Nutrition and Developmental Orthopedic Disease
Atlantic Coast Veterinary Conference 2002
Kathryn E. Michel, DVM, MS, Dipl ACVN
University of Pennsylvania, School of Veterinary Medicine
Philadelphia, PA, USA
18270928

There has been increasing evidence, particularly over the past decade, suggesting that overfeeding rapidly growing large and giant breed puppies can influence the expression of skeletal and joint abnormalities including osteochondrosis dissecans, cervical vertebral malformation and hip dysplasia. More and more breeders are recommending that their puppies be put on adult maintenance diets and even "lite" maintenance diets rather than growth formulas, ostensibly to avoid an overnutrition problem. Are these breeders attempting to do the right thing in restricting nutrient intake in their puppies?

To address this question, it is necessary to review the research that has been done looking at the effects of overfeeding puppies. It is important to understand that these are difficult studies to do because there are many variables to take into consideration. It is also necessary to stress that the issue is not whether diet causes these abnormalities. All of the breeds studied in these investigations have a strong genetic predisposition to develop various types of skeletal disease. The question here is: What kind of role can diet play in the expression of these genetic tendencies? Can diet influence the development and ultimate severity of certain skeletal diseases? And finally, this is a diverse group of diseases ranging from problems with cartilage development in osteochondrosis dissecans to joint laxity leading to the development of hip dysplasia.

The studies reviewed here all use approximately the same design. Littermates are matched for weight and sex and the one puppy is fed the experimental diet or overfed and the other is fed the control diet or has intake restricted. They are monitored for food intake, growth, biochemical parameters, and skeletal development. Approximately thirty years ago, Hedhammar and colleagues conducted a study, which involved the overfeeding of Great Dane puppies. In this original study, the overfed puppies received excessive amounts of several nutrients including calcium, phosphorus, vitamin D and protein because they were allowed to eat ad libitum while the control group was restricted to 33% less food (same diet) than the amount consumed by their pairs. Skeletal abnormalities did occur to a greater extent in the overfed group but it was impossible to say which, if any, of the excess nutrients were involved.

Since that study, a group of investigators in the Netherlands led by Hazewinkel have tried to look at this problem in a systematic fashion, again using Great Dane puppies. They have looked at the influence of calcium intake, calcium phosphorus ratio and protein intake. In one report all puppies were fed ad lib. The control group received a ration containing nutrient levels according to the 1974 NRC recommendations. The experimental group was fed the same ration supplemented with calcium carbonate so that it contained three times the NRC calcium recommendation. The experimental dogs ate less food and gained less weight than the control dogs. They ultimately consumed 2.5 times the calcium that the control dogs did. They were hypercalcemic and hypophosphatemic and developed several types of osteochondroses including retained cartilage cone in the distal ulna and cervical malformations. The control dogs also showed similar abnormalities but in significantly fewer numbers and with less severity. Therefore, excessive calcium in the diet seemed to exacerbate skeletal disease in these puppies.

Another member of Hazewinkel's group published an investigation in 1991 looking at protein consumption and skeletal disease in Dane puppies. They fed three groups of littermates high, normal, and low protein diets (32%, 23%, 14% of calories respectively) ad lib. They found no differences between the groups in calcium metabolism or skeletal development (there were the kinds of abnormalities seen in other studies in all groups). They concluded that protein did not play a causative role in the development of osteochondroses in dogs.

A 1992 JAVMA report by Kealy et al. focused on hip dysplasia. Here the investigators fed a diet that was similar to commercial premium growth formulas to 48 Labrador retriever puppies from 8 to 102 weeks of age. Pairs were housed together but fed separately. One pup ate ad lib and the other got 75% of its pair's intake. They were carefully evaluated for hip dysplasia using several different scoring methods. At two years of age, using OFA scoring, the ad lib group showed 16/24 dysplastic, 0/24 borderline, and 8/24 nondysplastic vs. the restricted group with 7/24 dysplastic, 1/24 borderline, and 16/24 nondysplastic. The restricted pups grew normally but weighed 25% less than the ad lib pups. The investigators concluded that restricted feeding was able to influence the expression of hip dysplasia.

