The possibilities for and problems with including information from later lactations are discussed. The breeding goal (H ) should reflect lifetime performance. The best way to ensure this in a complex industry situation is to use a systems analysis approach when calculating economic weights in H. Multiple-trait models seem to practically eliminate the problems with selection bias in parameter estimation and breeding value prediction but problems with preferential treatment will persist. Including information on later lactation yield improves the data structure and accuracy o f prediction and has been shown to increase expected genetic improvement even if young bulls only have 1st lactation daughters when selected. Apart from yield, the change in yield from 1st to 2nd lactation could be o f additional value, as well as mastitis, somatic cell counts, udder traits, and dystocia in later lactations. In a single-stage selection it is probably enough to include a part (4-5 mo) of 2nd lactation to avoid a large increase in generation interval. Also, the choice o f progeny-tested bulls to be mated to elite dams could be based on 1st lactation information while the selection of bull calves for entry into progeny testing could be based on 1st and 2nd lactation information, then available on half-sisters o f the bull. Stayability to e.g. 17 mo o f productive life adjusted for, at least, milk yield could possibly be used as a proxy for disease, conformation, and workability traits. Alternatively, stayability could be used to predict future daughter life length for use in a total merit index.

E. Strandberg

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XIV. Dairy cattle genetics and breeding, adaptation and conservation., , 5–14, 1990
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