Strategic palmar trimming before conventional shoeing shows potential for managing underrun heels in horses

Background Underrun heels are among the most hoof imbalances, causing poor performance in hoses. Several corrective shoeing protocols have been performed, but the outcomes have yet to be consistent. In this study, we proposed an alternative trimming protocol for managing underrun heels: strategic palmar trimming before conventional shoeing. Therefore, the current study aimed to investigate the potential of strategic palmar trimming before conventional shoeing for managing hoof imbalance in horses with underrun heels. Methods Eleven affected horses were divided into control (5 horses with 14 defective hooves) and experimental (6 horses with 16 defective hooves) groups. The experimental group underwent strategic palmar trimming before conventional shoeing, while the control horses received regular trimming before traditional shoeing. Dorsal hoof wall angle (DHWA)/heel angle (HA) ratios, heel-bulb distance, and six parallel lines indicating solar surface dimension were determined before, and after 5, 10, 15, 20, 25, and 30 weeks of the different trimming protocols. Palmar trimming distance was only measured in experimental horses. Results A group-by-time interaction was observed for DHWA/HA ratios and solar surface dimension. Separate effects for group and time were observed in the heel–bulb distance. A modification in hoof conformation was detected at 25-30 weeks only in horses in the experimental group, including decreases in DHWA/HA ratio, heel–bulb distance, and palmar trimming distance, coinciding with an increase in palmar width of trimmed hooves. Conclusions Different trimming protocols produced a different effect on hoof conformation. Therefore, tactical remedial trimming can potentially control poor hoof conformation in horses with underrun heels.


Introduction
Underrun heels, also known as collapsed heels or long toe-low heel conformation, are among the most common hoof distortions causing poor performance in horses (Bigham and Tabatabaei 2007).The condition is characterised by a palmar angle that is more than 5°smaller than the hoof angle (Dabareiner and Carter 2003, Hunt 2012, Sigafoos 1990).The hoof wall grows distally from the coronet with a uniform slope from toe to heel (O 'Grady 2008).The dorsal hoof wall angle (DHWA) and heel angle (HA) should thus theoretically be the same.However, the HA is generally smaller than the DHWA.A higher likelihood of wear at the heel than at the toe region during locomotion might contribute to angle disparity (Barrey 1990, Moleman et al. 2006).
In principle, the palmar hoof region has an important role in shock absorption and management of the mechanical force applied to the hoof structure (Eliashar 2007, Hood et al. 2001, O'Grady 2012).Repetitive disproportionate loading on the palmar area during movement is thought to result in underrun heels in horses (Hunt 2012).In a severely distorted hoof, the horn tubules in the heel region are bent forward and run parallel to the ground surface (Dabareiner and Carter 2003).As a result, this forward shift of the weight-bearing surface causes mechanical overloading of the palmar region and may generate bruising and chronic palmar pain (Hunt 2012).Moreover, repetitive overloading, concomitant with a low heel and interphalangeal joint dorsiflexion, creates a negative angle between the distal phalanx's solar surface and the ground (Floyd 2010, O 'Grady 2006).This negative angle may induce tissue injuries in the palmar region, thereby reducing its ability to dissipate the descending mechanical force during locomotion (Floyd 2010, Hunt 2012).Overloading also applies abnormal forces to the navicular bone and related apparatus.This induces degenerative changes in the navicular bone, leading to navicular syndrome (McGuigan andWilson 2001, Wilson et al. 2001).
The management goal in horses with underrun heels is to establish a normal hoof capsule and increase the palmar angle, which will restore hoof function and exercise performance (Hunt 2012, O'Grady et al. 2018).Appropriate hoof trimming procedures have been shown to correct a negative palmar angle accompanied by a long toe-low heel conformation (Floyd 2010).After basic trimming, heart bar shoes, straight bar shoes, or shoeing with heel plates or wide-webbed heel shoes have been utilised to support regrowth and repair; however, the shape of these shoes make them unsuitable for long-term use in competition horses (Hunt 2012).Elevating the heel using a shoe with a built-in wedge pad to produce a normal hoof angle has also been used to correct this defect (Dabareiner andCarter 2003, Hunt 2012); however, this method may induce progressive overloading and lead to perpetually curved horn tubules (Hunt 2012).
The outcomes of underrun heel correction by various corrective shoeing approaches have been inconsistent.In this study, we proposed an alternative trimming protocol for managing underrun heels: strategic palmar trimming before conventional shoeing.The objectives of the present study were as follows: first, to evaluate the potential of the alternative trimming protocol to improve hoof conformation and palmar angle, and second, to investigate the estimated time required for this proposed method to improve hoof conformation variables in horses with underrun heels.It was hypothesised that the hoof conformation in horses receiving strategic palmar trimming differed from those undergoing conventional trimming before shoeing in underrun-heeled horses.

