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A Deficiency of Available Choline in Soybean Oil and Soybean Oil Meal*†
A Deficiency of Available Choline in Soybean Oil and Soybean Oil Meal*1" E. P. BEERY, C. W. CAREICK, ROY E. "ROBERTS, AND S. M. HAUGE Departments of Poultry Husbandry and Agricultural Chemistry, Purdue University Agricultural Experiment Station, Lafayette, Indiana (Received for publication May 17, 1943)
EXPERIMENTAL Two trials were conducted to ascertain * Journal Paper No. 104 of the Purdue University Agricultural Experiment Station. t This investigation was supported in part by a grant from The Borden Company.
the supplementary choline value of soybean oils from both the expeller and the solvent processes upon expeller and solvent processed soybean oil meal. Through the kind cooperation of one of the large soybean oil meal producing plants, a uniform sample of soybeans was divided into two lots. One lot was solvent processed and the other was expeller processed. The methods used by the company for processing commercial soybean oil meal were followed. The percentage protein, fat, and moisture were, respectively, for the solvent meal 45.52, 0.63, and 11.11, and for the expeller meal 45.46, 4.33, and 9.37. Barred Plymouth Rock day-old chicks were used in each trial. The chicks were kept on wire-floored brooder tables as described by Carrick (1925). At the beginning of each trial, the chicks were distributed into lots on the basis of weight. At four weeks, each lot was reduced to 25 by keeping the median weight chick and 12 chicks on each side of the median weight chick. Individual weights were taken at twoweek intervals. The all-mash rations were fed ad libitum, and water was available at all times. These two trials were started in September and with chicks from the same hatch. A method described by Quinn and Knox (1939) was used in sexing the chicks. The male chicks were used in trial 1, and the female chicks were used in trial 2. Trial 1. This trial was designed to study the availability of choline in expeller and
[442]
Downloaded from http://ps.oxfordjournals.org/ at Swinburne University of Technology on July 8, 2015
J
UKES (1940a, b) found 25 to 40 percent of soybean oil meal to be a satisfactory source of choline for the prevention of perosis. The amount of total choline in soybean oil meal as given by Engel (1942) is sufficient to satisfy the chick's requirement for choline, if the total choline were available. Berry £t al. (1943) have presented data indicating the lack of an adequate amount of available choline for rapid growth in rations containing approximately one-third soybean oil meal. In studies on whey solubles, choline was the limiting factor in the rations used. Jukes (1942) used expeller processed soybean oil meal. Communication with the processor indicates that the soybean oil settlings or "foots" were added back to the meal at the time that Jukes obtained his meal. The settlings from soybean oil are known to be rich in lecithin, from which choline is derived (Record and Bethke, 1942). Therefore, it seemed advisable to try a diet containing crude soybean oil as a source of choline. The efficient utilization of fats in soybean oil was demonstrated by Whitson et al. (1943), who used rations containing as much as 20 percent of soybean oil in which 94 percent of the fat was utilized.
DEFICIENCY OF AVAILABLE CHOLINE IN SOYBEAN OIL MEAL
-Comparison of expeller and solvent soybean oils in rations containing expeller soybean oil meal {trial 1, males)
Ingredient
Lotl
Lot 2
Lot 3
Lot 4
Lot 5
Lot 6*
Ground yellow corn
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
3
3
3
3
3
3
4
4
4
4
4
4
34.5
34.5
34.5
34.5
4
4
Whey solubles (dry basis) Ground limestone Salt mixture 1 400-D oil Riboflavin concentrate" Nicotinic acid Expeller soybean oil meal Solvent soybean oil meal Solvent soybean oil Refined corn oil Choline chloride Total
Av. wt. six weeks (grams) f. . . . Standard deviation Coefficient of variation Grams feed per gram of gain... Number of chicks at six weeks..
s
34.5 4
34.5 4
4 100.00
4 100.00 6
100.00
100.00
100.00
100.00
20.22
20.22
20.22
20.22
20.22
20.22
219 89 41 4.70 24
371 122 33 3.08 25
221 68 31 3.95 24
242 58 24 5.15 21
246 106 43 3.58 19
204 71 35 5.28 18
* Ration modified as described in text at three weeks. 11 values between lots are: 1 and 2, 5.02; 1 and 3, 0.07: 1 and 4,1.06; 1 and 5, 0.90; 1 and 6, 0.62; 3 and 4, 11.16. 950 grams iodized salt, 50 grams MnSCU. 2 280 micrograms riboflavin per gram of concentrate. 3 30 mg. nicotinic acid per 100 grams of feed. 4 1.95 mg. calcium pantothenate per 100 grams of feed. 6 150 mg. choline chloride per 100 grams of feed.
