The Effect of Antibiotics upon the Requirement of Turkeys for Unidentified Vitamins1

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Halick, J. V., and J. R. Couch, 1951. Antibiotics in mature fowl nutrition. Proc. Soc. Exp. Biol. Med. 76: 58-62.

Lowry, 0 . H., and T. H. Hunter, 1945. The determination of serum protein concentration with a gradient tube. J. Biol. Chem. 159: 465-474. Lowry, O. H., J. A. Lopez and O. A. Bessey, 1945. The determination of ascorbic acid in small amounts of blood serum. J. Biol. Chem. 160:609615. Quaife, M. L., N . S. Scrimshaw and O. H. Lowry, 1949. A micromethod for assay of total tocopherols in blood serum. J. Biol. Chem. 180: 12291235. Scrimshaw, N . S., R. L. Goodland and F. B. Hutt, 1949. Variations in the ascorbic acid blood levels of hens. Poultry Sci. 28: 45-51. Squibb, R. L., E. Salazar, N. S. Scrimshaw and M. Guzman, 1951. Growth of pigs fed corn and banana rations and the effect of aureomycin and a vitamin concentrate on several constituents of the blood stream of pigs. (In press.) Whitehill, A. R., J. J. Oleson and B. L. Hutchings, 1950. Stimulatory effect of aureomycin on the growth of chicks. Proc. Soc. Exp. Biol. Med. 74: 11-13. Wintrobe, M. M., 1946. Clinical Hematology. 2d ed., Lea and Febiger, Philadelphia.

T h e Effect of Antibiotics upon the Requirement of Turkeys for Unidentified Vitamins 1 M. L. SCOTT AND L. S. JENSEN Agricultural Experiment Station and School of Nutrition, Cornell University, Ithaca, New York (Received for publication March 24,1952)

reports (Scott, Heuser and SEVERAL Norris, 1948; Scott, 1951) from this iaboratory have presented evidence demonstrating that young poults require an unidentified vitamin or vitamins for nor1

1 his work was aided by a grant to Cornell University from the Cerophyl Laboratories, Kansas City, Mo. The work was conducted in the Nutrition Laboratories of the Department of Poultry Husbandry.

mal growth. Indeed, it appeared from from these results that at least two unknown factors are required. One of these factors was found to be present in products of animal origin, especially in fish meal and liver meal. While vitamin B12 may represent a part of the growth-promoting activity of the animal protein supplements, the complete answer concerning the growth-promoting activity

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phosphatase with five cubic millimeters of serum. J. Biol. Chem. 164: 321-329. Bessey, 0 . A., 0 . H. Lowry, M. J. Brock and J. A. Lopez, 1946. The determination of vitamin A and carotene in small quantities of blood serum. J. Biol. Chem. 166: 177-188. Burch, H. B., 0 . A. Bessey and 0 . H. Lowry, 1948. Fluorometric measurements of riboflavin and its natural derivatives in small quantities of blood serum and cells. J. Biol. Chem. 17S: 457-470. Couch, J. R., J. F. Elam and L. L. Gee, 1941. Effect of penicillin on growth, egg production and hatchability. Fed. Proc. 10: 379. Goodland, R. L., R. R. Sealock, N . S. Scrimshaw and L. C. Clark, 1949. Interference with tbe ultramicro ascorbic acid method of Lowry, Lopez and Bessey. Science, 109: 494-495. Groschke, A. C , and R. J. Evans, 1950. Effect of antibiotics, synthetic vitamins, vitamin B 12 and an APF supplement on chick growth. Poultry Sci. 29: 616-618.

987

ANTIBIOTICS AND UNIDENTIFIED VITAMINS

EXPERIMENTAL METHODS AND RESULTS

Studies with Young Poults White Holland and Broad Breasted Bronze poults were used in these experiments as indicated. The poults were housed in thermostatically controlled heated pens having raised wire-mesh floors. Studies with Vitamin Bu and Aureomycin Experiment 1.—This experiment was conducted with White Holland poults obtained from two different breeding flocks. One flock received a breeding ra-

tion complete in all known required nutrients, but containing no animal protein. The other flock received a commercial turkey breeding mash which contained generous amounts of fish meal and meat scrap. The basal diet fed to the poults is presented in Table 1. This diet was fed alone TABLE 1.—Mixed cereal-soybean meal basal starting diet A

