Abstract:

In the current study follicular dynamics, pituitary function, ovulatory response and luteal activity of 30 maiden Barbarine sheep were analyzed according to oestrus occurrence and lambing outcome after oestrus synchronisation with cloprostenol.

Animals were retrospectively classified in three groupsnamed asO−(n = 7, ewes not displaying oestrus), O+L−(n=7, ewes showing oestrus but failing to lamb) and O+L+ (n = 16; ewes showing oestrus and lambing thereafter). All the sheep ovulated and daily transrectal ultrasonographies revealed that preovulatory follicleswere present at cloprostenol injection in all the animals.

In sheep O+L+ and O+L−, 50% and 57% of the ovulatory follicles were the largest follicles at cloprostenol treatment (mean size of 4.1±0.26mm and 4.3±0.74mm, respectively). In O− ewes, the same percentage was higher (86%, P < 0.05 when compared to group O+L+; mean size of 4.0±0.46 mm). The number of large follicles and the final diameter of the ovulatory follicles at oestrous tended thereafter to be higher in group O+L+ (1.4±0.1 and 6.4±0.2) than in groups O+L− (1±0.2 and 5.7±0.36) and O− (0.9±0.2 and 5.9±0.5, respectively). Conversely, the number of medium follicles at oestrus detection was higher in the group O+L− (2.1±0.3, P < 0.05) than in the other two groups (1±0.2 and 1±0.3 for O+L+ and O− respectively).

Timing of preovulatory LH surge was earlier for ewes O− (24.0±4.75, P < 0.05) than for sheep O+L+ and O+L− (37.9±2.45 h and 38.0±4.75 h, respectively) and 94% of O+L+ ewes had a LH surge between 16 h and 64 h after cloprostenol injection compared to 57% in O+L− and O− groups (P < 0.05). Thus, maiden Barbarine sheep failing to display oestrus or conceive showed alterations in their follicular dynamics and, thereafter, pituitary function and ovulatory response.