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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Bovine respiratory disease (BRD) continues to be the most common cause of feedlot death loss, despite improved vaccines and expensive long-acting antibi- o t i c s f o r m u l a t e d s p e c i f i c a l l y against the bugs commonly found in a diseased bovine lung. Beyond death loss due to severe pneumo- nia, the costs of treatment (antibi- otics) and prevention (vaccines), loss of production, and reduced carcass value in chronic cases must also be considered to under- stand the full economic loss to the industry. In the face of these chal- lenges, consumers are increasingly demanding reduced antimicrobial use in the production of whole- some beef. The FDA, concerned that over- use of antibiotics in animals will create resistance and reduce their effectiveness in people, has al- ready limited the use of antibiotics in feed through the Veterinary Feed Directive. Many cattle pro- ducers are concerned injectable antibiotics may be FDA's next tar- get. While antibiotic resistance does occur, it is not the only rea- son for treatment failure. Given the need to continue using antibi- otics in food-producing animals, it is important to review their cor- rect usage and why antibiotics may fail to work. BRD relies on the mixture of host susceptibility, pathogens (viral and bacterial) and the environment to cause disease. Mannheimia hemolytica (formerly known as Pasteurella hemolytica), the most common bacteria found in bovine pneumonia, is an opportunist that gets in the lungs when the calf's de- fenses are down due to a respira- tory virus and stress. Weaning, co- mingling, transportation, castration and dehorning, bad weather, over- crowding, and poor quality air are known to compromise a calf's im- mune system. A persistently-infected (BVD-PI) calf in a pen results in con- tinuous exposure of the pen mates to the BVD virus and a constant re- duction in their ability to fight sick- ness. Lightweight calves weaned on the truck that have not begun eating and drinking are at exceptionally high risk for disease and death. Each of these situations leads to poor antibiotic response. It is important to understand why successful treatment of pneu- monia is not simply a matter of grabbing a bottle of the latest and greatest antibiotic, drawing up a dart-full, shooting it in the sick calf and waiting for the magic bullet to take effect. Instead, full recovery is a joint effort between the calf's immune system and the selected drug to stop the growth of bacteria and destruction of lung tissue. An- tibiotics hold bacterial growth "in check" and give the calf's immune system time to gear up and effec- tively fight the disease. Treatment failure may be due to calf factors including overwhelming stress, in- fection with BVD virus, or nutri- tion-related factors such as trace mineral deficiencies or subacute ruminal acidosis. Sound nutrition and manage- ment, especially around weaning, will substantially increase the re- sponse to antibiotics. Calves vac- cinated 2-3 weeks pre-weaning 10 FEED•LOT  November 2017 FEEDLOT FOCUS B y MICHELLE ARNOLD, DVM, DABVP RUMINANT EXTENSION VETERINARIAN UNIVERISTY OF KENTUCKY Antibiotics Fail Hint: It's probably not the drug's fault WHY If a calf requires retreatment, selection of an antibiotic from a different class will attack the bacteria through a different route and often enhances treatment response. A veterinarian is well-trained in antibiotic selection and is the best source of information when choosing therapy.

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