As feed additives

Not many fine chemicals have a production value exceeding 10 million per year. Less than a do2en achieve production volumes above 10,000 metric tons per year and sales of > 100 million per year. Apart from the pharmaceutical and pesticide fine chemicals these comprise the amino acids (qv), L-lysine and n,T-methionine used as feed additives (see Feeds AND FEED ADDITIVES), and vitamins ascorbic acid and nicotinic acid. 

Thiostrepton family members are biosynthesized by extensive modification of simple peptides. Thus, from amino acid iacorporation studies, the somewhat smaller (mol wt 1200) nosiheptide, which contains five thiazole rings, a trisubstituted iadole, and a trisubstituted pyridine, is speculated to arise from a simple dodecapeptide. This work shows that the thiazole moieties arise from the condensation of serine with cysteiae (159,160). Only a few reports on the biosynthesis of the thiostrepton family are available (159,160). Thiostrepton is presently used ia the United States only as a poly antimicrobial vetetinary ointment (Panalog, Squibb), but thiazole antibiotics have, ia the past, been used as feed additives ia various parts of the world. General (158) and mechanism of action (152) reviews on thiostrepton are available. 

Copper compounds are used as feed additives in Europe and the United States primarily for chickens and swine (see Feeds and feed additives) (90,91). Copper increases the rate of gain and feed efficiencies of the animals. It is unclear whether this results from overcoming animal deficiencies or by enhancing preservation of feedstuffs. 

Oxytetracycline is a broad-spectrum antibiotic, which has been used worldwide in veterinary medicine and in aquaculture for the prevention and treatment of disease and as feed additives to promote growth. The maximum residue limits (MRLs) of OTC and relative substances as described by the US Food and Drug Administration [66] and European Union [67] are presented in Table 4. 

Various phenylarsonic acids — especially arsanilic acid, sodium arsanilate, and 3-nitro-4-hydroxyphenylarsonic acid—have been used as feed additives for disease control and for improvement of weight gain in swine and poultry for almost 40 years (NAS 1977). The arsenic is present as As+5... 

Since the discovery of penicillin, an enormous number of antibiotic compounds have been isolated. They have found uses both in treatment of human disease and in various aspects of agriculture, including treatment of animal and plant diseases, and as feed additives to promote growth of animals. Some antibiotics such as tylosin were developed specifically for agricultural use. 

This book was developed to provide a current perspective on agricultural use of antibiotics. Topics include some major uses of antibiotics, problems associated with their use from a regulatory standpoint, residues in food including methods of detection, risks to human health from use in feeds, trends in use, and overall risks and benefits. The scope, therefore, is much broader than in several other recent symposia that have focused mainly on the controversy regarding the use of antibiotics as feed additives. Many of the topics included in the present volume have not been discussed under one cover before. 

Feed Additives. Some antibiotics are also administered in the feed for the treatment of disease. These are listed in Table III. For the most part, they are used for the treatment of bacterial infections and are the same as those listed in Table II. Although these antibiotics are incorporated into the feed, their use differs from what has become known as "feed additive antibiotics" or growth permittants. 

Table III. Fermentation Products Used as Feed Additives for the Treatment of Disease...

Exposure of animals to therapeutic levels of antibiotics will markedly raise the level of resistance and a long period of time is required for the resistance levels to return to the pre-treatment level In an experiment replicated five times (Lang lo is et al ifi.) we found that exposure of animals to subtherapeutic levels of gram-positive spectrum antibiotics also resulted in increased levels of tetracycline resistance During the course of our study we have sampled pigs on two separate occasions (1974 and 1985) from another research herd in which antibiotics have never been used as feed additives but only for therapeutic purposes Of the 100 pigs sampled in 1974 only one had been... 

In 1971, Great Britain implemented a ban on subtherapeutic use of tetracyclines in animal production. This action was taken after considerable debate and was greatly influenced by antibiotic resistant Sa Imone 1 la infections (S. typhimurium phage type 29) in humans in the mid-1960 s, which appeared to be related to similar infections in calves (Anderson, 23 Antibiotics were not approved as feed additives for calves at that time nor previously. Thus, earlier implementation of the Swann Committee (Ifi) recommendations would have had no apparent impact on that particular epidemic, nor did it prevent a similar epidemic later (Rowe et al., 12J. 

Antibiotics are used extensively in raising meat animals and poultry in the United States (USA) and other nations. The antimicrobials are used as feed additives or medicants they allow for faster weight gain and more concentrated rearing practices, and protect the maturing animals against the various diseases that may occur on the farm. 

The nitrofurans are synthetic antibacterial compounds, all containing in their molecule a characteristic 5-nitrofuran ring (Fig. 3.5). Furazolidone, nitrofurazone, furaltadone, and nitrofurantoin are all nitrofiirans that have been widely used in the prophylactic and therapeutic treatment of infections caused by bacteria and protozoa in swine, cattle, poultry, rabbits, and fish. They have been also used as feed additives in animal husbandry. They are very effective drugs and do not appreciably contribute to the development of resistance (120). 

They are still widely used as feed additives for treatment or prevention of coccidiosis. In ruminants, sulfaquinoxaline, sulfadimethoxine, and sulfame-thoxypyridazine are the most useful coccidiostats, although sulfachlorpyrazine, sulfathiazole, and sulfamonomethoxine are also highly effective. Additional coccidiostats or adjuvants such as amprolium, chlortetracycline, and ethopabate are often combined with sulfonamides for synergistic effects in poultry. 

Table 11.7 Veterinary Drugs Authorized as Feed Additives Within the European Union... 

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