- Email: [email protected]
The Application of the Self-Adjusting Palmar Angle Shoe for the Promotion of Sole Growth in Horse Feet
The Professional Animal Scientist 22 (2006):463–466
CSelf-Adjusting S : The Application of the Palmar Angle Shoe ASE TUDY
for the Promotion of Sole Growth in Horse Feet J. HAFFNER,*1 M. WOOTEN,† D. DUNSON,† D. BOWERS,† and R. HOFFMAN,* PAS *Department of Agribusiness and Agriscience, Horse Science Center, Middle Tennessee State University, Murfreesboro 37129; and †Nolensville Veterinary Clinic, Nolensville, TN 37135
Abstract
Introduction
The objective of this case study was to determine if applying a self-adjusting palmar angle shoe (SAPAS) influenced sole thickness in horses as compared to using flat shoes or leaving horses unshod. Eighteen horses were allocated into 3 groups of 6 horses each. The front feet of the horses in 2 groups were shod with either a SAPAS or flat shoe in a 2 × 2 factorial crossover design with 5-wk periods. The third group remained unshod for the study. At the beginning and end of each period, the horses’ front feet were radiographed to measure the sole thickness, as determined to be the distance between the sole and the distal tip of the third phalanx, and its change over time. The sole thickness of the horses shod with either shoe increased more than the sole thickness of the unshod horses (P = 0.003). Sole thickness increased when a SAPAS was applied after the flat shoe (P = 0.003), and sole thickness decreased when a flat shoe was applied after a SAPAS (P = 0.003).
The economic loss due to lameness in horses is estimated between $678 million and $1 billion annually (USDA-APHIS, 2001). Sole bruising is a common cause of lameness in horses. A thin sole provides insufficient protection to the foot and predisposes a horse to sole bruising (Stashak, 1987; Dabareiner et al., 2003). Lack of adequate sole thickness may be predisposed by genetics or caused by laminitis or injury. Because shoeing alone does not provide adequate protection to the sole, one of the goals addressed in shoeing laminitic and other thin-soled horses is to provide the best circumstances for the sole to achieve maximum thickness. Many types of shoes have been used to treat laminitis, but few attempts have been made to document observable effects of those shoes on sole thickness. One of the shoes of interest in this study is a self-adjusting palmar angle shoe (SAPAS). In an effort to treat laminitic horses using a SAPAS, it was observed by the authors that after the application of the SAPAS, soles appeared to grow more rapidly. Additionally, a loss of sole thickness was observed in the soles of horses that
Key words: palmar angle, sole thickness, self-adjusting palmar angle shoe, laminitis 1
To whom correspondence should be addressed: [email protected]
were shod with the SAPAS and then changed back to flat shoes. To more adequately investigate these observations, a study was designed to determine if application of the SAPAS does promote sole growth when compared to a flat shoe or to being unshod. The hypothesis was that sole growth would be greater in horses wearing SAPAS compared to horses wearing flat shoes or no shoes.
Materials and Methods In accordance with a protocol approved by the Middle Tennessee State University Institutional Animal Care and Use Committee, 18 horses were selected for study. They were randomly assigned to 1 of 3 groups. Both front feet of the horses in 2 groups were shod with either a SAPAS or flat shoe in a 2 × 2 factorial crossover design with 5-wk periods. The third group remained unshod during the study to determine the normal variation in sole thickness without the effect of shoes over a 5-wk period. All horses were shod by the same farrier and assistant. The flat shoes were applied in a standard fashion with nails. Proper application of the SAPAS required lateral radiographs of the front feet as
464
Haffner et al.
