Inherited Defects in Sheep By Jennifer Edge

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Inherited Defects in SheepBy Jennifer Edge

• GA Agriculture Education Curriculum Office
• July 2001

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Inherited Defects

• Atresia Ani
• Dwarfism
• Cryptochidism
• Entropion
• Rectal Prolapse
• Spider Lamb

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Atresia Ani

• If a male lamb, anus is not present.
• If a female lamb, then it is sterile.

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Dwarfism

• This disease is carried by a single recessive
  gene. Signs short legs, enlarged head, broad
  skull, etc.
• Dont confuse dwarfism with possible summer
  dwarfs, which is not single gene recessive.

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Cryptorchidism

• Single gene recessive.
• If unilateral then only one testes has descended,
  this lamb would be fertile.
• If bilateral then both testes have not descended.
• Diagnosis is by palpation of the scrotal
  contents.
• Identify rams early to remove from breeding stock.

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Entropion

• Not known at this time if single gene recessive.
• inverted eyelid disease
• Highly heritable but can be aggravated by
  environmental conditions.

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Rectal Prolapse

• Inherited
• Influenced by short docking, high concentrate
  feeds, and coughing precipitated by dusty
  conditions or virus infections.
• Ways to fix
• PVC pipe
• Iodine shots at certain areas

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Spider Syndrome

• Due to a recessive gene
• Involves serious abnormalities of the
  muscular-skeletal system.
• Lamb must have two spider genes to exhibit
  condition (ss).
• Symptoms extreme curvature of the spine, outward
  bending of the front legs at the knees, arched or
  crooked nose,etc.

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Major Genes for Important Traits

• Booroola-The Booroola Merino is a highly prolific
  strain of Australian Merino. Their exceptional
  reproduction performance is due to a major
  autosomal allele. The allele is known as Fec B.
  Each copy of the allele has been found to
  increase ovulation by 1.5 ova.

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Major Genes for Important Traits

• The related increase in litter size is not
  completely additive the first copy of the allele
  increases litter size by .7 to .9 lambs, and the
  second copy results in an additional .4 to .5
  lambs.
• Problems performance in lamb survival, lamb
  growth, and ewe conception.

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Callipyge

• Single allele is responsible for the condition.
  It is located on chromosome 18 in sheep.
• Animals with one copy of the allele who received
  it from the sire express the condition.
• Animals with one or two copies from the dam dont
  express the condition.

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What is seen in callipyge?

• Higher dressing
• Greater shoulder and rump width
• Less 12th rib fat
• Lower fat than normal lambs

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Infectious Disease

• Scrapie
• Attacks the central nervous system
• Fatal
• Differences in amino acids of the prion protein
  in at least 2 positions or codons appear to have
  an effect on susceptibility of sheep to scrapie
  strain A and scrapie strain C.

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Infectious Disease

• At the 136 codon two amino acids have been
  identified in sheep alanine decreases
  susceptibility and valine increases
  susceptibility to strain A.
• At the 171 codon arginine is associated with
  decreased susceptibility and glutamine increases
  susceptibility to strain C.