The use of antibiotics as feed additives for farm animals.

Antibiotics are added at low concentrations to feeds as growth stimulants and at therapeutic levels to cure known diseases. As their action in both instances is to modify bacterial, protozoal or fungal populations, the division between the two categories is indistinct ; this is especially so when intermediate levels are considered. The present outline of use includes other feed additives which stimulate growth if they act or might act in a similar way to antibiotics, but hormones, enzymes and other chemicals (Shillam, 1971)) which have a different mode of action, are excluded. The scientific literature on growth stimulants is very extensive and many reviews and symposia have been published, There is a wealth of evidence and detail on antibiotics which, although proven to be effective in improving the performance of poultry, especially broilers, pigs, calves, beef cattle and, sometimes, lambs, are no longer allowed to be used in the United Kingdom without veterinary prescription. The object of the present review is to consider those additives which may now be used.