acids. J. Amer. Dietet. Assoc. 20: 69-76. Cruickshank, Ethel M., 1941. The effect of diet on the chemical composition, nutritive value and hafchability of the egg. Nutrition Abstr. Rev. 10: 645-659. Harding, T. S., 1944. Foraging for food nutrients. J. Amer. Dietet. Assoc. 20: 544-546. Hawkins, O. G., and Harry W. Titus, 1939. Growth, fattening, and meat production. Food and Life, Yearbook of Agric, pp. 450-468. Heiiser, G. F., 1941. Protein in poultry nutrition—a review. Poultry Sci. 20: 362-368. Kaucher, Mildred, Harry Galbraith, Virginia Button and Harold H. Williams, 1943. The distribu-' tion of lipids in animal tissues. Archiv. Biochem. 3: 203-215. Needham, Joseph, 1931. Chemical embryology. Vol. 3. The Macmillan Co., New York. Sherman, Henry C , 1933. Food products. Third edition The Macmillan Co., New York, pp. 176— 177. Sumner, Emma E., 1938. The biological value of milk and egg protein in young and mature rats. J. Nutrition 16: 129-139. Sumner, Emma E., and J. R. Murhn, 1938. The biological value of milk and egg protein in human subjects. J. Nutrition 16:141-152. Titus, Harry W., 1939. Practical nutritive requirements of poultry. Food and Life, Yearbook of Agric. pp. 787-818.
A
LTHOUGH vegetable proteins can be produced more cheaply and efficiently, soybean protein being outstanding in this respect, in terms of agricultural resources eggs and chicken are second only to whole milk as economical sources of animal protein for human beings (Anonymous, 1944; Harding, 1944). The protein of eggs has long been regarded as superior in nutritive quality, and recent studies have demonstrated that the proportion of essential amino acids apparently is ideal (Harding, 1944; Sumner, 1938). During the development of the embryo there is adequate material to produce such diversified proteins as muscles, organs, immune bodies, hormones, blood, and cartilaginous and keratin proteins. As Sherman (1933) has pointed out, "the nature of the nutrients in eggs is of almost as much interest and importance as their amount. The fact that when an egg is kept at a proper temperature for about three weeks without the addition of anything from without, it produces a chick so well developed as to begin at once to walk and to eat the same food as the adult, suggests that the egg must contain substances which are very efficient as sources both of the energy and the materials for growth and development." This paper is concerned with the amounts and distribution of nine amino acids in the white, yolk and membrane
of chicken egg and similar values for the skeletal muscle of chicken. The lipid distribution in the egg and muscle tissues has already been reported (Kaucher, Galbraith, Button, and Williams, 1943). Inasmuch as the food requirement of young poultry encompasses the demands for egg production as well as for growth, such data are useful in determining the most efficient feed mixture. Analyses of the tissues produced indicate both the total and the relative amounts required. This is particularly true, in poultry nutrition, of the protein requirement in terms of the essential amino acids as was stressed in a recent review (Heuser, 1941). EXPERIMENTAL
One dozen grade B eggs was weighed, boiled for 15 minutes and reweighed. The coagulated whites and yolks were separated and prepared for analysis (Beach, Munks, and Robinson, 1943). Another dozen eggs was weighed, the raw white separated from the yolks and both weighed. The yolks and whites were recombined, mixed, and poured into centrifuge bottles, which were placed in a steam bath until the material coagulated. Membranes were peeled from the shells of eggs, washed with saline until the biuret reaction of the washings was negative, air dried, and then ground into powder. The analytical procedures applied to these materials have been re459
460
BERTHA MUNKS, ABNER ROBINSON, ELIOT F. BEACH, HAROLD H. WILLIAMS
ported (Beach, Munks, and Robinson, 1943). RESULTS
Approximately 12 percent of the total egg weight was shell. Of the edible portion, 65 percent was white and 35 percent yolk. The amounts of nine amino acids in the several egg fractions and in the muscle are given in Table 1. For all of the amino acids determined, with the exception of phenylalanine, threonine and
represent the amounts and proportions of these amino acids which must be made available to produce one egg. In Table 3, the amino acid pattern of the egg proteins is compared with those of the muscle tissues. The molecular proportionality takes into account the different molecular weights of the amino acids and permits a truer comparison than percentage composition data. It is evident that the relative amino acid pattern of egg protein is quite different than that of muscle
TABLE 1.—Amino acid content of chicken egg and muscle protein Egg (Edible Portion)
Arginine Histidine Lysine Phenylalanine Tyrosine Tryptophane Threonine Cystine Methionine
Whitef
Yolkf
Totalt
5.7 1.4 4.9 6.2 4.5 1.4 4.0 1.9 6.6#
6.8 1.5 5.7 4.4 4.7 1.4 3.5 2.2 3.0#
6.4 2.0 5.2 5.8 4.8 1.4 3.9 2.2 5.2#
(values in per cent of dry protein) Muscle**
Egg§ Membrane
Light
Dark
6.7 2.6 2.8 2.6 2.0 2.5 5.2 11.2 5.4#
6.9 2.3 8.4 3.8 4.2 1.3 4.7 0.8 3.4
7.1 2.3 8.4 4.6 4.3 1.2 4.6 0.9 3.6
* Fat-extracted dry weight corrected for ash and moisture, and nitrogen content calculated to 16 percent t Averages per egg from analyses of the whites and yolks (separately) of one dozen cooked eggs, j Averages per egg from analyses of mixed whites and yolks of one dozen eggs. Average total weight, (inch shell) uncooked, 58.1 gm.; average weight, yolk+white, 51.2 gm. (protein, 5.4 gm.) § Averages per egg from analyses of composite of membranes from several dozen eggs (protein, 0.12 gm.) ** Beach, Munks and Robinson, 1943. $ Calculated as total organic sulfur less cystine sulfur.
