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Evaluation of pain and inflammation associated with hot iron branding and microchip transponder injection in horses

Authors:
  • Lindegaard Veterinary Consulting

Abstract and Figures

To compare effects of hot iron branding and microchip transponder injection regarding aversive behavioral reactions indicative of pain and inflammation in horses. 7 adult horses. In a randomized controlled clinical crossover study, behavioral reactions to hot iron branding and microchip transponder injection were scored by 4 observers. Local and systemic inflammation including allodynia were assessed and compared by use of physiologic and biochemical responses obtained repeatedly for the 168-hour study period. Serum cortisol concentration was measured repeatedly throughout the first 24 hours of the study. Sham treatments were performed 1 day before and 7 days after treatments. Hot iron branding elicited a significantly stronger aversive reaction indicative of pain than did microchip transponder injection (odds ratio [OR], 12.83). Allodynia quantified by means of skin sensitivity to von Frey monofilaments was significantly greater after hot iron branding than after microchip transponder injection (OR, 2.59). Neither treatment induced signs of spontaneously occurring pain that were observed during the remaining study period, and neither treatment induced increased serum cortisol concentrations. Comparison with sham treatments indicated no memory of an unpleasant event. The hot iron branding areas had significantly increased skin temperature and swelling (OR, 14.6). Systemic inflammation as measured via serum amyloid A concentration was not detected after any of the treatments. Microchip transponder injection induced less signs of pain and inflammation and did not seem to pose a higher long-term risk than hot iron branding. Consequently, results indicated that hot iron branding does inflict more pain and should be abandoned where possible.
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840 AJVR, Vol 70, No. 7, July 2009
According to legislation in Denmark and the Euro-
pean Union,1–3 individual identification of horses is
required for animal health reasons and to ensure com-
pliance with certain public health requirements because
horses may be slaughtered for human consumption.
Furthermore, unique identification is important to en-
sure correct identification at competitions and shows
and when buying and selling horses.
Methods of identification of horses and foals born
in several European countries as well as other parts of
the world include hot iron branding and microchip
transponder injection. Hot iron branding is still widely
Evaluation of pain and inflammation associated
with hot iron branding and microchip
transponder injection in horses
Casper Lindegaard, DVM, PhD; Dorte Vaabengaard, DVM; Mogens T. Christophersen, DVM;
Claus T. Ekstøm, PhD; Julie Fjeldborg, DVM, PhD
Objective—To compare effects of hot iron branding and microchip transponder injection
regarding aversive behavioral reactions indicative of pain and inflammation in horses.
Animals—7 adult horses.
Procedures—In a randomized controlled clinical crossover study, behavioral reactions to
hot iron branding and microchip transponder injection were scored by 4 observers. Local
and systemic inflammation including allodynia were assessed and compared by use of
physiologic and biochemical responses obtained repeatedly for the 168-hour study period.
Serum cortisol concentration was measured repeatedly throughout the first 24 hours of the
study. Sham treatments were performed 1 day before and 7 days after treatments.
Results—Hot iron branding elicited a significantly stronger aversive reaction indicative of
pain than did microchip transponder injection (odds ratio [OR], 12.83). Allodynia quanti-
fied by means of skin sensitivity to von Frey monofilaments was significantly greater after
hot iron branding than after microchip transponder injection (OR, 2.59). Neither treatment
induced signs of spontaneously occurring pain that were observed during the remaining
study period, and neither treatment induced increased serum cortisol concentrations. Com-
parison with sham treatments indicated no memory of an unpleasant event. The hot iron
branding areas had significantly increased skin temperature and swelling (OR, 14.6). Sys-
temic inflammation as measured via serum amyloid A concentration was not detected after
any of the treatments.
Conclusions and Clinical Relevance—Microchip transponder injection induced less signs
of pain and inflammation and did not seem to pose a higher long-term risk than hot iron
branding. Consequently, results indicated that hot iron branding does inflict more pain and
should be abandoned where possible. (Am J Vet Res 2009;70:840–847)
used as a means of identification. The availability of
microchip transponders has led to an ongoing discus-
sion regarding whether hot iron branding or microchip
transponder injection has different effects regarding the
welfare of the horse. To the authors’ knowledge, only
1 study4 comparing hot iron branding and microchip
transponder injection of horses (or any other species)
has been reported in the scientific literature. That study
was conducted with Warmblood foals, and on the basis
of heart rates and behavioral observations, it was con-
cluded that hot iron branding caused more discomfort
than microchip transponder injection or no treatment.
The author also concluded that there was no evidence
of prolonged consequences for the foals; however, this
was based on behavioral observations lasting < 24 hours
after treatment, and no other physical or biochemical
analyses were performed. However sparse the scientific
literature regarding this issue in horses might be, sev-
Received June 27, 2008.
Accepted September 16, 2008.
