Interaction Effects of Somatic Cell Count and Milk Yield on Milk Composition in Lactating Dairy Cows: A Synergistic Analysis*

Objective: This study aimed to investigate the interaction effect between somatic cell count and milk yield on the composition of milk components in dairy cows. Material and Methods: The study involved 165 clinically healthy lactating Holstein cows with an average parity of 1.76 and an average of 221 days in milk. Cows were grouped using K-means clustering analysis based on somatic cell count and milk yield. Milk samples were collected daily during the 30-day experimental period and analyzed for composition. A 2x2 factorial design was employed to examine the main and interaction effects of somatic cell count and milk yield on milk components. Results: The interaction affected various milk components. Specifically, a higher somatic cell count combined with increased milk yield was associated with higher levels of solids at 12.70% ± 0.02, fat at 3.76% ± 0.02, true protein at 3.26% ± 0.01, casein at 2.42% ± 0.01, and milk urea nitrogen at 10.84 mg/dL ± 0.13. Lactose concentration significantly increased to 5.06% ± 0.01 (P=0.01). Notably, this interaction effect resulted in a significant increase in lactose concentration (P=0.01). Conclusion: The study confirms an interaction effect between somatic cell count and milk yield on milk composition, emphasizing the need to consider both factors for optimizing milk quality. The observed increase in lactose concentration due to the interaction effect underscores the complexity of somatic cell count and milk yield dynamics, suggesting potential implications for udder health and dairy management practices. Keywords: somatic cell count, milk yield, milk composition, dairy cows, udder health, milk quality.