Downloaded from http://ps.oxfordjournals.org/ at Swinburne University of Technology on July 8, 2015
ciency of available choline in lot 1. Four percent of expeller soybean oil was used in lot 3 to replace the refined corn oil in the basal ration. The result from lot 3 indicates that expeller soybean oil failed to contribute enough available choline to increase growth over lot 1. The addition of choline chloride to a ration containing expeller soybean oil meal and expeller soybean oil (lot 4) increased growth slightly, but not significantly over lots 1 and 2. The lack of a significant difference between lots 3 and 4 is incompatible with results in trial 2 where solvent soybean oil meal was involved. When 4 percent of solvent soybean oil was included in the ration (lot S) there was no significant increase in growth over the
solvent processed soybean oil used in rations containing expeller processed soybean oil meal. Thirty-one chicks were started in each lot. Rations, with the results from the male chicks, are shown in Table 1. The fat content of rations not containing soybean oil was equilibrated by using refined corn oil. A ration which had previously been proved deficient in available choline (Berry et al., 1943) was modified by including 4 percent refined corn oil to form the negative control (lot 1). For lot 2, ISO milligrams of choline chloride per 100 grams of feed were added to the negative control ration. The increased growth resulting when choline chloride was added was highly significant, indicating a defiTABLE 1.
443
444
E. P. BERRY, C. W. CARRICK, ROY E. ROBERTS, AND S. M. HAUGE
TABLE 2.—Comparison of expeller and solvent soybean oils in rations containing solvent soybean oil meal {trial 2, females) Ingredient
Whey solubles (dry basis) Ground limestone 400-D oil Riboflavin concentrate 2 Calcium pantothenate Solvent soybean oil meal
Lot 7
Lot 8
Lot 9
Lot 10
Lot 11
Lot 12
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
3 4
3 4
3 4
3 4
3 4
4
34.5
34.5
34.5
Expeller soybean oil
34.5 4
Total Percentage protein Av. wt. six weeks ( g r a m s ) * . . . . Standard deviation Grams feed per gram of gain... Number of chicks at six weeks..
. 34.5
3
34.5
4 4
4
4 5
100.00
4 100.00
100.00
100.00
100.00
100.00
20.22
20.22
20.22
20.22
20.22
20.22
172 45 26 5.81 23
5
270 97 36 4.27 24
169 45 27 5.95 23
266 65 24 3.47 24
179 52 29 4.91 23
222 42 19 4.16 25
Vitamin additions same as in Trial 1. * t values between lots are: 7 and 8, 4.6; 7 and 9, 0.20; 7 and 10, 5.98; 7 and 11, 0.54; 7 and 12, 4.05;9 and 10, 5.97.
