General Commission for Scientific Agricultural Research-
Administration of Animal Wealth Research
Damascus University, Faculty of Agriculture
This study was performed at Deir al-Hajar Station for Improving Shami Cattle, Administration of Livestock during 2005-2007.
Twelve growing Shami heifers weighing 90±2 kg and 148±3.4 days old were used to study the growth dynamic of ovarian follicles (daily numbers, size, length and number of waves, rate of growth and regression) and to determine the concentrations of progesterone (P4) and estradiol 17² (E2) during the pre- and post- puberty, ovarian activities, characteristics of estrus cycle (length, time of dominancy, diameter of Graffian follicle and estrus and ovulatory times), length of corpus luteum (CL) and its activity duration, the importance of those parameters in determining the puberty age and the effect of body growth and animal age on those reproductive parameters in growing Shami heifers.
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 pre- and post-ovarian follicles, the formation and regression of corpus luteum in the left and right ovaries during the estrus cycle. Enzyme Linked Immune Sorbent Assay (ELISA) was applied to determine the weekly hormonal concentrations and a balance with accuracy of 0.1kg was used to weight weekly the animal body weight (BW).
The results indicated that the growth turnover of ovarian follicles was observed and developed in a wave pattern in all Shami heifers when they were 6 months old 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 for continued growth and becomes dominant and later on being regressed during the pre-pubertal stage.
During the post-pubertal period, the follicular dynamics was characterized by the presence of waves of follicular growth at different times 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 dominant follicle became functional and ovulated or entered atresia.
Significant effects (P < 0.01) for the BW, animal age and their interaction on the number of follicles, on the maximum diameter of the dominant follicle and on the length of ovarian wave (P < 0.05) during the pre- pubertal stage were found. The number of follicles with a diameter 9 ‰ mm and E2 concentration were increased as the heifers approach puberty.
The daily average of total follicles 2‰ mm observed during the post pubertal stage (11.80±0.09) was greater than that observed during prepubertal period (10.72±0.09) but no significant differences related to the growth or regressive rates and the length of follicular growth waves were found between the pre- and post- pubertal stages.
Puberty age was determined in growing Shami heifers when they reached 400±21 days old and weighed 250±11 kg according to the disappearance of the dominant follicle (ovulation) and subsequent formation of a CL at the same location in the ovary and according to the serum level of P4 (3.81±1.37 ng/ml).
The average length of estrus cycle was 20.92±0.87 days and 1 to 5 follicular waves occurred during estrus cycle. However, estrus cycle with one follicular wave occurred only in heifers exhibited the first post pubertal cycles with an average length equals 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, 22.44آ±0.74, 26.4±0.72, 26.50±3.50 days in cycles having 1, 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 non-ovulatory waves or than that the dominant follicles observed during the pre-pubertal stage.
Results also showed that there were significant differences (P < 0.05) in the averages of hormonal concentrations of P4 (5.34±0.43 vs. 0.29±0.01 ng/ml) and of E2 (22.27±1.20 vs. 16.37±0.37 pg/ml) between post- and pre- pubertal stages and there was a positive and significant correlation (P < 0.05) between the CL diameter and P4 concentration. It was found that r=0.75, 0.58 and 0.51 in short, intermediate and long estrus cycle, respectively, with an overall average equals to 0.56.
It was concluded that ovarian follicles in Shami heifers grow and regress in waves during the pre- and post- pubertal stages and puberty occurs at 400±21 days old and 250±11 kg weight according to the first ovulation and subsequent formation of a CL at the same location in the ovary and according to serum level of P4 (3.81±1.37 ng/ml) and E2 (20.26±2.64pg/ml). It was suggested that further study is required to determine the reason(s) stand behind the increase level of E2 during the pre- and post- puberty in Shami heifers.
Key Words: Ovarian follicles, Reproductive hormones, Follicular waves, Sexual puberty, Estrus cycle, Ovulation, Corpus luteum, Shami cattle.