Effects of tension of the girth strap on respiratory system mechanics in horses at rest and during hyperpnea induced by administration of lobeline hydrochloride.

This study investigates how the tightness of a saddle’s girth strap affects the breathing mechanism of horses. The researchers found that although tightening the strap caused measurable changes in respiration mechanics like restricted rib motion and increased lung resistance, it did not appear to restrict overall ventilation in the horses.

Research Methodology

• The study included ten healthy adult horses. To measure the effects of a tightened girth strap on the horses’ respiratory systems, the researchers applied a strap with 15 kg of tension. They focused specifically on the pulmonary dynamics during normal breathing (eupnea) and forcibly accelerated or deep breathing (hyperpnea).
• Respiratory impedance was measured using oscillometry. This technique monitors breath-like oscillations of a subject’s lungs, determining resistance and reactance data for the lung and chest wall components.
• They measured the contribution of the rib cage and abdomen to the volume of air displaced during a normal breath using respiratory inductance plethysmography.
• The researchers also measured the functional residual capacity (the amount of air left in the lungs after a normal exhalation) during normal breathing using a helium-dilution technique.
• In a subgroup of six horses, they measured the pressures across the diaphragm during normal and forcibly accelerated or deep breathing, which was induced by administering lobeline hydrochloride.

Research Findings

• The research showed that tightening the girth strap increased pulmonary lung resistance when measured using oscillometry. However, this was not shown when classical measuring methods were used.
• Interestingly, the increase in pulmonary resistance couldn’t be explained by a decrease in functional residual capacity. This contradicts an intuitive assumption that tightening the girth would lead to squeezed lungs and less air retention.
• The study displayed significant reduction in the motion of the rib cage during both the normal and forcibly accelerated or deep breathing phases when the girth was tightened.
• Despite these changes, the researchers found that key indicators of ventilation – tidal volume (air moved during normal inhalation and exhalation), minute ventilation (total volume of air inhaled in a minute), peak flows, pressures across the diaphragm during normal and forcibly accelerated breathing, and functional residual capacity – were unaffected by the tension from the girth strap.

Conclusions

• Although the saddle’s strap tension caused discernable changes in the way horses breathe (evident in loss of rib motion and increased pulmonary resistance), it didn’t limit their ventilation.
• These results contribute to a better understanding of how equine equipment may impact animal welfare and could have implications for saddle fitting practices, equine health, and overall performance in horse racing and other equine sports.