Induction of Ovulation of Ovulatory Size Non-Ovulatory Follicles and Initiation of Ovarian Cyclicity in Summer Anoestrous Buffalo Heifers (<i>Bubalus bubalis</i>) Using Melatonin Implants

Abstract

This study was conducted on summer anoestrous buffalo heifers to monitor the efficacy of melatonin for induction of ovulation and ovarian cyclicity. During pre-treatment period of 24 days, the ovarian dynamics of five cycling and 10 summer anoestrous heifers was monitored on each alternate day using a transrectal ultrasound scanner. Thereafter, during treatment period, these 10 anoestrous heifers along with additional seven anoestrous heifers were randomly allocated into non-implanted (n = 5) and implanted (n = 12, one melatonin implant/50 kg, 18 mg melatonin/implant) group. Non-implanted heifers were monitored on each alternate day till the confirmation of second-ovulation in implanted heifers. Pre-treatment period revealed the presence of dominant follicles in anoestrous heifers which attained the diameter comparable with ovulatory follicles of cycling heifers but failed to ovulate and regressed. Between 6 and 36 days (15.3 +/- 2.9 days) post-treatment, all the implanted heifers (p < 0.05) exhibited ovulation of dominant follicles; however none of the non-implanted heifers ovulated during the corresponding period. The first-interovulatory period in implanted heifers ranged between 8 and 28 days (18.0 +/- 1.8 days). The implanted heifers with short (<or=16 days) interovulatory period had short-lived corpus luteum (CL) that had smaller diameter and secreted less progesterone (p < 0.05). The diameter of CL was large (p < 0.05) and plasma progesterone was high (p < 0.05) following second-ovulation compared with first-ovulation in implanted heifers. In conclusion, using melatonin implants, ovulatory size nonovulatory follicles observed in summer anoestrous buffalo heifers can be successfully ovulated to initiate ovarian cyclicity.