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Samenvatting Genetic Improvement of Livestock

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  • 2 november 2022
  • 66
  • 2022/2023
  • Samenvatting
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michouweimar
Grade = 80% exam + 20% case

Case = 15% report + 5% presentation

Exam  4 open questions




Basic principles genetic improvement
Chapter 1: introduction
 What is the best animal?
 How do you breed animals so that their descendants will be better than today’s animals?
- This course



What is the best animal

 Best = relative & subjective
 Describe animal through traits
- Trait => any observable or measurable characteristic of an animal
- Observable trait = appearance
- Measurable trait = performance
- Trait = coat colour & weaning weight
 P+G+E
- Phenotype => observed categories or measured levels for traits
- Phenotypes = red, 343kg
- Genotype => genetic background for its phenotype
- Environmental effects => effects that external factors have on animal’s performance
 Importance of traits depends on: physical environment, management system & economic
factors
- Genotype determines degree to which animals are suited for their function in society
- Breeding objective => sensible goals for breeding programs


Selective breeding: past, present & future (L0)
Domestication selection
 Pre domestication: natural selection
- Genetic adaptation of organism to environment
- Survival of the fittest: fitness determined by nature
 Domestication => tame an animal, especially by generations of breeding
- Genetic adaptation of animals to new environment
- New env: captivity, food provided, protection
 Artificial selection => human determines fitness
- Selective breeding
- Selection for confirmation

, - Exploiting genetic variation



Selective breeding theory
 Mendelians vs biometricians
 Fisher
- Infinitesimal model => traits are result of infinite #genes each with small effect



Selection index theory

 Chapter 3
 Optimal weighing of info from relatives & traits
 I = b’ X
H = v’ A
Pb = Gv <-> b = P-1 Gv



Mixed model

 Chapter 5
 Addition to selection index theory
 Adjusts for systematic environmental differences




Infinitesimal model

 Most of the times: no clue about what genes affect trait
- Animal breeders practice genetics without genes



Genomics revolution
 Make polymorphisms visible in lab
 More cheap to genotype animal for SNPs
 Still hard to detect which gene affects which trait
- Trait affected by many genes
 Genomic selection
- Genomic selection can increase selection response  still without knowing genes



What has been achieved?

 Milk production NL
- Trend: +75kg milk/year

, - Selective breeding does not result in large & fast changes
- Effects of selective breeding are cumulative!  makes breeding unique
 Selection limits?
- There are limits, but we don’t know what they are
 Correlated responses
- By selecting, other parts can also be unconsciously modified
- Fertility decreases when milk yield increases in cows
 Balanced breeding
- Multiple trait selection (chapter 3)
- Economic values (chapter 4)
 Selection in broilers
- Fast growth, less feed required
- Improved efficiency of food production
- Discussion on responsible breeding
 Negative consequences of selective breeding can be avoided by balanced breeding 
multiple trait selection
- Mistakes will still be made: we don’t know everything
- Mistakes due to wrong breeding goal



Recent developments
 Global challenge regarding food security
- Increased demand for food
- Economics, environment & animal welfare
 Additional phenotypes: traits to include in breeding goal
- Methane emission reduction
- Longevity
 General problem genetic improvement
- Translate phenotypic observations into breeding values
- Select parents for next generation  improvement maximised, while maintaining
genetic diversity
- Extension of breeding goal with new traits (environmental impact)  novel tech
- Improve prediction of breeding values, inbreeding & phenotypes  based on genomic
info
- Understanding relation between genotype & phenotype  genome editing
 Novel phenotyping technologies
- Sensors (camera, sound, GPS)
- Omics (protein content, antibodies)
- Organoids in vitro (feed efficiency, stress)
 Genomic info & prediction
- Whole genome sequencing (lethal recessives, recombination)
- Gene expression
- DNA methylation
 Genome editing
- Precise insertion, deletion, or replacement of DNA with molecular scissors
- CRISPR-CAS

, Chapter 2: response to selection (L1)
Part I
 What are expected responses to selection of various plans?
 Basic principles of genetic improvement
 Understand different types of selection
 Understand key components of response to selection



Breeding goal => specific traits with their desired direction of change over generations

Genetic model

 Describe genetic quality
 Phenotypic value = breeding value + environmental effect (+ µ)




Heritability => proportion of var(P) due to additive genetic effects




 Other genetic models
- Repeated observations: repeatability (r)




Ep = permanent env effect
Et = temporary env effect
 Repeated measurements model
- Multiple offspring: common env effects (c2)




 Transmission model
 Breeding value => prediction of genetic merit
- A≠G
- Gives an indication of performance of offspring
- Bull with A = +1000 kg milk  daughters produce +500 kg more than average



Selection of parents = key to genetic improvement



Different types of selection

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