FIELD OF THE INVENTION
This invention relates generally to methods for reducing
hip joint laxity in animals and more particularly, to dog food compositions and
feeding methods which reduce the incidence and severity of hip dysplasia and osteoarthritis
BACKGROUND OF THE INVENTION
Canine hip dysplasia (CHD) is a common problem in veterinary
medicine. CHD is a coxofemoral joint deformity which is not apparent at birth but
develops during puppyhood, frequently resulting in severe arthritic pain and immobility.
CHD occurs among many breeds of dogs, but has a higher incidence and severity among
larger dog breeds having an average adult body weight of 35 pounds or more. Generally,
the larger the size of a breed, the higher the incidence of CHD.
The principal clinical symptom of CHD is subluxation of
the hip joint, an indicator of hip joint laxity, which causes abnormal wear and
degeneration of hip joint tissue. Laxity of the hip joint begins a cycle in which
movement by the animal forces the femoral head into an abnormal position in the
joint. The abnormal positioning of the femoral head causes erosion of the joint
cartilage and inflammation of the synovial membrane surrounding the joint. The end
result of chronic joint laxity is an abnormally shallow acetabulum and a flattened
femoral head, resulting in joint pain, instability and immobility. A similar mechanism
is involved in the development of osteoarthritis. Research has shown that reduction
of hip joint laxity during early growth helps to prevent the development of CHD
and osteoarthritis in dogs.
Research also suggests a correlation between accelerated
bone growth during the first nine months of puppyhood, and the development of CHD.
The first nine months of life are considered to be a critical period for hip joint
development in the dog. During this period the acetabulum is growing at an accelerated
rate relative to the femoral head. The accelerated growth rate renders the acetabulum
more plastic and particularly susceptible to malformation under the influence of
hip joint laxity. It has been postulated that reduction of overall bone growth rate
during the first nine months of life can improve hip joint congruity by reducing
the disparate growth rate between the acetabulum and the femoral head.
Typically, diagnosis of CHD is accomplished by standard
radiographic methods, which are approximately 70% accurate overall, with increasing
accuracy of diagnosis the closer the animal is to 2 years of age. Radiographic diagnosis
relies on a finding of subluxation of the femoral head. The severity of CHD as deduced
from clinical presentation does not always correlate well with actual radiographic
measurements because of the confounding influence of individual and breed variations
in temperament and body structure.
CHD has a genetic basis, with heritability most frequently
estimated to be about 0.30. For example, a heritability of about 0.3 indicates that
about 30% of the variation in occurrence of CHD is attributed to parentage, while
the remaining 70% is attributable to environmental factors or interactions with
environmental factors. The exact nature of the environmental factors which affect
CHD incidence and severity is not known for certain, and clinically the disease
is highly variable among individual dogs. However, evidence supports the contention
that diet and feeding are significant factors affecting hip joint laxity and the
development of CHD, and suggests that manipulation of diet, especially during the
early stages of bone development, might be one way to treat CHD. Dietary methods
for treating CHD are especially attractive because typically they are easily practiced.
A known dog food composition and feeding method exists
for reducing hip joint instability in dogs. The composition has a specified dietary
anion gap (DAG) of no more than about 20 milliequivalents/100g of food. Dietary
anion gap is calculated as: Na (mEq/100g) + K (mEq/100g)- Cl (mEq/100g). The feeding
method relies on administration of the composition during the early years of growth,
and reduces subluxation of the femoral head. Another known feeding method, limit
feeding, improves hip joint stability and reduces the incidence and severity of
CHD by reducing the overall growth rate and bone maturation rate of pups. However,
the known dog food compositions and feeding methods provide incremental amelioration
of subluxation, and a need remains for dog food compositions and feeding methods
which further reduce hip joint laxity and the severity of CHD.
US 5,015,485 describes the provision of a dog biscuit having
a coating containing at least one pyrophosphate. Also described is a process for
preventing tartar accumulation on the teeth of dogs by the chewing and eating of
the described dog biscuits. US 5,000,973 describes nutritionally-balanced dog biscuits
containing at least one inorganic pyrophosphate salt, which are intended to reduce
or prevent tartar accumulation on teeth when eaten by dogs.
US 4,772,476 describes a method for reducing the severity
of hip dysplasia in animals, wherein animals are fed a nutritionally balanced composition
in which the dietary electrolyte balance in the composition is not greater than
about 20 milliequivalents/100g.
