The first experiment was performed in April 2002 on 36 does kept outdoors in sand-floored stables with access to indoor facilities at the experimental farm. Two blood samples (5 ml) were drawn for determining progesterone (reflecting ovulatory activity or anestrus) 11 days before and on the first day the does were exposed to vasectomized bucks for 9 days, for induction
of the male effect (Day 0). Blood was collected into heparinized vacuum tubes (Vacutainer1 Systems Europe, Becton Dickinson, Meylan Cedex, France) and centrifuged at 1500 g for 15 min. Plasma was stored at 20 8C until progesterone analysis. Progesterone was determined in duplicate by a radioimmunoassaydescribed previously , whose sensitivity is 0.06 ng/ml and intra- and inter-assay coefficients of variation are 10.4 and 13.6%, respectively.