An echographic study of follicular growth during induced estrus in female Azawak zebu in Niger

An echographic study of follicular growth up to ovulation was carried out on 42 lactating Azawakh 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 ten-day period and the injection of a PGF2α and an eCG (400 and 800 IU) on withdrawal. All the animals treated in this way were inseminated 12 and 24 hrs 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 hrs) than after withdrawal of the PRID® (59.2 ± 5.8 hrs). The average duration of the estrus was significantly shorter after its induction by PGF2α (12.6 ± 2.6 hrs) than after induction by progesterone (22.9 ± 2.7 hrs). There was not a significant difference in the interval between the beginning of estrus and ovulation in animals treated by PGF2α (30.3 hrs) and progesterone (28.4 hrs). 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 Bos indicus.