Feed Lot

NOV 2017

Feedlots and cow/calf operations in the beef industry who feed 500 or more has annually on grains and concentrates; maintain 500 or more beef cows; backgrounder, stocker/grower, preconditioner; veterinarian, nutritionist, consultant

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between antibiotics that are con- sidered "time dependent" (effec- tiveness depends on exposure to the drug for a certain length of t ime) versus "concentration de- p endent" (bacteria must be ex- posed to a high concentration of the drug). If label directions are not followed and only a partial dose is administered or perhaps a second dose is required but not given, the drug is unlikely to work effectively because it cannot reach the necessary minimum tar- get concentration. Selection of the best antibiotic class or "family" is an equally impor- tant success factor. Figure 2 is an il- lustration of the mechanisms antibi- otic classes use against bacterial cells. Beta-lactams (penicillin, Ex- cede, ® Naxcel, ® Excenel ® ) cripple production of the bacterial cell wall that protects the cell from the ex- ternal environment. Aminoglyco- sides (gentamicin) and Tetracy- clines (LA-300, ® Biomycin, ® and many others) interfere with protein synthesis by grabbing on to the ma- chinery in the ribo- some needed to build proteins. Macrolides (Draxxin, ® Micotil, ® Zactran, ® Zuprevo, ® Ty- lan ® ) and Chloram- phenicol derivatives (Nuflor ® ) also interfere with protein synthesis although at a different location on the ribo- s o m e . T h e F l u o r o - quinolones (Baytril, ® Advocin ® ) block genet- ic replication by inter- fering with DNA and RNA synthesis. Why is this informa- tion important? If a calf requires retreatment, selection of an antibi- otic from a different class will attack the bacteria through a dif- ferent route and often enhances treatment response. An- other good example is treatment for Mycoplasma bovis, a bacterium frequently found in chronic pneu- monia cases. Mycoplasma has no c ell wall so treatment with a Beta- l actam will prove absolutely use- less. A veterinarian is well-trained in antibiotic selection and is the best source of information when choosing therapy. Another issue that may affect success is mishan- dling the product; an antibiotic that gets too hot or is allowed to freeze inactivates the drug in most cases. Sometimes treatment failure is not a "failure" but rather an inability to recognize recovery. A calf that is eating, drinking and looks better af- ter treatment but still has a slight fever often just needs time, rather t han more medicine, to fully recov- e r since fever is one of the last clin- ical signs to disappear. Strategic and correct use of an- tibiotics will continue to be of im- portance for the cattle industry from this point forward. Careful at- tention to timing of treatment, drug selection, dose, and handling of the product will reduce the human fac- tors that contribute to antibiotic failure. Calf factors including over- whelming stress, infection with BVD, environmental or nutrition- related disorders must be mini- mized in order for the calf's im- mune system to work effectively with the antibiotic to stop disease in its tracks. Judicious or proper use of antibiotics will ultimately curb the development of antibiotic resistance and help protect human health, a win-win situation. FL 12 FEED•LOT  November 2017 Figure 2: Drawing of a bacterium illustrating the ways different "classes" of antibiotics attack them. Why antibiotics fail... from previous page Careful attention to timing of treatment, drug selection, dose, and handling of the product will reduce the human factors that contribute to antibiotic failure.

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