Invited review: Assessing dairy cow agency in automatic milking systems

Automatic milking systems (AMS) are increasingly used in dairy farming for their benefits to farmers (e.g., increased milk production, saving labor, positive lifestyle changes) and cows (e.g., voluntary milking). Providing cows choice over when to be milked allows for a form of behavioral freedom (i.e., agency) within an environment where control may otherwise be limited. Our narrative review critically explores how cows interact with AMS, including the timing and frequency of accessing the milking unit. We describe how external system-based factors can affect access to the AMS. For example, we note that "voluntary" milking still requires cows to be milked at regular intervals, typically incentivized through rewards such as feed. Within this constraint, free-flow systems (in contrast to forced-flow systems) provide animals with greater control over the milking process and other activities. However, feed reward predictability tends to be lower in free-flow systems compared with forced-flow systems, as too-frequent AMS entries are unrewarded. We also describe how characteristics of the individual cow affect access to the AMS, including the positive effects of prior experience with milking robots (e.g., multiparous cows, AMS training), higher social status, personality, and motivation to obtain AMS-associated rewards. Animals lacking these characteristics, such as primiparous or lower-ranking individuals, may be more susceptible to barriers restricting access to the AMS. We conclude that AMS can increase agency over the milking process, but design characteristics aimed at enhancing labor efficiency and milk production constrain agency. Moreover, the degree of control over the milking process is limited by characteristics of the cow. New research is required to understand how AMS can be managed to better accommodate individual differences and enhance animal agency.