Downloaded from http://ps.oxfordjournals.org/ at Swinburne University of Technology on July 8, 2015
negative control (lot 1), thus indicating rations containing solvent processed soythat solvent soybean oil did not contribute bean oil meal. Forty-three chicks were sufficient available choline for a growth started in each lot. The rations, with the difference. After the two-week weights were results from the female chicks, are given obtained, it was evident that the solvent in Table 2. soybean oil meal negative control (lot 6) Lot 7 served as a negative control, defiwas showing a choline deficiency, so far as cient in available choline. When ISO milligrowth was concerned. grams of choline chloride per 100 grams of Since it seemed desirable to test wheat feed were added (lot 8), the growth increase and wheat by-products for choline value, over lot 7 was highly significant. When 4 at three weeks the ration fed to lot 6 was percent of solvent soybean oil (lot 9) rechanged so that expeller soybean oil meal placed the refined corn oil of the negative replaced the solvent soybean oil meal, and control, the growth remained the same as 20 percent of ground wheat, 5 percent of that from lot 7, indicating that solvent soywheat bran, and 5 percent of wheat mid- bean oil did not contain an adequate dlings were included. This modified ration amount of available choline to increase failed to improve the growth, probably in- growth. The addition of choline to a ration dicating that the wheat products used did containing solvent soybean oil meal and not supply sufficient amounts of available solvent soybean oil (lot 10) resulted in a choline. highly significant increase in growth over Trial 2. This trial was designed to study that of lot 9, The use of 4 percent expeller the availability of choline in both expeller soybean oil with solvent soybean oil meal and solvent processed soybean oil used in (lot 11) failed to produce growth different
DEFICIENCY OF AVAILABLE CHOLINE IN SOYBEAN OIL MEAL
from that of solvent oil (lot 9) or refined corn oil (lot 7). Lot 12 included expeller soybean oil meal rather than solvent soybean oil meal. A highly significant difference in growth is shown betweeen these two meals (lots 7 and 12), indicating that the expeller soybean oil meal used apparently contained more available choline than the solvent soybean oil meal.
The chicks fed rations containing approximately one-third soybean oil meal with no choline supplement did not develop perosis. Apparently there was sufficient choline present to prevent perosis, but not to support satisfactory growth. The choline requirement seems to be higher for growth than for the prevention of perosis. The addition of 4 percent soybean oil failed to add sufficient choline to increase growth. These data further substantiate a previous publication of the authors (Berry et al., 1943) and justify the conclusion that soybean oil meal, when composing approximately one-third of the ration, does not supply an adequate amount of available choline for satisfactory growth. A highly significant difference in growth in favor of expeller soybean oil meal (lot 12) as compared with solvent soybean oil meal (lot 7) is shown. These two rations are both deficient in choline and the reader is cautioned against the conclusion that this same relative difference would necessarily exist in a normal ration containing an adequate amount of available choline. The interrelationship or transmethylation occurring between methionine and choline is probably not yet completely understood. That heated soybean protein is slightly deficient in methionine for the chick at the 20 percent protein level was shown by Almquist et al. (1942). These workers obtained better growth from the supplementation of their basal ration with methionine than with choline, but their best growth was ob-
tained when the basal ration was supplemented with both choline and methionine. SUMMARY 1. In the type of rations fed neither solvent nor expeller processed soybean oil meal supplied an adequate amount of available choline for satisfactory growth. 2. Neither solvent nor expeller processed soybean oil, at levels of 4 percent, supplied sufficient available choline to increase growth over that of a soybean oil meal negative control ration shown to be deficient in choline. 3. Expeller soybean oil meal, without a choline supplement, supported significantly better growth than did solvent soybean oil meal without a choline supplement. REFERENCES
Almquist, H. J., E. Mecchi, F. H. Kratzer, arid C. R. Grau, 1942. Soybean protein as a source of amino acids for the chick. J. Nutrition 24:385-392. Berry, E. P., C. W. Carrick, Roy E. Roberts, and S. M. Hauge, 1943. Whey solubles as a source of growth factors in chick rations. Poultry Sci. 22:252-263. Carrick, C. W., 1925. A brooder for indoor use in nutritional experiments with young chicks. Poultry Sci. 5:98-101. Engel, R. W., 1942. Modified methods for the chemical and biological determination of choline. Jour. Biol. Chem. 144:701-710. Jukes, T. H., 1940a. Effect of choline and other supplements on perosis. J. Nutrition 20:445-458. , 1940b. Studies of perosis in turkeys. I. Experiments related to choline. Poultry Sci. 20:251-254. , 1942. Personal communication, August, 1942. Quinn, J. P., and C. W. Knox, 1939. Sex identification of Barred Plymouth Rock baby chicks by down, shank, and beak characteristics. Poultry Sci. 18:259-264. Record, Paul R., and R. M. Bethke, 1942. Further observations on choline and yeast in chick nutrition. Poultry Sci. 21:271-276. Whitson, D., C. W. Carrick, R. E. Roberts, and S. M. Hauge, 1943. Utilization of fat by chickens—a method for determining the absorption of nutrients. Poultry Sci. 22:137-141.
