The prevalence of the commonly occurring developmental joint diseases that affect the growing canine, including hip and elbow dysplasia and osteochondrosis dissecans, is thought to be affected by environmental factors as well as genetic ones. There has been a marked effort to reduce the incidence of these conditions through selection of parents that are thought to be less likely to breed affected offspring, through schemes such as the kennel club hip and elbow schemes. As these developmental conditions are most often polygenic traits with variable heritance demonstrated between different breeds (Leppanen et al, 2000), the incidence remains high in some breeds despite the introduction of these schemes.
Alongside this effort to reduce the number of affected individuals, there has also been a marked effort by the veterinary community to provide client education on the environmental factors that are also thought to be influential. These factors may include:
- Exercise provided to growing dogs (Sallander et al, 2006)
- Nutrition for the growing dog (Richardson and Zentek, 1998)
- The body condition score of growing dogs (Kasstrom, 1975)
- Age of neutering (Hart et al, 2014)
- The environment in which puppies are raised (van Hagen et al, 2005).
Each factor may be influential at different stages in a puppy's development, and will be discussed individually below.
Exercising the growing dog
Advice on how to exercise the growing dog should vary depending on breed size, as this affects the timeframe for longitudinal bone growth and growth plate closure. While load-bearing exercise is essential for normal musculoskeletal development as gradual mechanical loading is required for the stimulation of bone growth and metabolism, continuous over-loading through excessive exercise can be the cause of altered growth length and developmental abnormalities such as developmental joint disease. Evidence supports the avoidance of the following activities in skeletally immature animals:
- High impact, concussive activities, (examples include running at speed, jumping from a height, ball chasing — Figure 1)
- Lengthy, long duration activities (Figure 2)
- Activities that are very high in intensity (for example, sprinting — Figure 3).
Exercise that is high impact, long duration or high intensity can impact the soft tissues surrounding the joints, which offer support including muscles, ligaments and tendons. This type of exercise has the potential to damage the soft tissues, which cannot repair quickly enough and so do not develop with the skeletal structures as they should. This is particularly important in the case of hip dysplasia, where puppies are born with normal hips, but develop laxity as they grow (Riser, 1974). As well as genetic factors predisposing the hips to laxity, it may also be affected by other factors, including traumatic injury, hormonal imbalance, reduced muscle strength and environmental factors (Fries and Remedios, 1995).
Individual studies have been performed in an attempt to identify risk factors for the development of hip and elbow dysplasia in growing dogs. Exercise that involves chasing balls and sticks thrown for the dog by the owner has been shown to be a risk factor (Sallander et al, 2006), as has being born during the months where the weather is favourable, thought to be as a result of owners walking puppies for longer duration than those born when the weather is less favourable (Leppanen et al, 2000).
Some of the early studies performed on hip dysplasia indicated that restricting exercise during development could lead to an increased risk of developing the condition (Riser, 1974). Evidence also suggested that providing some off-leash outdoor exercise to growing dogs on soft ground reduces the incidence of hip dysplasia (Krontveit et al, 2012). Controlled exercise will support the development of muscle mass, which could be important in the prevention of hip laxity. Daily outdoor exercise for puppies is also important to support socialisation and mental stimulation, and so a balance must be reached to ensure that enough exercise of the right kind is provided, without overdoing it.
There have been no specific studies published on exactly how much exercise is the right amount to provide to growing dogs. In order to minimise the increased risks associated with the particular activities described above, it is good practice to provide owners with guidance on exercise to ensure that the joints of growing dogs are not subject to over-load while the growth plates are open. This period of time varies depending on the breed (or in more general terms, size) of the dog, with small breeds experiencing growth plate closure much earlier than large breeds. The advice that is given should therefore take into account the size of the dog, as this will determine for which time period the owner should consider their dog as in the developmental stages and pay close attention to the amount and type of exercise provided. Table 1 demonstrates the difference in timescale for growth plates to close in dogs of different sizes.
