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Musculoskeletal Development of the Puppy: Birth to Twelve Months

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Dogs are one of the most morphologically diverse species as they can range from a 1kg Chihuahua to a 100kg English Mastiff. With gestation ranging from 58 to 68 days all puppies begin life at a similar size, with no teeth and their eyes closed. There is little difference between gestation timescales, however growth and size post-partum varies greatly, depending on the breed (Table 1). Although there is such a variation in size, nutritional and exercise advice for the first twelve months of life scarcely differs. This can have an impact on the growth of a puppy and result in a number of pathological and skeletal conditions.
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41 Animal Therapy Magazine | ISSUE 15
DOGS are one of the most
morphologically diverse
species as they can range
from a 1kg Chihuahua to a
100kg English Masti. With gestation
ranging from 58 to 68 days all puppies
begin life at a similar size, with no
teeth and their eyes closed. ere is
little dierence between gestation
timescales, however growth and size
post-partum varies greatly, depending
on the breed (Table 1). Although there
is such a variation in size, nutritional
and exercise advice for the rst twelve
months of life scarcely diers. is
can have an impact on the growth
of a puppy and result in a number of
pathological and skeletal conditions.
Long bones, are responsible for
providing strength and structure to the
body to enable locomotion (Figure 1).
e cartilaginous precursors of long
bones are laid down during the foetal
period. At birth the scapula, os ischi,
os ilium and the cartilaginous scaold
of the diaphysis are almost totally
replaced by bone. Ossication begins
in the diaphysis where cartilage is
enclosed by forming an outer layer
of bone. As a result, the still rapidly
dividing chondrocytes (cartilage cells),
are forced to arrange themselves on
top of each other forming columnar
cartilage. e growing cartilage is
forced to grow in peripheral directions
as the cortex now prevents outward
expansion and makes bone form
lengthways. As the cortex thickens,
diused chondrocyte nourishment
decreases. Capillary vessels begin to
sprout through gaps in the bone
cortex and supply nutrients, osteoblasts
and osteoclasts to the diaphysis,
enabling the initiation of endochondral
ossication (Figure 1).
Endochondral ossication continues
until the animal has reached maturity.
e process involves the replacement of
hyaline cartilage to bone by osteoblastic
cells. Primary ossication centres are
located in the diaphysis of long bones
where osteoblasts lay down new bone
towards bone ends. Secondary centres
of ossication then develop at the
epiphysis, where mineralisation occurs
and results in the development of true
articular cartilage. Osteoclastic cells
then begin to remove bone from the
centre of the diaphysis which forms
the marrow cavity and trabeculae of
the cancellous bone. e epiphyseal
(growth) plate remains cartilage-bound
to enable bone to continue lengthening.
Once the dog has reached its full size,
growth will cease and the cartilage in
the growth plate is replaced by bone,
creating a total and bony skeleton
(Figure 2). Depending on bone type
and region within the body, growth
plates will close at dierent times
(Table 2).
Musculoskeletal
Development of the Puppy
Birth – Twelve Months
continued overleaf
by Georgia Lewis PhD Candidate, BSc (Hons) VN RVN
Dog Dog Breeds Weight Rapid Growth Timescale to Fully
Size Range (kg) Period Grown (Entire)
Toy Chihuahua, Pomeranian, < 5 Birth–11 weeks 6 – 12 months
Maltese, Toy Poodle
Small Jack Russell Terrier, 5 - 10 Birth–14 weeks 8 – 12 months
Dachshund, Pug,
Miniature Schnauzer
Medium Border Collie, Cocker 10 - 25 Birth–16 weeks 8 – 18 months
Spaniel, Beagle
Large German Shepherd, 25 - 40 Birth–18 weeks 11 – 18 months
Labrador Retriever,
Golden Retriever,
Bulldog, Boxer,
Siberian Husky
Giant Great Dane, Masti, > 40 Birth–20 weeks 12 – 24 months
St. Bernard
Figure 1: Development of a Long Bone; Le:
Open Growth Plate During Endochondral
Ossication, Right: Ceased Cell Proliferation
and Maturation in Closed Growth Plate.
