Professor Internal Medicine-Companion Animals Department of Small Animal Clinical Sciences, Swedish University of Agricultural Sciences
Since the classical studies by Sir Edward Mellanby on vitamin D and Calcium, also other risk factors related to skeletal diseases in Dogs have been indicated by experimental as well as epidemiological studies. Preventive measures based on these studies are mainly advices on breeding and feeding. In a critical appraisal, risk factors (A) and generalised (B) as well as more specific (C) measures against skeletal diseases will be reviewed with reference to these studies.
A. Risk factors
1. Large size
Developmental and degenerative skeletal disorders are more common in large sized dogs (Bonnett et al. 1997, LaFond et al. 2002). When Sir Edward Mellanby between 1921 and 1944 published classical studies on the need for vitamin D, calcium and phosphorus for skeletal health in growing dogs, he also noticed that large sized dogs were more severely affected by Rickets and that those that ate less were less affected than those eating large amount of diets deficient in these nutrients (Mellanby 1944). Besides the need for specific nutrients it indicates how genetic factors for large size and rapid growth as well as feeding patterns promoting that, also influences incidence and severity of skeletal disorders.
Developmental Skeletal diseases like hip dysplasia and osteochondroses but also skeletal diseases like panosteitis and metaphyseal osteopathy do mainly affect large sized dogs. The greater risk in large sized dogs has been related to increased weight as well as increased height. For example the higher risk to get Osteosarcoma is closer related to height than to weight in both man and dogs (Ru et al. 1998).
Selecting a large sized dog either by breed or as an individual increases the risk of skeletal disease in general. Exception to this is congenital luxation of shoulders and elbows, craniomandibular osteopathy, Perthes Disease and medial patellar luxation mainly seen in smaller dogs.
Developmental skeletal diseases are diagnosed to a great extent during growth but resulting degenerative processes also accelerates with age (Egenvall et al. 2000, Wood et al. 2003).
Breed predispositions to skeletal disease have been indicated in several case series as well as epidemiological studies based on hospital populations and national populations of dogs. Giant breeds and breeds like Bernese Mountain Dog and Rottweiler have increased risk of various skeletal disease whereas others have significantly greater risk to specific diseases as i.e., Boxer to develop metaphyseal osteopathy (LaFond et al. 2002). Part of the breed predisposition can be related to conformity like unproportional giant size--acromegaly--in giant breeds and unsuitable angulations of knees and hocks as in Chow-Chows.
Male dogs do encounter skeletal diseases to greater extent and worse than females (Egenvall et al. 2000). Selecting a male dogs within a breed or litter increases the risk of skeletal disease in general but in some breeds prevalence of hip displace is documented to be higher in females than in males (Swenson et al. 1997a).
Neutered males as well as females are more prone to injuries to cruciate ligaments than intact males and females (Duval et al. 1999) and neutered dogs do develop osteosarcoma to greater extent than intact Dogs (Rue et al. 1998).
6. Rapid growth
Rate of growth is genetically determined to great extent with variations between as well as within breeds. To achieve large size at a rapid rate specific nutrients have to be furnished in large amounts. The most important factor though is the amount of energy furnished (Hedhammar et al. 1974).
7. Genetic influences
Although some causes of dwarfism have a simple recessive inheritance, and that it also has been indicated that osteochondrodysplasia and Perthes disease might be caused by a simple recessive inheritance, it is not common that skeletal disease are caused by variation in just one gene. Exceptions are skeletal manifestations of mucopolysaccharidoses (Campbell et al. 1997)and metaphyseal osteopathy in Irish Setters when caused by CLAD (Trowald-Wigh et al. 2000)
Most skeletal diseases have a polygenic inheritance, although major genes may exert stronger influences than other. Hip Dysplasia and Elbow Arthrosis resulting from Elbow Dysplasia regardless of its primary cause (osteochondrosis, FPRC, UPC) are example of entities that have shown heritability estimates between 0.2 and 0.6 (Swenson et al. 1997a,b).
Rickets defined as a deficiency in vitamin D and also deficiency of calcium is extremely rare conditions in small animal veterinary practice today. Nutritional Secondary Hyperparathyroidism can be seen in puppies fed all meat diets by its high phosphorus and low calcium content, but is rarely seen nowadays in affluent societies.
a. Overfeeding-to much food
Since we performed at Cornell University our studies on the effects of overnutrition on skeletal diseases in general in the early seventies (Hedhammar et al. 1974) several groups have used the same design to look at the effects of excessive amount of food during growth by allowing littermates ad lib feeding or just 75 % of that amount. Some of these studies have also been done on Great Danes and elucidated on the role of specific nutrients. Others have been on other breeds and in particular on the effects of overfeeding on the development of hip dysplasia (Kasström 1975,Kealy et al. 2000).
b. Oversupplementation--excessive amounts of specific nutrients
In our study at Cornell, by design, we used a diet with a high calcium content (2,1 %). During our study it became apparent that such a high calcium content add to the detrimental effects of overfeeding. It was postulated that excessive food--overfeeding as well as excessive amounts of calcium--oversupplementation with calcium is not compatible with optimal skeletal characteristics in large sized breeds. The Dutch research group in Utrecht have then proven that a too high calcium content in a diet have negative effects also when fed in more restricted amounts (Goedegebuure et al. 1986) and that negative effects are not caused by level of protein (Nap et al. 1991)
9. Exercise / Training
Very little is actually documented regarding effects of exercise and training methods applied unwisely on growing dogs with a vulnerable skeleton (Slater et al. 1992, Sallander et al. 2001). Heavy training programs, however, may result in changes, which predispose to development of osteoarthritis in dog as well as man (Arokoski et al. 1994). It is feasible to assume that physeal fractures and injuries to the cruciate ligaments, to some extent, can be related to training and exercise.
