Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Animal Science


Antibiotic reed supplements have been extensively used in major livestock producing countries tor more than 15 years. In the United States, more than 1.25 million kg are used annually as diet supplements. The wide acceptance of antibiotics by livestock producers has been based on established benefits such as increased growth rate, improved reed conversion, and reduced mortality and morbidity from clinical and subclinical infections. Expenditures for antibiotics used as feed additives totaled $42 million in 1965 while the total spent for feed additives approached $142 million. It is evident that antibiotics make up a large part of the total reed additives used in livestock diets. A wide variety of antibacterial compounds have been used in diets tor nonruminant livestock and a number or these have also been tested for ruminant animals. Of these compounds, chlortetracycline has received more attention than other antibacterial agents in research with cattle and sheep. While the response to chlortetracycline additions has been favorable as computed across experiments, the response has been inconsistent in many experiments. To improve feedlot performance more consistently, combinations of antibacterials have been proposed to increase the effectiveness of antibacterial therapy. One of the combinations that has gained interest in recent years is that of chlortetracycline with sulfamethazine. Sulfamethazine by itself has not appeared to be effective as a feed additive in improving feedlot performance, but experimental evidence indicates that it improves the effectiveness of chlortetracycline when added in combination. The basis for this study was to more precisely delineate the responses to be expected when supplementing feedlot lambs with a high level of ohlortetracycl1ne, sulfamethazine, or the combination of both antibacterial agents under a variety of feedlot conditions and types of diets. Responses measured under these various regimes included average dally gain, feed utilization, death losses, adaptation time to various diets, general health and incidence of disease.

Library of Congress Subject Headings

Lambs -- Feeding and feeds
Sheep -- Feeding and feeds



Number of Pages



South Dakota State University