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Genetics > Sheep Selection > Flashcards

Sheep Selection Flashcards

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1
Q

What are the types of sheep industry?

A

purebred, commercial, and dairy

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2
Q

Is the sheep industry large in the US?

A

no, it’s small

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3
Q

What does Purebred industry include?

A
  • seedstock for commercial producers

- show sheep (4-H)

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4
Q

What are show sheep (4-H)?

A
  • club lambs

- “collectors”

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5
Q

What are “collectors”?

A

purebred breeders that trade among themselves

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6
Q

What is part of Commercial sheep industry?

A

lamb/meat and wool

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7
Q

Where does the majority of income for commercial industry come from?

A

lamb/meat

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8
Q

What is dairy industry for?

A

cheese

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9
Q

What are traits of economic importance for sheep?

A
  • meat production
  • wool production
  • milk
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10
Q

What are traits under meat production?

A
  • number of lambs born/weaned

- growth rate

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11
Q

What are traits under wool production?

A
  • fiber diameter

- fleece weight

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12
Q

What are traits under milk?

A

-pounds/lactation

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13
Q

How heritable are reproductive traits?

A

lowly heritable

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14
Q

Dressing % formula?

A

(carcass weight/live weight) x 100

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15
Q

What is the formula for carcass weight?

A

live weight - eviscerated weight

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16
Q

What is eviscerated weight?

A

weight of carcass without internal organs

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17
Q

Is fleece lowly or highly heritable?

A

highly

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18
Q

How many breeds of sheep are there worldwide?

A

425

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19
Q

How many sheep breeds are in the US?

A

47

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20
Q

Does the sheep industry use inbreeding?

A

some in purebreds, especially breeds with smaller numbers or imported breeds with limited numbers

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21
Q

Does the sheep industry use crossbreeding?

A

used extensively in commercial production

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22
Q

What does the National Sheep Improvement Program do?

A

calculates cross flock EPDs for sheep

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23
Q

What sheep does the National Sheep Improvement Program apply to?

A
  • Targhee
  • Suffolk
  • Polypay
  • Dorset
  • Hampshire
  • Columbia
  • Katahdin
  • Romney
24
Q

Is National Sheep Improvement Program used in most breeds?

A

no

25
Q

What are Central Ram Tests most effective for?

A

traits of moderate to high heritability which can be measured in a young growing ram

26
Q

What is a danger of Central Ram Tests?

A

danger of emphasis on easily measured traits at the expense of other traits

27
Q

What are some major genes for important traits sheep can get?

A
  • Spider Syndrome
  • Scrapie
  • Callipyge
  • Booroola
28
Q

What is Spider Syndrome?

A

a lethal or semi-lethal skeletal abnormality

29
Q

What breeds has Spider Syndrome been found in?

A

Suffolk, Hampshire, Shropshire, Southdown, and Oxford breeds

30
Q

What kind of disease is Spider Syndrome?

A

single gene, recessive

31
Q

What gene is defected that causes Spider Syndrome?

A

fibroblast growth factor receptor

32
Q

Can Spider Syndrome be genetic tested for?

A

yes

33
Q

What is Scarpie?

A

a central nervous system disease, scrape off their wool

34
Q

What is Scrapie similar to?

A
  • mad cow disease
  • chronic wasting disease
  • Creutzfeldt-Jakob disease
35
Q

What is the consumer perception of Scrapie?

A
  • some negative impact

- has never been transmitted to humans

36
Q

Why does Scrapie cost the US sheep industry millions?

A
  • lost export opportunities
  • increased offal disposal costs
  • reduced productivity
37
Q

How is Scrapie diagnosed in dead animals?

A

examine brain and lymph nodes for lesions of scrapie and presence of abnormal prions

38
Q

How is Scrapie diagnosed in live animals?

A

examination of 3rd eyelid for abnormal prion protein

39
Q

Is there a treatment of Scrapie?

A

no

40
Q

What is Scrapie Susceptibility in codon 136?

A

AA low susceptibility, AV or VV high suscpetibility

41
Q

What is Scrapie susceptibility in codon 154?

A

RR or no effect, HR or HH overides Q171 in some cases

42
Q

What is Scrapie susceptibility to codon 171?

A

QR or RR low susceptibility, QQ high susceptibility

43
Q

What good does Booroola do?

A

increase ovulation rate, results in higher litter size

44
Q

What bad does Booroola do?

A

poor lamb survival, lamb growth, and ewe conception

45
Q

What is Booroola mapped to?

A

chromosome 6

46
Q

What is Booroola also called?

A

Fec or fecundancy allele

47
Q

What is Callipyge?

A

muscle hypertrophy, “big butt gene”

48
Q

What chromosome is Callipyge mapped to?

A

chromosome 18

49
Q

How is meat affected by Callipyge?

A

extremely tough meat

50
Q

What is Callipyge the result of?

A

polar overdominance

51
Q

What does Callipyge increase?

A
  • higher dressing percentage

- larger loin eye

52
Q

How can polar overdominance occur?

A
  • one copy from sire express trait (Parent of origin effect)
  • One copy from dam normal appearing
  • Two copies normal appearing
53
Q

When does muscle hypertrophy manifest in offspring?

A

one month after birth

54
Q

What is muscle hypertrophy accompanied by?

A

a decrease in all measures of fatness

55
Q

What do animals affected by muscle hypertrophy have improved?

A

feed efficiency and dressing percentage

Genetics (24 decks)

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