Monitoring lab animal feeding by using subcutaneous microchip transponders: validation of use with group-housed rats

Groups of three rats were fitted with subcutaneous microchip transponders typically used for animal identification. Each group was housed in a custom-designed plastic cage, which contained a pellet feeder tunnel instrumented with a ring-type sensor. The animals were continuously videorecorded for 24 h by using illumination invisible to them during the dark cycle. We performed four experiments in which video confirmation of feeding (i.e., pellet dispensing) was compared to identification of a specific animal by the automated microchip scanning system. When the system was optimized in two experiments, the accuracy of feeding with detection was 96% and 99%. These figures represent 420 pellets dispensed per 24 h in one study and 252 pellets dispensed per 24 h in the other. The use of subcutaneous microchip transponders is an effective method to monitor the individual feeding behaviors of rats housed in groups.