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Abstract :

Bovine respiratory disease is the most frequent disease in newly-received feedlot cattle. Current knowledge is too limited to make a choice, during BRD outbreaks, between individual treatment of visually detected sick cattle or mass medication. The objective of this study was to assess the under detection of sick cattle by visual appraisal and further estimate its impact on growth performance, and to study the horizontal transmission of Mannheimia haemolytica and Mycoplasma bovis within pens. Continuous monitoring of body temperature revealed numerous delays and defects in the detection of sick animals associated with decreased growth performance. Pulsed-field gel electrophoresis typing revealed for M. haemolityca isolates, a high within pen genetic variability, which is in favour of a low occurrence of transmission, and a unique clone of M. bovis per BRD outbreak, which is in favour of a frequent transmission. Concerning under detection, our results suggest that individual treatment of only visually detected sick animals is not optimal when considering the best growth performance at the pen level. Concerning transmission, our results suggest that mass medication appears justified in cases of M. bovis implication and more disputable in cases of M. haemolytica implication. Finally, in the future, alert systems providing a sensitive detection of sick cattle should be implemented as well as methods enabling to detect a highly contagious bacterium within a pen.

Key words :

Cattle, Respiratory disease, Temperature monitoring, Molecular epidemiology