Ethics approval and consent to participate
The Ethics Committee for Animal Experiments of Kasetsart University approved all procedures included in this study (ACKU64-VET-040) on June 4, 2021.Since the study was conducted as routine shoeing practice in horses under veterinary supervision.Moreover, no invasive operation was performed in this study.There was, therefore, the most

REVISED Amendments from Version 1
In response to the reviewer's feedback, the modifications to the article included: 1.More information and additional supplementary file 2 were provided in the material and method section to confirm the standardized trimming and shoeing protocol by one experienced equine practitioner, even though two main farriers performed the corrective shoeing.
2. We have discussed and provided more evidence in terms of additional supplementary file 2 on the benefit of palmar trimming before the conventional shoeing that not only reduced weight bearing on hooves' palmar regions but also promoted the rapid growth of palmar hoof wall and improved the heel angle in underrun-heeled horses.
3. Much of the texts were modified to convey a consistent term of message in the article.
4. All statistical significances were modified to depict exact P-values throughout the study.
Any further responses from the reviewers can be found at the end of the article negligible probability of suffering during shoeing protocol throughout the study.The owners of the animals have signed an informed consent to use their animals in this study.This article is reported inline with Animal Research: Reporting of in vivo Experiments (ARRIVE) guidelines (Sanigavatee 2023a).

Animals
Eleven client-owned horses (6 geldings and 5 mares, aged 13-19 years and weighing 420-480 kg) suffering from underrun heels were studied.These horses had underrun heels as determined by a difference of at least 5°between the toe and heel angles (Hunt 2012), which was the inclusion criterion for this study (Supplemental File 1; Table S1).They were excluded from this study if the injury or lameness occurred, causing severe lameness during the study period.Horses were recruited from equestrian riding clubs, including the Horse Lovers' Club (13.995917138209828, 100.68551338185088),Checkmate Horse Club (13.976257409277178, 100.70805959728767),House of Horse riding club (13.812821261748075, 100.78691136835704), and Bang Phli riding school (13.597609837219945, 100.6835924548628).Affected horses were randomly divided into control (5 horses, 14 defective hooves) and experimental (6 horses, 16 defective hooves) groups.The number of horses was based on clinical cases that showed underrun heel conditions.In this study, four horses suffering from underrun heels in four hooves, six horses with underrun heels in both fore hooves and a horse showing underrun heels in both hind hooves (Extended data, Supplementary File 1; Table S1; Sanigavatee 2023b).To categorise into control and experiment groups, four horses that showed underrun heels in four hooves were distributed evenly to the control and experiment groups.Seven horses with underrun heels on either fore or hind hooves were randomly selected by drawing from a hat as a lottery method.Thus the sample size (number of underrun-heeled hooves) in the control and experiment groups was 14 and 16, respectively.There were no differences in mean DHWA/HA between groups in this study (15.09AE 1.28 (control) vs 16.69 AE 1.43 (experiment), p = 0.42).Before the trial, they were conventionally shod at four-to six-week intervals and usually performed aerobic exercise during 20-50 min on 2-4 days per week.The horses were kept in their usual environment.They were housed in individual stables (4 Â 4 Â 6 m 3 ).Commercial pellets and Pangola hay were provided three times a day, and clean water was freely accessible.There were no therapeutic interventions before the start of the study.The horses were allowed to perform light exercise during the study if lameness was reduced to slightly irregular gait or no foot pain.

