Abstract: A detection and weighing device for selectively distinguishing two groups of animals, such as for instance cocks and hens, one of the groups to be distinguished being provided with a detection element, for instance a label, consisting of or provided with amorphous magnetic material. This material is recognized with the aid of an alternating magnetic field and a receiving coil suitable for that purpose, and the presence or absence of the detection element, together with the weight determined by the weighing device on which the detection system is arranged, indicates whether an animal from one group or the other group is involved, so that, for instance, the average weight of the two groups can be determined. Instead of being used in combination with a weighing device, this detection device can also be used while being coupled to other presence-detection devices.