Characteristics of follicular dynamics and reproductive hormone profiles during oestrous cycles of jennies over an entire year.

Although donkeys have been domesticated for over 6,000 years, limited information is available concerning their reproductive physiology, especially under intensive rearing conditions. The aims of this experiment were to study follicular dynamics and reproductive hormone variation in jennies during the inter-ovulatory interval in different seasons. A total of 12 continuous cycles of six Dezhou Black (DB) donkey jennies were examined in four different seasons. The diameters of the six largest follicles of each jenny were measured daily by ultrasonography, and blood samples were collected at fixed times for reproductive hormone assays. The results demonstrated that most jennies displayed regular oestrous cycles in all seasons. The follicular dynamics were similar in Spring, Summer and Winter, while the jennies had longer oestrous cycles with delayed follicular deviation and dominant selection in Autumn. At least two follicular waves were observed in each oestrous cycle, throughout the study, but two jennies presented oestrous cycles with three follicular waves in the Autumn. The numbers of follicular waves were consistent with the numbers of FSH surges. Oestrous characteristics of the jennies in a large herd were also analysed. The results showed that the rates of regular oestrous cycles were 83.1% (265/319), 89.6% (215/240), 80.2% (235/293) and 77.1% (178/231), with 26.4% (70/265), 19.5% (42/215), 22.1% (52/235) and 23.0% (41/178) double ovulation rates in Spring, Summer, Autumn and Winter, respectively. The results presented may be useful for donkey farms in the design of breeding strategies.