Some Results of Feeding Antibiotics to Chickens*

Some Results of Feeding Antibiotics to Chickens*

Some Results of Feeding Antibiotics to Chickens* G. F. HEUSER AND L. C. NORRIS Agricultural Experiment Station and Department of Poultry Husbandry, Co...

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Some Results of Feeding Antibiotics to Chickens* G. F. HEUSER AND L. C. NORRIS Agricultural Experiment Station and Department of Poultry Husbandry, Cornell University, Ithaca, N. Y. (Received for publication February 25, 1952)

the vegetable protein ration and 1 microgram per 100 grams to the animal protein ration. Crystalline antibiotics were fed in all of the experiments. It is believed that the experimental rations were complete and met the requirements for all of the known nutrients.


TABLE 1.—Composition of rations


Age of chicks. The greatest effect of the antibiotics occurred at an early age. As the chicks grew older the differences became smaller and finally disappeared in

Five experiments have been conducted. Cockerel chicks of a Red-Rock Cross from three sources were used in the experiments. Twenty-five chicks were included per lot in four of the experiments and 30 chicks per lot in the fifth. All of the chicks were brooded on wire-mesh floors. The rations are given in Table 1. A diet which is primarily a vegetable protein ration, and is so designated, was fed in all of the experiments. In Experiments 1 and 2 a comparable ration containing animal proteins from meat and fish was also fed. Crystalline vitamin B12 was added at the rate of 2 micrograms per 100 grams to


lbs. 200 100 80 80 60 8 5 1

Wheat flour middlings Fine ground oats Dried distillers' solubles Dried whey product* Alfalfa meal Riboflavin supplementf Iodized salt Vitamin DJ Yellow corn meal Soybean meal, solvent process Meat scrap Fish meal Condensed fish Dicalcium phosphate Ground limestone Manganese sulfate

* This work was aided by grants to Cornell University from Commercial Solvents Corporation, Terre Haute, Indiana, Grange League Federation, Ithaca, N . Y. and Chas. Pfizer & Co., Inc., Brooklyn, N . y . . 857

Animal protein ration

Vegetable protein ration




— — —

400 60 60 40 20 20

2,000 6oz.

2,000 6oz.

41 30.7

* Fortified with riboflavin to contain a minimum of 22 milligrams per pound. f 114 milligrams of riboflavin per pound. % 681,000 International chick units of vitamin D per pound.

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AFTER the growth response of chicks •**• due to the feeding of antibiotics was reported by Stokstand and Jukes (1950), experimentation along this line was stimulated and many reports of investigations have appeared. Many phases of the problem, however, have not yet been explained or fully explored. The results of experiments conducted in this laboratory are presented, therefore, in order to assist in an understanding of the problem and hence in the application of the use of antibiotics in feeding poultry.





Terramycin (Regular Ration) •




Penicillin (Vegetable Protein Ration)





10 12 14 16 18 2 0 2 2 2 4 2 6 2 8 AGE WEEKS

the case of two comparisons at 16 and 24 weeks. In Figure 1 are shown the percentage increases in weight at different ages due to the feeding of antibiotics. In Table 2 are presented results which show the index of growth-stimulation at different ages due to the feeding of penicillin. The increases in weight during the first 4 weeks of age were greater than the increases during the next four weeks except in Experiment 2 in which the growthstimulation was maintained for 8 weeks. In two experiments the greatest difference occurred during the first week, in two experiments it occurred during the second week and in one experiment the

TABLE 2.—Growth stimulation of chicks at different ages due to penicillin* Age—Weeks

1 2 3 4 5 Average









108 116 112 113 113

100 117 108 108 115

108 117 110 110 114

106 110 109 108 110

105 115 106 108 109

107 116 104 106 105

99 116 105 107 100

101 115 105 106 99









Control Ration (Vegetable Protein) = 100. Red-Rock Cross Males. * Level—Exp. 1 and 2, 50 p.p.m. Exp. 3, 5, 10 and 20 p.p.m. Exp. 4, 1},.2$, 5 and 10 p.p.m. Exp. 5, 1}, 2J and 5 p.p.m.

