Seasonal variations in the cyclic luteal ovarian activity in the Tadmit ewe in Algeria.

Seasonal variations of the cyclic luteal activity were assessed by measurements of progesterone concentrations in peripheral plasma collected daily or every 4 days, throughout 15 months, in 16 Tadmit ewes, in Algeria. One female was cyclic at all times of the year; 15 ewes showed a period of cyclic luteal inactivity of less than 53 days in 10 animals and ranging between 2.5 and 3.5 months for the 5 others (mean duration 52 days). The onset of ovarian inactivity took place from the beginning of February to the end of April (mean data 19 March). The recovery of luteal function was much more definite; it occurred in May for 13 ewes (mean date for the 16 animals 10 May) when daylength was still increasing. These data suggest that at this latitude (36 degrees 30'N) and for this particular breed of sheep (Tadmit) declining daylength is not the major environmental stimulus for the resumption of breeding activity.