Lameness examinations
All horses underwent a full lameness examination before the beginning of the study.Lameness was evaluated by three equine practitioners and scored from 0 to 5 according to the scale outlined by the American Association of Equine Practitioners (AAEP) (Kester 1991), in which 0 denotes no lameness and 5 indicates non-weight-bearing lameness.In brief, the horses trotted on a hard surface over a total distance of 60 m.An additional lameness evaluation was performed on all defective hooves by hoof tester compression on the solar surface area.The joint flexion test, flexor tendon palpation, and extension test were performed sequentially.Palmar digital anaesthesia using 2% lidocaine hydrochloride (L.B.S. Laboratory Ltd., Bangkok, Thailand) was performed uniaxially to localise the area of the foot pain in case lameness was present in the horse.Gait analysis was also performed before each farriery session.

Radiographic examination
Before the first farriery session and at 15 weeks and 30 weeks, the 30 affected hooves were radiographed in dorsopalmar, lateromedial, and 65°dorsopalmar projection to assess bone defects and internal hoof configuration.The distal phalanx/ ground surface angle was also assessed radiographically (Poskom PXM-20 BT, Diagnostic Imaging Systems, Inc., SD, USA) in the affected limbs, as described previously (Kummer et al. 2006).

Strategic palmar trimming and shoeing adjustments
Each horse underwent hot-shoeing performed by experienced farriers under veterinary supervision every 5 weeks during the 30 weeks of the experiment.Of note, one horse with four defective hooves and two horses with defective fore hooves were excluded from the control group after 10 and 25 weeks due to the injury, regardless of the shoeing protocol.The strategic hoof trimming protocol in the experimental group was intended to eliminate the collapsed palmar tubules and prevent the palmar region from bearing weight.All trimming and shoeing protocols were performed under close supervision by one experienced equine practitioner to standardise the trimming method and farrier practice throughout the study.Before each farriery session, the injured hooves were measured from the toe to the heel bulb to calculate three equal areas using a Measure King™digital tool (ONTEL, Fairfield, New Jersey, USA).Each hoof was cut at the dorsal one-third and rasped to provide a ground contact surface of approximately the dorsal two-thirds of the hoof (Figure 1a and b).The hoof was then pressed onto Play-Doh to obtain a surface model to determine the solar surface dimensions.The rasped hoof was repeatedly measured to establish the three equal regions.The palmar third of the hoof was trimmed horizontally until the angle of the sole was visualised (Figure 1c).Finally, all horses were shod with metal shoes (Mustadfors Bruks, Dal Langed, Sweden) on the affected and healthy hooves, according to the standard method described elsewhere (Karle et al. 2010, Le sniak et al. 2017, Weishaupt et al. 2013).In this shoeing method, the size of metal shoes was selected to match the hoof conformation of each horse.Moreover, the length between the caudal part of the shoes and the imaginary line from the heel bulb perpendicular to the ground was restricted to no longer than 1 inch.In addition, the metal shoe's caudal parts were expanded to offer sufficient support to the hooves' palmar region (Supplementary File 2; Figure S1, Sanigavatee 2023b).

Hoof conformation
Before and after each sequential shoeing session, lateral view images of affected hooves were captured at a distance of 40 cm using a Canon EOS 500D Digital SLR Camera (Canon Inc., Tokyo, Japan) (Figure 2a and b).The DHWA, HA, and distance of the heel bulb to the caudal ground contact of the hoof were evaluated before each shoeing session.The palmar trimming distance was estimated after each shoeing session.The data were calculated using the ImageJ program (version 1.52a) (LOCI, University of Wisconsin, Madison, WI, USA) and expressed as DHWA/HA ratio, absolute heelbulb distance, and palmar trimming distance.

Hoof surface dimension measurements
The hoof surface dimensions were determined according to a method described previously (Chanda et al. 2020).Briefly, Play-Doh solar surface images were captured at a constant distance of 70 cm using a Canon EOS 500D digital SLR camera (Canon Inc., Tokyo, Japan) (Figure 2c).The circumference of the hoof ground surface was calculated using the GoodNotes 5 application (Time Base Technology Limited, Kowloon, Hong Kong).The surface was then divided by six parallel lines perpendicular to the central line of the solar surface using the AutoCAD software program (version O.49.0.0) (Autodesk Inc., San Rafael, California, USA) (Figure 2d).Each parallel line was measured (in mm) from the medial to the lateral side using the ImageJ program (version 1.52a) (LOCI, University of Wisconsin, USA) to determine changes in the solar surface dimension.