From the Departments of Large Animal Sciences (Lindegaard, Vaaben-
gaard, Christophersen, Fjeldborg) and Natural Sciences (Ekstrøm),
Faculty of Life Sciences, University of Copenhagen, DK-2630 Taas-
trup, Copenhagen, Denmark. Dr. Vaabengaard’s present address is
Dyrlægecentralen Sydvest A/S, DK-6240, Løgumkloster, Denmark.
Supported by Kongeriget Danmarks, Hesteforsikring; Foreningen
KUSTOS; Forskningsfonden ved Institut for Produktionsdyr og
Heste, LIFE/KU; Dansk Varmblod; Hestens Værn; Den Danske Dyr-
lægeforening, Sektion vedrørende Heste; and Intervet, Denmark.
The authors thank Asger Lundorff Jensen for assisting with the bio-
chemical analysis and Svend Sørensen for technical assistance.
Address correspondence to Dr. Lindegaard.
AbbreviAtions
NRS Numeric rating scale
OR Odds ratio
SAA Serum amyloid A
VFM von Frey monofilaments
VAS Visual analogue scale
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AJVR, Vol 70, No. 7, July 2009 841
eral studies5–11 conducted on cattle have compared hot
iron branding to freeze branding and sham branding,
but not microchip transponder injection. The overall
impression from these studies is that hot iron branding
is substantially more painful and induces more inflam-
mation than freeze branding or sham branding. Behav-
ioral reactions were compared in 5 studies5–8,11 in cattle,
and all 5 revealed that hot iron branding elicited signifi-
cantly stronger escape-avoidance reactions indicative of
pain than freeze branding or sham branding. Three of
those studies compared heart rates and concluded that
heart rates were significantly increased after hot iron
branding, compared with freeze branding and sham
branding7; significantly increased after hot iron brand-
ing and freeze branding, compared with sham brand-
ing5; or substantially increased after hot iron branding
and freeze branding, compared with sham branding.6
Serum cortisol concentrations were measured in 4 stud-
ies, of which 2 revealed that hot iron branding and freeze
branding resulted in significantly increased concentra-
tions, compared with sham branding,5,9 and 2 revealed
significantly increased serum cortisol concentrations
after all treatments (hot iron, freeze, and sham brand-
ing), although concentrations did not differ among
treatments.6,7 Some of these studies also deal with other
important variables such as serum epinephrine concen-
tration,6,7 skin temperature,6,10 and sensitivity to touch9
and subsequent handling ease indicative of memory of
a bad experience.8 The only study dealing with hot iron
branding of horses, reported by Pollmann,4 has several
limitations because only heart rate and behavior were
observed and observations were terminated < 24 hours
after treatment. To conclude whether microchip tran-
sponder injection or hot iron branding should be pre-
ferred from an animal welfare perspective, observations
on physical and biochemical indicators of inflamma-
tion, including skin reaction and skin sensitivity as well
as behavioral observations, are needed. Furthermore, a
study period lasting for > 24 hours is needed to follow
the course of the inflammatory reaction.
Because hot iron branding causes skin damage, it
is reasonable to assume that it causes pain and elicits
an inflammatory reaction. Therefore, the aim of the
study reported here was to evaluate the relative degree
of pain as determined by behavioral responses to hot
iron branding and microchip transponder injection (re-
ferred to as treatments). Secondary aims of the study
were to quantify the relative degree of stress as well as
local and systemic inflammatory reactions associated
with the 2 treatments by measuring serum cortisol con-
centration, SAA concentration, and the classical inflam-
matory indicators edema, skin temperature, and skin
sensitivity. Our hypotheses were that hot iron branding
would induce greater aversive reactions, higher serum
concentrations of cortisol, and more marked local and
systemic inflammatory reactions than microchip tran-
sponder injection as measured via SAA concentration,
skin temperature, skin edema, and skin sensitivity.
Materials and Methods
Study design—The study was conducted as a
randomized controlled clinical crossover study with 7
horses subjected to both treatments with a washout pe-
riod of 14 days. On day 0 at hour 0 in the first trial pe-
riod, horses were subjected to the treatment randomly
assigned by drawing lots and received the other treat-
ment on day 0 at hour 0 in the second trial period. Four
horses received hot iron branding in the first study
period, and 3 horses received microchip transponder
injection in the first study period; the situation was re-
versed in the second study period. The experimental
protocol was approved by the Danish Animal Experi-
mentation Inspectorate.
Horses and preexperimental procedure—Seven
research horses of different breeds (4 Standardbred
trotters, 1 pony, and 2 horses of a mixed riding-type
breed), 6 to 18 years of age, owned by the University
of Copenhagen were included in the study after pass-
ing a thorough clinical examination including serum
biochemical and hematologic analyses with results
within reference limits. All horses were stabled in 3 X
4-m box stalls with a constant temperature of 13 ± 1°C
and fed a grain mixture twice daily as well as hay and
water ad libitum. Horses were accustomed to frequent
handling, including the entire experimental setup for
2 weeks prior to the beginning of the trial. At 3 days
prior to the treatments, horses had bilateral hair clip-
ping on the thighs for hot iron branding (approx 30
X 30 cm) or on the middle of the neck from the mane
down for microchip transponder injection (approx 10 X
10 cm). Contact areas for the heart rate monitors were
also clipped. After antiseptic preparation, an indwell-
ing jugular vein catheter was inserted under local an-
esthesia at 24 hours prior to the treatments. One hour
prior to the treatments, horses were fitted with a heart
rate monitoring systema set to record heart rate every 15
seconds for a period of 12 hours.