10. Exposure to Tick-borne infections
Among infectious agents involved in arthritis, Borrelioses and TBE (Tick-Borne Encephalitis) make tick exposure a risk factor to get arthritis. Hunting dogs and other working Dogs are more exposed to ticks and therefore at greater risk.
B. General preventive measures
Selection of breeding stock is of utmost importance to decrease prevalence of most orthopaedic conditions except truly traumatic ones. Individuals affected by any orthopaedic condition if not truly of traumatic origin but including those with unknown aetiology are not suitable for breeding. When it comes to conditions like hip dysplasia and elbow arthrosis with formal screening programs, also information on relatives--parents, siblings and progeny already produced, should be considered. (Hedhammar et al. 1979, Hedhammar et al. 1999)
Growing dogs should be fed complete and balanced diets. That is diets with neither to little or too much of any specific nutrients. In large sized dogs calcium level should neither be to high or to low and in balanced proportion to the level of phosphorus. Large sized dogs should be fed even complete and balanced diets in restricted amounts rather than ad-lib.
Nutraceuticals as glucosamine, chondroitin sulfate and polyunsaturated fatty acids have been evaluated for their chondro-protective and anti-inflammatory effects and were found to positively impact cartilage conditions. Further studies are needed to advice on their optimal usage as preventive measures.
3. Exercise /Training
Exercise and training of especially growing dogs should be performed with care.
C. Specific measures
1. Metaphyseal osteopathy (MOP)
Affected dogs should not be bred from. Usage of complete and balanced diets in restricted amount are the only preventive measures that can be instituted in this idiopathic condition and that is also of utmost importance during recovery. Cases of MOP caused by Canine Leucocyte Adhesion Deficiency (CLAD) can be prevented by screening Irish setters for the gene causing that condition (Kijas et al. 1999)
Affected dogs should not be bred from. Usage of complete and balanced diets in restricted amount is the only preventive measures that can be instituted in this condition and of utmost importance during recovery. As excessive calcium intake during an early phase of growth (3-6 weeks of age) have been related to panosteitis (Hazewinkel et al. 2000), it is essential to keep the calcium level at an optimal level already from that age.
3. Patella luxation
Affected dogs should not be bred from. Screening of breeding stock is advisable in many breeds.
Affected dogs should not be bred from. Usage of complete and balanced diets in restricted amount is essential in large sized breeds.
5. Retained cartilage
Affected dogs should not be bred from. Usage of complete and balanced diets in restricted amount is essential in large sized breeds.
6. Elbow Dysplasia / Elbow arthrosis
Dogs affected by any of the primary causes of elbow dysplasia and resulting elbow arthrosis should not be used for breeding. In several countries and many breeds, screening programs assist in selecting unaffected breeding stock. Based on that and information on verified clinical cases also family information can be made available and should be taken into account when selecting suitable breeding stock in breeds as i.e., Bernese Mountain Dog, German Shepherd, Golden Retriever, Labrador Retriever, Rottweiler and New Foundlands.
Usage of complete and balanced diets is essential in growing dogs of breeds prone to develop Elbow Dysplasia as well as a restricted food intake.
7. Hip Dysplasia
In most large sized breeds, screening for Hip Dysplasia, is an effective tool to identify unaffected breeding stock. In most breeds, affected individuals should not be used for breeding. By extensive screening in many breeds and several countries, results from relatives, including progeny already produced, can be included and thereby improve the selection of breeding stock.
Complete and balanced diets should be fed in restricted amounts to growing dogs of any breeds prone to develop Hip Dysplasia.
Affected dogs should not be bred from. Concern about further breeding from breeding stock that has produced affected progeny.
9. Cruciate ligament injuries
Affected dogs should not be bred from unless proven that the cause is truly traumatic
10. Fragmented sesamoid bone
In Greyhounds, Labradors, Rottweilers and other breeds predisposed to develop fragmentation of the sesamoid bones there should be a concern about breeding affected animals.
11. Degenerative Osteoarthritis
Individual dogs having developed osteoarthritis from developmental skeletal disease should not be used for breeding. To prevent further joint damage, weight reduction is advised and the further development might benefit from chondro-protective and anti-inflammatory nutraceuticals.
12. Arthropod arthritis
To prevent from exposure to Tick- borne infections usage of Tick- repellent products is recommended for use in exposed Dogs.
In giant dogs, maximal height by excessive food intake should not be promoted.
D. Future developments
Most of the risk factors discussed here were not known 50 years ago and it is plausible that over the years to come, several others will be added. To refine tools to select breeding stock with reference to skeletal health, gene tests might be available to identify major genes affecting structure and function of articular cartilage, bone tissue and ligaments. Applying such information to breeding programs, together with results from conventional screening programs and registries, call for open registries and computer assisted calculations of breeding values and risk predictions.
Chondro-protective and anti-inflammatory properties of nutraceuticals might be better understood and proven to prevent from degenerative processes in the skeleton during growth and aging.
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