This invention relates to a birthing sensor (1) for mounting on the tail of a pregnant animal. The birthing sensor comprises a casing (3) and an adjustable strap (5) for securing the casing to the tail of the pregnant animal. The casing houses monitoring equipment, communication equipment and a power supply. There is provided a padding insert (7, 37, 47) for location between the casing, the strap and the animal's tail. The padding insert comprises a sheet of resiliently deformable material, such as rubber, having a plurality of ventilation passageways formed therein. The ventilation passageways allow passage of air over the cow's tail underneath the sensor and further allow escape of urine and faeces from under the sensor. The passageways may be formed by having a plurality of upstanding bosses (9) on the surface of the padding insert and the passageways are the spaces between these upstanding bosses (9).