Statistical analyses
Statistical analyses were performed using GraphPad Prism version 9.5.1 (GraphPad Software, San Diego, CA, USA).Due to missing data in the repeated measurements, a mixed-effects model (Restricted Maximum Likelihood: REML) was used to analyse the change in the DHWA/HA ratio, absolute heel-bulb distance, and length of the six parallel lines on the solar surface in horses in the control and experimental group.Tukey's multiple comparisons test was used to compare results within the group.Šídák's multiple comparisons test was applied to compare parameters between the groups at given times.Palmar trimming distances were analysed by the Friedman test with a Dunn's multiple comparisons test because this parameter showed a non-normal distribution following the Kolmogorov-Smirnov test.Data were expressed as the mean AE SEM.Statistical significance was set at p < 0.05.

Lameness examination
The results of the lameness examination of horses in the control and experimental groups are shown in Tables 1 and 2, respectively (Sanigavatee 2023a).Approximately half the horses exhibited mild lameness on the front legs.Furthermore, all affected horses demonstrated sensitivity to compression by the hoof tester on the sole, particularly in the palmar region.Most horses in the control group were positive for the fetlock flexion test.In contrast, only a few horses in the experimental group were positive for the fetlock flexion test.All lame horses responded to palmar digital nerve desensitisation, showing a dramatic decrease in lameness following the regional anaesthesia protocol.The radiographic images demonstrated bone defects, including synovial invagination, irregular shape of the navicular bone's distal border, and negative palmar angle of the hoof in some horses in this study (Extended data, Supplementary File 3; Sanigavatee 2023b).

Palmar trimming distance
Compared to the hooves' palmar trimming length in the early sessions, the trimming length of the defective hooves was shorter in later shoeing sessions.A considerable shortening in palmar trimming length was detected at 20 weeks (36.44 AE 1.88 vs 28.48 AE 0.88 mm; p = 0.0056) 25 weeks (36.44 AE 1.88 vs 27.86 AE 0.97 mm; p = 0.0048) and 30 weeks (36.44 AE 1.88 vs 26.33 AE 1.04 mm; p = 0.0018) (Figure 3).A decrease in DHWA/HA ratio in experimental horses was initially detected at 25 weeks (1.60 AE 0.08 vs 1.33 AE 0.06; p = 0.0198) and remained at 30 weeks (1.60 AE 0.08 vs 1.34 AE 0.05; p = 0.0164) (Figure 5).The radiographic images also showed an improved hoof angle after 30 weeks compared to the negative hoof angle at the initial farriery session in the experimental horses (Extended data, Supplementary File 6; Sanigavatee 2023b).

Solar surface dimension
Table 3 shows the modification of the solar surface, indicated by a change in the length of the six parallel lines.There was a group-by-time interaction for change in the length of all measured parallel lines (line 1; p = 0.0127, line 2; p = 0.0003, and lines 3-6; p < 0.0001).Time on its own interacted with a change in the length of lines 1 (p = 0.0113), 3 (p = 0.0202), 4 (p = 0.0047), and 5 (p = 0.0381), but not of lines 2 (p = 0.0565) and 6 (p = 0.4566).There was no separate group effect for the modification of any of the parallel lines in this study.
The solar surface dimension was unchanged in horses in the control group throughout the study period (Extended data, Supplementary File 4; Figure S3d-f; Sanigavatee 2023b).In contrast, the solar surface of the hooves in the experimental group changed over time (Extended data, Supplementary File 5; Figure S4d-f; Sanigavatee 2023b).Even though a fluctuation in length was observed in lines 3 and 4 of hooves in control group at 10, 20, and 30 weeks of the shoeing protocol (10 vs 20 weeks; p = 0.0032 and 0.0012 in lines 3 and 4 respectively) (20 vs 30 weeks; p = 0.0348 and 0.0210 in lines 3 and 4, respectively), the length of the six parallel lines after 30 weeks did not differ from the length before the first session in horses in the control group.Similarly, there was a marked fluctuation in the length of line 1 at 25 and 30 weeks (p = 0.0163) and line 2 at 10 and 30 weeks of the shoeing protocol (p = 0.0416) in horses in the experimental group.Nonetheless, the length of lines 1-4 at 30 weeks was not different from the value before corrective shoeing.
There was a difference between groups in the length of lines 5 and 6 at the start of the trial (p = 0.0030 and 0.0078, respectively).A change in lines 5 and 6 was observed in the experimental group over time.The length of line 5 was increased at 25 and 30 weeks compared to the start of the trial (p = 0.0429 and 0.0410, respectively).An increase in the length of line 6 was detected earlier, at 10 weeks, until the end of the study at 30 weeks compared to before corrective shoeing (p = 0.0058, 0.0086, 0.0283, 0.0004 and 0.0007, respectively).

