Genetic Change
Estimated Breeding Values are used to optimize mating and choose the the parents of the next generation. It also allows us to keep track of the success of selections and the effect on the genetic average of a population.
Measuring Genetic Change
- By Year of Birth
- Measure animals that were born and kept in the herd for milk production. Has a big standard error, but over long periods a trend will emerge.
- By Year of Production
- Measuring each animal that lactated in each year of production. Again shows who is kept in herd for milk production.
- Trends in Males
- Have to be stricter on males because a small percentage of the calves born are chosen to be sires of the next generation. Therefore, the average EBV of bull calves will be higher than that of female.
- Can average EBV of bull chosen to breed. Bulls can still breed but be a less popular choice than others.
Pathway Selection
- Sires of males (SF) - Represent the best 5% of all males chosen for breeding
- Sires of females (SF) - Choosing the males who will breed with female population
- Dams of Males (DM) - Choosing females from which to obtain males for breeding
- Dams of females (DF) - Choosing Females for breeding to produce future female replacements
Predicting Genetic Change
$EBVprogency = 0.5*(EBVsire+EBVdam)$
Formula for predicting genetic change assuming the initial population is normal distributed:
- $ΔG$ - genetic change in trait,
- $rT_I$ - accuracy of selection
- $i$ - selection intensity
- $σ_a$ - the additive genetic standard deviation of the trait
- $L$ - generation interval in years