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Original Article
Behavioural assessment of pain in 66 horses, with and without a bit
W. R. Cook
†
* and M. Kibler
‡
†
Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton,
Massachusetts; and
‡
Department of Mathematics and Computer Science, Washington College, Chestertown,
Maryland, USA
*Corresponding author email: bob.cook@tufts.edu
Keywords: horse; bit; pain; pain-related behaviour; proprioception; stereotypic behaviour; welfare; poor performance
Summary
Horses can be ridden with or without a bit. Comparing the
behaviour of the same horse in different modes constituted a
‘natural experiment’. Sixty-nine behaviours in 66 bitted horses
were identified as induced by bit-related pain and
recognised as forms of stereotypic behaviour. A prototype
questionnaire for the ridden horse was based on 6 years of
feedback from riders who had switched from a bitted to a
bit-free bridle. From a template of 69 behavioural signs of
pain derived from answers to the questionnaire, the number
of pain signals shown by each horse, first when bitted and
then bit-free, was counted and compared. After mostly
multiple years of bit usage, the time horses had been bit-
free ranged from 1 to 1095 days (median 35). The number of
pain signals exhibited by each horse when bitted ranged
from 5 to 51 (median 23); when bit-free from 0 to 16 (median
2). The number of pain signals for the total population when
bitted was 1575 and bit-free 208; an 87% reduction.
Percentage reduction of each of 69 pain signals when bit-
free, ranged from 43 to 100 (median 87). The term ‘bit
lameness’was proposed to describe a syndrome of
lameness caused by the bit. Bit pain had a negative effect
on proprioception, i.e. balance, posture, coordination and
movement. Only one horse showed no reduction in pain
signals when bit-free. The welfare of 65 of 66 horses was
enhanced by removing the bit; reducing negative emotions
(pain) and increasing the potential to experience positive
emotions (pleasure). Grading welfare on the Five Domains
Model, it was judged that –when bitted –the population
exhibited ‘marked to severe welfare compromise and no
enhancement’and –when bit-free –‘low welfare compromise
and mid-level enhancement.’The bit-free data were
consistent with the ‘one-welfare’criteria of minimising risk and
preventing avoidable suffering.
Introduction
Pain in animals is defined as an aversive sensation caused by
actual or threatened tissue damage; a negative mental
state. Pleasure is defined as fulfilment of a biological drive for
comfort and safety; a positive mental state. Current animal
welfare thinking (Mellor 2015a) refers to ‘pleasure’as a
‘positive affective experience’(Table 1). The term ‘affect’
describes emotion (feeling), either positive or negative. It
encompasses ‘motivation’; an animal’s urge to move
towards or away from a stimulus, i.e. stereotaxis.
Used since the Bronze Age, metal bits have been
accepted as part of the furniture of horsemanship and not
subjected to scrutiny until quite recently (Cook 1999). In a
review of equine pain assessment, the absence of data on
‘abnormal bit behaviour’[sic] was noted by Ashley et al.
(2005). Since then, three studies have compared ridden horse
behaviour, with and without a bit. First, two unschooled 2-
year-old horses in a 10-day period of foundational training
performed “at least as well, if not better”without bits as two
matched horses in snaffle bridles (Quick and Warren-Smith
2009). Second, four mature horses, in their maiden bit-free
test, exhibited statistically improved ridden behaviour (Cook
and Mills 2009). In two concurrent four-minute tests, first bitted
then bit-free, riders’scores increased from a mean of 37
(‘fairly bad’)to64(‘satisfactory’). Finally, a study of 16
therapeutic riding horses showed significantly more negative
behaviours when bitted and positive behaviours when bit-
free (Carey et al. 2016).
Pain studies in animals have not generally included
removal of the pain’s source. The arrow of direction in
assessing most management interventions (e.g. castration) is
from painless to painful. In the current study, the direction
was reversed. Bit usage is an elective and almost daily
intervention during many horses’working lives. Assessment of
its effect on welfare is overdue.
As bits have been standard equipment for millennia, they
are widely assumed to be indispensable and ethically
justified. This being so, an opinion by welfare researchers is
cited ... “Most horses exhibit clear behavioural evidence of
aversion to a bit in their mouths, varying from the bit being a
mild irritant to very painful”(Mellor and Beausoleil 2017). The
same authors observe that evidence of aversion is available
to all who seek by comparing the open mouth, head tossing
and restricted jaw angle of many bitted horses –clearly
apparent on YouTube videos –with the absence of these
behaviours in videos of wild horses and of domestic horses
when ridden bit-free or bridleless. The need for a list of ridden
horse behaviours to be developed was noted by Hall et al.
(2013).
The study objective was to start answering six questions:
•What behaviours are caused by the bit?
•How prevalent are they?
•How many bit-induced behaviours might one horse
exhibit?
•Are they reversible when the bit is removed?
•Is a horse’s welfare improved by removal of the bit?
•Can a horse be controlled without a bit?
The null hypothesis was that removal of the bit would
cause no behavioural change.
©2018 The Authors Equine Veterinary Education published by John Wiley & Sons Ltd on behalf of EVJ Ltd
This is an open access article under the terms of the Creative Commons Attribution License, which permits use,
distribution and reproduction in any medium, provided the original work is properly cited.
