New Techniques to Evaluate Functional Impact of Bovine Respiratory Disease

Abstract

Despite prophylactic measures, mainly including vaccination programs and management measures, respiratory disease remains the major cause of economic losses in bovine species. Therapeutic strategies include three targets: the etiologic agents, the inflammatory reaction and the mechanical disorders. Choice of treatment is currently main based on the clinician's 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). However, objective methods to evaluate immediate, in an easy and cheap way, the functional impact of respiratory pathologies and to determine the level of severity are not available.

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.

Measurement of arterial hemoglobin oxygen saturation is an important means to evaluate effectiveness of the oxygen transport chain. Assessment is usually performed based on an arterial blood sample analyzed by a blood gas analyzer. This technique presents several disadvantages: it's invasive, discontinuous and expensive. Pulse oximetry is a non-invasive, immediate and cheap method of measuring percentage oxygen saturation of arterial hemoglobin, based on differential absorption of red and infrared light. It showed to be useful and accurate in bovines when the probe was fitted to the animal's tail, even with low values of hemoglobin saturation.

Blood lactate levels are elevated in case of severe bovine respiratory disease because of diminished tissue oxygenation and because of elevated respiratory muscle effort. Assessment used to be done by a complex laboratory test. Recently a handportable apparatus, named "Accusport" and measuring blood lactate concentration immediately, has been introduced in equine medicine. It proved also to be reliable and useful in the evaluation of severity of bovine respiratory disease.

Finally, assessment of ventilatory reserve capacity by administration oflobeline, a respiratory analeptic, revealed to be very sensitive and especially valuable in animals with minor respiratory problems.

The theoretical classification into four grades of severity of bovine respiratory disease is worthless without practical means to evaluate functional impact in the field. The three presented tests could help us to realize this objective and finally economize therapeutic strategies in bovine respiratory disease.