Ripon Chandra Paul PhD Associate Professor Dept of Genetics and Animal Breeding FANSVM PSTU What is selection Selection is process of preferring or allowing certain individual in a population to become parent of the next generation while depriving other of this opportunity ID: 1012280
Download Presentation The PPT/PDF document "Selection in Animal breeding" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
1. Selection in Animal breedingRipon Chandra Paul, PhDAssociate ProfessorDept. of Genetics and Animal BreedingFANSVM, PSTU
2. What is selection Selection is process of preferring or allowing certain individual in a population to become parent of the next generation while depriving other of this opportunity. It is the keystone of the arch of animal or poultry improvement. The opposite word of selection is culling.
3. Types of selectionGenerally two types Natural selection/ automatic selection: Controlled by natural forces. Darwin’s Theory :Survival for the fittest in a particular environment 2. Artificial selection/ deliberate selection: Practiced by animal breeders or commercially used.
4. Types of selection
5. Genetic effects of Artificial selectionfA=0.5; fa = 0.5P1: AA X aaG1 A X aF1 AafA=0.5; fa = 0.5P2: AA X AaG2 A.A X A.aF2 AA. 2Aa. aafA=0.67; fa = 0.33Gene frequency constant generation after generationA= desirable genea = undesirable gene Gene frequency changes due to selection and culling F3 Select: AA, Aa and cull aa
6. Components of Selectiona. Selection objectiveb. Selection criteriac. Recording d. identification of superior animals using recordse. Efficient use of selected animals for maximizing genetic progress
7. Selection ObjectivesTo produce desirable progenyTo change gene frequency to better fit animals/ birdsIncreased overall profit per birdsTo attain higher meat, egg and body weight, etc.
8. Selection Criteria Selection criteria are the characters which are evaluated in order to predict the breeding value. Properties of selection criteria Closely related to the objective Measurable in both sexes, early in life, preferably before sexual maturity Measurable in terms of ease, speed, accuracy and cheapness
9. Selection MethodsSingle trait selection Multi trait selection
10. Selection MethodsSingle trait selection: Selection of animals based on one trait only. It is 4 types- Individual/Mass selectionFamily selection Pedigree selection Progeny testing
11. Individual/Mass SelectionIndividuals are selected on the basis of its own performance or own merit No consideration of father or mother performance. The term “Individual selection’ is used incase of large animals like cattle, sheep, goat, etc. and the term “Mass selection” is used incase of poultry.
12. Individual/Mass SelectionApplicationCharacters with moderate to high heritability. E.g. Body weight, growth rate, weight gain, etc.Characters which can be measured in both sexes. i.e. both male or female.
13. Individual/Mass SelectionDisadvantages Characters which are sex limited like egg production can only be measured in female. For low heritable traits (0.05-0.10) like viability, the individual merit is a poor indicates of its breeding value. Performance record like egg production cannot be measured in the early life of individual until they come into production.
14. Family Selection In family selection, whole families are selected or rejected according to the mean phenotypic value (average performance) of the family. Family may be of (i) Full sib family (ii) Half sib family. Family selection may be practiced when family size is large. Family selection is mainly practiced in poultry in developing special strain for production. For breeding practice, male from one family are mated with female of other family to avoid inbreeding.
15. Family SelectionApplication When the heritability of characters is low. eg. Egg production, Fertility, etc. When the characters are sex-limited. eg. Egg production, Semen production, etc. When the characters cannot be measured in live individuals. eg. Dressing percentage, Meat quality, etc.
16. Pedigree SelectionSelection on the basis of ancestor performance is called pedigree selection.
17. Pedigree SelectionPedigree selection depends on- The degree of relationship between the ancestor and the individual. An individual is related by 0.50 to each parent, 0.25 to each grandparent and 0.125 to each great-grandparent, providing no inbreeding is involved.The degree of heritability of the trait.Environment correlations among animals used in the prediction.