• Ingredients*

Percent

Cornmeal Wheat, ground Oats, pulverized Soybean meal, 44% protein Dicalcium phosphate Limestone Salt, iodized Fish liver oil, 3..000A, 400D MnS0 4

20 15 10 48.46 3.7 1.5 0.8 0.5 0.04

* Following vitamins added: choline chloride, 200 mg.; niacin, 10 mg.; vitamin K (menadione), 2 mg.; riboflavin, 1 mg.; and folic acid, 0.5 mg. per lb. of diet.

and supplemented with crystalline vitamin B12, and APF supplement known to contain aureomycin and vitamin B12, and with a combination of fish meal and meat scrap. The results of the experiment, presented in Table 2, showed that the "normal" poults grew at a significantly faster rate than the poults from animal protein-deficient hens regardless of treatment. Supplementation of the poult diet with vitamin B12 had no eSect upon the growth of either group. The inclusion of the APF supplement in the diet produced a slight increase in the growth of both groups of poults, but did not increase the rate of growth of the poults from animal protein-deficient hens to a level equivalent to that obtained with the "normal" poults receiving the basal diet. Supplementation with meat scrap and fish meal also produced only slight increases in the growth of both groups of poults under these conditions.

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of fish meal and liver meal still remains to be determined. In addition to the factor or factors present in animal products, at least one other factor is required for optimum growth in turkeys. The properties and distribution of the second factor resemble those of factor S, an unidentified vitamin required by chicks. Casein, dried skimmilk, dried brewers' yeast, dried distillers' solubles, dried whey product and grass juice have all been found to be sources of this factor. With the discovery by Stokstad and Jukes (1950), confirmed by McGinnis et al. (1950), Branion and Hill (1951) and others, that a few parts per million of crystalline aureomycin hydrochloride produce a marked increase in growth when added to the diet of turkeys, it appeared desirable to determine the effect of antibiotic supplementation upon the requirement of turkeys for unidentified vitamins. It is the purpose of this report to present evidence indicating the extent to which antibiotic supplementation may spare the requirements for the unidentified factors and to show which unidentified vitamins must be present in the diet of turkeys in order to obtain a maximum growth response from the antibiotic.

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M. L. SCOTT AND L. S. JENSEN

TABLE 2.—Effect of vitamin Bn, "APF" supplement was in the order of 10% above that proand "animal protein" supplements upon the growth duced by the basal diet. of "normal" and "animal protein deficient" White Holland poults

Studies with Fish Meal and Meat Scrap Average weight, 4 weeks

Experiment J.—The results of the first two experiments indicated that an un"Normal" identified factor required by turkey poults poults* had been omitted from the basal diet. In view of earlier studies (Scott, Heuser gm. gm. 402 Basal diet A 497 and Norris, 1948) showing that poults 411 Vitamin Bi2, 10 mcg./lb. 504 require an unidentified vitamin present APF supplement^ 1.25. 440 gm./lb. 521 in casein, dried skimmilk and dried Fish meal, 5 % + m e a t brewers' yeast, a third experiment was 425 533 scrap, 5% Fish meal, 5 % + m e a t conducted using the same basal diet modi424 493 scrap, 5%+vitamin Bi2 fied to contain 18% of casein. Since ani* "Normal" poults were those obtained from a mal protein-deficient poults were not breeding flock receiving a commercial turkey available for further study, it was necbreeding mash. "Animal protein deficient" poults were obtained from a flock of the same strain of essary to use poults from a commercial hens receiving an all-plant breeding ration. hatchery. Therefore, Broad Breasted fLederle's APF-5 containing approximately 2 gm. of aureomydn and 2 mg. of vitamin B12 per lb. Bronze male poults were selected for use in these studies. In a preliminary experiExperiment 2.—When crystalline au- ment the modified diet was fed alone and reomydn became available for experi- supplemented with vitamin B12. Since mental use, a second experiment was con- vitamin B12 produced no increase in the ducted using the same basal diet. White growth of the poults, this vitamin was Holland poults obtained from the breed- added to the basal diet at a level of 2 ing flock receiving the all-vegetable ra- micrograms per 100 grams of diet in order tion were fed the basal diet alone and to eliminate the possibility that any resupplemented with vitamin B12 and aureo- sponse obtained with fish meal and meat mydn hydrochloride singly and in com- scrap could be due to this vitamin. When bination. The results of this experiment this diet was fed alone, the average weight are presented in Table 3. It is apparent of the poults at 4 weeks was 615 grams. from these results that vitamin B12 had The addition of 5 percent of fish meal and little or no effect upon the growth rate 5 percent of meat scrap produced an average weight of 705 grams at 4 weeks of age. TABLE 3.—Effect of vitamin Bn and crystalline Treatment

