Effects of body composition variations on the duration of the postpartum anovulatory period in milked ewes submitted to two different photoperiods

: Forty-four dairy ewes were placed at lambing under long (n = 22) or short (n = 22) artificial photoperiods. In each photoperiodic treatment 2 diets (high or low) were offered to 11 group-fed ewes. The duration of the anovulatory period (DAP, in d) was estimated by bi-weekly blood progesterone measurements. Within 2 months, ewes exposed to the long photoperiod had no resumption of ovulation, while most of the ewes (18/22) exposed to the short photoperiod ovulated. In vivo measurements of body composition (D2O) showed that the shortest DAP (ie 36 d) was observed for ewes which gained 1 kg body lipids during the first month postpartum. Above and below this threshold, DAP increased. Other relationships between DAP and ewe body composition variations (dynamic) and/or total chemical body mass (static) were determined. In dairy ewes, it seems that the dynamic aspects are more closely related to DAP than the static aspects. Results were compared to the available literature on anestrus in dairy cows.