An on-demand feed actuator includes a sealing portion disposed within a feed reservoir and connected to a downwardly extending stem portion protruding a distance past a discharge opening. The sealing portion includes a first component and a second component that are adjustable relative to each other in order to define an overall static dimension of the sealing portion. A spring biases the first and second components away from each other while permitting the first and second components to be compressible relative to each other in response to movement of the actuator by the animal to provide the first and second components with a corresponding combined overall dynamic dimension that is less than the combined overall static dimension.