Faculty of Veterinary Medicine, Companion Animal Clinical Sciences, Norwegian University of Life Sciences, Oslo, Norway.
Haukeland University Hospital, Bergen, Norway.
Equine Vet J. 2021 Jan;53(1):44-50. doi: 10.1111/evj.13287. Epub 2020 Jun 17.
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.
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.
Intervention study using each horse as its own control in a block randomised order.
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.
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 cmH O) was significantly greater (P < .001) than in the snaffle bit bridle (-9.8 ± 7.9 cmH O). Mean inspiratory pressure during the free phase was significantly (P < .001) more negative with the snaffle bit bridle (-32.3 ± 6.3 cmH O), vs the bitless bridle (-28.5 ± 6.9 cmH O). Mean pressures in flexion phase, snaffle bridle (-42.1 ± 10.8 cmH O), vs bitless bridle (-43.7 ± 15.6 cmH O) where not significantly different between bridles (P = .2).
Small sample size due to difficulty recruiting suitable clinical cases.
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.
马的上呼吸道阻塞常被归咎于衔铁；然而，没有科学研究可以证实或反驳这些说法。当易感马被骑乘或驱赶进入衔铁时，会引起与低头有关的动态喉塌陷（DLC）的临床症状。
确定使用库克博士无衔铁马勒而不是常规的衔铁马勒是否会降低受影响马的 DLC 严重程度，使用吸气气管压力客观测量。
采用每匹马作为自身对照的随机分组干预研究。
9 匹挪威瑞典冷血快步马被诊断患有 DLC，使用标准高速跑步机方案连续两天进行运动，使用常规马勒和带衔铁的马勒，或库克博士无衔铁马勒。获得头颈部位置、缰绳张力、吸气气管压力测量值和喉视频内窥镜记录。必须在两种马勒中都达到心率大于 200 bpm 和相似程度的低头/头部高度，才能将个别马的数据纳入比较。
7 匹马的数据符合纳入标准。无衔铁马勒在自由和低头阶段之间的平均吸气气管压力变化（-15.2±12.3 cmH2O）显著大于衔铁马勒（-9.8±7.9 cmH2O）（P<.001）。在自由阶段的平均吸气压力在带衔铁的马勒（-32.3±6.3 cmH2O）显著更负（P<.001），与无衔铁的马勒（-28.5±6.9 cmH2O）相比。在低头阶段，两种马勒的平均压力（衔铁马勒-42.1±10.8 cmH2O，无衔铁马勒-43.7±15.6 cmH2O）之间没有显著差异（P=.2）。
由于难以招募合适的临床病例，样本量较小。
本研究不能提供任何明确的证据表明马口中衔铁的作用会影响 DLC 的发展或严重程度。相反，缰绳张力引起的头颈部角度似乎是易感性马引发 DLC 的关键事件。
