The subject of hormonal relationships and applications was reviewed in Publication 
266 of the National Research Councilin 1953 (10) and again in Publication 714 in 1959 (11). 
The developments in the use of antibiotics largely date from 1949 when fermentation 
residues were found to have growth-promoting effects in poultry and swine apart from the 
vitamin B12 content. The disease level concept was introduced to explain the effectiveness 
of antibiotics in correcting slow growth and generally in accelerating growth rates. A 
great number of researches followed the early observation and in a remarkably short 
period the use of antibiotics was adopted for general commercial feeding practices. 
Numerous reviews on antibiotics in nutrition have been published. The list of antibiotics 
is an ever-expanding one. Some 17 antibiotics that have been noted in research papers 
are given below: 
Some Antibiotics Tested as Feed Additives 
Actidione Neomycin 
Bacitracin Oleandomycin 
Chloramphenicol Oxytetracycline 
Chlortetracycline Penicillin 
Erythromycin Polymyxin 
Fumagillin Streptomycin 
Gramicidin Subtilin 
Hygromycin Tyrothricin 
Tlotycin 
Of relatively recent interest are tranquilizers, with greatest emphasis on beef cattle 
and sheep. Some of the tranquilizers that have been tested in feedlot studies are shown 
below. There are many more of these that have been prepared and tested pharma- 
cologically. 
Some Tranquilizers Tested as Feed Additives 
Chlorpromazine Rauwolfia 
Ethyl isobutrazine Reserpine 
Hydroxy zine Tetrahydrozoline 
Mepazine Trifluomeprazine 
Perphenazine Trifluoperazine 
Prochlorperazine 
Various other classes of feed additives, the principal group being the arsenicals 
with two types--the arsonic and the arsanilic acids--are given below, The beneficial ef- 
fects of feeding arsenicals to chickens were observed as early as 1877 and were redis- 
covered in 1946, 
Other Feed Additives Tested in Feeding Experiments 
Organic arsenicals Enzymes 
Arsonic acids Surfactants 
Antioxidants Live rumen cultures 
Fowler's solution was once a widely usedtonic for livestock. Research in recent years 
has largely revolved around organic arsenicals in the feeding of growing poultry and 
swine. The main concentration of research dates from about 1951 and the major interest 
has been in poultry. 
Other classes of materials include surfactants, enzyme preparations, live rumen 
cultures, and others. Research interest has not been as widespread although numerous 
reports have appeared in the last few years. While antioxidants do not function in the way 
38 
