Livestock Production Science 81 (2003) 183–195 www.elsevier.com / locate / livprodsci Genetic parameters and evaluations from single- and multiple- trait analysis of dairy cow fertility and milk production a, b c d * Haja N. Kadarmideen , Robin Thompson , Michael P. Coffey , Mohamad A. Kossaibati a Statistical Animal Genetics Group, Institute of Animal Science ( INW), Swiss Federal Institute of Technology, ETH Zentrum, CH 8092 Zurich, Switzerland b IACR, Rothamsted Experiment Station, Harpenden, Herts AL52JQ, UK c Animal Breeding and Genetics Department, Scottish Agricultural College, West Mains Road, Edinburgh EH93JG, UK d Department of Agriculture, The University of Reading, Reading RG66AT, UK Received 8 May 2001; received in revised form 25 September 2002; accepted 23 October 2002 Abstract Genetic parameters and breeding values for dairy cow fertility were estimated from 62 443 lactation records. Two-trait analysis of fertility and milk yield was investigated as a method to estimate fertility breeding values when culling or selection based on milk yield in early lactation determines presence or absence of fertility observations in later lactations. Fertility traits were calving interval, intervals from calving to first service, calving to conception and first to last service, conception success to first service and number of services per conception. Milk production traits were 305-day milk, fat and 2 protein yield. For fertility traits, range of estimates of heritability ( h ) was 0.012 to 0.028 and of permanent environmental 2 variance ( c ) was 0.016 to 0.032. Genetic correlations ( r ) among fertility traits were generally high ( . 0.70). Genetic g correlations of fertility with milk production traits were unfavourable (range 2 0.11 to 0.46). Single and two-trait analyses of 2 2 fertility were compared using the same data set. The estimates of h and c were similar for two types of analyses. However, there were differences between estimated breeding values and rankings for the same trait from single versus multi-trait analyses. The range for rank correlation was 0.69–0.83 for all animals in the pedigree and 0.89–0.96 for sires with more than 25 daughters. As single-trait method is biased due to selection on milk yield, a multi-trait evaluation of fertility with milk yield is recommended.  2002 Elsevier Science B.V. All rights reserved. Keywords: Dairy cattle; Genetic parameters; Multi-trait analysis; Fertility; Milk yield 1. Introduction Impaired fertility in dairy cows is a major cause of *Corresponding author. Tel.: 141-1-632-3266; fax: 141-1- involuntary culling in many countries. Dairy cow 632-1260. fertility is important both economically and ethically. E-mail address: haja.kadarmideen@inw.agrl.ethz.ch (H.N. Kadarmideen). Dairy cow fertility, as measured by, for example, 0301-6226 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0301-6226(02)00274-9