Abstract
An echographic study of follicular growth up to ovulation was carried out on 42 lactating Azawak cows (Bos indicus) after estrus induction by means of a PGF2α or a procedure involving the administration of progesterone vaginally (PRID® DELTA: progesterone-releasing intravaginal device) for a 10-day period and the injection of a PGF2α and an ECG (400 and 800 IU) on withdrawal. All the animals were inseminated 12 and 24 h after the onset of estrus. The percentage of estrus induced was not significantly different between the two groups of animals (81 %). The average time delay before the onset of estrus was significantly longer after injection of a PGF2α (84.8 ± 26.0 h) than after withdrawal of the PRID® (59.2 ± 5.8 h). The average duration of the estrus was significantly shorter after its induction by PGF2α (12.6 ± 2.6 h) than after induction by progesterone (22.9 ± 2.7 h). There was not a significant difference in the interval between the beginning of estrus and ovulation in animals treated by PGF2α (30.3 h) and progesterone (28.4 h). Injection of a PGF2α was accompanied by a significantly lower rate of gestation than that obtained after treatment of animals by progesterone (31.2 vs 54.5 %). These results confirm the necessity to adapt an insemination policy to hormonal treatment for estrus induction in B. indicus.