Abstract
Vertical fissures (sandcracks) affect approximately 20% of adult beef cattle in western Canada. The risk factors associated with the formation of these lesions are not well understood. This paper describes a case-control study that identifies the role of increased claw size (claw volume >390 cm3, odds ratio 7.8) in the formation of the lesion. No connection was found between vertical fissures and horn hydration status. However, horn hydration was found to vary significantly between samples collected in the summer and winter, the latter samples having significantly reduced moisture content. The importance of these findings and the implications for the prevention of fissure formation are discussed.
Abstract
Résumé — Caractéristiques de l’onglon bovin associées à la présence de seimes (fissures longitudinales). Les seimes (fissures longitudinales) affectent environ 20 % des bovins de boucherie adultes de l’Ouest du Canada. Les facteurs de risque associés à la formation de ces lésions ne sont pas bien compris. Cet article décrit une étude de cas témoins identifiant le rôle de l’onglon de dimension accrue (volume de l’onglon > 390 cm3, PR 7.8) dans la formation de la lésion. Aucune relation n’a été trouvée entre les fissures longitudinales et l’état d’hydratation de la corne. Cependant, l’hydratation de la corne variait significativement entre les échantillons prélevés en été et ceux prélevés en hiver, ces derniers contenaient significativement moins d’humidité. L’importance de ces trouvailles et leurs implications dans la prévention de la formation des fissures est discutée.
(Traduit par Docteur André Blouin)
Introduction
Vertical fissures or sandcracks are longitudinal fissures of the dorsal horn wall of the hooves of ungulates (1) (Figure 1), which have been recognized since at least the 18th century (2). Vertical fissures may originate at any level of the dorsal horn wall and extend distad for a variable distance (3). They typically affect the more superficial aspect of the horn. Only rarely does the fissure extend completely through the dorsal horn wall to the underlying sensitive tissue, resulting in infection and lameness (1).
Figure 1.
A. Typical sandcrack extending entire length of dorsal wall of lateral fore claw. B. Cross section of a typical sandcrack showing hypertrophy of the dorsal wall and failure of fissures to reach sensitive laminae.
A number of cross-sectional surveys on the prevalence of vertical fissures in western Canada have consistently found that the prevalence in beef cows is approximately 20% (4–7). These surveys have also revealed that fissures are most commonly found in the lateral claw of the fore feet, with 60% to 80% of all fissures occurring in these claws (7). In contrast, the prevalence of this condition in dairy cows is very low (8,9).
There is a paucity of information on the risk factors associated with the development of vertical fissures. Westra (4) found that no animals less than 1 y old had vertical fissures, but that the prevalence increased up to 5 y of age (59%) and then decreased thereafter. Petrie et al (7) also found that cows with vertical fissures were significantly older than unaffected animals. In addition, Goonewardene and Hand (6) found that not only did the prevalence of fissures increase with age, but that the prevalence also increased with increasing weight and body condition score.
The pathogenesis of vertical fissures is not known with certainty, but increased “brittleness” of the dorsal wall horn due to dehydration, exacerbated by shear forces (10), hoof size (3), and the mechanical stresses associated with horizontal growth arrest lines (3) have been proposed as being important in their development.
The aim of this study was to use a case-control design to test 3 separate hypotheses: The presence of horizontal grooves is associated with the formation of vertical fissures; the presence of vertical fissures is associated with a difference in claw conformation; and, the hoof horn of cows with vertical fissures is more dehydrated than that of control cows. Furthermore, this dehydration occurs because of the extreme winter climate in western Canada.
Materials and methods
At a local abattoir, all 4 feet were collected from 20 mature beef cows with no vertical fissures present on any claw (group 1) and 20 mature beef cows with a vertical fissure on at least 1 claw (group 2). Mature beef cows were identified as such, based on abattoir records and visual inspection. Any animals being slaughtered during August 1999 were available for inclusion in the study. The animals were selected in a haphazard manner in which 5 sequential animals were followed along the slaughter line for ease of collection of hooves and determining carcass weights from abattoir records. The cows were primarily Hereford, Simmental, Charolais, and crosses of these breeds.
