Animal Breeding & Genetics Exam 2- Lecture 12: Multiple Trait Selection

What is an example of an aggregate breeding value utilized by the American Angus Association?

The $ profit EPDs.

Which of the following selection practices is in reality just a form of single trait selection:  tandem selection, independent culling levels, and economic selection indexes?

Tandem selection.

What are the advantages and disadvantages of tandem selection?

 

Advantages- Allows for faster improvement of a single trait; especially important for responding to market changes

Disadvantages- Highly susceptible to unfavorable genetic correlations. Switching focus to another trait may diminish progress made in the original trait

What are the advantages and disadvantages of independent culling levels?

Advantages

•Simple to execute

•Culling can be applied in a sequential order to reduce costs (ie. BW, WW, YW)

Disadvantages

•Can be difficult to determine appropriate parameters

•Strict exclusion could eliminate more advantageous animals

What are the advantages and disadvantages of economic selection indexes?

 

Advantages

•Most precise form of multi-trait selection

•Focus is placed on profitability not traits per se

Disadvantages

•Difficult to construct appropriately weighted models

•Economic variables are not fixed and thus the model is not entirely robust;  it must be altered as market conditions change

•It may promote or accept extremes which may become problematic at some point

Which of the following selection practices would a large commercial operation most readily utilize:  tandem selection, independent culling levels, and economic selection indexes?

Economic selection index.

Can multi-trait selection strategies be combined to yield more favorable selection practices?  Give an example.

 

Yes, to use tandem selection and economic selection index in order to select for a single trait that is economically relevant.

Describe the relationship between multi-trait selection and selection intensity?  Will selection intensity be increased or decreased with the more traits that you select at one time? 

The more traits you select for, the higher the selection intensity gets.

Consider a situation in which I am selecting for increased rib eye area and increased marbling (two unfavorably related traits).  Would selection intensity be greater or less if I were selecting for increased rib eye area and yearling weight (two favorably related traits)?  Why?

 

Selection intensity is greater when selecting for favorably related traits, because you do not have to lower your standards to find animals that quality.