Treatments—All hot iron brands were applied
on the left thigh of the horse by the same experienced
person from the Danish federation of breeding associa-
tions.b Horses were branded with a plate iron measur-
ing 6 X 9 cm with the letters DK. After being heated to
red heat over a propane flame, the iron was applied for
approximately 1 second.
For microchip transponder injection, a veterinar-
ian wearing sterile gloves used the 3-mm-diameter
sterile needle provided by the manufacturer of the
microchip transponderc to inject the cylindrical
microchip measuring 2 X 13 mm approximately 2.5 cm
into the middle of the neck at the border of the crest
fat and the rhomboid cervical muscle. This procedure,
including standard surgical preparation of the clipped
skin, was executed according to the standard operating
procedure at the Department of Large Animal Sciences
at the University of Copenhagen. All microchip tran-
sponder injections were performed by the same person.
To minimize movement and for safety reasons, horses
were placed at the same location outside the stable be-
tween 2 large bales of straw for both treatments.
Sham treatments—In each trial period, horses
were subjected to a sham treatment 1 day prior to the
treatment and again 7 days after treatment. Horses
were handled and positioned in the exact same fash-
ion as when intended for treatment, and the procedure
was videographically recorded and scored in the same
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842 AJVR, Vol 70, No. 7, July 2009
way as the treatment procedures. In the trial period in
which the horse was assigned to hot iron branding, the
unheated branding iron was placed on the right thigh
for approximately 1 second at both occasions.
In the trial period of microchip transponder in-
jection, the horse was subjected to standard surgical
preparation on the right side of the neck and the skin
handled in the same way as for microchip injection. In-
stead of injecting a microchip, a short period of moder-
ate pressure was applied to the skin by the tip of the
index finger of the operator.
Outcome measures—The primary outcome mea-
sure was the behavioral score at the time of treatment.
All treatments were recorded videographically as well
as observed by the 4 observers. All observers scored
each horse’s reaction individually on the basis of the
videographic recordings and according to definitions
(Appendix). Scores were masked from the other ob-
servers. After scoring, the values were transformed into
a dichotomous variable, where categories 0 and 1 were
considered as no or insubstantial aversive reaction and
therefore indicative of no pain (score = 0) and catego-
ries 2 and 3 were considered a true aversive reaction
and thereby indicative of pain (score = 1).
A clinical examination (including general well-
being, respiratory rate, heart rate, rectal temperature,
color of oral mucosa, capillary refill time, skin turgor,
and intestinal peristalsis) and the secondary outcome
variables skin temperature, skin sensitivity, skin reac-
tion, and scoring for signs of pain were measured at 24
hours and 30 minutes prior to treatments as well as 30
minutes, 1, 2, 4, 6, 8, 12, 24, 48, 72, 96, 120, 144, and
168 hours after treatment.
At each time point, skin temperature was measured
in the treated area as well as in the corresponding con-
tralateral control area by use of an infrared thermome-
ter.d The standard operating procedure and instructions
specific for the infrared thermometer were followed.
The emissivity on the infrared thermometer was set to
0.98 for skin, and each measurement was taken at the
recommended distance of approximately 20 cm from
the skin surface. Each measurement lasted
for 15 seconds, and the infrared thermom-
eter subsequently calculated a mean skin
temperature.
Skin sensitivity was evaluated by the
use of VFM.e At each time point, increasing
mechanical stimuli were applied within the
clipped areas of either the thigh or neck ap-
proximately 1 to 2 cm from the treated area
as well as on the contralateral control area.
Each stimulus lasted 1 second and was re-
peated 3 times at intervals of 3 seconds, each
in a slightly different place. When the base-
line threshold was being determined, the
first stimulus applied was a VFM exerting
a pressure of 4.0 g. If an avoidance response
was observed, VFMs of decreasing force
were applied until no response was made or
the minimum diameter (equaling a pressure
of 0.008 g) was applied. If no response was
made, VFMs of increasing force were ap-
plied until an avoidance response was made
or the maximum pressure of 300 g was applied. An avoid-
ance response was defined as tail flicking, movement of
the ears or head, avoidance of the stimulus by shrugging
of the skin musculature, kicking, or stepping to the side. A
simple movement reflex on first touch of the VFM to the
skin was not accepted as an avoidance response. During
a measurement period, the first VFM force used for each
time point was the threshold obtained from the previous
measurement. The same operator made all VFM threshold
measurements, and all measurements were made with the
horses standing in a walkway with minimal restraint.