Table 1: Table Depicting Dog Size, Typical Breeds, Average Weights and Growth Timescales.
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42 Animal Therapy Magazine | ISSUE 15
FACTORS AFFECTING GROWTH
Aside from the size of the dog,
there are a number of factors that
can contribute to their growth and
development. Depending on the
size of specic breeds, puppies have
exponential growth until they reach
certain ages (See Table 1). Males take
longer to reach adulthood than
females, so their sustained growth
needs to be considered with the
following factors.
Diet
Puppies begin weaning and start
eating solid food from three weeks
of age. ey are fully weaned from
their dams by the time of rehoming at
typically around eight weeks. During
the rst twelve months, it is crucial
that growing puppies have a sucient
diet which meets their high energy
requirements. Dietary imbalances are
commonly seen in growing dogs, so
it is important to ensure a dog’s diet is
suitable for its age and breed.
Resultant malnutrition from under-
feeding can cause stunted growth
and overfeeding can result in obesity.
Obesity has a direct impact on joint
and limb formation due to increased
loading forces on joints. is can
result in the malformation of a
joint, leading to conditions such as
secondary osteoarthritis. Although
obesity is a risk factor in all young
breeds, it can have a greater impact
on larger breeds due to excess
weight being carried on growing
bones for longer growing periods.
In order to ensure prevention of
malnutrition, puppies should be fed
a diet that consists of a calculated
calorie intake, utilising an individual
resting energy requirement (RER)
(Table 3). e RER, is the minimum
amount of energy a dog requires to
maintain homeostasis at rest, and can
be calculated by the formula; 70 x
(Bodyweight [kg]) 0.75
To avoid malnutrition and
consequential pathological conditions
or skeletal deformities, a sucient diet
must also include specic nutrients
and minerals. Larger breeds are
susceptible to over supplementation
of nutrients, which can result in a
number of skeletal conditions. It is
important to be aware of the size of
the puppy and its potential growth
to ensure it is given a diet with the
correct amounts of the following;
Calcium
Calcium is vital for the development
and maintenance of bone and is
absorbed through the intestines.
e average adult healthy dog
requires 0.1 to 0.2 mmol/L per day,
however growing dogs will require
a higher level of calcium in their
diet to account for bone growth. It
is especially important to ensure
puppies have ample time to feed
from their dams and avoid premature
weaning. Increased levels can result
in hypercalcaemia. is is detrimental
in giant breeds as more than 3.3g
of calcium per 100g can cause
osteochondrosis, whereas this only
results in microscopic irregularities
in miniature breeds. Low levels of
calcium; less than 0.55g per 100g
Growth Plate/ Physis Approximate Age Closure
Scapula: Supraglenoid tubercle 4 – 7 months
Proximal humerus: greater tubercle to humeral head 4 months
Proximal humeral physis 10 – 13 months
Distal humerus: lateral and medial condyle parts 6 weeks
Distal humerus: medial epicondyle 6 months
Distal humerus: condyle to diaphysis 5 – 8 months
Proximal radius 5 – 11 months
Proximal ulna: olecranon 5 – 10 months
Proximal ulna: anconeus 3 – 5 months
Distal radius 6 – 12 months
Distal ulna 6 – 12 months
Accessory carpal bone 2 – 5 months
Proximal metacarpal i 6 months
Distal metacarpals ii – v 5 – 7 months
Phalanges 4 – 6 months
Pelvis: acetabulum 4 – 6 months
Pelvis: iliac crest 12 – 24 months
Pelvis: tuber ischii 8 – 10 months
Proximal femur: neck 6 – 11 months
Proximal femur: greater trochanter 6 – 10 months
Proximal femur: lesser trochanter 8 – 13 months
Distal femur 6 – 11 months
Proximal tibia: medial and lateral condyle 6 weeks
Proximal tibia: tuberosity to condyle 6 – 8 months
Proximal tibia: condyle to diaphysis 6 – 12 months
Proximal bula 6 – 12 months
Distal tibia: physis 5 – 11 months
Distal tibia: medial malleolus 5 months
Distal bula 5 – 12 months
Tuber calcis 3 – 8 months
Lifestage RER Requirements
< 4 months 3.0 x RER
50% - 80% of adult weight 2.5 x RER
> 80% of adult weight 1.8 – 2.0 x RER
Table 2: Approximate Ages for Epiphyseal Plate Closure. (Hammond and McConnel, 2013)
Table 3: RER Requirements for First Twelve Months of Age. (Hemmings, 2018; Gajanayake et al., 2011)
PUPPY DEVELOPMENT
43 Animal Therapy Magazine | ISSUE 15
for giant breeds and 0.05g per 100g
for miniature breeds, can cause
pathological fractures as a result of
osteopenia and osteoporosis.