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FIG. 1. Increase in weight of chicks at different ages due to antibiotics.

greatest difference occurred during the fourth week of age. Kind of ration. The results of Experiments 1 and 2 make possible comparisons of the average weights of the chicks on animal and vegetable protein rations. In Table 3 are given the weights of the various lots at 6 weeks of age. For the two experiments the chicks fed the animal protein ration averaged 4.75% heavier than those on the vegetable protein ration. The better response on the former ration is thought to be due to the unknown factors supplied by the animal protein (Heuser and Norfis, 1951). The chicks on the vegetable protein ration plus antibiotics were heavier than the vegetable protein ration control by 8.65%. This was only slightly below the average weight of the chicks on the animal protein ration plus antibiotics which was 10.25% heavier than the vegetable protein ration control. The effect of antibiotics in the animal protein ration was therefore to increase growth by only 5.5% instead of 8.65%. These results are in agreement with those reported by Matterson and Singsen (1951) in which they obtained a greater percentage growth response with antibiotics on the poorer-quality rations (all-plant protein) but the greater weight



on the better-quality rations (all plant protein plus fish meal) supplemented with antibiotics. A possible explanation of the results on the vegetable protein ration with antibiotics is that some of the unknown factor or factors found normally in animal proteins was synthesized by the favorable influence of the antibiotic on the intestinal flora and thus the vegetable protein ration was rendered more complete and made more comparable to the animal protein ration. I t is also possible that the antibiotic as shown by Biely and March (1951) might have a sparing effect on known vitamins by reducing the numbers of intestinal microflora which might compete with the host for members of the vitamin Bu complex and/or by permitting the proliferation of the microorganisms which synthesize these vitamins.

TABLE 3.—Effect

of antibiotics and animal protein on

Different Kinds and Amounts of Antibiotics. The experiments here reported involved a comparison of a number of antibiotics at various levels. The results are presented in Table 4. The response to the different antibiotics within single experiments was variable and variability was apparent for the same antibiotic in different experiments. Growth stimulation was obtained with very small amounts of the antibiotic (1J p.p.m.). Penicillin gave the most consistent and slightly better results than the other antibiotics, although in individual experiments about equally good results were also obtained with aureomycin, terramycin and bacitracin. Streptomycin was fairly effective only at the higher levels. Chloromycetin was relatively ineffective. Discontinuing the antibiotic. Berg, Bearse, McGinnis and Miller (1950) reported a cessation of the accelerated growth response when the antibiotic was discontinued at 4J weeks. Our results failed to confirm those of Berg et al. The

effect on chick growth upon stopping the feeding of antibiotics at the end of the first four weeks is shown in Table 5. In two out of nine lots, as nearly comparable as possible on the basis of growth stimulation at 4 weeks, the relative response was approximately the same in both groups. In four lots the chicks receiving the ration without the antibiotic did not gain quite as much as those receiving the ration in which the antibiotic was concontinued. However, their weights were very nearly the same as the control lots which did not receive any antibiotic at any time. In three of the paired lots the increase in weight was the same or slightly in favor of the lot which had the antibiotic discontinued. The average relative growth response at eight weeks of age was approximately the same whether the antibiotic was continued or discontinued during the second four week period. This might also be considered as further evidence that the chief effect of antibiotics is upon early growth.

the growth of chicks at 6 weeks of age Expi . Ration

Vegetable protein plus Aureomycin Streptomycin Terramycin Bacitracin Penicillin Tyrothricin Subtilin

Expi . 2



Relative growth


Relative growth .





736 701 746 701 720

108.9 103.7 110.4 103.7 106.5

617 604 632 637 654 629 598

109.4 107.1 112.1 112.9 116.0 111.5 106.0

— —

— —

721(5) 676(2)

106.7 100 6.7

624(7) 564(2)

J10.6 100 10.6

731 718 732 712 747

108.1 106.2 108.3 105.3 110.5

638 632 632 635 639 620 654

113.1 112.1 112.1 112.6 113.3 109.9 116.0

Average Animal protein Difference, percent

728(5) 698(2)

636(7) 599(2)

112.8 106.2 6.6

— —

— — 107.7 103.3 4.4

( ) numbers in parentheses represent the number of lots. Red-Rock males. Vegetable protein ration = 100. Level of antibiotic=50 p.p.m.

