sheep genetics 4 Flashcards
What is lambplan indices?
- Gives genetic information on
o terminal, maternal and dual-purpose breeds - benchmarks
- uses ASBV’s and standard selection indices and accuracy values
- Can customise indices (sheepobject)
what lambplan indices should be -ve and why?
Traits that should be small/-ve
o Birth weight (too big = lambing difficulties)
o PFAT- post weaning fat (leaner lamb)
o WEC- worm egg count (more resistant)
how are the indices values used?
- ASBV (top) value/2 as sire only provides half
o Bottom value = accuracy
The higher the accuracy the closer it is to the true breeding value
what are the 3 major lambplan indices?
lambplan terminal, maternal and dual purpose indices
what is the maternal lambplan indices and what is it used for?
- Lambplan maternal ASBV o Gives values of progeny o –ves ok FAT and WEC breed that excels in maternal traits (e.g. mothering ability and milk production)
o Maternal $ index (MAT $)
aimed at maternal breeds of specific breeds, doesn’t include FD
e.g. border and coopworth
balances the key economic traits relevant to most maternal breeds
o Dual Purpose $ Index (DP$)
aimed at self-replacing maternal flocks with additional focus on wool quality, such as Corriedales, SAMMs and Dohnes
same breeding objectives as MAT $ index, and moderate emphasis on improving greasy fleece weight and a small emphasis on reducing micron
o Self-Replacing Carcase $ Index (SRC$)
self-replacing flocks (+ terminal sires) producing a self-replacing flock with a strong emphasis on carcase traits
e.g. Dorper, Wiltshire Horn, Wiltipoll and Boer Goats
same breeding objectives as MAT $ index, except for no economic values for fleece traits = higher gains to be made for growth and carcass traits.
what are the does MAT, DPS and SRC stand for?
Maternal $ index (MAT$)
dual purpose $ index (DPS$)
self-replacing carcass $ index (SRC$)
what is the MAT $ index used for?
o Maternal $ index (MAT $)
aimed at maternal breeds of specific breeds, doesn’t include FD
e.g. border and coopworth
balances the key economic traits relevant to most maternal breeds
what is the DPS $ used for?
aimed at self-replacing maternal flocks with additional focus on wool quality, such as Corriedales, SAMMs and Dohnes
same breeding objectives as MAT $ index, and moderate emphasis on improving greasy fleece weight and a small emphasis on reducing micron
what is the SRC $ used for?
self-replacing flocks (+ terminal sires) producing a self-replacing flock with a strong emphasis on carcass traits
e.g. Dorper, Wiltshire Horn, Wiltipoll and Boer Goats
same breeding objectives as MAT $ index, except for no economic values for fleece traits = higher gains to be made for growth and carcass traits.
what are the 4 lambplan terminal indices
- carcass plus indices
- trade $ index
- export $ index
- lamb 2020 index
what is the carcass plus index and how is it evaluated?
WWT, PWT, PFAT and PEMD
Designed for high growth and muscle depth with low fat
what is the trade $ index and how is it evaluated?
PWT, PFAT and PEMD
Target 19kg carcass
what is the export $ index and how is it evaluated?
PWT, PFAT and PEMD
Target 26 kg carcass
what is the export $ index and how is it evaluated?
BWT, WWT, PWT, PFAT, PEMD, PWEC
Target 22kg carcass lamb from merino or 1st X ewe
what is the dual purpose $ index and how is it evaluated?
o Dual Purpose $ Index (DP$)
aimed at self-replacing maternal flocks with additional focus on wool quality, such as Corriedales, SAMMs and Dohnes
same breeding objectives as MAT $ index, and moderate emphasis on improving greasy fleece weight and a small emphasis on reducing micron
what is the self-replacing carcass $ index and how is it evaluated?
- Self-Replacing Carcass $ Index (SRC$)
self-replacing flocks (+ terminal sires) producing a self-replacing flock with a strong emphasis on carcass traits
e.g. Dorper, Wiltshire Horn, Wiltipoll and Boer Goats
same breeding objectives as MAT $ index, except for no economic values for fleece traits = higher gains to be made for growth and carcass traits.
what is heterosis and what are 2 kinds?
- hybrid vigour
o wider range of genes= better at coping
o can cross between breeds and within to generate
o maternal
advantage of the crossbred mother over the average of purebred mothers
E.g. Hereford x Angus cow is generally a better mother
o Individual
advantage of the crossbred individual relative to the average of the purebred individuals
e.g. Limousin x Hereford calf may grow faster than the average of purebred Limousin and Hereford.
what is an F1 cross
o Only progeny has hybrid vigour
o A x B
what is a 3 breed cross?
- 3 breed cross
o Progeny have both maternal and individual hybrid vigour
o e.g. 1st X ewe x terminal ram (AB x C)
o most common is poll dorest (or similar) x F1 border Leicester x merino ewe
what is a 2 breed composite?
- 2 breed composite
o No. of generations after initial F1, considered an even mix of the 2 breeds
o 50% maternal and 50% individual
what is a backcross?
- back cross
o full maternal heterosis , 50% individual heterosis
o e.g. 1st X ewe x purebred ram (A x AB)
what is an open composite?
- Open composite
o Import any sire based on merit (any breed)
o Heterosis but unpredictable progeny
o E.g. white Suffolk, new genetics to stablise
what is MAS and when is it used?
- Marker assisted selection (MAS)
o Single Nucleotide Polymorphisms (SNPs), thousands identified
o Markers for different production traits to estimate EBVs
o First commercial sheep 2009
Combined with traditional EBVs to increase accuracy
o Boroola and inverdale gene
Ovulation gene, more present = more ovulation (can get 0,1 or 2)
what are the benefits of MAS?
- Greatest benefit for traits of low heritability, difficult/expensive to measure, only measureable in one sex or expressed later in life
o E.g. fertility, disease resistance, longevity etc. - Potential to increase response to selection substantially
o Breed earlier with increased confidence
allows information nucleus flock
o 500 sires of different breeds progeny tested for a range of traits across different environments – combined with SNP’s
