This study was carried out to determine the effects of some fertility traits on lactation yield of the Holstein cows (n=218), to estimate correlations between these traits and best linear regression model in Kocas State Farm. The data relating to lactation yield and fertility traits (n=810) in the period of 1992–2001 was used at the Kocas State Farm.

Data were fitted for lactation number, year and season affecting on lactation yield, age of cow, first service age, first calving age, lactation length, gestation length, calving interval, service period and birth weight of calf and correlations between these traits were investigated. The model shut out gestation length was determined by The Best Regression Analysis, with regard to R² and Cp.

As a result; age of cow, first service age, first calving age, lactation length, calving interval, service period and calf birth weight affected significantly to lactation yield for Kocas State Farm.