Ovarian follicular dynamics in buffaloes during different estrus synchronization protocols

The current study was carried out on 26 normal cycling buffaloes. Animals were divided into 4 groups according to the hormonal treatment regime. Group 1 included 11 buffaloes without hormonal treatment. Group 2: five buffaloes injected with one dose of 25 mg prostaglandin F2alpha (PGF2α) after ultrasound diagnosis of a mature corpus luteaum in one ovary. Group 3: five buffaloes injected blindly with two doses of 25 mg PGF2α 11-days interval. Group 4: five buffaloes treated with ovsynch protocol. The pattern of follicular growth (FG) and the corpus luteum (CL) regression were monitored by transrectal ultrasound scanning. Estradiol 17β and progesterone profiles were estimated by radioimmunoassay for all groups. Buffaloes in Group 1 showed two (72.7%) or three (27.3%) waves-like patterns of follicular development. The average length of the estrous cycle was 21.75±0.53 and 27.0±0.58 days in 2- and 3- wave cycle respectively. The duration of the CL was 16.63±0.53 and 22.3±0.88 days in 2- and 3- wave cycles. One buffalo in Group 2 did not respond to injection of a single dose of PGF2α, while the other 4 responded. On the day of injection the diameter of the CL was 1.90±0.11 cm and that of dominant follicle was 0.97±0.07 cm. On day 2 after injection the follicle diameter was 1.4±0.09 cm and the preovulatory follicle on days 3-4 was 1.5±0.03 cm. The regressing CL diameter was 1.3±0.07 cm and progesterone level decreased from 6.27±0.82 ng/mL on day 0, to 0.13±0.06 ng/mL on days 3-4 post injection. Estradiol levels were increased from 5.40±1.2 pg/mL on day 0, to 15.09±1.97 pg/mL on day 3-4 post injection. After injection of the first dose of PGF2α, in group 3 the maximum follicle diameter was 1.10±0.04 cm on day 6, then started to regress (0.60±0.04 cm) on days 13-17 after injection. In the 2nd wave, the ovulatory follicle showed marked increase from day 2 (0.34±0.01 cm) till days 13-17 (1.33±0.08 cm). The diameter of CL increased from 1.53±0.03 cm on day 0 of treatment to 1.71±0.04 cm on day 7 of treatment. The second dose of PGF2α resulted in rapid decrease in the diameter of dominant follicle of the first wave from 0.88±0.05 cm on day 11 of treatment to 0.60±0.04 cm on days 13-17 (day of estrus) and rapid increase in the diameter of dominant follicle of the second wave from 0.89±0.08 cm on day 11 to 1.33±0.08 cm on days 13-17. Injection of the second dose of PGF2α on day 11 of treatment caused rapid decline in the progesterone level from 5.62±0.45 ng/mL on day 10, to 1.09±0.34 ng/mL on day 12, and 0.17±0.05 ng/mL on days 13-17. Estradiol levels were 0.76±0.42, 3.97±1.05 and 5.59±1.36 pg/mL on days 10, 12 and days 13-17. In group 4, the diameter of the largest follicle of the four ovulated buffaloes after first gonadotropin-releasing hormone administration was 1.24±0.09 cm, while that of the unovulated buffalo was 0.97 cm. The diameter of the largest follicle of the ovulated buffaloes was 1.03±0.07 and 1.32±0.03 cm on days 7 and 9 of the treatment. The diameter of the CL was 1.6±0.05 and 1.22±0.07 cm on days 7 and 9 of the treatment. The mean concentration of progesterone level was 1.89±0.56 ng/mL on day 6, 0.27±0.12 ng/mL on day 8 and to 0.04±0.01 ng/mL on day 9 of treatment. The mean concentration of estradiol level was 16.07±9.29, 1.11±0.68 and 2.41±0.93 pg/mL on days 6, 8 and 9 of the treatment.