Animal Husbandry Mimeograph
Series No. 57-2
PRESENT STATUS OF RESERACH ON ANTIBIOTICS
AND HORMONES IN BEEF CATTLE AND CALF FEEDS
James F. Hentges, Jr.
The value of adding antibiotics and hormones to beef cattle feeds has
been proved by extensive experimentation but the full potential of their
use and inter-relationship is still a subject for research.
A survey of college experiment results will show that cattle and calves
fed aureomycin chlortetracyclinee) and terramycin oxytetracyclinee) gain
slightly faster and with a small saving of feed. The largest response is
observed on high roughage rations.
SUMMARY OF REPRESENTATIVE AUREOMYCIN FEEDING TRIALS
Av. Da. Gain $ Feed/Ib..ain %
Ration No.Trials Control Aureo Increase Control Aureo Saved
Grain 9 2.10 2.20 4.8 12.5 11.5 8.0
Roughage 9 1.34 1.48 10.4 19.4 17.9 7.7
Concentrates 3 0.99 1.05 6.0 -
Too few studies have been conducted with bacitracin, penicillin, illoty-
cin and other antibiotics to justify recommendations for their use. Of
especial interest are preliminary reports that bloat can be controlled by
antibiotic feeding (I).
Considerable variation in response to antibiotic feeding has been obtain-
ed between experiments. For example, a recent survey (3) showed that weight
gains were not increased in ten of thirty-two college experiments reviewed.
Efficiency of feed utilization was not increased in eight of the thirty-two
experiments. One obvious explanation for such variation would be the health
of the feeder cattle at the time they were started on feed. Another might
be the length of time that the antibiotic was included in the fattening
ration. Florida workers (2) have reported that the response to aur ntv
feeding subsides after approximately one month and may actually d
thereafter. This has led to their recommendation of adding appr lately
-j- 25 15
IAssociate Animal Husbandman, Department of Animal Husbandry an triton.
Presented at Nutrition Conference, University of Florida, Gaine vi e, on .
November 9, 1956. ',,S
200 milligrams aureomycin (30 mg. per 100 pound live weight) to a starter or
conditioning ration during only the first few weeks while the cattle are
getting on full feed. Such a recommendation is supported by recent reports
that antibiotics may depress fiber digestion in the rumen (7, 9).
Cull beef-type calves weighing from 100 to 300 pounds often flood South-
eastern markets in the fall months. Such calves may be wintered and sold at
prices reflecting a wide margin but the risk of death losses has made such an
operation unattractive. These calves are usually weak and heavily parasitized
at purchase. They usually remain subject to respiratory diseases throughout
the wintering period. A preliminary Florida study (5) has shown that good
management coupled with the feeding of 75 milligrams aureomycin daily through-
out the wintering period will improve the apparent health of the calves,
increase weight gains and decrease feed costs.
A survey of college experimental results will show that the combination
of aureomycin or terramycin and diethylstilbestrol may be no better than
diethylstilbestrol fed alone.
SUMMARY OF REPRESENTATIVE FEEDING TRIALS
Ration No.Trials Antibiotic Hormones Control Antibiotic Hormone Combination.
Grain 4 Aureo. Stilb. 2.39 2.40 2.71 2.61
I Terr. Stilb. 2.12 2.40 2.37
Silage 2 Aureo. Stilb. 0.92 1.09 1.10 1.04
I Terr. Stilb. 2.19 2.34 2.38
Pasture I Aureo. Stilb. 1.52 1.48 2.03 1.70
I Terr. Stilb. 1.46 1.54 1.85 1.56
Table 2 shows that gains are increased when antibiotics are added to silage
rations and when diethylstilbestrol is added to heavy grain rations. It should
be noted that a combination of the two gave less response than diethylstilbestrol
alone in every case. A Florida experiment (6) with fattening steers has shown
the combination to stimulate a greater gain than either alone during the initial
three weeks. After 7 weeks, gains on the combination fell sharply below diethyl-
stilbestrol alone but remained above aureomycin alone. Here again, the benefit
from adding an antibiotic is demonstrated only in the initial phase of the
Hexestrol, a synthetic estrogen similar to deithylstilbestrol, has been
fed in combination with aureomycin with good results in one experiment. Further
studies are needed, however, before recommending its use.