1EQUINE VETERINARY EDUCATION
Equine vet. Educ. (2018) ()-
doi: 10.1111/eve.12916
TABLE 1: Prevalence of 69 pain indices in 66 horses, when bitted and bit-free. The mean reduction when bit-free was 85% (range 43–
100) with a median of 87%. Many of the bit-induced pain indices jeopardised the safety of both horse and rider
Order
when
bitted PAIN INDICES
Number of
horses
affected
BITTED
number of
horses
affected
BIT-FREE
Reduction
when
bit-free (%)
Inferred likelihood of horse having POSITIVE AFFECTIVE
EXPERIENCES e.g., pleasures of safety, confidence, comfort,
compliance, enthusiasm, motivation following removal of
the bit and cessation or easement of pain
1 Hates the bit 53 0 100 The relief, pleasure and comfort of being without pain
2FRIGHT: 46 4 87 One of the five major categories of fear (the five ‘F’s),
replaced by calmness, ease and comfort
3 Stiff-necked 45 7 84 Freedom of the head: Ability to balance; smoothness
and fluidity in the ‘way of going’
4 Lack of control 43 6 86 Horse/rider high accident hazard replaced by willing
cooperation, harmony and partnership
5=Resents bridling 41 3 93 Drops head eagerly into bridle; exhibits enthusiasm for work
5=Above the bit 41 3 93 Able to select the physiologically most comfortable (optimally
balanced) head position
6 Muzzle rubbing 40 9 77 Relief from the persistent irritation and distraction of facial
neuralgia
7=Head shaking 37 8 78 As above for ‘muzzle rubbing’- the relief from nerve ache
7=Unfocused 37 1 97 Focused; not distracted; ‘listens’to and complies with
rider’s signals
8FLIGHT 35 1 97 Contentment; energy conservation; no propensity to bolt,
rush or run away
9=FIGHT 34 2 94 Calm, quiet, cooperative and willingly offers compliance
9=Pig-rooting 34 2 94 See ‘fight’above: Does not grab the bit and snatch reins
from rider’s hands
10 Difficult to steer 33 8 76 Ability to balance; steers straight and turns comfortably
(also see ‘lack of control’above)
11=Stiff or choppy stride 32 2 94 Enjoys the natural rhythm of motion (also see
‘stiff-necked’above)
11=Reluctant to rein-back 32 10 69 Return of normal agility; one of many signs of reduced
‘bit lameness’
12 Tail swishing 31 1 97 Removal of discomfort; tail movement in synchrony with
spinal movement
13=Hair-trigger response
to bit
29 0 100 Calm and confident as opposed to ‘highly strung,’anxious
and apprehensive
13=Sneezing & snorting 29 13 55 Restoration of normal breathing pattern; reduction of nasal
irritation (facial neuralgia)
14 Yawning 28 4 86 Absence of yawning suggestive of reduced need to
ease/interrupt pain signals (see facial neuralgia above)
15 Slow learner 27 1 96 Return of ability to learn - a vital survival strategy (see
unfocussed above)
15 Uncooperative 27 3 89 See ‘fight’above
15 Heavy on the forehand 27 6 78 Unhampered ability to balance, return of normal agility,
elimination of stress and pain
16 Fails to stand still 26 0 100 Return of species specific default behaviour of calmness
and contentedness
17 Pulling on bit 26 0 100 No need to defend itself from the bit and become unbalanced
in the process
18=Grazing on the fly
at exercise
25 11 56 Less need to ‘interrupt’pain signals (see ‘yawning’above)
18=Inverted frame 25 5 80 No pain - no high head carriage - return of ability to balance
19=Dislikes wind/rain/sunlight 24 10 58 Relief from trigeminal hypersensitivity
19=Tilts head at exercise 24 5 79 Proper balance with no need to try and avoid bit pain
19=Fails to maintain
trot or canter
24 4 83 Engaged, lively, energised, exhibits vitality of fitness
20=Difficult to mount 23 3 87 Reduced anxiety and apprehension
20=Grabs the bit 23 0 100 No need for defensive behaviour at exercise
20=Lacks courage 23 5 78 Confident, engaged and curious about its environment
21=Napping 22 4 82 Reduction of fear; reduced pain increases comfort
(see ‘Freeze’)
21=Stumbling 22 7 68 Reduction of ‘bit lameness’with unfettered proprioception
enabling a horse to keep itself upright and safe
22=FREEZE 21 4 81 Keen to explore. Relief from the ‘frozen’state of a prey animal
when attacked by a predator
22=Resents unbridling 21 1 95 Optimism rather than pessimism (see ‘hates the bit’above)
©2018 The Authors Equine Veterinary Education published by John Wiley & Sons Ltd on behalf of EVJ Ltd
2 Ridden horse pain
Method
Study design
Owner/rider assessment of horse behaviour, with and without a
bit; a longitudinal, retrospective, questionnaire-based study. The
number of behavioural signs of pain in each of 66 horses when
bitted was compared with the number of signs when bit-free.