The anatomical location of the claw was identified as the feet came off the slaughter line by placing a staple in the toe of the lateral claw of each of the 2 fore feet and in the heel of the lateral claw of each of the 2 hind feet. Each set of 4 feet was then placed in a uniquely identified plastic bag. The feet were brought back to the Western College of Veterinary Medicine and stored in sealed plastic bags at 4°C until processing. Processing occurred within 72 h of collection.
Vertical fissures and horizontal grooves
Each claw was examined for the presence of a vertical fissure (Figure 1), which is defined as a fissure aligned in a vertical orientation found in the dorsal wall of the hoof. The fissure may originate at any level of the dorsal wall and extend distad for a variable distance (3). Any fissures present were classified according to Greenough et al (3). A type 1 is a vertical fissure that starts at the coronary band and extends distad only a short distance down the dorsal hoof wall; type 2 is a vertical fissure that starts at the coronary band and extends distad past the midpoint of the dorsal hoof wall; type 3 is a vertical fissure that starts at the coronary band and extends the entire length of the dorsal hoof wall; type 4 is a vertical fissure that starts at a variable point on the hoof wall away from the coronary band and extends down the dorsal hoof wall to the toe; and type 5 is a vertical fissure that does not extend to either the coronary band or the toe.
The claw walls were also examined for the presence of horizontal grooves (growth arrest lines). A horizontal groove was defined as any visibly obvious groove parallel to the coronary band (3). The distance of the groove, or grooves, from the coronary band was also recorded. Throughout the study, the claws were examined by 2 investigators who reached a consensus regarding the presence of a lesion. In a separate study, 80 claws from cows without vertical fissures were assessed independently by the same 2 investigators for the presence of horizontal grooves, and their scores were compared for agreement.
Determination of claw volume, sole surface area, and toe length
The hair around the coronary band was removed by clipping and the hoof was carefully removed from the digit at the hoof horn-skin junction with a band saw. The volume of each claw was determined by placing each claw in an Archimedes’ chamber and measuring the overflow of water into a 500-mL measuring cylinder to the nearest 5 mL during a 5 min period. The sole surface area of each claw was determined by pressing the claw onto a sheet of paper covered with a film of polyethylene placed over an inkpad (Trodat, Wels, Germany) for 2 s with a force of 13.64 kg (30 lbs). Three imprints were made of each claw. The resulting images were digitized by using a black and white charge coupled device (CCD) camera (Hammamatsu Corporation, Bridgewater, New Jersey, USA) and the mean weight bearing surface area was calculated by using imaging software (Northern Eclipse Imaging Software; Empix Imaging, Mississauga, Ontario). To standardize between inkpad and investigator variation, a plastinated cow hoof was used as a control. Before imprinting the claws of each cow, an imprint of the plastinated hoof was made, as described above, and the sole surface area was calculated. All subsequent results were standardized to this value.
The length of the toe was measured following longitudinal sectioning of the claw 1.5 cm from the axial wall.
Hoof horn hydration
A section of dorsal hoof wall, approximately 1 cm wide was obtained by making a 2nd longitudinal cut 1 cm from the 1st cut through the abaxial portion of the hoof. A 3 cm long section of uniform thickness was removed from the dorsal wall (Figure 2). The soft tissue was removed from the internal surface of the horn sample and the sample was blotted dry. Samples were weighed (Mettler PC2200; Mettler Instrumente AG, Zurich, Switzerland) and oven dried at 60°C for 5 d. After reweighing, the samples were dried in the oven for a further 24 h. If the 2 weights differed by less than 0.03 g, the mean value was recorded. If the specimen lost more than 0.03 g over the extra 24-hour drying period, oven drying continued for further 24-hour periods until a steady weight was found. The percentage moisture content was then calculated. To determine if climate had a significant effect on the moisture content of the hoof horn, the front feet of 20 additional mature beef cows were collected in February 2000 from the same source. Hydration samples were prepared as above and compared with the main study samples.