Table 1. Size of breed and approximate age of growth plate closure
| Dog size | Weight range | Time until fully grown |
|---|---|---|
| Toy | Less than 5 kg | 6–12 months |
| Small | 5–10 kg | 8–12 months |
| Medium | 10–25 kg | 8–18 months |
| Large | 25–40 kg | 11–18 months |
| Giant | >40 kg | 12–24 months |
From this information, advice can be given to owners based on the size of the dog they own as to how long they should avoid the activities that could put their dog at an increased risk of joint disease (those that are high impact, long duration and high intensity).
The kennel club recommends that a duration of 5 minutes per month of life should be used as a guideline when considering how much exercise to provide to growing dogs (Kennel Club, 2022). This guidance works well up to 6 months of age, which brings dogs of all breed types gradually up to 30 minutes of exercise. However, beyond 6 months of age for dogs that continue to have open growth plates (particularly large and giant breeds), care should be taken that the recommended 5 minutes per month is divided into several walks, as providing 1 hour of exercise at any one time to a 12-month-old giant breed dog that still has open growth plates is likely to be considered as overload.
As far as the author is aware, there is no evidence to date to support the theory that over-exercising skeletally immature dogs results in early or delayed growth plate closure or growth plate injuries.
Because of the impact on growing dogs' joints from highly concussive activities/sports such as agility, flyball and greyhound racing, there is a minimum age for participation in official activities of this nature. This minimum age is 18 months for the three activities mentioned, however it should be considered that if owners of giant breeds are considering entering their dogs into sports such as agility, flyball or Canicross, that 24 months would be a more suitable age for starting, to ensure that growth plate closure has taken place.
Nutrition and weight management
Nutritional deficiencies in growing dogs appear to carry far less significance than the over-provision of nutrients. Both over-feeding (leading to an excess of multiple nutrients and energy provided) and supplementation of nutrients such as calcium could increase the risk of developmental disease including hip dysplasia, elbow dysplasia and osteochondrosis dissecans.
Energy
Studies on the incidence of hip dysplasia have shown that puppies with heavier birth weights and higher growth rates are associated with a reduction in femoral head coverage by the acetabulum at 4 months of age, and an increase in degenerative changes. The latter is thought to be as a result of elevated contact stress because of an increase in focal, eccentric loading (Vanden Berg-Foels et al, 2006). Rapid growth rates have also been associated with an increased incidence of other skeletal disorders, including osteochondrosis (Richardson and Zentek, 1998). Rapid development through ad-lib feeding rather than calorific restriction has also been shown to be a risk factor for the development of hip dysplasia (Kasstrom, 1975). Restricted calorie feeding will slow growth rates, which reduces the likelihood of developing these conditions.
The over-provision of nutrients that leads to rapid growth rates and obesity in developing dogs is preventable. Regular weight checks and body condition scoring carried out by nurses in practice for puppies throughout their development could allow owners to adjust feeding regimens as soon as there is any indication that their puppy is being overfed. This could lead to a reduction in the risk of developmental joint disease for the animal in question.
Protein
Provision of adequate levels of dietary protein is essential for development. There is no evidence to support an increased risk of disturbed endochondral ossification (resulting in osteochondrosis dissecans) through the feeding of excessive amounts of dietary protein (Nap et al, 1991). The feeding of elevated protein levels was in this particular study associated with higher bodyweights, which as discussed above may in theory increase eccentric loading through the joints, which could increase the risk factor for alternative developmental joint diseases such as hip dysplasia.
Fat
Dogs fed a high fat diet, and those where a higher proportion of their overall energy comes from fat have been shown to have an increased incidence of elbow dysplasia (Sallander et al, 2006). As a high fat diet is likely to result in a higher than desirable body condition score, this is also likely to be a risk factor for other forms of developmental joint disease.
Calcium
Provision of excessive amounts of dietary calcium has been shown histologically to cause changes in both bone and cartilage tissue. Possible articular and physeal cartilage changes include irregularities of retained cartilage with disturbances in enchondral ossification, similar to osteochondrotic lesions (Goedegebuure and Hazewinkel, 1986).
Vitamin D
The supplementation of vitamin D to the diets of growing dogs does not appear to reduce the risk of skeletal disease as was once thought (Kealy et al, 1991), and so would appear unnecessary if the puppy is fed a balanced, complete food.
