Inherited defects in sheep by jennifer edge
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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 l.jpg

Inherited Defects in SheepBy Jennifer Edge

GA Agriculture Education Curriculum Office

July 2001

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Inherited Defects

*Atresia Ani




*Rectal Prolapse

*Spider Lamb

Atresia ani l.jpg
Atresia Ani

  • If a male lamb, anus is not present.

  • If a female lamb, then it is sterile.

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  • 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.

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  • 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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  • 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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  • 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.

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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.