Animal protein defic. poults*

Treatment

Basal diet A Vitamin B12, 10 mcg./lb. Aureomycin hydrochloride, 10 mg./lb. Vitamin Bi2+aureomycin hydrochloride

Average weight, 4 weeks gm. 468 474 524 510

of the poults. The increase in growth produced by the addition of the antibiotic

Experiment 4.—In order to eliminate the possibility that Broad Breasted Bronze poults react in a different manner than White Holland poults, and to determine if a combination of dried skimmilk, dried brewers' yeast and whey at levels of 5, 4 and 2 percent respectively would supply a sufficient amount of the factor present in casein, these supplements were used in place of the casein in the diet. The protein level of the diet was adjusted to

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aureomydn upon growth of poults from animal protein deficient hens

989

ANTIBIOTICS AND UNIDENTIFIED VITAMINS

The Effect of Aureomycin and Certain Vitamin Carriers upon Poult Growth When Added to a Diet Containing a High Level of Animal Protein Supplements Experiment 5.—The results presented in the first two experiments showed that supplementation of an all-vegetable poult ration with aureomycin produced only a slight increase in growth over the basal diet. An experiment was conducted, therefore, to determine the type of response that could be obtained by addition TABLE 5.—Effect

of aureomycin to a diet containing a high level of fish meal. The basal diet used in this study is presented in Table 4. This TABLE 4.—Composition of basal diet for Experiment 5 Ingredients*

Percent

Cornmeal Whole wheat, ground Oats, pulverized Soybean meal, 50% protein Fish meal, menhaden Dicalcium phosphate Limestone Salt, iodized MnS0 4 Fish liver oil (Nopco XX, 2.250A, 400D)

40.5 5 5 33 12.5 0.5 1 0.5 0.04 2.0

* Following vitamins added: Riboflavin, 1 mg.; niacin, 5 mg.; choline, 225 mg.; and betaine, 900 mg. per lb, of diet.

diet was fed alone and supplemented with dried brewers' yeast, dried skimmilk, dried whey and grass juice with and without additional supplementation with aureomycin. The effects of these supplements upon growth and feed efficiency at 4 and 8 weeks of age are shown in Table 5. These results show that the addition of aureomycin produced a consistently high rate of growth which is believed to be near the maximum rate of growth for this strain of turkeys. The addition of aureomycin to this type of diet also consistently

of various vitamin carriers and aureomycin hydrochloride on growth and feed efficiency when added to a diet containing a high level of animal protein With aureomycin

Without aureomycin Treatment*

Feed Avg. Feed Avg. wt. efficiency wt. efficiency 4 wks. 4 wks. 8 wks. 8 wks. gm. '

Basal Dried Dried Dried Dried Grass

diet brewers' yeast distillers' solubles skimmilk wheyf juicet

446 528 406 532 454 652

gm. feed/gm. gain 1.90 1.77 2.54 2.15 2.13 1.77

gm. 1,651 1,687 1,497 1,698 1,667 2,043

gm. feed/gm. gain 2.50 2.47 2.59 2.52 2.48 2.21

Avg. wt. 4 wks. gm. 691 653 655 681 656 697

Avg. Feed wt. efficiency 4 wks. 8 wks. gm. feed/gm. gain 1.52 1.67 1.59 1.64 1.74 1.52

* All supplements at 5%. t This sample of whey contained 73% lactose. % Rye grass juice obtained from Cerophyl Laboratories, Kansas City, Mo.

gm. 1,948 2,070 1,852 2,025 2,041 2,108

Feed efficiency 8 wks. gm. feed/gm. gain 2.22 2.18 2.27 2.22 2.32 2.10

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28 percent with soybean meal. The results of this experiment showed that the average weight of the poults receiving the basal diet at 5 weeks of age was 533 grams, whereas those receiving the same diet plus 5 percent of fish meal and 5 percent of meat scrap weighed 714 grams at the same age. These results indicate, therefore, that fish meal and meat scrap contain at least one unidentified factor, in addition to vitamin Bu, required for normal growth in turkey poults and that an unknown vitamin present in casein, yeast, and whey must be present in the diet before the maximum growth response is obtained from animal protein supplementation.