Figure 2.
Diagram to show how the individual claws were sectioned to allow the cross section of the digit to be examined and to facilitate production of a sample for hydration analysis.
Cross sectional analysis
The cut surface of the abaxial segment of the claw prepared above was photographed with a scale marker placed on the segment. The contour of the dorsal wall was examined independently for the presence of horizontal grooves by the same 2 investigators who scored the intact hoof and their results were compared with the horizontal groove scores described above.
Data analysis
Data were collected and entered into a spreadsheet program (Corel Quatro Pro, version 8.0; Corel Corporation, Ottawa, Ontario), which was used to perform all necessary transformations. Analysis was performed at 2 separate levels. Initially, the cow was regarded as the experimental unit; in this case, a simple mean was taken of claw level factors (average claw volume). The 2 groups of cows were then compared directly.
To address the possibility that vertical fissures may change the baseline physical characteristics of the claw, the data set was analyzed to find fissured claws that could be paired with a nonfissured claw from the corresponding claw position on the contralateral limb of the same cow (the right fore lateral claw was compared with the left fore lateral claw). Horn hydration was assessed by finding pairs of claws in which a fissured claw was compared with a nonfissured claw on the same limb of the same cow. If a significant difference was found, the variable for the fissured claw was replaced with an aggregate value derived from the nonfissured claws from the same cow.
Simple bivariate analysis of cow level data
After ensuring that either the data or the differences, as appropriate, were normally distributed by using the Shapiro-Wilk test, continuous variables were compared by using either the paired t-test for related variables or the independent t-test for unrelated variables. If the data were not normally distributed, or if the variance assumptions of the t-test were not met, the Mann-Whitney test was used. Discrete categorical variables were compared by using Fisher’s exact test (EPI-Info, version 6.04a; WHO, Geneva, Switzerland). Clinical agreement between investigators was evaluated by using the kappa statistic for 2 × 2 tables (12). Unless otherwise stated, all analyses were performed by using a standard commercial software program (SPSS 9.0 for Windows; SPSS, Chicago, Illinois, USA).
Multilevel analysis examining claw level data
Analysis of the individual claw data was complicated because significant clustering was present, potentially affecting the relationship of claws within legs and legs within individual cows, with each cow in the study having 4 legs and 2 claws for each leg. The data were explored initially in a simple bivariate manner by comparing fissured and nonfissured claws (data not shown). A multilevel mixed model with a logit link function was then used to evaluate each risk factor hypothesis at the claw level. This model allowed for correction for clustering, while determining the importance of clustering both within the leg and cow with the use of random intercepts for each level. The analysis was initially performed in a bivariate manner and the model built manually by using a forward manual stepwise procedure (14). Factors examined included the presence of horizontal grooves, horn hydration, and various measures of hoof conformation, as described previously. Statistical analyses were performed by using commercial software (MlwiN, version 1.10; Multilevel Models Project, University of London, United Kingdom).
Results
Vertical fissures
Fifty-one vertical fissures were observed in the hooves of the 20 cows in group 2 (cows with at least 1 vertical fissure), and 80% of these cows had more than 1 fissure (Figure 3). The average (mean) number of vertical fissures per cow was 2.5. The distribution of vertical fissures by hoof position is presented in Figure 4. The majority of all vertical fissures (32/51 [63%]) were found in the lateral fore claws. The next most common site was the medial hind claw (12/51 [24%]). Variation existed in the type of vertical fissures observed (Figure 5). Types 3 and 4 fissures (full length fissures and fissures affecting the distal half of the hoof wall, respectively) were the most commonly observed lesions (16/51 [31%] each).
Figure 3.
Graph to demonstrate the number of claws affected by vertical fissures per cow for the 20 cows in group 2 (beef cows with at least 1 vertical fissure).
Figure 4.