Discussion
The present study investigated the effect of conventional shoeing combined with strategic palmar trimming on hoof conformation and recovery time in horses with underrun heels.The significant findings of the experiment include: 1) there was a trimming protocol-by-time interaction for changes in DHWA/HA ratio and solar surface dimension, indicating a distinct impact of the trimming protocol on hoof conformation; 2) hoof angle, heel angle, and solar surface dimension increased simultaneously in response to strategic palmar trimming before conventional shoeing, but they were unchanged following the shoeing without the palmar trimming; 3) an increase in heel angle as a result of a decrease in DHWA/HA ratio was initially noted at 25 weeks; while a reduction in heel-bulb distance and palmar trimming length was detected at 25-30 weeks in response to the strategic trimming before shoeing; 4) hoof ground contact, particularly in the   palmar region, improved markedly from week 25 of the corrective shoeing with palmar trimming onwards.Therefore, strategic palmar trimming followed by conventional shoeing showed the potential to control underrun heels in horses.
The corrective shoeing protocol should be followed for at least 25 weeks to improve hoof conformation and heel angle in horses with underrun heels.
Several pathological lesions, including palmar bruising and abscesses, sheared heels, hoof wall separation, subcapsular soft tissue damage, and osteoarthritis of the interphalangeal joints, have been reported to accompany underrun heel conformation (Dabareiner and Carter 2003, Hunt 2012, Turner 2010, Turner 1988).Furthermore, hoof conformation defects in conjunction with the bone lesions of the navicular syndrome may be detected in horses with underrun heels (Dabareiner and Carter 2003).This conformation defect does not always result in lameness despite repetitive abnormal loading leading to underrun heels in horses (Hunt 2012).Moreover, the underrun heel conformation may persist without evidence of navicular syndrome (Wright 1993).Our results support this idea, as the horses in the present study showed unilateral lameness on the front legs, even though they showed underrun heel conformation in the other limbs (Extended data, Supplementary File 1; Tables S2 and S3; Sanigavatee, 2023b).Although evidence of degeneration, such as synovial invagination and irregular navicular bone shape, was not associated with lameness in the horses in this study, the mechanical force acting on the navicular bone in horses with underrun heels is still of concern (Hunt 2012).In addition, excessive compression of the navicular bone, exerted by the tensile force of the deep digital flexor tendon, was also reported to be caused by underrun heel conformation (Turner 1989).Hence, navicular syndrome secondary to underrun heels should still be considered.
The interval between consecutive shoeing sessions has been found to influence hoof conformation (Le sniak et al. 2017, O'Grady and Poupard 2003, Van Heel et al. 2005).Shoeing at 8-week intervals has been reported to increase dorsal hoof wall length and decrease DHWA, which puts the distal interphalangeal joint under certain stress (Moleman, et al. 2006).
A 4-6-week shoeing interval could optimise the prevention of excessive loading on the palmar region, thereby lowering the risk of long-term injuries (Le sniak et al. 2017).For this reason, shoeing in our recent study was carried out at fiveweek intervals to reap the maximum benefits of the corrective shoeing.Lameness in experimental horses was markedly reduced at 20-30 weeks (Extended data, Supplementary File 1; Table S4; Sanigavatee 2023b), while there was almost no change in gait abnormality in the control group.
In the present study, a change in DHWA/HA ratio and heel-bulb distance was detected in horses with strategic palmar trimming before conventional shoeing, while it was unchanged in horses with regular trimming and traditional shoeing.
It has been reported that appropriate trimming to restore the normal hoof angle is possibly more crucial than applying additional devices (O 'Grady 2006, O'Grady andPoupard 2001).It has been proven that hoof trimming has a significant effect on hoof conformation (Kummer et al. 2006).Theoretically, hoof trimming and shoeing in a horse with foot pain should re-establish balance and correct hoof problems.Trimming and shoeing are expected to diminish the biomechanical forces exerted on the palmar hoof area (Dabareiner and Carter 2003).Trimming and shoeing have been used to modify the external hoof capsule and the internal structures (O' Grady 2008).Therefore, hoof trimming and shoeing are crucial in distorted hoof management (Hunt 2012).The general concept of managing underrun heels incorporates