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A comparison of a linear and proportional hazards approach to analyse discrete longevity data in dairy cows

Published online by Cambridge University Press:  18 August 2016

R. Lubbers ,
S. Brotherstone ,
V.P. Ducrocq  and
P.M. Visscher
R. Lubbers
Affiliation:
University of Edinburgh, Institute of Ecology and Resource Management, West Mains Road, Edinburgh EH9 3JG Wageningen Agricultural University, PO Box 338, 6700 AH Wageningen, The Netherlands
S. Brotherstone
Affiliation:
University of Edinburgh, Institute of Cell, Animal and Population Biology, West Mains Road, Edinburgh EH9 3JT
V.P. Ducrocq
Affiliation:
Station de Génétique Quantitative et Appliquée, Institut National de la Recherche Agronomique, 78352 Jouy-en-Josas, France
P.M. Visscher*
Affiliation:
University of Edinburgh, Institute of Ecology and Resource Management, West Mains Road, Edinburgh EH9 3JG
*
† Corresponding author.
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Abstract

The objective of this study was to compare two methods for analysis of longevity in dairy cattle. The first method, currently used for routine genetic evaluation in the UK, uses a linear model to analyse lifespan, i.e. the number of lactations a cow has survived or is expected to survive. The second method was based on the concept of proportional hazard, i.e. modelling the conditional survival probability of a cow as a function of time. Comparisons were based on estimated heritabilities, ranking of estimated breeding values of sires, estimated effects of covariates used in the final models, and the distribution of residuals. The same data set, 21497 observations on the number of lactations cows had survived, was used for both analyses, even in the presence of censored observations. Cows in the data were progeny of 487 sires. Heritability estimates for lifespan or survival were approximately 0·06 for both methods, using the definition of heritability on a logarithmic scale for the proportional hazards model. Correlations between breeding values for sires were high, with absolute values ranging from 0·93 to 0·98, depending on the model fitted. It was concluded that it may be justified to use the standard Weibull model even for discrete time measures such as the number of completed lactations, but that more research is needed in the area of discrete time variates.

Keywords

dairy cattleheritabilitylifespanlongevitysurvival
Type
Breeding and genetics
Information
Animal Science , Volume 70 , Issue 2 , April 2000 , pp. 197 - 206
Copyright
Copyright © British Society of Animal Science 2000

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