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Title:   Author  item
                                            Vanraden, Paulitem
                                            Wiggans, George
  Submitted to: AIPL Research Reports
                                    Publication Type: Government Publication
                                    Publication Acceptance Date: 1/31/2001
                                    Publication  Date: N/A
                                    Citation: N/AInterpretive Summary: Genetic merit for longevity of dairy cattle can be predicted from both direct and indirect measurements of correlated traits (multitrait analysis). Advantages of multitrait analysis are greatest when daughters are in first lactation because yield and type data arrive before culling information. In August 2000, methods to compute multitrait  evaluations for productive life (PL) were updated at the Animal Improvement Programs Laboratory, and new programs were developed to combine direct and indirect information about longevity. Information on milk, fat, and protein yields; somatic cell score; and udder, feet and legs, and body size composites was included to increase the accuracy of PL evaluations. Revised genetic parameters were used for November 2000 PL calculations. The new parameters generally reduced the influence of information from yield, type, and health traits on PL. Correlations among  evaluations for yield and PL tended to be lower for bulls born in recent years than for those born in earlier years. Genetic merit for PL was more highly correlated with genetic merit for milk yield than with protein yield for earlier bulls but is more highly correlated with protein yield for recent bulls. Accuracy of the new multitrait PL evaluations was higher than single-trait accuracy, especially for recent bulls and cows, which should allow dairy breeders to select for animals with greater herd longevity.
                                Technical Abstract: Genetic merit for productive life (PL) can be predicted from both direct and indirect measurements of correlated traits (multitrait analysis). In August 2000, methods to compute multitrait PL evaluations were updated at the Animal Improvement Programs Laboratory, and new programs were developed to combine direct and indirect information about longevity.  Information on milk, fat, and protein yields; somatic cell score; and udder, feet and legs, and body size composites was included to increase the accuracy of PL evaluations. Revised genetic parameters were used for November 2000 PL calculations. The new parameters generally reduced the influence of information from yield, type, and health traits on PL. Across all breeds, 17 hours were required to obtain parent averages for the eight traits, to estimate Mendelian sampling for PL from Mendelian sampling of correlated traits, to adjust progeny PL evaluations for multitrait PL  evaluations of parents, and to compute net merit indexes for all bulls and cows. Correlations among evaluations for yield and PL tended to be lower for bulls born in recent years than for those born in earlier years. Genetic merit for PL was more highly correlated with genetic merit for milk yield than with protein yield for earlier bulls but is more highly correlated with protein yield for recent bulls. The changes in PL parameters between August and November 2000 evaluations caused November multitrait PL evaluations to become more similar to single-trait PL evaluations that were reported before August. Reliability of multitrait PL evaluations was 69% in August for bulls born during 1990 through 1995 but decreased to 65% in November with the lower genetic correlations. Average reliability for single-trait PL evaluations was 62%.


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