three principles: first, toe trimming to reduce the overgrown toe, thereby facilitating breakover and restoring the proper axis and position; second, multiple rounds of palmar trimming to eliminate the curved horn tubules, creating healthy horn that can withstand palmar loading; third, proper trimming and shoeing management to reduce palmar loading on the affected hooves (Hunt 2012).In the anatomy of the foot, the distal phalanx should reside in the dorsal two-thirds of the hoof capsule, while the soft tissues should occupy the palmar third of the hoof capsule (O'Grady 2012).In practical terms, underrun heels may still be present even though the hoof angle has been anatomically corrected with basic hoof trimming.The palmar tubules may still be in contact with the ground, producing a fulcrum at this point when loading.This may lead to the continuous forward growth of the distorted palmar tubules, resulting in curling horn in the palmar region.The strategic palmar trimming described in the present study was designed to adhere to these three principles and enable the hooves to bear the natural descending forces.The purpose of the cut at the dorsal one-third of the hoof capsule was to shorten the toe and raise the hoof-pastern axis position.After tactical rasping, the ground contact surface extended to the dorsal two-thirds of the capsule and this was believed to be sufficient to withstand natural loading on the distal phalanx.Strategic trimming of the palmar third was designed to eliminate the curling heel and the tubules' contact with the ground in the palmar region before shoeing.Thus, as the heels did not bear weight, the palmar horn tubules were allowed to grow distally, improving the heel angle.Moreover, this trimming protocol has considerable potential to improve the position of the axis to dissipate loading on the palmar region and promote heel growth, as demonstrated by the hoof-pastern axis improvement seen in the radiographs (Extended data, Supplementary File 7; Sanigavatee 2023b).In addition, following the strategic trimming protocol, the trimming length became shorter in the palmar third while retaining an appropriate ground contact length in the dorsal two-thirds of the hoof capsule (Extended data, Supplementary File 8; Sanigavatee 2023b).Lighter loading was likely experienced in the palmar region due to the strategic hoof trimming protocol.
The progressive shortening of both heel-bulb length and palmar trimming distance may indicate, at least in part, that the palmar horn tubules grew more distally when this tactical shoeing protocol was applied.In addition, with minimal loading on the palmar region, rapid growth of palmar horn tubules was observed indicated by dramatically reduced gap, causing extremely close contact of the trimmed palmar region to the metal shoes before the consecutive shoeing period (Extended data, Supplementary File 2; Figure S1c; Sanigavatee 2023b).Therefore, the present study provided objective evidence for the importance of strategic palmar trimming in correcting underrun heels in horses.
The solar surface dimension remained constant in shod horses without strategic palmar trimming, whereas it changed over time in horses with tactical remedial trimming.The length of lines 1-4 was unchanged in horses in the present study, as the toe and quarter portions are less elastic than the heel region (Chanda et al. 2020).The expansion of the palmar area, illustrated by the increased length of lines 5 and 6, was marked at 25 and 30 weeks of corrective shoeing.Although the length of lines 5 and 6 was different between the two groups before the start of the trial, there was no difference between groups in the length of both lines at the end of the study: the palmar size in horses with corrective shoeing increased, while it remained constant in shod horses without the strategic trimming.A decrease in heel-bulb distance and palmar trimming length, coinciding with an improvement in heel angle and other aspects of hoof conformation at 25-30 weeks of the corrective shoeing, suggest that this is the minimum time required to improve hoof conformation in horses with underrun heels.Nevertheless, this period may vary depending on the severity of hoof distortion, the level of experience of the farrier, the shoeing interval, and environmental factors such as riding ground surface, nutrition, and type of activity.
The small number of affected horses in each group was the main limitation of this study.Further validation of this alternative farrier practice with a larger sample size is required.In addition, hoof radiography could not be performed at every farriery session due to lack of machine availability, so the onset of the improvement in negative palmar angle could not be documented.