990

M. L. SCOTT AND L. S. JENSEN

Studies-with Aureomycin and Unidentified Vitamins in Turkey Growing Rations Experiment 1.—For the first study of growth between 8 and 24 weeks of age a basal diet was used which did not contain supplementation with special vitamin carriers other than 10 percent of meat scrap. The composition of this ration is

shown in Table 6. Broad Breasted Bronze male poults which had been raised to 8 weeks of age on good starting rations were distributed into 4 different lots in a manTABLE 6.—Basal growing ration Percent

Ingredients Cornmeal Standard middlings Pulverized oats Soybean meal Meat scrap Alfalfa meal Dicalcium phosphate Limestone Salt, iodized Fish liver oil, 2,2S0A, 300D Fermentation riboflavin supplement Manganese sulfate

36 20 10 13 10 6 2 1 1 1 0.05 0.04

ner so that all of the lots were of equal average weight. Each lot, which was composed of approximately 20 turkeys, was housed in a separate sun-porch equipped with slats and wiremesh floors. Approximately half of the sun-porch was covered with tarpaper to provide protection from the weather. The basal diet was fed alone and supplemented with 5 percent of distillers' solubles and 4 percent of dried brewers' yeast with and without further supplementation with aureomycin hydrochloride. All lots received the mash ad libitum plus an equivalent daily intake of scratch grains. The results of the experiment at 8, 16, 20 and 24 weeks of age are presented in Table 7. TABLE 7.—Effect of vitamin carriers on "antibiotic response" in growing BBB male turkeys Treatment

—" wks.

lb. Basal diet 4.22 Aureomycin HC1, 2.5 mg./lb. mash 4.21 Brewers' yeast, 4% of mash +distillers' solubles, 5% of mash 4.29 Brewers' yeast+distillers' solubles+aureomycin HCI 4.28

Average weight ~ ~ wks. wks.

wks.

lb. 13.42

lb. 16.28

lb. 21.44

12.78

15.90

19.46

~

13.68

17.00

21. 6

14.30

18.70

22.50

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improved feed efficiency at both 4 and 8 weeks of age. An interesting discovery obtained from this experiment is the fact that the addition of 5 percent of grass juice to the basal diet promoted a rate of growth in the poults of approximately the same magnitude as that produced by supplementation with aureomycin and that therefore, when grass juice was present in the diet the addition of the antibiotic caused only a very slight, if any further stimulation of growth. In two subsequent experiments, employing a similar basal diet and using Broad Breasted Bronze poults in Experiment 6 and White Holland poults in Experiment 7, the growth-promoting effects of grass juice and aureomycin, alone and in combination, were confirmed. Experiment 6.—The average weight at 4 weeks of the poults receiving the basal diet was 515 grams; those receiving the 5% grass juice supplement weighed 750 grams; 5 mg. of aureomycin hydrochloride per pound of basal diet produced an average weight of 713 grams; while the poults receiving both of these supplements weighed 740 grams. Experiment 7.—In this experiment the poults receiving the basal diet weighed 524 grams at 4 weeks of age; those receiving this diet plus 5% of grass juice weighed 605 grams; aureomycin supplementation alone produced a weight of 603 grams; and the poults receiving both grass juice and aureomycin weighed 592 grams.

991

ANTIBIOTICS AND UNIDENTIFIED VITAMINS

which received the antibiotic throughout the total growth period were superior in weight, feathering and market grade at 24 weeks of age. TABLE 8.—Effect of an antibiotic in practical turkey growing rations Basal

Aureomycin*

Diet fed 8-24 weeks

Basal

Aureomycinf

Basal

Aureomycin f

Weight Weight Weight Weight

lb. 3.74 9.61 13.66 17.23

lb. 3.83 11.20 14.66 17.82

lb. 4.41 10.10 13.78 17.20

lb. 4.50 11.90 15.38 18.56

at 8 weeks at 16 weeks at 20 weeks at 24 weeks

* Aureomycin hydrochloride, 5 mg./lb. of starting ration, t Aureomycin hydrochloride, 2.5 mg./lb. of growing mash with 50-50 grain feeding.

