A comparison of the follicular dynamics in heifers of the Czech Fleckvieh and Holstein breeds.

Differences in follicular development and repeatability of follicular growth pattern among Czech Fleckvieh (n = 20) and Holstein (n = 23) heifers were investigated. Follicular dynamics was evaluated by daily sonographic scanning during three interovulatory intervals. The mean duration of the interovulatory interval was 20.66 +/- 0.32 days, no differences between breeds were observed. The proportion of the non-alterna-ting pattern was nearly the same as that of the alternating pattern (54% and 46%, respectively). The majority of IOIs <= 21 days were of the 2-wave pattern (71%) whereas only 29% of them were of the 3-wave pattern. Conversely, the majority of IOIs = 22 days were of the 3-wave pattern (84%), whereas only 16% were of the 2-wave pattern. Differences could be observed in the Czech Fleckvieh heifers. Comparing 2- and 3-wave interovulatory intervals, 44.2% of the heifers exhibited 3 waves and 55.8% of the heifers exhibited 2 waves of follicular growth. The ratio of 3- to 2-wave heifers was about the same in the Holstein breed; in Czech Fleckvieh 2-wave cycles slightly dominated (11/12, 8/12; respectively). In Holstein heifers, the first follicular wave occurred 0.92 +/- 0.15 days after ovulation in 2-wave interovulatory intervals, and the emergence of the first wave in 2-wave Czech Fleckvieh heifers appeared later (P < 0.05), 1.83 +/- 0.3 days after ovulation. The maximal size reached by the dominant follicles in all animals and in the Czech Fleckvieh differed in the first and in the second wave of 2-wave cycles (P < 0.05). In 3-wave interovulatory intervals the dominant follicles in the second wave differed (P < 0.05) from the mean diameters of the first and the third wave in the Czech Fleckvieh. The ovulatory follicles were significantly (P < 0.05) smaller in 2-wave than in 3-wave interovulatory intervals among all animals and between the Holstein and Czech Fleckvieh heifers. In conclusion, we found a similar pattern of ovarian follicular dynamics in Czech Fleckvieh and Holstein heifers kept under identical nutritional and environmental conditions. Whether the significant difference in the emergence of the 1(st) follicular wave in 2-wave IOIs between C and H heifers is of real biological significance is ambiguous.