On its surface, electronic heat detection appears to be an easy proposition: all it needs to do is monitor an animal’s movement. Once the animal displays an increase in activity obviously, she’s in heat. All you need to do is breed her!
Yet, accurate heat detection is a much more complex in the real world.
Monitoring activity levels alone may still leave a few more subtler heats undetected. How the behavior is measured and where the sensor is placed on the animal play a factor in the accuracy obtained. In addition, accuracy can be improved by cross referencing other changes in animal behaviors to increase the probability of an accurate diagnosis.
An important component of electronic heat detection is the electronic sensor that collects the raw data from the animal. Early attempts at electronic heat detection utilized a tilt-switch. A tilt-switch is an electrical switch that opens and closes a circuit when a small amount of the liquid metal mercury (or a metal ball, as environmental regulations prescribed later) connects metal electrodes to close the circuit. As the animal moves around, the mercury moves and opens and closes an electrical circuit, a micro-processor counts the number of times the circuit was opened and closed in a pre-determined period of time and, voila, we have a measure of the animal’s activity level. The tilt-switch’s main drawback is that it records only two states: open and closed (circuit). Today, the majority of animal monitoring tags utilize accelerometers that monitor activity levels, intensity of movement and specific movements. This gives an accelerometer-based monitoring system a wider range of abilities to capture cow behavior more accurately than a tilt-switch based device.
Photo: Schematic of a tilt switch
The placement of the electronic sensor on the animal is paramount to obtaining more meaningful data on cow behavior.
Historically, leg mounted pedometers constituted the first attempt to measure activity levels, by counting the number of steps the animal is taking. However, an animal’s leg only records the number of steps it is taking, which does not have a full scope on identifying true heats. The neck/head might provide a few more meaningful behaviors, such as intensity of movement, eating time, rumination time and specific head movements, that will enhance our ability to heat detect.
Some animal monitoring systems utilize this additional behavior data to validate the “in heat” diagnosis. If she is increasing her activity, reducing her eating time and displaying reduced rumination time, her probability of actually being in heat is substantially higher. Another level of behavior analysis can be applied to look at her last identified heat to assign a higher heat probability to cows that are in cycle (i.e. approximately 21 days since their last identified heat).
Since its humble beginnings in the late-1970’s, automated heat detection has evolved to new highs with over 90% true heat detection rates achieved on a consistent basis. The combination of sophisticated sensors and an improved understanding of cow behavior has transformed automated animal monitoring into the reliable and valuable tool that it is today.