HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Interpretive Summary Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sæbø, S. Articles by Aastveit, A. H. Search for Related Content PubMed PubMed Citation Articles by Sæbø, S. Articles by Aastveit, A. H.

Genetic Evaluation of Mastitis Resistance Using a First-Passage Time Model for Wiener Processes for Analysis of Time to First Treatment

¹ Department of Chemistry, Biotechnology, and Food Science, and
² Department of Animal and Aquacultural Sciences, Agricultural University of Norway, N-1432 Å s, Norway

Corresponding author: S. Sæbø; e-mail: solve.sabo{at}ikbm.nlh.no.

A Wiener process is a Brownian-motion process initiated in a certain state in a state space, and the first passage time is defined as the time of the process to reach a predefined absorbing state where the process stops. Time from 31 d prepartum to first treatment of clinical mastitis (CM) was modeled as first passage times of such Wiener processes. Two processes were used to allow for several risk factors, and for each process, initiation was at some arbitrary time point, in a certain health state with drift toward or away from absorption (disease). The drift parameter of each process was expressed as linear functions of covariates (year of calving and sire). First passage time was de-fined as the time from process initiation until the first health status process reached zero (absorption). The model was fitted to records for 36,178 first-lactation daughters of 245 Norwegian cattle sires using a Bayesian approach and Markov chain Monte Carlo methods. Genetic evaluation of sires was carried out by calculating the posterior probability of no CM (the value of the survival function) by d 331, i.e., 300 d after first calving. Alternatively, sire evaluation was based on the integrated area under the survival curve. These measures were highly correlated (0.999), which indicates a small degree of crossings of the sire-dependent survival curves. Hence, sire-specific hazards were close to proportional, resulting in a higher rank-correlation to sire evaluations from a survival model with proportional hazards than to the results from a multivariate threshold model.

Key Words: genetic evaluation • clinical mastitis • survival analysis • Wiener process

Abbreviation key: AIS = adjusted and integrated survival function, CM = clinical mastitis, NRF = Norwegian cattle, S = survival function (probability of no treatment of CM by time T)

This article has been cited by other articles:

				E. Carlen, U. Emanuelson, and E. Strandberg Genetic evaluation of mastitis in dairy cattle using linear models, threshold models, and survival analysis: a simulation study. J Dairy Sci, October 1, 2006; 89(10): 4049 - 4057. [Abstract] [Full Text] [PDF]