Questionnaire
The questionnaire (Supplementary Item 1) was based on
6 years’feedback from 605 riders who had switched from a
bitted to a bit-free bridle (Cook 2003). As recommended,
questions were posed using vernacular terms (Wemelsfelder
et al. 2001). At the end of an 8-page manual for a bit-free
bridle, riders were informed that a questionnaire was
available for documenting behavioural changes. The
questionnaire was mailed on request or, more commonly,
downloaded online. The 6-page questionnaire comprised
signalment; 106 ‘yes/no’questions about horse behaviour
and signs of disease; and 10 questions describing a rider’s
feelings about riding. It was completed twice; once when
bitted and again when bit-free. From the answers, the
change in prevalence of 69 behaviours, occurring in not less
than 4 of 66 horses when bitted, was assessed (Table 1).
TABLE 1: Continued
Order
when
bitted PAIN INDICES
Number of
horses
affected
BITTED
number of
horses
affected
BIT-FREE
Reduction
when
bit-free (%)
Inferred likelihood of horse having POSITIVE AFFECTIVE
EXPERIENCES e.g., pleasures of safety, confidence, comfort,
compliance, enthusiasm, motivation following removal of
the bit and cessation or easement of pain
22=Behind the bit 21 1 95 Adopts head position based on proprioceptive signals (see
‘above the bit’)
22=Head shyness 21 12 43 Abatement of trigeminal hypersensitivity, hyperalgesia or
neuralgia
22=Salivates excessively 21 2 90 A relatively dry mouth betokens contentedness at exercise
23=Bucking or bounding 20 3 85 Less pain, more comfort
23=Lazy or dull 20 4 80 Engaged aliveness
23=Heads for the stable 20 6 70 Relishes exercise, fulfils biological drive and need for movement
23=Jigging 20 1 95 Walks quietly and contentedly
24=Unfriendly in stable 18 2 89 Return of normal (social) behaviour
24=Anxious eye 18 2 89 ‘Soft’(rounded) eye - an indicator of comfort
25=Ear pinning at exercise 17 4 76 Non-aggression equates with the default social behaviour of
the species
25=Open mouth (gaping) 17 2 88 Closed mouth and sealed lips; oral vacuum restored; default
condition for unobstructed airway at exercise
25=Lolling tongue 17 0 100 Another return to physiological and behavioural norm
25=Reluctant to change lead 17 5 71 Return of normal agility with correction of ‘bit lameness’
26 Bites at tack or
other horses
16 0 100 Reduced facial neuralgia enables disposition to move beyond
neutral to a more positive emotional state
27 Scuffs hind hooves 15 7 53 Soundness of limb returns with correction of ‘bit lameness’
28 Backing-up 14 1 93 See ‘fails to stand still’
29 Multiple wrinkles
around muzzle
13 2 85 Relaxation of tension with elimination of pain
30 Crossing the jaw 13 1 92 As above - return to ‘normal’behaviour when on the move
31=Evades capture
in paddock
12 2 83 Accepts rider as a member of its ‘herd’or ‘band’
31=Sweats excessively 12 1 92 No stress, less sweat
31=Over bends 12 0 100 Proprioceptively and physiologically comfortable head position
31=Tongue over bit 12 0 100 No need for defensive behaviour following removal of the bit,
unobstructed breathing
31=Interfering 12 4 67 Another aspect of ‘bit lameness’corrected
32 Rears 11 2 82 Reductionof bit-escape behaviour
33=Runs wild on bitted lunge 10 1 90 More comfortable
33=Lower lip slapping 10 3 70 More comfortable
33=Incoordination. 10 1 90 Unhampered proprioception corrects ‘bit lameness’
34=Eyes water 9 2 78 Reduction of corneal pain (facial neuralgia)
34=Exercise triggers cough 9 2 78 Reduction of pharyngeal angina (trigeminal neuralgia) and/or
inflammatory airway disease
34=Back problems 9 2 78 Relief of ‘bit-lameness’
35 Retracts tongue
behind bit
7 0 100 Return of default tongue position at exercise, oral vacuum,
soft palate stability, unobstructed airway
36 Drops food 6 0 100 Elimination of ‘sore mouth’(mandibular gingivitis)
37 Reluctant to drink
during ‘endurance’test
4 0 100 Ability to create an oral vacuum and relief of ‘sore mouth’
prevents dehydration
Upper case letters mark the five major categories of fear-induced behaviour (the five ‘F’s) in the questionnaire; i.e. fright, flight, fight,
freeze and facial (trigeminal) neuralgia. Pain indices specific to the bit are shaded grey.
©2018 The Authors Equine Veterinary Education published by John Wiley & Sons Ltd on behalf of EVJ Ltd
W. R. Cook and M. Kibler 3
Population selection
Owner/riders volunteered their participation in the study.
Each horse served as its own control, inasmuch as its
behaviour was compared before and after removing the bit.
Between 2002 and 2016, 96 questionnaires were received.
Sixty-six were completed correctly; a ‘usable’rate of 69%. The
inclusion criterion was that for each of the 69 behaviours
selected for analysis, a yes/no answer must have been
entered for both bitted and bit-free periods.
Statistical analysis
A matched pairs t-test was used to determine if there was
change in the number of pain signals (pain indices) when bit-
free. An alpha level of 0.05 was set for significance.
Welfare assessment
A numerical grading of behaviour was eschewed in favour of
the Five Domains Model (Mellor and Beausoleil 2015; Mellor
2017). Welfare compromise was graded on a five-tier scale
from A (no compromise) to E (very severe compromise).
Welfare enhancement was graded on a four-tier scale from
zero (no enhancement) to +++ (high-level enhancement).
