Method for determining at least one state variable of the organism of at least one farm animal, at least one probe device for measuring at least one physical parameter being arranged in the gastrointestinal tract of the farm animal, and at least one evaluation unit being arranged outside the gastrointestinal tract of the farm animal, characterized by the following steps: a1) Determining the acceleration of the probe device in all three spatial directions of a Cartesian coordinate system; a2) determining the acceleration according to step a1) as the first physical parameter by the probe device by performing at least one of the following steps: summing absolute values of the acceleration values determined in step a1), or summing the squares of the acceleration values determined in step a1), or root of the sum of the squares of the acceleration values determined in step a1), or arctan of the acceleration values determined in step a1) for y-axis and z-axis of the Cartesian coordinate system, or arctan of the root of the sum of the squares of the acceleration values determined in step a1) and the x-axis of the Cartesian coordinate system; b) converting the first physical parameter into the motility as a first state variable of the organism of the farm animal in a probe control unit of the probe device, measured values of the first physical parameter which are greater than, in particular greater than or equal to, a threshold value being assigned the value of a binary "1" and measured values of the first physical parameter which are less than a threshold value being assigned the value of a binary "1", which are smaller than a threshold value are assigned the value "0", wherein the threshold value is either stored predefined on the probe device or is transmitted by the evaluation unit to the probe device on an event-related basis or consists of a basic threshold value and a dynamic value which can be adapted as a function of the behavior of the first physical parameter and is added to the basic threshold value or subtracted from the basic threshold value; c) transmitting the first state variable as a binary square-wave signal from the probe device to the evaluation unit; d) converting the first state variable into a second state variable in the evaluation unit, wherein the determination of the first physical parameter in step a) is carried out in at least one of the following ways: continuously; at regular intervals; continuously, as soon as a physical parameter measured by the probe device, in particular the first physical parameter, has exceeded a threshold value; at regular intervals, as soon as a physical parameter measured by the probe device, in particular the first physical parameter, has exceeded a threshold value; continuously or at regular intervals for a predefined period of time, as soon as a physical parameter measured by the probe device, in particular the first physical parameter, exceeds a threshold value. a1) Determining the acceleration of the probe device in all three spatial directions of a Cartesian coordinate system; a2) determining the acceleration according to step a1) as the first physical parameter by the probe device by performing at least one of the following steps: summing absolute values of the acceleration values determined in step a1), or summing the squares of the acceleration values determined in step a1), or root of the sum of the squares of the acceleration values determined in step a1), or arctan of the acceleration values determined in step a1) for y-axis and z-axis of the Cartesian coordinate system, or arctan of the root of the sum of the squares of the acceleration values determined in step a1) and the x-axis of the Cartesian coordinate system; b) converting the first physical parameter into the motility as a first state variable of the organism of the farm animal in a probe control unit of the probe device, measured values of the first physical parameter which are greater than, in particular greater than or equal to, a threshold value being assigned the value of a binary "1" and measured values of the first physical parameter which are less than a threshold value being assigned the value of a binary "1", which are smaller than a threshold value are assigned the value "0", wherein the threshold value is either stored predefined on the probe device or is transmitted by the evaluation unit to the probe device on an event-related basis or consists of a basic threshold value and a dynamic value which can be adapted as a function of the behavior of the first physical parameter and is added to the basic threshold value or subtracted from the basic threshold value; c) transmitting the first state variable as a binary square-wave signal from the probe device to the evaluation unit; d) converting the first state variable into a second state variable in the evaluation unit, wherein the determination of the first physical parameter in step a) is carried out in at least one of the following ways: continuously; at regular intervals; continuously, as soon as a physical parameter measured by the probe device, in particular the first physical parameter, has exceeded a threshold value; at regular intervals, as soon as a physical parameter measured by the probe device, in particular the first physical parameter, has exceeded a threshold value; continuously or at regular intervals for a predefined period of time, as soon as a physical parameter measured by the probe device, in particular the first physical parameter, exceeds a threshold value.