Edema of the treated area was evaluated via direct
subjective observation and graded on a scale from 0 to
5, where 0 was equal to no reaction and 5 was equal
to a strong reaction. The same observer evaluated the
edema at all times, and edema was recorded by use of
digital photographs.
Evidence of pain was evaluated repeatedly through-
out the study period by 1 observer who used an NRS
modified after Pritchett et al12 and by use of a VAS. The
NRS is a combination of behavioral, postural, and so-
cialization measures that give indications of the well-
being of the horse. These variables include the horse’s
position in the box, the position of the head and neck,
position and movement of the ears, reaction to an
opened box door, reaction to the approach of the ob-
server, reaction to feed, and gross behaviors indicative
of pain (eg, pawing, sweating, flehmen, continuously
taking a foot off the ground, or standing up and lying
down repeatedly). Possible outcomes of each variable
were described and associated with a score from 0 to 4,
and scores were subsequently summed to yield a pain
score. The VAS is a more subjective type of pain score
where the observer assigns a score between 0 and 100
on the basis of his or her interpretation of the horse’s
well-being. With the VAS, 0 is considered no evidence
of pain, and 100 is considered evidence of the worst
imaginable pain.
The order of data collection was: signs of pain
evaluated by use of NRS and VAS, clinical examination,
skin temperature, skin sensitivity, edema, and blood
Figure 1—Mean ± SEM skin temperature in 7 horses after hot iron branding and
microchip transponder injection. *Significant (P < 0.05) difference between hot iron
branding control site and microchip transponder injection site.
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AJVR, Vol 70, No. 7, July 2009 843
sampling. Regarding skin temperature, skin sensitivity,
and edema, the control side was always scored first.
Blood sampling procedures—Blood samples were
collected from the indwelling jugular vein catheter 30
minutes before treatments to obtain a baseline and at
30 minutes and 1, 2, 4, 6, 8, 12, 24, 48, 72, and 168
hours after treatments. Ten milliliters of blood was col-
lected and discarded before collecting 20 mL into se-
rum tubes. The jugular vein catheter was flushed with
heparinized saline (0.9% NaCl) solution after each sam-
pling. Blood was stored at 5°C and analyzed within 24
hours for SAA concentration by use of a commercially
available automated turbidometric immunoassay,f and
serum cortisol concentration was measured by use of
chemiluminiscence.g The assays were subjected to daily
internal quality control, and only results from accepted
runs were used.
Statistical analysis—Skin temperature was ana-
lyzed by use of a generalized linear model where the
temperature was modeled as a function of time and the
interaction between treatment and side,
such that repeated measurements over
time on each horse could be positively
correlated.
The primary variable of interest of
this part of the experiment was the in-
teraction between side and treatment be-
cause this determined whether the tem-
perature changes between the treatment
side and the contralateral control side
differed by treatment. A test for trend for
time was performed, and the time effect
was fitted as a continuous second-degree
polynomial.
The number of VFM sizes was too
large to analyze with the present data set.
Instead, an increased skin sensitivity in-
dex was generated; this was defined as 1
if the skin sensitivity was increased on
the treated side relative to the control side
and 0 otherwise. Skin sensitivity index
and behavior score were both analyzed by
use of a logistic mixed effect model with
horse as a random effect. The mean effect
of skin sensitivity index was a function
of treatment and time whereas behavior
score was a function of treatment and ob-
server. The primary hypothesis for both
of these response variables was the differ-
ence between the 2 treatments as it related
to the different effects of hot iron brand-
ing versus microchip transponder injec-
tion. Regarding observer agreement, this
cannot be estimated properly with scores
from 4 observers on 7 horses. However,
in the logistic regression model, it can be
tested whether there is any effect of ob-
server (ie, whether the 4 observers typi-
cally agreed).
The edema score was modeled by use
of a polynomial regression model with
fixed effects of time, horse, and treatment.
The polynomial regression model is an extension of a
classical logistic regression model, in which multiple
ordered response categories are allowed. Values of P <
0.05 were considered significant.
Results
Behavioral score—Both hot iron branding
(OR, 17.93; P < 0.001) and microchip transponder
injection (OR, 14.85; P < 0.001) had an effect on be-
havioral scores, compared with their respective pre-
treatment sham procedures. However, the type of iden-
tification method had a significant (P < 0.001) effect on
behavioral scores as well. The final model had an OR of
12.83, meaning that with 95% confidence, the odds for
observing a reaction was between 3.10 and 53.10 times
as great in horses being hot iron branded as in horses
being injected with microchip transponders. There was
no difference between first and second sham treatments
for any of the treatments. Observer had no effect on
behavioral score (P = 0.81).
Figure 2—Mean ± SEM skin edema score in the same horses as in Figure 1. See
Figure 1 for key.
Figure 3—Mean ± SEM SAA concentrations in the same horses as in Figure 1. Base-
line values were obtained 30 minutes prior to treatments.