Vitamin D
Vitamin D is crucial for the growth
of bones and calcium absorption. It
has a signicant role in maintaining
the skeletal calcium balance which
promotes bone reabsorption
and subsequent function of the
parathyroid hormone. A diet
decient in vitamin D can result in
osteomalacia and rickets in all breeds.
It is imperative puppies are fed a
good quality diet, recommended
by a veterinary surgeon, as they
require supplementary amounts of
vitamin D, due to their inability to
photosynthesise sucient amounts
through their skin from natural
sunlight.
Protein
Protein is also an important factor
for a dog’s growth. A puppy’s protein
requirement peaks at weaning and
generally requires 22% to 23% of
protein daily. A diet low in protein
will result in weight loss and
retardation or cessation of growth. As
larger dog breeds will continue their
growth for longer, it is important
their diet does not reduce protein
at the same stage as small and
miniature breeds. Increased protein
in a puppy’s diet can result in skeletal
abnormalities and become a potential
contributing factor for conditions
such as hip dysplasia due to increased
development of the acetabulum and
femoral condyles. As a result of the
ill-tting joints, this can progress
into degenerative joint disease and
secondary osteoarthritis.
Phosphorus
Phosphorus is believed to combine
with calcium to strengthen and aid
the structure of bone. It is important
to maintain the calcium-phosphorus
ratio to ensure there is adequate
calcium within the bones. Young,
growing dogs are recommended to
have a daily phosphorus intake of 2 to
3 mmol/L.
ENVIRONMENTAL FACTORS
Home Environment
Puppies can be rehomed from eight
weeks of age. is results in a variation
of environmental factors impacting
how the puppy will develop. In a new
home, owners should avoid allowing
puppies the use of stairs and also from
playing on slippery surfaces to avoid
harsh impact on growing bones and
joints. e handling of puppies is
important and should be carried out
with great care. Owners with young
children should be especially mindful
when the children interact with the
puppy to ensure no injury is caused.
Similarly, it is also advised that puppies
within multi-dog households should
be monitored when interacting with
other dogs in the home. Young dogs’
bones are not fully developed and are
unable to sustain stress or force due
to their epiphyseal plates still being
cartilaginous (Figure 3). Exercise
therefore must be limited until dogs
have reached maturity to prevent
injury. It is advised that a dog is
exercised for ve minutes per month
of age. Stairs and large slopes should be
avoided to prevent any damage to the
puppy’s growth plates.
Neutering
Typically dogs reach adolescence and
sexual maturity between six to 18
months. For behavioural and potential
health reasons, dogs are usually
neutered between six and 24 months
of age. Neutering is the removal of
reproductive organs and results in a
consequential decrease in gonadal
steroid production. Gonadal hormones
regulate skeletal growth and it was
Figure 3: Depiction of Radiographic Puppy Bone Development; Le: at 1 week,
Centre: at 6 weeks, Right: at 12 weeks of age.