The consistently favorable results from the addition of 10 milligrams of
diethylstilbestrol to cattle fattening rations is well established. A survey
of college experimental results will reveal that weight gains have been increased
an average of 17 per cent and feed savings have averaged 12 per cent when 10 mil-
ligrams of diethylstilbestrol is fed daily with high energy rations. Some vari-
ation in response may be expected but a favorable response has been obtained on
each of the following systems of fattening cattle:
1. Heavy grain rations
2. Medium grain, medium roughage
3. Heavy corn silage
4. Pasture alone
5. Pasture plus limited concentrates
6. Pasture plus full concentrate feed
Ohio workers (8) have reported that a growth response from diethylstilbestrol
feeding is dependent upon the ration containing adequate protein. A medium level
(0.75 Ib. soybean oil meal) proved to be more economical than a high level (1.50
Ib. soybean oil meal) of protein supplementation for steers full fed a corn and
cob meal ration. Iowa workers (4) have reported that diethylstilbestrol feeding
may reduce the amount of protein required by calves. A ration containing 10.5
per cent protein was ample for calves when 10 milligrams diethylstilbestrol was
fed. A lesser amount, 5 milligrams daily, gave an equal response with a 13.5 per
cent protein ration. Although this aspect of hormone feeding needs further study,
it is apparent that medium protein rations plus 10 milligrams diethystilbestrol
may be the most economical.
Size and age apparently have little effect on the response to imone.feedingof
cattle weighing over 600 pounds. A lesser response is obtained with calves.
Sex apparently has little effect on response to hormone feeding as steers,
bulls, open heifers and spayed heifers have given favorable responses.
Other hormones and hormone-like substances which have been investigated for
cattle feeding are Hexestrol, Dienestrol, Synovex (an estradiol-progesterone com-
bination), cholesterol, testosterone, thyroprotein, thyroxine, thiouracil,
thiourea, various iodides and others. Each must be studied more extensively
before recommendations for their use are justified.
ORAL VS. IMPLANT DIETHYLSTILBESTROL
Early studies with large stilbestrol implants gave increased gains but
decreased carcass grades. Recent studies using low level implants have given
results comparable to oral feeding without lowering carcass grade. This method
may also hold real promise for pasture fattening.
SUMMARY OF EXPERIMENTS WITH IMPLANTED DIETHYLSTILBESTROL
Av. Da. Gain Feed/lb. gain
Ration No. Trials Control Oral Implant* Control Oral Implant
Pasture 2 (Ga.) 2.33 3.02(24)
3 (Calif.) 1.76 1.97(120)
Drylot I (Purdue) 2.24 2.47(60) 7.1 6.8
2.24 2.68(120) 7.1 6.2
4 (Calif.) 2.35 3.11(60) 17.3 13.8
I (Calif.) 2.40 2.96(120) 10.1 11.1
I (Purdue) 2.66 2.95 2.80(f2) 9.9 9.2 -
-- 3.17(36) 8.7
Lo protein 2.00 1.97 2.03(60) 8.8 8.5 8.3
Med protein 2.14 2.59 2.62(60) 8.3 6.9 7.7
Hi protein 2.37 2.85 2.75(60) 8.2 6.7 6.4
*Size of implant in milligrams shown in parentheses.
day in each case.
Oral intake is 10 mg. per
Although the subcutaneous implantation of stilbestrol in cattle has received
approval by the Federal Food and Drug Administration and has been shown in Table
3 to stimulate gains and effect feed savings, there is still a question as to
the most effective level to use. Levels between 24 to 48 milligrams administered
at the start of the feeding have proven best to date. No advantage has been
observed by administering the hormone during only a part of the feeding period
or by administering additional implants throughout the feeding period.
I. Barrentine, B. F., C. B. Shawver and L. W. Williams. 1956.
for the prevention of bloat in cattle grazing Ladino clover.
2. Black, John A. 1956. The use of aureomycin and diethylstilbestrol as
components of steer fattening rations. M.S. Thesis, University of Florida.
3. Burroughs, Wise.
1956. Stilbestrol and Hormone feeding to cattle and
4. Culbertson, C. C., Wise Burroughs, R. Preston, J. Staley, Paul Homeyer
and E. A. Kline. 1956. Amount of stilbestrol needed by high-gaining and
low-gaining steer calves fed medium protein and high protein fattening
rations. A. H. Leaflet 211. Iowa State College.
5. Hentges, J. F., Jr. and J. A. Black. 1956. Unpublished data. University
6. Hentges, J. F., Jr., J. A. Black, C. A. Tucker II and T. J. Cunha. 1955.
The effect of chlortetracycline and diethylstilbestrol on growth and car-
cass measurements of steers. J. Animal Sci. 14:1207.
7. Hungate, R. E., D. W. Fletcher and I. A. Dyer. 1955.
tetracycline feeding on bovine rumen microorganisms.
Effects of chlor-
J. Animal Sci. 14:997.
8. Klosterman, E. W., 0. G. Bentley, A. L. Moxon and L. E. Kunkle. 1956.
Relationship of sex hormones to protein levels for fattening cattle.
Feed Age. 6:32.
9. Lambert, M. R. and N. L. Jacobson. 1956. The effect of chlortetracycline
feeding on in vitro cellulose digestion by rumen microorganisms. J. Animal