Nutraceuticals
While there is limited evidence to support the addition of nutraceuticals that claim to be chondroprotective and reduce the incidence/severity of joint disease (despite a wide range of available pet supplements making such claims), there are some studies that do have interesting results. One study in particular found that feeding a fish-based diet supplemented with several nutraceuticals thought to have a chondroprotective and/or anti-inflammatory effect resulted in a reduced incidence in the development of severe osteoarthritis at 12 months of age (the feeding of this diet did not reduce the prevalence of hip or elbow dysplasia) (Manfredi et al, 2018).
From the available evidence, it can be concluded that supplementing commercial foods (which are labelled as complete) with calcium or vitamin D is not required; and that the provision of an appropriate quantity of commercial puppy food together with the prevention of obesity will help reduce the risk of developmental joint disease.
Home-made versus commercial food
There is no evidence to suggest that there is any significant difference in the incidence of dogs presenting with developmental joint disease such as hip and elbow dysplasia between dogs fed commercial versus home-made diets (Sallander et al, 2006). It is more difficult to ensure that a home-made diet provides adequate (not excessive) calories, protein and fat, and the correct ratio of calcium and phosphorus in the growing dog, and so owners wishing to do so should be advised to carry out extensive research to ensure the diet provided is suitable for the needs of the dog.
Home environment
The advice on home environment may be useful to pass on to breeders as well as owners of growing dogs, as the available evidence suggests that puppies are most impacted during their first 3 months of life. Factors in the home environment that may predispose a puppy to joint disease later in life include:
- Being raised on a slippery floor surface prior to weaning (van Hagen et al, 2005)
- Having daily access to stairs earlier than 3 months of life (Krontveit et al, 2012).
Providing a non-slip surface for rearing and using stair gates to prevent access to stairs are small changes that could have a huge impact on the prevention of joint disease.
Age of neutering
Depending on size, dogs reach sexual maturity anywhere between 6 and 18 months, with neutering typically carried out within the period of 6–24 months of age. Neutering results in the removal of gonadal hormones, which are involved in the regulation of skeletal growth. Neutering prior to growth plate closure may cause a delay in growth plate closure, resulting in elongation of the long bones (Stubbs et al, 1995). This alters conformation and muscular anatomy. Neutering prior to growth plate closure has been shown to:
- Increased the incidence of soft tissue injuries of the muscles, ligaments and tendons (Lewis, 2019)
- Increase the risk of developing hip dysplasia (van Hagen et al, 2005)
- Increase the risk of developing elbow dysplasia (Hart et al, 2014)
- Increase the risk of cranial cruciate ligament rupture (Hart et al, 2014).
The effect of early neutering on male dogs appears to carry an even greater significance than females, with the incidence of joint disease in males shown to five times greater in dogs neutered before 6 months of age when compared with entire dogs (the incidence was shown to be four times greater in females) (Hart et al, 2014).
Delaying neutering until growth plate closure prevents the increased risk associated with early neutering. Knowledge of the timing of growth plate closure in the various breed types allows for the correct advice to be given to owners on the recommended age of neutering. One published study provides a table assisting clinicians on decision-making in regards to the recommended age of neutering of 35 specific breeds of dog based on joint disorders, cancers and urinary incontinence. This table could be kept in practice to refer to to ensure that the advice given to owners considers all of these factors (Hart et al, 2020).
Conclusion
As a result of the high prevalence of developmental joint disease among the canine population, the environmental factors that may influence the risk of developing these conditions such as nutritional intake, weight management and exercise regimens should be discussed with the owners of growing dogs in order to equip them with the knowledge required to minimise the impact of these controllable factors. Together with breeding animals that have low hip and elbow scores, this client education will hopefully allow for a reduction over time in the number of dogs affected by these conditions, which can often be debilitating, affect quality of life and result in a reduced lifespan.
KEY POINTS
- Developmental joint diseases that affect the dog are influenced by both genetic and environmental factors.
- Many of the environmental factors can be controlled to reduce the risk of the development of these conditions.
- The main environmental factors include: exercise, nutrition, body condition, age of neutering and home environment.
- Educating owners on each of these factors may help reduce the incidence of these conditions alongside selecting parents less likely to breed affected offspring.