Results
The age of the population ranged from 3 to 24 years, with a
mean of 10 years and a median of 8 (Table 2). Including half-
breds, the breeds comprised Thoroughbreds (n =21),
Arabians (n =11), Warmbloods (n =7), Tennessee Walking
Horses (n =5), Appaloosas (n =4), Clydesdales (n =3) and
others (n =15). Gender distribution was male (n =40; 39
geldings and one stallion) and female (n =25). Categories by
predominant use were dressage (n =22), pleasure (n =21),
trail (n =13), eventing (n =5) and jumping (n =5). All owners
rode ‘English’style. Twenty-eight horses had been bitted for
five or more years. The time a horse had been bit-free before
the second assessment ranged from 1 to 1095 days (median
35; mean 108). Questionnaires were returned from North
America (n =46), UK (n =14), Australasia (n =3), Austria
(n =1), France (n =1) and Holland (n =1).
Bits used were snaffles, Pelhams and double bridles. The
bit-free bridle used throughout was a crossunder (Dr.Cook
â
)
1
Results are displayed in Tables 1–3and Figure 1. Answers
to the six questions are summarised as follows:
•All 69 behaviours were caused by the bit, as judged by
their significant reduction in prevalence when the bit was
removed. Excessive salivation was the only behaviour not
caused solely by bit-induced pain, being also a reflex
response to an oral foreign body.
•Bit-induced behaviours, as a group, were highly prevalent. The
total number of pain signals for the population when bitted
was 1575 and, when bit-free, 208; an 87% reduction. From 66
horses, the number of horses exhibiting each behaviour
ranged from 53 (80% of the population) to 4 (6%) (Table 1).
•The median number of behaviours per horse when bitted
was 23 (range 5–51); when bit-free 2 (range 0–16).
•Most bit-induced behaviours were eminently reversible and
the change was statistically significant (Table 2). The
matched pairs t-test gave a P-value of less than 0.005,
supporting a causal link between the bit and pain-induced
behaviour (Table 3).
•The welfare grade for the population when bitted was
judged to be D/0 (marked to severe compromise and no
enhancement) and, when bit-free B/++ (low compromise
and mid-level enhancement).
•None of the riders experienced loss of control when bit-
free, quite the opposite. In only one horse was control
unchanged.
The null hypothesis was refuted: 65 out of 66 horses
showed a change in behaviour following removal of the bit.
Discussion
The data support previous observations based on anecdotal
evidence (Cook 2003).
Horses exhibit stereotaxis; a word derived from the Greek
stereo, ‘hard, solid’. This fundamental property of (even)
primitive life forms, also known as thigmotaxis, is defined as
‘the positive (or negative) response of a freely moving
organism to cling to (or avoid) a solid object’. Indisputably, a
bit is a ‘solid’object. A horse is innately programmed to (try
and) move away from (evade) the bit, i.e. to display
negative stereotaxis. A definition for thigmotaxis (Greek:
thigmo,’touch’) emphasises the point –“the motion or
orientation of an organism in response to a touch stimulus”.
When the touch is painful, stereotaxic stimuli are stronger. It
follows that the equitation mantra requiring a horse to
‘accept the bit’is misconceived. Expecting a horse to
accept an oral foreign body is a biologically unrealistic
expectation.
Mason (2006) proposed a definition of stereotypical
behaviour based on three causal mechanisms, i.e. ‘repetitive
behaviours induced by frustration, repeated attempts to
cope and/or CNS dysfunction’. The reversibility of 69
behaviours in 65 of the bitted horses indicates that ‘CNS
dysfunction’was not their cause but ‘frustration’and
‘attempts to cope’are mechanisms consistent with the data.
In Mason’s words again, stereotypical behaviours are
generally ‘responses of normal animals to abnormal
environments’. In captive animals, they stem from ‘adeficit in
housing or husbandry, where a deficit means something that
the animal would change if it could (e.g. a motivational
deficit linked with frustration; a health deficit linked with
nausea or pain; or a safety deficit causing fear)’.
Observational evidence constitutes the foundation for
animal welfare assessment and this evidence –carefully
observed –is objective, not subjective. “Contemporary
animal welfare science understanding”accepts the need to
“focus on subjective experiences, known as affects, which
collectively contribute to an animal’s overall welfare status”
(Mellor 2017). Inferences based on such observational
evidence derive credibility from the underlying affective
neuroscience in a process that “involves cautiously exercising
scientifically informed best judgement”(Mellor and Beausoleil
2017). Thus, it is asserted that improvements in behaviour
following removal of the bit enable inferences to be made
about the aversive experience of bit-induced pain. The
improvements cannot be dismissed as ‘merely subjective’.