It would be desirable to provide a method of reducing the
incidence and severity of CHD and osteoarthritis by reducing hip joint laxity in
dogs. It would also be desirable to provide such a method which is dietary in nature
and easily practiced. It would be further desirable to provide a nutritionally balanced
dog food composition which substantially improves hip joint congruity and ameliorates
CHD and osteoarthritis. It would be still further desirable to provide such a dog
food composition which, when fed to puppies during the early years of growth, reduces
hip joint laxity and thus the severity of CHD in mature dogs.
SUMMARY OF THE INVENTION
These and other objects may be obtained with a nutritionally
balanced dog food composition containing a dietary source of pyrophosphate: The
dietary pyrophosphate source substitutes for other commonly used dietary phosphate
sources which lack effect on hip joint laxity. For example, and in one embodiment
of the dog food composition, about 2.0% sodium acid pyrophosphate, about 1.1% calcium
carbonate and about 0.65 % corn are together substituted for about 2.1 % dicalcium
phosphate and about 1.05 % sodium bicarbonate. In use, a puppy is fed the dog food
composition from weaning to about 2 years of age.
The dog food composition and feeding methods described
herein reduce subluxation of the femoral head, thus slowing the development of CHD
and osteoarthritis in dogs. Such methods are conveniently practiced by blending
a dietary pyrophosphate source into a nutritionally balanced dog food composition,
and then feeding the composition as substantially the sole diet to a puppy during
the early stages of growth.
The nutritionally balanced dog food composition for reducing
subluxation of the femoral head in the hip joint includes a source of dietary pyrophosphate
blended into an admixture of ingredients which provides a nutritionally balanced
food composition for dogs. The admixture may include a variety of suitable nutritious
ingredients. The term dog food composition as used herein refers to any nutritionally
balanced canned, dry or semi-moist dog food product such as those commonly commercially
available in retail pet and grocery stores. In use, the dog food composition is
fed to a puppy from weaning at about six weeks of age to about two years of age.
One embodiment of the dog food composition includes approximately
2.0% by weight of a dietary pyrophosphate source such as, for example, sodium acid
pyrophosphate. The dietary pyrophosphate replaces other typical sources of dietary
phosphate, such as dicalcium phosphate, which do not produce the same reduction
of subluxation and amelioration of CHD. One theory explaining the ameliorating effect
of dietary pyrophosphate on hip joint laxity is that by coating preformed bone crystal,
pyrophosphate retards bone mineralization and growth rate, thereby reducing disparate
growth between the femoral head and acetabulum.
In alternative embodiments, the amount of dietary pyrophosphate
or the type of pyrophosphate compound may be varied. Examples of suitable alternative
pyrophosphate compounds include calcium pyrophosphate and tetrasodium pyrophosphate.
In addition, sodium hexametaphosphate is thought to have the same effect as pyrophosphate
compounds on hip joint laxity, and is a suitable substitute for a pyrophosphate
compound. The amount of dietary pyrophosphate may range from about 0.1 % to about
2.0 % by weight. Although a precise dose-response relationship is not known, a practical
upper limit for the pyrophosphate content is determined by the need to balance calcium.
In particular, to avoid negative effects on bone mineralization, the percentage
of dietary phosphorus should not exceed the percentage of dietary calcium.
The dog food composition as described herein further generally
includes a nutritionally balanced mixture of proteinaceous and farinaceous ingredients,
based on the assumption that the composition provides substantially the sole food
intake for the dog. The dog food composition is not intended to be restricted to
a specific listing of ingredients since such a listing is largely dependent on the
desired nutritional balance of the dog food ration and also on the availability
of ingredients to the manufacturer. In addition to the proteinaceous and farinaceous
materials described above, the dog food composition generally may include vitamins,
minerals, and other additives such as preservatives, emulsifiers and humectants.
The nutritional balance, including for example the relative proportions of vitamins,
minerals, fat, protein and carbohydrate, is determined according to dietary standards
known in the nutrition art.
The proteinaceous material may include any material having
a protein content of at least about 15 % by weight including vegetable proteins
such as soybean, cotton seed, and peanut; animal proteins such as casein, albumin,
and meat tissue including fresh meat; and dried or rendered meals such as fish meal,
poultry meal, meat meal, bone meal and the like. Other types of suitable proteinaceous
materials include wheat gluten or corn gluten, and microbial proteins such as yeast.