Conclusions
Strategic hoof trimming accompanied by conventional shoeing can considerably improve hoof conformation by increasing the heel angle and expanding the hooves' palmar region in horses with underrun heels.Corrective shoeing should be continued for at least 25 weeks to achieve an improvement in the affected feet.A close collaboration between a specialised veterinarian and an experienced farrier is paramount to obtain a positive outcome from strategic shoeing management in horses with underrun heels.
Data are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).
Introduction-Well referenced and provides an appropriate background to the study Consider using the term palmar angle of the distal phalanx instead of palmar angle where appropriate Methods I am not quite clear on the exact definition of palmar trimming distance is.From figure 2 it appears to be the horizontal distance from the start of the horizontal heel trim to the end of the heel horn The exact definition you are using could be better clarified here so that in the results you can better comment on what made the palmar distance measurement shorter and then comment on why in the discussion

Results
Well presented with clear tables and figures.The authors responded satisfactorily to the suggested corrections.I am now in a position to recommend acceptance of the manuscript.

Is the work clearly and accurately presented and does it cite the current literature? Yes
Is the study design appropriate and is the work technically sound?Yes

Are sufficient details of methods and analysis provided to allow replication by others? Yes
If applicable, is the statistical analysis and its interpretation appropriate?Yes Are all the source data underlying the results available to ensure full reproducibility?Yes

Are the conclusions drawn adequately supported by the results? Yes
Competing Interests: No competing interests were disclosed.
I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

Version 1
Introduction -Include the study's hypothesis; -In the objectives, the authors refer to an "alternative farriery protocol", but in this case, the term "trimming" would be more appropriate, as this was the only difference between the groups.

Methods
-Use the terms "fore and hind limbs", and "fore and hind hooves" to refer to the limbs throughout the text.
-"Real hooves"?did you mean "hind hooves"?-The authors included lame animals in the study and indicated that some of them improved over the course of the study.How do the authors differentiate the improvement in hoof balance from the proposed treatment and not from the simple return of the hoof load to the lame limbs?-The manuscript indicates that several farriers perform hoof management, but with a small number of animals, this can be an important source of variation.Ideally, only one farrier should have performed the management.Please indicate how many farriers took part in the study and whether the authors considered this a source of variation in their data analysis.
-Three animals were removed from the control group, does this mean that only 3 animals finished the study?This reflects an important limitation for the analysis, as you probably cannot identify differences for this group.I suggest that the authors revise their statements to support their conclusions for the moments when all the animals were present in the study and only make assumptions for later moments.

Results
-The term "uneven gait" seems very subjective to me, what do the authors mean by this? -In the text there is a call for figures 3a, 3b and 3c, but there is only one figure 3. Check this.
-Include the exact probability values throughout the text.
-Figure 3: in the caption, there is mention of hoof images, but there is nothing of this in the figure, check this.
-Figure 4: place the figure after the caption in the text.
-Table 3: what do the superscript letters mean? Discussion -In the first paragraph the authors need to be clear in their statements about which groups were better in which aspects analyzed, just saying that "changes" happened is too general.
-"Remedial farriery", "corrective shoeing"... avoid using so many terms to refer to the same subject, as it creates confusion in understanding.

Is the work clearly and accurately presented and does it cite the current literature? Yes
Is the study design appropriate and is the work technically sound?Partly

Are sufficient details of methods and analysis provided to allow replication by others? Partly
If applicable, is the statistical analysis and its interpretation appropriate?Yes Are all the source data underlying the results available to ensure full reproducibility?Yes

Are the conclusions drawn adequately supported by the results? Yes
Competing Interests: No competing interests were disclosed.
I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.
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Figure 1 .
Figure1.Demonstration of the solar surface of a hoof before and after trimming.The length was initially measured (yellow line) and cut at the dorsal one-third (white double-headed arrow) (a).The horn was then rasped to allow ground surface contact for approximately the dorsal two-thirds of the hoof (b).After the second measurement, the palmar third was horizontally trimmed until the sole angle was visualised (black-headed arrows).The trimming was intended to create a space between the affected palmar region and the metal shoe (c).