Figure 1. Measuring sole thickness. The surface of the sole was marked with barium contrast paste. A line perpendicular to the weight bearing surface was drawn to the tip of the third phalanx. The sole depth was recorded as the distance from the surface of the sole to the tip of the third phalanx.
previously described (Redden, 2003b). The SAPAS was shaped and the foot was trimmed to produce an anteriorto-posterior breakover point at the widest part of the hoof. The SAPAS was applied with the shoe being bent so that the shoe formed a slight curve from front to back like that of a rocker on a rocking chair (Figures 1, 2, and 3). The SAPAS was applied according to the depth of sole. If the sole was thick, the foot was shaped, and the SAPAS applied with nails. If the sole was thin, epoxy material
(Equilox, Equilox International, Farrier Supplies, Pine Island, MN) was used to increase the thickness to provide contact between the SAPAS and the foot. Application of horse shoes by means of adhesive is becoming more prevalent in routine farriery. The epoxy material has no apparent or reported effect on sole growth, so this treatment was not included in the statistical model. The horses were housed in stables with rubber mats bedded with wood shavings while being used for riding
Figure 2. Determining palmar angle. The palmar angle is the angle formed between the solar surface of the third phalanx and the weight bearing surface. In a flat shoe the horse is restricted to the palmar angle determined by the application of the shoe.
instruction 4 d per week and were pastured during the weekend. Five weeks after the first shoeing, the shoe was removed without trimming the sole, and radiographs were repeated for comparison. The horses were then reassigned to the alternate shoeing technique, and the process was repeated. The order of shoe placement, either SAPAS first and then flat or vice versa was recorded as “shoe order.” The unshod horses were radiographed twice, 5 wk apart. During this time they were on pasture. Sole thickness was determined by radiographic analysis at 0 and 5 wk for unshod horses, and at 0, 5, and 10 wk for horses with shoeing treatments. Shoes were removed, and both front feet of each horse were placed on 5-cm positioning blocks of wood for equal weight distribution. The blocks contained a wire embedded in the top of the block to delineate the supporting surface. The radiographic film cassette was placed 66 cm from the x-ray tube. A line perpendicular to the positioning block upon which the horses were standing was measured from the distal edge of the cranial tip of third phalanx (PIII) to the surface of the sole. Barium sulfate paste placed on the sole of the unshod foot in front of the frog allowed specific identification of the solar surface. The sole thickness was determined radiographically as the distance between the sole and the distal tip of the PIII. (Figure 1). This radiographic measurement was correlated closely to direct measurements made on dissected cadaver feet (Olivier-Carstens, 2004). The sole thickness was measured in batches with no identification of treatment protocol by an experienced equine clinician. Comparisons were then made to determine the change in sole thickness as a percentage of the original thickness. Normality was tested using the Shapiro-Wilk statistic. Hoof sole data were analyzed using a mixed model with repeated measures (SAS Inst., Inc., Cary, NC); sources of variation included shoe type, shoe order, horse (shoe order), and the residual error
CASE STUDY: A Shoe for the Promotion of Sole Growth in Horse Feet
Figure 3. Self-adjusting palmar angle shoe applied to foot. The self-adjusting palmar angle shoe allows the horse to rest the foot in the most comfortable position.
horse shoe type shoe order. Horse (shoe order) was used as the error term to test the effects of shoe order. Means were compared using the Tukey test. Sole thickness of the unshod horses was compared to flat- and SAPAS-shod horses during the first 5-wk period only using a mixed model with repeated measures. (SAS Inst., Inc.).