These same investigators have published 3 and 5-year follow-ups of this study. Of the original 48 dogs, 46 were still in the study at 5 years of age and 43 at 8 years of age. At 5 years of age, 12/23 of the ad lib fed dogs versus only 3/23 of the limit fed dogs had radiographic signs of hip osteoarthritis. At 8 years of age, now 15/22 of the ad lib fed dogs versus only 3/21 of the limit fed dogs had radiographic signs of hip osteoarthritis.

An epidemiologic study appeared in the AJVR in 1992, which looked at diet and exercise as potential risk factors for OCD in dogs. The study involved 31 dogs with diagnosed OCD and 60 age, breed, and sex matched controls. Data was collected in telephone interviews. Increased risk of OCD was associated with high dietary calcium (median intake in affected dogs of 3.6 mg/1000 kcal vs. 3.1 in controls), playing with other dogs, and drinking well water (vs. municipal water). Feeding of specialty dry dog foods was associated with decreased risk. It is important to remember when looking at epidemiologic studies that unrecognized confounding factors may be at work and an association is not equivalent to a cause and effect.

One marketing strategy that the pet food industry has been using for many years is the specific purpose food concept. The specific purpose concept is based on scientific evidence that animals have different nutritional requirements for growth, maintenance, reproduction, physical exertion, and possibly old age. Most investigations of the nutritional requirements of dogs have focused on growth and reproduction since naturally those are the stages of the life cycle when nutrient requirements are the most stringent. According to the new AAFCO nutrient profiles (which have replaced the NRC as the standards for pet food formulation) the minimum recommendations for growth and reproduction exceed the minimum recommendations for adult maintenance for all ten essential amino acids, total protein and fat content and for calcium, phosphorus, sodium, and chloride. The increased requirements range from 20% more for protein and the essential amino acids, to 500% more for sodium and chloride. So clearly there is some scientific justification for formulating specific growth or reproduction rations that are distinct from a maintenance ration.

Table 1 (ed. note: not available) compares the nutrient content of one pet food manufacturer's large breed growth, growth, adult maintenance, and "lite" formulas. Examination of these different diets shows that, in this case at least, a switch from a growth formula (in particular from the large breed growth formula) to an adult formulation will not necessarily prevent "overnutrition" and could result in deficiencies for certain nutrients of concern. Some of the large breed puppy formulas that are available to date have been feeding trial tested in breeds such as Labrador Retrievers, Rottweilers, and Great Danes. They met the standard AAFCO feeding trial criteria for normal growth. In addition, some pet food companies have performed DEXA studies to verify that normal bone mineralization occurred despite the relatively low calcium content of these diets. The data is still preliminary; however, these diets appear to provide the consumer with a tested alternative to feeding adult foods to growing puppies. The lesson is that one cannot assume that simply because a product is labeled as a growth formula that it contains greater quantities of nutrients like calcium than a maintenance product. Furthermore, it is necessary to compare the nutrient content of one diet to another and to do so on an energy basis (rather than a dry matter or "as fed" basis) because the fat and moisture content of dog foods can vary considerably. And finally, we have to ask ourselves whether the differences we see in nutrient content from one food to another are actually clinically significant? In some case they will be, but more often the differences will be of a very small magnitude.

So while it is important to avoid overfeeding it is still necessary to feed a diet that is formulated to meet the nutritional requirements of growth. The key in avoiding "overnutrition" is to feed according to body condition. Growing large and giant breed puppies should have enough energy intake to grow but not enough to lay down extra fat. In other words they should be lean and a bit on the "ribby" side. It is absolutely necessary to insure that the pet owner understands how to evaluate their puppy's body condition and to adjust feeding portions accordingly since they and not their veterinarian will be making those day-to-day decisions how much to feed.

To summarize, large and giant breed dogs have been selected for early rapid growth and weight gain. Growth rate is dependent on dietary intake. So, if the skeletal diseases that these breeds are prone to are associated with rapid growth, modulating that growth by restricted feeding and avoidance of supplementation may decrease the severity of these problems. This has been demonstrated specifically with calcium and in general with over consumption of a balanced ration. The bottom line: do not supplement a balanced ration and keep them lean!

Speaker Information:
Kathryn E. Michel, DVM, MS, Dipl ACVN
University of Pennsylvania, School of Veterinary Medicine
Philadelphia, PA, USA

Reproduced with the permission of the author. Thanks to Angie Johnson, DVM, Kodiak Veterinary Clinic (Kodiak Alaska) for aid in acquiring this article.