Antimicrobial growth promoters

Antimicrobial growth promoters are substances that, when added to feeds at subtherapeutic dosages for an extended period of time, produce improvements in growth rate and feed conversion efficiency, mortality, and morbidity. 

Since many of the above-mentioned compounds possess major anti-infec-tious activity in addition to their role as growth promoters, their application in animal farming has already been discussed in previous chapters. Hence, this chapter concentrates on the remaining compounds within this group, namely the organic arsenicals, peptide antibiotics, quinoxaline-l,4-dioxides, and miscellaneous substances. 

Certain organic arsenicals are incorporated in pig and broiler feeds to improve weight gain and feed efficiency and to combat enteric infections. Arsanilic acid 

Organic arsenicals are poorly absorbed from the gastrointestinal tract and are excreted mainly in feces (1). After their absorption, organic arsenicals are distributed throughout the body and rapidly excreted in the urine without being metabolized to a great extent. Elimination of the parenterally administered compounds is nearly complete within 24-48 h, while several days are required for elimination of the compounds from the gut. 

Arsanilic acid is added to swine and poultry feeds at a dosage rate of up to 100 ppm for growth-promoting purposes. It is also effective for prophylaxis and treatment of many outbreaks associated with E. coli infections in swine. To treat scour in swine, arsanilic acid is administered in the feed, at a level of 250 ppm for up to 3 weeks. Arsanilic acid may also be administered to poultry for treatment of coliform septicemia at a level of 250 ppm in the feed for 5-8 days. 

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Rapid and sensitive HPLC methods were developed for the detection of an antimicrobial growth promoter and its main metabolites containing quinoxaline-2-carboxylic acid <2005MI1495>. The major phenazine pigments of Pseudomonas aeruginosa such as 1-hydroxyphenazine and phenazine-l-carboxylic acid <1997JCH(A)(771)99>, and 2-aminophenazine as an impurity in a bactericide <1999MI632>, were also analyzed by HPLC methods. 

Apart from the antimicrobial growth promoters, there have been some other hormonal-type compounds with anabolic activity that are administered usually... 

Table 29.12 Physicochemical Methods for Antimicrobial Growth Promoters in Edible Animal Products... 

Smulders, A.C.J.M., Veldman, A. and Enting, H. (2000) Effect of antimicrobial growth promoter in feeds with different levels of undigestible protein on broiler performance. In Proceedings of the 12th European Symposium on Poultry Nutrition, WPSA Dutch Branch, Veldhoven, The Netherland, 15-19 August, 1999. 

Situ, C., E. Gratters, P. van Wichen, et al. 2006. A collaborative trial to evaluate the performance of a multi-antibiotic enzyme-linked immunosorbent assay for screening five banned antimicrobial growth promoters in animal feeding stuffs. Anal. Chim. Acta 561 62-68. 

Tylosin is a polyketide lactone substituted with three deoxyhexose sugars. It is used as an antimicrobial growth promoter in animals. Acquired resistance has been observed in potentially human pathogenic strains isolated from animals (1). Of further concern is the fact that tylosin confers cross-resistance on erythromycin (2). 

Butaye P, Devriese LA, Haesbrouck F, Antimicrobial growth promoters used in animal feed Effect of less well known antibiotics on Gram-positive bacteria, Clin. Microbiol. Rev. 2003 16 175-178. 

Figure 1. (A) Influence ofdietary pectin on protein deposition (PD) and efficiency ofThr utilisation (Zhu et al., 2005) and (B) Influence of dietary Thr on body gain in growing pigs fed diets with or without antimicrobial growth promoter (Bikker et aL, 2007).

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