Results and Discussion Baseline hoof sole thickness was coincidentally less initially (d 0) in horses that were first fitted with the SAPAS compared to the flat shoe (P = 0.047); therefore, a covariate analysis was used so that only changes in hoof sole thickness over time were compared. During the first period, the sole thickness of the feet of the horses that were shod with a flat shoe increased 14.4% (1.7 mm) as compared to 24.3% (3.1mm) for the SAPAS group, and decreased 8.9% (−1.3 mm) for the unshod horses. Compared to the unshod horses, the change in sole thickness was greater in horses shod with the SAPAS (P < 0.0001) and the flat shoe (P = 0.003). There was no difference (P = 0.17) between horses
shod in the SAPAS or flat shoe during the first period. During the second period, the sole thickness of horses that were changed from a flat shoe to a SAPAS increased 17.6% (2.3 mm). The sole thickness of horses that were changed from a SAPAS to a flat shoe decreased 9.1% (−1.5 mm). Compared to horses that were changed from a SAPAS to a flat shoe, horses changed from a flat to SAPAS shoe had a significant increase in sole thickness (P = 0.004). The data indicated that when compared to being unshod, the application of either a flat shoe or a SAPAS allows for an increase in sole thickness. Although the increase produced by the SAPAS in the first 5 wk was greater than that of the flat shoe, the difference was not significant. It was also indicated by the data that changing from a flat shoe to a SAPAS had a significant positive influence on sole thickness. Conversely, changing from a SAPAS to a flat shoe had a significant negative effect on sole thickness. This study demonstrated that the perceived changes in sole thickness did occur. The change in sole thickness was a result of increase in sole thickness due to actual sole growth minus any de-
465
crease in sole thickness due to attrition from wear. This was reflected in the data by the unshod horses that lost sole thickness over a 5-wk period. This information is useful in that if a horse has a thin sole, sole thickness will increase by applying either a flat shoe or the SAPAS. Also, the increase in sole thickness of the horses that were initially flat-shod was enhanced by the SAPAS. This is clinically applicable because it showed that changing from a flat shoe to a SAPAS promoted an increase in sole thickness. It is also of interest that the sole thickness was decreased by changing from a SAPAS to a flat shoe. The palmar angle, measured on a lateral radiograph of the foot, is the angle produced by the intersection of the lines formed by the solar surface of the PIII and the surface upon which the foot is resting (Figure 2). If PIII is parallel to the ground, the palmar angle is zero. If the toe of PIII is lower than the wing of PIII, the palmar angle is positive. Finally, if the toe of PIII is higher than the wing, the palmar angle is negative. A slightly positive palmar angle is considered optimal (Redden, 2003a), but reported normal values range from 2 to 10 degrees, depending on type of horse and limb conformation (Parks, 2003). Flat shoes do not allow the horse to adjust its palmar angle (Figure 2). In comparison, because of its curved shape, the SAPAS allows the horse to place its foot so that it can find the most comfortable position and optimal palmar angle (Figure 3). One of the commonly accepted treatments for horses with lameness in the foot has been to change the point of initiation of movement from the weight-bearing to the flight phase of the stride. This aspect of the horse’s stride is termed "breakover." It is hypothesized that the advantage of the SAPAS over a flat shoe is in part due to the breakover point of the SA-
466
PAS being more caudal compared to the flat shoe. This reduces the stress on the tissues as the horse walks. It is also hypothesized that the curved shape of the SAPAS allows the horse to place the foot in a position that is most comfortable to the horse. This allowance of optimal foot placement by the horse may also aid and facilitate blood flow to the foot. These are areas that need investigation.
Haffner et al.
ing from a flat shoe to a SAPAS. This is clinically important in horses with thin soles that need an increased sole thickness to protect the internal structures of the foot. Since horses suffering from laminitis frequently suffer from lack of sole thickness as part of the disease process, this information may be useful for management of laminitic horses.
Implications This work demonstrated that by applying a flat shoe or a self-adjusting palmar angle shoe, the sole thickness of the foot of a horse increased compared to being unshod. Sole thickness increased by chang-
Literature Cited Dabareiner, R., W. Moyer, and G. K. Carter. 2003. Trauma to the sole and wall. In Diagnosis and Management of Lameness in the
Horse. W. Ross and S. Dyson, ed. p 275. Saunders, Philadelphia, PA. Parks, A. 2003. Form and function of the equine digit. Vet. Clin. N. Amer. Equine Pract. 19:285. Olivier-Carstens, A. 2004. Ultrasonography of the solar aspect of the distal phalanx in the horse. Vet. Radiol. Ultrasound 45:449. Redden, R. 2003a. Hoof capsule distortion: Understanding the mechanisms as a basis for rational management. Vet. Clin. N. Amer. Equine Pract. 19:443. Redden, R. 2003b. Radiographic imaging of the equine foot. Vet. Clin. N. Amer. Equine Pract. 19:379. Stashak, T. S. 1987. The relationship between conformation and lameness. In Adams’ Lameness in Horses. T. S. Stashak, ed. p 98. Lea & Febiger, Philadelphia, PA. USDA-APHIS. 2001. National economic cost of equine lameness, colic, and equine protozoal myeloencephalitis (EPM) in the United States. Info Sheet No. N348.1001. USDA Animal and Plant Health Inspection Service, Washington, DC.
