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Development of a Survival Model with Piecewise Weibull Baselines for the Analysis of Length of Productive Life of Holstein Cows in Japan

Y. Terawaki^*,1, T. Katsumi and V. Ducrocq

^* Dairy Science Institute, and
The Graduate School of Dairy Science, Rakuno Gakuen University, 069-8501 Ebetsu, Japan
Station de Génétique Quantitative et Appliquée, Département de Génétique Animale, Institut National de la Recherche Agronomique, 78352 Jouy en Josas, France

¹ Corresponding author: terawaki{at}rakuno.ac.jp

A total of 100,000 records of Holstein dairy cows in Hokkaido, Japan, were used to study the current characteristics of their length of productive life, to build up a suitable model for genetic survival analysis, and to apply the piecewise Weibull baseline model. The data for this analysis only included records of cows belonging to herds in which more than 60% of cows had type score. Compared with other studies, the proportions of cows with only 1 or 2 calvings were low (24 and 46%, respectively), indicating a very low culling rate in first or second parity in Hokkaido. The median length of productive life was about 1,250 d (3 yr and 5 mo). Four different definitions of stages of lactation were studied. The best fit of the data was obtained when stages of lactation were chosen with cutpoints at 0, 60, 250, and 350 d after calving. Whatever the definition of stages of lactation, the piecewise Weibull baseline model was better than a unique baseline model. The estimated shape Weibull parameters for the different parity x stage of lactation combinations varied greatly (1.0 to 5.0). The estimated hazard functions based on the piecewise Weibull baseline model were smooth and reflected the important changes in observed hazard within lactation. The results of this study are expected to contribute to the development of a genetic model for sire evaluation and to genetic improvement of length of productive life of Holstein cattle in Hokkaido, Japan.

Key Words: survival model • piecewise Weibull baseline • longevity • survival analysis

This article has been cited by other articles:

				Y. Terawaki and V. Ducrocq Nongenetic effects and genetic parameters for length of productive life of Holstein cows in Hokkaido, Japan J Dairy Sci, May 1, 2009; 92(5): 2144 - 2150. [Abstract] [Full Text] [PDF]