NUTRITION
PIH-31
pork industry handbook
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • WEST LAFAYETTE, INDIANA
Feed Additives for Swine
Authors
Mack D. Whiteker, University of Kentucky
Virgil W. Hays, University of Kentucky
Gary R. Parker, University of Kentucky
Reviewers
Vaylord D. Ladwig, University of Illinois
Jake L. Krider, Purdue University
Jim Butler, Austin, Minnesota
The use of feed additives in swine rations has been extensive in the United States for more than 25 years. Feed additives are used by most swine producers because of their demonstrated ability to increase growth rate; improve feed utilization; and reduce mortality and morbidity from clinical and sub-clinical infections.

In general, additives available for swine producers fall into three classifications: (1) antibiotics; (2) chemothera-peutics; and (3) anthelmintics (dewormers). Additives on the market can be used with reliability when recommended rates and specifications are followed.

Antibiotics
An antibiotic is a compound synthesized by a living organism which inhibits the growth of another. Therefore, it is biologically derived from bacteria and molds. The one thing antibiotics have in common in improving animal performance is their demonstrated ability to kill or inhibit the growth of certain microorganisms.

There are many antibiotics on the market, and they differ widely in chemical composition and mode of action. Thus, some have an antibacterial effect on a relatively smali number of organisms, whereas others are active against a wider variety of organisms.

Chemotherapeutics and Anthelmintics
Chemotherapeutics are organic compounds with bacteriostatic or bactericidal properties similar to those of antibiotics. But, unlike antibiotics, these compounds are produced chemically rather than microbiologically. Anthelmintics, or dewormers, are also organic compounds added to swine diets generally for short intervals to help control worm accumulation in growing-finishing swine and the breeding herd.
Some feed additives may remain in tissues longer than others. The level fed and the duration of feeding also influence clearance rates. Therefore, producers should abide by the required withdrawal times and use only the approved levels when incorporating additives into their swine rations. Tables 1 and 2 present some of the commonly used feed additives, their withdrawal times, and their approved usage levels.

Choosing a Feed Additive
Research has well documented the growth-promoting potential of feed additives. Most observations suggest that this effect is mainly a result of their influence on the parasitic microorganisms of the host animal. Also it is well documented that the degree of response varies with the control of specific or non-specific disease organisms in the animals' environment. Several feed additives are available to producers for growth promotion in swine. Table 1 lists several of the available feed additives and their approved growth-promoting levels.

Selection of a specific feed additive and the level needed for optimal response will vary with the existing farm environment, management conditions and the stage of the production cycle. In certain stages of the production cycle one can be rather sure of a response to feed additives; in other stages the likelihood of obtaining a response is less evident.

The first few weeks of the pig's life are by far the most critical in terms of nutritional needs or health protection. The pig is born with no protection against organisms into an environment that is highly saturated with a wide variety of bacterial organisms. The first milk, colostrum, of the sow will supply the pig with antibodies against the disease organisms in the surroundings, provided the sow has
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U. S. Department of Agriculture Cooperating. H. G. Diesslin, Director, West Lafayette, Ind. Issued in furtherance of the Acts of May 8 and June 30, 1914. It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have equal opportunity and access to its programs and facilities without regard to race, religion, color, sex or national origin.