CSelf-Adjusting S : The Application of the Palmar Angle Shoe ASE TUDY
for the Promotion of Sole Growth in Horse Feet J. HAFFNER,*1 M. WOOTEN,† D. DUNSON,† D. BOWERS,† and R. HOFFMAN,* PAS *Department of Agribusiness and Agriscience, Horse Science Center, Middle Tennessee State University, Murfreesboro 37129; and †Nolensville Veterinary Clinic, Nolensville, TN 37135
Abstract
Introduction
The objective of this case study was to determine if applying a self-adjusting palmar angle shoe (SAPAS) influenced sole thickness in horses as compared to using flat shoes or leaving horses unshod. Eighteen horses were allocated into 3 groups of 6 horses each. The front feet of the horses in 2 groups were shod with either a SAPAS or flat shoe in a 2 × 2 factorial crossover design with 5-wk periods. The third group remained unshod for the study. At the beginning and end of each period, the horses’ front feet were radiographed to measure the sole thickness, as determined to be the distance between the sole and the distal tip of the third phalanx, and its change over time. The sole thickness of the horses shod with either shoe increased more than the sole thickness of the unshod horses (P = 0.003). Sole thickness increased when a SAPAS was applied after the flat shoe (P = 0.003), and sole thickness decreased when a flat shoe was applied after a SAPAS (P = 0.003).
The economic loss due to lameness in horses is estimated between $678 million and $1 billion annually (USDA-APHIS, 2001). Sole bruising is a common cause of lameness in horses. A thin sole provides insufficient protection to the foot and predisposes a horse to sole bruising (Stashak, 1987; Dabareiner et al., 2003). Lack of adequate sole thickness may be predisposed by genetics or caused by laminitis or injury. Because shoeing alone does not provide adequate protection to the sole, one of the goals addressed in shoeing laminitic and other thin-soled horses is to provide the best circumstances for the sole to achieve maximum thickness. Many types of shoes have been used to treat laminitis, but few attempts have been made to document observable effects of those shoes on sole thickness. One of the shoes of interest in this study is a self-adjusting palmar angle shoe (SAPAS). In an effort to treat laminitic horses using a SAPAS, it was observed by the authors that after the application of the SAPAS, soles appeared to grow more rapidly. Additionally, a loss of sole thickness was observed in the soles of horses that
Key words: palmar angle, sole thickness, self-adjusting palmar angle shoe, laminitis 1
To whom correspondence should be addressed: [email protected]
were shod with the SAPAS and then changed back to flat shoes. To more adequately investigate these observations, a study was designed to determine if application of the SAPAS does promote sole growth when compared to a flat shoe or to being unshod. The hypothesis was that sole growth would be greater in horses wearing SAPAS compared to horses wearing flat shoes or no shoes.
Materials and Methods In accordance with a protocol approved by the Middle Tennessee State University Institutional Animal Care and Use Committee, 18 horses were selected for study. They were randomly assigned to 1 of 3 groups. Both front feet of the horses in 2 groups were shod with either a SAPAS or flat shoe in a 2 × 2 factorial crossover design with 5-wk periods. The third group remained unshod during the study to determine the normal variation in sole thickness without the effect of shoes over a 5-wk period. All horses were shod by the same farrier and assistant. The flat shoes were applied in a standard fashion with nails. Proper application of the SAPAS required lateral radiographs of the front feet as
464
Haffner et al.
Figure 1. Measuring sole thickness. The surface of the sole was marked with barium contrast paste. A line perpendicular to the weight bearing surface was drawn to the tip of the third phalanx. The sole depth was recorded as the distance from the surface of the sole to the tip of the third phalanx.
