The objectives of this study were to determine whether the infusion of platelet-activating factor would modify bovine pulmonary function, heart rate and platelet count and whether any such modifications could be antagonised by the prior intravenous injection of a specific antagonist (WEB 2086). In saline-pretreated calves, the respiratory rate, total lung resistance (RL) and maximal changes in transpulmonary pressure (delta Ptp) were significantly increased whereas lung dynamic compliance (CLdyn), tidal volume (VT), platelet count and heart rate were significantly decreased. The changes in RL, CLdyn, VT and delta Ptp were abolished by pretreatment with WEB 2086, whereas respiratory rate remained significantly increased to 125 per cent of the baseline value, but less than in the saline-pretreated calves in which it was 250 per cent of the baseline value.

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Despite prophylactic measures, mainly including vaccination programs and management measures, respiratory disease remains the major cause of economic losses in the bovine species. Choice of treatment is currently mainly based on the clinicians? personal experience. A theoretical method has been proposed earlier to classify this syndrome into four grades of severity: Grade 1, subclinical disease (no treatment); Grade 2, compensated clinical disease (antibiotics only); Grade 3, noncompensated clinical disease (antibiotics + antiinflammatory drugs); and Grade 4, irreversible clinical disease (no treatment). In order to realize this theoretical classification under field conditions, three techniques, each one evaluating the oxygen transport chain at a different level, have been studied and validated, i.e. pulse oximetry, lactate dosage and the lobeline test. Afterwards, measurements were performed on calves suffering from acute respiratory disease and a preliminary classification was established. This novel approach could orientate and economize therapeutic strategies in bovine respiratory disease.