Distribution of vertical fissures (n = 51) by claw position for the 20 cows in group 2, (beef cows with at least 1 vertical fissure).
Figure 5.
Distribution of 51 vertical fissures by type: Type 1 vertical fissure — coronary band and proximal hoof wall only; type 2 vertical fissure — extending from the coronary band to the middle of the dorsal wall; type 3 vertical fissure — full length fissure from the coronary band to the weight bearing surface; type 4 vertical fissure — middle of the dorsal wall to the weight bearing surface; and type 5 vertical fissure — involving only the middle third of the dorsal wall.
Horizontal grooves
One hundred and fifty-one horizontal grooves were found affecting the 40 cows in the study (Figure 6). Ninety-five percent of cows had at least 1 horizontal groove. There was no apparent pattern to the distribution of grooves by claw position (Figure 7), although the lesions were slightly more common in the lateral fore claw.
Figure 6.
Graph to demonstrate the number of horizontal grooves (n = 151) identified on the feet of each cow for the 40 cows in the study.
Figure 7.
Graph to demonstrate the distribution of the 151 horizontal grooves by claw position.
Effect of season on horn hydration
The horn collected from the fore feet of beef cows without vertical fissures collected during the summer was significantly more hydrated than that of horn collected from the fore feet of cows without vertical fissures collected at the end of the winter (23.5% and 20.8%, respectively). Data were not normally distributed and were analyzed by using the Mann-Whitney statistic (P = 0.001).
Analysis performed using the cow as the experimental unit
The initial analysis was performed using the cow as the experimental unit. The descriptive statistics for the continuous variables of interest and the results of a simple bivariate analysis are presented in Table 1. No significant difference was demonstrated between the 2 groups with respect to average claw volume, average horn hydration, average sole surface area, and cow carcass weight. How ever, cows with at least 1 vertical fissure were demonstrated to have a significantly longer average dorsal wall length.
Table 1.
Independent t-test used to assess mean claw volume, hoof horn hydration, sole surface area, carcass weight, and dorsal wall length of 2 groups of beef cows
| Mean (s) (n) | |||||
|---|---|---|---|---|---|
| Cow group | Claw volume (cm3)a | Hoof hydration status (%)a | Sole surface area (cm2)a | Carcass weight (kg)a | Length of the dorsal wall (mm)a |
| Group 1. Beef cows with no vertical fissures | 357 (52) (20) | 22.81 (1.44) (15) | 16.42 (2.38) (20) | 341 (48) (20) | 98.7 (6.8) (17) |
| Group 2. Beef cows with vertical fissures | 380 (52) (20) | 21.56 (2.42) (18) | 16.52 (2.18) (20) | 345 (61) (20) | 105.5 (7.4) (17) |
| t-test | −1.39 | 1.74 | −0.14 | −0.19 | −2.78 |
| P-value | 0.172 | 0.09 | 0.89 | 0.87 | 0.009 |
s — standard deviation
aAll data were shown to be normally distributed
A cow was categorized as suffering from horizontal grooves if 1 or more hooves showed evidence of a lesion, based upon the consensus from scoring the intact hoof; the association of this factor with the presence of vertical fissures was also analyzed (Table 2). The odds ratio was 10.2 (95% CI, 1.1–484.7), indicating that the odds of having a vertical fissure were 10.2 times greater in a cow with a horizontal groove than in a cow without a horizontal groove. However, when a separate group of 80 claws were assessed independently for the presence of horizontal grooves by 2 observers, the level of agreement measured by the kappa statistic (0.11) was extremely poor (Table 3). The level of agreement between the direct observations and the photographs of the claws from this study was also extremely poor (kappa −0.003) (Table 4) (12).
Table 2.
Relationship between the presence of horizontal grooves and vertical fissures at the cow level (n = 20)
| Vertical fissure status of the cow | |||
|---|---|---|---|
| Absent | Present | ||
| Horizontal groove | Absent | 7 | 13 |
| Status of cow | Present | 1 | 19 |
Odds ratio 10.2 (95% CI: 1.0, −484.7, P = 0.04)
Table 3.
