Bit-induced asphyxia in the racehorse as a cause of sudden death

• Published in: Equine veterinary education Vol. 28; no. 7; pp. 405 - 409
• Main Author: Cook, W. R.
• Format: Journal Article
• Language: English
• Published: Hoboken Blackwell Publishing Ltd 01-07-2016; Wiley Subscription Services, Inc
• Subjects: asphyxia; bit; Health risk assessment; horse; Hypotheses; sudden death
• ISSN: 0957-7734; 2042-3292
• DOI: 10.1111/eve.12455

Summary
The prevention of sudden death requires removal of its cause and this is unknown. The author's hypothesis is that bit‐induced asphyxia, partial or complete, is a cause of sudden death. Antemortem data on bit‐induced asphyxia were compared with post mortem data on sudden deaths to explore a possible cause‐and‐effect relationship. Causal categories from sudden death necropsy data were reclassified. Those causing a horse to fall (cardiopulmonary failures) were considered primary effects and those resulting from a fall (CNS trauma and haemorrhagic shock) secondary effects. Cardiac failure from negative pressure pulmonary oedema caused by bit‐induced obstruction of the nasopharynx was consistent with the hypothesis. In 1988, asphyxia from recurrent laryngeal neuropathy was posited as a cause of exercise‐induced pulmonary haemorrhage (EIPH). It is now suggested that the bit is another cause of asphyxia; EIPH is a sign of negative pressure pulmonary oedema which, in turn, causes cardiac failure and sudden death. By breaking the airtight lip‐seal at exercise, a bit dissipates negative pressure in the oral compartments, destabilises the soft palate and obstructs the nasopharynx. Bitted rein pressure, kinking the airway and rendering parts of it flaccid, is a further cause of asphyxia. The data comparison supports a unifying hypothesis on 4 problems currently considered idiopathic; that the bit is an ultimate cause of palatal instability, dynamic collapse of the upper respiratory tract, EIPH and sudden death. Bitless training and racing trials are recommended as a means of demonstrating that bitless racing is possible, preferable and predicted to reduce the prevalence of all 4 problems.