20: Breeding Programs pt2

Question 1

Important factors to consider when buying or retaining heifers

Answer 1

• 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

Question 2

Economic costs associated with replacement heifers

Answer 2

• 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)

Question 3

Examples of traits used as selection criteria to achieve the breeding goals for replacement heifers

Answer 3

Birth weight, 200d weaning weight, age at first calving

Heifer rebreeding (failure or success), RFI

Number of offspring over lifetime productivity

Question 4

Slide 15

Answer 4

Multi-trait selection index for replacement heifer selection

Question 5

What is genetic diversity

Answer 5

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

Question 6

The more alleles present, the…

Answer 6

larger the genetic diversity

Question 7

With no genetic diversity, what happens?

Answer 7

Selection will not result in improvement in the next generation

Question 8

factors influencing genetic diversity, their effects

Answer 8

Mutation = increased diversity
Selection = lose diversity
Genetic drift = lose diversity
emigration = lose, immigration= gain

Question 9

Equation for genetic diversity

Answer 9

DeltaG = h^2 * sd * a * (i/t)

Question 10

How does inbreeding affect genetic diversity

Answer 10

Inbred animals produce fewer unique gametes and therefore fewer unique zygotes leading to low variability in their progeny

Question 11

Does mating of relatives lead to permanent loss of genetic diversity?

Answer 11

Temporary, if you stop mating closely related animals on purpose and use random mating instead, cause of inbreeding would disappear

Question 12

Does genetic drift lead to permanent loss of genetic diversity?

Answer 12

Yes, alleles are lost forever

Question 13

What is genetic drift

Answer 13

Random change in allele frequencies within a population from one generation to another due to sampling events

Question 14

Three reasons we care about genetic diversity

Answer 14

• 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

Question 15

Is genetic diversity restricted to within a breed?

Answer 15

No, comprises within and between breeds

Question 16

When can genotyping/knowing DNA markers help measure diversity (2)

Answer 16

• when it is impossible or very costly to observe pedigree directly
• estimate actual proportion of DNA shared by relatives more precisely than pedigree information

Question 17

Genotyping animals (DNA markers) provides opportunities to… (4)

Answer 17

• 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

Question 18

How do we monitor genetic diversity

Answer 18

• deltaG
• monitor rate of inbreeding (deltaF)
• monitor population size

Question 19

What is the rate of inbreeding (deltaF)? How do we increase/decrease it

Answer 19

• 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

Question 20

Equation for rate of inbreeding

Answer 20

deltaF = (F2-F1)/Gi

Question 21

How does population size affect genetic diversity

Answer 21

Larger population size, lower chances for random drift and inbreeding

Question 22

Three ways of preventing loss of genetic diversity

Answer 22

1. Increase the size of the effective population
2. Implement restrictions in the use of parents (avoid excessive use of certain animals)
3. mating schemes to control and manage relationships

Question 23

How to increase size of the effective population

Answer 23

• import animals or genetic material (semen/embryos) from another population
• implement mating strategies such as outbreeding
• use more sires and dams, decrease selection intensity