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Selection within and across populations in livestock improvement
Journal of Animal Science
|June 1, 1991
Summary
Combined selection, integrating genetic evaluations across populations, enhances genetic gain. This strategy is particularly beneficial for smaller populations and can help poorer populations improve over time, impacting breeding strategies.
Area of Science:
- Animal breeding and genetics
- Quantitative genetics
- Population genetics
Background:
- Genetic evaluations enable ranking and selection of breeding individuals within and across populations.
- Combined selection, integrating individuals from multiple populations, is theoretically superior to within-population selection.
- Factors influencing combined selection benefits include population size, number of populations, initial genetic means, and breeding objective similarity.
Purpose of the Study:
- To evaluate the advantages of combined selection across populations.
- To assess the impact of population size, initial genetic means, and differing breeding objectives on selection response.
- To provide insights into optimal breeding strategies for genetic improvement.
Main Methods:
- Deterministic evaluation of combined selection using a common truncation line for estimated breeding values (EBVs).
- Analysis of selection response based on population sizes (100 to 1,000 males), initial genetic means, and genetic correlation of economic merit.
- Modeling scenarios with identical and differing initial genetic means and breeding objectives.
Main Results:
- Combined selection consistently increases overall response rates in cooperating populations.
- Small populations (100 males) show substantial benefits, while large populations (500-1,000 males) also benefit, though to a lesser extent.
- When initial genetic means differ, the genetically poorer population can improve and contribute to overall gains within 3-5 generations.
- Divergent breeding objectives lead to populations becoming less complementary and eventually separating.
Conclusions:
- Combined selection offers significant advantages for genetic improvement across populations, especially for smaller ones.
- The effectiveness of combined selection is influenced by population structure, genetic parameters, and the alignment of breeding goals.
- This approach has direct implications for designing breeding programs to maximize rates of genetic change and improve population structures.