Much has been improved in the basic and applied aspect of female reproduction after understanding of the wave-like developmental pattern of follicles ¡Ý4 mm. However, it is speculated that the understanding of the developmental pattern of small follicles <4 mm may bring about efficient management of ovarian functions for essential reproductive interventions. Present studies were therefore, carried out to characterize the developmental pattern of 1-3 mm follicles in cattle using ultrasonography and to validate a method to histologically characterize the developmental pattern of follicles <1 mm using non-serial data. Transrectal ultrasonography was used once daily (n=18 Hereford-cross heifers) to examine changes in the diameter of follicles ¡Ý1 mm for one interovulatory interval (IOI), as well as every 6 h (n = 9 Hereford-cross cows) from 5 to 13 days after ovulation to encompass emergence of Wave 2. A periodic shift in the peak number (P < 0.05) of 1-3 mm and ¡Ý4 mm follicles and a significant inverse relationship (P < 0.05) between them suggested a wave-like developmental pattern. The number of 1-3 mm follicles detected in anovulatory waves did not differ (P = 0.53) between 2- versus 3-wave IOIs. A difference (P < 0.05) was noticed between anovulatory and ovulatory waves in 3-wave IOIs but not (P = 0.63) in 2-wave IOIs. The future dominant follicle was identified at 1 mm and was found to emerge 6-12 h earlier than the largest subordinate follicle (P < 0.01). Emergence of the future dominant (r = 0.71) and 1st subordinate (r = 0.78) follicles was temporally associated (P < 0.05) with a rise in circulating concentrations of FSH. <p> The developmental pattern of follicles not detectable by ultrasonography (<1 mm) may be assessed histologically by examining the ovaries from different animals on different days (i.e., non-serial method) using follicle diameter or number profiles. A data set (n = 56 heifers) of follicles ¡Ý4 mm was tabulated in a serial (same set of heifers each day; n = 7/day, N = 7) and non-serial (different set of heifers each day; n = 7/day, N = 56) manner for number and diameter profiles around emergence of the first follicular wave. Profiling of serial and non-serial data (serial and non-serial methods) revealed a change in the number of follicles (4-5 mm, 6-8 mm, ¡Ý9 mm) over days (P < 0.01), but the effect of method and the day-by-method interaction were not different (P > 0.28). Similarly, the diameter of the dominant and first 2 subordinate follicles changed over days (P < 0.01), but the effect of method and the day-by-method interaction were not different (P > 0.06), indicating that non-serial data provide wave-like profile of follicles. <p> In conclusion, the hypothesis that follicles 1-3 mm develop in a wave-like manner was supported, and a new non-serial method was validated for the study of follicle dynamics using non-serial (e.g. histologic) data.

Much has been improved in the basic and applied aspect of female reproduction after understanding of the wave-like developmental pattern of follicles ¡Ý4 mm. However, it is speculated that the understanding of the developmental pattern of small follicles <4 mm may bring about efficient management of ovarian functions for essential reproductive interventions. Present studies were therefore, carried out to characterize the developmental pattern of 1-3 mm follicles in cattle using ultrasonography and to validate a method to histologically characterize the developmental pattern of follicles <1 mm using non-serial data. Transrectal ultrasonography was used once daily (n=18 Hereford-cross heifers) to examine changes in the diameter of follicles ¡Ý1 mm for one interovulatory interval (IOI), as well as every 6 h (n = 9 Hereford-cross cows) from 5 to 13 days after ovulation to encompass emergence of Wave 2. A periodic shift in the peak number (P < 0.05) of 1-3 mm and ¡Ý4 mm follicles and a significant inverse relationship (P < 0.05) between them suggested a wave-like developmental pattern. The number of 1-3 mm follicles detected in anovulatory waves did not differ (P = 0.53) between 2- versus 3-wave IOIs. A difference (P < 0.05) was noticed between anovulatory and ovulatory waves in 3-wave IOIs but not (P = 0.63) in 2-wave IOIs. The future dominant follicle was identified at 1 mm and was found to emerge 6-12 h earlier than the largest subordinate follicle (P < 0.01). Emergence of the future dominant (r = 0.71) and 1st subordinate (r = 0.78) follicles was temporally associated (P < 0.05) with a rise in circulating concentrations of FSH. <p> The developmental pattern of follicles not detectable by ultrasonography (<1 mm) may be assessed histologically by examining the ovaries from different animals on different days (i.e., non-serial method) using follicle diameter or number profiles. A data set (n = 56 heifers) of follicles ¡Ý4 mm was tabulated in a serial (same set of heifers each day; n = 7/day, N = 7) and non-serial (different set of heifers each day; n = 7/day, N = 56) manner for number and diameter profiles around emergence of the first follicular wave. Profiling of serial and non-serial data (serial and non-serial methods) revealed a change in the number of follicles (4-5 mm, 6-8 mm, ¡Ý9 mm) over days (P < 0.01), but the effect of method and the day-by-method interaction were not different (P > 0.28). Similarly, the diameter of the dominant and first 2 subordinate follicles changed over days (P < 0.01), but the effect of method and the day-by-method interaction were not different (P > 0.06), indicating that non-serial data provide wave-like profile of follicles. <p> In conclusion, the hypothesis that follicles 1-3 mm develop in a wave-like manner was supported, and a new non-serial method was validated for the study of follicle dynamics using non-serial (e.g. histologic) data.