Ovarian follicular dynamics, hormonal profiles and ovulation time in Mithun cows (Bos frontalis)

Abstract

The study aimed to evaluate follicular dynamics and concentrations of estradiol-17β (E2), progesterone (P4), follicle stimulating hormone (FSH) and luteinizing hormone (LH) during the oestrous cycle and to determine ovulation time in Mithun cows. Ovaries of experimental cows (n = 7) were examined daily by transrectal-ultrasonography for three consecutive oestrous cycles (n = 21). The characteristics of follicular waves, dominant follicle, largest subordinate follicle and corpus luteum and ovulation time were evaluated. The plasma samples were analysed throughout the interovulatory interval to determine the differences in the hormonal profiles (E2, P4, FSH and LH) between different follicular wave cycles. Out of eighteen oestrous cycles analysed, three-wave follicular cycles were maximum (n = 12: 66.66%) followed by two (n = 4: 22.22%) and four waves (n = 2: 11.11%). The two and three waves were statistically compared, and no significant (p > .05) differences were observed in day of wave emergence, number of follicles (≥3 mm) recruited, maximum diameter of the ovulatory dominant follicle, growth rates of ovulatory and anovulatory dominant follicles and maximum diameter of corpus luteum. The diameter of dominant follicles was significantly (p < .05) greater than subordinate follicles in both ovulatory and anovulatory waves. No significant differences were observed in peak concentrations of estradiol-17β and follicle stimulating hormone between ovulatory and anovulatory waves in all wave cycles. A preovulatory luteinizing hormone surge was observed a day before ovulation in all wave cycles. Progesterone concentrations were lower than 0.5 ng/ml during oestrus and increased sharply to the maximum levels of ≥3.8 ng/ml in all wave cycles. Ovulation time (mean ± SEM), irrespective of follicular waves was 10.5 ± 0.64 h after the end of oestrus. It was concluded that Mithun cows have a preponderance of three follicular waves with little difference between the two-and three-follicular waves and ovulation occurred 10.5 h after the end of oestrus.

Assisted reproductive technologies (ARTs) in Mithun (Bos frontalis): What progress has been made so far? An overview

“…Mithun exhibits either compact or cavitory corpus luteum (CL) and undergoes luteolysis with an appearance of estrus upon administration of a luteolytic dose of PGF2α (Ramesh et al, 2022). The luteolytic dose of PGF2α induces luteolysis after day 5 to 6 days similar to cattle (Wenzinger & Bleul, 2012).…”

“…In Mithun, female and male reproductive physiology has been studied in detail (Dhali et al, 2006; Perumal, De, et al, 2021). The length of the estrous cycle is in the range of 20–25 days with a longer duration of oestrus (50–67 h) and no distinct visible or behavioural signs of estrus (silent estrus) (Dhali et al, 2006; Ramesh et al, 2022). A recent study on follicular dynamics and hormonal profiles revealed that Mithun cows exhibit two, three and four follicular waves with a preponderance of three follicular waves (Ramesh et al, 2022).…”

“…The length of the estrous cycle is in the range of 20–25 days with a longer duration of oestrus (50–67 h) and no distinct visible or behavioural signs of estrus (silent estrus) (Dhali et al, 2006; Ramesh et al, 2022). A recent study on follicular dynamics and hormonal profiles revealed that Mithun cows exhibit two, three and four follicular waves with a preponderance of three follicular waves (Ramesh et al, 2022). There is no distinct seasonal breeding pattern in Mithun; however; calving is proportionately more during winter due to maximum breeding at the onset of rainfall and the availability of lush green fodder (Perumal, Kumar, & Rajkhowa, 2014).…”

“…A recent study on follicular dynamics and hormonal profiles revealed that Mithun cows exhibit two, three and four follicular waves with a preponderance of three follicular waves (Ramesh et al, 2022).…”

“…In Mithun, female and male reproductive physiology has been studied in detail (Dhali et al, 2006;Perumal, De, et al, 2021). The length of the estrous cycle is in the range of 20-25 days with a longer duration of oestrus (50-67 h) and no distinct visible or behavioural signs of estrus (silent estrus) (Dhali et al, 2006;Ramesh et al, 2022).…”