This study was performed with 18 German Shepherd female dogs whom previous cycles were recorded. Bitches were separated into three groups: two treated groups and a control one. The first group was selected from 7 bitches in early anestrous period, i.e., at the stage 108 to 124 days after the beginning of their last pro-oestrus. The second group consisted in 6 bitches in late anestrous period, i.e., at the stage 160 to 187 days after the beginning of their last pro-oestrus. The control group was constituted by 5 untreated bitches which reach their spontaneous pro-oestrus 173 to 204 days after the beginning of their preceding pro-oestrus.