Antibiotic: - Antimicrobial pharmaceutical, usually of plant or fungal origin. Although the primary use of antibiotics is in the treatment of infections, certain antibiotics are used as feed additives in order to improve growth and feed conversion. The modes of action of antibiotics used as growth promoters probably include reduction in sub-clinical disease, thinning of the wall of the intestine and, in ruminants, a change in the microflora and fauna in the rumen. In the late 1990s, some antibiotics previously licensed in the European Union for use as growth promoters (zinc bacitracin, virginiamycin, avoparcin) were banned because of fears that their use might encourage the development of antibiotic resistance and prejudice the treatment of human disease. All antibiotics must be used with care and the current data sheet should be consulted for dosage, contraindications and other precautions: many may be used by Category A manufacturers only. Some may be incorporated into feed blocks or used as top-dressing of feeds such as silage. Flavophospholipol is licensed for use in pigs, domestic fowls, turkeys, rabbits, calves, growing and fattening cattle and fur animals. It is a phosphoglycolipid, and is not absorbed from the digestive tract, so is not metabolized by the animal. It changes the pattern of rumen microorganisms by inhibiting some Gram-positive bacteria and by reducing the formation of peptidoglycan. Monensin is licensed for use in non-lactating cattle. It has had fatal effects when fed to horses, and when fed to cattle within 7 days before or after being treated with tiamulin. Monensin is an ionophore, and is poorly absorbed from the digestive tract, about twothirds being lost unaltered in faeces. Ionophores facilitate the movement of ions across membranes by forming hydrophobic complexes with ions such as potassium and sodium, and in so doing disrupt bacterial cell walls, and possibly the cell walls of protozoa. They thereby change the pattern of rumen microorganisms, reducing the production of acetate, butyrate and methane, and increasing the proportion of propionate. Since methane is a waste product, the efficiency of rumen activity is improved. Ionophores also reduce the total mass of bacteria and thereby decrease the amount of dietary protein degraded. Avilomycin is licensed for use in pigs, broiler chickens and turkeys. Salinomycin is an ionophore available for use in pigs and also used to prevent coccidiosis in broiler chickens. (The Encyclopedia of Farm Animal Nutrition)
Posted on: Sun, 21 Dec 2014 15:21:53 +0000
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