Collectively, the behaviours were predominantly
manifestations of pain experience, expressed by aberrant
movements of the head, spine and limbs. They ranged from
too little movement (e.g. stiffening, freezing) to too much
©2018 The Authors Equine Veterinary Education published by John Wiley & Sons Ltd on behalf of EVJ Ltd
4 Ridden horse pain
TABLE 2: Results for 66 horses switched from bit to bit-free, sorted on number of days bit-free. The number of pain indices when bit-free
was significantly (P<0.005) reduced in 65 of the 66 horses
Case # Age (yrs) BREED Gender USE
# of pain
indices bitted
Time bit-free
(days)
% reduction in pain
indices bit-free
39 4 TWH G Trail 7 1 86
24 5 Arab/TB F Dressage 23 1 100
15 6 TB G Pleasure 5 1 60
22 6 Arab F Trail 30 1 83
29 23 3/4 TB G Dressage/trail 22 1 100
3 8 WB G Dressage 16 4 62
7 9 TB F Equitation/jumper 39 5 53
32 5 Welsh G Trail/Pony Club 24 7 96
57 8 QH/App G Trail 24 7 96
9 12 WB G Dressage/eventing 6 7 100
44 19 Arab F Trail 32 7 84
35 6 TB F Pleasure/endurance 23 8 87
1 5 TB G Trail 34 14 100
10 7 TB/QH F Pleasure 17 14 35
51 7 cob F Trail 13 14 100
55 8 TB G Pleasure 24 14 96
50 4 App G Jumping/hunter trials 26 19 88
48 4 WB F Dressage 37 20 100
12 6 QH G Western pleasure 24 21 83
27 3 WB F Dressage/eventing 19 30 100
42 7 TB/Trotter G Pleasure 12 30 100
45 7 Arab/Pinto G Dressage/trail 39 30 100
60 9 Paint G Trail 23 30 57
26 10 Gaited G Pleasure 5 30 80
43 10 Arab/QH F Pleasure/dressage 42 30 98
64 12 Arab G Endurance 23 30 100
23 13 QH G Hunter 16 30 0
52 22 TB G Pleasure 23 30 78
5 ? TWH ? Pleasure 21 30 76
56 ? Andalusian G Classical riding 27 30 67
40 6 TB F Pleasure 15 35 100
25 16 App F Pleasure/trail 27 35 100
47 11 Morgan/WB F Dressage 29 40 100
49 12 cob G Jumping, dressage 21 42 90
13 14 TB G Dressage/pleasure 23 42 33
59 3 Draft/X F School horse 7 60 71
58 6 Draft F Trail 21 60 62
4 8 TWH G Trail 11 60 100
53 8 TB G Dressage/jumper 42 60 100
16 15 App G Dressage 43 60 93
31 ? TB F Dressage/trail 13 60 54
8 4 TB G Dressage/eventing 34 64 97
11 11 SDB G Pleasure/trail 24 64 77
2 11 Arab G Dressage/trail 31 72 94
28 5 TB F Dressage/eventing 10 90 70
18 7 WB F Dressage 29 90 100
17 8 WB G Dressage 29 90 100
19 9 WB G Dressage 27 90 100
62 11 Draft G Mounted patrol 9 90 35
63 18 WB F Dressage/jumping 34 90 97
34 8 TB/Paint G Eventing/pleasure 23 120 74
46 8 Arab F Pleasure/endurance 28 120 100
54 11 TB G Trail/ dressage 23 120 69
41 14 Saddlebred G Dressage/jumping 42 150 90
20 12 Arab/Pinto G Trail 18 180 83
65 14 TWH M Dressage/pleasure 28 180 89
6 22 Arab F Trail 12 180 83
61 3 Draft G Mounted patrol 17 240 87
14 13 TB/WB F Dressage/eventing 9 240 100
37 6 TB (OTTB) F Dressage 32 300 75
30 11 WB G Pleasure/trail 7 300 86
38 24 Arab/Welsh G Eventing/trail 43 330 93
©2018 The Authors Equine Veterinary Education published by John Wiley & Sons Ltd on behalf of EVJ Ltd
W. R. Cook and M. Kibler 5
movement (e.g. bucking, bolting). That some horses may
exhibit a few aversions to the bit is widely acknowledged.
That every horse is programmed to be averse to the bit and
that aversions are numerous is not. The current study showed
that at least 65 of 66 horses exhibited aversion to the bit and
that horses have not less than 69 ways of exhibiting
frustration, attempts to cope and efforts to avoid bit contact.
In a review of poor performance, 48 (72%) of these same
behaviours were recognisable among 67 behavioural signs of
pain compiled by Dyson (2016). Clearly, even though both
lists are incomplete, the mandible and tongue (a sense
organ in its own right) figure prominently as the seat of
musculoskeletal manifestations of pain experience in the
bitted horse. To this must be added pain from the lips, a
particularly sensitive area of another sense organ –skin.
A bit stimulates nociceptors mediated by the trigeminal
nerve in lips, tongue, teeth and bone. Gingiva is periosteum,
the most sensitive part of bone. A principle of saddle-fitting is
that saddles should not press on bone. A bit breaches this
principle. In the male horse, the peridontium of the canine
tooth roots lies immediately ventral to the dorsal edge of the
so-called ‘interdental’space. In the female, unerupted,
vestigial canine teeth are common (Sisson and Grossman
1938). In both sexes, ‘wolf’teeth (erupted and unerupted)
may be present in this space. In cross-section, bits are circular
and make point contact with the ‘knife edge’of bone at the
‘bars’. This can be assumed to cause a horse pain, just as it
causes us pain if we press the barrel of a pencil sideways into
our gums. When the edges of the tongue are pinched
between bit and bone, this too is likely to be painful. Pain is
also likely when lips are stretched longitudinally to twice their
normal length by the bit’s retractor effect. Finally, cuts at the
commissures will cause pain.
