J Dairy Sci 2001 Sep;84(9):2073-80
Department of Mathematics and Statistics, Utah State University, Logan 84322, USA.
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J Dairy Sci 2004 Oct;87(10):3518-25
Department of Dairy Science, niversity of Wisconsin, Madison 53706, USA.
Breeding values of Holstein sires for daughter longevity in each of 9 geographical regions of the United States were predicted using a Weibull proportional hazards model. Longevity (also commonly referred to as herd life or length of productive life) was defined as the number of days from first calving until culling or censoring. Records from 2,322,389 Holstein cows with first calving from 1990 to 2000 were used. Read More
J Dairy Sci 2005 Jan;88(1):368-75
Agriculture and Agri-Food Canada, Guelph, ON, N1G 4T2, Canada.
The objectives of this study were to identify the most important factors that influence functional survival and to estimate the genetic parameters of functional survival for Canadian dairy cattle. Data were obtained from lactation records extracted for the May 2002 genetic evaluation of Holstein, Jersey, and Ayrshire breeds that calved between July 1, 1985 and April 5, 2002. Analysis was performed using a Weibull proportional hazard model, and the baseline hazard function was defined on a lactation basis instead of the traditional analysis of the whole length of life. Read More
J Dairy Sci 1999 Oct;82(10):2178-85
Institute of Animal Science, Swiss Federal Institute of Technology, 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. Read More
J Dairy Sci 2004 May;87(5):1469-76
Department of Dairy Science, University of Wisconsin, Madison 53706, USA.
Predicted transmitting abilities (PTA) of US Jersey sires for daughter longevity were calculated using a Weibull proportional hazards sire model and compared with predictions from a conventional linear animal model. Culling data from 268,008 Jersey cows with first calving from 1981 to 2000 were used. The proportional hazards model included time-dependent effects of herd-year-season contemporary group and parity by stage of lactation interaction, as well as time-independent effects of sire and age at first calving. Read More