18. Pedigree SelectionApplication Sex limited traits i.e. milk yield.For the characters which can be measured relatively late in life or early life i.e. litter size in sow, lambing performance in ewe. It is important in detecting carriers of recessive genes.It helps to increase the accuracy of individual selection.
19. Pedigree SelectionDisadvantages Good performance records on each ancestor as compared to its own contemporaries.
20. Progeny TestingSelection on the basis of progeny performance that is to keep or cull a sire or dam on the basis of average merit of their offspring as compared to the average merit of the progeny of contemporary sires and dams.
21. Progeny TestingThe genetic principle behind progeny testing is simple. Progeny represents a sample of the gene of their father (mother) and if enough samples are drawn, these will give a reasonable idea of the superiority of that sire. The performance of a bull tells one what he might do if it is used, Pedigree tells what he ought to be , Whereas a progeny test tells ones what he is doing. Pedigree is Promise but progeny is proof
22. Progeny testingApplication for low inherited traits (0.01-0.10)for traits expressed in one sex only i.e. milk yield for traits expressed in only after death of the individual i.e. carcass quality and quantity, dressing percentage, etc.
23. Multi trait selection:Selection is practiced for several traits simultaneously to improve the overall merit of the individuals.Methods of Selection:Tandem methodIndependent Culling Level methodSelection Index or total score method Selection Methods
24. Multi trait selection. Practiced for improvement of several traits but at different times.Selection will continue for all the traits one by one.Efficiency depends on the genetic correlation among the traits under selection.Tandem method
25. AdvantagesThis method is easy to understand and easy to conduct.If genetic correlation between the traits is positive then improvement in any one trait would lead improvement in the correlated traits.Tandem Method
26. Disdvantages This method is less efficient than other methods.The genetic progress is less.It requires more time for improvement in all the traits.An undesirable genetic correlation between two traits would neutralize the genetic progress made in any one trait.Tandem Method
27. Independent Culling Level Two or more traits are taken at a time for selection of an individual.A minimum standard (level) is fixed for each and every trait.Each and every animal has to achieve the target fixed for each character for its selection.If an animal fails to meet the minimum standard fixed for any one character will be rejected even though it is exceptionally good for all other traits.
28. Example: ICL method of selection in buffaloTraitsStandard SetBuffalo No.12Age at first calving(AFC ,months)424044Lactation Milk Yield, (LMY, Kg)180018502200Fat %776.5Independent Culling Level
29. Advantages It is superior to tandem method because selection is practiced for more than one trait at a time.Culling process may be started at the early age for the traits expressed at early age.Independent Culling Level
30. DisadvantagesIt is inferior to Selection index or total score method.No compensation for superiority of an excellent trait.More emphasis is given to the traits expressed at early life. Intensity of selection is reduced with the increase in number of traits.Only mediocre animals are selected.Independent Culling Level
31. Selection Index/Total scoreSelection index is the numerical score assigned to an individual to estimate its breeding value on the basis of economic weight of the traits considered for selection. The animal with the highest score is then selected for breeding. Selection index was developed by Prof. R A Fisher in 1936 and first used for genetic improvement in animals by Hazel in 1943.
32. Selection index is the sum of the product of phenotypic value with the respective economic weight of different characters incorporated into the index. Selection index, I = ∑bixi = b1.x1 + b2.x2 + b3.x3 + ………….. + bn.xnWhere, xi (x1, x2, x3 ……..xn) represents the phenotypic values for different traits ‘bi’ are the weighting factors (partial regression coefficient) given to each trait.Selection Index
33. AdvantagesSuperior method.Overcomes disadvantages shown by tandem and ICL.More balanced approach since it combines information of various traits on the basis of their economic importance.Selection Index
34. AdvantagesIt allows individuals which are superior in some traits to be selected regardless of their inferiority in other traits.Efficiency of S.I. increases with the increase in the number of traits to be selected but the response in the individual traits become less.Hence, only those traits considered more important should be included into the index.Selection Index
35. THANK YOU