Figure 2 .
Figure 2. Representative images and Play-Doh models of a hoof with an underrun heel.The lateral views were captured before (a) and immediately after (b) shoeing.Measurements of the DHWA (1), hoof height (2), HA (3), heel height (4), palmar trimming distance (5), and heel-to-bulb distance (6) allowed for evaluation of the DHWA/HA ratio and the average heel-bulb and palmar trimming distances.A Play-Doh hoof model was constructed after basic trimming (c) and then divided by six parallel lines perpendicular to the central line for solar surface determination (d).
left forelimb; LH = left hind limb; RF = right forelimb; RH = right hind limb; +++ = strongly positive; ++ = moderately positive; + = mildly positive; -= negative.Heel-bulb distanceAlthough there was no group-by-time interaction (p = 0.6248), separate effects of group (p = 0.0045) and time (p = 0.0182) were observed for the change in the heel-bulb distance.The heel-bulb distance was unchanged in horses in the control group throughout the study period.However, in horses in the experimental group, it was significantly shorter at 25 weeks (25.50 AE 1.35 vs 20.51 AE 0.70 mm; p = 0.0080) and 30 weeks (25.50 AE 1.35 vs 20.57AE 1.15 mm; p = 0.0404) (Figure4).DHWA/HA ratiosThere was a group-by-time interaction (p = 0.0101) for change in DHWA/HA ratios in the present study, but no separate effects of group (p = 0.1208) and time (p = 0.0685) were found.There was no change in DHWA/HA ratio in horses in the control group (Extended data, Supplementary File 4; FigureS3a-c; Sanigavatee 2023b), but the ratio changed in the experimental group (Exteded data, Supplementary File 5; FigureS4a-c; Sanigavatee 2023b).

Figure 3 .
Figure 3. Palmar trimming distance changes in response to conventional shoeing in combination with strategic hoof trimming.The line chart illustrates the quantitative change in palmar trimming distance at each shoeing session (c).**p < 0.01 when compared to the values at the first shoeing session (0 wk) in horses with the strategic palmar trimming protocol.

Figure 4 .
Figure 4. Changes in heel-bulb distance following conventional shoeing with and without strategic palmar trimming in horses with underrun heels.*p < 0.05 and **p < 0.01 when compared to the values at the first shoeing session (0 wk) in horses with strategic palmar trimming.

Figure 5 .
Figure 5. Changes in DHWA/HA angle ratio following conventional shoeing with and without strategic palmar trimming in horses with underrun heels.*p < 0.05 when compared to the values at the first shoeing session (0 wk) in horses with strategic palmar trimming.
indicate the effects of group-by-time interaction and time on change in given parallel lines in response to palmar trimming before conventional shoeing.Different letters (a and b) indicate statistical significance within the group between pairs of comparison.x and y indicate statistical significance between groups at given time points.

Table 1 .
Lameness examination in horses in the control group before initial farriery protocols.

Table 2 .
Lameness examination in horses in the experimental group before initial farriery protocols.

Table 3 .
Measurement of six parallel lines (mm) from Play-Doh impressions before each farriery session in horses with (+) and horses without (-) strategic palmar trimming.

the work clearly and accurately presented and does it cite the current literature? Yes Is the study design appropriate and is the work technically sound? Yes Are sufficient details of methods and analysis provided to allow replication by others? Yes If applicable, is the statistical analysis and its interpretation appropriate?
This paragraph has some interesting points and summary statements but is the least directly related to the results and if needed for size purposes could be shortened to leave the last 3 sentences out.(okay the way it is if no space limitations) This paragraph might benefit from a sentence or two about what might be anticipated in the future for trimming after 30 weeks-expectation of ground contact with palmar heel tubules.As the heel tubule becomes straighter does this method always require trimming shorter than ground contact?Would that method of trimming be short enough for ground contact not to be achieved by the 5 week interval?often trimming that "floats" a heel will have considerable settling even within the first week post trim.how/why does this method differ.Also consider how this relates to number 4 in the first paragraph.What level of palmar ground contact do you want and what structures do you want loaded (eg wall tubules vs frog) Paragraph 5 Well stated.see comment about palmar trimming length noted in methods Paragraph 6 Another limitation or at least area for future study was not evaluating frog ground contact or potentially depth and elasticity of the digital cushion between control and experimental groups or before and after strategic trimming protocol for 30 weeks.These areas share load with the heel tubules and may affect results or conversely may be affected by the trimming protocol.Separating fore feet from hind feet in a larger study may also be informative.I cannot comment.A qualified statistician is required.

all the source data underlying the results available to ensure full reproducibility? Yes Are the conclusions drawn adequately supported by the results? Yes
Reviewer Expertise: equine lamenessI confirm that I

have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.
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