previously described (Redden, 2003b). The SAPAS was shaped and the foot was trimmed to produce an anteriorto-posterior breakover point at the widest part of the hoof. The SAPAS was applied with the shoe being bent so that the shoe formed a slight curve from front to back like that of a rocker on a rocking chair (Figures 1, 2, and 3). The SAPAS was applied according to the depth of sole. If the sole was thick, the foot was shaped, and the SAPAS applied with nails. If the sole was thin, epoxy material
(Equilox, Equilox International, Farrier Supplies, Pine Island, MN) was used to increase the thickness to provide contact between the SAPAS and the foot. Application of horse shoes by means of adhesive is becoming more prevalent in routine farriery. The epoxy material has no apparent or reported effect on sole growth, so this treatment was not included in the statistical model. The horses were housed in stables with rubber mats bedded with wood shavings while being used for riding
Figure 2. Determining palmar angle. The palmar angle is the angle formed between the solar surface of the third phalanx and the weight bearing surface. In a flat shoe the horse is restricted to the palmar angle determined by the application of the shoe.
instruction 4 d per week and were pastured during the weekend. Five weeks after the first shoeing, the shoe was removed without trimming the sole, and radiographs were repeated for comparison. The horses were then reassigned to the alternate shoeing technique, and the process was repeated. The order of shoe placement, either SAPAS first and then flat or vice versa was recorded as “shoe order.” The unshod horses were radiographed twice, 5 wk apart. During this time they were on pasture. Sole thickness was determined by radiographic analysis at 0 and 5 wk for unshod horses, and at 0, 5, and 10 wk for horses with shoeing treatments. Shoes were removed, and both front feet of each horse were placed on 5-cm positioning blocks of wood for equal weight distribution. The blocks contained a wire embedded in the top of the block to delineate the supporting surface. The radiographic film cassette was placed 66 cm from the x-ray tube. A line perpendicular to the positioning block upon which the horses were standing was measured from the distal edge of the cranial tip of third phalanx (PIII) to the surface of the sole. Barium sulfate paste placed on the sole of the unshod foot in front of the frog allowed specific identification of the solar surface. The sole thickness was determined radiographically as the distance between the sole and the distal tip of the PIII. (Figure 1). This radiographic measurement was correlated closely to direct measurements made on dissected cadaver feet (Olivier-Carstens, 2004). The sole thickness was measured in batches with no identification of treatment protocol by an experienced equine clinician. Comparisons were then made to determine the change in sole thickness as a percentage of the original thickness. Normality was tested using the Shapiro-Wilk statistic. Hoof sole data were analyzed using a mixed model with repeated measures (SAS Inst., Inc., Cary, NC); sources of variation included shoe type, shoe order, horse (shoe order), and the residual error
CASE STUDY: A Shoe for the Promotion of Sole Growth in Horse Feet
Figure 3. Self-adjusting palmar angle shoe applied to foot. The self-adjusting palmar angle shoe allows the horse to rest the foot in the most comfortable position.
horse shoe type shoe order. Horse (shoe order) was used as the error term to test the effects of shoe order. Means were compared using the Tukey test. Sole thickness of the unshod horses was compared to flat- and SAPAS-shod horses during the first 5-wk period only using a mixed model with repeated measures. (SAS Inst., Inc.).
