Milk yield and quality of dairy cows transitioning from milking parlour to automatic milking system

This study investigated the effects of changing from milking parlour (MP) to automatic milking system (AMS) on test-day milk yield and quality traits of dairy cows, using data from 2012 to 2024. Only cows present in both milking systems were considered. Two datasets were available: (i) a single-breed set (38,290 test-day records from 1463 Holstein cows in 31 herds) and (ii) a multi-breed set (8892 test-day records from 403 Holstein, Brown Swiss, and Simmental cows in 11 herds). A linear mixed model was applied, accounting for fixed effects of parity, lactation stage, milking system, and their interactions. Random effects of cow and herd-test-day were included. In multi-breed data, breed and milking system × breed were also added. Holstein cows in single-breed herds yielded 1.40 kg/d more milk in AMS than MP, especially in primiparous cows. However, AMS milked cows had higher somatic cell count (SCC), urea concentration, and pH, with a lower casein index. In multi-breed herds, milk yield differences between systems were not statistically significant. Across breeds, the casein index was lower in AMS than MP. Then, SCC was treated as binary trait (≤ and > 200,000 cells/mL) and logistic regression was performed using the models described above. Holstein cows milked with AMS were more likely to have SCC >200,000 cells/mL, with no such differences in other breeds. Even if switching to the AMS results in increased milk yield, it leads to a deterioration of milk quality, suggesting that the transition is a stressor for the cows.