On the farm where animals grazed natural pasture the retention and readability rates six months after tagging were 63% and 78.2%. Dynamic readings indicated 100% efficiency. In conclusion, the selection of the leg of replacement animals for attachment of these tags is appropriate because their normal development is not impeded. For different breeds, it might be necessary to identify the optimal age for tagging. Extensive rangeland grazing systems can reduce the retention of leg tags. The electronic tag evaluated in this study showed a high readability rate under dynamic conditions.