Ultrasonographic studies on ovarian dynamics and associated estrus manifestations of jennies under controlled management, Ethiopia
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A serial ultrasonographic study was conducted on nine jennies aged 5–15 years from January to April 2008 with the objective of studying ovarian follicular dynamics and estrus manifestations under controlled management. Ovarian follicular activity was determined from the number and size distribution of follicles, length of interovulatory interval (IOI), growth rate of preovulatory follicles, diameter of follicles at the onset of estrus, and incidence of ovulation. Estrus manifestations were characterized using length of estrus and estrous cycle. The mean (±SD) number of follicle detected per ovary was 5.45 ± 2.3 (range, 1–16) with sizes ranging from 2.9 to 44 mm. The mean (±SD) size of follicle encountered at the onset of estrus was 25.9 ± 3.7 mm (range, 20.9–34.4) while that of the preovulatory follicles at −1 day before ovulation was 36.81 ± 3.78 mm. The mean (±SD) IOI, estrus, and estrous cycle length were 25.4 ± 3.6, 7.9 ± 2.9, and 24.2 ± 7.4 days, respectively. The mean (±SD) growth rate of the preovulatory follicle after the day of divergence was 1.9 ± 0.3 mm/day. Serum progesterone profile followed the same patterns of ovarian dynamics with maximum values being detected during midluteal phase. Serum progesterone assay revealed blood progesterone profiles of <1.0 ng/ml during estrus and up to 11 ng/ml during midluteal phase with a pattern following follicular dynamics. Body condition of the study jennies steadily increased and was positively correlated (r = 0.52, p < 0.001) with the diameter of the preovulatory follicle. In conclusion, the ultrasonic evaluation has revealed that follicular dynamics of jennies were generally related with body condition which might have been influenced by the type of management.