Study of the estrous cycle in donkeys (Equus asinus) using ultrasonography and plasma progesterone concentrations (original) (raw)

Dynamic ovarian events, ovulation, and plasma progesterone concentration were studied in 20 estrous cycles of 13 jennies. The ovaries were examined by ultrasonography, and venous blood samples were collected daily. The lengths of estrus, diestrus, and the interovulatory interval were 6.3 ± 2.17, 17.95 ± 2.04, and 24.2 ± 3.2 days, respectively. The number of 2-10mm follicles increased in the postovulatory period and remained constant until Day 5 of diestrus. This was followed by a gradual reduction of the follicular population, with minimum variation until the next ovulation. Otherwise, the 11-20-mm follicular population increased from Days 7 and 8 postovulation, and reached a maximum number at the final phase of diestrus. A gradual reduction of this follicular population was observed during estrus. The dominant ovulatory follicle detected at the end of diestrus developed to more than 30 mm in diameter from Day 20 until ovulation at Day 24, and the remaining follicles regressed. On the first day of diestrus, the size of the CL was 28.53 ± 4.94 mm or 77.7% of the size of the preovulatory follicle. The mean concentration of progesterone was < 1 ng/ml during estrus, after which it increased, reaching a steady state between 5 and 14 days postovulation.

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