ORIGINAL PAPER Analysis of early survival of Holstein-Friesian heifers of diverse sire origins on commercial dairy farms in Kenya D. K. Menjo & B. O. Bebe & A. M. Okeyo & J. M. K. Ojango Accepted: 10 April 2008 / Published online: 23 April 2008 # Springer Science + Business Media B.V. 2008 Abstract The use of imported semen within the Holstein-Friesian cattle population in Kenya has contributed to increased milk production per cow, however, information on how this has impacted on functional traits, particularly early life survival and reproductive performance is scarce. This study eval- uated age at first calving (AFC), survival to age at first calving, and survival to four years of age using survival analyses techniques, in Holstein-Friesian cattle on four dairy farms in Kenya. The heritability estimate obtained for AFC was 0.15±0.06 for an average AFC of 1058 days. Animals sired by New Zealand and Australian born bulls had the earliest average AFC (907 days). On average, 25% of all the heifers born were culled prior to attaining a first calving, while 34% were culled prior to four years of age. Though the highest proportion of losses was due to unspecified reasons, the relative risk of being culled was highest when an animal had a specific disease, and the first 60 days of life were the most critical for survival. Daughters of sires from South- Africa and Israel tended to have better survival rates than those sired by bulls originating from other regions. Unfavourable selection towards animals sired by Kenyan born bulls was evident. The economic implications of the high rate of early mortality need to be evaluated in order to assist livestock producers make informed decisions on choice of sires for breeding. Keywords Early survival . Holstein-Friesian cattle . Imported semen . Tropics Abbreviations AFC Age at first Calving GxE Genotype by environment interaction LSF Large Scale Farm S-AFC Survival to first calving S-1460 Survival to 1460 days of age Introduction With sires sourced from all over the world, there has been an increase in the use of North-American Holstein semen in Kenya as in several other environ- ments (Dillon et al. 2006; Philipsson and Lindhe 2003). However, despite the evidence that global selection can increase rates of genetic progress in dairy cattle by up to 17% compared to within country and breed selection (Dillon et al. 2006), concerns have been raised about the effects of genotype by Trop Anim Health Prod (2009) 41:171–181 DOI 10.1007/s11250-008-9172-z D. K. Menjo : B. O. Bebe : J. M. K. Ojango Department of Animal Sciences, Egerton University, P. O. Box 536, 20107 Njoro, Kenya A. M. Okeyo : J. M. K. Ojango (*) International Livestock Research Institute (ILRI), P. O. Box 30709, 00100 Nairobi, Kenya e-mail: j.ojango@cgiar.org