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Sheep FAQs
Spider Lamb Syndrome
Scrapie Resistance
Do we have to have a vet draw the blood, or can we draw it ourselves?
The customers may draw the blood themselves by following the instructions provided with the kit or have a licensed veterinarian draw the blood.
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Are test results forwarded to the breed association?
Test results for any sheep tests are ONLY reported to the customer.
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What is Spider Lamb Syndrome?
Spider Lamb Syndrome (SLS) or ovine hereditary chondrodysplasia is a genetic disorder causing skeletal deformities in young lambs. Affected lambs commonly have abnormally long, bent limbs. Severe cases will also show twisted spines, shallow bodies, flattened rib cages, and long necks. SLS is a genetic recessive disorder meaning that an affected lamb must have inherited the mutation from both parents. Sheep that carry only one copy of the mutation will look normal but could produce an affected "spider lamb" if mated to another Spider gene carrier.
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What is the Spider gene test?
The Spider gene test is a simple DNA-based test that identifies whether an animal is homozygous normal (NN) and genetically "clean," or heterozygous (NS) and a spider carrier capable of producing spider lambs when mated to another carrier. The Spider gene test can clarify whether or not a "gray-pedigreed" individual is truly a Spider carrier.
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How accurate is the test?
Results of the Spider gene test are 99% accurate.
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Are test results confidential?
Yes! Test results are only reported to the customer whose name is on the GenMARK test request form. Results will only be reported by mail, fax or e-mail using information provided by the customer at the time samples are submitted. Under no circumstances will results be provided over the phone.
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What breeds are affected by Spider?
Spider was originally identified in Suffolk sheep in the early 1970's but has appeared in several other sheep breeds over the years, most likely due to cross-breeding.
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How do I know if I have the Spider gene in my flock?
Without DNA testing, Spider carriers can only be identified when they produce a Spider lamb.
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How do I eliminate the Spider gene from my flock?
The Spider gene can only be eliminated by using genetically clean (NN) breeding stock. A first step toward eliminating Spider would be breeding all ewes with NN rams and then DNA testing all replacement ewe lambs to begin identifying older Carrier ewes that could be culled and replaced with young Normal ewe lambs.

Here are three possible mating schemes for managing the Spider gene in your flock.

Mating a Normal (NN) animal with a Normal (NN) animal will always produce Normal (NN) offspring.

Mating a Normal (NN) animal with a Carrier (NS) animal will produce:

  • 50% Normal (NN) animals
  • 50% Carrier (NS) animals
  • All animals will appear phenotypically normal
Mating a Carrier (NS) animal to a Carrier (NS) animal will produce:
  • 25% Normal (NN) animals
  • 50% Carrier (NS) animals
  • 25% Affected Spider (SS) animals
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Why is DNA testing important?
DNA testing can help you manage your flock to dramatically reduce, if not eliminate, the possibility of your flock becoming infected with scrapie. Think of testing as an "insurance policy" - by knowing if your sheep are genetically resistant to scrapie you can rest assured that your flock will be safe from infection and should not be considered as a source flock.

As an example, consider the potential for genetic testing in humans. If you know that certain genetic diseases such as diabetes or breast cancer run in your family, then you should realize the importance of managing your health and lifestyle to reduce the risk of that disease affecting your life.