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844 AJVR, Vol 70, No. 7, July 2009
Skin temperature—Treatment method had an effect
on skin temperature. The difference in skin temperature
between horses that were hot iron branded and micro-
chip transponder injected appeared 24 hours after treat-
ment and lasted throughout the study period (Figure 1).
Horses in the hot iron–branded group had significantly (P
< 0.001) higher skin temperature (1.43°C higher) in the
treated area, compared with the nontreated contralateral
control area. Horses in the microchip transponder–in-
jected group had a nonsignificantly (P = 0.27) lower skin
temperature (0.16°C) in the treated area, compared with
the nontreated contralateral control area.
Skin sensitivity—There was a continuous signifi-
cant (P = 0.01) difference between the 2 treatments re-
sulting in an OR of 2.59 for increased skin sensitivity
after hot iron branding, compared with microchip tran-
sponder injection, indicating that with 95% confidence,
the odds for observing increased skin sensitivity were
between 1.39 and 4.82 as great after hot iron branding,
compared with microchip transponder injection.
Edema—Method of identification had a significant
(P < 0.001) effect on the degree of edema with an OR
of 14.6, indicating that with 95% confidence, the odds
for observing a skin reaction in the form of swelling or
edema were from 6.97 to 30.83 as great after hot iron
branding, compared with microchip transponder injec-
tion. These differences were significant at 1, 2, 4, 6, 8,
12, 24, 48, and 120 hours after treatment (Figure 2).
Serum amyloid A and serum cortisol concentra-
tions—Neither hot iron branding nor microchip tran-
sponder injection elicited an increase in SAA concen-
tration (Figure 3). Serum cortisol concentrations did
not differ between the 2 treatments. Values were within
reference limits and followed the typical circadian pat-
tern (Figure 4).
NRS and VAS pain scoring—No signs of pain were
recognized in the subsequent study period. The NRS
pain scores were between 0 and 1 of a maximum of 22,
and VAS pain scores were 0 at all time points after both
treatments.
Heart rate—All horses had an increased heart rate
in association with both treatments, and although the
heart rate appeared slightly more increased after hot
iron branding than after microchip transponder injec-
tion, this difference was not significant
(Figure 5; P = 0.12).
Discussion
Hot iron branding caused significant-
ly greater aversive reactions indicative of
pain than did microchip transponder in-
jection. Because it was concluded to be
impossible to mask the treatments (sim-
ply because of the different nature of the 2
treatments), the study was not masked. To
compensate for this, a rigid guide regard-
ing the scoring of behavioral reactions
was made to make the reaction scores
as objective as possible, and scoring was
conducted by 4 individuals; their scores
were based on videographic sequences of
the treatment procedures without know-
ing the scores of the 3 other observers.
Because no differences existed among
observers (P = 0.81), we concluded that
results of the study should be considered
valid and pertinent regarding the discus-
sion of hot iron branding of horses.
Results of the present study were in
complete agreement with several stud-
ies5–8,11 in cattle (hot iron branding was
compared with freeze branding or sham
treatment) and to the results obtained by
Pollmann4 in a study comparing hot iron
branding and microchip transponder in-
jection of foals, although there were cer-
tain important differences. There has been
a lack of investigation of other reactions
and longer-term reactions than behav-
ioral, heart rate, and hormonal changes
(serum cortisol and epinephrine concen-
trations) immediately after the treatment,
and Pollmann4 concluded that hot iron
Figure 4—Mean ± SEM serum cortisol concentrations in the same horses as in Fig-
ure 1. Baseline values were obtained 30 minutes prior to treatments.
Figure 5—Mean ± SEM heart rates in the same horses as in Figure 1. Time 0 is the
time of treatment. bpm = Beats per minute.
08-06-0205r.indd 844 6/23/2009 1:36:52 PM
AJVR, Vol 70, No. 7, July 2009 845
branding did not cause any long-term consequences
to the foals. However, this conclusion was based solely
on behavioral observations of < 24 hours after treat-
ment. The present study, which lasted 168 hours after
treatment, revealed that there were several important
long-term consequences to horses subjected to hot iron
branding.