In common with other mammals, the vestibular labyrinths
and receptors in skin, muscle, tendon and temperomandibular
joints of the horse’s head mediate perception of orientation
and motion in three planes; i.e. proprioception. Head
proprioception controls not only movement and posture of the
head but also dominates that of the trunk and limbs
(Sherrington 1907). In the ridden horse, imbalance can result in
a fall with potentially fatal consequences. Head
proprioception constitutes a central balancing mechanism
and is key to a horse’s agility and athleticism. Painful restraint of
the head by a bitted rein interferes with a horse’s ability to
balance. As a horse’s head movement is synchronised with
limb movement for energy economy in the work of breathing
and locomotion, proprioception unfettered by nociception is
crucial. A bit also obstructs breathing and probably triggers the
negative affective experiences of breathlessness, i.e.
respiratory effort, air hunger and chest tightness (Mellor and
Beausoleil 2017). These unpleasant physical and emotional
consequences of bit pain are also antithetical to athleticism.
Thus, the bit represents an impediment to welfare, safety and
performance. Noxious stimuli from the bit are proposed to be
incompatible with the unimpeded function of at least four
systems critical to performance: the nervous, musculoskeletal,
proprioceptive and respiratory systems.
Dyson et al. (2018) observe that, since 2013 “there is an
increasing awareness that horses can exhibit lameness when
ridden, while appearing sound when trotted in hand”.In
common usage, the word ‘lame’denotes a gait abnormality
caused by pain in a limb. Another sense of the word is not
limited to limbs and carries the wider meaning of ‘disabled,
imperfect and lacking in smoothness’(Webster). In this sense,
at least 65 of the 66 horses when bitted were shown to be
‘disabled’. When trotted-up in a halter, they were not limb-
lame, but when bitted and ridden they developed an
abundance of gait abnormalities. The term ‘bit lame’is
proposed to describe a syndrome of bit-induced disability, i.e.
the 69 pain indices here studied. As bit usage is the norm in
‘English’equitation and still frequent in ‘Western’equitation, it
seems likely that bit lameness will be found to be common in
the ridden horse.
A provisional diagnosis of ‘bit lameness’is testable. If, by
removing the bit, a gait abnormality is corrected this confirms
a diagnosis of bit lameness and differentiates it from primary
limb and thoraco-lumbar-sacral lameness or the
incoordination of equine protozoal myeloencephalitis (EPM).
As the definitive diagnosis of EPM and other subtle gait
abnormalities can be difficult, removal of the bit is
recommended as an early step in the differential diagnosis of
lameness and the evaluation of poor performance. Such a
step is especially indicated to help interpret the findings of
computerised gait analysis, a diagnostic methodology that
has introduced a dilemma over defining the term ‘lameness’
(Van Weeren et al. 2017).
TABLE 2: Continued
Case # Age (yrs) BREED Gender USE
# of pain
indices bitted
Time bit-free
(days)
% reduction in pain
indices bit-free
21 10 Arab G Dressage/pleasure 21 365 67
36 10 TB/Conn F Dressage/eventing 51 720 85
33 8 TB/Paint G Dressage/jumping/trail 42 730 93
23 TWH F Trail 24 1095 100
App =Appaloosa; Conn =Connemara; QH =Quarter Horse; STB =Standardbred; TWH =Tennessee Walking Horse; TB =Thoroughbred;
WB =Warmblood.
TABLE 3: Results of the matched pairs t-test for means
Bitted Bitless
Mean 23.86 3.15
Standard deviation 10.88 3.99
Observations 66 66
Actual mean difference 20.71
Hypothesised mean difference 0
Degrees of freedom 65
tStat 14.50144
Two-tailed P-value 4.75E-22
tcritical two-tail 1.997138
The test was significant (P<0.005).
©2018 The Authors Equine Veterinary Education published by John Wiley & Sons Ltd on behalf of EVJ Ltd
6 Ridden horse pain
After owning a horse for years, riders discovered that
many ‘unwanted’behaviours they had assumed to be
immutable character traits were corrected by removing the
bit. They were sometimes aware that their horse was
exhibiting signs of pain but, until they removed the bit, did
not recognise the source. Often, the signs themselves were
not even noticed until, following bit removal, they
disappeared. Norm theory explains how signs of bit lameness,
being so familiar, fail to elicit surprise and are assumed to be
‘normal’. What ultimately did surprise owners was the
unexpectedly large number of pain indices each discovered.
It follows that riders need to carry out a bit-free test before
asserting that their horse shows no sign of bit pain.
The most prevalent pain index was ‘hates the bit’,a
family of behaviours shown by 53 horses (80% of the
population) (Table 1). The full line in the questionnaire read,
“Hates the bit, chomping, chewing or clenching the bit,
grinding the teeth (bruxism), constant fussing with the bit,
‘busy mouth,’evading contact”(Supplementary Item 1).
The second most prevalent index was ‘fright’, shown by
46 horses (70% of the population). In the questionnaire, the
line read “Fright: Anxious, unpredictable, ‘hot,’nervous,
painful, shy, spooky, panicky, tense, stressed”. It seems
reasonable to assume that at least a quarter of the 69 pain
indices imperil the safety of horse and rider (Table 1). The
data support the opinion that bit-induced fear is the cause of
many horse-related accidents (Jahiel 2014). Removal of the
bit in 65 horses appeared to ‘minimise risk and prevent
avoidable suffering,’in accord with the concept of ‘one-
welfare’(Campbell 2013; Pinillos et al. 2016). In the feral
horse, pain or the anticipation of pain (fear) is adaptive and
promotes survival. In the ridden horse, pain is inimical to
performance. A bolting horse can be in such fear and panic
that it behaves as though blind and can run straight into
standing objects. Case No. 36, with 51 pain indices when
bitted, was described as dangerous to ride (Table 2,Fig 1).
