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===Chondrodysplasia===
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===[[Chondrodysplasia]]===
 
   
 
   
*Literally means “abnormal cartilage development”
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*Defective cartilage growth at the physis
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*Usually genetic cause
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*Occurs in cattle, dogs, sheep, pigs and cats
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*Leads to '''disproportionate dwarfism''' (contrast with miniature breeds)
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**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)
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<u>In Dogs:</u>
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*'''Localised''' forms occur in dogs (e.g. affecting skulls of Pekingese and Bulldogs or the limbs of Dachshunds and Bassett hounds)
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*Occasionally seen in immature Beagles, Poodles, Alaskan Malamutes, Scottish Deerounds and Norwegian Elkhounds
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<u>In Cattle:</u>
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*'''Dexter cattle'''
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**Are heterozygous for incompletely dominant gene
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**When homozygous - lethal, producing 'buldog calf'
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**Usually aborted prior to seven month of pregnancy
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**Also occurs in Holstein, Jerseys and Charolais
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**Grossly:
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***Limbs and vertebral column are short
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***Domed cranium
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***Protruding [[Tongue - Anatomy & Physiology|tongue]]
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***Absent hard palate
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***Large umbilical hernia with eventrated abdominal organs
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**Histologically:
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***Proliferative and hypertrophic zones in the physes are irregularly separated by fibrovascular tissue
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***Chondrocytes are not properly arranged
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***Irregular ossification and mineralisation
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*'''Telemark type'''
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**Cattle of Norwegian origin
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**Also seen in Jersey cows
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**Calves born alive, unable to stand and die soon after birth
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**Grossly:
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***Domed cranium
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***Brachygnatic face
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***Protruding [[Tongue - Anatomy & Physiology|tongue]]
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***Cleft palate
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***Short neck and limbs
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*'''Brachycephalic 'Snorter' type'''
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**Hereford and Aberdeen Angus
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**Show nasal dyspnoea and chronic rumenal tympany
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**Grossly:
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***Short, broad head
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***Prominent, laterally displaced eyes
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***Short and compressed vertebral column
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***Distal long bones shorter than proximal
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**Histologically:
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**Physes appear normal
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**Pallisading chondrocytes fewer in number
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**Less hypertrophy
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<u>In Sheep:</u>
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*'''Ancon type'''
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**Short limbs due to premature closure of growth plates
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**Now rare
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*'''Spider lamb'''
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**Hereditary (autosomal recessive) in Suffolk and Hampshire breeds in North America
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**Long, thin, angular limbs
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**May be born alive or dead, aborted or develop symptoms within a month of birth
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**Grossly:
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***Fine bones, poor musculature, small heads, scoliosis
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**Histologically:
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***Abnormal centres of [[Bone & Cartilage Development - Anatomy & Physiology|endochondral ossification]]
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***Nodular cartilage hypertrophy
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<u>In Pigs:</u>
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*Occurs in Danish Landrace
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*Autosomal recesive inheritance
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*Dwarfs with short legs, forelegs shorter than hind legs
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*Abnormal movement is noticable at weaning
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*Sequel is [[Joints Degenerative - Pathology#Degenerative joint disease (DJD)|arthrosis]]
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[[Category:Bones - Developmental Pathology]]
       
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