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Average Vegetable protein Difference, percent Animal protein plus Aureomycin Streptomycin Terramycin Bacitracin Penicillin Tyrothricin Subtilin



TABLE 4.—Relative growth response of chicks with different antibiotics fed at varying levels 4 weeks Level

Animal protein ration


Exp. 1 Exp. 2 Exp. 1 Exp. 2 Exp. 3 Exp. 4 Exp. 5


Terramycin hydrochloride


Procaine penicillin

Potassium penicillin G Streptomycin sulfate


Tyrothricin Subtilin Polymixin B sulfate

1.25 2.5 5.0 10.0 20.0 50.0 1.25 2.5 5.0 10.0 20.0 50.0

107 110 106 107







5.0 10.0 20.0 50.0

106 108 113 109



110 113 107



99 99 103

110 105 105



102 107 104 109

106 106 100



106 109 108 107

108 118 105




1.25 2.5 5.0 10.0 20.0 50.0

104 103 102 104


109 108 109 103



111 108 106 105


119 101 99 102





1.25 2.5 5.0 20.0

100 102

50.0 50.0

103 111

109 107




99 106 99

Control ration =100. Red-Rock males.

Feed Efficiency. A saving of feed has been reported when antibiotics are included in the ration (Davis and Briggs, 1951; Machlin, Denton, Kellogg and Bird, 1952; Nutrition Symposium, 1950). The effect, of antibiotics on feed utilization in our experiments is shown by the results given in Table 6. In three of the experiments the average feed efficiency

at 4 weeks was definitely in favor of the rations containing an antibiotic. In the other two experiments the differences were small, in one case in favor of antibiotic feeding and in the other in favor of the control ration. However, in both of these experiments there was lack of agreement in the two control rations. Considerable variation was observed in

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Aureomycin hydrochloride

1.25 2.5 5.0 10.0 20.0 50.0

Vegetable protein ration



TABLE 5.—Effect of discontinuing an antibiotic on the relative growth response of chicks Antibiotic 1-8 wks.* 4 wk. wt.

8 wk. wt.

4 wk. wt.

8 wk. wt.

109 107 108

107 102 99

109 106 106

104 103 99

109 103 107 108 110 105 107.3

105 97 102 96 105 105 102.0

108 102 104 105 107 105 105.8

102 101 98 98 104 101 101.1

Red-Rock males. 100=Control without antibiotic. * Level, 1-8 weeks: Exp. 3, 5 p.p.m.; Exp. 4, 2J p.p.m.; Exp. 5, 1J p.p.m. t Level, 1-4 weeks: Exp. 3, 20 p.p.m.; Exp. 4 and Exp. 5, 5 p.p.m.

the individual lots but there was a trend for the lots with the largest growth stimulation to have a greater feed efficiency. The average pounds of feed to produce a pound of weight at four weeks for 58 lots receiving an antibiotic was .14 pound less than that for 14 lots not receiving an antibiotic. This represents a saving in feed of 6.8%. At 8 weeks of age the values for feed efficiency were relatively the same for the different experiments although the magnitude of the difference was somewhat smaller. Mortality. For all experiments the mortality up to eight weeks of age was 2.6 percent for the control lots and 2.1 percent for the lots receiving antibiotics. Since the mortality was very low in all the experiments no definite conclusions can be drawn concerning the effect of antibiotics on mortality. Uniformity of birds. Some investigators have reported the observation that the birds tend to be more uniform when fed

in favor Lbs feed/lb. weight Differences Numof antibiotics Experi- ber of ment antiC ntrol feed/ ° Wott Lbs biotics % lb. wt. 4.6 13.8


5(V) 5(A)

2.06(2) 2.24(2)

1.94(5) 1.93(5)



2.17(2) 2.08(2)

1.99(6) 1.86(6)
















.12 .31 .18 .22

8.3 10.6









^Vegetable protein ration. Animal protein ration. Numbers in parentheses represent the number of lots. Red- Rock males.

antibiotics. In the experiments described here the effect of the antibiotics on weight appeared to be general because it affected all of the chicks uniformly. The results, presented in Table 7, show the coefficients of variability of the two control lots as contrasted to the coefficients of variability of two comparable lots receiving antibiotics and showing the greatest growth response. Only in Experiment 3 were the coefficients of variability for both of the lots receiving the antibiotics lower than the comparable controls. In the other four experiments one of the control lots showed less variability than one or both of the TABLE 7.—Uniformity of chicks as expressed by the coefficient of variability Antibiotic

Control Exp.

