from 49 to 95 Euros per affected animal, with costs rising to 118 Euros per affected
animal when re-treatments are required (Potter 2007 ). Bovine respiratory disease
(BRD) is an infectious bronchopneumonia, manifested clinically by sudden onset of
depression, pyrexia, anorexia and respiratory signs, which may include dyspnoea,
tachypnoea, nasal discharge and abnormal lung sounds. Young calves are particu-
larly susceptible. Transport (sometimes over long distances), mixing, dense hous-
ing conditions and climate stress are the common risk factors. Beef calves in feedlot
systems and dairy calves used for replacement or for meat production are prone to
BRD when subjected to pre-disposing conditions. It seems likely that many cases of
BRD are initiated by a viral pathogen (such as bovine respiratory syncytial virus
(BRSV), parainfluenza 3 virus (PI3) or bovine herpes virus 1 (BHV-1)), which
renders affected calves more susceptible to secondary bacterial invasion. The most
commonly isolated bacterial pathogens areMannheimia haemolytica,Pasteurella
multocidaandHistophilus somni. Field observations of clinical cases and epidemi-
ology suggest thatMycoplasma bovisis also an important cause of respiratory
infections in cattle; it is estimated that in France, the Netherlands, the UK, and
Ireland,M. bovismay be isolated from approximately 20% of pneumonic lungs and
involved in 20–30% of herds with BRD outbreaks (Nicholas and Ayling 2003 ).
A recent survey investigated the prevalence ofM. bovisin French veal calf feedlots
during BRD outbreaks (Arcangioli et al. 2008 ). The isolation and seroconversion
rates were 60–100% in affected feedlots, an indication of the importanceM. bovis
clearly has in the BRD complex.
Although good herd management practice and vaccination against respiratory
viruses andM. haemolyticaare important components of an effective BRD preven-
tive strategy, antimicrobial therapy is commonly required to minimise the produc-
tion losses and animal welfare consequences of a bacterial and/or mycoplasmal
respiratory disease outbreak. Beta-lactams, tetracyclines, trimethoprim-potentiated
sulfonamides, fluoroquinolones, macrolides and florfenicol are antimicrobial
classes and compounds commonly used in the treatment of BRD (of these the
beta-lactams and sulfonamides have no activity against mycoplasmal pathogens).
The in vitro susceptibility of BRD pathogens to antimicrobials is presented in
Table 7. and the main pharmacokinetic properties of commonly used agents in
cattle are summarised in Table 8. In many outbreaks of calf pneumonia, there is
high morbidity, and, on welfare grounds, it is advisable to treat both diseased and
in-contact animals (Gibbs 2001 ). Metaphylactic use of tilmicosin, tulathromycin
and florfenicol has been reported to reduce significantly the incidence of BRD in
healthy in-contact animals during disease outbreaks (Godinho et al.2005b; Catry
et al. 2008 ; Van Donkersgoed et al. 2008 ). The use of antibacterial drugs should be
integrated with other preventive measures (avoidance of animal mixing, good
ventilation, appropriate stocking density, adequate nutrition, adherence to vaccina-
tion programmes), and the metaphylactic use should be limited to those situations
wherein the disease outbreak is likely to become severe and affect healthy animals
living in the same air space. A BRD outbreak is often defined as 10–15% of the herd
becoming clinically affected within a 3-day period. When presented with an
outbreak of calf pneumonia, visual assessment alone to detect respiratory signs
128 H. Benchaoui