Introduction

The Huntaway and the Heading dog (NZ Collie) are the most common working dog breeds in New Zealand. The Border Collie breed was introduced to NZ by early Scottish shepherds to work sheep however the extensive sheep farming conditions favoured a more short-haired dog with greater stamina that could be heard by the shepherd. The NZ Huntaway originated in the early 1900's from a mixture of breeds and is a large, intelligent, dog renown for its deep bark and ability to drive and herd sheep and cattle. The Heading dog is a direct descendant of the Border Collie used for herding sheep.

In this lecture I would like to present the results of a survey of the most common types of orthopaedic injuries in working dogs seen by rural (first-opinion) veterinarians in the North Island of New Zealand.

There were two distinct working dog environments encountered:

1.  The more intensive dairy farming situation where working dog injuries were primarily traumatic in origin and often involved accidents relating to machinery.

2.  The extensive sheep and beef farms where injuries tended to traumatic or overuse injuries. Less machinery injures were observed in this group and injuries were usually related to working with stock or to the demanding terrain.

Fractures

Hind limb fractures were more common than forelimb fractures.

The most common fracture observed was the tibial fracture. Femoral and metatarsal fractures were also observed frequently. Fractures were usually caused by vehicle or machinery accidents or following kicks from stock.

Joint Injuries

Hind limb joint injuries were more common.

The most common joint injury reported was rupture of the cranial cruciate ligament; multiple ligamentous injuries of the stifle were also commonly seen in working dogs from sheep and beef stations. Hip luxation was the next most common joint injury and often caused by falls from moving vehicles. Hock and carpal injuries were frequently observed and chronic carpal osteoarthritis was a commonly reported reason for retirement from work.

Musculo-tendinous Injuries

These were the least common injuries observed in working dogs; injury to the common calcanean tendon (Achilles tendon) was the most frequently reported.

Working dogs are an important part of New Zealand's pastoral-based economy and are highly valued on-farm. Never-the-less, the cost of invasive surgical repair is typically weighed against the owner's perception of their dog's intrinsic and replacement value. This decision is often problematic as the cost of therapy could be put towards replacing the dog. The level of training, breeding potential and the owner's personal attachment to the dog all influence the decision as to whether or not to treat. In these circumstances it is vital that the consulting veterinarian has objective data on which to base a prognosis.

Unfortunately, the veterinary literature contains little specific information relating to the long-term outcome of specific orthopaedic injuries in working dogs. However, two studies have recently been published from the Massey University Teaching Hospital, Palmerston North, New Zealand, on the long-term outcome following common calcanean tendon repairs and pancarpal arthrodesis in working dogs. These studies used owner assessment as the means of evaluation because the authors deemed that the athletic performance of a working dog could not be adequately assessed by a follow-up orthopaedic examination alone. The aim of these retrospective studies was to assess the results of surgery from the owner's perspective in order to better prognosticate for future working dogs. The owner's assessment of their dog's ability to return to work was seen as the most important outcome measure.

Ability to Work and Owner Satisfaction Following Surgical Repair of Common Calcanean Tendon Injuries in Working Dogs in New Zealand (Worth et al 2004).

In this study, the results of 10 Huntaway or Heading dogs with complete or partial tears of the common calcanean tendon and treated by locking-loop suturing and casting, with (7) or without (3) calcaneo-tibial screw fixation, were reported. The ability to work and owner satisfaction were investigated using a telephone questionnaire at a mean follow-up interval of 14.6 months.

Seven out of the 10 dogs returned to full or substantial levels of work but only five of these dogs where considered by their owners to be completely sound (3) or only had mild or intermittent lameness (2). Two dogs had moderate lameness but still returned to full or substantial levels of work. Interestingly, nearly all dogs had slight hyper-flexion of their hocks at follow-up. Post-operative complications occurred in two dogs that did not return to full or substantial levels of work and these were primarily relating to casting of the limb. There was a poor outcome in all dogs supported by external casting alone, without additional calcaneo-tibial screw fixation.

In total, six owners were satisfied or very satisfied and seven owners felt the financial investment in opting for surgical repair was worthwhile. Only five of the owners whose dogs had returned to full or substantial levels of work were satisfied with the treatment and this correlated with their assessment of their dogs limb function.

The authors concluded that surgical treatment of injuries to the common calcanean tendon in working dogs has a good prognosis provided post-operative complications are avoided. Rigid immobilization of the hock for six weeks by a combined screw and casting technique appeared to have better results than casting alone. Lameness may persist in some dogs despite an acceptable ability to work, as judged by owner assessment.

Long-term Assessment of Pancarpal Arthrodesis Performed on New Zealand Working Dogs (Worth and Bruce, 2007).

This study assessed the long-term outcome of unilateral pancarpal arthrodesis (PCA) in eight Heading dogs, five Huntaways and two gun-dogs (a Springer Spaniel and a Golden Retriever) with carpal pathology requiring arthrodesis. Pancarpal arthrodesis surgery was performed by dorsal plate application, bone grafting and casting. All dogs were actively in work on sheep or cattle farms at the time of injury, and return to work was the desired outcome. Ability to work and owner satisfaction were investigated by a telephone questionnaire at a mean follow-up interval of 5 years.

Eight out of fifteen dogs (53%) could perform normal duties and a further four dogs (27%) could perform most duties (albeit with some allowances for lowered athleticism) at long-term follow up. Overall, 80% of the dogs treated by PCA returned to full or substantial levels of work. Five dogs were completely free of post-operative lameness or gait abnormalities (33%); five dogs were only mildly lame with a slight gait abnormality (33%).

Thirteen of 15 owners said the surgery had met their expectations, 11 felt the investment was worthwhile and 12 owners were satisfied or very satisfied with the resultant mobility and work performance of their dogs. There was a trend towards poorer performance and return to work in dogs from hill country properties.

Post-operative complications occurred in 60% of dogs. Major complications were encountered in 33% of cases. These included plate breakage (1) and implant loosening / infection (5). Most complications were resolved and did not affect the eventual outcome.

The authors concluded that unilateral PCA carries a reasonably good prognosis for return to work in NZ working dogs. Good surgical technique and appropriate post-operative immobilisation is required to achieve successful arthrodesis. Care must be taken to limit post-operative complications.

References

1.  Worth AJ, Danielsson F, Bray JP, et al (2004) Ability to work and owner satisfaction following surgical repair of common calcanean tendon injuries in working dogs in New Zealand. New Zealand Veterinary Journal 52(3), 109-16.

2.  Worth AJ, Bruce WJ. (2007) Long-term assessment of pancarpal arthrodesis performed on New Zealand working dogs. New Zealand Veterinary Journal (in press)