The present study revealed significantly increased
skin sensitivity around the treatment site after hot
iron branding, compared with microchip transpon-
der injection. This was in contrast to a study9 in
heifers in which increased skin sensitivity, tested by
simply placing a hand on the branded site and on the
contralateral control site, was not observed 1 and 7
days after branding. The reason for this difference
might be that the stimulus applied in that study was
too irregular. More likely, as suggested by the authors
themselves, this might be the result of not accustom-
ing heifers to this so-called touch test and thereby
observing similar escape-avoidance reactions to the
branded site and the unbranded contralateral con-
trol site. In the present study, skin sensitivity was as-
sessed by use of VFM, which has been used to quan-
tify skin sensitivity after tissue damage in horses.13
Additionally, the horses were thoroughly accustomed
to the procedure for 2 weeks prior to treatment. The
hypersensitivity observed is termed hyperalgesia or
allodynia, depending on whether the applied stimu-
lus is considered noxious or not.14 Furthermore, it
might be defined as primary or secondary hyperal-
gesia or allodynia depending on whether it is caused
by local or central sensitization caused by the inflam-
matory reaction.15,16 In the present study, mechani-
cal stimuli were applied by the use of VFM, which
is generally believed to be a non-noxious stimulus17;
the increased reaction is therefore considered allo-
dynia. The stimulus was applied close to the injured
area and not directly on it, so the reaction observed
in the present study was considered secondary al-
lodynia. However, whether allodynia is primary or
secondary was not important in this setting because
both are the results of sensitization caused by a local
inflammatory reaction.15
This local inflammatory reaction was also indicated
by increased skin temperature and edema after hot iron
branding, compared with microchip transponder injec-
tion. Increased skin temperature at the hot iron–brand-
ing site was observed from 8 hours after treatment and
throughout the study period (168 hours), which was in
accordance with 2 studies in cattle in which increased
skin temperature was observed 4 days6 and 2 to 168
hours10 after hot iron branding.
Heart rate was increased immediately after hot iron
branding in several studies in cattle5–7 and in foals,4
which is in accordance with results in our study. Al-
though an increase of a similar magnitude was detect-
ed after microchip transponder injection, heart rates
remained consistently higher after hot iron branding
than after microchip transponder injection for the first
5 minutes after treatment.
Plasma cortisol concentration has been identified
as a potential indicator of pain in horses18 but is also
increased after stressful nonpainful situations such as
transportation19,20 and excercise.21 To avoid bias of the
serum cortisol concentrations and behavioral scorings,
the present study used adult horses thoroughly accus-
tomed to handling and to all procedures included in
the experimental setup prior to the actual treatment.
Serum cortisol concentrations after hot iron branding
and microchip transponder injection were compared,
but not with a control group or the sham treatments.
Serum cortisol concentrations did not differ between
the 2 treatments. Because values were within reference
limits at all sampling points and followed the typical
circadian pattern (Figure 4), it was concluded that
neither hot iron branding nor microchip transpon-
der injection elicited a meaningful change in serum
cortisol concentrations. This differed from results of
studies5,7,9 in cattle where serum cortisol concentrations
were significantly increased between 5 and 40 minutes
after hot iron branding or freeze branding. In 2 stud-
ies,6,7 however, serum cortisol concentrations were also
increased after sham treatments, so it is suggested that
serum cortisol concentration is a less sensitive indica-
tor of pain than it is of stress, which we attempted to
eliminate in our study. Other reasonable explanations
to account for these differences might be that the pain
response elicited by the 2 treatments was either too
small or too short-lived to induce an increase in this
hormone, or the sampling intervals of 30 minutes might
have been too long, although a significant increase in
serum concentration of this hormone would have been
expected at 30 minutes after treatment.
Hot iron branding results in a hairless scar because
of the inflammatory reaction instigated by the second-
or third-degree burn that it causes.22 Serum amyloid A is
a major acute phase protein that is useful for evaluating
inflammatory reactions in horses and other species.23
A variety of inflammatory as well as infectious condi-
tions including aseptic arthritis,24 castration,25 strepto-
coccal lymphadenitis,26 and IM injection of turpentine
oil27 cause increased SAA concentrations. In the present
study, SAA concentrations were not affected by either of
the 2 treatments. This was interesting because hot iron
branding, but not microchip transponder injection, re-
sulted in substantial classic local signs of inflammation
including heat, edema, and pain. However, this local
reaction may have been too small to induce a systemic
inflammatory response within the 168-hour study pe-
riod. A reasonable explanation might be that the dam-
aged area constituted too small a fraction of the entire
skin area of each horse. Alternatively, damage to the
skin may not elicit an SAA response.
Infections and chronic hyperplastic and neoplastic
cutaneous lesions at the brand site have been reported
in cattle subjected to hot iron branding,28,29 and infec-
tion and neoplastic growth at the microchip injection
site have been reported in dogs and a cat.30–32 Conse-
quently, these adverse reactions should also be consid-
ered potential sequelae to microchip transponder injec-
tion and hot iron branding in horses. To the authors’
knowledge, other sequelae or long-term sequelae (>
168 hours) from hot iron branding or microchip tran-
sponder injection in horses have not been reported in
the scientific literature and have not been observed by
the authors at the Large Animal Hospital of the Univer-
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846 AJVR, Vol 70, No. 7, July 2009
sity of Copenhagen. Furthermore, there are no reports
on the proportion of adverse reactions induced by either
treatment in any species. However, Hooven28 stated that
hot iron branding in cattle is often followed by open-
wound infections and parasite infestations, and the Brit-
ish Small Animal Veterinary Association considers that
microchip transponder injection represents a safe and
reliable form of companion animal identification. Only
3 cases of infection after microchip transponder injec-
tion were reported to the Federation of European Com-
panion Animal Veterinary Associations and the British
Small Animal Veterinary Association from members
throughout Europe in 2000 and 2001.30 It is difficult
to make an objective evaluation of the long-term safety
of either identification method, but it seems reasonable
to conclude that microchip transponder injection does
not seem to pose a higher risk for long-term sequelae
than hot iron branding. Therefore, recommendations
regarding permanent identification of horses are based
on short-term animal welfare aspects in combination
with an evaluation of the usefulness of the identifica-
tion method.
