Method comprising the steps: • providing an enclosure for at least one animal with an outer sidewall; • providing activity measurement means for measuring at least one parameter related to physical activity of at least one animal, wherein the activity measurement means comprise a heat image camera; • providing data processing means; • capturing heat images by the heat image camera; • calculating center-of-heat points for the at least one animal for a sequence of heat images; • calculating a distance between the center-of-heat points of sequential heat images; and • using the distances between sequential center-of-heat points to determine a parameter related to the physical activity of said animal, wherein the activity measurement means comprise at least one photo sensor unit, each comprising at least one transmitter and receiver and wherein the step of measuring the parameter related to physical activity comprises detecting how often an animal interrupts a light barrier defined by the at least one transmitter and receiver within a preset time frame, wherein the light barrier is adapted in height such that it is only interrupted when the animal rears; and/or wherein the heat images are 2-dimensional images and the method further comprises the steps: • defining a threshold temperature; • defining a heat area in such a way that only parts of the heat image with a temperature being greater than the threshold temperature constitute part of the heat area; • defining for the part of the heat image corresponding to a sub enclosure a threshold heat area such that the heat area in the part of a image being smaller, or greater, respectively, than the threshold heat area corresponds to a rearing animal and the heat area in the part of a image being greater, or smaller, respectively, than the threshold heat area corresponds to a non-rearing animal; • determining for the captured heat image whether the animal is in a rearing position, and/or wherein the heat image camera is positioned above the enclosure and comprises a depth sensor and the method comprises to measure, by the depth sensor, how often the animal rears within a given time frame. • providing an enclosure for at least one animal with an outer sidewall; • providing activity measurement means for measuring at least one parameter related to physical activity of at least one animal, wherein the activity measurement means comprise a heat image camera; • providing data processing means; • capturing heat images by the heat image camera; • calculating center-of-heat points for the at least one animal for a sequence of heat images; • calculating a distance between the center-of-heat points of sequential heat images; and • using the distances between sequential center-of-heat points to determine a • defining a threshold temperature; • defining a heat area in such a way that only parts of the heat image with a temperature being greater than the threshold temperature constitute part of the heat area; • defining for the part of the heat image corresponding to a sub enclosure a threshold heat area such that the heat area in the part of a image being smaller, or greater, respectively, than the threshold heat area corresponds to a rearing animal and the heat area in the part of a image being greater, or smaller, respectively, than the threshold heat area corresponds to a non-rearing animal; • determining for the captured heat image whether the animal is in a rearing position, and/or