TABLE 1.--Summary of Experimental Comparisons of Feed Additives in Beef Cattle Rations 
(From Iowa State University - AH 805) 
A Expt'1 Gain Feed Return per 
feed adds otve increase saving animal 
Stilbestrol - oral Number Percent Percent Dollars 
Fattening ration 105 13 10 6.94 
Growing ration 58 12 10 5.63 
Stilbestrol - implant 
24 mg. 35 9 6 -19* 
36 mg. 45 15 10 3.00% 
Hexestrol - oral 14 ms) 10 
Dienestrol - oral 4 9 8 
Progesterone - estradiol implant i153 WZ 8 2.40 
Tranquilizers 72 3 aL 90 
Enzyme ( Agrozyme) 12 7 4 3305 
Antibiotics 112 4 3) S\G INS) 
*Incomplete comparison. 
The summary from Iowa State University shows that antibiotics, mainly chlortetra- 
cycline and oxytetracycline, prom ted some increase in gainand in feed saving averaging 
4 and 3 percent, respectively,i: fattening beef cattle. Actually, researchreports have 
been somewhat conflicting as tc - fects of the antibiotics on the rumen flora and on the 
digestive process. The level and ‘ve of antibiotic used and the proportions of roughage 
and concentrates making up the 1.:ti: 1 all appear to be factors, It appears that relatively 
low levels of an antibiotic that does x.ot unduly upset the rumen flora balance and suitable 
rationing does promote some inc ¢::se in rate of gain and in feed economy. There has 
been some benefit noted in use of antibiotics in supplemental feeding of suckling calves. 
The use of tranquilizers first came into prominence inconnection with shipment of 
feeder calves and their adjustment to the feedlot, Subsequently, tests have been made on 
responses during the feeding period. The data summarized in Table 1 do not suggest any 
great advantage in the use of tranquilizers thus far tested. 
Several enzyme preparations that have been tested have given relatively modest 
positive responses. Undoubtedly, before full appraisal is made, additional studies on 
more preparations will be needed. 
With beef cattle and other species as well, many tests on various combinations of 
feed additives, such as hormones combined with antibiotics, have been made. The number 
of such combinations is too large to attempt any detailed analysis at this time. Fre- 
quently there are added benefits. 
The effect of the various feed additives on quality and grade of beef carcasses has 
been much debated. It appears that some lowering of carcass grades frequently results 
from the use of sex hormones. On the other hand, the antibiotics promote a small im- 
provement, Data compiled by Burroughs on the oral feeding of stilbestrol indicate that 
the carcasses averaged very close in grade to the controls and differences would not be 
apparent to the average person. In general, however, carcasses of stilbestrol-treated 
animals represented in Table 1 would be heavier, so for equal weights, the grade differ - 
ential could be expected to be somewhat greater. There are reports that show that less fat 
and more lean tissue for hormone-treated animals of weights equal to controls. Most 
of the extreme cases of carcass differences have occurred where high doses of drugs 
have been used. 
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