ville (12) on gilt pigs using a wide range of oral doses. An impressive feature of this 
study was the changing effects observed onestrus manifestations with increase in dosage. 
Whether swine are more sensitive to compounds, suchas stilbestrol, and optimal dosages 
have not been found, remain as unanswered questions. Side effects in both males and 
females have been prominent in many studies. 
The use of antibiotics in swine feeding presents a much more favorable picture than 
for hormones. Numerous reviews have been published showing benefits in terms of rate 
of gain, feed savings, disease level, and others. The data in Table 3 for antibiotics as a 
group are based on figures from Jukes (6). They represent an average for five antibiotics 
most used in swine feeding. The ranking ineffectiveness for growth is: chlortetracycline, 
oxytetracycline, streptomycin, penicillin, and bacitracin. There has been a question for 
several years whether presently used antibiotics would lose their effectiveness of whether 
the disease level would be soimprovedas to render the antibiotics less useful. A summary 
compiled by J. D. Drain and W. F. Kwoek (3) on 10 years of tests at experiment stations 
indicated that control lots of pigs have improved in performance while chlortetracycline- 
treated pigs have maintained high performance. In other words, the gap between treated 
and untreated pigs has narrowed during the 10-year period. There have been questions as 
to effects on fatmess of swine carcasses. However, the data do not show any appreciable 
increase in fatness through the use of antibiotics. 
TABLE 3.--Summary of Experimental Comparisons of Feed Additives in Swine Feeding 
How til Gain Feed 
Mg. Number Percent Percent 
Arsenicals oral 15-45/1b. 8 2 2 
Antibiotics? do 5-10/1b. 325 19(35-9) 5(10-0) 
Chlortetracycline? do 10/1b. 87 14 4 
Stilbestrol do 0.5-2.5/1b. 4 fo) 3 
Do implant 3-50 1 O 2 
Other sex do -- 7 -5 9 
Testosterone oral 20-40/day 5 ) 0 
Iodinated protein do 1.35-80/1b. 7 0 © 
Thiouracil do 227-1134/l1b. 10 -23 al 
1 Adapted from Jukes (6) » as average for chlortetracycline, oxytetracycline, streptomy- 
cin, penicillin, and bacitracin. 
2 Adapted from American Cyanamid Co., Public. (1959) Production Performance of Swine-- 
Ten Years After Introduction of Aureomycin. 
Of the other feed additives, the chief group studied in swine is the arsenicals. Re- 
search data are somewhat conflicting. Used therapeutically, arsenicalsare quite effective 
in preventing or controlling swine dysentery. Arsanilic acid has been reported effective 
as an agent in reduction or prevention of selenium toxicity in growing pigs fed diets con- 
taining dangerously high levels of this element. The growth and feed savings from the use 
of arsenicals do not show significant trends and have been so indicated in Table 3. 
In general, the few tests with tranquilizers have failed to show beneficial effects. 
In one case at least, reduced activity was noted with resulting reduction in feed con- 
sumption and rate of gain. A few tests with enzymes have shown some promise. Certain 
types of diets may be benefited more than others. Starter diets for young pigs may be 
improved, for example. 
As with other classes of livestock, various combinations of hormones, antibiotics, 
arsenicals, tranquilizers, and other chemicals have been tested. A few have shown some 
additive effects. 
43 
