Introduction

Tail docking has been recorded since ancient Roman times, when it was believed the amputation of a portion of the tail would protect a dog from contracting rabies.¹ Prior to the 19th century, dogs were taxed according to tail length, and docking was performed to decrease the tax burden of the owner.² In addition, long-tailed dogs used for hunting, fighting, or watching over the herd were docked to prevent tail injury resulting from interactions with other animals.^1–3 Modern tail docking primarily for cosmetic purposes was formalized in the United States and Canada in the mid-1950s when the rules for pedigree dog shows were established.³ Currently, tail docking for working dogs is being revisited in the United Kingdom, where the practice has been banned since 2007.⁴ The main concern is to prevent injury to the tail, and although dogs with tails have a higher incidence of tail injury than docked dogs, it was shown that ∼500 tails would need to be docked in order to prevent one injury.⁴ Tail docking has not been shown to produce a demonstrable benefit for most dogs. In fact, there has been very little empirical study on the docking of canine neonates and its long-term consequences and implications; however, the practice remains commonplace for >60 breeds of dog in the United States and Canada, including rottweilers.^5,6

Tail docking is the amputation of the tail, most often performed within the first 3–5 days of life either by scalpel or alternatively by placing an elasticized band around the tail causing ischemic necrosis and sloughing of the tail.^7,8 Rottweilers have an aggressive tail-docking standard, leaving only one to two caudal vertebrae.⁹ This controversial procedure is not required for maintaining the health of the animal, is classified as a medically unnecessary surgery, and is considered a cosmetic operation.^10,11 The American Veterinary Medical Association and Canadian Veterinary Medical Association both have official position statements opposing tail docking for cosmetic purposes.¹¹ In contrast to the American and Canadian Veterinary Medical Associations’ position, this practice is described by the Canadian Kennel Club as not cosmetic, but necessary for the health and welfare of the breed.¹² The American Kennel Club describes tail docking as an animal husbandry practice that causes minimal-to-no pain.⁶ However, the latter statement is in direct opposition to scientific literature in noncanine species, which document acute and chronic pain in response to tail docking.^13–15 The American Kennel Club purports no lasting negative issues associated with tail docking, when in fact, docking the tail has been linked to surgical complications and chronic health and behavioral issues in dogs.^5,16 In addition, the long-term biomechanical consequences of tail docking are lacking scientific study.^5,16

Electromyographic and kinematic studies of tail movements in dogs have suggested that tail movements are important in maintaining body balance during locomotion and more complicated movements such as leaping, walking on narrow structures, and climbing.^1,17 Removing the tail eliminates an important counterbalance component and could lead to changes in the lumbar spine because the dorsal muscles of the tail are direct continuations of the epaxial musculature of the trunk with insertions on the caudal vertebrae.¹⁸ The lumbar spine protects, supports, and acts as a bendable rod from which the propelling force produced by the pelvic limbs is transferred to the rest of the body.¹⁸ Normal stress forces on the lumbar spine, in the absence of a tail, may overload the site of attachment of peripheral annular fibers to the vertebral endplate and make the lumbar spine more susceptible to degenerative changes such as spondylosis deformans.¹⁹ Because the tail muscles are an important component in stabilizing the vertebral column and supporting the extensor paraspinals, the effect of tail docking on the peripheral annular fibers is worth exploring. Limited spinal flexibility resulting from spondylosis deformans may inhibit normal daily activity.²⁰ Additionally, fusing two or more adjacent intervertebral disc spaces from spondylosis deformans may result in adjacent segment disease at the immediate adjacent mobile intervertebral disc space.^19,21 Given the paucity of research on the osteokinematic and biomechanical effects of tail docking, the primary objective of this cross-sectional comparative study was to compare the prevalence and severity of spondylosis deformans in a sample of rottweilers with and without tails.

Materials and Methods

Twenty-five client-owned tailed and 39 docked rottweilers ≥5 yr old from the United States, Canada, and Australia were enrolled in the study from January to December 2017. The age requirement was based on the rottweiler’s average life span of 9–10 yr and research reporting that spondylosis deformans is evident radiographically in mostly older dogs.^9,22 All docked participants had their tails removed at the level of CD1-2 or CD2-3, but the method of removal and age of subject at time of tail removal was not known. Subjects were recruited via outreach to veterinarians (n = 91), rottweiler clubs/rescues (n = 5), breeders (n = 20), and online forums (n = 5) with a potential reach of >30,000 rottweiler owners. All dog owners were informed about the study protocol and research topic, and each owner was required to sign a consent form allowing for participation in the study. The study protocol followed established guidelines for the ethical conduct in the care and use of animals.

A cross-sectional comparative study was used to compare tailed and docked rottweilers. Lateral and ventrodorsal radiographs of the lumbar spine were performed via digital radiography by local veterinarians and transmitted to the investigators electronically. Radiographs were scored according to presence and severity of spondylosis deformans on a 0–3 scale, where 0 = no spondylosis, 1 = mild spondylosis (spur does not protrude beyond the caudal/cranial edge of the vertebral border), 2 = moderate spondylosis (spur does protrude beyond the caudal/cranial edge of the vertebral border), and 3 = severe spondylosis (a bony bridge is formed).²⁰ Each dog was scored separately by two veterinarians (D.A. and M.T.), and in instances of disagreement, a third veterinarian (D.I.), blinded to the previous scores, provided a tie-breaking assessment. Owners provided information about their dogs’ medical histories via online survey including height, body weight, neuter status, and activity level. The clients were blinded to their dogs’ spondylosis deformans score prior to completing the survey.

