Twelve growing Shami heifers available in Dier-Al-Hajar Station for
improving Shami Cattle weighing 115±3 kg and 178±4 days old were used to
monitor the daily growth of ovarian follicles (daily numbers, size, length and
number of waves, rate of gr
owth and regression) using Transrectal Ultrasound
Echo System (7.5 MHz probe) in 6-14 months-old heifers. Results indicated that
ovarian follicles developed in a wave pattern in all Shami heifers when they
were 6 months old and no significant differences in the number and size of
ovarian follicles were found between right and left ovaries. A cohort of 4 to 7
small follicles with a diameter 2-5 mm developed together and one of them was
selected for continual growth, became dominant and later regressed during the
pre-pubertal stage.
Twelve growing Shami heifers available in Dier-Al-Hajar Station for
improving Shami Cattle during 2005-2007 weighing 250±11 kg and 400±21
days old were used to monitore the growth of dynamic of ovarian follicles (daily
numbers, size, length and nu
mber of waves, rate of growth and regression) and
characteristics of estrus cycle (length, time of dominancy, diameter of Graffian
follicle and estrus and ovulatory times), length of corpus luteum (CL) during
the estrous cycle. Heifers were maintained under uniform conditions and fed
according to their daily growth. Transrectal Ultrasound Echo System (7.5 MHz
probe) was used to study the ovarian structures and to monitor the daily
development and regression of ovarian follicles, the formation and regression of
corpus luteum in the left and right ovaries during the estrus cycle. Results
indicated that the growth turnover of ovarian follicles was observed and
developed in a wave pattern in all Shami heifers and no significant differences
in the number and sizes of ovarian follicles were found between right and left
ovaries. A cohort of 5 to 7 small follicles with a diameter 2-5 mm developed
together and one of them was selected to continue growing and becomes
dominant and later on being regressed or ovulated during the estrus cycle. One
to five follicular waves were observed per cycle and each wave was
characterized by the development of one large (dominant) follicle and a
variable number of smaller follicles. The estrus cycle with one follicular wave
occurred only in heifers exhibited the first post pubertal cycles with an average
length equaled to 8.67±0.33 days. Frequency of estrus cycle according to the
number of follicular waves was 8.4, 25.3, 44.2, 20 and 2.1% in cycles having 1,
2, 3, 4 and 5 follicular waves, respectively. Furthermore , the length of estrus
cycle was also related to the number of follicular waves and it was 21.87±0.62,
22.44±0.74, 26.4±0.72, 26.50±3.50 days in cycles having 2, 3, 4 and 5 follicular
waves, respectively with significant differences (P < 0.05) in cycles with 2 or 3
vs. 4 and/or 5 waves. The functional duration of CL was extended to 9, 12 and
15 days in a short (17-19 days), intermediate (20-24 days) and long estrus cycle
(≥ 25 days). The maximum diameter of dominant follicles in ovulatory waves
was significantly larger (P < 0.05) than that of dominant follicles in nonovulatory
waves. In conclusion, this study showed that the development of
ovarian follicles in Shami heifers occurs in waves and the most common pattern
is three waves per estrous cycle.
