A method and system for monitoring the physiological condition, and/or suitability of animal feed, of ruminant animals, by: sensing actions of the animal indicating a ruminating activity; and accumulating the time of the ruminating activities over a predetermined time period to provide an indication of the physiological condition of the animal, and/or of desirable changes in its feed for maximizing milk production and/or for maintaining animal health. In one described preferred embodiment, the sensed actions of the animal are chewing actions produced by the animal while chewing animal feed according to a predetermined chewing rhythm indicating a ruminating activity as distinguished from an eating activity. In a second described embodiment, the sensed actions of the animal are regurgitations of a bolus from the animal's rumen to the animal's mouth sensed by a collar around the animal's neck.