Agreement between observers regarding the case definition of a horizontal groove
| Observer 1: Horizontal groove status of the claw | ||||
|---|---|---|---|---|
| Present | Absent | Total | ||
| Observer 2: | Present | 10 | 10 | 20 |
| Horizontal groove status of the claw | Absent | 22 | 38 | 60 |
| Total | 32 | 48 | 80 | |
Kappa = 0.11 (Standard Error 0.107)
Two observers independently assessed 80 claws for the presence of horizontal grooves. Their results were compared. Observer 1 identified horizontal grooves in 32 of 80 claws examined, while observer 2 identified horizontal grooves in 20 of 80 claws examined
Table 4.
Comparison of 2 different methods of assessing the presence of horizontal grooves in cattle claws by a single observer
| Observer 1: Direct examination of the claw Horizontal groove status of the claw | ||||
|---|---|---|---|---|
| Present | Absent | Total | ||
| Observer 1: | Present | 81 | 17 | 98 |
| Examination of cross section of claw | Absent | 127 | 26 | 153 |
| Horizontal groove status of claw | Total | 208 | 43 | 251 |
Kappa = −0.003 (Standard Error 0.041)
An observer assessed 251 claws for the presence of horizontal grooves. The claws were then sectioned and photographed. The same observer then assessed the photographs for the presence of horizontal grooves and the results compared. Through direct examination of the claw observer 1 identified horizontal grooves in 208 of 251 claws examined. In contrast, horizontal grooves were identified in only 98 of 251 cross sectional photos examined of the same claws
Analysis performed with the claw as the experimental unit
Before starting this section of the analysis, it was important to address the fact that changes in claw parameters could have occurred prior to, or after, fissure formation. Examination of the data set found 15 pairs of claws with a fissure on 1 claw and no fissure on the contralateral claw. These pairs were used to assess the effect of fissures on claw volume, surface area of the sole, and length of the dorsal wall (not all data were available for dorsal wall calculations). Thirty-three pairs were identified for assessing the effect of fissures on horn hydration status.
No significant difference was found in the claw volume, sole surface area, and dorsal wall length between fissured and nonfissured claws (Table 5). However, the hydration of the horn from the fissured claws was significantly greater. To deal with this effect in the remainder of the analyses, the measured hoof horn hydration value was replaced with an aggregate value based on all the nonfissured claws from the same cow, because it was considered that the changes were due to the presence of organic matter that had accumulated after fissure formation.
Table 5.
Comparison of claw volume, sole surface area, dorsal wall length, and hoof horn hydration between fissured and non-fissured claws from the same claw position on the same cow
| Variable | Mean fissured claws (s) | Mean non-fissured claws (s) | t-value | P-value |
|---|---|---|---|---|
| Claw volume (cm3) (n = 15) | 371.3 (78.8) | 373.3 (99.2) | −0/13 | 0.90 |
| Sole surface area (cm2) (n = 15) | 15.1 (2.5) | 16.1 (2.1) | −1.82 | 0.08 |
| Length of dorsal wall (cm) (n = 10) | 108.3 (8.2) | 105.2 (10.2) | 1.89 | 0.09 |
| Hoof horn hydration (%) (n = 33) | 23.7 (4.0) | 21.3 (2.8) | 4.02 | 0.0003 |
Note: The n-value for the comparative tests is not constant, this is due to the fact that in a number of cases measurement of claw size either by volume, length of the toe or sole surface area could not be measured due to the abnormal shape of the claw (corkscrew claw abnormality, etc.)
s — standard deviation
During the initial bivariate analysis, it was noted that all variables, with the exception of claw volume, showed a simple linear relationship. However, claw volume did not have a linear association with the presence of vertical fissures; instead, a binary model was suggested (Figure 8, Table 6). The odds of claws having a vertical fissure were 7.8 times greater for claws with a volume of greater than 390 cm3 than for claws with a smaller volume.
Figure 8.