DISCUSSION

The results presented in this report furnish further evidence indicating that the turkey requires two unidentified growth factors. One of these factors appears to be present in products of animal origin such as fish meal and meat scrap. This factor does not appear to be identical with vitamin Bi2. The second growth factor is contained in such materials as casein, dried brewers' yeast, dried skimmilk and grass juice. Supplementation of the poult starting ration with aureomycin hydrochloride appears to spare the requirement for the second factor to a much greater extent than the requirement for the factor present in animal products. Indeed, in order to obtain maximum effect from antibiotic supplementation in starting rations, these starting rations must contain sufficient amounts of the factor present in animal products. Conversely, the growth response of young turkeys to supplementation with fish meal and meat scrap is relatively small unless the diet contains a source of the second factor or an antibiotic. The results of studies with growing rations for turkeys showed that supplementation with an antibiotic produced superior growth, feathering and finish

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These results show that neither the vitamin carriers nor the antibiotic produced an increase in growth over that obtained with the basal diet unless they were fed in combination (Lot #4). The turkeys receiving a combination of yeast and distillers' solubles plus aureomycin hydrochloride were superior in growth, feathering and finish at 24 weeks as compared to the turkeys in the other lots. Experiment 2.—A second experiment was conducted using poults which had been raised to 8 weeks of age on two different rations. One ration was the same as that presented in Table 4. The other was the same with the addition of 10 milligrams of aureomycin hydrochloride per pound of ration. At the end of 8 weeks the poults from these two lots were each subdivided into two groups. A commercial turkey growing ration containing distillers' solubles and dried whey product but no antibiotic was used as the basal diet. This ration was fed to one half of the poults which had been carried to 8 weeks without an antibiotic and one half of the poults which had been carried to 8 weeks with the antibiotic. The remainder of the poults received the same growing ration plus aureomycin at a level of 2.5 mg. per lb. of mash. The outline of the experiment and the results at 8, 16, 20, and 24 weeks are presented in Table 8. These results show that supplementation of this type of growing ration with an antibiotic produced an increased rate of growth during the growing period irrespective of the treatment that the poults received up to 8 weeks of age. The poults which had received the antibiotic to 8 weeks but received no antibiotic in the growing ration rapidly lost the weight advantage that they had at 8 weeks and therefore reached the age of 24 weeks weighing approximately the same as the turkeys which had received no antibiotic at all. The turkeys

992

M. L. SCOTT AND L. S. JENSEN

tion of 3 percent of dried brewers' yeast and 2 percent of dried distillers' solubles to a basal ration containing 10 per cent of fish meal. In view of the relatively low response obtained with 5 percent of dried brewers' yeast as compared to 5 percent of grass juice (Experiment 5) it is possible that the levels of yeast and distillers' solubles used by McGinnis were not sufficient to produce a growth response or that the particular samples used by these workers did not contain the unidentified factor shown in previous reports from this laboratory (Scott, 1951,1952) to be present in yeast and distillers' solubles. In one of these reports (Scott, 1951) evidence was presented showing that this unidentified factor is somewhat labile and is destroyed in dried skimmilk and dried brewers' yeast after prolonged standing or in cereal grasses upon dehydration. In view of the discovery that the addition of grass juice to the poult starting ration produced an approximately maximal rate of growth which, therefore, could not be increased appreciably by antibiotic supplementation, it appears possible that the use of an antibiotic in the growing ration for turkeys would be of little effect if the turkeys were given access to good green pasture during the growing period. SUMMARY

Further evidence is presented indicating that the turkey requires two unidentified growth factors. One factor appears to be present in products of animal origin such as fish meal and meat scrap. This factor does not appear to be identical with vitamin Bi2. The growth-promoting activity of fish meal and meat scrap may be due either to the presence in these materials of an unknown vitamin or to an improvement in the combination of essential amino acids brought about by the addition of the animal products to the ration.