methionine, the egg yolk protein has concentrations equal to or higher than egg white. The membrane protein contains an exceptionally high concentration of cystine (11.2 percent), but has relatively low contents of lysine, phenylalanine and tyrosine. The concentration of the amino acids in the two types of muscle protein is practically the same. In contrast to egg protein, the muscle protein is notably higher in lysine and threonine and lower in phenylalanine and the sulfur-containing amino acids—cystine and methionine. Table 2 gives the average amounts of amino acids found per egg. The data
protein. To illustrate, for each two molecules of tryptophane in the whole egg there are three molecules of cystine and four of histidine, whereas in muscle there are. one molecule of cystine and five molecules of histidine for each two molecules of tryptophane. DISCUSSION
Only recently has it been feasible to study the amino acid requirements of the chicken, which appears to have relatively complicated nutritional requirements. The fowl is extremely sensitive to inadequate amounts of some dietary factors and until provision was made for
AMINO ACIDS IN PRODUCTION OF CHICKEN EGG AND MUSCLE
these it was not possible to feed highly purified diets in which sources of protein or amino acids could be specifically defined. The determination and provision of such factors, free of protein contaminants recently has made possible extensive studies on the amino acid requirements of the chicken, by several groups of investigators (Almquist, 1942). The chicken appears unable to synthesize arginine, histidine, lysine, tryptophane, methionine, leucine, isoleucine, phenylalanine, threonine and valine. These amino acids, therefore, must be supplied by the diet. Glycine and glutamic acid are essential for good growth but can be synthesized only to a limited TABLE 2.-—Average amino acid content of one chicken egg* {values in milligrams) Edible Portion
Arginine Histidine Lysine Phenylalanine Tyrosine Tryptophane Threonine Cystine Methionine
White
Yolk •
Total
Egg Membrane
169 42 145 184 133 42 119 56 196
168 37 141 108 116 34 86 54 74
344 108 280 312 258 75 210 118 280
8 3 3 3 2 3 6 14 6
* See footnotes to Table I.
extent. Tryosine and cystine are not essential in the diet if sufficient amounts of phenylalanine and methionine are present. However, tyrosine and cystine can spare parts of the requirements for phenylalanine and methionine, respec* Mol.wt. of phenylalanine: mol. wt. of tyrosine 165.09 : 181.09 x=237 237+315 = 552 t 2Xmol. wt. of methionine: mol. wt. of cystine 2X 149.15 : 240.23 x=?164 164+286=450
461
tively, and therefore can be considered to be only semi-dispensable (Almquist, 1942; Almquist, 1944). From the analyses reported in this paper it is possible to estimate the quantitative dietary requirements of certain amino acids for egg production and also for growth. The amino acids herein determined represent all but three (leucine, isoleucine and valine) of the indispensable amino acids required by the chicken. To produce one egg (Table 2) the hen requires in her diet the following minimums of amino acids: arginine, 352 mg.; histidine, 111 mg.; lysine, 283 mg.; tryptophane, 78 mg.; threonine, 216 mg.; phenylalanine, 315 mg., methionine, 286 mg.; tyrosine, 260 mg.; and cystine, 132 mg. If tyrosine was not present in the diet the requirement could be met by an addition 237mg. of phenylalanine* (total 552 mg.) and a diet in which cystine was not present would fill the need for that amino acid if it contained an additional 164 mg. of methionine f (total 450 mg.). It is evident that for very good egg production—200 eggs or more per year (Titus, 1939), considerable quantities of high quality protein must be provided for the laying hen. The usual practice has been to feed a diet containing 15 to 20 percent high quality protein, of which not less than 20 percent comes from such animal sources as liquid skim milk, liquid buttermilk, dried skim milk, dried buttermilk, meat scrap, or fish meal (Titus, 1939). These animal proteins are expensive ingredients of the poultry ration but are fed to insure sufficient in:: gms. of phenylalanine : gms. of tyrosine :: x : 260 :: gms. of methionine : gms. cystine :: x : 132
462
BERTHA MUNKS, ABNER ROBINSON, ELIOT F. BEACH, HAROLD H. WILLIAMS
take of the indispensable amino acids. With the knowledge of the amino acid requirements for egg production it will be possible, as knowledge of the amino acid composition of various inexpensive sources of vegetable proteins becomes available, to substitute proteins in the poultry ration and insure the most economical feeding of the required amino
