Use of antibiotics as feed additives: a burning question

INTRODUCTION Antibiotics are chemotherapeutic agents used for the clinical management of infectious diseases in humans, plants and animals. However a sizeable fraction of antibiotics produced every year all over the world is used for non-therapeutic purposes. In US alone, about 24.6 million pounds of antibiotics are used in animal agriculture annually and a substantial portion of this is used as growth promoters and not for the treatment of infections (Oliver et al., 2011). According to a recent report, out of 13 million kg of antibiotics administered to animals in 2010, the major portion was meant for promoting the growth of the livestock (Spellberg et al., 2013). The ability of low doses antibiotics to promote growth of animals and birds was discovered serendipitously in the 1940s (Gustafson and Bowen, 1997). Subsequently, it was widely exploited and by this time, addition of antibiotics to the animal feed to stimulate growth has turned into a global practice. The basis of growth-promoting effect of antibiotics is not clearly known. It is postulated that microorganisms present in the animal feed consume a considerable portion of nutrients in the feed. They also inhibit absorption from the intestine and produce toxins having adverse effect on the health of the animals. The growthpromoting effect of antibiotics might stem from their ability to suppress these harmful organisms. It is also suggested that animals reared in the unhygienic environments always bear some latent infections, which trigger a cascade of events in their immune system. Cytokines produced in the process lead to the release of some catabolic hormones which cause wastage of muscles. Antibiotics relieve the animals of the need to produce cytokines by suppressing the causative agents of infections.