Mechanism of antimicrobial growth promoters used in animal feed.

Denis E Corpet 1, *
* Corresponding author
Abstract : Most feeds for broilers, pigs and veal calves, but 1/3 of feeds for beef cattle, are supplemented with an antimicrobial growth promoter. A European regulation list allows antimicrobial growth promoter, concentrations, animal species, and withdrawal periods (often null). Presently, avilamycin, flavomycin, lasalocid, monensin, and salinomycin are allowed. Avoparcin, bacitracin, carbadox, olaquindox, spiramycin, tylosin, and virginiamycin use was suspended by EU in 1997 and 98. Permitted doses are around 20 ppm (=20 g/t feed). Animals given antimicrobial growth promoter supplemented feeds grow faster and more uniformly than controls (average daily gain improved by 3 to 9%). They have a lower feed intake per weight gain (the feed conversion ratio is reduced by 3 to 12%), and release less nitrogen in the environment. The mechanism of growth promotion by antimicrobial growth promoters is still speculative. However, the growth promotion is likely due to a modification of the gut flora, since antimicrobial growth promoters do not promote the growth of germfree animals. Moreover, a modified antimicrobial growth promoter molecule promotes growth only as long as it retains antimicrobial potency. Most studies show no or little changes in the composition of gut flora during antimicrobial growth promoter supplementation. By contrast, antimicrobial growth promoters strongly suppress the bacterial catabolism of urea and amino-acids, both in vitro and in vivo. Antimicrobial growth promoters also decrease the fermentation of carbohydrates and the decomposition of bile salts. These changes increase the availability of nutrients and energy to the animal host (sparing effect), and decrease the concentration of toxic molecules like ammonia or amines in the gut, leading to a reduced turnover in the gut epithelium. In cattle, the rumen flora fermentations are oriented toward propionic acid production, instead of acetic acid, favouring the meat deposit, and less methane is produced. Because antimicrobial growth promoters show maximum efficacy in farms with poor hygiene, some authors argue that another beneficial effect of antimicrobial growth promoters lies in an improved control of pathologies (e.g., necrotic enteritis in poultry, swine dysentery in pigs).
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Denis E Corpet. Mechanism of antimicrobial growth promoters used in animal feed.. Revue de Médecine Vétérinaire, Ecole Nationale Vétérinaire de Toulouse, 2000, 151 (2), pp.99-104. ⟨hal-00411009⟩



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