Results and Discussion Baseline hoof sole thickness was coincidentally less initially (d 0) in horses that were first fitted with the SAPAS compared to the flat shoe (P = 0.047); therefore, a covariate analysis was used so that only changes in hoof sole thickness over time were compared. During the first period, the sole thickness of the feet of the horses that were shod with a flat shoe increased 14.4% (1.7 mm) as compared to 24.3% (3.1mm) for the SAPAS group, and decreased 8.9% (−1.3 mm) for the unshod horses. Compared to the unshod horses, the change in sole thickness was greater in horses shod with the SAPAS (P < 0.0001) and the flat shoe (P = 0.003). There was no difference (P = 0.17) between horses
shod in the SAPAS or flat shoe during the first period. During the second period, the sole thickness of horses that were changed from a flat shoe to a SAPAS increased 17.6% (2.3 mm). The sole thickness of horses that were changed from a SAPAS to a flat shoe decreased 9.1% (−1.5 mm). Compared to horses that were changed from a SAPAS to a flat shoe, horses changed from a flat to SAPAS shoe had a significant increase in sole thickness (P = 0.004). The data indicated that when compared to being unshod, the application of either a flat shoe or a SAPAS allows for an increase in sole thickness. Although the increase produced by the SAPAS in the first 5 wk was greater than that of the flat shoe, the difference was not significant. It was also indicated by the data that changing from a flat shoe to a SAPAS had a significant positive influence on sole thickness. Conversely, changing from a SAPAS to a flat shoe had a significant negative effect on sole thickness. This study demonstrated that the perceived changes in sole thickness did occur. The change in sole thickness was a result of increase in sole thickness due to actual sole growth minus any de-
465
crease in sole thickness due to attrition from wear. This was reflected in the data by the unshod horses that lost sole thickness over a 5-wk period. This information is useful in that if a horse has a thin sole, sole thickness will increase by applying either a flat shoe or the SAPAS. Also, the increase in sole thickness of the horses that were initially flat-shod was enhanced by the SAPAS. This is clinically applicable because it showed that changing from a flat shoe to a SAPAS promoted an increase in sole thickness. It is also of interest that the sole thickness was decreased by changing from a SAPAS to a flat shoe. The palmar angle, measured on a lateral radiograph of the foot, is the angle produced by the intersection of the lines formed by the solar surface of the PIII and the surface upon which the foot is resting (Figure 2). If PIII is parallel to the ground, the palmar angle is zero. If the toe of PIII is lower than the wing of PIII, the palmar angle is positive. Finally, if the toe of PIII is higher than the wing, the palmar angle is negative. A slightly positive palmar angle is considered optimal (Redden, 2003a), but reported normal values range from 2 to 10 degrees, depending on type of horse and limb conformation (Parks, 2003). Flat shoes do not allow the horse to adjust its palmar angle (Figure 2). In comparison, because of its curved shape, the SAPAS allows the horse to place its foot so that it can find the most comfortable position and optimal palmar angle (Figure 3). One of the commonly accepted treatments for horses with lameness in the foot has been to change the point of initiation of movement from the weight-bearing to the flight phase of the stride. This aspect of the horse’s stride is termed "breakover." It is hypothesized that the advantage of the SAPAS over a flat shoe is in part due to the breakover point of the SA-
466
PAS being more caudal compared to the flat shoe. This reduces the stress on the tissues as the horse walks. It is also hypothesized that the curved shape of the SAPAS allows the horse to place the foot in a position that is most comfortable to the horse. This allowance of optimal foot placement by the horse may also aid and facilitate blood flow to the foot. These are areas that need investigation.
Haffner et al.
ing from a flat shoe to a SAPAS. This is clinically important in horses with thin soles that need an increased sole thickness to protect the internal structures of the foot. Since horses suffering from laminitis frequently suffer from lack of sole thickness as part of the disease process, this information may be useful for management of laminitic horses.
Implications This work demonstrated that by applying a flat shoe or a self-adjusting palmar angle shoe, the sole thickness of the foot of a horse increased compared to being unshod. Sole thickness increased by chang-
Literature Cited Dabareiner, R., W. Moyer, and G. K. Carter. 2003. Trauma to the sole and wall. In Diagnosis and Management of Lameness in the
Horse. W. Ross and S. Dyson, ed. p 275. Saunders, Philadelphia, PA. Parks, A. 2003. Form and function of the equine digit. Vet. Clin. N. Amer. Equine Pract. 19:285. Olivier-Carstens, A. 2004. Ultrasonography of the solar aspect of the distal phalanx in the horse. Vet. Radiol. Ultrasound 45:449. Redden, R. 2003a. Hoof capsule distortion: Understanding the mechanisms as a basis for rational management. Vet. Clin. N. Amer. Equine Pract. 19:443. Redden, R. 2003b. Radiographic imaging of the equine foot. Vet. Clin. N. Amer. Equine Pract. 19:379. Stashak, T. S. 1987. The relationship between conformation and lameness. In Adams’ Lameness in Horses. T. S. Stashak, ed. p 98. Lea & Febiger, Philadelphia, PA. USDA-APHIS. 2001. National economic cost of equine lameness, colic, and equine protozoal myeloencephalitis (EPM) in the United States. Info Sheet No. N348.1001. USDA Animal and Plant Health Inspection Service, Washington, DC.