The influence of behavioural oestrus on the manifestation of oestrus and ovulation of herd mates was studied by ultrasonogrophical examination (US) of ovarian activity. Ten non-pregnant animals divided into two groups (A and B) were treated with a 9-day implant of Synchromate B (SMB) with nine days of difference between treated groups. Seven pregnant cows (Group Q remained within the herd to keep the social structure intact. Animals were observed continuously for 100 h after implant withdrawal. Three sexually active groups (SAG) on three different dates were recorded
each formed by cows from groups A, B and even C. Sixty percent (3/5) ovulated in the 2nd SAG and 83% (5/6) in the 3rd. It may be concluded that: 1) Cows may display mounting behaviour without apparent follicular support even with a SMB implant in place and 2) Cows induced into oestrus may hasten behavioural activity and ovulation in non-treated herd mates.