Originally, hot iron branding was used as a method of
identifying animals by applying the specific brand of the
owner. Nowadays, brands may include a number (typical-
ly 3 digits) for better identification. However, a non–peer-
reviewed publication of the German Equestrian Associa-
tion33 indicated that it was impossible to read all 3 digits
in 30% to 50% of the studied horses. In contrast, Sorenson
et al34 were able to read all microchip transponders 1 year
after implantation in 49 dogs and cats.
The present study revealed that hot iron branding
elicited a substantial aversive reaction indicative of pain
followed by a week-long local inflammation including
allodynia of the skin. Because use of a microchip is su-
perior to hot iron branding regarding correct identifi-
cation and microchip transponder injection does not
seem to pose a higher risk than hot iron branding for
long-term complications, we conclude that applying a
hot iron brand to a horse does inflict more pain and
should be abandoned where possible.
a. Polar Equine Heart Rate Monitor S720i or S810i, Polar Electro
Danmark Aps, Holte, Denmark.
b. Dansk Landbrugsrådgivning, Landscentret/Heste, Århus,
Denmark.
c. RID Microtransponder, Datamars SA, Bedano-Lugano,
Switzerland.
d. Raytek Raynger MX4, Raytek, Santa Cruz, Calif.
e. Touch Test Sensory Evaluator, North Coast Medical Inc, Morgan
Hill, Calif.
f. LZ-SAA R1/R2, EIKEN Chemical Co Ltd, Tokyo, Japan.
g. Immulite 2000 Advanced Immunoassay System, Siemens
Healthcare Diagnostics, Tarrytown, NY.
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Behavioral score Definition
0 No reaction, ear twitching, shrug, or shiver
of skin musculature
1 Raises the neck or moves it to the side,
steps to the side, looks back
2 Pins down the ears, restless, snorts, tail
flick, escape behavior (jumps to the side,
forward, or back)
3 Kicks, rears, stomps, excessive movement
Appendix
Behavioral scores used in a study of hot iron branding and
microchip transponder injection in horses.
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Twenty-seven crossbred calves (1/2 Simmental, 1/4 Hereford, 1/4 Brahman) averaging 257 +/- 11 d of age were either hot-iron-branded (H), freeze-branded (F), or sham-branded (S). Calves were blocked for temperament, weight, and sex and were randomly assigned to day and order in which treatments were applied. To reduce stress from handling at treatment time, each calf was herded through the squeeze chute daily for 5 d before the experiment. Jugular cannulas were inserted in each calf 1 d before application of treatment. Blood samples and heart rate measures were obtained at -5, -3, 0, .5, 1, 3, 5, 10, 15, and 20 min after application of the treatments. Mean concentrations of plasma epinephrine (EPI) were higher for H calves at time .5 min than for either S or F calves (P = .10). To account for individual differences, prebranding heart rates and hormone concentrations were subtracted from subsequent samples and were also used to calculate a proportion for each subsequent sample. Analyses of subtracted values found that EPI concentrations were greater for H calves than for either S or F calves (P = .007) at .5 min postbranding. No other differences were found for the subtracted analyses. Analyses of proportion data also revealed that H calves had greater EPI than did either S or F calves (P = .027) at .5 min postbranding. Only three animals vocalized during branding, one H calf and two F calves. Despite the 5-d acclimation period, handling and restraint elevated plasma cortisol concentrations and heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)
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Physiological and behavioral parameters were determined in 27 horses to identify potential indicators of postoperative pain following exploratory celiotomy for colic. Experimental groups were 10 horses that received no treatment (Control), 10 horses anesthetized for a non-painful procedure (Anesthesia), and 7 horses that presented for emergency surgery for acute gastrointestinal disease (Surgery). Physiological and behavioral data were collected on the horses 0, 4, 8, 12, 16, 20, and 24–30h after entry into a stall in the equine intensive care unit of the Veterinary Teaching Hospital at Washington State University. Physiological data included: heart rate, respiratory rate, and plasma cortisol concentration. For the entire period of observation the surgery group had significantly higher plasma cortisol concentration and significantly elevated heart rate compared to the Control and Anesthesia groups, which did not differ for either variable. A numerical rating scale (NRS) of behavior was used to visually score the horses at the same time physiological data were collected. In addition, time budgets of behavior were calculated from 1h segments of real-time video recording beginning at the 0, 4, 8 or 12h, and 20 or 24–30h time points. Time budgets for the Control and Anesthesia groups did not differ in the time spent in locomotor activities and both groups spent significantly more time in locomotion than the Surgery group. The Surgery group spent significantly more time displaying painful behavior compared to the Control and Anesthesia groups; however, the amount of time the Surgery group displayed painful behavior was small compared to the amount of time with no movement. The NRS scores substantiated the video taped behavioral data with significantly different scores for the Surgery group versus the Control and Anesthesia groups for multi-factor ratings of body posture and response to stimuli. We conclude that reduced locomotion, elevated plasma cortisol concentration, and elevated heart rate are potential indicators of postoperative pain in horses.
