UNCOMFORTABLE TRUTH
The fact that most canine joint problems were caused by humans is an uncomfortable truth. Sadly, our ancestors didn’t know that selecting dogs based on desirable traits like loyalty would eventually have a cost. In this case, the price was paid by dogs, who became the victims of a gradual accumulation of harmful genes. These include genes which code for hip dysplasia, elbow dysplasia, patellar luxation, and knee ligament injuries. The easiest way to deal with uncomfortable truths is to create an alternative (false) reality. A popular false reality is the myth that very restricted exercise during skeletal development lessens the impact of developmental joint diseases. Exercise advice in puppies has become confused by this myth. In this article, veterinary orthopaedic specialist Mike Farrell summarises the evidence linking joint damage with exercise in puppies.
WHY AREN’T I TALLER?
I'm only 5'8". How much taller would I be if my parents had restricted my exercise when I was still growing? If they'd been a bit more careful, would I be a 6'6" centre for the Chicago Bulls instead of a diminutive veterinary surgeon? You don't need a genetics degree to spot the false dichotomy: My height has nothing to do with childhood exercise and everything to do with my family's genetic tendency to be short. If it's so obvious people can't outrun their genetic destiny, why do so many people believe dogs can?
In the early 1970's, the National Institutes of Health (NIH) funded clinical research into canine hip dysplasia. In a groundbreaking study, the NIH’s veterinary team analysed the effects of restricting exercise on puppies [1]. They proved that crate-confined German shepherd dog puppies were less likely to develop hip dysplasia compared to unrestricted puppies. The NIH’s study was published in Veterinary Pathology in 1975, and the authors attributed the protective effect of restriction to the use of excessively small cages. Their unfortunate puppies grew taller than the cages, forcing them to stand with a wide-based stance. Anyone familiar with the Ortolani test can appreciate the advantages conferred by a wide-based stance. Specifically, it improves hip congruity by rotating the femoral head into the acetabulum. The NIH used their study to support the practice of fitting Pavlic harnesses to produce a hip-abducted posture in dysplastic children.
A. The relationship between splayed hips and improved femoral head capture is shown with a positive Ortolani test. B. The Pavlic harness
LONG DISTANCE RUNNING
The NIH study’s authors could never have guessed that their work would form the basis for an unhealthy veterinary myth. Sadly, their genuine conclusion that hip abduction limits dysplasia gradually evolved into the fallacy that exercise restriction prevents hip dysplasia. Fast-forward to 1988.... A team of Finnish researchers re-tested the NIH's hypothesis in dramatic fashion. In two studies, Beagle puppies ran for 5 days/week on a 15-degree incline treadmill. In the first study, they ran for 1 hour/day for 15 weeks [2]. In the second study, they ran up to 40km/day for a year [3]. How did their developing joints handle the strain of a daily marathon? Did their cartilage endure or did it crumble? When researchers microscopically analysed articular cartilage, synovium and synovial fluid, all three appeared grossly normal. The only difference between the test group and control group was focal superficial cartilage matrix change. This lack of degeneration shouldn’t surprise anyone. Human studies prove long-distance runners have a lower osteoarthritis risk than couch potatoes [4].
No caring veterinary surgeon would suggest puppies should be forced to run marathon distances. However, the awful experience endured by these experimental puppies should teach us valuable lessons. It's my task as a veterinary orthopaedic specialist and dog lover to pass their message to the public.
BORN TO RUN
If laboratory data doesn't suit someone's personal beliefs, they can choose to ignore it. However, ignoring 750,000 years of evolution might pose a sterner test. Extensive genetic analyses prove that all domestic dogs originate from wolves [5]. Wolf cubs are famous for their vigorous play and awe-inspiring endurance. In Winter, adult wolves usually bring the whole family on hunts. Some of the longest recorded wolf migrations involve cubs. For instance, one radio-collared pack including an 8 week old cub travelled up to 32km per day [6]. Despite myriad documented feats of wolf cub endurance, the vast veterinary database contains only a single case report of (non-clinical) hip dysplasia in an adult wolf [7]. If exercise was the trigger, wolves wouldn't have survived for 750,000 years and domestic dogs wouldn’t exist. This fact is both indisputable and difficult to ignore.
The guide dog paradox: (A) Wolf cubs cover marathon distances without increasing their risk of joint disease (B) ‘Ideal’ exercise doesn’t prevent one-third of guide dogs retiring because of musculoskeletal problems.
THE GUIDE DOG PARADOX
Evolutionary science isn't everyone's cup of tea. Sceptics can scoff while they highlight the obvious morphological differences between wolves and Chihuahuas. However, even a hardened sceptic would struggle to explain the guide dog paradox. While wolves teach us that running doesn't harm developing joints, guide dogs teach us that limiting exercise doesn't help. According to popular opinion, guide dog puppies receive "ideal" exercise. In theory, a puppyhood of low-impact leash walks should protect their "vulnerable" joints. Unfortunately, the theory isn't supported by reality. The commonest reason for guide dog health withdrawal is musculoskeletal disorders. In 2016, it accounted for 28% of retirements [8]. Historical guide dog hip dysplasia and elbow dysplasia prevalence is 20-30%. Cruciate ligament injuries are also common. Guide dog charities’ success reducing joint disease prevalence owes everything to careful breeding and nothing to limited exercise.
