Ovarian Follicular Patterns and Hormone Profile in Thai Native Cattle (Bos indicus)

The objective of this study was to characterize the patterns of ovarian follicular waves, and FSH and P4 concentration during estrous cycle in Thai native cattle (Bos indicus). Transrectal ultrasound examination of ovaries was performed daily using a 7.5 MHz transducer and blood samples were collected after the ultrasound examination during May to August, 2010. There were 1-, 2or 3-follicular waves per cycle in heifers, and 1-, 2-, 3or 4-follicular waves per cycle in cows. Moreover, in cows, only one cycle exhibited 4-follicular wave pattern. The majority of TNC cows (82.76%) exhibited a 3-follicular wave pattern, whereas the majority of heifers exhibited 2-(38.10%) and 3(47.62%) follicular wave patterns, respectively. The numbers of follicles per wave were 6.67±0.69, 7.71±0.45, and 6.29±0.45 in heifers and 4.50±0.85, 4.00±0.85, 4.82±0.29, and 5.00±1.20 in cows, respectively. The length of estrous cycle was 9.33±0.79, 15.13±0.48, and 18.57±0.51 days in heifers and 10.50±0.96, 15.50±1.46, 21.63±0.51, and 25.00±1.36 days in cows. The maximum diameters of dominant ovulatory follicles in heifers were 12.13±0.62, 11.31±0.38, and 11.28±0.34 and in cows 12.65±0.76, 12.45±0.76, 12.82±0.22, and 12.80±1.08 mm. The growth rates were 1.17±0.14, 1.12±0.08, and 1.16±0.07 and 1.16±0.17, 1.34±0.17, 1.16±0.05 and 1.29±0.24 mm/day in heifers that had 1-, 2-, or 3follicular waves and cows that had 1-, 2-, 3-, or 4-follicular waves, respectively. The greater numbers of small follicles emerged more in heifers than in cows (p<0.05), while the duration of the dominant ovulatory follicle was longer in cows than in heifers (p<0.05). The plasma FSH concentrations slightly increased on days 0-1, 6-7, 13-14, and 18 of the estrous cycle, then the wave emerged on the next day. Plasma P4 concentrations slightly increased on days 5-6 and remained high 3-5 days before ovulation. In conclusion, the ovarian follicular dynamic in Thai native cattle developed into 1-, 2-, 3or 4-follicular waves. In cows 3-follicle waves were mostly found whereas in heifers 2and 3follicular waves were mostly found. The duration of estrous cycle correlated to the number of follicular wave. The waves of follicular development were consistent with the increase in amount of FSH. Moreover, when the level of P4 decreased, the largest follicle usually underwent ovulation. The results revealed differences in ovarian follicular dynamics, and in plasma concentrations of FSH and P4, which may account for the differences in the characteristics of ovarian follicular development between heifers and cows of Thai native cattle.