The minimum protein content of the food is varied according to the age and breeding
status for the animal. For example, a nutritionally balanced food dog food composition
for breeding females and puppies requires a minimum protein content of at least
about 20% by weight on a 90% dry matter basis. A nutritionally balanced dog food
composition for non-breeding and adult dogs requires a minimum protein content of
about 12 % by weight on a 90% dry matter basis.
The farinaceous material may be defined as any material
having a protein content of less than about 15 % by weight and containing a substantial
proportion of starches or carbohydrates, including grains such as corn, milo, alfalfa,
wheat, soy hulls, and other grains having low protein content. In addition to the
proteinaceous and farinaceous materials, other materials such as dried whey and
other dairy by-products, and other carbohydrates, may be added.
In addition, it has been shown that control of dietary
anion gap improves hip joint stability in dogs. When dietary anion gap is defined
as the level of sodium ions plus potassium ions minus chloride ions in the food
composition, control of the balance at a level not greater than about 30 milliequivalents/100
grams of a dog food composition reduces hip joint laxity in dogs. To maximize the
ameliorating effects of the dog food composition on hip joint stability, the dog
food composition includes about 2.0% by weight of a dietary pyrophosphate source
plus a dietary anion gap not greater than about 30 milliequivalents/100 g food.
To make one embodiment of the dog food composition, the
proteinaceous and farinaceous materials and additional desired materials, as chosen
by availability and nutritional desirability, are combined to form an admixture,
and the dietary pyrophosphate source is added in a dry form, such as, for example,
granular, powdered or encapsulated form, and well blended throughout the admixture.
The admixture is then transferred to a steam conditioner and subjected to steam
and moisture to adjust the moisture content of the admixture to between about 20%
and 40% by weight. The conditioned admixture is then extruded under conditions of
elevated temperature and pressure to form a continuous strand of product. The product
is segmented into discrete particles or pieces by a rotating cutting knife as the
product is extruded. The particles or pieces are then conveyed to a forced air drying
system and the moisture level is reduced to below about 10% by weight while the
temperature of the particles or pieces is raised to about 140°F. The hot dried
particles or pieces are then transferred by bulk conveyor to a spray chamber and
dropped through the spray chamber. A plurality of spray heads located within the
spray chamber, on both sides of the falling particles or pieces, spray a solution
of animal fat onto the hot pieces or particles as they drop through the spray chamber.
The temperature of the pieces or particles within the forced
air drying system may be adjusted to facilitate further processing. For example,
a temperature of 140°F, as described above, facilitates coating of the pieces
or particles with animal fat, where the melting point of the animal fat is below
140°F. The spray coated pieces or particles are collected at the bottom of
the spray chamber and transported to a tumbling drum. The temperature of the tumbling
drum is maintained above the melting point of the animal fat and the particles or
pieces are tumbled until they have a substantially uniform surface coating of animal
fat. The coated particles or pieces are then removed from the drum and cooled to
ambient temperature. The resultant dry dog food composition has a moisture content
of less than about 12% by weight, and a protein content above about 15% by weight
on a 90% dry matter basis. In an alternate method, the dietary pyrophosphate source,
in powdered, granulated or encapsulated form, may be applied to the hot particles
or pieces after they have been coated with animal fat, for example by dusting onto
the particles or pieces.
In use, a puppy owner purchases the dog food composition
and feeds the composition to the puppy from weaning at about 6 to about 8 weeks
of age to about 2 years of age. The owner may also continue to feed the composition
beyond 2 years of age.
The study was done on Labrador Retrievers, a breed of dog
with known risk for canine hip dysplasia. At 6 - 8 weeks of age, forty-four pups
were blocked by litter, gender and body weight and randomly assigned to dietary
treatment with either a control diet (R1) containing dicalcium phosphate, or a treatment
diet (R2) in which sodium acid pyrophosphate and calcium carbonate were substituted
for the dicalcium phosphate. The formulae for R1 and R2 are given in Table 1. Pups
were individually fed ad libitum for 15 minutes, three times per day until 16 weeks
of age. After 16 weeks of age, pups were fed individually once per day. The test
was conducted over 104 weeks. Dietary anion gap was the same in both R1 and R2 diets
and maintained at 27.5 mEq/100g.
