Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Animal Science


Growth stimulation in domestic animals due to dietary supplementations of antibiotics has received a great deal of attention in the last few years. Moore and co-workers in 1946 (35) observed that the addition of streptomycin to the diet of chicks led to increased growth responses and in 1948 Harned et al. (17) administered aureomycin to chicks and he also noted an increased growth rate. Little significance was attached to these discoveries and the present interest in antibiotics as feed supplements is the result of investigations by Stokstad and co-workers in 1949 (40) with cultures of Streptomyces griseus and Streptomyces aureofaciens as sources of vitamin B12. These workers found that growth promotion using these cultures was not entirely due to the presence of vitamin B12 because accelerated growth was observed when the basal diet contained adequate amounts of that vitamin. Other workers became interested and their experimental work soon demonstrated the economic practicability of antibiotic supplementations in the diets of certain farm animals.The diets of growing pigs and poultry at the present time are quite generally supplemented with antibiotics. Improved feed efficiency, an increased rate of gain and a reduction in the incidence of scours have been demonstrated through numerous experiments in which antibiotics have been administered to calves. There is considerable disagreement regarding the economic practicability of antibiotics in the rations of older ruminants. Several workers have observed definite deleterious effects as a result of antibiotic supplementation; while others have been able to detect no change and still others report increased rates of gain and greater feed efficiency when older ruminants are feed antibiotics. Nutritionists interested in ruminant antibiotic supplementation are confronted with several problems which have not been completely solved. There are the problems of evaluating the usefulness of the antibiotics in relation to milk production in cattle, wool production in sheep, growth, carcass quality, reproductivity and hardiness of offspring in both species, and establishing the most practical level of antibiotic in relation to basal diet, size and species of animal. Many have speculated and some have attempted to determine experimentally the mode of antibiotic action in feed supplements. Since ruminant nutrition basically depends on bacterial synthesis, antibiotics might be expected to alter or affect this synthesis by changing the number or kinds of microorganisms present. This research was begun to determine whether or not such changes do occur when a given level of antibiotic is included in the diet of an adult sheep.

Library of Congress Subject Headings

Antibiotics in animal nutrition
Sheep -- Feeding and Feeds
Rumen -- Microbiology


Includes bibliographical references (pages 30-33)



Number of Pages



South Dakota State University


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