Relative weight


Relative weight


100 100

7.9 10.4



100 100

10.3 12.1

119 119

9.6 Bacitracin, 10.5 Penicillin,

50 p.p.m. 50 p.p.m.


100 100

8.5 9.8

113 111

6.8 Penicillin, 7.6 Bacitracin,

20 p.p.m. 5 p.p.m.


100 100

9.3 10.4

109 109

8.4 Aureomycin, 5 p.p.m. 10.5 Penicillin, 2} p.p.m.


100 100

9.9 13.7

118 113

21 p.p.m. 11.8 Penicillin, 12.0 Terramycin, 24 p.p.m.



8.5 Terramycin, 50 p.p.m. 8.8 Aureomycin, 50 p.p.m.


Red-Rock males. Vegetable protein ration=:100.

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Exp. 3 Aureomycin Terramycin Bacitracin Exp. 4 Penicillin Terramycin Aureomycin Exp. 5 Penicillin Terramycin Bacitracin Average

discontinued after 4 wks.f

TABLE 6.—Effect of antibioticson


lots receiving antibiotics. No differences could be observed or measured in the uniformity of the various lots of birds. SUMMARY

Acknowledgment is made to the following companies for supplying the antibiotics: Lederle Laboratories, Pearl River, N. Y. for the aureomycin hydrochloride. Chas. Pfizer Co., Brooklyn, N. Y. for the terramycin hydrochloride, streptomycin sulfate, polymixin B sulfate and penicillin G potassium. Commercial Solvents Co., Terre Haute, Indiana, for the bacitracin. Merck & Co., Rahway, N. J. for the subtilin and procaine penicillin. Bristol Laboratories, Syracuse, N. Y. for procaine penicillin. Parke, Davis & Co., Detroit, Michigan for the Chloromycetin. Wallerstein Co., Inc., New York for the tyrothricin. REFERENCES Berg, L. R., C. E. Bearse, J. McGinnis and V. L. Miller, 1950. The effect of removing supplemental aureomycin from the ration on the subsequent growth of chicks. Arch. Biochem. 29: 404-407. Biely, J., and B. March, 1951. The effect of aureomycin and vitamins on the growth rate of chicks. Science 114: 330-331. Davis, R. L., and G. M. Briggs, 1951. Studies with antibiotics in chick and poult starting rations. Poultry Sci. 30: 767-771. Heuser, G. F., and L. C. Norris, 1951. An unknown nutritive factor in feeds of animal origin. Poultry Sci. 30: 470-471. Machlin, L. J., C. A. Denton, W. L. Kellogg and H. R. Bird, 1952. Effect of dietary antibiotics upon feed efficiency and protein requirement of growing chickens. Poultry Sci. 31:106-109. Matterson, L. D., and E. P. Singsen, 1951. A comparison of several antibiotics as growth stimulants in practical chick starting rations. Storrs Agr. Exp. Sta. Bui. 275. Nutrition Symposium. 1950. Proc. Semi-annual Meeting, Nutrition Council of the Amer. Feed Mfg. Assn., Chicago, Nov. 26-28:8-24. Stokstad, E. L. R., and T. H. Jukes, 1950. Further observations on the "animal protein factor." Proc. Soc. Exp. Biol. Med. 73: 523-528.

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Growth stimulation has been obtained with a number of different antibiotics. Variability was apparent for the same antibiotic in different experiments. Improved growth was obtained with as little as 1J parts per million of the antibiotic. Penicillin gave the most consistent and slightly better results than the other antibiotics fed although in individual trials equal responses were also obtained from aureomycin, terramycin, and bacitracin. The greatest relative growth stimulation of chicks due to antibiotics was found to occur during the first four weeks. The differences in weight disappeared as the chicks grew older. A greater relative growth response with antibiotics was obtained in chicks fed vegetable protein rations than in those fed rations containing animal protein. In general the best weight was obtained with rations containing animal protein supplemented with antibiotics. However, the growth response obtained with vegetable protein rations plus antibiotics was nearly as large as that obtained with animal protein rations supplemented with antibiotics and greater than with animal protein rations without antibiotics. Considerable variation was observed in feed efficiency. The trend, however, showed that less feed was required to produce a pound of gain with antibiotics. This was especially true when there was an appreciable growth stimulation. No measurable difference was observed under the conditions of the experiments in the uniformity of the chicks as expressed by the coefficient of variability.