Bones Developmental - Pathology

Generalised

Literally means “abnormal cartilage development”
Defective cartilage growth at the physis
Usually genetic cause
Occurs in cattle, dogs, sheep, pigs and cats
Leads to disproportionate dwarfism (contrast with miniature breeds)
- Generally, growth is disproportionate because only the growth of bones which form from cartilage models is retarded – growth of other bones is normal (i.e. long bones shorter than normal)

In Dogs:

Localised forms occur in dogs (e.g. affecting skulls of Pekingese and Bulldogs or the limbs of Dachshunds and Bassett hounds)
Occasionally seen in immature Beagles, Poodles, Alaskan Malamutes, Scottish Deerounds and Norwegian Elkhounds

In Cattle:

Dexter cattle
- Are heterozygous for incompletely dominant gene
- When homozygous - lethal, producing 'buldog calf'
- Usually aborted prior to seven month of pregnancy
- Also occurs in Holstein, Jerseys and Charolais
- Grossly:
  - Limbs and vertebral column are short
  - Domed cranium
  - Protruding tongue
  - Absent hard palate
  - Large umbilical hernia with eventrated abdominal organs
- Histologically:
  - Proliferative and hypertrophic zones in the physes are irregularly separated by fibrovascular tissue
  - Chondrocytes are not properly arranged
  - Irregular ossification and mineralisation

Telemark type
- Cattle of Norwegian origin
- Also seen in Jersey cows
- Calves born alive, unable to stand and die soon after birth
- Grossly:
  - Domed cranium
  - Brachygnatic face
  - Protruding tongue
  - Cleft palate
  - Short neck and limbs

Brachycephalic 'Snorter' type
- Hereford and Aberdeen Angus
- Show nasal dyspnoea and chronic rumenal tympany
- Grossly:
  - Short, broad head
  - Prominent, laterally displaced eyes
  - Short and compressed vertebral column
  - Distal long bones shorter than proximal
- Histologically:
- Physes appear normal
- Pallisading chondrocytes fewer in number
- Less hypertrophy

In Sheep:

Ancon type
- Short limbs due to premature closure of growth plates
- Now rare
Spider lamb
- Hereditary (autosomal recessive) in Suffolk and Hampshire breeds in North America
- Long, thin, angular limbs
- May be born alive or dead, aborted or develop symptoms within a month of birth
- Grossly:
  - Fine bones, poor musculature, small heads, scoliosis
- Histologically:
  - Abnormal centres of endochondral ossification
  - Nodular cartilage hypertrophy

In Pigs:

Occurs in sheep, dogs, cattle, horses
Failure of resorption by osteoclasts -> failure of remodelling of cancellous bone
Bones become thickened and dense but brittle
Marrow cavites are full of unresorbed primary spongiosa
Thickened intramembranous bones of skull -> altered shape of brain
Associated with severe viral infections, e.g. FeLV, BVD
Hereditary in Angus cattle

Hyperostosis (Image sourced from Bristol Biomed Image Archive with permission)

Rare, genetic
Diaphysial dysplasia
Excessive periosteal intramembranous bone, particularly in long bones
Grossly:
- Greatly thickened long bones
- Tense, shiny skin, closely adherent to tissues below
Born dead or die soon after birth

Equine disease
Narrowing of the vertebral canal due to malalignment or maldevelopment of the vertebrae
Fast growing male TBs ranging from 8 months to 4 years
Hind limb ataxia due to cord compression