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Cows' Lactation Milk Yield (LMY) is a crucial factor in animal breeding operations. Investigating the influence of potential environmental factors on lactation milk yield is of paramount importance and in order to identify the various factors influencing lactation milk yield, dairy cattle records were analysed using the regression tree approach. Age, Parity (P), Lactation Length (LL), and Calving Season (CS) were taken into account as explanatory variables while 305-day Milk Yield (MY) as a dependent variable. Decision tree study revealed that Lactation Length, followed by Parity, Age, and Calving Season, had the greatest impact on the 305-d milk output of cross-bred cows. It was evident from nodes (branches) in regression tree, that cows with parities of 1 and 4 (node 11) produced less milk than cows with parities of 2, 3, 5, 6, 7 and 8 (node 10). More milk was produced by cows older than 4.3 years and whose calving seasons were spring and summer (node 40). With the use of the regression tree method, we were able to extract sub-homogenous groups based on the explanatory variables from records of cross-bred cattle and determine the combinations of environmental conditions that produced the maximum 305-d milk yield.