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Twenty-four Angus calves averaging 293 ± 38 kg were either hot-iron branded (H), freeze branded (F), or served as a sham (S). Calves were blocked for temperament, weight, and sex, and randomly assigned to day and order in which treatments were applied. To reduce stress from handling at treatment time, each calf was herded through the squeeze chute for 5 days prior to the experiment. Jugular cannulae were established in each calf 1 day prior to application of treatment. Blood samples and heart rate were obtained at −5 and −3 min prior to and 0, 0.5, 1, 3, 5, 10, 15 and 20 min after calves were branded on the hip. Mean plasma cortisol concentration increased for all treatments during the sampling times (P = 0.0001). Mean plasma epinephrine concentration was greater (P < 0.01) for H calves at 0.5 min after branding than either S or F calves. Hot-iron branded calves had greater (P < 0.02) mean heart rate during branding and 30 s post-branding than did either S or F calves. The escape-avoidance reaction of H calves, quantified as the amount of vertical movement the calf exhibited during branding, was also greater (P < 0.05) than either the F or S calves. Five H calves, four F calves, and no S calves vocalized during treatment. The greater escape-avoidance reaction as well as the elevated heart rate and plasma epinephrine concentration of the H calves indicate that a greater pain sensation is perceived by hot-iron branded Angus cattle.
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Objective To evaluate the pre-emptive analgesic effect of pre-incisional epidural ketamine. Study Design A blinded, randomized experimental study. Animals Sixteen mixed breed mares, 7.6 ± 2.8 years old, weighing 352 ± 32 kg. Methods In a pilot study, an incision was made on one lateral thigh using a lidocaine block and no further analgesics, and it was verified that the nociceptive threshold was lower on the incised side than nonincised side (p ≤ 0.05), and that von Frey filaments evoked a pain response. The 16 animals were divided into group A (ketamine, n = 9) and B (saline, n = 7). An epidural catheter was inserted 24 hours before the trials. The thigh was shaved bilaterally, and the right side was blocked (incised side) using lidocaine. Twenty-five minutes later, ketamine (A) or saline (B) was administered epidurally. Five minutes later, a 10-cm skin incision was made on the right side, and then sutured. Nociceptive threshold was determined with von Frey filaments at 1, 3, and 5 cm around the incision at 15-minute intervals for 2 hours, then at 4, 6, and 8 hours. Behavioral alterations, heart and respiratory rates were recorded. Nociceptive thresholds from these points were averaged to obtain mean values at each time, converted to a logarithmic scale, and submitted to a nonparametric analysis (Mann–Whitney and one-way repeated measures anova test, p ≤ 0.05). Results After 8 hours, the global range score revealed reduced hyperalgesia (p < 0.01) around the incision in 92% (4.65–4.27) of evaluated intervals in group A (ketamine). There were no significant changes in behavior, heart and respiratory rates. Conclusions It was concluded that pre-emptive epidural ketamine reduced post-incisional pain in the horse, and that von Frey filaments were able to quantify cutaneous sensitivity after tissue damage. Clinical relevance Epidural ketamine injection can reduce post-incisional sensitivity in the horse.
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A public debate has recently arisen, largely surrounding the issue of pain, over whether freeze or hot-iron branding should be the preferred method of permanently identifying cattle. This study addressed that question by quantifying the following accepted measures of distress and pain over a 25-min sampling period: elevated heart rate, concentrations of cortisol, epinephrine, and norepinephrine, and escape-avoidance reactions and vocalizations. Twenty-four dairy cows (15 Holsteins and 9 Jerseys) were assigned to one of three treatments: freeze-branded (F), hot-iron-branded (H), or sham-branded (S), in which a room-temperature brander was applied. Plasma epinephrine and norepinephrine concentrations showed no discernible trends. Plasma cortisol concentrations were elevated in the F and H cows from 5.5 min to 25.5 min postbranding (P = .04). Heart rate, analyzed as a proportion of the prebranding mean, showed that H cows had a greater, more acute, response than did F cows (P = .04), which exhibited a more prolonged response (P = .07). No cows vocalized during branding; however, H cows had a greater escape-avoidance reaction toward branding than did the F and S cows. Both methods of branding produced elevated heart rates and cortisol concentrations indicative of pain sensations. Because the cows exhibited a greater escape-avoidance reaction and heart rate proportions to hot-iron branding, freeze banding would be preferable to hot-iron branding when feasible.