A‘stiff neck’was the third most prevalent behaviour and
shown by 45 horses (68% of the population). Its 84% reduction
when bit-free is important for reasons over and above the
relief of pain. Bitted-rein tension restricts movement of the
head and neck, handicapping a horse’s ability to breathe,
stride and balance. Bedouin horsemen apparently
understood this long ago. When their very lives depended on
their horse’s peak performance, Bedouins rode bit-free
(Hanson and Cook 2015). Over half of the 69 pain indices
when bitted were expressed by abnormal positions of the
head and neck at exercise. Unfettered movement of the
head-and-neck pendulum is a vital locomotory mechanism.
Freedom of the neck is key to freedom of gait. Except when
ridden by a master horseman (someone who rides with a
loose rein and does not apply rein tension) a bitted horse
can be unbalanced by rein tension and is likely to stumble.
The fourth most prevalent sign of pain when bitted was
‘lack of control’(65% of the population). Its reduction by 86%
when bit-free questions the rationale of competition rules
which mandate bit usage on the grounds that bits control
horses.
Twelve horses were assessed for the second time after
having been bit-free for 14 days or less. Five riders completed
the second assessment on day one (Table 2). Because of this
and the persistent nature of neuropathic pain compared with
nociceptive pain, the number of horses documented as
having recovered from facial (trigeminal) neuralgia may not
reflect the population’s full potential for recovery from what
0
10
20
30
40
50
60
0 10203040506070
Numberofpainindices
CaseNumber
Numberofpain-induceddistressresponses
in66horseswhenbittedandbit-free
BITTED BIT-FREE
CaseNo. 23istheonly horse
thatshowed nochange
Fig 1: Individual value plot of pain index numbers in 66 horses when bitted and bit-free. When bitted, all 66 horses (100%) exhibited
pain, with a range of indices from 5 to 51 (median 23). When bit-free, for a median time of 35 days, 66% still exhibited some pain but
the range of indices was from zero to 16 (median 2).
©2018 The Authors Equine Veterinary Education published by John Wiley & Sons Ltd on behalf of EVJ Ltd
W. R. Cook and M. Kibler 7
was listed in the questionnaire as ‘Facial neuralgia (the
headshaking syndrome)’. The percentage reduction in the
prevalence of this syndrome in the population was the lowest
of the five major categories of fear (Supplementary Item 2).
Yet the reduction was still encouraging compared with results
from other treatments for headshaking (Mills et al. 2002). The
‘headshaking syndrome’line item was checked for 37 of the
66 horses when bitted; eight when bit-free –a 78% reduction
(Table 1). The word ‘bit’derives from the word ‘bite.’Clearly,
bits bite. It is considered no coincidence that the
headshaking syndrome includes many of the same
behaviours caused by biting flies.
Space does not permit a paragraph on every one of 69
pain indices but the ‘positive affective experiences’column
of Table 1 provides a pr
ecis.
Cognitive bias was recognised in the population. Mellor
(2015c) describes the bias as follows –“negative emotional
states may be accompanied by greater attention to
threatening stimuli and more pessimistic interpretations of
ambiguous information, whereas positive states may be
accompanied by more optimistic judgments”. The
behavioural changes matched such a description; for
example, the greater frequency with which bitted horses
shied and spooked compared with their calmness when bit-
free (see ‘Fright’Table 1).
The 69 pain indices assessed in this study represent only a
fraction of possible bit aversions. If, for example, a study was
done on racehorses, it is predicted that many more bit-
induced, pain-related indices (diseases and disabilities) would
be identified. From a performance perspective, the most
critical years in the working life of a Thoroughbred racehorse
are those between the ages of one and four. These are the
years in which canine teeth are developing in the interdental
space. Bit-induced mandibular periostitis (‘sore mouth’) is the
aetiological equivalent of metacarpal periostitis (‘sore shins’).
Both sides of the mouth are traumatised on a daily basis. The
mouth is even more sensitive than the shin. Bit pain can
trigger a cascade of locomotor and respiratory
consequences; separation of the jaws –open lips –loss of the
intraoral vacuum –instability of the soft palate –asphyxia –
followed by fatigue, sprains, dislocations, fractures and falls –
and/or negative pressure pulmonary oedema (‘bleeding’)
and sudden death (Cook 2002, 2014, 2016; Mellor and
Beausoleil 2017).
A horse learns to defend itself from the bit by gripping it
between the premolars (‘grabbing the bit’); trapping it under
the tongue (‘tongue over bit’); or placing it against the rostral
edge of the first mandibular cheek teeth. Horses that try to
disarm the bit in these ways are unfairly blamed for being
‘hard-mouthed’or ‘pullers’. The strategies result in bone spur
development at the interdental space and/or dental erosion.
Both defects are highly prevalent (Van Lancker et al. 2007;
Cook 2011; Mata et al. 2015).
