C7; Pig breeding methods: pure breeding, continuous and discontinuous hybridization Flashcards
what are the 4 main breeding groups of pigs?
4 Main Breed Groups:
* Large white
* Landrace -Belgian Landrace
* Color (culture and local variety) — Hampshire, Pietrain, Duroc, Mangalitsa
* Asian — Meishan, Vietnamese lop eared
* (hybrids)
what are the most common mating methods used in pig breeding?
Mating Methods:
* Harem: Group of sows. gilts & one boar
* Stud/hand mating: individual mating
* Artificial Insemination: very common in pig breeding using locally produced, fresh, diluted semen.
what processes must a bore go through before entering an AI station?
-> remain in quarantine for 40 days before entering AI station.
-> Blood test for swine flu, aujeszkys disease etc
what are the sex ratios of natural amting and AI
Natural mating = 1:60/70
* Artificial Insemination (single diluted ejaculation) = 1: 10-15
why is pure-breeding practiced?
- Selective breeding & breed improvement, maintenance of purebred (pedigree) breeds
inbreeding
linebreeding
outcrossing
what is inbreeding
Inbreeding: more closely related than population average,
increases homozygosis and uniformity, decreases genetic
variability. (within 4 generations)
what is line breeding
Line breeding: purebred lines are bred. a form of inbreeding. Inbreeding depression might be a problem. not as close as inbreeding.
what is outcrossing
Preserving pure breeds: pure breeding without close inbreeding - usually do not have common ancestors.
what is gene breed and conservation?
● Pure breeding without close inbreeding.
● Maintenance of variability & regular selection to preserve breed for future.
● Used to preserve rare breeds without causing severe inbreeding.
what is cross breeding?
mating 2 different breeds
what is the importance of crossbreeding?
● Breed evaluation.
● Utilization of heterosis ( hybrid vigour).
● Upgrading – improving existing desirable traits even further e.g litter size.
● Avoiding inbreeding or gene deteriation.
● Formation of a new hybrid breed.
what is hybrid vigour / heterosis?
-> Is observed when the offspring of two unrelated different breeds crossed show superior traits and performance than either of their parents.
-> This phenomenon is due to a combination of different genes of the two parents, compared to the smaller gene pool of
offspring whose parents are of the same breed and/or closely related.
Heterosis has both a genetic and profit advantage.
what is hybridisaiton?
-> Combination of breeds to optimal use of meat production.
-> a hybrid (or crossbreed) is the result of combining the qualities of two organisms of different breeds, variety or species through sexual reproduction. Hybrids are not always intermediates between their parents, but can show hybrid vigour, often growing larger or taller than either parent.
what hybridisation methods are used in practice?
1) Discontinuous -> all hybrid swines are slaughtered.
2) Continuous -> * Keep the best crossbred gilts
for replacement.
* Market all crossbred boars and surplus gilts.
* Continuous demand on boars of more parental breeds.
* Alteration of carcass.
3) Crossing wild and domestic forms
what are the types of discontinuous crossing
discontinuous crossing: all hybrid offspring are slaughtered for meat production.
1) Direct/single – involves use of 2 breeds
– e.g Large White boar x Landrace sow
– Combined characteristics, bigger piglets and larger litter size in F1 generation.
2) Indirect, 3 breed – use of F1 generation with a new breed
– e.g Large white/landrace x Duroc boar, used for production of salami
3) Indirect, 4 breed – using 2 sets of crossed F1 generations.
– e.g Large White/Hampshire x Landrace/Duroc
see camera roll for diagrams
advantages of discontinuous hybridisation
● Pure genotypes
● Different breeds
● Heterosis effects
Disadvantages of Discontinuous hybridization
● Maintains all breeds permanently
● F2 breeding animal production
● Need of more pens
what are the types of continuous crossing?
● Keeps best gilts as replacements for old/infertile/injured sows
● Market all crossbred boars and surplus gilts
● Continuous demand for boars of paternal breeds
1) Two way cross – CRISS CROSSING: Involves 2 breeds that bring desirable production traits and these breeds are crossed to produce the F1 generation. e.g Mangalitsa x Berkshire.
The F1 generation is then crossed each time with a sire of one of the two original breeds. i.e The F1 generation is crossed with a Berkshire boar. The F2 generation is then crossed with a Mangalitsa boar - the 2 breeds are ‘’criss-crossed’’.
2) Three way cross – Rotational crossing: Similar to criss-crossing only that a third breed is injected to the F1 generation that consisted of cross between the 2 parent breeds. One of the parent breeds is then brought back in to sire the F2 generation.
e.g Large White x Berkshire
F1 Large White/Berkshire x Mangalitsa
F2 LW/B/M x Large White etc.
Often more than 3 breeds, no limit to no. of different breed sires that can be used.
Results in loss of breed uniformity.
3) Lauprecht system
4) Open synthetic
* rare method
* used for new breed formation
* combination of different valuable breed characteristics to establish new synthetic breeds
what does crossing wild and domestic breeds have an effect on?
Hybrids:
* litter size
* body proportion
* taste of the meat
* mental capacities
* colour variances