Downloaded from http://ps.oxfordjournals.org/ at Swinburne University of Technology on July 8, 2015
DISCUSSION
445
EXPERIMENTAL Two trials were conducted to ascertain * Journal Paper No. 104 of the Purdue University Agricultural Experiment Station. t This investigation was supported in part by a grant from The Borden Company.
the supplementary choline value of soybean oils from both the expeller and the solvent processes upon expeller and solvent processed soybean oil meal. Through the kind cooperation of one of the large soybean oil meal producing plants, a uniform sample of soybeans was divided into two lots. One lot was solvent processed and the other was expeller processed. The methods used by the company for processing commercial soybean oil meal were followed. The percentage protein, fat, and moisture were, respectively, for the solvent meal 45.52, 0.63, and 11.11, and for the expeller meal 45.46, 4.33, and 9.37. Barred Plymouth Rock day-old chicks were used in each trial. The chicks were kept on wire-floored brooder tables as described by Carrick (1925). At the beginning of each trial, the chicks were distributed into lots on the basis of weight. At four weeks, each lot was reduced to 25 by keeping the median weight chick and 12 chicks on each side of the median weight chick. Individual weights were taken at twoweek intervals. The all-mash rations were fed ad libitum, and water was available at all times. These two trials were started in September and with chicks from the same hatch. A method described by Quinn and Knox (1939) was used in sexing the chicks. The male chicks were used in trial 1, and the female chicks were used in trial 2. Trial 1. This trial was designed to study the availability of choline in expeller and
[442]
Downloaded from http://ps.oxfordjournals.org/ at Swinburne University of Technology on July 8, 2015
J
UKES (1940a, b) found 25 to 40 percent of soybean oil meal to be a satisfactory source of choline for the prevention of perosis. The amount of total choline in soybean oil meal as given by Engel (1942) is sufficient to satisfy the chick's requirement for choline, if the total choline were available. Berry £t al. (1943) have presented data indicating the lack of an adequate amount of available choline for rapid growth in rations containing approximately one-third soybean oil meal. In studies on whey solubles, choline was the limiting factor in the rations used. Jukes (1942) used expeller processed soybean oil meal. Communication with the processor indicates that the soybean oil settlings or "foots" were added back to the meal at the time that Jukes obtained his meal. The settlings from soybean oil are known to be rich in lecithin, from which choline is derived (Record and Bethke, 1942). Therefore, it seemed advisable to try a diet containing crude soybean oil as a source of choline. The efficient utilization of fats in soybean oil was demonstrated by Whitson et al. (1943), who used rations containing as much as 20 percent of soybean oil in which 94 percent of the fat was utilized.
DEFICIENCY OF AVAILABLE CHOLINE IN SOYBEAN OIL MEAL
-Comparison of expeller and solvent soybean oils in rations containing expeller soybean oil meal {trial 1, males)
Ingredient
Lotl
Lot 2
Lot 3
Lot 4
Lot 5
Lot 6*
Ground yellow corn
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
3
3
3
3
3
3
4
4
4
4
4
4
34.5
34.5
34.5
34.5
4
4
Whey solubles (dry basis) Ground limestone Salt mixture 1 400-D oil Riboflavin concentrate" Nicotinic acid Expeller soybean oil meal Solvent soybean oil meal Solvent soybean oil Refined corn oil Choline chloride Total
Av. wt. six weeks (grams) f. . . . Standard deviation Coefficient of variation Grams feed per gram of gain... Number of chicks at six weeks..
s
34.5 4
34.5 4
4 100.00
4 100.00 6
100.00
100.00
100.00
100.00
20.22
20.22
20.22
20.22
20.22
20.22
219 89 41 4.70 24
371 122 33 3.08 25
221 68 31 3.95 24
242 58 24 5.15 21
246 106 43 3.58 19
204 71 35 5.28 18
* Ration modified as described in text at three weeks. 11 values between lots are: 1 and 2, 5.02; 1 and 3, 0.07: 1 and 4,1.06; 1 and 5, 0.90; 1 and 6, 0.62; 3 and 4, 11.16. 950 grams iodized salt, 50 grams MnSCU. 2 280 micrograms riboflavin per gram of concentrate. 3 30 mg. nicotinic acid per 100 grams of feed. 4 1.95 mg. calcium pantothenate per 100 grams of feed. 6 150 mg. choline chloride per 100 grams of feed.
