The study main objective was to explore how lactation length and service period affect milk yield in dairy cows. It explained that measuring the duration a cow produces milk (lactation length) and the gap before a new pregnancy period after calving (service period) helps determine overall productivity of the cow. The study used an advanced statistical modelling, specifically the Generalized Additive Model for Location, Scale, and Shape (GAMLSS). The chosen statistical approach is optimal because it successfully analyses complex non-linear data patterns to reveal the initial milk production boost from increased days in milk after lactation peak followed by the subsequent gradual decrease. The approach uses graphical modelling to simplify intricate data relationships while teaching fundamentals of statistical prediction improvement through smart selection. This study analysed lactation records from 212 cows at 14 dairy farms during a period of 22 years, comprising more than 71,000 recorded data points. The extensive data collection system enhanced the reliability of results because it was based on numerous actual observations. The use of such a rich dataset is compared to having a detailed diary of every cow's performance, making it easier to see patterns in milk production over time. From the results observed, study finds milk production to be highest around 100 days after calving and then it gradually declines. Additionally, extending the service period can have a positive effect on milk yield in a case of the high peak of lactation if done within an optimal window (specifically, a 90-day service period appears most promising) but extending it too much can actually cause a drop in milk production. The study also confirmed that the use of the GAMLSS method is suitable for modelling lactation curves of dairy cows. Finally, the study suggested some practical implications of these findings and procedure for modelling annual milk yield in different lactation lengths for dairy farmers decisions making. Farmers who properly manipulate lactation length through timing of insemination will achieve maximum milk production and enhanced herd productivity outcomes. Better management systems allow dairy producers to sustain profitable milk operations and maintain dairy cattle health.