Descriptive statistics were reported for all variables. Categorical variables were reported as number (percent) and compared between dogs with intact versus docked tails using Fisher exact tests. Continuous variables (body weight and height) were not normally distributed based on tests of skewness and kurtosis; these variables were reported as median (interquartile range) and compared between the groups using Wilcoxon rank-sum tests. All tests were two-sided, and P < .05 was considered statistically significant.

Results

Sixty-four rottweilers were enrolled in the study, including 39 (60.9%) with docked tails and 25 (39.1%) with intact tails. Survey responses pertaining to dogs’ baseline characteristics are presented in Table 1 according to tail docking status. Spondylosis was observed radiographically in 17 (68.0%) intact dogs and 30 (76.9%) docked-tail dogs. This difference was not statistically significant (P = .563). Among dogs with spondylosis, distribution of disease severity also did not significantly differ between intact and docked-tail groups (P = .102). Mild disease was observed in 4 (16.0%) intact and 12 (30.8%) docked dogs, moderate disease was observed in 8 (32.0%) intact and 5 (12.8%) docked dogs, and severe disease was observed in 5 (20.0%) intact and 13 (33.3%) docked dogs. Upon logistic regression, moderate or severe spondylosis was not associated with a docked tail (odds ratio 0.51, 95% confidence interval [CI] 0.16–1.60; P = .248) but was associated with age and sex. Female dogs had three times greater odds of moderate or severe spondylosis compared with male dogs (odds ratio 3.10, 95% CI 1.06–9.08; P = .039), and the odds of moderate to severe spondylosis increased by 1.4 times for each additional year of age (odds ratio 1.43, 95% CI 1.02–1.99; P = .036).

TABLE 1 Baseline Characteristics of 64 Rottweilers Obtained via Owner-Reported Online Survey

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Discussion

This project represented a unique opportunity to study the effects of aggressive tail docking and its relationship with spondylosis deformans in a single breed of dog. In this study, although the tail-docked dogs had a higher prevalence and severity of spondylosis deformans than tailed dogs, the differences were not statistically significant. CIs around the main outcomes indicated that tail docking status could be associated with spondylosis but were not identified in this study because of small sample size. These findings suggest that spondylosis deformans may have a complex pathogenesis and tail docking may not have an impact or its relevance to spondylosis may only play a minor role. The study did find that moderate to severe spondylosis was associated with advancing age, and although previous studies have found spondylosis deformans to be more prevalent in older dogs, we estimated the odds increase by 1.4 times for each year of life.²¹ Furthermore, we estimated that females have three times greater odds than males of developing moderate to severe spondylosis as they age, which has not been previously reported. This information may be clinically relevant as a differential diagnosis for the practitioner when assessing the senior female patient given that severe (grade 3) spondylosis deformans may cause stiffness of the back, lameness, and changes in gait.²⁰ Larger longitudinal studies could be useful to further characterize risk factors for clinical spondylosis, including any potential association with tail docking.

Sample size, the use of radiographs, and subjective scoring criteria are other potential limitations of the study. Although sample size was based on previous studies regarding spondylosis, it is possible that sample size was too small to statistically identify relevant differences between docked and tailed groups, or that differences in unmeasured factors obscured associations of interest.^21,23–25 Based on our results, it is possible that a modest association between spondylosis and tail docking exists but was not statistically identified. Larger studies would be required to rule out such an association. Although radiology is the most common diagnostic tool to determine if spondylosis deformans is present and to what degree, advanced imaging via MRI or computed tomography scans are more sensitive tools when looking for early grade 1 spondylosis.²³ Furthermore, radiographic scores were subjectively evaluated, which could introduce bias, although duplicate scoring was used in an effort to reduce individual biases. A validated scoring system could help standardize spondylosis evaluation, but such a tool does not exist to the authors’ knowledge.

Perhaps the greatest limitation associated with the study was whether this study population is sufficiently representative of all rottweilers. Given that dog owners often hold strong opinions regarding tail docking, their attitudes could influence their likelihood of participating in the study. As found in other studies, our dialogue with owners found that many either could not explain the reason for tail docking or thought the rottweilers were born with their short tails.¹¹ In addition, there is staunch resistance of some rottweiler owners to participate in a study, unrelated to issues of study protocol, with disdain for the study subject of tail docking. Those in support of tail docking align with the philosophy of the United Kingdom–based Council of Docked Breeds, the Canadian Kennel Club, and the American Kennel Club in that tail docking is a freedom of choice issue for the breeder and owner, not an animal welfare issue.^12,26 These organizations are adamantly opposed to any legal restrictions to tail docking, and some members are resistant to participate in a project that may possibly produce results showing tail docking in an unfavorable light. This increases the difficulty in finding study subjects, even with a potential for outreach to tens of thousands of owners, and introduces a potential bias in terms of which dogs and owners participate.

Conclusion

We looked at the relationship between tail docking and spondylosis deformans of the lumbar spine in rottweilers. Although not statistically significant, this population of tail-docked dogs had a higher prevalence and severity of spondylosis deformans than tailed dogs, lending support for further study of the role tail docking may play in the development of spondylosis deformans in docked rottweilers. The new identification of the increased risk of moderate to severe spondylosis for females merits continued research as to whether the association holds up in larger studies, and if so, why females are more severely affected, how to medically manage these patients, and how to mitigate the degenerative changes as they age. Various factors can influence the pathophysiology of spondylosis deformans in rottweilers, and investigating the long-term biomechanical and osteokinematic impact of tail docking in a larger population may help to more clearly determine the impact of this procedure.