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In this study, the effect of the lactation sequence and the calving season, which are one of the factors influencing the milk yield in Holstein Friesian breed cows, were studied with meta-analysis method. Meta-analysis is a statistical technique that allows a re-evaluation of the studies conducted by other researchers for the same purpose by bringing them together. Meta-analysis combines and summarizes the results of the studies conducted on various fields, and contributes in making a common judgment among researchers. For these reasons, the studies of 7 different researchers that have been made in this field were brought together and it was aimed to create a common view about the studied parameters. In addition, the heterogeneity in this study was investigated by Chi-Square and I2 test statistics, and these values were found as ×^2=50.205 and I2= 88%, respectively. Therefore, for combining the studies, the fixed effect model wasn’t used in meta-analysis. In this study, the results of the researchers’ studies’ regarding the subject in question were scanned with meta-analytical screening method, and were combined by using the odds ratio (OR) which is the effect size criterion in meta-analysis. As a result of the meta-analysis, the Odds ratio value was found as 0.759 and the effect level was determined middle. With this study conducted, as a result of this meta-analysis conducted, it was found that the contribution done by the lactation sequence on 305-day lactation milk yield in Holstein Friesian cattles in obtaining high milk yield was 0.759 times more compared to the calving season.