Graph to demonstrate the effect of claw volume on the odds ratio of the claw being affected with a vertical fissures.
Table 6.
Breakdown of claw position, horizontal grooves, claw size (greater than 390 cm3) and vertical ) fissure status for the 320 claws
| Vertical fissure status | ||
|---|---|---|
| Absent | Present | |
| Claw position | ||
| Fore-lateral | 48 | 32 |
| Fore-medial | 74 | 6 |
| Hind-lateral | 77 | 3 |
| Hind-medial | 70 | 10 |
| Horizontal groove status | ||
| Absent | 148 | 21 |
| Present | 121 | 30 |
| Claw size (volume) | ||
| Small (< 390 cm3) | 190 | 12 |
| Large (>390 cm3) | 79 | 39 |
The results of the mixed-effects multilevel analysis are presented in Table 7. Only claw position and claw size were significantly associated with the presence of vertical fissures. However, these factors are not independent, as claw size is highly dependent on claw position (Figure 9). No other measures of claw conformation were important in this model (data not shown).
Table 7.
Association between claw position, horizontal grooves, claw size (greater than 390 cm3) and vertical fissures status for the 320 claws based on multilevel analysis accounting for clustering within leg and cow
| Vertical fissure status | ||
|---|---|---|
| OR (95% CI) | P-value | |
| Claw position | ||
| Fore-lateral | 7.0 (3.6, 13.9) | 0.004 |
| Fore-medial | 1.0 (0.5, 2.2) | 0.99 |
| Hind-lateral | reference category | |
| Hind-medial | 7.0 (3.3, 15.1) | 0.01 |
| Horizontal groove status | ||
| Absent | reference category | |
| Present | 1.5 (1.0, 2.3) | 0.34 |
| Claw size (volume) | ||
| Small (<390 cm3) | reference category | |
| Large (>390 cm3) | 8.0 (4.5, 14.1) | <0.001 |
| Horn hydration | ||
| (% hydration) (n = 263) | 0.9 (0.8, 1.0) | 0.51 |
There was no additional variance accounted for in the model by including a random intercept for leg after including a random intercept for cow. The variance accounted for by correcting for clustering at the cow level was significant (P = 0.02)
Figure 9.
Relationship between claw position and claw volume for 40 mature beef cows.
Discussion
The design of this study as a case-control study has 2 important implications: first, because of the design, we cannot comment regarding the absolute prevalence or incidence of vertical fissures within the beef cattle population of western Canada. Second, since all measurements were taken only once on the feet of dead cows, it is difficult to comment on the causality of the observed relationships. To overcome this problem, contralateral affected and nonaffected claws from within the same cow were compared to determine if the investigated factors were likely to have been present prior to the formation of a fissure. The results indicated that the hydration of samples of fissured horn was significantly greater than that of samples of nonfissured horn. In nearly all cases, the fissures were impacted with a large amount of organic debris. It was our opinion that the measured increase in moisture content of the hoof was likely due to the presence of moisture within the organic debris impacted into the fissure. Consequently, the measured hydration status of fissured horn was replaced with an aggregate value based on the nonfissured claws from the same cow. No difference was found in the various measures of claw size. Therefore, in the remainder of the analysis, it was assumed that the formation of a vertical fissure did not affect any measure of claw size. However, it should be noted that in nearly all the cows in the study (15/20), both lateral fore claws were affected by vertical fissures and the majority of the pairs used in this analysis represent other claw positions.
The number of vertical fissures observed per cow (mean 2.5) is much higher than in other reports in the literature. Petrie et al (7) found 1.48 vertical fissures per cow in a study of more than 3000 beef cows from the same population as ours. The reason for the increased number of lesions is not clear, but the small sample may not be completely representative (15). It is possible that as this study is the first done of vertical fissures in slaughterhouse specimens, it represents underreporting bias in field studies. It is easier to see vertical fissures in isolated specimens than in the standing cow. It is also possible that vertical fissures increase the probability of culling and that a higher prevalence would be expected in samples collected from cull cows.
