Culling of dairy cows. Part I. Effects of diseases on culling in Finnish Ayrshire cows P.J. Rajala-Schultz a,b,* , Y.T. Gro Èhn a a Section of Epidemiology, Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA b Department of Clinical Veterinary Sciences, Faculty of Veterinary Medicine, University of Helsinki, PO Box 57, FIN-00014, Finland Accepted 9 March 1999 Abstract The effects of 15 diseases on time until culling were studied in 39727 Finnish Ayrshire cows that calved during 1993 and were followed until the next calving or culling. The diseases studied were: dystocia, milk fever, retained placenta, displacement of the abomasum, metritis, non-parturient paresis, ketosis, rumen disorders, acute mastitis, hypomagnesemia, lameness, traumatic reticuloperitonitis, anestrus, ovarian cysts, and teat injuries. Survival analysis, using the Cox proportional hazards model, was performed and diseases were modeled as time-dependent covariates. Different stages of lactation when culling can occur were also considered. Parity, calving season and herd were included as covariates in every model. Parity had a significant effect on culling, the risk of culling being four times higher for a cow in her sixth or higher parity than for a first parity cow. The effects of diseases varied according to when the diseases occurred and when culling occurred. Mastitis, teat injuries and lameness had a significant effect on culling throughout the whole lactation. Anestrus and ovarian cysts had a protective effect against culling at the time when they were diagnosed. In general, diseases affected culling decisions mostly at the time of their occurrence. The effect seemed to decrease with time from the diagnosis of the disease. However, milk fever, dystocia and metritis also had a significant effect on culling at the end of the lactation. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Culling; Cattle-management; Survival analysis; Time-dependent covariates Preventive Veterinary Medicine 41 (1999) 195±208 * Corresponding author. Tel.: +1-607-253-3572; fax: +1-607-2533083; e-mail: pjr5@cornell.edu 0167-5877/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII:S0167-5877(99)00046-X