Inherited Defects in Sheep By Jennifer Edge

1. Inherited Defects in SheepBy Jennifer Edge GA Agriculture Education Curriculum Office July 2001

2. Inherited Defects *Atresia Ani *Dwarfism *Cryptochidism *Entropion *Rectal Prolapse *Spider Lamb

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

4. 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.

5. 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.

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

7. 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

8. 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.

9. 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.

10. 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.

11. 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.

12. What is seen in callipyge? • Higher dressing % • Greater shoulder and rump width • Less 12th rib fat • Lower % fat than normal lambs

13. 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.

14. 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.