EFFECTS OF BODY-COMPOSITION VARIATIONS ON THE DURATION OF THE POSTPARTUM ANOVULATORY PERIOD IN MILKED EWES SUBMITTED TO 2 DIFFERENT PHOTOPERIODS

Forty-four dairy ewes were placed at lambing under long (n = 22) or sh ort (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 o f body composition (D2O) showed that the shortest DAP (ie 36 d) was ob served for ewes which gained 1 kg body lipids during the first month p ostpartum. Above and below this threshold, DAP increased. Other relati onships between DAP and ewe body composition variations (dynamic) and/ or total chemical body mass (static) were determined. In dairy ewes, i t 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.