The dynamic upper airway functional (URT) problems of Colombian paso horses (CPH) have not been investigated in literature up to date. These horses perform special walking gaits with high poll flexion of the neck. Our goal is to evaluate the upper airway mechanics in CPH, showing abnormal respiratory sounds and poor performance during exercise. Resting and overground endoscopy was performed in 40 CPHs. Statistical analyses were performed using the sciPy package. One-tailed Fisher exact tests were used to check for positive contingency between each pair of upper respiratory tract disorder (P < .05). Arytenoid cartilage collapse was observed in 35 of 40 cases during exercise. Among these, dynamic laryngeal collapse (DLC) was the most significant finding, but ventromedial luxation of the apex of the corniculate process of the arytenoid and recurrent laryngeal neuropathy was also observed. Dorsal displacement of the soft palate was only detected in 4 of 40 cases. DLC was significantly associated with vocal cord collapse, nasopharyngeal collapse, and medial collapse of the margins of the epiglottis, and medial collapse of the margins of the epiglottis was associated with nasopharyngeal collapse. DLC is only a typical feature in some special breeds worldwide. We suggest that the extensive poll flexion and the relatively small laryngeal lumen and high intensitivity workload are the most important predisposing factors of DLC. Ventromedial luxation of the apex of the corniculate process of the arytenoid was over-represented in our caseload, compared with other studies. Whereas, despite the intensive workload, dorsal displacement of the soft palate was relatively uncommon. We presume that this could also be tailored to the high poll flexion performed during the special gaits.

BACKGROUND: Bits have often been incriminated as a cause of upper respiratory tract obstruction in horses; however, no scientific studies are available to confirm or refute these allegations. Clinical signs of dynamic laryngeal collapse associated with poll flexion (DLC) are induced when susceptible horses are ridden or driven into the bit.
OBJECTIVE: To determine whether use of Dr Cook\'s™ Bitless Bridle, instead of a conventional snaffle bit bridle, would reduce the severity of DLC in affected horses measured objectively using inspiratory tracheal pressures.
METHODS: Intervention study using each horse as its own control in a block randomised order.
METHODS: Nine Norwegian Swedish Coldblooded trotters previously diagnosed with DLC were exercised on two consecutive days using a standardised high-speed treadmill protocol with either a conventional bridle with a snaffle bit, or Dr Cook\'s™ Bitless Bridle. Head and neck position, rein tension, inspiratory tracheal pressure measurements, and laryngeal videoendoscopy recordings were obtained. A heart rate greater than 200 bpm, and similar degrees of poll flexion/head height, had to be achieved in both bridles for the individual horse\'s data to be included for comparison.
RESULTS: Seven horses\' data met the inclusion criteria. The change in mean inspiratory tracheal pressure between free and flexion phases in the bitless bridle (-15.2 ± 12.3 cmH2 O) was significantly greater (P < .001) than in the snaffle bit bridle (-9.8 ± 7.9 cmH2 O). Mean inspiratory pressure during the free phase was significantly (P < .001) more negative with the snaffle bit bridle (-32.3 ± 6.3 cmH2 O), vs the bitless bridle (-28.5 ± 6.9 cmH2 O). Mean pressures in flexion phase, snaffle bridle (-42.1 ± 10.8 cmH2 O), vs bitless bridle (-43.7 ± 15.6 cmH2 O) where not significantly different between bridles (P = .2).
UNASSIGNED: Small sample size due to difficulty recruiting suitable clinical cases.
CONCLUSIONS: This study could not provide any clear evidence that the effect of a snaffle bit in a horse\'s mouth influences the development or severity of DLC. Instead, head and neck angles induced by rein tension seem to be the key event in provoking DLC in susceptible horses.

Dynamic obstructions of the larynx are a set of disorders that occur during exercise in equines and humans. There are a number of similarities in presentation, diagnosis, pathophysiology and treatment. Both equines and humans present with exercise intolerance secondary to dyspnea. During laryngoscopy at rest, the larynx appears to function normally. Abnormalities are only revealed during laryngoscopy at exercise, seemingly triggered by increased ventilatory demands, and quickly resolve after cessation of exercise. Lower airway disease (asthma being the most prevalent condition), cardiac disease and lack of fitness are the major differentials in both species. Laryngoscopic examination during exercise should be performed from rest to peak exertion to allow for a comprehensive diagnosis, including where the airway collapse begins, and thereafter how it progresses. Dynamic disorders with most visual similarity between humans and equines are: aryepiglottic fold collapse (both species); equine dynamic laryngeal collapse (DLC) relative to some forms of human combined supraglottic/glottic collapse; and epiglottic retroversion (both species). Quantitative grading techniques, such as airway pressure measurement, that have proven effective in veterinary research are currently being piloted in human studies. Conditions that appear visually similar are treated in comparable ways. The similarities of anatomy and certain types of dynamic collapse would suggest that the equine larynx provides a good model for human upper respiratory tract obstruction during exercise. Thus, close collaboration between veterinarians and medical personal may lead to further advancements in understanding pathophysiologic processes, and enhance the development of improved diagnostic tests and treatments that will benefit both species.

BACKGROUND: Upper respiratory tract (URT) endoscopy at rest is commonly used to evaluate competition draught horses with URT conditions. Overground endoscopy might be preferred for draught horse URT evaluation as it allows the horses to be driven with harness, overcheck and cart-load under similar conditions to those experienced in the show ring where airway conditions are most prominent.
OBJECTIVE: To describe the exercising URT findings of competition draught horses with abnormal respiratory noise and/or poor performance.
METHODS: Case series.
METHODS: Medical records of competition draught horses undergoing overground endoscopic evaluation between January 2013 and January 2018 with a presenting complaint of abnormal respiratory noise and/or poor performance were reviewed. Video recordings of resting and overground endoscopy were evaluated in all horses. Spearman\'s rank correlation coefficient was calculated between laryngeal function at rest and at exercise.
RESULTS: Fifty competition draught horses were examined. Thirteen had previously undergone URT surgery. There was significant correlation between resting and exercising laryngeal function (ρ = 0.77, P<0.01). Abnormalities were detected in 46 horses and included arytenoid cartilage collapse (n = 31), vocal fold collapse (n = 27), palatal dysfunction (n = 14), epiglottic disorders (n = 11), dynamic laryngeal collapse (n = 1), rostral deviation of the palatopharyngeal arch (n = 3) and medial deviation of the aryepiglottic folds (n = 16). The majority of horses had a complex of abnormalities (n = 31) or required exercising examination for identification (n = 41). Incidental upper oesophageal incompetence was observed in nine horses.
CONCLUSIONS: Retrospective collection of data.
CONCLUSIONS: Overground endoscopic evaluation was a useful technique for identifying URT disorders in competition draught horses. The spectrum of upper airway conditions identified in exercising draught horses supports the use of overground endoscopy as a diagnostic technique and could influence treatment considerations. The Summary is available in Portuguese - see Supporting Information.