MENTAL IMAGERY
Advocates of strict exercise restriction in puppies might try a little mental imagery. Here's how it works. Picture a paediatrician diagnosing your child with hip dysplasia. You're referred to a physiotherapist who explains the problem. Your daughter's dysplastic hips have weak primary stabilisers. They tell you her hip joint capsule isn’t working properly, leaving her secondary stabilisers to pick up the slack. They explain that her overworked hip stabilisers form part of her core. Everything's making perfect sense…. until your daughter’s physio suggests a programme to weaken her core. Here it is:
1. Restrict exercise to 10 minutes of slow crawling three times daily.
2. Feed the recommended amount for a normal child even though your child isn't allowed to exercise. This is an excellent way to promote obesity.
3. Ensure your daughter doesn't socialise with other children. Socialising is bad for hip dysplasia.
A. Loose hips rely on a strong core to improve stability.
B. The classic false dichotomy: "This puppy has immature bone, therefore exercise causes inherited joint dysplasias."
A caring parent should have no problem sniffing out the glaring flaws in this severely restrictive programme. Even so, some veterinary professionals promote similar illogical and unsupported arguments. In the UK, dog owners are often subjected to the "5-minutes of exercise per month of age" fallacy. A well-informed veterinary professional who calls out the 5-minute myth should anticipate the following response: ”It's a guideline created to discourage irresponsible exercise." At first glance, this answer might seem moderate and sensible. At second glance, it’s anything but. This is a perfect example of what’s termed a slippery slope fallacy. How would it sound if we applied the same argument to diet? For example, imagine a friend suggested feeding your dog one carrot per month of age. When you counter that a 100% carrot diet is unbalanced, this is what they might say: “It's only a guideline to stop you feeding grapes and chocolate." It might be easier to accept this guideline fallacy if exercise restriction was safe, but it isn't. We have published evidence that restricted puppies have a higher incidence of hip dysplasia [9]. As an orthopaedic specialist and dog lover, my professional advice is simple. Focus on keeping puppies lean and fit. Being lean decreases risk of hip dysplasia five-fold, so limiting body fat must be our priority. If puppies want to run and play, let them run and play. If they want to rest, let them rest.
ABOUT THE AUTHOR
Mike Farrell graduated from the Royal Veterinary College in 1997 and completed internships at Bristol and Edinburgh Universities. He’s worked in the UK and Australia as a general practitioner and in the USA and Switzerland as a veterinary anaesthetist.
Mike completed a surgery residency at Glasgow University in 2006 and gained his European Diploma in Small Animal Surgery in 2007. He’s an EBVS and RCVS board certified specialist in small animal surgery.
REFERENCES
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Kiviranta et al (1988) Moderate running exercise augments glycosaminoglycans and thickness of articular cartilage in the knee joint of young beagle dogs. J Orthop Res 6: 188-195 LINK
Arokoski et al (1993) Long-distance running causes site-dependent decrease of cartilage glycosaminoglycan content in the knee joints of beagle dogs. Arthritis Rheum 36: 1451-1459 LINK
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Chase et al (2004) Bilaterally asymmetric effects of quantitative trait loci (QTLs): QTLs that affect laxity in the right versus left coxofemoral (hip) joints of the dog (Canis familiaris). Am J Med Genet A 124: 239-247 LINK
Savolainen et al (2002) Genetic evidence for an East Asian origin of domestic dogs. Science 298: 1610-1613 LINK
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National Geographic Kids - Article about wolves LINK
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Mech LD. Long-term research on wolves in the Superior National Forest. In: Recovery of Gray Wolves in the Great Lakes Region of the United States 2009 (pp. 15-34). Springer, New York, NY LINK
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Douglass (1981) Hip dysplasia in a timber wolf. Vet Med Small Anim Clin 76: 401-403 LINK
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Caron-Lormier et al (2016) Using the incidence and impact of health conditions in guide dogs to investigate healthy ageing in working dogs. The Veterinary Journal 207, 124-130 LINK
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James et al (2020) Effectiveness of canine hip dysplasia and elbow dysplasia improvement programs in six UK pedigree breeds. Front Vet Sci 6: 490 - DOI: 10.3389/fvets.2019.00490 LINK
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Krontveit et al (2012) Housing-and exercise-related risk factors associated with the development of hip dysplasia as determined by radiographic evaluation in a prospective cohort of Newfoundlands, Labrador Retrievers, Leonbergers, and Irish Wolfhounds in Norway. AJVR 73: 838-846 LINK