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Where to start with DNA testing?
It makes economical sense to start by testing your stud rams and then avoid using QR rams for your next lamb crop. Testing all lambs in the next lamb crop will help identify those ewes that carry Q and provide a guideline for selecting next year's replacement ewe lambs, or breeding stock that you intend to sell. Using genotypes to make mating decisions doesn't mean you have to cull QR's that are of high genetic merit but genotypes will help you avoid mating QR x QR.
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Will the DNA tests for Scrapie tell me if my sheep are infected?
No. DNA testing for Scrapie Resistance codons 171 and 136 will not identify scrapie-infected sheep. In reality, DNA testing identifies individuals that could contract scrapie if exposed to a scrapie-infected individual. The DNA tests for Scrapie Resistance identify mutations within the prion protein gene (PrP), a gene that is associated with Scrapie Susceptibility. The portions of the PrP gene that provides resistance to certain strains of Scrapie are referred to as codon 171 and codon 136.
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Are test results confidential?
Yes! Test results are only reported to the customer whose name is on the GenMARK test request form. Results will only be reported by mail, fax or e-mail using information provided by the customer at the time samples are submitted. Under no circumstances will results be provided over the phone.
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What is meant by Codon 171 or Codon 136?
A codon designates portions of DNA sequence that code for a specific amino acid that ultimately produces a gene-specific protein. Variations in DNA sequence of two codons within the PrP gene (codon 171 and codon 136) are associated with a sheep's susceptibility to being infected with scrapie if exposed to the scrapie agent.
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What breeds should be tested for Scrapie Resistance?
All breeds should be considered for testing. Scrapie can affect any sheep breed but has been reported primarily in the Suffolk breed in the United States. Scrapie has also been diagnosed in Border Leicester, Cheviots, Corriedales, Cotswold, Dorsets, Finn sheep, Hampshires, Merinos, Montadales, Rambouillets, Shropshires, Southdowns, as well as several crossbreeds. Prevalence in the Suffolk breed doesn't necessarily mean that they are more susceptible to scrapie but may be more likely because Suffolk sheep predominate in small farm flocks.
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What do the results QQ, QR and RR mean?
The R represents the amino acid arginine (R) at codon 171 and is associated with resistance to scrapie. The Q represents the amino acid glutamine at codon 171 instead of arganine and is associated with susceptibility to scrapie. Because every individual has two copies of each chromosome, an animal can have the genotype RR, QR, or QQ. An animal that has the genotype RR at codon 171 is considered resistant to certain strains of scrapie common to the U.S. - virtually no sheep homozygous for arginine (RR) have been identified with scrapie in the United States. RR animals will always pass one R allele to their offspring. A QR animal (heterozygous) is believed to have a low level of susceptibility to scapie but will pass Q to its offspring 50% of the time. Individuals that have two copies of Q (homozygous) are considered susceptible and may contract scrapie if exposed to an affected animal.
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How accurate are these tests?
Results of the tests are 99% accurate.
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How important is testing for codon 136?
Codon 136 is associated with strain A scrapie which is not commonly found in the U.S but has been reported in the U.K. Current research indicates that scrapie strain "A" can infect sheep that have valine (V) at codon 136 rather than alanine (A). AA individuals are considered resistant whereas, AV are susceptible and VV are considered highly susceptible. Suffolk sheep, however, rarely carry the V allele and, any individual that is resistant at codon 171 (RR) will most likely be resistant at codon 136 (AA) due to genetic linkage. Bottom line: Testing for codon 136 may not be as important as codon 171 due to the rarity of the V allele in many US sheep breeds. However, if you want to ensure that your animals have the highest level of resistance, you may want to test your QR animals for Codon 136.
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What is scrapie?
Scrapie is a fatal, degenerative disease that affects the central nervous system in sheep. Scrapie is caused by a tiny, infectious protein called a "prion" (PREE-on). Scrapie belongs to a family of prion diseases known as "spongiform encephalopathies" which earns its name from the appearance of holes in the brains of infected individuals.
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What are clinical signs of scrapie?
Clinical signs vary widely but include scratching and rubbing against fixed objects (hence, the name "scrapie"), loss of coordination and gait abnormalities such as high-stepping, hopping and swaying of the back end, weight loss, biting of feet and limbs and lipsmacking. Normal-appearing, infected animals will respond to sudden noise or stresses by trembling or falling down in a convulsive-like state. Because symptoms of scrapie may not appear until 5 years after an animal is exposed, a producer may be unaware that his flock has been exposed to or infected with scrapie. Scrapie symptoms may appear as early as 1year following exposure.
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Is scrapie a genetic disease?
No, scrapie is not a genetic disease, but there is a genetic component that affects an animal's susceptibility to scrapie and the length of time before symptoms appear.
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How is scrapie transmitted among sheep?
Scrapie is thought to be passed from an infected ewe to her offspring and to other sheep during lambing season through contact with placenta and placental fluids. Rams are not thought to be a risk for spreading scrapie.
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Why is scrapie a concern?
Awareness and concern for controlling scrapie greatly increased in the late 1980's due to the acknowledgement that Mad Cow Disease (bovine spongiform encephalopathy, or BSE) in Great Britain was thought to be caused by cattle feed supplements. A possible link between BSE and the human form, Creutzfeldt-Jacob disease, has created much concern by public health officials world-wide. In the United States, the first case of scrapie was diagnosed in 1947 in a Michigan flock. Since that first case, more than 950 flocks have been diagnosed in the United States.
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Is it necessary to re-test sheep for scrapie resistance every few years?
No, an animal needs to be tested only once in its lifetime for any DNA test. The sequence of an individual's DNA remains constant throughout its lifetime.
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How do I select for Scrapie Resistance in my flock?
The best way to produce scrapie-resistant sheep is to use only RR rams and RR ewes to produce your lamb crop. Of course, getting to that level without spending the money to completely replace your current flock takes time and chances are you'll have high quality QR sheep that you will want to keep in your breeding program. DNA testing can help by identifying RR or QR rams and ewes that will increase the frequency of R in your flock. Consider these possible mating schemes and their outcomes for managing genotypes of Scrapie Resistance.

Mating RR animals to RR animals will produce 100% RR offspring and will eliminate the need to DNA test future offspring.

Mating an RR animal to a QR animal will produce:

  • 50% RR animals
  • 50% QR animals
Mating an RR animal to a QQ animal will produce 100% QR animals

Mating a QR animal to a QR animal will produce:

  • 25% RR animals
  • 50% QR animals
  • 25% QQ animals
Mating a QR animal to a QQ animal will produce:
  • 50% QR animals
  • 50% QQ animals
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