out breeding.pptx

Outbreeding
Types of outbreeding
Uses

1. Outbreeding

2. Outcrossing Mating of unrelated animals within a breed. It usually applies only to matings within a purebred but show no relationship for at least 4 to 6 of its previous generations. Outcrossing within a herd by use of selected sires is also called as selective breeding. E ffective for characters governed by additive effect of genes having high heritability . The outcrossing is practised to exploit intra herd variability.

3. Uses of outcrossing It can be practised in a purebred herd/flock when there is lack of selection response due to decrease in genetic variability. To reduce inbreeding in a closed population. To introduce new genes with reference to colour , horn type etc. Highly effective for characters under the control of genes with additive effects. It is the effective system for genetic improvement, if carefully combined with selection.

4. Top crossing Mating of a inbred males of a certain family to females of another family or non-inbred population of the same breed. A top cross is made when a breeder goes back to the original genetic source of the breed or strain for some new genetic material for further genetic improvement of the breed / strain. e.g . 1 . Angus breeders from America return to Scottland to buy a stud sire to top cross their Angus breed. 2. Indian Jersey is top crossed with newly imported Jersey.

5. Line crossing Crossing of inbred lines within a specific breed. T akes advantage of both increased homozygosity and increased heterozygosity Incrossing : Mating between inbred lines within a breed Incross breeding : Mating between inbred lines of different breeds.

6. Strain crossing Mating between strains within the same breed. e.g . Crossing of different White Leghorn Strains. WLH strains A (England) x WLH strain B (Australia) WLH strain crossbred AB

7. Grading or Grading-up Breed substitution or breed replacement Grading is the continuous use of sires of one pure breed on the females of non-descript animals and its female progenies generation after generation. The objective is to change the genetic makeup of a non-descript (mixed population/mongrel/ Scrup ) to a ‘pure bred’ –To raise the performance of ND to the level of purebred quickly

8. Merits It is followed to increase the number of purebred population, if they are relatively scare or new to that area. To introduce a new gene or desirable quantitative traits in a population For grading-up programme minimum number of bulls / sire is sufficient or even frozen semen straws are enough.

9. Disadvantages This process requires 4-5 generations/ several years The first cross usually shows marked improvement in productivity over the original female stock. Due to increase in the level of exotic inheritance - poor in adaptation to local environment It can be practised after fixing the target for level of exotic inheritance based on the level of performance. In dairy cattle the level of Jersey / H.F. inheritance should not exceeds 50 – 62.5%.

10. Species Hybridization Defined as the mating of individuals which belong to two different species. It is the widest possible kind of outbreeding .

11. Crossbreeding The mating of animals from different established breeds is called crossbreeding. The progeny produced is called crossbred. Purposes: To exploit hybrid vigour or heterosis Complementarity Development of new breeds or synthetics.

12. Types of crossbreeding

13. Types of crossbreeding

14. Two breed cross Two pure breed cross Inter se mating Back crossing Criss crossing

15. Two pure breed crosses

16. crossing of crossbred progeny having the same level of inheritance of two breeds like crossing of F1 with F1. Inter se mating

17. Back crossing Crossing of F1 generation progeny with either of its parents.

18. Criss -crossing It is similar to back crossing except that both the parental breeds (P1 and P2) are used alternately in each generation

19. Three-way cross or triple cross In this system of cross breeding three breeds are used (A, B, C). First generation crossbred female (AB) are crossed with males of third breed/line.

20. Four breed crosses or Double two breed crosses or Four-way cross Four breeds are used. In this four-way cross, the crossbred progeny from two separate two-way crosses are mated to produce commercial progeny called „double hybrids‟ (AB.CD).

21. Rotational crossing The males of two or three breeds are used in regular sequence (rotation) in successive generations on crossbred females of the previous generations. Thus it is called as rotational crossing which may involve two or three breeds. In pig breeding , this method have been used widely with different breeds for the production of market animals / hybrids.

22. Close inbreeding

23. Line breeding

24. The mating of unrelated individuals is called as outbreeding Outbreeding is the mating of animals which are distinctly less closely related to each other than the average of the population i.e. the individuals that have no common ancestors in the proceeding 4 to 6 generations of their pedigree. Outbreeding increases the heterozygosity and variability of the population. The general effects of outbreeding are the opposite of those of inbreeding. Outbreeding

25. Reason for Outbreeding

26. HETEROSIS or HYBRID VIGOUR

27. Heterosis G.H.Shull Heterosis is a phenomenon in which progeny of crosses between purebred populations or inbred lines exceed the average of the two parental populations. Heterosis is the superiority of the outbred animals (F1) over the average of their parents in individual merit.

28. HV is measured as the difference between the average performance of crossbreds and the average performance of their purebred parent lines or breeds, mathematically, HV = M F1 – M P Where HV = hybrid vigor measured in units of a trait M F1 = the average performance of crossbreds M P = the average performance of both parent lines = M P1 – M P2 2 Where M P1 = the average performance of the first parent line M P2 = the average performance of the second parent line Hybrid vigor is often expressed on a percentage basis %HV = M F1 – M P x 100 M P

29. For example, if 21 day litter weight average 98 lb for purebred pigs of breed A, 106 lb for purebreds of breed B, and 113 lb for F1 A x B cross pigs, then M p = M p1 +M p2 2 = 98 + 106 2 =102 lb and %H F1 = M F1 – M P M P = 113 - 102 x 100 102 = 10.8 %

30. Hybrid vigor MP1 MP MP2 MF1 MP1 MP MF1 MP2 Hybrid vigor

31. Here is another example, if milk production for breed A averages 12,000 lb, for breed B 18,000, and for F1 A x B crosses 16,000 lb then M p = M p1 +M p2 2 = 12,000 + 18,000 2 =15,000 lb and %H F1 = M F1 – M P M P = 16,000 - 15,000 x 100 15,000 = 6.7 %

32. Types of heterosis Parental heterosis : - Paternal heterosis - Maternal heterosis Individual heterosis :

33. Causes of heterosis Dominance Overdominance Epistasis Difference in gene freq. between two populations

34. Dominance AA Bb Cc dd 1 1 1 0.5 3.5 Kg Inbreding AA BB cc dd 1 1 0.5 0.5 3.0 Kg Outbreeding Aa Bb Cc Dd 1 1 1 1 4.0 Kg

35. Over dominance AA Bb Cc dd 1 1.5 1.5 0.5 4.5 Kg Inbreding AA BB cc dd 1 1 0.5 0.5 3.0 Kg Outbreeding Aa Bb Cc Dd 1.5 1.5 1.5 1.5 6.0 Kg

36. Additive AA Bb Cc dd 2 1.5 1.5 1 6.0 Kg Inbreding AA BB cc dd 2 2 1 1 6.0 Kg Outbreeding Aa Bb Cc Dd 1.5 1.5 1.5 1.5 6.0 Kg