The uneven distribution of fissures, with the majority being present in the lateral front claws, confirmed previous studies. In the present study, the 63% of all vertical fissures being found in the lateral fore claws is lower than the approximately 85% observed by Westra (4) and Petrie et al (7). A possible explanation for the lower value in this study was the finding of a relatively large number of fissures in the medial hind claw (10/51 = 20%), which may be the hardest to examine in the standing animal, so that these lesions may have been underreported by previous researchers. The importance of classifying vertical fissures by type is not known. It is likely that these classifications represent the chronological development and resolution of a lesion, but their relationship to one another has not yet been demonstrated. For this reason, the different types of vertical fissures were considered as a single lesion in the remainder of the study.
Horizontal grooves were relatively common, affecting 80% of cows in the study. They affected all claws equally. However, if horizontal grooves are due to diet change or a systemic stress placed upon the cow (3), one might expect them to affect either all or none of the claws within an animal. In this study, the number of claws affected by horizontal grooves was highly variable. Any study of horizontal grooves is complicated by the absence of a good case definition. Our studies show that there is a high level of variation among experienced investigators in scoring the presence of horizontal grooves either directly or in cross-section. This will have led to a severe misclassification bias. As the bias is likely to be nondifferential, it would have the effect of reducing the observed association between horizontal grooves and vertical fissures (15). Finally, the association between cows with horizontal grooves and cows with vertical fissures is significant (odds ratio 10.2, P = 0.04). However, this analysis was performed using the cow as the experimental unit. There is no evidence to suggest that the vertical fissures and the horizontal grooves are actually present on the same claw, only that cows with the one lesion are predisposed to the other. This is similar to what is termed “ecological fallacy” (17). The argument regarding the strength of the association may be of limited importance, as theoretical fracture mechanics states that when a material has a surface defect, it will fracture along the plane of the defect in a manner described by Griffith (16). It is, therefore, unlikely that a horizontal defect would result in a vertically orientated fissure.
In a study such as this, the analysis is complicated, because the variables of interest are present at 2 different levels: the cow level (group, age, carcass weight, etc.) and the claw level (claw volume, horn hydration, presence of a vertical fissure). To deal with this problem, the analyses were initially performed at the cow level and then repeated considering both claw and cow level factors. When the cow level variables were compared between the 2 groups (beef cows with and beef cows without vertical fissures), the only significant difference found was in the average length of the dorsal wall; the dorsal wall length was greater in cows with vertical fissures. No difference was found in the mean weight of the 2 groups; this contrasts with the findings of Goonwardene and Hand (6), who demonstrated an approximately 50 kg mean difference in live weight of cows with and without vertical fissures. The difference in mean carcass weight between the groups in this study was only 4 kg. The reason for this discrepancy is not clear, although possible explanations include that the group of cows used in this study was small and that carcass weight was used as opposed to live weight. Another possible explanation is that we found cow carcass weight and claw volume to be highly correlated; therefore, it is possible that in previous studies cow weight was an important predictor of vertical fissures only because it was actually indicating increased claw volume.
On multilevel analysis, 2 main factors were found to be significantly related to the presence of vertical fissures: Claw position was the most significant, which confirmed previous studies (4,7,6). The distribution of vertical fissures by claw position in beef cows contrasted strongly with the distribution of claw lesions typically seen in dairy cows, in which the lateral hind claw is most commonly affected and the lateral fore claw the least commonly affected (9). The reason for these contrasting effects is not known, but researchers in both beef and dairy tend to implicate weight bearing as a major factor in their formation (3,18). Inherently, these 2 contradictory arguments cannot both be correct. Claw volume was also demonstrated to be related to claw position. However, even when the effect of claw position was controlled for, the effect of claw volume remained highly significant. Interestingly, this appeared to be a threshold effect, with the odds of claws bigger than 390 cm3 developing a vertical fissure being 8.0 times greater than the odds of the smaller claws developing a fissure. The way in which the increase in claw volume may influence the formation of vertical fissures is not known. It is possible that larger claws are subjected to a greater mechanical stress on the dorsal wall during walking, which results in fissure formation. As hoof horn grows at a relatively constant rate (3), a larger claw indicates the presence of older horn. This horn may have a lower hydration level or, as a result of its age, may have developed more microcracks (16), which may grow to form the vertical fissure.
