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Inherited Defects in Sheep By Jennifer Edge. GA Agriculture Education Curriculum Office July 2001. Inherited Defects. *Atresia Ani *Dwarfism *Cryptochidism *Entropion *Rectal Prolapse *Spider Lamb. Atresia Ani. If a male lamb, anus is not present. If a female lamb, then it is sterile.

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Inherited defects in sheep by jennifer edge

Inherited Defects in SheepBy Jennifer Edge

GA Agriculture Education Curriculum Office

July 2001


Inherited defects

Inherited Defects

*Atresia Ani

*Dwarfism

*Cryptochidism

*Entropion

*Rectal Prolapse

*Spider Lamb


Atresia ani
Atresia Ani

  • If a male lamb, anus is not present.

  • If a female lamb, then it is sterile.


Dwarfism
Dwarfism

  • This disease is carried by a single recessive gene. Signs: short legs, enlarged head, broad skull, etc.

  • Don’t confuse dwarfism with possible “summer dwarfs”, which is not single gene recessive.


Cryptorchidism
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.


Entropion
Entropion

  • Not known at this time if single gene recessive.

  • “inverted eyelid” disease

  • Highly heritable but can be aggravated by environmental conditions.


Rectal prolapse
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


Spider syndrome
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.


Major genes for important traits
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.


Major genes for important traits1
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.


Callipyge
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 don’t express the condition.


What is seen in callipyge
What is seen in callipyge?

  • Higher dressing %

  • Greater shoulder and rump width

  • Less 12th rib fat

  • Lower % fat than normal lambs


Infectious disease
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.


Infectious disease1
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.


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