Feed Lot

DEC 2018

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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with primarily Western and Mid- western states in the USA and Canada but cases are now being diagnosed throughout the U.S. Most comprehensive studies have been conducted in Canada where HS accounts for an estimated 40% of the death loss in feedlots. Unlike typical BRD outbreaks that peak at 14 days after arrival to the feedlot, HS acute pneumonia cases peak at 25 days on feed. In the absence of consistently effective treatment or vaccine options, man- agement practices are crucial to controlling Histophilus pneumonia. Metaphylaxis, where treatment is applied to the whole group (either on arrival or once 10-20 % of the calves are showing clinical signs of BRD), along with prompt individ- ual treatment of sick cattle is one recommended control approach. Vaccines are available against HS but their ability to prevent disease has not been proven. The common BRD-associated bacteria (Mannheimia haemo- lytica, Pasteurella multocida, Histophilus somni and Myco- plasma bovis) are considered nor- mal bacteria in the nasal passages of healthy calves but with stress (such as transportation and com- mingling) and viral infection, they can descend into the lungs and sometimes spread throughout the body, causing disease. This sim- ple disease model is now under scrutiny with the realization that multiple factors contribute to com- binations and complex interac- tions between the environment, the bacteria and viruses, and the calf's immune system. Stressed cattle are more sus- ceptible to the viral components of BRD, including Infectious Bovine Rhinotracheitis (IBR), Bovine Viral In this era of advanced vaccine technology and long-acting, expen- sive, powerful antibiotics, why do cases of Bovine Respiratory Dis- ease (BRD) continue to increase? One reason is the re-emergence of Histophilus somni (formerly known as Haemophilus somnus) as a major bacterial pathogen re- sponsible for the development of pneumonia in feeder operations. While Mannheimia haemolyti- ca is the bacteria known to cause the dramatic pneumonia signs of fever, depression, appetite loss and rapid death, Histophilus somni (HS) can cause similar symptoms and is proving very difficult to treat and control with traditional meth- ods. The organism is often found in combination with Pasteurella multocida or other BRD bacteria in "biofilms" which are clusters of bacteria in a matrix that serves as protection from antibiotics and host immune system responses. Stress can trigger dispersal of large numbers of bacteria from the biofilm that can then invade the lower respiratory system. Once it establishes infection in the lungs, it can travel in the bloodstream to joints, organs (especially the heart), and to the brain. These calves may develop pneumonia, pleuritis (infection of the mem- brane surrounding the lungs), myocarditis (infection in the heart muscle), thrombotic meningoen- cephalitis (infection in the brain), tenosynovitis (infection within joints), and otitis media (middle ear infection). The disease can happen anytime in the year but most clinical cases occur between October and Janu- ary. Previously, disease due to HS or "histophilosis" was associated FEEDLOT FOCUS BY 0,&+(//($512/''90580,1$17 (;7(16,219(7(5,1$5,$18.9'/ PNEUMONIA IN FEEDER CALVES? Don't Forget Histophilus Somni 6 FEED•LOT December 2018

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