INFLUENCE OF DIETARY ANTIBIOTICS ON NITROGEN, AMINO ACID AND ENERGY DIGESTION BY RATS AND ADULT ROOSTERS

Abstract

The influence of antibiotics (a 2:1 mixture of bacitracin and neomycin sulfate at 0.7% of the diet) on the availability of energy from barley-fishmeal-based diets was assessed using rats and adult roosters. Changes in estimates of protein quality, as influenced by dietary antibiotics were also determined in the study with rats. Gut biomass content was estimated by measuring the content of adenosine triphosphate (ATP) in gut samples of rats and fresh excreta samples of roosters. Antibiotic addition to the diet significantly (P < 0.01) reduced apparent digestible energy in rats and tended to reduce the true metabolizable energy measured with roosters. Biological value of the protein for rats was increased significantly (P < 0.01) by antibiotics as were net protein utilization values even though true digestibility of protein was decreased significantly (P < 0.01). The availability of some amino acids (e.g. histidine) showed a marked depression (12.1 percentage units) when antibiotics were added to the diet while others were not influenced (e.g. lysine and methionine) or markedly (7.6 percentage units) increased (e.g. alanine). The extent of microbial activity, which was shown to be markedly higher in the hindgut of rats fed no antibiotics as compared to rats fed antibiotics, may have contributed to the positive influence of antibiotic feeding on biological value of dietary protein and to the changes noted in excretion of amino acids by rats and roosters. Key words: Antibiotics, Nitrogen, amino acids, energy, rats, rosters