20: Breeding Programs pt2 Flashcards
Important factors to consider when buying or retaining heifers
- individual growth performance and feed efficiency
- ability to stay in the herd as profitable unit (fertility and longevity)
- potential to promote genetic improvement and increase production rates of the herd
Economic costs associated with replacement heifers
- market value of purchase
- opportunity cost: revenue a producer foregoes when retaining a heifer rather than selling them at weaning ($/Lb weaned)
- cash cost: expenses incurred from wean to the point of pregnancy
- lost opportunity cost: cash lost for not weaning a calf (died before weaning, aborted, open cows)
Examples of traits used as selection criteria to achieve the breeding goals for replacement heifers
Birth weight, 200d weaning weight, age at first calving
Heifer rebreeding (failure or success), RFI
Number of offspring over lifetime productivity
Slide 15
Multi-trait selection index for replacement heifer selection
What is genetic diversity
Measure of genetic differences between animals in a pop
Presence of various number of alleles with different distribution frequencies in certain populations
Variation of genomes at the individual level or at the species level
The more alleles present, the…
larger the genetic diversity
With no genetic diversity, what happens?
Selection will not result in improvement in the next generation
factors influencing genetic diversity, their effects
Mutation = increased diversity
Selection = lose diversity
Genetic drift = lose diversity
emigration = lose, immigration= gain
Equation for genetic diversity
DeltaG = h^2 * sd * a * (i/t)
How does inbreeding affect genetic diversity
Inbred animals produce fewer unique gametes and therefore fewer unique zygotes leading to low variability in their progeny
Does mating of relatives lead to permanent loss of genetic diversity?
Temporary, if you stop mating closely related animals on purpose and use random mating instead, cause of inbreeding would disappear
Does genetic drift lead to permanent loss of genetic diversity?
Yes, alleles are lost forever
What is genetic drift
Random change in allele frequencies within a population from one generation to another due to sampling events
Three reasons we care about genetic diversity
- Allows for flexibility and adaptability in a population (more suitable under selection pressures)
- Prevents inbreeding depression
- Reduced genetic diversity results in increased homozygosity, and the frequency of alleles that have deleterious effects
Is genetic diversity restricted to within a breed?
No, comprises within and between breeds
When can genotyping/knowing DNA markers help measure diversity (2)
- when it is impossible or very costly to observe pedigree directly
- estimate actual proportion of DNA shared by relatives more precisely than pedigree information
Genotyping animals (DNA markers) provides opportunities to… (4)
- evaluate genetic diversity by allele frequency
- estimate genomic breed composition or genetic distance between breeds
- estimate frequency of heterozygotes
- count the number of different alleles in a population
How do we monitor genetic diversity
- deltaG
- monitor rate of inbreeding (deltaF)
- monitor population size
What is the rate of inbreeding (deltaF)? How do we increase/decrease it
- change in average inbreeding level in a population from one generation to the next
- can be temporarily decreased by avoiding mating of related animals, increased by mating related animals
Equation for rate of inbreeding
deltaF = (F2-F1)/Gi
How does population size affect genetic diversity
Larger population size, lower chances for random drift and inbreeding
Three ways of preventing loss of genetic diversity
- Increase the size of the effective population
- Implement restrictions in the use of parents (avoid excessive use of certain animals)
- mating schemes to control and manage relationships
How to increase size of the effective population
- import animals or genetic material (semen/embryos) from another population
- implement mating strategies such as outbreeding
- use more sires and dams, decrease selection intensity
