Sheep Selection Flashcards
What are the types of sheep industry?
purebred, commercial, and dairy
Is the sheep industry large in the US?
no, it’s small
What does Purebred industry include?
- seedstock for commercial producers
- show sheep (4-H)
What are show sheep (4-H)?
- club lambs
- “collectors”
What are “collectors”?
purebred breeders that trade among themselves
What is part of Commercial sheep industry?
lamb/meat and wool
Where does the majority of income for commercial industry come from?
lamb/meat
What is dairy industry for?
cheese
What are traits of economic importance for sheep?
- meat production
- wool production
- milk
What are traits under meat production?
- number of lambs born/weaned
- growth rate
What are traits under wool production?
- fiber diameter
- fleece weight
What are traits under milk?
-pounds/lactation
How heritable are reproductive traits?
lowly heritable
Dressing % formula?
(carcass weight/live weight) x 100
What is the formula for carcass weight?
live weight - eviscerated weight
What is eviscerated weight?
weight of carcass without internal organs
Is fleece lowly or highly heritable?
highly
How many breeds of sheep are there worldwide?
425
How many sheep breeds are in the US?
47
Does the sheep industry use inbreeding?
some in purebreds, especially breeds with smaller numbers or imported breeds with limited numbers
Does the sheep industry use crossbreeding?
used extensively in commercial production
What does the National Sheep Improvement Program do?
calculates cross flock EPDs for sheep
What sheep does the National Sheep Improvement Program apply to?
- Targhee
- Suffolk
- Polypay
- Dorset
- Hampshire
- Columbia
- Katahdin
- Romney
Is National Sheep Improvement Program used in most breeds?
no
What are Central Ram Tests most effective for?
traits of moderate to high heritability which can be measured in a young growing ram
What is a danger of Central Ram Tests?
danger of emphasis on easily measured traits at the expense of other traits
What are some major genes for important traits sheep can get?
- Spider Syndrome
- Scrapie
- Callipyge
- Booroola
What is Spider Syndrome?
a lethal or semi-lethal skeletal abnormality
What breeds has Spider Syndrome been found in?
Suffolk, Hampshire, Shropshire, Southdown, and Oxford breeds
What kind of disease is Spider Syndrome?
single gene, recessive
What gene is defected that causes Spider Syndrome?
fibroblast growth factor receptor
Can Spider Syndrome be genetic tested for?
yes
What is Scarpie?
a central nervous system disease, scrape off their wool
What is Scrapie similar to?
- mad cow disease
- chronic wasting disease
- Creutzfeldt-Jakob disease
What is the consumer perception of Scrapie?
- some negative impact
- has never been transmitted to humans
Why does Scrapie cost the US sheep industry millions?
- lost export opportunities
- increased offal disposal costs
- reduced productivity
How is Scrapie diagnosed in dead animals?
examine brain and lymph nodes for lesions of scrapie and presence of abnormal prions
How is Scrapie diagnosed in live animals?
examination of 3rd eyelid for abnormal prion protein
Is there a treatment of Scrapie?
no
What is Scrapie Susceptibility in codon 136?
AA low susceptibility, AV or VV high suscpetibility
What is Scrapie susceptibility in codon 154?
RR or no effect, HR or HH overides Q171 in some cases
What is Scrapie susceptibility to codon 171?
QR or RR low susceptibility, QQ high susceptibility
What good does Booroola do?
increase ovulation rate, results in higher litter size
What bad does Booroola do?
poor lamb survival, lamb growth, and ewe conception
What is Booroola mapped to?
chromosome 6
What is Booroola also called?
Fec or fecundancy allele
What is Callipyge?
muscle hypertrophy, “big butt gene”
What chromosome is Callipyge mapped to?
chromosome 18
How is meat affected by Callipyge?
extremely tough meat
What is Callipyge the result of?
polar overdominance
What does Callipyge increase?
- higher dressing percentage
- larger loin eye
How can polar overdominance occur?
- one copy from sire express trait (Parent of origin effect)
- One copy from dam normal appearing
- Two copies normal appearing
When does muscle hypertrophy manifest in offspring?
one month after birth
What is muscle hypertrophy accompanied by?
a decrease in all measures of fatness
What do animals affected by muscle hypertrophy have improved?
feed efficiency and dressing percentage