Downloaded from http://ps.oxfordjournals.org/ at Swinburne University of Technology on July 8, 2015
ciency of available choline in lot 1. Four percent of expeller soybean oil was used in lot 3 to replace the refined corn oil in the basal ration. The result from lot 3 indicates that expeller soybean oil failed to contribute enough available choline to increase growth over lot 1. The addition of choline chloride to a ration containing expeller soybean oil meal and expeller soybean oil (lot 4) increased growth slightly, but not significantly over lots 1 and 2. The lack of a significant difference between lots 3 and 4 is incompatible with results in trial 2 where solvent soybean oil meal was involved. When 4 percent of solvent soybean oil was included in the ration (lot S) there was no significant increase in growth over the
solvent processed soybean oil used in rations containing expeller processed soybean oil meal. Thirty-one chicks were started in each lot. Rations, with the results from the male chicks, are shown in Table 1. The fat content of rations not containing soybean oil was equilibrated by using refined corn oil. A ration which had previously been proved deficient in available choline (Berry et al., 1943) was modified by including 4 percent refined corn oil to form the negative control (lot 1). For lot 2, ISO milligrams of choline chloride per 100 grams of feed were added to the negative control ration. The increased growth resulting when choline chloride was added was highly significant, indicating a defiTABLE 1.
443
444
E. P. BERRY, C. W. CARRICK, ROY E. ROBERTS, AND S. M. HAUGE
TABLE 2.—Comparison of expeller and solvent soybean oils in rations containing solvent soybean oil meal {trial 2, females) Ingredient
Whey solubles (dry basis) Ground limestone 400-D oil Riboflavin concentrate 2 Calcium pantothenate Solvent soybean oil meal
Lot 7
Lot 8
Lot 9
Lot 10
Lot 11
Lot 12
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
51 5 0.5 2.5 1 0.5 0.5 0.5
3 4
3 4
3 4
3 4
3 4
4
34.5
34.5
34.5
Expeller soybean oil
34.5 4
Total Percentage protein Av. wt. six weeks ( g r a m s ) * . . . . Standard deviation Grams feed per gram of gain... Number of chicks at six weeks..
. 34.5
3
34.5
4 4
4
4 5
100.00
4 100.00
100.00
100.00
100.00
100.00
20.22
20.22
20.22
20.22
20.22
20.22
172 45 26 5.81 23
5
270 97 36 4.27 24
169 45 27 5.95 23
266 65 24 3.47 24
179 52 29 4.91 23
222 42 19 4.16 25
Vitamin additions same as in Trial 1. * t values between lots are: 7 and 8, 4.6; 7 and 9, 0.20; 7 and 10, 5.98; 7 and 11, 0.54; 7 and 12, 4.05;9 and 10, 5.97.
Downloaded from http://ps.oxfordjournals.org/ at Swinburne University of Technology on July 8, 2015
negative control (lot 1), thus indicating rations containing solvent processed soythat solvent soybean oil did not contribute bean oil meal. Forty-three chicks were sufficient available choline for a growth started in each lot. The rations, with the difference. After the two-week weights were results from the female chicks, are given obtained, it was evident that the solvent in Table 2. soybean oil meal negative control (lot 6) Lot 7 served as a negative control, defiwas showing a choline deficiency, so far as cient in available choline. When ISO milligrowth was concerned. grams of choline chloride per 100 grams of Since it seemed desirable to test wheat feed were added (lot 8), the growth increase and wheat by-products for choline value, over lot 7 was highly significant. When 4 at three weeks the ration fed to lot 6 was percent of solvent soybean oil (lot 9) rechanged so that expeller soybean oil meal placed the refined corn oil of the negative replaced the solvent soybean oil meal, and control, the growth remained the same as 20 percent of ground wheat, 5 percent of that from lot 7, indicating that solvent soywheat bran, and 5 percent of wheat mid- bean oil did not contain an adequate dlings were included. This modified ration amount of available choline to increase failed to improve the growth, probably in- growth. The addition of choline to a ration dicating that the wheat products used did containing solvent soybean oil meal and not supply sufficient amounts of available solvent soybean oil (lot 10) resulted in a choline. highly significant increase in growth over Trial 2. This trial was designed to study that of lot 9, The use of 4 percent expeller the availability of choline in both expeller soybean oil with solvent soybean oil meal and solvent processed soybean oil used in (lot 11) failed to produce growth different
DEFICIENCY OF AVAILABLE CHOLINE IN SOYBEAN OIL MEAL
from that of solvent oil (lot 9) or refined corn oil (lot 7). Lot 12 included expeller soybean oil meal rather than solvent soybean oil meal. A highly significant difference in growth is shown betweeen these two meals (lots 7 and 12), indicating that the expeller soybean oil meal used apparently contained more available choline than the solvent soybean oil meal.