peculiarly characterized by the increase in the protein content of its body. Since protean is the most valuable constituent of meat, it can readily be seen that the growth of animals—especially of cattle, swine, sheep, and poultry-—is the basis of meat production." From data available (Hawkins, and Titus, 1939) on the chemical composition
TABLE 3.—Molecular proportions of amino acids in proteins of chicken egg and muscle* {ratio with respect to tryptophane) Egg (Edible Portion)
Arginine Histidine Lysine Phenylalanine Tyrosine Tryptophane Threonine Cystine Methionine
White
Yolk
Total
Egg Membrane
9.6 2.6 9.8 11.0 7.3 2.0 9.9 2.3 13.0
11.5 2.8 11.5 7.8 7.6 2.0 8.6 2.7 5.9
10.5 3.8 10.5 10.3 7.8 2.0 9.6 2.7 10.2
6.3 2.8 3.1 2.6 1.8 2.0 7.1 7.6 5.9
Muscle Light
Dark
12.4 4.6 18.0 7.2 7.2 2.0 12.3 1.0 7.1
13.8 5.0 19.5 9.4 8.0 2.0 13.1 1.2 8.2
* See footnotes to Table I.
acids for the highest egg production efficiency. The analyses of muscle tissue indicate amino acid requirements for growth different from those for egg production (Table 3). The higher contents of arginine, histidine, lysine and threonine in chicken muscle, over those of the egg, indicate a relatively greater need for these amino acids during the period of muscle formation, or growth. The needs for glysine and cystine for feather formation are high during growth and thereafter for maintenance, since feather replacement is a continuing requirement. Hawkins and Titus (1939) have pointed out: "From the standpoint of animal nutrition, growth is essentially a storage of protein. It is true that other substances are stored simultaneously, and that water is stored in even greater quantity than is protein: nevertheless, the growth of an animal is
of the empty body of poultry and the analyses given herein, it is possible to estimate the amino acid requirements for a given growth weight of poultry. On the average, a chicken with an empty body weight of 1 kilogram (2.2 pounds) would be 20 percent protein, or 200 grams. A bird with an empty body weight of 2.5 kilograms (5.5 pounds) would be approximately 22 percent protein, or 550 grams. To produce 200 grams of body protein on the basis of the figures in Table 2 would require a minumum of 14 grams of arginine, 4.6 grams of histidine and 16.8 grams of lysine in the diet. Thus, to increase the empty weight of the chicken two and one-half times would require almost three times as much of these amino acids. The importance of such values lies in the fact that as the requirements for growth are defined in more precise terms,
AMINO ACIDS IN PRODUCTION or CHICKEN EGG AND MUSCLE
it is possible to feed animals more economically and efficiently. It has been shown that the greatest relative average efficiency of the utilization of feed for growth in chickens occurs when the total food consumed contains 20 to 21 percent protein (Titus, 1939). This varies with the biological value of the protein and would be less the higher the protein quality or the more efficient the protein in supplying the indispensable amino acids. Since protein is one of the most, if not the most, expensive components of the ration, it is of great economic importance to formulate rations from cheap vegetable proteins. This may be possible with knowledge of the amino acid requirements for growth and production and knowledge of the amino acid content of various protein sources. The function of the egg is the production of a new and viable organism, for which it contains the necessary materials. The relationship between the primary chemical constituents of the egg may have a different significance, therefore, than that between similar constituents of body tissues such as muscle and organs where functional capacity and purpose are interdependent. For example, the quantity of fat and protein in the chicken egg appears to be very constant (Cruickshank, 1941), whereas the fat content of a tissue like muscle may be quite variable (Kaucher, Galbraith, Button, and Williams, 1943). Furthermore, the amount of fat in the egg appears to be characteristic of the species, being highest for the egg of the chicken as compared to lower values for reptiles, frogs and fish (Needham, 1931). The protein to fat ratio of the chicken egg is approximately 1; other species lower in the evolutionary scale have more protein in proportion to fat in their eggs and protein to fat ratios of 2 to 10 or greater. A low protein to fat ratio in the egg, which
463