€
Odberg and Bouissou (1999) reported that many horses
are slaughtered at a young age, perhaps because of
‘unresolved behavioural problems’. McGreevy and McLean
(2005) stressed the need for physical causes of undesirable
behaviour to be ruled-out before behavioural therapy was
adopted. They noted that bits are ‘...a potential source of
tremendous discomfort’.
The horse is motivated to avoid pain and seek comfort.
Mankind has an obligation to promote positive emotions for
the horse –the neuroscience-supported concept (see
Table 1)of‘positive affective engagement’(Mellor 2015a).
Contingent on the absence of pain a horse can probably
derive pleasure from being ridden, similar to that derived
from ‘play’with conspecifics (Mellor 2015b). Bonding
between horse and rider seems optimal when rein cues are
devoid of pressure, painless and proprioceptively supportive
(Hanson and Cook 2015).
Limitations of the study
Study design
The case-study population was not a random population.
Questionnaire
The prototype questionnaire does not meet recently
developed standards for questionnaire-based research (Hall
et al. 2013; Muir 2013; Reid et al. 2013). A future questionnaire
could be based on the Five Domains Model (Mellor and
Stafford 2001; Jones and McGreevy 2010; Mellor and
Beausoleil 2015; Mellor 2017). Future questionnaires might also
include input from the work of Mullard et al. (2017) and
Dyson et al. (2017) who have developed a ridden horse
ethogram based on facial expression. Most recently, Dyson
et al. (2018) have developed a pain scoring ethogram for
the ridden horse with the objective of differentiating lame
from nonlame horses.
Assessors were not ‘blinded’
Nevertheless, as recommended by current welfare science,
the assessors were the people most familiar with the animals
studied, having triple credentials as owners, caretakers and
riders.
Data grading
A simple count of pain indices represents the most basic of
welfare grading systems. As a result, the homocentric ‘lack of
control’carried no more weight than, for example,
‘yawning’. Absence of relative weighting will have
underestimated the harm of the bit. That said, current welfare
science thinking recommends non-numerical grading (Mellor
and Beausoleil 2015; Mellor 2017).
Standardisation
Lack of standardisation prevents this study from being
compared with others, e.g. Hockenhull and Creighton (2013).
To permit comparisons, a standard glossary (McGreevy et al.
2005), ethogram and protocol is needed. None of the 24
behavioural markers of pain in the ridden horse ethogram
developed by Dyson et al. (2018) were identical in wording
to the 69 markers of pain in the current study. However, many
were clearly descriptions of the same behaviours.
Comparisons cannot be made because of the terminology
differences and because none of Dysons’37 horses were
assessed when bit-free. The authors concluded “None of the
horses ... had evidence of oral pain”.
Crib-biting, wind-sucking and other stereotypic
behaviours in stabled horses
A footnote to the questionnaire read: “To date there is no
evidence to link wind-sucking or crib-biting as problems that
might be caused by the bit but it would be worth noting the
occurrence of such items in case a pattern of correlation
could be demonstrated”. Six out of 66 horses (9%) were
©2018 The Authors Equine Veterinary Education published by John Wiley & Sons Ltd on behalf of EVJ Ltd
8 Ridden horse pain
reported as showing stable-based stereotypic behaviour
when bitted; four windsuckers, one wood-chewer and one
self-mutilator. Information was not collected on whether this
behaviour changed when the bit was removed. In a survey
of stereotypic behaviour in a randomly selected population
of 650 riding-school horses, 46 exhibited stereotypies
(Normando et al. 2002). A statistically significant difference
was recognised in the prevalence of stereotypies between
stabled horses ridden Western style (9 out of 348 horses –3%)
and ‘English’(37 out of 302 horses –12%). The authors noted
that “the latter employs more hand to bit contact”.
Conclusions
When bitted, the median number of behavioural signs of
pain per horse was 23. After being bit-free for a median
period of 35 days, the median was 2. Removal of the bit
reduced the prevalence of pain signals by 87%; showing the
bit to be a predominant cause of pain in the population.
The null hypothesis was refuted. Following the criteria
proposed by Campbell (2013) for distinguishing use from
abuse, removal of the bit in 65 horses minimised risk (for the
rider) and prevented avoidable suffering (for the horse). In
sum, 65 horses out of 66 benefitted from removal of a
foreign body.
Authors’declaration of interests
No current conflict of interests have been declared.
Ethical animal research
No ethical review was required.
Source of funding
There was no formal funding for this research. The data were
collected by W.R. Cook during a period of years when he
was the CEO of a small company, Bitless Bridle Inc. The costs,
small as they were, were part of the general running costs of
the company and did not figure in any line item for research
in the annual accounts.
Acknowledgements
Pioneering owners made the study possible.
Authorship
The study design was conceived by W. R. Cook, as was the
execution, data entry and preparation of the manuscript. The
statistical data analysis was carried out by M. Kibler. Both
authors approved the final manuscript.
Manufacturer's address
1
PHS Saddlery, Colorado Springs, Colorado, USA.
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Supporting information
Additional Supporting Information may be found in the online
version of this article at the publisher’s website:
Supplementary Item 1: Questionnaire.
Supplementary Item 2: Prevalence of five major categories of
fear in 66 horses compared by their order when bitted.
©2018 The Authors Equine Veterinary Education published by John Wiley & Sons Ltd on behalf of EVJ Ltd
10 Ridden horse pain