POULTRY 
The ability of estrogens administered to growing chickens to increase the fat content 
of the tissues was known for some time before interest was aroused in the practical ap- 
plication of the procedure. When diethylstilbestrol became available, Lorenz of California 
(8) demonstrated the feasibility of increasing the fat content of breast and leg muscle by 
implantation of the hormone. Numerous subsequent studies have clearly proven that 
hormone administration is effective in fattening and improving the finish in most classes 
of poultry. 
Experimental results concerning the effect of hormone treatment on growth rate are 
not clear cut. About half of the investigators have reported some improvement, while the 
others found no effect. Studies at the Texas Station (2) on the effect of protein level on the 
growth rate indicated that the greatest response of implanted diethylstilbestrol was ob- 
tained on lower levels of protein, 14 and 16 percent. No growth response was obtained on 
a 2l-percent diet. Similar results have been observed with turkeys at Beltsville. These 
findings, however, have no particular practical application since hormone treatment on 
the lower protein levels did not give optimum growth and feed conversion, 
There is general agreement that hormone administration does not enhance feed 
conversion, A number of investigations show that the efficiency of feed utilization is 
decreased by the treatment. 
Carcass analyses have shown that the increase infat content resulting from hormone 
treatment is accompanied by a percentage decrease in protein, thus indicating that the 
live-weight gain is almost entirely due to greater deposition of fat. It has also been re- 
ported that higher cooking losses were encountered in hormonized birds, which in some 
cases amounted to 20 percent more than those obtained with the control groups. 
Since these findings showed no economic advantages of using stilbestrol in broiler 
production the practice was not widely adopted, and in recent years has been essentially 
discontinued. 
As to the use of estrogens in the specialized production of capons, the practice of 
which was terminated late in 1959, there was, no doubt, some economic advantage. For 
example, reports of experiments showed that hormonized birds were heavier, required 
less feed, and excelled in finish as compared to either normal males or surgical capons 
at 24 weeks of age. 
The preponderance of experimental evidence shows that antibiotics enhance the 
growth and feed efficiency of chickens. By no means, however, have the experiments 
indicated a real advantage from antibiotic supplementation. These conflicting findings 
have led to numerous investigations of factors that influence antibiotic response. The 
general conclusion can be drawn that, under conditions of stress, that is, presence of 
unfavorable organisms, extremes in ambient temperature, disease, and crowding, anti- 
biotics have proven most effective. In commercial broiler production one or more of 
these conditions is almost invariably present. 
Studies on the interrelationship of antibiotics with other nutrients, such as the spar- 
ing effect on protein and B-vitamins, have provided some very interesting but extremely 
confusing information. Until sufficient knowledge is obtained concerning these relation- 
ships, they are useful as possible explanations for discrepancies in experimental results, 
but have no obvious practical application. An exception is the interaction between dietary 
calcium and antibiotics. It has been shown that low calcium enhances absorption of 
chlortetracycline. This has been advantageous when it is necessary to use the antibiotic 
at therapeutic levels. 
There has been a considerable amount of work published indicating that antibiotics 
lose their effectiveness when used over a period of time and that the newer antibiotics 
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