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1 Institute of Animal Science, Swiss Federal Institute of Technology, CH-8092 Zurich, Switzerland
This study was conducted to investigate the impact of censoring on the accuracy of sire evaluation for the length of productive life estimated by means of survival analysis using simulated and real dairy cattle data from the Swiss Braunvieh population. Data were simulated under a Weibull model with two fixed effects and a random sire effect with a sire variance of 0.04. Two different family structures investigated were 1000 sires with 10 daughters each and 200 sires with 50 daughters each. Sires were assumed to be related through their sires. The reference data were generated assuming no censoring. Sire effects were estimated from the reference data with and without considering the relationships among sires and referred to as the estimated transmitting abilities (ETA) of sires. The impact of censoring on accuracy of ETA and ranking of sires was investigated by computing rank correlations among true and estimated sire effects and among estimated sire effects from the reference data and from several different data files with increased proportion of censored records. Estimated transmitting abilities were generally more accurate with a large number of daughters. The rank correlations among the ETA of sires from the data with censored records and the ETA from the reference data decreased with an increased proportion of censored records. Considering relationships among sires resulted in higher rank correlations when the proportion of censored records was large. With 50 daughters per sire, accuracy of 70% can be achieved approximately 2 yr after first calving of the daughters with about 50% censored records. With the real data, a rank correlation with the ETA of sires from the reference data of 0.70 to 0.80 can be achieved with about 65% of records censored and about 2.5 yr after the first calving of the youngest daughters of the sires.
Key Words: length of productive life • genetic evaluation • censoring
Submitted on November 16, 1998
Accepted on May 28, 1999
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