reflects a high fat content, appears to have been successfully accomplished only by the birds, although the reptiles show an approximation to this achievement, which may indicate a particular character associated with terrestrial eggs (Needham, 1931). As has been suggested (Needham, 1931), the small egg, such as that of the fishes, starts its development rapidly and in a matter of hours gives rise to a free-swimming larva, capable of independent existence, with digestive and nervous systems already formed. But from this time on development proceeds very slowly because, containing only scanty supplies of nourishment within itself, much of its energies must be devoted to hunting for and digesting food. In contrast, the large egg of the chicken shows very little development in the first few days, but in the later stages it develops more rapidly and attains adult form in much shorter time because the chick embryo has an abundant food supply within the egg, and having no occasion to spend its time searching for food, can devote its total energies to further development. The importance of the high fat content of the chicken egg is further borne out by a comparison of the sources of energy used by the developing embryos of different species. For example, it has been shown that the main source of energy in the chicken egg combusted during em-> bryonic development is fat. However, other embryos do not use fat to the sameextent. The developing chick embryo utilizes, in terms of total material burnt, about 3 percent carbohydrate, 6 percent protein and 91 percent fat, whereas the frog embryo utilizes 7 percent carbohydrate, 71 percent protein, and 22 percent fat (Needham, 1931). This difference appears to be associated with the difference between terrestrial and aquatic forms
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BERTHA MTJNKS, ABNER ROBINSON, ELIOT F. BEACH, HAROLD H. WILLIAMS
and leads to the generalization that "aquatic embryos use a great deal of protein during their ontogeny, but terrestrial ones are sparing of it" (Needham, 1931). It appears to be very significant that as animals became more complicated and adaptable to varied surroundings, that is, higher in the taxonomic scale, they loaded their eggs to a greater extent with fat and, the chicken being an outstanding example of complexity and adaptability in evolutionary evolvement among egg producers, has been most successful in doing this. It appears likely, therefore, that most of the fatty materials of the egg used for energy by the developing chick embryo arise from the neutral fat or "nonessential" lipid portion. In the case of the egg, however, this fraction should probably not be designated by the latter term as has been done in the case of the lipids of muscles or other body tissues (Kaucher, Galbraith, Button, and Williams, 1943). For, although the ultimate disposal of the neutral fat fraction may be similar in the egg to that of muscle, that is, as a source of energy, unlike the cellular lipids (phospholipid, cholesterol and cerebroside) which are a relatively constant fraction characteristic of a tissue, the neutral fat fraction of muscle or other body tissues is variable depending on the nutritive state of the animal, whereas in the egg it is relatively constant in quantity and thus may be considered of equal biological significance to the cellular type lipids. Thus, it seems that most of the amino acids in the egg are utilized as structural material, being incorporated directly into
the newly-formed, diversified tissue proteins of the chick, and not wasted in supplying the energy demands of the developing embryo. REFERENCES
Almquist, H. J., 1942. The amino acid requirements and protein metabolism of the avian organism. Federation Proceedings 1: 269-273. Almquist, H. J., and C. R. Grau, 1944. The amino acid requirements of the chick. J. Nutrition 28: 325-331. Anonymous, 1944. Relations between feed, livestock, and food. Nutrition Rev. 2: 51-54. Beach, Eliot F., Bertha Munk's and Abner Robinson, 1943. The amino acid composition of animal tissue protein. J. Biol. Chem. 148:431-439. Block, Richard J., 1944. Nutritional opportunities with amino acids. J. Amer. Dietet. Assoc. 20: 69-76. Cruickshank, Ethel M., 1941. The effect of diet on the chemical composition, nutritive value and hafchability of the egg. Nutrition Abstr. Rev. 10: 645-659. Harding, T. S., 1944. Foraging for food nutrients. J. Amer. Dietet. Assoc. 20: 544-546. Hawkins, O. G., and Harry W. Titus, 1939. Growth, fattening, and meat production. Food and Life, Yearbook of Agric, pp. 450-468. Heiiser, G. F., 1941. Protein in poultry nutrition—a review. Poultry Sci. 20: 362-368. Kaucher, Mildred, Harry Galbraith, Virginia Button and Harold H. Williams, 1943. The distribu-' tion of lipids in animal tissues. Archiv. Biochem. 3: 203-215. Needham, Joseph, 1931. Chemical embryology. Vol. 3. The Macmillan Co., New York. Sherman, Henry C , 1933. Food products. Third edition The Macmillan Co., New York, pp. 176— 177. Sumner, Emma E., 1938. The biological value of milk and egg protein in young and mature rats. J. Nutrition 16: 129-139. Sumner, Emma E., and J. R. Murhn, 1938. The biological value of milk and egg protein in human subjects. J. Nutrition 16:141-152. Titus, Harry W., 1939. Practical nutritive requirements of poultry. Food and Life, Yearbook of Agric. pp. 787-818.