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at market time provided that the diet also contained sources of both the factor present in animal products and the factor present in brewers' yeast and dried distillers' solubles. These results indicate, therefore, that during the growing period the antibiotic is not capable of sparing completely the requirement for either of the unidentified growth factors but when these factors are present in the diet the further addition of an antibiotic improves growth, possibly by aiding in utilization of these and perhaps other nutrients. Further studies with growing rations for turkeys showed that the growth advantage obtained by feeding an antibiotic to 8 weeks of age was rapidly lost when the antibiotic was withdrawn from the feed after the eighth week. These results also showed that the addition of an antibiotic to the rations of poults which had not received this material up to 8 weeks of age caused a stimulation in the rate of growth as compared to poults receiving the same growing ration minus the antibiotic. The best rate of growth was obtained, however, in turkeys which received the antibiotic throughout both the starting and growing periods. The results presented in this report confirm those of McGinnis and associates (1951) which showed that aureomycin gave a greater growth response when added to a basal diet containing fish meal than it did when added to a basal diet which contained no fish meal. McGinnis and associates concluded that these results were due to the presence of an unidentified growth factor in the fish meal or to a better combination of essential amino acids in the soybean-fish meal diet than in the diet containing soybean meal as the major protein source. Either of these explanations would also account for the results presented in this report. McGinnis and associates (1951) failed to obtain a growth response from the addi-

993

BOOK REVIEW

increase but that the best rate of growth, feathering and finish at market age were obtained in the turkeys which received the antibiotic, together with sources of both of the unknown growth factors, throughout both the starting and growing periods. ACKNOWLEDGEMENTS The authors wish to thank Dr. T. H. Jukes, Lederle Laboratories Division, American Cyanamid Co. for the crystalline aureomycin hydrochloride; Dr. G. 0 . Kohler, Cerophyl Laboratories for the grass juice; and Dr. R. D. Seeley, Anheuser-Busch, Inc. for the dried brewers' yeast used in these studies. REFERENCES Branion, H. D., and D. C. Hill, 1951. The comparative effect of antibiotics on the growth of poults. Poultry Sci. 30: 793-798. McGinnis, J., L. R. Berg, J. R. Stern, R. A. Wilcox and G. E. Bearse, 1950. The effect of aureomycin and streptomycin on the growth of chicks and turkeys. Poultry Sci. 29:771. McGinnis, J., J. R. Stern, R. A. Wilcox and J. S. Carver, 1951. The effect of different antibiotics on growth of turkey poults. Poultry Sci. 36:492496. Scott, M. L., 1951. The grass juice factor in turkey nutrition. Poultry Sci. 30: 293-297. Scott, M. L., 1952. Effect of dried distillers' solubles, whey and lactose upon enlarged hocks in turkeys. Poultry Sci. 31: 175-176. Scott, M. L., G. F. Heuser and L. C. Norris, 1948. Energy, protein and unidentified vitamins in poult nutrition. Poultry Sci. 27: 773-780. Stokstad, E. L. R., and T. H. Jukes, 1950. Growthpromoting effect of aureomycin on turkey poults. Poultry Sci. 29: 611-612.

BOOK REVIEW (Continued from page 961) breeding for those who will care to undertake further study of the subject and a well arranged index. The author deals at once into the history of Mendelism and into the mechanics of inheritance as they are presently understood. He seems to make the facts about heredity more simple and understood then actually they are. He commands words beautifully, he senses relationships and leads from one phase of the subject to another with such cleverness

as to carry the reader on page after page without realization that he has been tackling one of the most complicated" subjects in modern science. I t is the sort of book which may well be used as a reference text for all students of Genetics. It is the sort of book which will open to everyone a new and fresh understanding of Heredity. —W. C. T. in World's Poultry Science Journal.

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A second growth factor is contained in such materials as casein, dried brewers' yeast, dried skimmilk and grass juice. Supplementation of the poult starting ration with an antibiotic appears to spare • the requirement for the second growth factor to a much greater extent than the requirement for the factor present in animal products. In order to obtain maximum benefit from antibiotic supplementation in turkey starting rations, these rations must contain sufficient amounts of the unknown factor present in animal products. During the growing period most beneficial results were obtained when the antibiotic was added to a ration containing sources of both of the unknown factors. These results indicate, therefore, that during the growing period the antibiotic is not capable of sparing completely the requirement for either of the unknown growth factors. However, when these factors were present in the diet the further addition of an antibiotic improved growth, possibly by aiding in the utilization of these and perhaps other nutrients. Results with growing rations showed that the growth advantage obtained by feeding an antibiotic to 8 weeks of age was rapidly lost when the antibiotic was withdrawn from the feed after the eighth week. These results also showed that the addition of an antibiotic to the ration of poults which had not received this material up to 8 weeks of age caused a growth