R1 (weight %)
Corn gluten meal
Dog vitamin premix
Sodium acid pyrophosphate
Evaluation of the extent of hip joint subluxation was based
on Norberg angle measurements taken from standard radiographs of properly positioned
animals. Radiographs were taken under general anaesthesia. Norberg angle measurements
were obtained using a protractor-like device to measure the closeness of fit between
the femoral head (ball) and the acetabulum (hip socket). To obtain the Norberg angle
from each radiograph, a line was drawn between the center of the femoral head of
each hip and another line was drawn between the center of each femoral head and
the cranial rim of the respective acetabulum. On each hip, the angle formed between
these lines is the Norberg angle. Animals were evaluated at 16, 30, 42, 52, 78,
and 104 weeks of age. Higher Norberg angles indicate superior hip joint fit, or
congruity. Evaluation of whole body bone mineral density were based on Dual Energy
X-ray Absorptiometry (DEXA) scan at 8, 17, 31, 43, 53, 79 and 105 weeks of age.
Table 2 gives mean Norberg angle measurements for animals
at 16, 30, 42, 52, 78 and 104 weeks of age.
Norberg Angles, ° R1
Norberg Angles, ° R2
At 30, 42, 52, and 78 weeks of age, a significant (p <
0.05) improvement was observed in the mean Norberg angles of dogs fed R2 with dietary
pyrophosphate, over the mean Norberg angles of dogs fed control ration R1.
Mean bone mineral density measurements from DEXA scans
are given in Table 3 and show a significant (p < 0.05) reduction in bone mineral
density, which accompanied the improved Norberg angles. Bone mineral density was
lower in R2-fed dogs than in R1-fed dogs at all ages tested except for 43 and 79
The data shown in Tables 2 and 3 demonstrate reduced hip
joint subluxation in the presence of slowed bone mineralization. The data cover
the period of 0 - 9 months of age, the critical period for hip joint development.
Avg. bone mineral density g/cm
Avg.bone mineral density g/cm
Significance (p value)
Dietary analysis of pyrophosphate levels indicated that
pyrophosphate was present in the R2 diet, and blood plasma pyrophosphate levels
showed that pyrophosphate was being absorbed by the animals from the R2 diet. The
results show that administration of dietary pyrophosphate during the first two years
of growth reduces subluxation in canine coxofemoral joints, and also reduces the
rate of bone mineralization, both of which contribute to the development of CHD.
Forty six Labrador Retriever and German Shepherd pups were
blocked by litter, gender and body weight and randomly assigned to dietary treatment
with either a control diet (R1) containing dicalcium phosphate, or a treatment diet
(R2) in which calcium pyrophosphate and calcium carbonate were substituted for dicalcium
phosphate. Both R1 and R2 were fed puppy-type diets formulated to contain approximately
12 % by weight fat and approximately 25% by weight protein. Laboratory analysis
of diets indicated that diets were made accurately.
Norberg angle measurements were taken at 5 and 10 weeks
of age. Bone mineral density was evaluated by DEXA scan also at 5 and 10 weeks of
age. No significant treatment effect was observed on Norberg angle measurements,
but DEXA analyses indicated a significant lowering of bone mineral content and bone
mineral density in R2-fed pups. The lack of treatment effects on hip joint measurements
was expected because dietary treatment effects on canine hip dysplasia are almost
never observed before 6 months of age. However, the results show that administration
of dietary pyrophosphate reduces the rate of bone mineralization in growing Labrador
Retriever and German Shepherd pups, an effect associated with long term amelioration
of hip dysplasia symptoms.
In alternative embodiments of the dog food composition,
a mixture of ingredients nutritionally balanced for cats or other animals afflicted
with hip joint laxity may be used to encourage the development of proper hip conformation
in those animals. In these alternative embodiments, the dietary pyrophosphate level
is maintained at about 0.1% to about 2.0% by weight. For each such composition,
the remaining ingredients and nutritional balance are determined by nutritional
standards known in the art. In additional alternative embodiments, a dietary pyrophosphate
source may be included in powdered, encapsulated form with other materials, such
as vitamins and minerals.
The dog food composition and feeding methods described
herein reduce subluxation of the coxofemoral joint in dogs, thus improving hip joint
stability and retarding the development of CHD and osteoarthritis in dogs. The feeding
methods are a simple, convenient and effective treatment for dogs known to be at
risk for the development of CHD and osteoarthritis.
From the preceding description of various embodiments of
the present invention, it is evident that the objects of the invention are attained.