Abstract :
[en] Bovine Respiratory Disease, or BRD, are common in young cattle in the first year of life but occurs mainly before 6 months. A peak of incidence is noticed between 2-10 weeks, due to a decline of immunity. BRD is associated with the well-known shipping-fever that may come from cumulative stress. This condition can reach 5-20% case fatality rate and a morbidity rate up to 100%. Most of the time, the treatment administered is effective. In other cases, a relapse within 2 weeks, associated or not with mortality, can be observed.
BRD induces economic losses with treatments (antibiotics), prevention (vaccination) and mortalities. There are also zootechnical consequences with growth retardation, circulation of infectious agents, and increased sensitivity to other pathogens.
Cattle are more susceptible to BRD for many reasons. They have narrow upper airways that increase air speed and allow a deeper colonization of particles in the lower respiratory tract. There is also a link between the digestive and respiratory system in bovines. Inhalation of eructation gaz occurs regularly. The respiratory tract in cattle is more sensitive to endotoxins. In case of rumen acidosis, a paralysis of the mucociliary escalator is observed. Finally, cases such liver abscess or Vena Cava Caudale thrombosis, a metastatic pneumonia can follow.
BRD often begins with virus attack, which may be complicated with surroundings bacterial infections. Among the different viral aetiologies, Bovine Respiratory Syncytial Virus (B-RSV), Parainfluenza virus (PI-3), Bovine Herpes Virus (BHV-1 or IBR), Bovine Viral Diarrhoea Virus (BVD, for its immunosuppression effect) are the most frequent encountered. Adenovirus and Coronavirus, BHV-4, Rhinovirus, Reovirus, and Enterovirus can also be present, in a lesser extent. Among bacteriological causes, Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Trueperella pyogenes, and Mycoplasma bovis (dispar) are commonly met. Chlamydophila and Salmonella dublin can sometimes also provoke pneumonias.
An onset of BRD can begin with only an increased rectal temperature. That is why it is recommended to the owner to check for temperature in the different batches of animals. After, other symptoms will appear, such as cough, nasal discharge, dyspnea, etc. BRD can be categorized in 4 clinical grades, from 1 to 4, according to the severity of the disease. Grade I does not need a treatment, as well as grade IV that is so severe that the animal may probably die within a few days. Other scores exist and they also take into account symptoms such cough, rectal temperature, nasal discharge, etc. The grade or score of the disease is important to establish a treatment, a prognosis or an ancillary exam. Measurement of blood L-Lactate (with portable spectrophotometer, e.g. Accutrend-Plus, Cobas, ~150€ and ~3€/test) allows on the field the determination of the grade of BRD as well as prognosis. L-Lactate ≥ 4 mmol/L in calves with BRD (up to 13 months) is associated with grade IV BRD and poor prognosis (death within 3 days) with 95% sensitivity and 80% specificity (Coghe et al., 2000). Another study shows that L-Lactate > 3.7 mmol/L is associated with 44 times more risk to die in calves with BRD, compared to calves with L-Lactate <1.3 mmol/L (Buczinski et al., 2014).
BRD is clearly a multifactorial disease. Its management must include the resistance of animal (genetic, nutrition, vaccination), the environment (ventilation, hygiene) and the identification of the infectious agents. This conference is focused on the last topic.