Figure 2: Complete Ossied Skeleton of a Dog Post Growth Plate Closure.
continued overleaf
44 Animal Therapy Magazine | ISSUE 15
Georgia Lewis,
PhD Candidate, BSc (Hons) VN RVN
Animal Department
Hartpury University,
Hartpury, Glos, GL19 3BE
anecdotally believed that early neutering
stunted growth through inhibition of
hormones. Decreased levels as a result
of early neutering in fact delay growth
plate closure and lead to elongated
long bones. ese elongated limbs can
result in altered function of muscular
anatomy which also predisposes the dog
to muscle, tendon and ligament injuries
and calcication. Males take longer to
reach full maturity so early castration
can result in underdeveloped muscles
and denition as well as elongated
limbs. A similar state of poor muscle
development also occurs in premature
spays. Owners and veterinary sta
should be mindful that dogs have
reached their adult size before neutering
to reduce the chance of delayed growth
plate closure, unless it is for a diagnosed
issue.
CONCLUSION
e growth of a dog is very complex.
Due to the diversity within the species,
bone growth can range from six months
to two years. Other factors, including a
puppy’s diet and exercise, can inuence
the development of bones. As a result,
bone malformation leads to secondary
conditions such as degenerative
joint disease and osteoarthritis. It is
important for breeders, owners and
veterinary sta to be aware of these
factors to ensure dogs develop at the
correct rate to reduce the repercussions
of poor development in the dog’s later
life stages.
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PUPPY DEVELOPMENT
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... The morphologic examination of 111 Mannara dogs showed that, on average, the indications of the provisional breed standard are satisfied (ENCI 2013): the dogs can be classified as large/giant (mean weight was 41 kg for males and 32 kg for females), with a meso-dolichomorphic body (mean body index was 85 for males and 90 for females) and a mesocephalic head (mean cephalic index was 53 for both the sexes). A certain degree of variability was observed, particularly in the Thoracic index, probably due to the different age of animals (1-5 years old) and therefore their development: due to the diversity of breeds with very different shapes and sizes, growth patterns are also noticeably different, with very small dog breeds reaching maturity between 8 and 12 months of age and larger breeds taking up to 24 months to reach the adult body weight and conformation (Hawthorne et al. 2004;Lewis 2019). The average birth weights measured on 50 puppies, equal to 720 g for males and 580 g for females, are in accordance with published data referred to large/giant dog breeds (Groppetti et al. 2017;Schrank et al. 2019). ...
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The influence of dietary calcium on calcium metabolism was investigated in growing dogs that reach an adult body weight similar to that of humans. Seven groups of dogs (n greater than or equal to 5) were raised on a diet with a composition meeting the National Research Council (NRC) requirements (1974), but differing in calcium content, with or without a constant ratio to phosphorus. Control dogs fed 1.1% calcium and 0.9% phosphorus (all on a dry matter basis) were fed ad libitum (n = 10) or in restricted amounts (n = 6); dogs fed high calcium (3.3%) diets received either 0.9% phosphorus (n = 6) or 3.0% phosphorus (n = 6); dogs fed low calcium (0.55%) diets received either 0.9% phosphorus (n = 5 + 6) or 0.5% phosphorus (n = 8). Food intake, circulating total calcium and inorganic phosphorus concentrations and calcium metabolism, with 45Ca kinetics, were studied at 8, 14, 20 and 26 wk of age. Except for the difference in food intake in two groups at 14 wk (i.e., 0.55% calcium-0.9% phosphorus higher and 3.3% calcium-0.9% phosphorus lower, respectively, than the controls) no differences were noticed during the rest of the study. The mean plasma calcium concentrations did not differ between groups during the studies, whereas that of inorganic phosphorus revealed temporal aberrations in two groups. An absorption coefficient alpha of 45-66% was found for the control group. High and low calcium diets gave rise to values of 23-43% and 70-97%, respectively, for alpha irrespective of the phosphorus content of the diet.(ABSTRACT TRUNCATED AT 250 WORDS)