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Major advances in determining appropriate selection goals.
1Dairy Science Department, University of Wisconsin-Madison, 53706-1284, USA. geshook@wisc.edu
Journal of Dairy Science
|March 16, 2006
Summary
Genetic selection has boosted dairy cow milk production significantly over 20 years, but also increased calving to conception intervals. Incorporating non-yield traits into selection indexes is crucial for balanced genetic improvement in dairy cattle.
Area of Science:
- Animal Genetics and Breeding
- Dairy Science
- Reproductive Biology
Background:
- Dairy cattle breeding has achieved substantial yield increases (milk, fat, protein) over the past two decades.
- Concurrent with yield gains, a negative trend in reproductive efficiency (increased calving to conception interval) has been observed.
- Genetics plays a significant role, accounting for a large portion of yield improvements and contributing to reproductive changes.
Purpose of the Study:
- To analyze the impact of genetic selection on dairy cow yield and reproductive traits over the last 20 years.
- To evaluate the evolution and effectiveness of selection indexes in incorporating both yield and non-yield traits.
- To explore the potential of molecular genetics in future dairy cattle improvement strategies.
Main Methods:
- Analysis of genetic trends for milk, fat, protein yield, productive life, conception interval, and somatic cell score.
- Review of the historical development and components of selection indexes, including the integration of non-yield traits.
- Examination of molecular genetic studies and the potential application of DNA markers and major gene discovery.
Main Results:
- Significant genetic gains in yield traits (1.7 genetic SD) and productive life (1.2 genetic SD) since 1980.
- Unfavorable genetic trends observed for conception interval (1.0 genetic SD) and somatic cell score (0.12 genetic SD).
- Selection indexes have evolved to include non-yield traits, with economic weights increasing to 45%, improving theoretical selection responses.
Conclusions:
- Genetic selection has driven substantial yield increases but requires careful balancing with reproductive and health traits.
- The inclusion of non-yield traits in selection indexes is a critical advancement for holistic dairy cattle improvement.
- Future genetic evaluations and selection indexes will benefit from advances in molecular genetics, including genome sequencing and major gene identification.