Dairy cattle production in Kenya has been growing into an important agricultural sector, but it still faces numerous difficulties in environmental constraints. The purpose of this study was to identify significant non-genetic effects on milk production to give advices for farm management and estimate genetic and phenotypic parameters for milk traits. Data consisting of 4475 lactation records from 10 large-scale Ayrshire herds collected from 1980 to 2005 were used to evaluate effects of non genetic factors and determine genetic and phenotypic parameters and trends of 305 d milk yield (305d MY). The data analyses using least square techniques of Proc GLM of SASidentified significant sources of variation by herd, parity and year of calving on 305d MY. The overall mean for305d MY was 3009.8 ±1098 kg, with the corresponding heritability and repeatability estimates of 0.12 ±0.05 and 0.35 ± 0.01 respectively. Genetic trend for 305d MY was -2.1 kg/yr and statistically significant (P<0.01) indicating annual decrease in breeding values over the study period. The high variation as indicated by both large standard errors and low heritability’s of the milk trait indicate that much improvement in this trait could be achieved through improved management. The negative annual genetic changes in milk yield observed could largely be due to ineffective breeding strategies both at herd and national level.