The chicks fed rations containing approximately one-third soybean oil meal with no choline supplement did not develop perosis. Apparently there was sufficient choline present to prevent perosis, but not to support satisfactory growth. The choline requirement seems to be higher for growth than for the prevention of perosis. The addition of 4 percent soybean oil failed to add sufficient choline to increase growth. These data further substantiate a previous publication of the authors (Berry et al., 1943) and justify the conclusion that soybean oil meal, when composing approximately one-third of the ration, does not supply an adequate amount of available choline for satisfactory growth. A highly significant difference in growth in favor of expeller soybean oil meal (lot 12) as compared with solvent soybean oil meal (lot 7) is shown. These two rations are both deficient in choline and the reader is cautioned against the conclusion that this same relative difference would necessarily exist in a normal ration containing an adequate amount of available choline. The interrelationship or transmethylation occurring between methionine and choline is probably not yet completely understood. That heated soybean protein is slightly deficient in methionine for the chick at the 20 percent protein level was shown by Almquist et al. (1942). These workers obtained better growth from the supplementation of their basal ration with methionine than with choline, but their best growth was ob-
tained when the basal ration was supplemented with both choline and methionine. SUMMARY 1. In the type of rations fed neither solvent nor expeller processed soybean oil meal supplied an adequate amount of available choline for satisfactory growth. 2. Neither solvent nor expeller processed soybean oil, at levels of 4 percent, supplied sufficient available choline to increase growth over that of a soybean oil meal negative control ration shown to be deficient in choline. 3. Expeller soybean oil meal, without a choline supplement, supported significantly better growth than did solvent soybean oil meal without a choline supplement. REFERENCES
Almquist, H. J., E. Mecchi, F. H. Kratzer, arid C. R. Grau, 1942. Soybean protein as a source of amino acids for the chick. J. Nutrition 24:385-392. Berry, E. P., C. W. Carrick, Roy E. Roberts, and S. M. Hauge, 1943. Whey solubles as a source of growth factors in chick rations. Poultry Sci. 22:252-263. Carrick, C. W., 1925. A brooder for indoor use in nutritional experiments with young chicks. Poultry Sci. 5:98-101. Engel, R. W., 1942. Modified methods for the chemical and biological determination of choline. Jour. Biol. Chem. 144:701-710. Jukes, T. H., 1940a. Effect of choline and other supplements on perosis. J. Nutrition 20:445-458. , 1940b. Studies of perosis in turkeys. I. Experiments related to choline. Poultry Sci. 20:251-254. , 1942. Personal communication, August, 1942. Quinn, J. P., and C. W. Knox, 1939. Sex identification of Barred Plymouth Rock baby chicks by down, shank, and beak characteristics. Poultry Sci. 18:259-264. Record, Paul R., and R. M. Bethke, 1942. Further observations on choline and yeast in chick nutrition. Poultry Sci. 21:271-276. Whitson, D., C. W. Carrick, R. E. Roberts, and S. M. Hauge, 1943. Utilization of fat by chickens—a method for determining the absorption of nutrients. Poultry Sci. 22:137-141.
Downloaded from http://ps.oxfordjournals.org/ at Swinburne University of Technology on July 8, 2015
DISCUSSION
445