A new study has shown that the degree of poll flexion in a ridden horse can affect his welfare.
Horses are obligate nasal breathers, meaning they cannot swap to breathing through their mouths when their oxygen needs increase, as humans do. Because of this, horses have limitations on how much air they can take in, which may constrain their athletic performance.
Though the horse can flare his nostrils, abduct his larynx and dilate the bronchioles to a degree, these physiological adaptations can only do so much to adjust to the increase in airspeed during exercise. A horse has frictional resistance placed on his airways when he is asked to exert himself while being ridden. This creates negative pressure in the upper airways, which could cause them to collapse.
To prevent this, horses being asked to work hard will extend their head and necks to prevent collapse.
In ridden disciplines like showjumping and dressage, horses often go in a frame that bends their airway at the upper trachea and the larynx. Dr. Paula Tilley, with the Centre for Interdisciplinary Research in Animal Health in Portugal, and the team of scientists sought to evaluate the effects of two poll flexion positions on respiratory system and behavior of ridden horses. There was just a 15-degree difference between the positions.
The team used 20 upper-level dressage horses and 20 showjumpers for the study. They were ridden twice for 40 minutes each, three weeks apart. For the first ride, the horses were asked for 85 degrees of ground angle (the angle between the ground and the line from the forehead to the muzzle); the second time they were asked for 100 degrees of ground angle. The 85-degree angle was more open.
All horses were monitored for conflict behavior as well as for signs of upper respiratory collapse using a dynamic endoscope (one that is worn while ridden). The horses had their heart and respiratory rates evaluated, as were their arterial blood oxygen and lactate, pleural pressure, and pharyngeal diameter.
The horses asked to work at the 100-degree angle showed more conflict behaviors (like tail swishing, mouth gaping, excessive salivating and head shaking) and had higher intrathoracic pressure. These horses also exhibited multiple upper-airway dynamic dysfunctions like nasopharyngeal collapse, palatal instability/dysfunction and intermittent bilateral arytenoid cartilage collapse.
Considered together, blood lactate levels were significantly higher in the horses asked for the 100-degree flexion.
Horses working at the 85-degree angle were more likely to have their ears forward.
The study team concluded that more studies are needed to determine whether the amount of time a horse ridden with a poll flexion ground angle of greater than 85 degrees should be minimized to address equine welfare issues.
Read more at HorseTalk.
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