2010-Cecchinato_et_al_b - A comparison between different...

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A. Cecchinato, O. González-Recio, E. López de Maturana, L. Gallo and P. Carnier piglet preweaning survival in a dry-cured ham-producing crossbred line A comparison between different survival and threshold models with an application to doi: 10.2527/jas.2009-2460 originally published online February 26, 2010 2010, 88:1990-1998. J ANIM SCI http://jas.fass.org/content/88/6/1990 the World Wide Web at: The online version of this article, along with updated information and services, is located on www.asas.org by guest on June 14, 2011 jas.fass.org Downloaded from
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ABSTRACT: Different approaches for predicting ge- netic merit of piglet preweaning survival were compared using proportional hazard, threshold (TM), and sequen- tial threshold (STM) models. Data were from 13,924 crossbred piglets (1,347 litters), born from 2000 to 2006, and originated by mating 189 Large White C21 Gorza- gri boars to 328 Large White-derived crossbred sows. A frailty proportional hazard model was fitted assuming 2 different baseline hazard functions (Cox and Weibull time-dependent model) and including sire and nursed litter as random effects. The TM and STM included the same effects as considered in the proportional hazard model. Model fitting was evaluated in terms of good- ness of fit and predictive ability. The goodness-of-fit was evaluated using the local weighted regression and the mean squared error, whereas the predictive ability was assessed by using a cross-validation procedure. Es- timated sire variances for piglet preweaning mortality were low, and heritability ranged from 0.04 to 0.06. All 4 models led to similar ranking of sires. Results suggest that STM may be preferred to the other models for genetic evaluation of piglet preweaning survival, both for its better predictive ability and its easier interpreta- tion. Further, STM is computationally less demanding than survival models and allows for estimating different variance components from birth up to weaning. Key words: piglet, preweaning mortality, survival analysis, threshold model ©2010 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2010. 88:1990–1998 doi:10.2527/jas.2009-2460 INTRODUCTION Preweaning mortality of piglets has become an im- portant issue because of economic and animal welfare concerns (Grandison et al., 2002). Recent studies used different approaches and methodologies to analyze preweaning survival. One possible option is to consider survivability as a binary outcome (e.g., 0 = alive at time t ; 1 = dead at time t ), and analyze it using a thresh- old model ( TM ; Gianola, 1982; Gianola and Foulley, 1983). Most investigations have traditionally used lin- ear models to analyze piglet mortality (or piglet sur- vival) assuming the continuous distribution of the trait, but ignoring its categorical nature and censoring (Van Arendonk et al., 1996; Knol et al., 2002). Another pos- sible approach is the analysis of failure time during the period of interest (i.e., time from birth to death) with regression models (Cox, 1972; Prentice and Gloeckler, 1978). The advantage of using a time-to-event model is that there is no need to restrict the observations to an
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This note was uploaded on 01/26/2012 for the course ECON 2272 taught by Professor Gay during the Spring '08 term at Birmingham-Southern College.

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2010-Cecchinato_et_al_b - A comparison between different...

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