We initially hypothesized that small claws may be at risk of developing fissures, because more weight of the cow would be carried on a small claw. We could find no evidence to support this theory. In this study, the assumption was made that weight bearing is evenly distributed among the 8 claws of the cow. Scott (19) demonstrated that in the dairy cow, approximately 55% of body weight is borne by the forelimbs. The situation in beef cattle is unknown, but it is likely to be similar (in the horse 60% to 65% of body weight is also carried on the forelimbs [20]). In order to investigate this effect further, it would be necessary to complete a detailed analysis of normal weight bearing in beef cattle.
Based on the analysis of the data, we now believe that large claw size is associated with the presence of vertical fissures. Interestingly, vertical fissures in horses have long been associated with overgrowth of the toe (21), although in this case, the fissures form at the distal extremity of the toe and extend proximad.
An interesting application of this observed association is the possibility that if the cow’s feet are regularly trimmed to keep the length of the dorsal wall and the volume of the claw to a minimum, the prevalence of vertical fissures would be reduced. Such a hypothesis could be tested in a relatively simple randomized controlled clinical trial.
The study of horn hydration was complicated by the requirement that samples be cleaned before being stored and that the volume be measured by immersion in water; however, in a simple preliminary study, it was found that 20 min immersion in water did not significantly affect the hydration status of horn samples (data not shown).
When hoof horn samples were collected in the winter, they had significantly reduced water content. Although the reduction in absolute water content is small (3%), when it is regarded as relative hydration (RH) (100% relative hydration = 37.5% weight [data not shown]), this amounts to a 7% difference. The effect of hydration status on the mechanical properties of hard keratin has been demonstrated by a number of researchers. In particular, Bertram and Gosline (22) showed that the fracture toughness of equine hoof horn increased 4-fold between 53% RH and 75% RH. Based on their data, a change in RH of 7% would be equivalent to doubling the fracture toughness. Consequently, dehydration of the hoof horn in the dry Saskatchewan winter may contribute to fracture formation. This hypothesis obviously requires further investigation.
A limitation of this study was the fact that the age of the animals could not be determined, as there were no age records available at the abattoir and hardly any animals had ear tags indicating their age. Previous studies have consistently shown that age is an important factor in fissure formation (4,6,7). Furthermore, when a multivariate approach was used (23), it was apparent that weight was not significantly associated with the presence of vertical fissures when the effect of age was controlled for. The potential for bias, therefore, exists between the 2 groups in the study; with the cows in group 2 being older than the cows in group 1.
This study’s objectives were to determine if there were any physical properties of the bovine hoof that could be associated with the presence of vertical fissures. Three separate hypotheses were formulated regarding the role of horizontal grooves, decreased hoof horn hydration, and decreased claw size.
The results have also indicated that increased claw size (both volume and length of the dorsal wall) is associated with the formation of vertical fissures. This new theory has some interesting applications regarding the role of routine foot trimming in reducing the prevalence of vertical fissures. The results also indicate that hoof horn hydration does vary over the year, although this finding could not be related to the formation of vertical fissures.
Acknowledgments
The authors acknowledge the help and assistance received from all the employees of Western Canadian Beef Packers, Moose Jaw, Saskatchewan, who provided the majority of specimens for this study. We thank Glenna Miller for her assistance in processing specimens and Ian Shirley for his assistance with the image analysis. Dr. Hugh Townsend and Dr. John Campbell also provided significant advice and assistance during the design and analysis of this project. CVJ
Footnotes
Reprints will not be available from the authors.
Autumn Wendell was supported by a University of Saskatchewan, Short Term Employment Program.
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